Central Nervous System

Brain Basics

The brain is part of your central nervous system (CNS) and controls every part of your daily life, including thought and movement. It is a living communication system similar to a supercomputer. Signals that travel to and from the brain can reach speeds as fast as 170 miles per hour, and the human brain can store five times as much information as the Encyclopedia Britannica. The brain allows us to think, have emotions, move, and even dream.

This Lesson will be an introduction to this amazing control center of our bodies. You will study the specific parts of the brain and learn how each part functions.

The average human brain weighs about three pounds and looks like a large pinkish-gray walnut. The brain can be divided down a mid-saggital plane into two halves called the cerebral hemispheres. Each cerebral hemisphere is divided into four lobes.

The brain has sulci, or fissures. They are the grooves in the brain. The gyri are the bumps that are visible on the surface of the brain. The folding by the sulci and gyri increases the amount of cerebral cortex that can fit into the skull. The total surface area of the cerebral cortex is approximately 324 square inches, or about the size of a full page of newspaper.

Similar to a fingerprint, each person has a unique pattern of gyri and sulci. Explore the rest of the brain below. Be sure to label each part of the brain and provide a brief description of its function in your guided notes.

Cerebrum

The cerebrum is the largest region of the human brain. It is responsible for voluntary, or conscious, body activities and emotions. It is also the site responsible for intelligence, learning, and judgment. A deep groove divides the cerebrum into left and right hemispheres.

Cerebellum

The cerebellum is located behind the hindbrain and is tucked partially beneath the cerebrum. It is responsible for the coordination of movement. It receives sensory information from nerves near joints and muscles, as well as information from visual and auditory systems. It uses this information to provide unconscious coordination of movement and balance. Hand-eye coordination is one example of the cerebellum's function.

Cerebral Cortex

The outer layer of the cerebrum is called the cerebral cortex. It is made up of densely packed nerve cell bodies often called gray matter. The cerebral cortex controls body movements and processes information from the sense organs, thoughts, plans, and learning abilities. Each hemisphere of the cerebral cortex deals mainly with the opposite side of the body: Impulses from the left side of the body are processed in the right hemisphere, and those from the right side of the body are processed in the left hemisphere. Both hemispheres of the cerebrum can be divided into four lobes, each associated with different functions.

Corpus Callosum

The corpus callosum is a bundle of fibers that connects the right and left hemispheres of the brain, allowing communication between the two.

Pons

The pons is located just above the medulla oblongata, and they work together to relay sensory information and regulate blood and oxygen flow. The pons has roles in your level of arousal or consciousness and sleep and is important to keep the body alive and functioning.

Medulla Oblongata

The medulla oblongata is found in the lowest part of the brain stem, just above the spinal cord. It is responsible for controlling several autonomic body functions that occur even without you thinking about them. These functions include breathing, heartbeats, blood vessel activity, swallowing, vomiting, and digestion.

Thalamus

The thalamus is a pair of egg-shaped masses lying beneath each cerebral hemisphere in the brain. This region of the brain is a major relay station for information on its way to the cerebrum from the spinal cord. It sorts sensory information by type and then sends it on to the appropriate area of the higher brain for further processing.

Hypothalamus

The hypothalamus is the central area on the underside of the brain. It is important for regulating homeostasis, hunger and eating, thirst and drinking, emotions, and many other functions of basic survival. This section of the brain is the major link between the nervous system and the endocrine system.

Pituitary Gland

The pituitary gland is a small oval gland at the base of the brain that is controlled by the hypothalamus. This gland secretes many of the hormones that regulate the endocrine system.

Brain Stem

The brain stem is located at the bottom of the brain, connecting the brain to the spinal cord. It includes three regions: the midbrain, pons, and medulla oblongata. Each of these regions helps regulate the flow of information between the brain and the rest of the body. This region of the brain controls some of the body's most important functions, such as blood pressure, heart rate, breathing, and swallowing.

Frontal Lobe

The frontal lobe is the front part of each hemisphere. This lobe processes information from all other areas of the brain. This area of the brain is our emotional control center and the area we use for problem solving, judgment, impulse control, and social and sexual behavior. The frontal lobe in a human does not fully develop until around 25 years of age.

Parietal Lobe

The parietal lobe is the middle region of each hemisphere, lying beneath the crown of the skull. It is the cognition part of the brain. The parietal lobe works by instinct as it receives signals of different sensations—such as pain, warmth, cold, pressure, and movement—from the skin.

