Anatomy & Physiology · Study Guide

Exam 4 Study Guide

These four chapters all turn on one habit: match a finding to a place. First you map the brain and the cord. Then you follow sensation in, from a touch receptor to the visual cortex, and out again through a reflex. Then you learn the two automatic branches that run your organs. Last you learn the bedside exam that works backward from a sign to the region behind it. Learn the maps and the exact pathways, then practice reading them in reverse. The cram sheet at the end holds every map, value and pathway in one place.

Chapter 13 Chapter 14 Chapter 15 Chapter 16 Cram sheet

What this guide covers

Chapter 13 · the cerebral lobes, the four brain regions, the ventricles and cerebrospinal fluid, the meninges, the spinal cord, and the twelve cranial nerves.
Chapter 14 · sensory receptors, the eye, the visual pathway, the ear, taste and smell, and the reflex arc.
Chapter 15 · the two autonomic divisions, the two-neuron pathway, fight or flight and rest and digest, the two messengers, the baroreceptor reflex, and somatic against autonomic.
Chapter 16 · the five parts of the neurological exam, language and the aphasias, the cranial nerve tests, dermatomes and the two sensory pathways, strength grading, and coordination.

Chapter 13Anatomy of the Nervous System

What to know

The cerebrum is the biggest part of the brain and the place where thinking happens. Its outer layer is the cerebral cortex, only a few millimeters thick, and it is gray matter packed with nerve cell bodies. Under it lies white matter, made of coated axons that wire one part of the brain to another.

The wrinkles have a purpose. Each ridge is a gyrus and each groove is a sulcus, and a deep groove is a fissure. Folding lets a huge sheet of cortex fit inside the skull, like a crumpled towel in a cup. About two thirds of the cortex is hidden down in the grooves.

Each half of the brain is a hemisphere, and each one has four lobes. Every lobe is named for the skull bone right on top of it. Two grooves mark the borders. The central sulcus splits the frontal lobe from the parietal lobe. The deep lateral sulcus marks off the temporal lobe below. The insula is tucked inside the lateral sulcus and is often called a hidden fifth lobe.

The two halves split up the work, which is called lateralization. Language is usually on the left, while space and music skills are often on the right. They talk all the time through the corpus callosum, a thick bridge of white matter.

Two strips sit on either side of the central sulcus. Just in front is the primary motor cortex, which sends the orders for movements you choose. Just behind is the primary somatosensory cortex, which takes in touch, pressure and temperature from the whole body. Each strip holds a map of the body that is upside down and out of shape, with huge areas for the hands and face.

Slice the brain down the middle and you see four main regions. They stack from the thinking parts on top to the life-support parts below. Here is a rough rule. The higher a part sits, the more chosen its job. The lower it sits, the older and more automatic its job. You can lose a lot of cerebrum and still live, but a tiny stroke in the brainstem can kill you.

Inside the brain is a set of linked hollow rooms, the ventricles, filled with cerebrospinal fluid. The choroid plexus makes about 500 mL of that fluid a day, yet the total amount stays near 150 mL, because the fluid is drained and replaced several times each day. It flows on a one-way path.

Three thin sheets, the meninges, wrap the brain and cord. Learn them from outside in, because the spaces between them are where the big emergencies happen. The Latin names tell you what they feel like. Dura mater means tough mother, and pia mater means tender mother.

The spinal cord runs from the bottom of the brainstem down a tunnel in the backbone and ends near L1 or L2. Below that it splits into a spray of nerve roots called the cauda equina, which means horse's tail. It carries messages up and down, and it also works as its own local switchboard for reflexes.

Twelve pairs of cranial nerves come straight out of the brain, numbered I through XII from front to back. The first two grow out of the cerebrum and diencephalon. The other ten sprout from the brainstem.

Lock these in

Each lobe is named for the skull bone above it.
Motor cortex is in front of the central sulcus. Sensory cortex is behind it.
In the brain, gray matter is outside. In the cord, gray matter is inside.
Meninges from outside in: dura, arachnoid, pia.
Dorsal root is sensory in. Ventral root is motor out.
The vagus is the only cranial nerve that leaves the head and neck.

Worth memorizing

The lobes and the two strips. The motor strip is the precentral gyrus and the sensory strip is the postcentral gyrus. Broca's area is in the frontal lobe and Wernicke's area is in the temporal lobe.

Lobe	Sits under	Main jobs
Frontal	Frontal bone	Movements you choose, planning, judgment, personality, and making speech in Broca's area
Parietal	Parietal bone	Touch, pressure, pain and temperature; sense of space
Temporal	Temporal bone	Hearing, smell, memory, and understanding language in Wernicke's area
Occipital	Occipital bone	Vision; holds the primary visual cortex

Brain region	Key parts	Main job
Cerebrum	Two hemispheres, cortex, corpus callosum	Thinking, feeling, chosen movement, memory, language
Diencephalon	Thalamus, hypothalamus, epithalamus	Relays sense signals; keeps the body steady and runs hormones
Brainstem	Midbrain, pons, medulla oblongata	Life-saving reflexes, hub for cranial nerves, highway between brain and cord
Cerebellum	Two hemispheres, folia, vermis	Teamwork of muscles, balance, smooth and exact movement

Two parts of the diencephalon do most of the work. The thalamus is the brain's main train station, and almost every sense signal heading to the cortex stops there first to be sorted and sent on. Smell is the one sense that skips it. The hypothalamus is about the size of an almond, yet it controls body temperature, hunger, thirst and the sleep and wake cycle, and it runs the pituitary gland hanging below it. It is where the nervous system and the hormone system shake hands.

The medulla oblongata holds the reflex centers that set heart rate, blood pressure and breathing. The cerebellum fine-tunes movement and keeps balance. It does not start a movement. It edits one, like an editor fixing a draft, which is why damage there makes a person clumsy and unsteady rather than paralyzed.

Step	Structure	What happens
1	Choroid plexus in the lateral ventricles	Cerebrospinal fluid is made from filtered blood plasma
2	Interventricular foramina	Fluid passes into the third ventricle
3	Cerebral aqueduct	Fluid flows down to the fourth ventricle
4	Openings into the subarachnoid space	Fluid bathes the brain and spinal cord
5	Arachnoid granulations	Fluid goes back into the blood in the veins

There are four ventricles. Two big C-shaped lateral ventricles sit one in each half of the brain. A thin slit-like third ventricle sits in the middle of the diencephalon. A diamond-shaped fourth ventricle sits between the brainstem and the cerebellum. The fluid does three jobs. Buoyancy lets the brain float, so a brain of about 1,400 g presses down with a weight of only about 50 g. Protection soaks up shocks, so the brain bobs gently instead of slamming into the skull. Chemical stability brings food in, washes waste out, and holds the exact mix of salts that nerve cells need. A blocked flow causes hydrocephalus, with swollen ventricles and rising pressure.

Meninx	What it is like	Space or feature
Dura mater	Tough outer coat, like leather	Forms the dural venous sinuses; the epidural space lies outside it
Arachnoid mater	Thin middle layer, like a web	The subdural space is above it; the subarachnoid space, holding cerebrospinal fluid, is below it
Pia mater	Thin inner film, full of blood vessels	Sticks right onto the brain and cord, following every fold

The spaces name the bleeds. An epidural bleed comes from an artery and looks lens-shaped. A subdural bleed comes from veins and looks crescent-shaped. Infection of the meninges is meningitis. One dura fold, the falx cerebri, dips down between the two halves of the brain and holds it steady.

