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Week 13 · Chapter

Chapter 13 — The Central Nervous System

Human Anatomy and Physiology I Free sample edition

The module's primary reading · ~45–55 minutes · Objective 7 (describe the organization of the nervous system — the brain's major regions and their functions, the spinal cord, the meninges, cerebrospinal fluid, and the reflex arc in the central nervous system; the cranial and spinal nerves, afferent and efferent traffic, and the somatic and autonomic divisions in the peripheral nervous system; and the opposing sympathetic and parasympathetic branches as a homeostatic pair), Objective 3 (identify the four primary tissue types and their subtypes from their structural features, name an epithelium by its layers and cell shape, and describe the layers, accessory structures, and homeostatic functions of the integumentary system, including thermoregulation as a negative-feedback loop) · Read it first this week; the lecture, the slides, the tutorial, the quiz, and the Map the Brain lab all build on it.

In plain language

Your brain and spinal cord are the body's headquarters, where every signal is sorted and every command begins. This week you learn the map: which part of the brain sees, which part hears, which part moves you, and which part keeps you breathing. You meet the meninges (three wrappings that protect the brain and spinal cord) and the clear fluid that cushions them. You finish with the reflex arc (the short, fixed path a fast, automatic response takes), the reason your hand leaves a hot pan before you feel the burn. Once you know where each job lives, you can predict what goes wrong when one place is hurt.

Why you already care about this

Picture a kitchen on a busy evening. You reach for a pan without looking, and the handle is hot. Your hand jerks back before you even feel the burn. Only afterward does the sting arrive, and then the thought: that pan was hot. Something moved you before you knew there was a problem.

Now picture 2 other moments. You carry a full mug of tea up a flight of stairs, and your arm keeps it level on every step without a single conscious correction. On a cold morning you step outside, start to shiver, and your skin turns to goosebumps, though you never decided to do either. Each of those moments was run by a different part of your central nervous system, and each part has a place you can point to on a map of the brain or the spinal cord.

This chapter draws that map. You start with the two big divisions and the two kinds of tissue. Then you tour the brain from its folded surface down to the stem. Then you wrap it in its protective layers. Finally you follow the fast loop that pulled your hand off the pan.

By the end of this chapter you will be able to:

sort the nervous system into the CNS and the PNS, and tell gray matter from white matter;
place the four lobes of the cerebrum and give each lobe its job;
tell the cerebellum's job from the cerebrum's, and the thalamus's job from the hypothalamus's;
name the three parts of the brainstem in order and explain why the medulla matters so much;
order the meninges from outer to inner and say where cerebrospinal fluid circulates and what it does;
put the five parts of the reflex arc in order and explain why a reflex does not wait for the brain;
predict a lost ability from the place an injury reaches, and stop at the prediction.

Carry this sentence with you: occipital sees, temporal hears — never the other way round.

Where we are

Already covered: Week 1, Body Organization, Homeostasis & Anatomical Terminology, gave you the three parts of a feedback loop and the dorsal cavity that holds the brain and spinal cord. Week 5, Tissues, named nervous tissue as neurons plus neuroglia. Week 9, The Skeleton & Joints, built the vertebral column that houses the spinal cord. Week 11, The Muscular System, showed muscles working in agonist and antagonist pairs. Week 12, Nervous Tissue, the Neuron & the Action Potential, opened the neuron, its myelin, its neuroglia, and the synapse.
This week: the central nervous system as a map. You sort gray from white matter, then tour the four lobes, the cerebellum, the thalamus and hypothalamus, the brainstem, and the spinal cord. Then come the meninges and cerebrospinal fluid, and the reflex arc in order.
How they connect: Week 12 showed one neuron firing; this week shows where those firings are organized. The control center of Week 1's loops finally gets its name.
Where we're going next: Week 14, The Peripheral & Autonomic Nervous System, follows the nerves out of the brain and spinal cord and meets the body's autopilot.

Here is what you lean on this week. In Week 1 you learned that every homeostatic loop has a receptor that senses, a control center that compares the report with a set point, and an effector that responds. In Week 12 you learned that a neuron receives on its dendrites, integrates in its cell body, and sends an impulse down its axon. You also learned that myelin speeds that impulse, that oligodendrocytes make myelin in the brain and spinal cord, and that ependymal cells help make the fluid that fills the brain's spaces. In Week 11 you saw that a muscle only pulls, so a flexor needs an antagonist on the other side. All three return this week.