Occipital Lobe

The occipital lobe is found at the back of each hemisphere. Although it is located farthest away from the eyes, this lobe of the brain deals with visual interpretation. It receives measurements taken from the eyes' lenses and processes those signals into information about what the eyes are seeing.

Temporal Lobe

The temporal lobe is located on the side of each hemisphere, behind the ears. It is associated with speech, hearing, and memory skills. It houses the hippocampus (the area of the brain associated with memory) and contains the auditory centers responsible for hearing.

Regions of the Brain

Focus Question

What are the three main regions of the brain?

How many brains do you have? Actually, this is quite easy to answer…you have only one brain. However, the cerebral hemispheres are divided right down the middle into a right hemisphere and a left hemisphere. Each hemisphere appears to be specialized for specific behaviors. The hemispheres communicate with each other through a thick band of 200–250 million nerve fibers called the corpus callosum.

The right side of the brain controls muscles on the left side of the body, and the left side of the brain controls muscles on the right side of the body. Sensory information from the left side of the body crosses over to the right side of the brain, and information from the right side of the body crosses over to the left side of the brain. Therefore, damage to one side of the brain will affect the opposite side of the body.

The right brain is dominant for spatial abilities, face recognition, visual imagery, and music. The left brain may be more dominant in language, calculations, math, and logical abilities.

The brain is made of three main regions: the forebrain, the midbrain, and the hindbrain. Explore the regions below. Record the differences between these parts in your guided notes.

The front of the card:

Forebrain

Image of the brain with the forebrain highlighted

Show the back of the card:

Forebrain

The forebrain is composed of the cerebrum, thalamus, and hypothalamus. It is responsible for thought, personality, senses, and voluntary movement.

The front of the card:

Midbrain

Image of the brain with the midbrain highlighted

Show the back of the card:

Midbrain

The midbrain, or mesencephalon, is the smallest region near the center of the brain associated with vision, hearing, motor control, alertness, and temperature regulation. The midbrain, pons, and medulla oblongata are referred to as the brainstem.

The front of the card:

Hindbrain

Image of the brain with the hindbrain highlighted

Show the back of the card:

Hindbrain

The hindbrain is also referred to as the “Reptilian brain” because it is the oldest part of the human brain and is the most primitive. It is composed of the cerebellum, pons, and medulla. It is responsible for our most basic functions, such as breathing, heart rate, sleep, and respiration.

Spinal Cord Basics

Focus Question

What are the main regions of the spinal cord and their functions?

The spinal cord starts at the base of the cranium, at the occipital bone. It runs through the central canal of the vertebrae and ends between the first and second lumbar vertebrae.

There are thirty-one pairs of spinal nerves that leave the spinal cord and move out to the body. 

The spinal nerves are part of the peripheral nervous system and are divided into five regions: 

1. cervical nerves

2. thoracic nerves

3. lumbar nerves

4. sacral nerves

5. coccygeal nerve[käk-ˈsij-(ē-)əl]

The spinal cord is broken into sections: cranial, cervical, thoracic, lumbar, and sacral. Explore the interactive below to learn some of the responsibilities of the central nervous system. Select an organ and then note which part of the central nervous system it is located in using the bottom box to the right. The choices are cranial, cervical, thoracic, lumbar, or sacral. Record these locations in your guided notes.

• Armpit—Thoracic

• Biceps—Cervical

• Big toe—Lumbar

• Bladder—Sacral

• Diaphragm—Cervical

• Ear—Cranial

• Eye—Cranial

• Frontalis—Cranial

• Gluteus maximus—Sacral

• Heart—Cervical

• Knee—Lumbar

• Intestines—Lumbar

• Lips—Cranial

• Liver—Thoracic

• Lungs—Cervical

• Nose—Cervical

• Rectus abdominis—Thoracic

• Tongue—Cervical

Spinal Cord Structures

Focus Question

What structures make up the spinal cord?

The spinal nerves are attached to the spinal cord by two roots: the posterior dorsal roots and the anterior ventral roots . A dorsal root comprises sensory neurons that carry information towards the brain and spinal cord. A ventral root consists of motor neurons that carry information away from the brain and spinal cord.

The gray matter of the spinal cord is divided into two sections: the dorsal horns and the ventral horns. The gray matter of the dorsal horn receives sensory information from the dorsal roots of the spinal nerves. The gray matter of the ventral horn contains motor neurons that send signals for movement through the ventral roots.