One-way traffic at the roots. This is the Bell and Magendie rule. Note the layout is the reverse of the brain, with gray matter in the center and white matter around it.

Cord structure	Type	Function
Dorsal (posterior) horn	Gray matter	Takes in sensory signals
Ventral (anterior) horn	Gray matter	Sends motor orders to muscles
Dorsal root, with its ganglion	Sensory	Carries feeling into the cord
Ventral root	Motor	Carries orders out of the cord
White columns and tracts	White matter	Highways going up with feeling and down with movement orders

Small lateral horns sit at the sides, in the chest and upper belly part of the cord, and they hold nerve cells of the automatic system. A lumbar puncture is done below the end of the cord, to be safe.

Number	Name	Type	Main function
I	Olfactory	Sensory	Smell
II	Optic	Sensory	Vision
III	Oculomotor	Motor	Most eye movements; makes the pupil smaller; lifts the eyelid
IV	Trochlear	Motor	Moves the eye with the superior oblique muscle
V	Trigeminal	Both	Feeling in the face; chewing muscles
VI	Abducens	Motor	Moves the eye out to the side
VII	Facial	Both	Facial expressions; taste at the front of the tongue; tears and saliva
VIII	Vestibulocochlear	Sensory	Hearing and balance
IX	Glossopharyngeal	Both	Taste at the back of the tongue; swallowing; saliva
X	Vagus	Both	Calming control of the heart, lungs and gut
XI	Accessory	Motor	Moves the neck and shoulders
XII	Hypoglossal	Motor	Moves the tongue

Two memory sentences carry the list. For the names, use "On Old Olympus' Towering Tops, A Finn And German Viewed Some Hops." For the types, use "Some Say Marry Money, But My Brother Says Big Brains Matter Most." The first letters give S, S, M, M, B, M, B, S, B, B, M, M, which tells you whether each nerve from I to XII is sensory, motor or both.

How to reason through it

Walk-through 1 · a finding to a region

Most items here hand you a lost function and want the place.

Step 1 · name the functionVision, hearing, chosen movement, touch, balance, breathing, and so on.

Step 2 · match it to a lobe or regionVision is occipital. Hearing and understanding language are temporal. Chosen movement is the strip in front of the central sulcus. Touch is the strip behind it. Balance and smoothness are the cerebellum. Heart rate and breathing are the medulla.

Step 3 · check the height ruleHigher means chosen and survivable. Lower means automatic and life-threatening.

Try itA person walks unsteadily and cannot touch a target cleanly, but is not weak. Strength is fine, so the motor strip is fine. Smoothness and balance are lost, so the problem is in the cerebellum.

Walk-through 2 · following the fluid

Flow items ask what comes next, or what a blockage would do.

Step 1 · start where it is madeThe choroid plexus in the lateral ventricles.

Step 2 · follow the one-way chainLateral ventricles, interventricular foramina, third ventricle, cerebral aqueduct, fourth ventricle, out into the subarachnoid space, then back to the blood at the arachnoid granulations.

Step 3 · a block swells everything upstreamFluid keeps being made, so pressure climbs behind the block.

Try itWhat happens if the cerebral aqueduct is blocked? Fluid cannot reach the fourth ventricle, so it backs up into the third and both lateral ventricles. They swell and pressure rises, which is hydrocephalus.

Walk-through 3 · root and nerve items

Cord items test one rule and one layout.

Step 1 · apply the one-way ruleDorsal means sensory in. Ventral means motor out. The dorsal root ganglion holds the sensory cell bodies.

Step 2 · remember the reversed layoutIn the cord, gray matter is in the center and white matter is around it. The brain is the other way around.

Step 3 · name the result of cutting one rootCut the dorsal root and feeling is lost but movement remains. Cut the ventral root and movement is lost but feeling remains.

Try itA patient keeps full strength in one arm but has lost feeling in it. Movement is intact, so the ventral root is fine. The loss is sensory, so the damage is at the dorsal root on that side.

Traps people fall into

Putting motor cortex behind the central sulcus. Motor is in front, sensory behind.
Keeping gray matter outside in the cord. In the cord it is inside.
Letting smell stop at the thalamus. Smell is the one sense that skips it.
Reversing the meninges. Outside in it is dura, arachnoid, pia.
Putting the cord all the way down the back. It ends near L1 or L2.
Giving the cerebellum the job of starting movement. It edits movement, not starts it.
Keeping the vagus in the head. It is the one that wanders into the chest and belly.

Chapter 13 self-test · ten items

1. Name the four cerebral lobes and one main job of each.

Frontal for chosen movement and planning, parietal for touch, temporal for hearing and memory, occipital for vision. Each is named for the skull bone above it.

2. Which groove splits the motor strip from the sensory strip, and which side is which?

The central sulcus. The primary motor cortex is just in front of it and the primary somatosensory cortex is just behind it. Each strip holds an upside-down map of the body with huge areas for the hands and face.

3. What joins the two halves of the brain, and what is the splitting of work between them called?

The corpus callosum joins them, and the splitting of work is lateralization. Language is usually on the left, while space and music skills are often on the right.

4. Name the four main brain regions from top to bottom.

Cerebrum, diencephalon, brainstem, cerebellum. Higher parts do chosen tasks and lower parts do automatic ones. The cerebellum sits behind the brainstem, tucked under the occipital lobe.

5. What does the thalamus do, and which sense skips it?

It sorts almost every sense signal and sends it on to the cortex. Smell skips it. The hypothalamus below it runs temperature, hunger, thirst, sleep and the pituitary gland.

6. Name the three parts of the brainstem and say what the lowest one controls.

Midbrain, pons, medulla oblongata. The medulla holds the reflex centers for heart rate, blood pressure and breathing. All the cranial nerves except the first two attach to the brainstem.

7. Trace cerebrospinal fluid from where it is made to where it returns to the blood.

Choroid plexus in the lateral ventricles, interventricular foramina, third ventricle, cerebral aqueduct, fourth ventricle, subarachnoid space, then the blood through the arachnoid granulations. About 500 mL is made a day, but the total stays near 150 mL.

8. Name the three jobs of cerebrospinal fluid.

Buoyancy, protection and chemical stability. A brain weighing about 1,400 g presses down with a weight of only about 50 g while floating in it.

9. Where does the spinal cord end, and what continues below it?

It ends near L1 or L2, and below that it continues as the nerve roots of the cauda equina. There are 31 pairs of spinal nerves, each a mixed nerve made from a sensory dorsal root and a motor ventral root.

10. Which cranial nerves are purely sensory, and which one leaves the head and neck?

I olfactory, II optic and VIII vestibulocochlear are purely sensory. The vagus, X, leaves the head and neck. The vagus carries most calming signals to the heart, lungs and gut.

Chapter 14The Somatic Nervous System

What to know

The somatic nervous system deals with the outside world. It carries sensation in and sends chosen commands to skeletal muscle out.

Everything you sense starts with a sensory receptor, a special nerve ending that turns some kind of energy into an electrical signal. That change is called transduction, and it is the first step in every sense.

The senses come in two families. The general senses are touch, pressure, vibration, temperature, pain, and the sense of where your body parts are. Their receptors are spread all over the body. The special senses are vision, hearing, balance, taste and smell, and they sit in complex organs in the head.