1. Sort the nervous system: two divisions and two kinds of matter

Think of a city's power system. There is a central station where the decisions are made, and there are cables that run out to every house. Your nervous system is built the same way.

The central nervous system is the brain and the spinal cord, the part of the nervous system that processes signals and issues commands; abbreviated CNS.
The peripheral nervous system is every part of the nervous system outside the brain and spinal cord, the nerves and ganglia; abbreviated PNS.

Inside the CNS, the tissue sorts into two kinds you can tell apart by eye on a cut brain. One kind looks grayish; the other looks pale. The difference is what each region is packed with.

Gray matter is a region of the central nervous system dense with neuron cell bodies and dendrites, where signals are processed.
White matter is a region of the central nervous system dense with myelinated axons, the wiring that carries signals from one region to another.

Read the pair as structure to function. Cell bodies and dendrites are where a neuron receives and integrates, so a region crowded with them is a region that processes. Myelinated axons carry impulses fast over a distance, so a region crowded with them is wiring.

Worked example — sort four structures. You sort each structure into the CNS or the PNS, then sort two tissue regions into gray or white.

The spinal cord: part of the CNS.
A nerve in the forearm: outside the brain and spinal cord, so part of the PNS.
A region packed with neuron cell bodies: gray matter, a processing region.
A region packed with myelinated axons: white matter, wiring.

In words: the CNS is the headquarters, the PNS is the cables, gray matter processes, and white matter carries.

Misconception check. Students often call white matter "where the thinking happens," because the word white sounds clean and important. It is tempting, but the cure is to ask what the region is packed with. Cell bodies and dendrites, the processing parts, fill gray matter. Myelinated axons, the wiring, fill white matter.

2. Map the cerebrum: gyri, sulci, and four lobes

Crumple a sheet of paper into a ball. A large sheet now fits in a small fist, and its surface is all ridges and grooves. The surface of the brain's largest part looks the same way.

The cerebrum is the largest part of the brain, folded into ridges and grooves and divided on each side into the frontal, parietal, temporal, and occipital lobes. Its outer layer is the cortex, the cerebrum's outer layer of gray matter, where signals are processed.

A gyrus is a ridge of cortex on the folded surface of the cerebrum; the plural is gyri.
A sulcus is the groove between two gyri on the surface of the cerebrum; the plural is sulci.

Now read the cerebrum as a labeled figure, seen from the side with the face to the left. Four lobes divide each side, and their names tell you where they sit.

The frontal lobe sits at the front, behind the forehead.
The parietal lobe sits on top, behind the frontal lobe.
The temporal lobe sits at the side, near the ear.
The occipital lobe sits at the back.

Worked example — the CNS key, the four lobes placed. You place each lobe, then count them.

Frontal: the front.
Parietal: the top, behind the frontal lobe.
Temporal: the side.
Occipital: the back.
Count the lobes: 1 + 1 + 1 + 1 = 4 lobes on each side of the cerebrum.

In words: four lobes, front, top, side, and back, and the same four sit on each side.

Misconception check. Students often think a gyrus and a sulcus are two separate organs. It is tempting because both get Latin names. The cure is the crumpled paper: a gyrus is a ridge of the same folded cortex, and a sulcus is the groove between two ridges. They are two shapes of one surface.

3. Give each lobe its job

Think about the last time you waved to a friend across a street, heard them call your name, felt the cold railing under your hand, and saw them step off the curb. Four different jobs happened at once, and each one ran in a different lobe.

Each lobe has a main job, and the job follows from the lobe's place.

The frontal lobe is the lobe at the front of the cerebrum that runs motor functions, produces language in Broca's area, and ties personality, short-term memory, and consciousness to its prefrontal areas.
The precentral gyrus is the ridge of the frontal lobe that is the primary motor cortex, where commands for voluntary movement begin.
Broca's area is a region of the frontal lobe responsible for the production of language.
The prefrontal areas are the front-most regions of the frontal lobe, tied to personality, short-term memory, and consciousness.
The parietal lobe is the lobe on top of the cerebrum, behind the frontal lobe, that processes body sensation on its postcentral gyrus.
Somatosensation is body sensation: touch, pressure, pain, and position, processed in the parietal lobe.
The postcentral gyrus is the ridge of the parietal lobe where somatosensation, the sense of touch, pressure, pain, and position, is processed.
The temporal lobe is the lobe at the side of the cerebrum that holds primary auditory sensation and works with memory through the limbic system.
The occipital lobe is the lobe at the back of the cerebrum that holds primary visual perception.

