3.02 Central Nervous System: System Comprehensive Study Guide

Brain Basics and Structural Organization

• Central Nervous System (CNS) Context: The brain is an integral part of the central nervous system, serving as the master control center for every aspect of daily life, including thought processes and physical movement.

• Physiology and Weight: The average human brain weighs approximately $3\,pounds$.

• Cerebral Hemispheres: The brain is divided into two distinct halves known as the cerebral hemispheres. Each of these hemispheres is further subdivided into four specialized lobes.

• Surface Anatomy Definitions:

  • Sulci: These are the grooves or indentations found on the surface of the brain.

  • Gyri: These are the visible bumps or ridges on the brain's surface.

  • Functional Purpose of Folding: The presence of sulci and gyri increases the surface area of the cerebral cortex, allowing a greater amount of neural tissue to fit within the confines of the skull.

Functional Regions and Internal Structures of the Brain

• Cerebrum:

  • Location: Situated at the top of the head.

  • Function: Responsible for voluntary body activities, emotions, intelligence, learning, and judgment.

• Cerebellum:

  • Location: Located behind the hindbrain, tucked beneath the cerebrum.

  • Function: Receives sensory information from nerves near joints and muscles, as well as the visual and auditory systems; utilizes this data to provide unconscious coordination of movement and balance.

• Cerebral Cortex:

  • Location: The outermost layer of the cerebrum.

  • Function: Controls body movements and processes information from sense organs; it is the site for thoughts, planning, and learning abilities.

• Corpus Callosum:

  • Location: A bundle of nerve fibers connecting the hemispheres.

  • Function: Connects the left and right hemispheres, enabling communication between the two; it consists of a thick band of approximately $200 \times 10^{6}$ to $250 \times 10^{6}$ nerve fibers.

• Pons:

  • Location: Positioned above the medulla oblongata.

  • Function: Relays sensory information and regulates the flow of blood and oxygen.

• Medulla Oblongata:

  • Location: Positioned directly above the spinal cord.

  • Function: Controls involuntary body functions.

• Thalamus:

  • Location: Located beneath the cerebral hemispheres.

  • Function: Acts as a sorting center that categorizes sensory information by type before sending it to the higher brain for further processing.

• Hypothalamus:

  • Location: Found on the underside of the brain.

  • Function: Regulates homeostasis, hunger and eating, thirst and drinking, emotions, and other essential survival functions.

• Pituitary Gland:

  • Location: At the base of the brain.

  • Function: Secretes hormones that regulate the endocrine system.

• Brain Stem:

  • Location: The bottom portion of the brain.

  • Function: Controls vital involuntary actions such as blood pressure, heart rate, breathing, and swallowing.

Functional Specialization of the Cerebral Lobes

• Frontal Lobe: Located at the front of each hemisphere; serves as the emotional control center and is utilized for problem-solving, judgment, and impulse control.

• Parietal Lobe: Found in the middle region of each hemisphere; works primarily by instinct as it receives and processes various sensations.

• Occipital Lobe: Located at the back of each hemisphere; receives measurements from the lenses of the eyes and provides information regarding visual stimuli.

• Temporal Lobe: Located at the side of each hemisphere; responsible for speech, hearing, and memory skills.

Hemispheric Specialization and Crossover

• Contralateral Control:

  • The right side of the brain controls muscles on the left side of the body.

  • The left side of the brain controls muscles on the right side of the body.

• Sensory Crossover:

  • Sensory information from the left side of the body crosses over to the right hemisphere of the brain.

  • Information from the right side of the body crosses over to the left hemisphere.

• Injury Implications: Damage sustained by one side of the brain will typically affect the opposite side of the body.

• Functional Dominance:

  • Right Brain Dominance: Tends to be dominant for spatial abilities, face recognition, visual imagery, and music.

  • Left Brain Dominance: Tends to be more dominant in language, calculations, mathematics, and logical reasoning.

Major Brain Divisions: Forebrain, Midbrain, and Hindbrain

• Forebrain:

  • Components: Composed of the cerebrum, thalamus, and hypothalamus.