How many receptors sit in one spot decides how sensitive it is. Fingertips are crowded with receptors, each covering a tiny patch of skin called its receptive field, so you feel two close points as two. That is why you read Braille with a fingertip, not an elbow. Many receptors are also phasic, which means fast-adapting. They fire hard when a touch starts or stops but go quiet if it holds steady, which is why you stop noticing your shirt. Pain receptors hardly adapt at all.

The eyeball is built from three coats, each called a tunic. The cornea is the eye's main window and bends light more than any other part. The lens makes the fine changes. Two fluids keep the eye firm, and the watery one in front feeds the cornea and lens, which have no blood vessels.

The retina has two kinds of light receptors. Rods work very well in dim light but see no color. Cones need bright light and give color and detail. A small pit called the fovea centralis is packed almost only with cones and gives the sharpest vision. Where the optic nerve leaves the eye there are no light receptors at all, and that spot is the blind spot.

The visual pathway matters because damage at each point causes a loss you can predict. The key stop is the optic chiasm, an X-shaped crossing under the brain. There, fibers from the nasal half of each retina cross to the other side, and fibers from the temporal half stay on the same side. The result is that each side of the brain handles the opposite half of what you see.

The ear does two jobs at once. It hears and it keeps you balanced. It passes a wave inward through three parts. In the cochlea, pitch is coded by place. The base of the basilar membrane is narrow and stiff and answers high tones. The tip is wide and floppy and answers low tones. So the brain knows the note by which hair cells fire.

Taste and smell both use chemoreceptors, so they detect molecules rather than energy. The only difference is where the molecules are. Taste reads chemicals dissolved in saliva. Smell reads chemicals floating in air. There are only about 400 kinds of smell receptor, yet the nose tells apart thousands of odors, because each smell turns on its own mix of receptors.

A reflex is a fast, automatic reaction you can predict, and its key feature is that it does not wait for you to think. The signal runs a short built-in loop that often turns around in the spinal cord, firing a muscle before the brain even knows.

Lock these in

Transduction turns a stimulus into a nerve signal. Every sense starts there.
The cornea bends light the most. The lens fine-tunes it.
Rods are for dim light. Cones are for color and detail.
At the chiasm, nasal fibers cross and temporal fibers stay.
Smell is the only sense that skips the thalamus.
Every reflex arc has five parts, always in the same order.

Worth memorizing

Receptor type	Responds to	Example
Mechanoreceptor	Being pushed or bent out of shape: touch, pressure, stretch, vibration, sound	Tactile corpuscles; hair cells of the ear
Thermoreceptor	Temperature and changes in it	Warm and cold free nerve endings in skin
Nociceptor	Tissue damage; these are the pain receptors	Free nerve endings that signal cuts, burns and swelling
Chemoreceptor	Chemicals in liquid or in the air	Taste and smell receptors; blood gas sensors
Photoreceptor	Light	Rods and cones of the retina

Skin receptor	What it senses
Free nerve endings	Pain, temperature and rough touch; the simplest kind
Tactile (Merkel) discs	Fine texture and edges, just under the surface
Tactile (Meissner's) corpuscles	Light touch and gentle slow vibration, in bumps of the dermis in hairless skin
Lamellated (Pacinian) corpuscles	Deep pressure and fast buzzing vibration; built in layers like an onion
Bulbous (Ruffini) corpuscles	Skin stretch and steady pressure

Tunic of the eye	Structures	Job
Fibrous (outer)	Sclera, cornea	Protects the eye and gives it shape; the cornea does most of the focusing
Vascular (middle)	Choroid, ciliary body, iris	Brings blood, makes aqueous humor, controls the lens and pupil
Neural (inner)	Retina, with rods, cones and relay nerve cells	Turns light into nerve signals

Light travels cornea, then aqueous humor, then pupil, then lens, then vitreous humor, then retina. Accommodation is how the eye focuses on something close. The ciliary muscle tightens, which loosens the small ligaments holding the lens, and the stretchy lens bulges into a rounder, stronger shape. For distance the ciliary muscle relaxes, the ligaments pull tight, and the lens flattens.

The chiasm is the whole story. Partial crossing lets the brain blend the two slightly different views into one three-dimensional picture.

The full route runs retina, then optic nerve, then optic chiasm, then optic tract, then the lateral geniculate nucleus of the thalamus, then the optic radiations, then the primary visual cortex. From the cortex the signal splits again, with an upper stream toward the parietal lobe for where and how, and a lower stream toward the temporal lobe for what.

Lesion site	Visual field result
Optic nerve on one side	Total blindness in that one eye
Center of the optic chiasm	Loss of both outer halves of vision, called bitemporal hemianopia
Optic tract or beyond, on one side	Loss of the same half of vision on the opposite side in both eyes, called homonymous hemianopia

Ear region	Key structures	Job
Outer ear	Auricle, ear canal, tympanic membrane	Gathers sound and makes the eardrum vibrate
Middle ear	Malleus, incus, stapes; auditory tube	Makes the vibration stronger and passes it to the oval window
Inner ear	Cochlea; vestibule and semicircular canals	Turns vibration into hearing; senses head position and motion

Follow the wave once. The stapes rocks the oval window and sends a pressure wave through fluid. The wave makes the basilar membrane shiver. Sitting on that membrane is the organ of Corti, dotted with hair cells whose tiny hairs brush the tectorial membrane hanging over them. When the hairs bend, ion channels pop open, the hair cell depolarizes, and it fires the cochlear nerve, part of cranial nerve VIII. The round window bulges out to let the pressure off so the wave keeps moving. Next door, the vestibule senses gravity and straight-line movement, and the semicircular canals sense spinning and turning, both through the same eighth nerve. Hair-cell loss is permanent.

Basic taste	Signals	Trigger
Sweet	Sugars, energy	Glucose and other carbohydrates
Sour	Acids, unripe or spoiled food	Hydrogen ions
Salty	Minerals and body salts	Sodium ions
Bitter	Possible poisons	Alkaloids and many poisons
Umami	Protein, a savory taste	Glutamate, as in broth or aged cheese

Taste happens in taste buds, most of them on the bumps of the tongue called papillae. Mushroom-shaped, ridged and large circumvallate papillae all carry taste buds. The pointed filiform papillae carry none, and they only grip food and sense texture. Each bud is a cluster of gustatory cells whose taste hairs poke up through a taste pore, and basal cells behind them replace worn-out taste cells every week or two.

Smell receptor cells are true nerve cells, high in the roof of the nose. Their fibers thread up through tiny holes in the cribriform plate of the ethmoid bone to reach the olfactory bulb. Two things make smell unusual. Its signals go straight to the smell and limbic areas without stopping in the thalamus, which ties smell tightly to memory and feeling. And smell neurons grow back all through life.

The arc never changes. Receptor, sensory neuron, integration center, motor neuron, effector. Only the number of synapses changes from one reflex to the next.

The classic stretch reflex is the knee-jerk. Tapping the tendon stretches the thigh muscle, the muscle spindle fires, the sensory nerve cell links straight to a motor nerve cell, the quadriceps tightens and the leg kicks out. At the same moment an interneuron blocks the hamstring so it relaxes and gets out of the way, and that trick is called reciprocal inhibition. Other reflexes are polysynaptic. A withdrawal reflex yanks your foot off a tack, paired with a crossed-extensor reflex that stiffens the other leg so you do not fall.