Worked example — the CNS key, the four lobes and their jobs. You pair each lobe with its place and its job, then count.

Frontal (front): movement from the precentral gyrus, language production in Broca's area, and personality, short-term memory, and consciousness in the prefrontal areas.
Parietal (top): touch, pressure, pain, and position on the postcentral gyrus.
Temporal (side): hearing and memory.
Occipital (back): vision.
Count: frontal + parietal + temporal + occipital, so 1 + 1 + 1 + 1 = 4 lobes on each side of the cerebrum.

In words: the street scene used all four. The wave came from the frontal lobe, the cold railing from the parietal lobe, your name from the temporal lobe, and the sight of your friend from the occipital lobe.

Misconception check. Students often give hearing to the occipital lobe and vision to the temporal lobe. It is tempting because both lobes sit toward the back half of the head and neither name sounds like an eye or an ear. The cure is the carry line: occipital sees, temporal hears. The occipital lobe is at the back and holds primary visual perception; the temporal lobe is at the side, by the ear, and holds primary auditory sensation. This pairing costs more points than any other this week.

Honesty note: the limbic system, the other language areas, and the detailed map of the cortex are beyond this course. You need the four lobes, the two named gyri, Broca's area, and the prefrontal areas.

Pause and think, then choose one. (a) Describe a moment from your own day and name the lobe behind each part. (b) Explain to a friend why two ridges in different lobes do different jobs.

4. Polish the move: the cerebellum

Carry that full mug of tea up the stairs again. You decided to climb, and your legs started. But on every step the mug tilted a little, your arm felt the tilt, and the mug came level again. Something compared what you meant to do with what actually happened and fixed the gap.

The cerebellum is the brain region that compares the motor command with sensory feedback about the movement and so coordinates movement, balance, and posture.

The division of labor is clean. The cerebrum plans the move and sends the command from the precentral gyrus. The cerebellum compares that command with the feedback from the body and polishes the move while it is happening.

Worked example — who does what on the stairs. You assign each part of the climb to the cerebrum or the cerebellum.

Deciding to climb and starting the legs: the cerebrum plans and commands.
Feeling the mug tilt: sensory feedback arrives.
Comparing the tilt with the plan and leveling the mug: the cerebellum coordinates.
Keeping your body upright on a narrow step: the cerebellum's balance and posture.

In words: the cerebrum writes the plan, and the cerebellum keeps the plan on course.

Misconception check. Students often say "the cerebrum coordinates movement," because the cerebrum is the biggest part of the brain and seems to run everything. It is tempting, but the cure is to separate planning from polishing. The cerebrum plans and commands; the cerebellum compares the command with feedback and coordinates.

5. Tell the relay from the regulator: the thalamus and the hypothalamus

Step outside on that cold morning again. Two things happen. The cold you feel on your face travels up to your cortex so you notice it. And, without your noticing, your body starts to shiver and raise goosebumps to hold its temperature near 37 °C. Two small neighbors deep in the brain handle those two jobs.

The diencephalon is the part of the brain that holds the thalamus and the hypothalamus. The two names differ by one prefix, and the jobs differ completely.

The thalamus is the relay of the brain: every sensory signal except smell passes through it on its way to the cortex.
The hypothalamus is a cluster of nuclei whose main job is holding the body's internal conditions steady, the control center of many homeostatic loops.

The hypothalamus is the control center you met in Week 1 without a name. In the body-temperature loop, receptors report the temperature, the control center compares the report with the set point of about 37 °C, and effectors such as shivering and sweat respond. That comparing job belongs to the hypothalamus.

Worked example — sort the cold-morning signals. You assign each event to the thalamus or the hypothalamus.

The feeling of cold on your face travels to the cortex: it passes through the thalamus, the relay.
The sight of frost on the step travels to the occipital lobe: it passes through the thalamus too.
Your body temperature is compared with the set point, and shivering starts: the hypothalamus regulates.
The smell of a neighbor's wood fire: the one sense that does not pass through the thalamus.