  • Function: Responsible for high-level thought, personality, sensory processing, and voluntary movement.

• Midbrain (Mesencephalon):

  • Description: The smallest region located near the center of the brain.

  • Function: Associated with vision, hearing, motor control, alertness, and temperature regulation.

  • Structural Note: The midbrain, pons, and medulla oblongata collectively form the brainstem.

• Hindbrain ("Reptilian Brain"):

  • Description: Referred to as the "Reptilian brain" because it is the oldest and most primitive part of the human brain.

  • Components: Composed of the cerebellum, pons, and medulla.

  • Function: Responsible for basic survival functions including breathing, heart rate, sleep, and respiration.

Spinal Cord Anatomy and Peripheral Connections

• Spinal Nerve Basics: There are $31$ pairs of spinal nerves that exit the spinal cord and extend to the rest of the body.

• System Classification: While the spinal cord is part of the CNS, the spinal nerves themselves are part of the peripheral nervous system (PNS).

• Spinal Regions and Associated Organs:

  • Cranial: Ear, eye, frontalis, lips, nose, pancreas, pupillary dilator, pupillary sphincter, teeth, tongue.

  • Cervical: Biceps brachii, carotid artery, diaphragm, heart, index finger, lungs, mosquito bite, sternocleidomastoids.

  • Thoracic: Armpit, humerus, liver, abdominals (abs).

  • Lumbar: Big toe, grazed knee, knee, large intestine, quadriceps (quads).

  • Sacral: Ball and socket joint, bladder, gluteus maximus.

• Coccygeal: The fifth and final region of the spinal nerves.

Internal Spinal Cord Structures and Neural Pathways

• Root Attachment: Spinal nerves attach to the spinal cord via two distinct roots:

  • Posterior Dorsal Roots: Composed of sensory neurons that carry information towards the brain and spinal cord.

  • Anterior Ventral Roots: Composed of motor neurons that carry information away from the brain and spinal cord.

• Gray Matter Organization:

  • Dorsal Horns: Receive sensory information from the dorsal roots.

  • Ventral Horns: Contain motor neurons that transmit signals for movement through the ventral roots.

• Interneurons:

  • Located within the gray matter.

  • Unique Characteristics: They can transmit signals in both directions and are found exclusively within the central nervous system.

• Tissue Types: The spinal cord cross-section includes white matter and gray matter.

CNS Protection and the Consequences of Injury

• Protective Layers: The brain is shielded by the hard skull, protective fluid (it floats in fluid to buffer impacts), and three specific layers of supporting tissue/membranes.

• Brain Damage:

  • A single severe blow can disrupt normal operations and cause unconsciousness, even if the skull remains intact.

  • Repeated blows can lead to permanent damage over time.

  • Damage to the brain stem is particularly critical as it is the automatic control center for involuntary actions and the primary pathway for all impulses moving between the body and brain.

• Spinal Cord Injury:

  • When damaged, regions of the body located below the site of the injury will be disconnected from the brain and the remainder of the spinal cord.

  • Case Study (Cody Williams): For the athlete Cody Williams, rapid surgical intervention and spinal stabilization played a crucial role in his recovery process.

Questions & Discussion

• Focus Question: What are the three main regions of the brain?

  • Answer: The Forebrain, Midbrain, and Hindbrain.

• Focus Question: What are the main regions and structures of the spinal cord?

  • Answer: The spinal cord consists of $31$ pairs of nerves divided into the cervical, thoracic, lumbar, sacral, and coccygeal regions. Structurally, it includes dorsal and ventral roots, dorsal and ventral horns, and gray and white matter.

• Focus Question: What can happen when the brain and spinal cord are injured?

  • Answer: Injuries can lead to minimal impulse pathway damage or catastrophic disconnection. Brain stem damage can disrupt involuntary vital functions, while spinal damage results in sensory and motor disconnection for all areas below the injury site.

• Identify Spinal Cord Structures under the image:

  • 1. Ventral horn

  • 2. Dorsal horn

  • 3. White matter

  • 4. Gray matter