CHAPTER 3

BASIC NEUROANATOMY AND CRANIAL NERVES

Nervous Tissue

Central Nervous System

Peripheral Nervous System

Cranial Nerves

Clinical Correlates

Questions

Nervous Tissue

GENERAL INFORMATION

Nervous tissue is divided into 2 major cell types:

• Neurons

• Neuroglial cells (the neuroglia)

NEURONS

The structural and functional cells in the nervous system

Respond to a nervous stimulus and conduct the stimulus along the length of the cell

A neuron’s cell body is called the perikaryon, or soma

Cell bodies are classified by their location:

• Ganglion—a collection of nerve cell bodies located in the peripheral nervous system (e.g., dorsal root ganglion, trigeminal ganglion, ciliary ganglion)

• Nucleus—a collection of nerve cell bodies located in the central nervous system (e.g., Edinger-Westphal nucleus, chief sensory nucleus of cranial nerve V, motor nucleus of cranial nerve VII)

Neuron’s cell bodies contain typical cellular organelles within their cytoplasm:

• Mitochondria

• Nucleus

• Nucleolus

• Ribosomes

• Rough endoplasmic reticulum (Nissl substance)

• Neurotubules

• Golgi apparatus

• Lysosomes

Neurons have 2 types of processes that extend from the nerve cell body:

• Dendrite—process that carries nerve impulses toward the nerve cell body; neurons may have multiple dendrites

• Axon—process that carries nerve impulses away from the nerve cell body; neurons can have only 1 axon

3 major types of neurons:

• Unipolar—has only 1 process from the cell body (sensory neurons)

• Bipolar—has 2 processes from the cell body: 1 dendrite and 1 axon (sensory neurons; located only in the retina, olfactory epithelium, and the vestibular and cochlear ganglia)

• Multipolar—has 3 or more processes from the cell body: 2 or more dendrites and 1 axon (motor neurons and interneurons)

NEUROGLIA

Neuroglia is the supporting nervous tissue for neurons, although neuroglial cells also have assistive roles in neuron function

Neuroglial cells have only 1 type of process

Classification:

• Astrocytes—located in the central nervous system; help keep neurons in place, provide nutritional support, regulate the extracellular matrix, form part of the blood-brain barrier

• Oligodendrocytes—located in the central nervous system; responsible for axon myelination in the central nervous system; 1 oligodendrocyte can myelinate 1 segment of multiple axons

• Microglia—located in the central nervous system; responsible for phagocytosis to remove waste

• Schwann cells—located in the peripheral nervous system; responsible for axon myelination in the peripheral nervous system; 1 schwann cell can myelinate 1 segment of 1 axon

• Satellite cells—located in the peripheral nervous system; surround the nerve cell bodies of ganglia

Central Nervous System

GENERAL INFORMATION

The central nervous system is composed of the:

• Brain

• Spinal cord

BRAIN

CEREBRUM

The surface of the cerebral cortex of the brain is divided by:

• Gyri (singular gyrus)—the elevations of brain tissue on the surface

• Sulci (singular sulcus)—the grooves or fissures located between the gyri

There are 3 large sulci that help divide the cerebral hemispheres into 4 of its lobes:

• Central sulcus (of Rolando)—divides frontal lobe from parietal lobe

• Lateral sulcus (of Sylvius)—divides the frontal and parietal lobes from the temporal lobe

• Parieto-occipital sulcus—divides the parietal lobe from the occipital lobe

The brain is divided into 5 lobes:

• Frontal—motor movement, motor aspect of speech (Broca’s area), reasoning, emotions, personality, and problem solving

• Parietal—sensory perceptions related to pain, temperature, touch and pressure, spatial orientation and perception, sensory aspect of language (Wernicke’s area)

• Temporal—auditory perceptions, learning, and memory

• Occipital—vision

• Insula—associated with visceral functions including taste

DIENCEPHALON

Composed of 4 parts:

• Thalamus—major relay center of the somatosensory system and parts of the motor system

• Hypothalamus—controls the autonomic nervous system and endocrine system

• Epithalamus—major structures include the pineal gland (which controls circadian rhythms) and the habenula

• Subthalamus—an extrapyramidal nucleus of the motor system; if lesioned, will result in a contralateral hemiballismus

BRAINSTEM

Composed of 3 parts:

• Midbrain

• Pons

• Medulla

CEREBELLUM

Part of the motor system

Receives sensory input of all forms that use the deep cerebellar nuclei

Associated with:

• Equilibrium

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