How to reason through it

Walk-through 1 · visual field items

These items put damage somewhere and ask what vision is lost. The chiasm rule answers all of them.

Step 1 · is the damage before the chiasm?Before it, only one eye's fibers are hit, so that one eye goes blind.

Step 2 · is it at the center of the chiasm?The center holds only the crossing nasal fibers from both eyes. Nasal retina sees the outer world, so both outer halves are lost. That is bitemporal hemianopia.

Step 3 · is it past the chiasm?Then the fibers for one half of the world are gathered together, so the same half is lost in both eyes. That is homonymous hemianopia.

Try itA tumor presses on the center of the chiasm. Which fibers are hit, and what is lost? Only the crossing nasal fibers from both retinas, so the patient loses both outer halves of vision.

Walk-through 2 · naming the receptor

Receptor items hand you a sensation and want the sensor.

Step 1 · ask what kind of energyPushing or bending is mechanical. Heat is thermal. Damage is pain. A molecule is chemical. Light is photo.

Step 2 · for skin, pick by depth and speedLight touch near the surface is Meissner's. Deep pressure and buzzing vibration are Pacinian. Stretch and steady pressure are Ruffini. Fine texture and edges are Merkel. Pain and temperature are free nerve endings.

Step 3 · check adaptationIf the item says the feeling fades, the receptor is phasic. If it says the feeling will not fade, think pain.

Try itYou stop noticing a watch on your wrist after a minute, but a cut keeps hurting. The watch is steady pressure sensed by fast-adapting phasic receptors. The cut is sensed by nociceptors, which hardly adapt.

Walk-through 3 · reflex items

Reflex items ask for a part, a count of synapses, or where the loop breaks.

Step 1 · list the five parts in orderReceptor, sensory neuron, integration center, motor neuron, effector.

Step 2 · count the synapsesSensory straight onto motor is monosynaptic, like the knee-jerk. Any interneuron in the middle makes it polysynaptic.

Step 3 · use a failed reflex to find the breakA reflex tests the whole arc, so a missing reflex means one of the five parts has failed.

Try itWhy does the hamstring relax while the quadriceps kicks? An interneuron in the cord blocks the opposing muscle at the same moment. That is reciprocal inhibition, and it keeps the two muscles from fighting each other.

Traps people fall into

Giving the lens most of the focusing. The cornea bends light the most.
Flattening the lens for close work. It gets rounder, and the ciliary muscle tightens.
Swapping rods and cones. Rods are for dim light with no color. Cones are for color and detail.
Crossing the temporal fibers at the chiasm. Only nasal fibers cross.
Mapping pitch by loudness. Pitch is mapped by place: base for high, apex for low.
Running smell through the thalamus. Smell is the one sense that skips it.
Sending a reflex up to the brain first. It turns around in the cord or brainstem.

Chapter 14 self-test · ten items

1. What is transduction, and name the five receptor groups.

Transduction is turning a stimulus into an electrical signal. The groups are mechanoreceptors, thermoreceptors, nociceptors, chemoreceptors and photoreceptors. Each group is named for what it detects.

2. Which skin receptor senses deep pressure and fast vibration, and how is it built?

The lamellated, or Pacinian, corpuscle. It is built in layers, like an onion. Meissner's corpuscles sense light touch and slow vibration and sit nearer the surface in hairless skin.

3. Name the three tunics of the eye and one structure in each.

Fibrous with the sclera and cornea, vascular with the choroid, ciliary body and iris, and neural which is the retina. The cornea does most of the focusing. The retina turns light into nerve signals.

4. Trace a ray of light from the world to the retina.

Cornea, aqueous humor, pupil, lens, vitreous humor, retina. The aqueous humor feeds the cornea and lens, which have no blood vessels, and it drains out all the time.

5. What happens to the lens during accommodation, and which muscle does it?

The ciliary muscle tightens, the holding ligaments loosen, and the lens bulges rounder to bend light more. For distance the ciliary muscle relaxes, the ligaments pull tight and the lens flattens.

6. Which part of the retina gives the sharpest vision, and which part has no receptors at all?

The fovea centralis gives the sharpest vision, because it is packed almost only with cones. The optic disc has no receptors, which makes it the blind spot. That is where the optic nerve leaves the eye.

7. Which fibers cross at the optic chiasm, and what does that crossing achieve?

The nasal fibers cross; the temporal fibers stay on the same side. The result is that each side of the brain handles the opposite half of what you see. That lets the brain blend two slightly different views into one three-dimensional picture.

8. Name the three middle-ear bones in order and say what they do.

Malleus, incus, stapes. They act like levers, passing the vibration across and pressing it onto the oval window. They are the three smallest bones in the body. The auditory tube evens out pressure with the throat.

9. How does the cochlea code pitch?

By place on the basilar membrane. The base is narrow and stiff and answers high tones; the tip is wide and floppy and answers low tones. The hair cells of the organ of Corti fire the cochlear nerve, part of cranial nerve VIII.

10. Give the five parts of a reflex arc in order, and say what makes the knee-jerk the simplest kind.

Receptor, sensory neuron, integration center, motor neuron, effector. The knee-jerk is monosynaptic, with just one synapse between the sensory and motor cells. Withdrawal reflexes are polysynaptic and add interneurons.

Chapter 15The Autonomic Nervous System

What to know

Your nervous system sends out two kinds of motor commands. The somatic system carries the commands you choose, to skeletal muscle. The autonomic nervous system does everything else. It is the involuntary motor system for your organs, and it controls smooth muscle, heart muscle and glands.

It has two divisions, and they usually work against each other. The sympathetic division is the gas pedal, the fight-or-flight system that revs you up to face a threat. The parasympathetic division is the brake, the rest-and-digest system that runs the body when you are calm.

Most organs get nerves from both divisions, which is called dual innervation, and the two push the organ in opposite ways. Your heart rate at any moment is the balance between them. The body steers an organ by shifting that balance, not by switching one side on from off, and that steady background firing is autonomic tone.

Where each division leaves the brain and cord is the easiest way to tell them apart. All sympathetic fibers come out of the chest and lower-back part of the cord, from T1 through L2, so the division is called the thoracolumbar outflow. Parasympathetic fibers come out of the two ends. Some leave the brainstem in four cranial nerves, which are III, VII, IX and the long vagus, X. The rest leave the sacral cord at S2 through S4. That top-and-bottom pattern gives the name craniosacral outflow.

One fact sets the whole system apart. It takes two neurons to carry a signal from the center to an organ, and they meet at a relay station called a ganglion. The somatic system uses a single neuron the whole way, with no relay. Where the ganglion sits is the biggest difference between the two autonomic divisions.

Because sympathetic fibers fan out widely and the adrenal medulla adds a hormone boost, the sympathetic division acts as one team, all at once. Every change in the surge has a purpose. Each one moves resources away from long-term upkeep and toward instant muscle power.

The system controls a lot but uses a very small set of words. Almost every autonomic message is carried by just two neurotransmitters. A neuron that releases acetylcholine is called cholinergic. One that releases norepinephrine is called adrenergic.

Here is the idea you most need. The same chemical can speed one organ up and slow another down. The receptor on the target cell decides the effect, not the chemical. That is also why autonomic drugs can be so precise.

The autonomic system also runs steady, silent reflexes. The most important one guards your blood pressure second by second, and it is a classic negative feedback loop with a sensor, a control center and effectors.