In words: the thalamus passes sensations along; the hypothalamus keeps conditions steady.

Misconception check. Students often swap the thalamus and the hypothalamus, because the names are nearly identical and the two sit side by side. The cure is two verbs: the thalamus relays, and the hypothalamus regulates. If the job is passing a sensation to the cortex, it is the thalamus. If the job is holding an internal condition steady, it is the hypothalamus.

6. Descend the brainstem: midbrain, pons, and medulla

Every breath you took while reading this page happened without a decision. Your heart kept time without one too. Those life-sustaining rhythms are regulated low in the brain, in the stalk that connects the brain to the spinal cord.

The brainstem is the midbrain, the pons, and the medulla oblongata, which together regulate the cardiovascular and respiratory systems. Read its three parts from top to bottom.

The midbrain is the uppermost of the brainstem's three parts, above the pons.
The pons is the middle part of the brainstem, between the midbrain and the medulla oblongata.
The medulla oblongata is the lowest part of the brainstem, which helps regulate the heartbeat and breathing and is the most life-and-death region of the body.

Worked example — the CNS key, the brainstem in order. You order the three parts and count them.

Top: midbrain.
Middle: pons.
Bottom: medulla oblongata, the medulla for short.
Order: midbrain → pons → medulla oblongata, so 1 + 1 + 1 = 3 parts, with the medulla's controls of the heartbeat and breathing at the bottom of the chain.

In words: three parts, top to bottom, and the lowest one holds the controls you can least afford to lose.

Run the three-step read from Week 8 on the medulla. Name it: the medulla oblongata, the lowest part of the brainstem. State its function: it helps regulate the heartbeat and breathing. Name the clinical connection: an injury to the medulla threatens those life-sustaining controls, which is why it is the most life-and-death real estate in the body. You name the structure and stop.

Misconception check. Students often assume the largest part of the brain must be the most vital part, because size sounds like importance. It is tempting, but the cure is the job. The cerebrum is the largest part; the medulla is small, yet it helps run the heartbeat and breathing, so an injury there is the most dangerous.

7. Read the spinal cord in cross-section

Picture a cord cut straight across, the way you would slice a carrot. On the cut face of the spinal cord you would see a darker gray region in the middle, surrounded by a paler ring.

The spinal cord is the part of the central nervous system inside the vertebral column, with gray matter inside and white matter outside, that conducts signals to and from the brain and integrates reflexes.

The horns are the regions of gray matter on the inside of the spinal cord, seen in a cross-section.
The columns are the bundles of white matter on the outside of the spinal cord that carry signals up and down the cord.

Read it as structure to function. The white columns on the outside are wiring, carrying signals up to the brain and down from it. The gray horns on the inside are processing, which is how the cord can integrate a reflex on its own without waiting for the brain.

Worked example — the CNS key, gray and white sorted. You compare the cerebrum with the spinal cord.

Cerebrum: the cortex is gray matter on the outside.
Spinal cord: the gray matter, in horns, is on the inside.
Spinal cord: the white matter, in columns, is on the outside.

In words: the cerebrum keeps its gray on the outside, and the cord keeps its gray on the inside.

Misconception check. Students often assume the spinal cord is built like the cerebrum, gray outside and white inside, because both are CNS. It is tempting because the same two tissues appear in both. The cure is the carrot slice: in the cord the gray horns are inside and the white columns are outside, the reverse of the cerebrum's cortex.

8. Layer the protection: the meninges, outer to inner

A cyclist's helmet has a hard shell, a soft liner, and a strap that holds it snug against the head. The brain and spinal cord wear something similar, but it is made of living membranes.

The meninges are the three protective membranes around the brain and spinal cord: the dura mater, the arachnoid mater, and the pia mater, from outer to inner. Read them as a labeled figure from the skull inward.

The dura mater is the tough outer covering of the brain and spinal cord, the outermost of the meninges.
The arachnoid mater is the fine, web-like middle layer of the meninges, draped loosely over the brain.
The subarachnoid space is the space under the arachnoid mater, above the pia mater, where cerebrospinal fluid circulates.
The pia mater is the delicate innermost layer of the meninges, which clings to the brain's surface and dips into every sulcus.

