3: Basic Neuroanatomy and Cranial Nerves

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)

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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

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Central Nervous System

GENERAL INFORMATION

The central nervous system is composed of the:

Brain

Spinal cord

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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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Jan 5, 2015 | Posted by in General Dentistry | Comments Off on 3: Basic Neuroanatomy and Cranial Nerves
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