Lock these in

Sympathetic is thoracolumbar, from T1 to L2. Parasympathetic is craniosacral.
Every autonomic path uses two neurons and a ganglion.
Sympathetic ganglia sit near the cord. Parasympathetic ganglia sit at the organ.
All preganglionic fibers release acetylcholine.
Most sympathetic postganglionic fibers release norepinephrine.
The receptor decides the effect, not the chemical.

Worth memorizing

Target organ	Sympathetic, fight or flight	Parasympathetic, rest and digest
Heart	Beats faster and stronger	Beats slower
Pupil	Dilates, so it gets wider	Constricts, so it gets smaller
Airways	Dilate, letting in more air	Constrict
Digestive tract	Slows down; blood is sent elsewhere	Speeds up; juices flow
Salivary glands	A little thick saliva, so a dry mouth	Lots of watery saliva
Urinary bladder	Relaxes, so it holds urine	Contracts, so it empties
Liver	Releases sugar into the blood	Stores sugar

Where the ganglion sits changes everything. Sympathetic chain ganglia run as a beaded column beside the spine. Parasympathetic ganglia sit in or right next to the target organ.

Feature	Sympathetic	Parasympathetic
Where it leaves the center	Thoracolumbar, T1 to L2	Craniosacral: brainstem plus S2 to S4
Where the ganglia are	Near the spinal cord, in chain and prevertebral ganglia	Near or in the target organ
Preganglionic fiber	Short	Long
Postganglionic fiber	Long	Short
Fanning out	High, so a body-wide response	Low, so a local response

Most sympathetic ganglia form the chain ganglia, a beaded double column along each side of the spine. A few sit in front of the aorta as the prevertebral ganglia, such as the celiac and mesenteric ganglia, reached by the splanchnic nerves. The adrenal medulla is a changed sympathetic ganglion, and it releases epinephrine straight into the blood as a hormone.

Fight-or-flight change	How it helps you survive
Heart beats faster and harder	Gets oxygen and fuel to muscle faster
Small airways dilate	More air flows in, so you take in more oxygen
Pupils dilate	You see the threat more sharply and widely
Liver releases glucose	Ready fuel for a burst of effort
Blood shifts to skeletal muscle	Power goes to muscles, not the gut
Digestion and urination stop	Saves energy for the emergency
Sweating increases	Cools the body before hard work

Epinephrine in the blood lasts longer than the nerve signals, which is why the rush fades slowly after a scare. The two divisions are not enemies. The sympathetic side is the sprint and the parasympathetic side is the recovery.

Fiber	Neurotransmitter	Receptor on target
Preganglionic, both divisions	Acetylcholine	Nicotinic
Parasympathetic postganglionic	Acetylcholine	Muscarinic
Sympathetic postganglionic, most	Norepinephrine	Adrenergic, alpha or beta
Sympathetic fibers to sweat glands	Acetylcholine	Muscarinic
Adrenal medulla into the blood	Epinephrine, as a hormone	Adrenergic, alpha or beta

Nicotinic receptors sit in all autonomic ganglia and where nerves meet skeletal muscle, and they always excite. Muscarinic receptors sit on the organs that parasympathetic fibers control, and they can excite or inhibit depending on the organ. Adrenergic receptors come in alpha and beta types. Acting on alpha-1 receptors tightens blood vessels. Acting on beta-2 receptors relaxes and opens the airways. Norepinephrine does most of the alpha-1 work and binds beta-2 only weakly, so opening the airways falls to epinephrine in the blood from the adrenal medulla, and to beta-2 drugs. A postganglionic axon does not end in one neat tip either. It is dotted with beads called varicosities that spray the chemical loosely over a wide patch of smooth muscle.

Blood pressure	Baroreceptor firing	Autonomic response	Result
Goes too high	Goes up	Parasympathetic up, sympathetic down	Heart slows and vessels widen, so pressure falls
Goes too low	Goes down	Sympathetic up, parasympathetic down	Heart speeds up and vessels tighten, so pressure rises

The sensors are baroreceptors, stretch sensors packed into the wall of the carotid sinus and the aortic arch. Their reports travel along cranial nerves IX and X to the cardiovascular center in the medulla, which is the control center. The medulla then adjusts heart rate, how hard the heart squeezes, and how wide the vessels are. You count on this every time you stand up. Gravity pulls blood into your legs, pressure at the head drops, the baroreceptors sense it, and sympathetic drive goes up so pressure comes back within a heartbeat or two. When the reflex is slow, from aging, losing body water or some drugs, you feel lightheaded on standing, and that is orthostatic hypotension.

Feature	Somatic	Autonomic
Control	Voluntary, you choose	Involuntary, automatic
Target	Skeletal muscle	Smooth muscle, heart muscle, glands
Neurons to target	One	Two, relaying at a ganglion
Neurotransmitter	Acetylcholine only	Acetylcholine or norepinephrine
Effect on target	Always excites	Excites or inhibits

A somatic motor neuron can only tell a muscle to contract, never to relax, so the center stops a movement by simply stopping the signal. The vagus, by contrast, can actively slow the heart. There is also a third player, the enteric nervous system, a huge web of neurons built into the wall of the digestive tract. It has so many neurons that people call it the second brain, and it can run gut reflexes on its own even if its links to the brain and cord are cut.

How to reason through it

Walk-through 1 · predicting an organ's response

These items name a division and an organ and want the effect.

Step 1 · ask what the body is doingSympathetic means getting ready to run or fight. Parasympathetic means resting and digesting.

Step 2 · ask whether the organ helps that goalAnything that helps a sprint gets turned up. Anything that can wait gets turned down.

Step 3 · name the direction, not just the divisionFaster or slower. Wider or narrower. Flowing or stopped.

Try itWhat does the sympathetic division do to the gut and to the liver, and why the difference? The gut can wait, so digestion slows and its blood goes elsewhere. Muscle needs fuel now, so the liver releases sugar into the blood.

Walk-through 2 · chemical and receptor items

These items hand you a fiber or a drug and want the messenger or the effect.

Step 1 · place the fiber in the chainAll preganglionic fibers release acetylcholine onto nicotinic receptors. That part never varies.

Step 2 · then split by divisionParasympathetic postganglionic fibers release acetylcholine onto muscarinic receptors. Most sympathetic postganglionic fibers release norepinephrine onto adrenergic receptors.

Step 3 · check the two exceptions, then the receptorSympathetic fibers to sweat glands use acetylcholine, and the adrenal medulla pours epinephrine into the blood. Then remember that the receptor decides the effect.

Try itWhy does one chemical family tighten blood vessels but open airways? Because the receptors differ. Acting on alpha-1 receptors tightens vessels, while acting on beta-2 receptors relaxes the airways.

Walk-through 3 · baroreceptor reflex items

Work these as a feedback loop, the same way you worked loops in chapter 1.

Step 1 · name the three partsBaroreceptors in the carotid sinus and aortic arch are the sensors. The medulla is the control center. The heart and vessels are the effectors.

Step 2 · read the firing rateMore stretch means more firing, which means pressure went up. Less firing means pressure went down.

Step 3 · pick the correcting shiftPressure too high calls for parasympathetic up and sympathetic down. Too low calls for the reverse. The response always opposes the change.

Try itYou stand up quickly. Pressure at the head drops for a moment, so the baroreceptors fire less. The medulla turns sympathetic drive up, so the heart speeds and the vessels tighten. If the fix lags, you feel lightheaded, and that is orthostatic hypotension.