The names carry their meaning. The dura is tough. The arachnoid is web-like. The pia is delicate and hugs every groove.

Worked example — the CNS key, the meninges in order. You order the layers from the outside in and count them.

Outer: dura mater.
Middle: arachnoid mater.
Below the arachnoid: the subarachnoid space, with its cerebrospinal fluid.
Inner: pia mater, on the brain's surface.
Order: dura mater → arachnoid mater → pia mater, so 1 + 1 + 1 = 3 layers, with the subarachnoid space and its CSF between the arachnoid mater and the pia mater.

In words: tough, web, delicate — outside in, with the fluid under the web.

Misconception check. Students often reverse the meninges and put the pia on the outside, because the names are unfamiliar and the list is easy to read backward. The cure is the meaning of each name. The tough layer has to face the skull, so the dura is outer; the delicate layer has to follow every sulcus, so the pia is inner. The arachnoid sits between them.

9. Follow the cerebrospinal fluid

Think of an egg yolk floating in its white. Shake the egg gently and the yolk drifts but rarely breaks, because the liquid around it takes the jolt. Your brain floats in a clear fluid that works much the same way.

The fluid has a name, a source, and three jobs.

Cerebrospinal fluid is the clear fluid made by the choroid plexus that circulates in the subarachnoid space, cushions and floats the brain, and carries away metabolic wastes; abbreviated CSF.
The ventricles are the four fluid-filled spaces inside the brain, two lateral ventricles, a third, and a fourth, each with a choroid plexus.
The choroid plexus is the tissue in each ventricle where ependymal cells filter blood to make cerebrospinal fluid.

The amount made is roughly 500 milliliters a day. Learn that figure in words; it varies with the estimate and it is never a quiz answer.

Worked example — the CNS key, the ventricles counted. You count the ventricles that make CSF.

Lateral ventricles: 2.
Third ventricle: 1.
Fourth ventricle: 1.
Count: 2 lateral + 1 third + 1 fourth = 4 ventricles, each with a choroid plexus that makes CSF.

In words: four spaces, each with its own choroid plexus, keep the fluid coming.

CSF does three jobs. It is a liquid cushion that takes the jolt of a bump. It floats the brain, giving it buoyancy. And it carries away metabolic wastes.

Misconception check. Students often say CSF carries oxygen to the brain the way blood does, because it is a body fluid that flows around the brain. It is tempting, but the cure is to list its three jobs: cushion, buoyancy, and waste removal. Carrying oxygen is not on the list.

That is the clinical connection, in standard terms: a lumbar puncture is a procedure in which a needle reaches the subarachnoid space of the lower back, below where the spinal cord ends. You name the space and stop.

Worked example — trace a needle's path. You order the meninges a lumbar puncture's needle crosses.

First layer crossed: dura mater.
Second layer crossed: arachnoid mater.
Arrival: the subarachnoid space, where the CSF is.
Order: dura mater → arachnoid mater → subarachnoid space, so the needle crosses 2 layers to reach the CSF and stops short of the pia mater.

In words: the needle passes the tough layer and the web, and it reaches the fluid under the web.

Caveat: the egg-in-its-white picture is a classroom model of cushioning and buoyancy, not a description of how the brain is held in place.

10. Order the reflex arc

Back to the hot pan. Your hand was already moving before the burn reached your awareness. The signal never went up to the cortex and back. It took a short loop through the spinal cord, and every link in that loop sits in a fixed order.

A reflex arc is the ordered pathway of a reflex: receptor, sensory neuron, an interneuron in the spinal cord, motor neuron, and effector.
A sensory neuron is a neuron that carries a signal from a receptor toward the central nervous system; also called an afferent neuron.
An interneuron is a neuron inside the central nervous system that connects one neuron to another; in a spinal reflex it integrates the signal between the sensory neuron and the motor neuron.

You already know the motor neuron from Week 10: it carries the command out to a muscle. Here it is the efferent link.

Worked example — the CNS key, the reflex arc in order. You follow the hot pan through all five parts.

