Nervous System and Central Nervous System: Study Guide (Chapters 11 & 12)

Chapter 11: Fundamentals of the Nervous System and Nervous Tissue

Overview of the Nervous System

The nervous system is the master control and communication system of the body. It is responsible for integrating sensory input, coordinating motor output, and maintaining homeostasis.

• Key Terminology: Neuron, glial cell, synapse, action potential, neurotransmitter, etc.

Divisions of the Nervous System

The nervous system is divided into two main parts, each with distinct structures and functions.

• Central Nervous System (CNS): Consists of the brain and spinal cord; responsible for integrating and processing information.

• Peripheral Nervous System (PNS): Includes all neural tissue outside the CNS; connects the CNS to limbs and organs.

Division	Main Components	Function
CNS	Brain, Spinal Cord	Integration, command center
PNS	Cranial nerves, Spinal nerves	Communication lines between CNS and body

Glial Cells

Glial cells (neuroglia) support and protect neurons. They differ between the CNS and PNS.

• CNS Glial Cells:

  • Astrocytes: Maintain blood-brain barrier, regulate nutrients.

  • Microglia: Act as immune defense cells.

  • Ependymal Cells: Line ventricles, produce cerebrospinal fluid (CSF).

  • Oligodendrocytes: Form myelin sheaths in CNS.

• PNS Glial Cells:

  • Schwann Cells: Form myelin sheaths in PNS.

  • Satellite Cells: Surround neuron cell bodies in ganglia, regulate environment.

Structure and Function of a Neuron

Neurons are the functional units of the nervous system, specialized for communication.

• Cell Body (Soma): Contains nucleus and organelles; metabolic center.

• Dendrites: Receive incoming signals from other neurons.

• Axon: Transmits electrical impulses away from the cell body.

• Myelination: Myelin sheaths (formed by oligodendrocytes in CNS, Schwann cells in PNS) insulate axons, increasing signal speed.

• Non-myelinated Axons: Lack myelin, conduct impulses more slowly.

Example: Motor neurons have long axons to transmit signals from the spinal cord to muscles.

Functional Classification of Neurons

• Sensory (Afferent) Neurons: Transmit impulses from sensory receptors to CNS.

• Motor (Efferent) Neurons: Carry impulses from CNS to effectors (muscles/glands).

• Interneurons: Connect sensory and motor neurons within the CNS.

Membrane Potential

Neurons communicate via changes in membrane potential, which is the voltage difference across the cell membrane.

• Resting Membrane Potential: The stable, negative charge of a neuron at rest (typically around -70 mV).

• Graded Potentials: Short-lived, localized changes in membrane potential; occur in dendrites and cell body; can summate to trigger action potentials.

• Action Potentials: Rapid, long-distance electrical signals along axons; involve voltage-gated Na+ and K+ channels.

Key Steps in Action Potential:

1. Resting state: All voltage-gated channels closed.

2. Depolarization: Na+ channels open, Na+ enters cell.

3. Repolarization: Na+ channels inactivate, K+ channels open, K+ exits cell.

4. Hyperpolarization: K+ channels remain open briefly, membrane potential becomes more negative than resting.

5. Return to Resting Potential: Ionic balance restored by Na+/K+ pump.

Equation for Resting Membrane Potential (Nernst Equation):

$E = \frac{RT}{zF} \ln \left( \frac{[\text{ion outside}]}{[\text{ion inside}]} \right)$

Multiple Sclerosis (MS)

MS is a disease where the immune system attacks myelin in the CNS, disrupting nerve signal transmission and causing neurological symptoms.

Synapse

A synapse is the junction between two neurons or a neuron and an effector cell, where information is transmitted.

• Structure: Presynaptic terminal, synaptic cleft, postsynaptic membrane.

• Chemical Synapse Steps:

  1. Action potential arrives at axon terminal.

  2. Voltage-gated Ca2+ channels open.

  3. Ca2+ enters terminal, triggering neurotransmitter release.

  4. Neurotransmitter diffuses across synaptic cleft.

  5. Neurotransmitter binds to receptors on postsynaptic membrane.

  6. Postsynaptic potential generated; neurotransmitter removed from cleft.

• Synaptic Delay: The brief time required for neurotransmitter release, diffusion, and binding (about 0.3–5 ms).

Neurotransmitters

• Definition: Chemical messengers that transmit signals across synapses.

• Examples: Acetylcholine, dopamine, serotonin, GABA, glutamate.

• Functions: Can be excitatory (promote action potentials) or inhibitory (suppress action potentials).

Chapter 12: The Central Nervous System

Overview of the Central Nervous System (CNS)

The CNS consists of the brain and spinal cord, serving as the main processing center for the entire nervous system.

• Key Terminology: Cortex, nuclei, tracts, ventricles, etc.

Regions of the Brain

• Cerebrum

• Diencephalon

• Brainstem

• Cerebellum

Cerebrum

The cerebrum is the largest part of the brain, responsible for higher brain functions such as thought, memory, and voluntary movement.

• Structures: Cerebral cortex (outer gray matter), white matter, basal nuclei.

• Function: Sensory perception, voluntary motor actions, reasoning, language, and learning.

• Lobes of the Cerebrum:

  • Frontal Lobe: Voluntary movement, planning, reasoning, speech (Broca's area).

  • Parietal Lobe: Sensory perception, spatial awareness.

  • Temporal Lobe: Auditory processing, memory, language comprehension.

  • Occipital Lobe: Visual processing.

  • Insula: Taste, visceral sensation, emotion.

• Overlap and Unique Functions: Some functions (e.g., language) involve multiple lobes, while others (e.g., vision) are localized.

• Gray vs. White Matter: Gray matter contains neuron cell bodies; white matter consists of myelinated axons.

• Parkinson’s Disease: Degeneration of dopamine-producing neurons in basal nuclei, causing motor deficits.

• Huntington’s Disease: Genetic disorder causing degeneration of basal nuclei and cerebral cortex, leading to uncontrolled movements and cognitive decline.

Cerebral Cortex

The cerebral cortex is the outer layer of the cerebrum, involved in conscious thought, perception, and voluntary movement.

• Four Generalizations:

  1. Three types of functional areas: motor, sensory, association.

  2. Each hemisphere is concerned with the opposite side of the body.

  3. Hemispheres are not entirely equal in function (lateralization).

  4. No functional area acts alone; conscious behavior involves the entire cortex.

Functional Areas – Motor

• Primary Motor Cortex: Controls voluntary movements; located in precentral gyrus.

• Motor Mapping (Homunculus): Specific regions control specific body parts; larger areas for finer control.

• Premotor Cortex: Plans movements, coordinates learned motor skills.

• Broca’s Area: Controls muscles involved in speech production.

Functional Areas – Sensory

• Primary Sensory Cortex (Somatosensory): Receives sensory input from skin, muscles, joints.

• Somatosensory Association Cortex: Integrates sensory input for understanding objects.

• Primary Visual Cortex: Receives visual information from the retina.

• Visual Association Area: Interprets visual stimuli (color, form, movement).

• Primary Auditory Cortex: Receives auditory information from the inner ear.

• Auditory Association Area: Interprets sounds (speech, music, noise).

Example: Damage to Broca’s area impairs speech production but not comprehension.

Additional info: The study guide references labeling figures and being familiar with terminology; students should review diagrams of neuron structure and brain regions for visual reinforcement.