The gray matter of the spinal cord consists of interneurons. They are unique because they can move signals in both directions, and they are only found in the central nervous system.

CNS Injuries

Focus Question

What can happen when the brain and spinal cord are injured?

Cross-section x-ray of brain showing both hemispheres.

The brain has several protective layers, including the hard skull, fluid, and tissues. However, sustaining a blow hard enough to damage the tissue is still relatively easy. 

Brain injuries can cause minimal damage to the pathway of an impulse or catastrophic damage. For instance, damage to the brain stem will cause an inability to perform essential functions like breathing. 

Watch the video to see what a severe brain injury can look like. 

Text Version

The brain is a very delicate organ. For protection, it floats in fluid, it is wrapped in three layers of supporting membranes, and, finally, it is incased in bone, the skull.

Despite its protective covering, the brain is still a vulnerable organ. Repeated blows can cause permanent damage over time, and a single severe blow, even if it doesn’t crack the skull or damage the brain, can disrupt the brain's normal operation and knock the victim unconscious. Thinking ceases, conscious control of muscle is lost, sensory information is not heeded, and yet the heart continues to beat and the lungs to draw air. These vital mechanisms are controlled by one of the brain's most durable parts, the brain stem.

The brain stem is an automatic control center for many such important involuntary actions of the body, and it is a pathway for impulses travelling back and forth between the body and the rest of the brain.

If the spinal cord is damaged in an accident, the regions below the injury will be disconnected from the brain and the rest of the spinal cord. For example, if a person sustained an injury to the L3 spinal nerve of the lumbar region, all the nerves below that point, and all the body parts linked to them, would stop functioning.

Watch the video below about a sports-related spinal injury and recovery steps.

Text Version

Health Specialist—Denise Dedor: "Less than two years ago, it looked pretty bad for 18-year-old Cody Williams. Today, he is making quite a comeback.”

ABC Female Reporter:
“September 11th, 2009, Santa Monica high school junior Cody Williams tackles a quarterback as he tries to enter the end zone.”

Cody Williams:
“And as he was going up, his knee made contact with my face mask and just kind of jerked my neck back, and I just kind of blacked out for a little bit.”

ABC Female Reporter:
“It is hard to see in this UCLA video but Cody was paralyzed. Paramedics transported him to the Ronald Reagan UCLA Medical Center. The force of the injury snapped his neck.”

Dr. Langston Holly:
“As soon as I saw the films, I knew that it was a very devastating injury.”

ABC Female Reporter:
“The severity and location was close to the injury actor Christopher Reeves suffered. It takes nine hours for Dr. Langston Holly to stabilize the front and back of Cody’s neck, but how well he’d recover was unknown.”

Dr. Langston Holly:
“History just shows that the vast majority of these people will not make a significant life-changing improvement.”

ABC Female Reporter:
“Today, this home video shows how Cody can use his arms and his legs.”

Cody Williams:
“With braces on my legs I can take about 20-30 steps.”

Health Specialist—Denise Dedor:
“One of the keys in Cody’s recovery was the fact that he got into surgery so quickly and surgeons were able to stabilize his spine."

Vital Signs

Vital signs give a quick snapshot about the health of the body and how the systems are functioning. Let's practice the new terms and processes from this Lesson. 

A - Points to the largest part of the brain that starts in the front of the cranium and continues to the back

• Cerebral Cortex

B - Points to the part of the brain towards the front of the cranium

• Frontal Lobe

C - Points to the part of the brain that is at the back of the cranium, just below the crown of the head

• Parietal Lobe

D - Points to the center of the cranium at a small structure shaped like a quarter moon or half circle

• Corpus Callosum

E - Points to small structure just behind the eye sockets of the skull

• Hypothalamus

F - points to part of the brain that is situated at the sides of the cranium, just above where a person's ears would be

• Temporal Lobe

G - points to the very back of the brain, just above where the beginning of the cervical spine

• Occipital Lobe

H - points to large triangular structure at the lower back of the brain

• Cerebellum

I - points to a small structure at the base of the skull above the cervical spine

• Brain Stem

J - points to small seed-shaped structure at the base of the skull, at the center of the neck, just above the cervical spine

• Medulla Oblongata

Which letters represent the locations of the ventral horns, dorsal horns, white matter, and gray matter?

Check your answers

1. Ventral horn

2. Dorsal horn

3. White matter

4. Gray matter