Receptor: heat receptors in the skin of the hand sense the hot handle.
Sensory (afferent) neuron: carries the signal to the spinal cord.
Interneuron in the spinal cord: integrates the signal.
Motor (efferent) neuron: carries the command out to the arm.
Effector: the flexor muscles pull the hand away.
Order: receptor → sensory (afferent) neuron → interneuron in the spinal cord → motor (efferent) neuron → effector, so 1 + 1 + 1 + 1 + 1 = 5 parts.

In words: in, across, and out, with the spinal cord doing the deciding.

The withdrawal reflex is the reflex that pulls a body part away from a harmful stimulus, integrated in the spinal cord before the pain reaches awareness, with the antagonist's motor neuron inhibited so the flexor can act. That last clause links back to Week 11. A muscle only pulls, so the flexor that bends your elbow has an antagonist that would straighten it. The interneuron quiets the antagonist's motor neuron so the flexor can pull without a fight.

Why is a reflex faster than a decision? A decision sends the signal up through the cord to the cortex, waits for a plan, and sends a command back down. A reflex fires without the higher centers in the loop, so the hand is moving while the pain is still on its way up.

Misconception check. Students often say "a reflex has to go through the brain first," because the brain seems to be in charge of every movement. It is tempting, but the cure is the arc. The interneuron that integrates the withdrawal reflex sits in the spinal cord, so the cord decides, and the brain hears about it afterward.

Pause and think, then choose one. (a) Describe a reflex you have noticed and name its five parts in order. (b) Explain to a friend why the spinal cord, not the brain, integrates the withdrawal reflex.

11. Predict the deficit from the place

Now put the map to work. If every job lives in a place, then damage to a place predicts which job is lost. You can read an injury this way, as long as you stop at the prediction.

A stroke is an event that damages a region of the brain. The week's clinical connection, in standard terms: a stroke in the occipital lobe predicts vision loss, because the occipital lobe holds primary visual perception.

Worked example — the CNS key, a location read in three moves. You read the place, name its job, and predict the lost job.

Place: a stroke in the occipital lobe.
Job of that place: primary visual perception.
Prediction: a stroke in the occipital lobe → the primary visual area is damaged → vision loss.

In words: the place names the job, and the job names the loss.

Worked example — count the whole key. You add every item the week's CNS key holds.

Lobes: 4.
Brainstem parts: 3.
Meninges: 3.
Ventricles: 4.
Reflex-arc parts: 5.
Count every item in the key: 4 lobes + 3 brainstem parts + 3 meninges + 4 ventricles + 5 reflex-arc parts, so 4 + 3 + 3 + 4 + 5 = 19 items.

In words: nineteen places and links make up the map you carry into the lab.

Misconception check. Students often predict a hearing loss after damage to the occipital lobe, because the occipital lobe is near the back of the head where sounds seem to arrive. The cure is the carry line again: occipital sees, temporal hears. A stroke in the occipital lobe predicts vision loss.

Honesty note: this chapter predicts a lost job from a place and stops there. How a stroke is diagnosed or treated, and any care for it, are not part of this course.