Traps people fall into

Giving the autonomic system one neuron. It always uses two, with a ganglion between them.
Swapping the fiber lengths. Sympathetic is short then long. Parasympathetic is long then short.
Blaming the chemical for the effect. The receptor decides.
Giving sweat glands norepinephrine. Those sympathetic fibers use acetylcholine.
Thinking one division is switched off. Both fire all the time, and the balance shifts.
Letting a somatic neuron relax a muscle. It can only excite.
Making the baroreceptors control the heart directly. They only sense; the medulla decides.

Chapter 15 self-test · ten items

1. What does the autonomic nervous system control, and how is that different from the somatic system?

It controls smooth muscle, heart muscle and glands, and it is involuntary. The somatic system carries chosen commands to skeletal muscle. The autonomic system can also inhibit, while a somatic neuron can only excite.

2. Where does each division leave the brain and spinal cord?

Sympathetic fibers leave from T1 to L2, the thoracolumbar outflow. Parasympathetic fibers leave in cranial nerves III, VII, IX and X and from S2 to S4, the craniosacral outflow. That is the quickest way to tell the two apart.

3. What is dual innervation, and what is autonomic tone?

Dual innervation means one organ gets nerves from both divisions, pushing it in opposite ways. Autonomic tone is the steady background firing of both. The body steers an organ by shifting the balance, not by switching one side on from off.

4. Describe the two-neuron pathway and name the relay point.

A preganglionic neuron starts in the center and runs to a ganglion. A postganglionic neuron starts in the ganglion and runs to the organ. The somatic system has no relay. One neuron runs all the way to the muscle.

5. Why does a sympathetic response sweep the whole body while a parasympathetic one stays local?

Sympathetic ganglia sit near the cord and each preganglionic fiber branches to many postganglionic neurons, which is high fanning out. Parasympathetic ganglia sit at the organ, with little fanning out. So you can slow the heart without also cramping the gut.

6. Name four changes in the fight-or-flight surge and say what each one buys you.

The heart beats faster to move oxygen quickly, the airways widen for more air, the pupils dilate to see more, and the liver releases sugar for fuel. Blood also shifts to skeletal muscle, digestion and urination pause, and sweating rises to cool you.

7. Which fibers release acetylcholine, and which release norepinephrine?

All preganglionic fibers and all parasympathetic postganglionic fibers release acetylcholine. Most sympathetic postganglionic fibers release norepinephrine. The two exceptions are sympathetic fibers to sweat glands, which use acetylcholine, and the adrenal medulla, which pours epinephrine into the blood.

8. Name the two kinds of acetylcholine receptor and where each sits.

Nicotinic receptors sit in all autonomic ganglia and where nerves meet skeletal muscle. Muscarinic receptors sit on the organs parasympathetic fibers control. Nicotinic always excites. Muscarinic can excite or inhibit, depending on the organ.

9. Trace the baroreceptor reflex when blood pressure rises too high.

Baroreceptors in the carotid sinus and aortic arch stretch more and fire faster. They report through cranial nerves IX and X to the medulla, which raises parasympathetic output and lowers sympathetic output. The heart slows, vessels widen and pressure falls. It is negative feedback, so the response always opposes the change.

10. What is the enteric nervous system, and how do the two divisions relate to it?

A huge web of neurons in the wall of the digestive tract that can run gut reflexes on its own, even with its links to the brain and cord cut. Parasympathetic signals speed digestion and sympathetic signals slow it, but the day-to-day churning mostly runs itself.

Chapter 16The Neurological Exam

What to know

Most exams in medicine ask what is wrong. This one adds a sharper question: where. The nervous system is wired in a neat, mapped-out way. One region handles language. One nerve runs the tongue. One strip of skin belongs to one spinal segment. So a few findings can point to a single place, and that skill is called localization. It is the whole game.

Here is the pattern. A weak right arm, slurred speech and a drooping right face all point to the left side of the brain. A numb band around the belly points to one level of the spinal cord.

The exam has five parts, and they stack neatly from the top of the nervous system down. Do them in order and you have checked everything from head to toe.

The mental status exam checks the brain's highest-level work, in the cortex. It checks alertness, whether the person knows who and where they are and what time it is, attention, memory and, most telling of all, language. A two-minute chat already tells you a lot.

Language is lateralized, which means it lives mostly on one side, and in nearly everyone that is the left. It is split between two areas with two different jobs. Broca's area in the frontal lobe produces speech. Wernicke's area in the temporal lobe understands it. Damage to each one causes a very different loss of language, and the type tells you which area failed.

The cranial nerve exam has a rhythm. Each nerve has one quick bedside test. If a test fails, it points straight to that nerve, or to the part of the brainstem the nerve comes from. The best part is how much a tiny difference between sides can tell you.

Each spinal nerve carries feeling from one band of skin called a dermatome, and side by side the dermatomes cover the body like stripes on a map. Read a numb strip backward and you have the spinal level. You do not have to memorize all thirty or so. A handful of landmarks anchors the map and the rest fall into place between them.

Feeling travels on two roads, not one, and the exam tests them apart because they cross the midline in different places. Since they cross in different spots, one cord injury can knock out one sense on one side and the other sense on the other side.

The motor exam starts by grading strength from 0 to 5, one muscle group at a time. Gravity is the key to the scale, and grade 3 is the turning point. Above 3, muscles can hold against your push. Below 3, they cannot even beat gravity.

The motor pathway has two relays, and weakness can come from either. The exam tells them apart by the other signs that come with the weakness. Upper damage takes away the brain's control over the cord below, so the muscle gets stiff and its reflexes get too strong. Lower damage cuts the muscle's only lifeline, so the muscle goes limp, wastes away and twitches.

The last part tests polish. Strength moves a limb, but the cerebellum makes the movement smooth, accurate and well-timed. A patient can be fully strong and still not touch their own nose cleanly. When the cerebellum fails, movements overshoot, wobble and stagger, and that group of signs is ataxia.

Lock these in

The five parts run mental status, cranial nerves, sensory, motor, coordination and gait.
Broca's is broken speech. Wernicke's is wordy nonsense.
The tongue and a facial droop lean toward the damaged side.
Pain and temperature cross in the cord. Touch, vibration and position cross in the medulla.
Grade 3 means against gravity only.
A positive Romberg is a position-sense sign, not a cerebellar one.

Worth memorizing

Exam part	What it tests	Points to
1. Mental status	Alertness, knowing where and when you are, memory, language	The cerebral cortex
2. Cranial nerves	Vision, eye movement, face, hearing, tongue: the twelve nerves	The brainstem and the nerves themselves
3. Sensory	Touch, pain, temperature, vibration, position	A spinal nerve, the cord, or a sensory pathway
4. Motor	Strength, tone, muscle size, and reflexes	The motor pathway: upper against lower motor neuron
5. Coordination and gait	Smooth movement, balance, walking	The cerebellum

Area	Its job	If damaged
Broca's area	Produces speech: words and grammar	Broca's aphasia: slow, hard, choppy speech with few small words. The patient still understands, knows the speech is wrong, and feels frustrated.
Wernicke's area	Understands language and attaches meaning	Wernicke's aphasia: smooth-flowing but meaningless speech. The patient cannot understand and often does not realize anything is wrong.
Prefrontal cortex	Judgment, planning, personality, self-control	Acting without a filter, poor judgment, personality change
Hippocampus	Makes new long-term memories	Cannot make new memories, though old ones remain

Testing is simple. To check speech output, ask the person to name objects and repeat a phrase. To check understanding, give a command they must follow, such as pointing to the ceiling and then the door. To check short-term memory, name three words and ask for them back a few minutes later, which tests the hippocampus.

