Chapter 11: Nervous System Fundamentals – Study Guide

Chapter 11: Nervous System Fundamentals

Overview

This chapter introduces the basic structure and function of the nervous system, focusing on neuron types, neuroglia, action potentials, and the organization of the nervous system. Understanding these fundamentals is essential for further study of the nervous system's role in controlling and coordinating body functions.

1. Neuromuscular Junction: Structure and Function

The neuromuscular junction is the synapse between a motor neuron and a skeletal muscle fiber. It is crucial for muscle contraction.

• Key Structures: Synaptic vesicles, calcium ions, synaptic cleft, postsynaptic membrane, ion channels, acetylcholine (ACh), acetylcholinesterase.

• Process:

  1. Action potential arrives at the axon terminal of the motor neuron.

  2. Calcium channels open, Ca2+ enters the terminal.

  3. Synaptic vesicles release ACh into the synaptic cleft.

  4. ACh binds to receptors on the muscle fiber membrane, opening ion channels.

  5. Sodium ions enter the muscle cell, leading to depolarization and muscle contraction.

  6. Acetylcholinesterase breaks down ACh, ending the signal.

• Example: Voluntary movement such as picking up an object involves neuromuscular junctions.

2. Structural and Functional Classifications of Neurons

Structural Classification

• Multipolar: Many processes (1 axon, many dendrites); most common in CNS.

• Bipolar: Two processes (1 axon, 1 dendrite); found in special senses (e.g., retina).

• Unipolar: Single process that divides into two branches; found in sensory neurons of PNS.

Functional Classification

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

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

• Association (interneurons): Connect sensory and motor neurons within CNS; most abundant type.

3. Action Potential: Depolarization and Repolarization

• Action Potential: A rapid, temporary change in membrane potential that travels along the axon.

• Depolarization: Membrane potential becomes less negative as Na+ enters the cell.

• Repolarization: Membrane potential returns to resting as K+ exits the cell.

• Hyperpolarization: Membrane potential becomes more negative than resting potential.

Key Equation:

$\text{Resting Membrane Potential} \approx -70\ \text{mV}$

Example: Nerve impulse transmission along a motor neuron to a muscle.

4. Functional Regions of a Neuron

• Receptive Region: Dendrites and cell body; receive signals.

• Trigger Zone: Axon hillock; initiates action potential.

• Conducting Region: Axon; transmits action potential.

• Secretory Zone: Axon terminals; release neurotransmitters.

5. Neurotransmitters: Histamine, Norepinephrine, etc.

• Histamine: Involved in wakefulness, appetite control, and learning.

• Norepinephrine: Arousal, alertness, and the fight-or-flight response.

• Serotonin: Mood regulation, sleep, and appetite.

• Acetylcholine: Muscle activation, learning, and memory.

6. Neuroglia: Types and Functions

Neuroglia are supporting cells in the nervous system, each with specialized functions.

• Astrocytes: Star-shaped; support neurons, maintain blood-brain barrier, regulate environment, guide migration.

• Microglial Cells: Small, phagocytic; remove debris and pathogens.

• Ependymal Cells: Line brain and spinal cord cavities; produce and circulate cerebrospinal fluid (CSF).

• Oligodendrocytes: Form myelin sheaths around CNS axons.

• Satellite Cells: Surround neuron cell bodies in PNS; regulate environment.

• Schwann Cells: Form myelin sheaths around PNS axons; aid in regeneration.

Table: Major Types of Neuroglia and Their Functions

Neuroglia Type	Location	Main Function
Astrocytes	CNS	Support, blood-brain barrier, regulate environment
Microglial cells	CNS	Phagocytosis, immune defense
Ependymal cells	CNS	Line cavities, circulate CSF
Oligodendrocytes	CNS	Form myelin sheaths
Satellite cells	PNS	Support neuron cell bodies
Schwann cells	PNS	Form myelin sheaths

7. Organization of the Nervous System

• Central Nervous System (CNS): Brain and spinal cord; integration and control center.

• Peripheral Nervous System (PNS): Cranial and spinal nerves; communication lines.

• Sensory (Afferent) Division: Transmits sensory information to CNS.

• Motor (Efferent) Division: Transmits commands from CNS to effectors.

• Somatic Nervous System: Voluntary control of skeletal muscles.

• Autonomic Nervous System: Involuntary control of smooth muscle, cardiac muscle, and glands.

• Sympathetic Division: Mobilizes body systems during activity (fight-or-flight).

• Parasympathetic Division: Conserves energy, promotes housekeeping functions (rest-and-digest).

8. Ganglia, Nuclei, Nerves, and Tracts: Differences

• Ganglia: Clusters of neuron cell bodies in the PNS.

• Nuclei: Clusters of neuron cell bodies in the CNS.

• Nerves: Bundles of axons in the PNS.

• Tracts: Bundles of axons in the CNS.

Example: The dorsal root ganglion contains sensory neuron cell bodies (PNS), while the basal nuclei are found in the brain (CNS).