Key terms

Central nervous system — The brain and the spinal cord, the part of the nervous system that processes signals and issues commands; abbreviated CNS. (first used: 1. Sort the nervous system: two divisions and two kinds of matter)
Peripheral nervous system — Every part of the nervous system outside the brain and spinal cord, the nerves and ganglia; abbreviated PNS. (first used: 1. Sort the nervous system: two divisions and two kinds of matter)
Gray matter — A region of the central nervous system dense with neuron cell bodies and dendrites, where signals are processed. (first used: 1. Sort the nervous system: two divisions and two kinds of matter)
White matter — A region of the central nervous system dense with myelinated axons, the wiring that carries signals from one region to another. (first used: 1. Sort the nervous system: two divisions and two kinds of matter)
Cerebrum — The largest part of the brain, folded into ridges and grooves and divided on each side into the frontal, parietal, temporal, and occipital lobes. (first used: 2. Map the cerebrum: gyri, sulci, and four lobes)
Cortex — The cerebrum's outer layer of gray matter, where signals are processed. (first used: 2. Map the cerebrum: gyri, sulci, and four lobes)
Gyrus — A ridge of cortex on the folded surface of the cerebrum; the plural is gyri. (first used: 2. Map the cerebrum: gyri, sulci, and four lobes)
Sulcus — The groove between two gyri on the surface of the cerebrum; the plural is sulci. (first used: 2. Map the cerebrum: gyri, sulci, and four lobes)
Frontal lobe — The lobe at the front of the cerebrum that runs motor functions, produces language in Broca's area, and ties personality, short-term memory, and consciousness to its prefrontal areas. (first used: 3. Give each lobe its job)
Precentral gyrus — The ridge of the frontal lobe that is the primary motor cortex, where commands for voluntary movement begin. (first used: 3. Give each lobe its job)
Broca's area — A region of the frontal lobe responsible for the production of language. (first used: 3. Give each lobe its job)
Prefrontal areas — The front-most regions of the frontal lobe, tied to personality, short-term memory, and consciousness. (first used: 3. Give each lobe its job)
Parietal lobe — The lobe on top of the cerebrum, behind the frontal lobe, that processes body sensation on its postcentral gyrus. (first used: 3. Give each lobe its job)
Somatosensation — Body sensation: touch, pressure, pain, and position, processed in the parietal lobe. (first used: 3. Give each lobe its job)
Postcentral gyrus — The ridge of the parietal lobe where somatosensation, the sense of touch, pressure, pain, and position, is processed. (first used: 3. Give each lobe its job)
Temporal lobe — The lobe at the side of the cerebrum that holds primary auditory sensation and works with memory through the limbic system. (first used: 3. Give each lobe its job)
Occipital lobe — The lobe at the back of the cerebrum that holds primary visual perception. (first used: 3. Give each lobe its job)
Cerebellum — The brain region that compares the motor command with sensory feedback about the movement and so coordinates movement, balance, and posture. (first used: 4. Polish the move: the cerebellum)
Diencephalon — The part of the brain that holds the thalamus and the hypothalamus. (first used: 5. Tell the relay from the regulator: the thalamus and the hypothalamus)
Thalamus — The relay of the brain: every sensory signal except smell passes through it on its way to the cortex. (first used: 5. Tell the relay from the regulator: the thalamus and the hypothalamus)
Hypothalamus — A cluster of nuclei whose main job is holding the body's internal conditions steady, the control center of many homeostatic loops. (first used: 5. Tell the relay from the regulator: the thalamus and the hypothalamus)
Brainstem — The midbrain, the pons, and the medulla oblongata, which together regulate the cardiovascular and respiratory systems. (first used: 6. Descend the brainstem: midbrain, pons, and medulla)
Midbrain — The uppermost of the brainstem's three parts, above the pons. (first used: 6. Descend the brainstem: midbrain, pons, and medulla)
Pons — The middle part of the brainstem, between the midbrain and the medulla oblongata. (first used: 6. Descend the brainstem: midbrain, pons, and medulla)
Medulla oblongata — The lowest part of the brainstem, which helps regulate the heartbeat and breathing and is the most life-and-death region of the body. (first used: 6. Descend the brainstem: midbrain, pons, and medulla)
Spinal cord — The part of the central nervous system inside the vertebral column, with gray matter inside and white matter outside, that conducts signals to and from the brain and integrates reflexes. (first used: 7. Read the spinal cord in cross-section)
Horns — The regions of gray matter on the inside of the spinal cord, seen in a cross-section. (first used: 7. Read the spinal cord in cross-section)
Columns — The bundles of white matter on the outside of the spinal cord that carry signals up and down the cord. (first used: 7. Read the spinal cord in cross-section)
Meninges — The three protective membranes around the brain and spinal cord: the dura mater, the arachnoid mater, and the pia mater, from outer to inner. (first used: 8. Layer the protection: the meninges, outer to inner)
Dura mater — The tough outer covering of the brain and spinal cord, the outermost of the meninges. (first used: 8. Layer the protection: the meninges, outer to inner)
Arachnoid mater — The fine, web-like middle layer of the meninges, draped loosely over the brain. (first used: 8. Layer the protection: the meninges, outer to inner)
Subarachnoid space — The space under the arachnoid mater, above the pia mater, where cerebrospinal fluid circulates. (first used: 8. Layer the protection: the meninges, outer to inner)
Pia mater — The delicate innermost layer of the meninges, which clings to the brain's surface and dips into every sulcus. (first used: 8. Layer the protection: the meninges, outer to inner)
Cerebrospinal fluid — The clear fluid made by the choroid plexus that circulates in the subarachnoid space, cushions and floats the brain, and carries away metabolic wastes; abbreviated CSF. (first used: 9. Follow the cerebrospinal fluid)
Ventricles — The four fluid-filled spaces inside the brain, two lateral ventricles, a third, and a fourth, each with a choroid plexus. (first used: 9. Follow the cerebrospinal fluid)
Choroid plexus — The tissue in each ventricle where ependymal cells filter blood to make cerebrospinal fluid. (first used: 9. Follow the cerebrospinal fluid)
Lumbar puncture — A procedure in which a needle reaches the subarachnoid space of the lower back, below where the spinal cord ends. (first used: 9. Follow the cerebrospinal fluid)
Reflex arc — The ordered pathway of a reflex: receptor, sensory neuron, an interneuron in the spinal cord, motor neuron, and effector. (first used: 10. Order the reflex arc)
Sensory neuron — A neuron that carries a signal from a receptor toward the central nervous system; also called an afferent neuron. (first used: 10. Order the reflex arc)
Interneuron — A neuron inside the central nervous system that connects one neuron to another; in a spinal reflex it integrates the signal between the sensory neuron and the motor neuron. (first used: 10. Order the reflex arc)
Withdrawal reflex — The reflex that pulls a body part away from a harmful stimulus, integrated in the spinal cord before the pain reaches awareness, with the antagonist's motor neuron inhibited so the flexor can act. (first used: 10. Order the reflex arc)