Nerve	How it is tested
I Olfactory	Name a familiar smell with eyes closed, one nostril at a time
II Optic	Sharpness of vision, side vision, and how the pupil reacts to light
III Oculomotor	Pupil shrinking to light and most eye movements. A wide, fixed pupil or a drooping lid points here.
IV Trochlear	Look down and in toward the nose. Weakness causes up-and-down double vision, often noticed on stairs.
V Trigeminal	Feeling on the face in three zones; clench the jaw to feel the chewing muscle
VI Abducens	Look out to the side. If it fails, the eye cannot turn out.
VII Facial	Smile, raise the eyebrows, puff the cheeks. A droop on one side signals a facial nerve problem.
VIII Vestibulocochlear	Hearing, with a whisper or a finger rub, and balance. Tuning-fork tests add detail.
IX Glossopharyngeal	The gag reflex and taste at the back of the tongue, tested along with X
X Vagus	Say "ahh." The soft palate and uvula should rise evenly. Also check voice and swallowing.
XI Accessory	Shrug the shoulders and turn the head while you push back
XII Hypoglossal	Stick out the tongue. It points toward the weak side.

Read a numb strip backward to its spinal level. Several landmarks also pair with a muscle action or a reflex, which lets one finding confirm another.

Level	Landmark
C6	The thumb and the thumb side of the forearm
C7	The middle finger; C7 also powers the triceps
C8	The little finger and the pinky side of the forearm
T4	The nipple line
T10	The belly button
L1	The groin
L4	The inner knee and shin; L4 powers the knee-jerk
L5	The top of the foot and the big toe; L5 lifts the foot up
S1	The little toe and the sole; S1 powers the ankle-jerk

Pathway	Carries	Crosses	Tested with
Spinothalamic tract	Pain and temperature	In the cord, right away	Pinprick, warm or cold
Dorsal columns	Touch, vibration, position	In the medulla, high up	Tuning fork, sensing toe position

Grade	What it means
5	Normal power: full strength against full push
4	Moves against gravity and some push, but weaker than normal
3	Moves against gravity only: can lift the limb, but not against a push
2	Moves only with gravity taken away, such as sliding side to side
1	A flicker or trace of squeeze, but the joint does not move
0	No squeeze at all: complete paralysis

Sign	Upper motor neuron	Lower motor neuron
Location	Brain to spinal cord	Spinal cord to muscle
Tone	Higher, so spastic and stiff	Lower, so flaccid and limp
Reflexes	Stronger than normal	Weaker or missing
Babinski sign	Present, with the big toe going up	Absent
Muscle wasting	Little, and late	A lot, and early
Twitches you can see	Absent	Present

Coordination test	What it checks	Abnormal finding
Finger-to-nose	How well you aim	Dysmetria, meaning overshooting or undershooting, plus a tremor that worsens near the target
Rapid alternating movements	Switching a movement back and forth smoothly	Clumsy, uneven switching
Heel-to-shin	Leg coordination	A heel that wobbles off track
Romberg test	Position sense	Steady with eyes open but falling with eyes closed, which is a dorsal-column problem
Gait	Overall balance and walking	A wide-based, staggering walk, which points to the cerebellum
Pronator drift	Mild upper motor neuron weakness	One arm slowly drifts down and turns palm-down

The Romberg test is the clever detective in that list, and it is not a cerebellar test at all. Balance rests on three inputs: vision, the inner ear and position sense. Closing the eyes takes vision away, so the body must rely on the other two. Someone steady with eyes open who sways or falls with eyes closed has a position-sense problem. A person with a true cerebellar problem is unsteady either way, because the cerebellum never relied on the eyes to begin with.

How to reason through it

Walk-through 1 · naming the aphasia

Language items describe how someone talks and want the area.

Step 1 · listen to the flowSlow, hard and choppy means the speech itself is broken. Smooth and easy means production is fine.

Step 2 · check understandingStill understands means Broca's. Cannot understand means Wernicke's.

Step 3 · check awarenessFrustrated and aware fits Broca's. Unaware anything is wrong fits Wernicke's.

Try itA patient speaks smoothly but the words make no sense, and she does not seem to know. Smooth output rules out Broca's, and lost understanding with no awareness fits Wernicke's aphasia, from the temporal lobe.

Walk-through 2 · upper or lower motor neuron

Weakness is only the start. The companion signs give the answer.

Step 1 · feel the toneStiff and resisting is upper. Limp is lower.

Step 2 · test the reflexesToo strong is upper. Weak or missing is lower.

Step 3 · look at the muscleEarly, heavy wasting with visible twitches is lower. Little and late wasting is upper. A Babinski sign in an adult is upper.

Try itAn arm is weak, stiff, has very strong reflexes and a Babinski sign, with no wasting. Every sign points one way, so this is an upper motor neuron problem, between the brain and the cord.

Walk-through 3 · localizing from a mixed picture

The hardest items give you several findings at once. Take them one at a time, then find what they share.

Step 1 · assign each finding to a levelLanguage and confusion are cortex. A cranial nerve sign is brainstem or that nerve. A numb band is a cord level. Clumsiness is cerebellum.

Step 2 · use the sidesThe tongue and a facial droop lean toward the damage. A weak arm and a drooping face on the same side point to the opposite side of the brain.

Step 3 · pick the one place that explains all of itIf one spot can explain every finding, that is the answer.

Try itA patient has a weak right arm, slurred speech and a drooping right face. All three findings are on the right side of the body, and movement and speech both come from the cortex, so the damage is on the left side of the brain.

Traps people fall into

Swapping the two aphasias. Broca's is broken speech with understanding kept. Wernicke's is smooth nonsense with understanding lost.
Calling Romberg a cerebellar test. A positive result is a position-sense sign.
Crossing both sensory pathways in the same place. Pain and temperature cross in the cord; touch, vibration and position cross in the medulla.
Misreading grade 3. It means against gravity only, with no extra push.
Giving lower motor neuron damage strong reflexes. Those reflexes are weak or missing.
Calling an adult Babinski sign normal. It is normal only in babies.
Pointing the tongue away from the damage. It points toward the weak side.

Chapter 16 self-test · ten items

1. What is the goal of this exam, and what are its five parts in order?

The goal is localization, working back from a finding to a region. The parts are mental status, cranial nerves, sensory, motor, and coordination and gait. They stack from the cortex down to the cerebellum and the walking feet.

2. Which side of the brain usually handles language, and which two areas split the work?

The left side in nearly everyone. Broca's area in the frontal lobe produces speech, and Wernicke's area in the temporal lobe understands it. That split of work between the halves is lateralization.

3. Describe Broca's aphasia and Wernicke's aphasia, including what the patient notices.

Broca's gives slow, hard, choppy speech with understanding kept, and the patient knows and feels frustrated. Wernicke's gives smooth but meaningless speech with understanding lost, and the patient often does not realize. Broca's is broken speech. Wernicke's is wordy nonsense.

