Study Notes: The Nervous System (Chapter 7) – Anatomy & Physiology

Chapter 7: The Nervous System

Overview of the Nervous System

The nervous system is a complex network responsible for coordinating body activities and processing sensory information. It is divided into the central nervous system (CNS) and peripheral nervous system (PNS), each with specialized structures and functions.

• Central Nervous System (CNS): Consists of the brain and spinal cord. Occupies the dorsal body cavity and acts as the integrating and command centers.

• Peripheral Nervous System (PNS): Composed of nerves and ganglia outside the CNS. Connects the CNS to limbs and organs.

Cranial Nerves

Cranial nerves are twelve pairs of nerves that emerge directly from the brain. Some extend beyond the head and neck to innervate other regions.

• Vagus Nerve (X): The only cranial nerve that extends beyond the head and neck, carrying parasympathetic fibers to the thorax and abdomen.

• Glossopharyngeal Nerve (IX): Supplies motor fibers to the pharynx, promotes swallowing and saliva production, and carries sensory impulses from taste buds and pressure receptors.

• Facial Nerve (VII) & Glossopharyngeal Nerve (IX): Mediate the sense of taste from different regions of the tongue.

Functional Areas of the Brain

The brain contains specialized areas responsible for different functions, including movement and sensation.

• Primary Motor Area: Located anterior to the central sulcus in the frontal lobe; allows conscious movement of skeletal muscles.

• Somatic Sensory Area: Located in the parietal lobe; processes sensory information.

Neuronal Structure and Function

Neurons are the basic functional units of the nervous system, with specialized structures for transmitting electrical impulses.

• Dendrites: Conduct nerve impulses toward the neuron cell body.

• Axons: Conduct impulses away from the cell body.

• Nodes of Ranvier: Gaps in the myelin sheath between successive Schwann cells, facilitating rapid impulse transmission.

• Dorsal Root Ganglion: Contains cell bodies of sensory neurons entering the spinal cord via the dorsal root.

Glial Cells

Glial cells support and protect neurons in both the CNS and PNS.

• Schwann Cells: Produce myelin in the PNS.

• Oligodendrocytes: Produce myelin in the CNS.

• Astrocytes, Ependymal Cells, Microglia: All are CNS glial cells with various support functions.

Protective Structures of the CNS

The CNS is protected by connective tissue membranes and specialized structures.

• Meninges: Three connective tissue membranes (dura mater, arachnoid mater, pia mater) covering and protecting CNS structures.

• Dura Mater: The outermost, leathery layer of the meninges.

Major Brain Structures

The brain contains several important anatomical features that separate and connect its regions.

• Longitudinal Fissure: Deep groove separating the right and left cerebral hemispheres.

• Corpus Callosum: Large fiber tract connecting the right and left cerebral hemispheres.

Production and Function of Cerebrospinal Fluid (CSF)

Cerebrospinal fluid cushions the brain and spinal cord, providing nutrients and removing waste.

• Choroid Plexuses: Clusters of capillaries in the ventricles that produce CSF from blood.

Blood-Brain Barrier

The blood-brain barrier restricts the passage of substances from the bloodstream into the brain tissue.

• Essential Amino Acids: Can easily enter brain tissue due to tight junctions in capillary walls.

• Water-soluble substances: Including water and glucose, also pass through the barrier.

Action Potentials

An action potential is a rapid change in membrane potential that propagates along a neuron, enabling nerve impulse transmission.

• Threshold: Action potential occurs when local potential reaches a critical threshold.

• All-or-None Rule: Once initiated, the action potential proceeds with constant magnitude.

• Depolarization and Repolarization: Characterized by a series of changes in membrane polarity.

• Equation:

$\text{Action Potential:} \, V_m = V_{rest} + \Delta V$

Example: As Na+ ions diffuse rapidly into the cell, the inside becomes more positive, and the outside more negative.

Brain Stem and Associated Structures

The brain stem controls vital functions and contains important nuclei and tracts.

• Corpora Quadrigemina: Four rounded protrusions involved in visual and auditory reflexes.

• Medulla Oblongata: Regulates vital visceral activities but does not play a role in consciousness or circadian rhythms.

• Pons: Involved in control of breathing.

• Reticular Activating System (RAS): Plays a role in consciousness and circadian rhythms.

Cerebellum

The cerebellum is essential for coordination and maintenance of balance and posture.

• Function: Coordinates skeletal muscle activity, maintains balance, and posture.

Summary Table: Key Nervous System Structures and Functions

Structure	Location	Function
Vagus Nerve (X)	Cranial Nerve	Parasympathetic fibers to thorax and abdomen
Dorsal Root Ganglion	Spinal Cord	Sensory neuron cell bodies
Schwann Cells	PNS	Produce myelin
Oligodendrocytes	CNS	Produce myelin
Choroid Plexuses	Brain Ventricles	Produce cerebrospinal fluid
Corpus Callosum	Between Cerebral Hemispheres	Connects right and left hemispheres
Nodes of Ranvier	Axons (between Schwann cells)	Facilitate rapid impulse transmission

Additional info: Some explanations and definitions have been expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.