Summary

The CNS is the brain and spinal cord; the PNS is everything outside them.
Gray matter processes; white matter is the wiring.
Gyri are ridges; sulci are grooves.
Frontal: movement, language production, personality.
Parietal: touch, pressure, pain, position.
Temporal: hearing and memory.
Occipital: vision.
The cerebrum plans; the cerebellum coordinates.
The thalamus relays; the hypothalamus regulates.
The brainstem runs midbrain, pons, medulla, top to bottom.
The spinal cord has gray inside and white outside.
Meninges, outer to inner: dura, arachnoid, pia.
CSF cushions, floats, and cleans; it does not carry oxygen.
Reflex arc: receptor, sensory neuron, interneuron, motor neuron, effector.
A place predicts a deficit: occipital damage predicts vision loss.

Check your understanding

Work these before looking at the answers — they are ungraded, and the answers (with reasoning) are at the bottom of the page.

A made-up study card lists the meninges "pia mater, arachnoid mater, dura mater, from outer to inner," and says the CSF sits under the pia. Find both errors and correct them.
In a made-up case, a small injury damages the postcentral gyrus on one side and leaves every other region untouched. Which lobe is that, and which ability would you predict is affected?
Sort these three made-up jobs between the thalamus and the hypothalamus: (a) passing the sound of a doorbell to the cortex; (b) raising goosebumps in a cold garage; (c) passing the feel of a cat's fur to the cortex.
A classmate says, "When you step on a tack, the signal goes to the brain first, and then the cerebrum coordinates the foot pulling away." Say what is wrong with each half and correct it.

Answers (worked reasoning — read after attempting)

The order is reversed: from outer to inner the meninges are dura mater, arachnoid mater, pia mater. The CSF circulates in the subarachnoid space, which lies under the arachnoid mater and above the pia mater, not under the pia. The pia clings to the brain's surface, so nothing lies between it and the brain.
The postcentral gyrus is a ridge of the parietal lobe, where somatosensation is processed. You would predict a loss of touch, pressure, pain, or position sense. You stop at the prediction.
(a) Thalamus, the relay that passes a sound on its way to the cortex. (b) Hypothalamus, the regulator that holds body temperature steady. (c) Thalamus, the relay for touch. Count: 2 relay jobs + 1 regulating job = 3 jobs.
The first half is wrong because the withdrawal reflex is integrated by an interneuron in the spinal cord, not the brain, so the foot moves before the pain reaches awareness. The second half is wrong because the cerebellum, not the cerebrum, coordinates movement; in a reflex neither one is in the loop, and the arc runs receptor, sensory neuron, interneuron, motor neuron, effector.

Next up in this module: the lecture, the slides, the Readings & Resources page, the tutorial, the practice set, and the quiz. Next week the sympathetic and parasympathetic branches, the body's autopilot model, take over the organs this map controls.

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