4. How would you test cranial nerve XII, and what does an abnormal result show?

Ask the person to stick out the tongue. It points toward the weak, damaged side. A facial droop from nerve VII is also on the damaged side. An uneven soft palate on saying "ahh" points to nerve X.

5. What is a dermatome, and name the landmarks for T4, T10 and S1.

A dermatome is the strip of skin served by one spinal nerve. T4 is the nipple line, T10 is the belly button and S1 is the little toe and sole. Numbness in a strip reads backward to that spinal level.

6. Name the two sensory pathways, what each carries, and where each crosses.

The spinothalamic tract carries pain and temperature and crosses in the cord right away. The dorsal columns carry touch, vibration and position and cross high up in the medulla. Because they cross in different spots, one cord injury can cause a split pattern of loss.

7. What does a strength grade of 3 mean, and why is it the turning point?

The limb moves against gravity only, not against any extra push. Gravity is the key to the scale, so above 3 the muscle can hold against your push and below 3 it cannot even beat gravity. The scale runs 0 to 5.

8. Give three signs that separate upper from lower motor neuron weakness.

Tone is stiff in upper and limp in lower. Reflexes are too strong in upper and weak or missing in lower. Wasting is little and late in upper, but heavy and early with visible twitches in lower. The Babinski sign is present in upper and absent in lower.

9. What is dysmetria, and which test shows it?

Poor aim, overshooting or undershooting a target, shown by the finger-to-nose test. A tremor that gets worse near the target comes with it. Both are cerebellar signs, part of ataxia.

10. A patient is steady with eyes open but falls with eyes closed. What does that mean?

A positive Romberg, which is a position-sense problem in the dorsal columns, not a cerebellar one. Balance rests on vision, the inner ear and position sense. Someone with a true cerebellar problem is unsteady with eyes open too.

One pageCram sheet

Everything from chapters 13 to 16 in one place. Cover the right side of each row and try to rebuild it.

Sequences and pathways, in order

Sequence	The order
Brain regions, top down	Cerebrum → diencephalon → brainstem → cerebellum
Brainstem, top down	Midbrain → pons → medulla oblongata
Cerebrospinal fluid	Choroid plexus → lateral ventricles → interventricular foramina → third ventricle → cerebral aqueduct → fourth ventricle → subarachnoid space → arachnoid granulations → blood
Meninges, outside in	Dura mater → arachnoid mater → pia mater
Light through the eye	Cornea → aqueous humor → pupil → lens → vitreous humor → retina
Visual pathway	Retina → optic nerve → optic chiasm → optic tract → thalamus → optic radiations → primary visual cortex
Sound inward	Auricle → ear canal → eardrum → malleus, incus, stapes → oval window → fluid wave → basilar membrane → organ of Corti → cochlear nerve
Reflex arc	Receptor → sensory neuron → integration center → motor neuron → effector
Autonomic path	Preganglionic neuron → ganglion → postganglionic neuron → organ
Baroreceptor reflex	Baroreceptors → cranial nerves IX and X → medulla → heart and vessels
Neurological exam	Mental status → cranial nerves → sensory → motor → coordination and gait
Motor pathway relays	Upper motor neuron (cortex to cord) → lower motor neuron (cord to muscle)

Numbers, values and maps

Item	Value from the book
Cerebral lobes	4, plus the insula as a hidden fifth
Cortex hidden in the grooves	About two thirds
Ventricles	4: two lateral, third, fourth
Cerebrospinal fluid	About 500 mL made a day; total stays near 150 mL
Brain weight, and weight while floating	About 1,400 g; about 50 g while floating
Meninges	3
Cord ends at	About L1 to L2; the cauda equina continues below
Spinal nerves	31 pairs
Cranial nerves	12 pairs, I to XII; all but the first two come from the brainstem
Cranial nerve types	S, S, M, M, B, M, B, S, B, B, M, M
Receptor groups	5: mechano, thermo, noci, chemo, photo
Eye tunics	3: fibrous, vascular, neural
Basic tastes	5: sweet, sour, salty, bitter, umami
Kinds of smell receptor	About 400, yet thousands of odors can be told apart
Middle-ear bones	3: malleus, incus, stapes; the smallest bones in the body
Reflex arc parts	5
Sympathetic outflow	T1 to L2, thoracolumbar
Parasympathetic outflow	Cranial nerves III, VII, IX, X and S2 to S4, craniosacral
Autonomic neurons per path	2; the somatic system uses 1
Autonomic neurotransmitters	2: acetylcholine and norepinephrine
Strength scale	0 to 5; grade 3 is against gravity only
Dermatome anchors	C6 thumb, C7 middle finger, C8 little finger, T4 nipple, T10 belly button, L1 groin, L4 inner knee, L5 big toe, S1 sole

Rules that decide an answer

Topic	The rule
Lobe names	Each lobe is named for the skull bone above it.
The central sulcus	Motor cortex in front, sensory cortex behind.
Gray and white matter	Brain: gray outside. Cord: gray inside.
Height rule	Higher means chosen and survivable. Lower means automatic and life-threatening.
Thalamus	Every sense stops there except smell.
Cerebellum	It edits movement, never starts it, so damage brings clumsiness, not paralysis.
Blocked fluid	Pressure climbs upstream of the block, which is hydrocephalus.
Meningeal spaces	Epidural bleeds are arterial and lens-shaped. Subdural bleeds are venous and crescent-shaped.
Root traffic	Dorsal is sensory in, ventral is motor out. Cutting one leaves the other intact.
The vagus	The only cranial nerve that leaves the head and neck.
Focusing	The cornea bends light the most; the lens fine-tunes it and rounds up for close work.
Rods and cones	Rods for dim light with no color. Cones for color and detail, packed in the fovea.
The chiasm	Nasal fibers cross, temporal fibers stay. Before it, one eye. At the center, both outer halves. Past it, the same half in both eyes.
Pitch	Mapped by place: base of the basilar membrane for high tones, apex for low.
Smell	Skips the thalamus, goes straight to the limbic system, and its neurons grow back.
Adaptation	Phasic receptors stop firing for a steady stimulus. Pain receptors hardly adapt.
Synapse count in a reflex	Sensory straight onto motor is monosynaptic. Any interneuron makes it polysynaptic.
Ganglion position	Sympathetic near the cord gives a body-wide surge. Parasympathetic at the organ gives a local effect.
Fiber lengths	Sympathetic: short then long. Parasympathetic: long then short.
Which messenger	All preganglionic fibers use acetylcholine. Parasympathetic postganglionic use acetylcholine too. Most sympathetic postganglionic use norepinephrine.
Which effect	The receptor decides, not the chemical. Alpha-1 tightens vessels; beta-2 opens airways.
Negative feedback	The baroreceptor response always opposes the pressure change.
Somatic against autonomic	Somatic: one neuron, acetylcholine only, always excites. Autonomic: two neurons, two chemicals, excites or inhibits.
The aphasias	Broca's is broken speech, understanding kept, patient aware. Wernicke's is smooth nonsense, understanding lost, patient unaware.
Side of the sign	The tongue and a facial droop lean toward the damage. Body weakness points to the opposite side of the brain.
Sensory crossings	Pain and temperature cross in the cord. Touch, vibration and position cross in the medulla.
Upper against lower	Upper: stiff, strong reflexes, Babinski, little wasting. Lower: limp, weak reflexes, early wasting, twitches.
Romberg	Falls only with eyes closed means position sense. Unsteady either way means cerebellum.