Anatomy and Function of the Nervous System: Study Guide

Anatomy of the Nervous System

Overview

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

Histology of Nervous Tissue

Cell Types

Nervous tissue is highly cellular, with little extracellular space. It consists of two principal cell types:

• Neurons: Excitable cells that transmit electrical signals.

• Neuroglia: Supporting cells that surround and wrap delicate neurons. Types include:

  • CNS: Astrocytes, microglia, ependymal cells, oligodendrocytes

  • PNS: Satellite cells, Schwann cells

Neurons

Structure and Function

Neurons are the structural units of the nervous system, specialized for conducting impulses. They have unique characteristics:

• Long-lived, amitotic (do not divide), high metabolic rate

• Require continuous supply of oxygen and glucose

Structural Classification

• Based on the number of processes extending from the cell body (e.g., multipolar, bipolar, unipolar)

Functional Classification

• Based on direction of impulse relative to CNS: sensory (afferent), motor (efferent), interneurons

Functions and Divisions of the Nervous System

Functional Overview

The nervous system is organized into divisions that manage sensory input, integration, and motor output. The CNS processes information, while the PNS transmits signals between the CNS and the rest of the body.

Brain Regions & Organization

Major Regions

The adult brain is divided into several regions, each with specialized functions:

• Cerebral hemispheres

• Diencephalon

• Brain stem (midbrain, pons, medulla)

• Cerebellum

Pattern of Distribution of Gray and White Matter in the CNS

Gray vs. White Matter

Gray matter consists of neuron cell bodies, while white matter is composed of myelinated axons. The distribution varies by region:

• Spinal cord: Central gray matter, surrounding white matter

• Brain stem: Additional gray matter scattered within white matter

• Cerebral hemispheres: Outer layer of gray matter (cortex), internal white matter, deep basal nuclei

Ventricles of the Brain

Structure and Function

The brain contains interconnected ventricles filled with cerebrospinal fluid (CSF), lined by ependymal cells. The ventricles include:

• Paired lateral ventricles

• Third ventricle (connected to lateral ventricles via interventricular foramen)

• Fourth ventricle (connected to third via cerebral aqueduct)

The Cerebral Hemispheres

Surface Markings and Regions

The cerebral hemispheres are divided by grooves (gyri and sulci) and deep fissures. Each hemisphere contains three basic regions:

• Cerebral cortex (gray matter)

• White matter (internal)

• Basal nuclei (deep within white matter)

Cerebral Cortex

Functional Areas

The cerebral cortex is the "executive suite" of the brain, responsible for conscious mind, awareness, sensory perception, voluntary motor initiation, communication, memory, and understanding. It contains three functional areas:

• Motor

• Sensory

• Association

Each hemisphere handles sensory and motor functions for the contralateral side of the body. The cortex is largely symmetrical but not equal in function.

Motor Areas

Primary Motor Cortex and Associated Areas

Motor areas are located in the posterior part of the frontal lobes and include:

• Primary (somatic) motor cortex: Controls voluntary movements of skeletal muscles

• Premotor cortex: Plans movements by selecting and sequencing basic motor tasks

• Broca's area: Motor speech area, usually in the left hemisphere

• Frontal eye field: Controls voluntary movements of the eyes

Motor Homunculus

Representation of Motor Control

The motor homunculus is a spatial map of the primary motor cortex, representing the control of muscles. It illustrates the complexity and precision of motor control, with larger areas devoted to regions requiring fine movements.

Sensory Areas

Primary Sensory Cortex and Association Areas

Sensory areas are responsible for conscious awareness of sensation and are located in the parietal, temporal, and occipital lobes. They include:

• Primary somatosensory cortex

• Somatosensory association cortex

• Visual areas

• Auditory areas

• Vestibular (equilibrium) cortex

• Gustatory cortex

• Visceral sensory area

Multimodal Association Areas

Integration of Information

Multimodal association areas integrate information from multiple sensory modalities and are involved in higher cognitive functions, memory, and emotional responses. They are divided into:

• Anterior association area (prefrontal cortex): Intellect, cognition, recall, personality

• Posterior association area: Recognition of patterns, faces, localization in space

• Limbic association area: Emotional impact, memory formation

Lateralization of Cortical Function

Hemispheric Specialization

Lateralization refers to the division of labor between the hemispheres. Most individuals have left hemisphere dominance for language, math, and logic, while the right hemisphere is involved in visual-spatial skills, intuition, and emotion.

Cerebral White Matter

Fiber Types

Cerebral white matter consists of myelinated fibers responsible for communication between different areas of the brain:

• Commissural fibers: Connect corresponding gray areas of the two hemispheres (e.g., corpus callosum)

• Association fibers: Connect different parts of the same hemisphere

• Projection fibers: Connect the cortex with lower CNS centers

Clinical Examples

Case Studies

• Ian Waterman: Loss of proprioception and touch, illustrating the importance of somatosensory input for movement.

• Kevin Chappell: Visual agnosia, demonstrating the role of visual association areas in object recognition.

• Phineas Gage: Personality changes after frontal lobe injury, highlighting the function of the prefrontal cortex.

Summary Table: Major Brain Regions and Functions

Region	Main Function
Cerebral Cortex	Conscious mind, sensory perception, voluntary motor initiation, communication, memory
Basal Nuclei	Motor control, procedural learning
White Matter	Communication between brain regions
Diencephalon	Homeostasis, hormone regulation
Brain Stem	Basic life functions, relay center
Cerebellum	Coordination of movement, balance