HSS 391 Ch. 14 Nervous Tissues

What are the structural divisions of the nervous system?

The central nervous system (CNS) and peripheral nervous system (PNS)

What is the CNS composed of?

The brain and spinal cord

What is the PNS composed of?

Nerves and ganglia

What are the functional divisions of the nervous system?

Motor output (efferent → exits CNS) and sensory input (afferent → arrives at CNS)

White matter

Nervous tissue composed of myelinated axons (outer spinal cord and inner brain)

Gray matter

Nervous tissue composed of neuronal cell bodies, dendrites, and unmyelinated axons (inner spinal cord and outer brain)

Tracts

Bundles of myelinated axons in the CNS

Nerves

Bundles of myelinated and unmyelinated axons in the PNS

Nuclei

Clusters of nuclei (cell bodies) in the CNS

Ganglia

Clusters of nuclei (cell bodies) in the PNS

Neurons

Largest and least numerous cells in nervous tissue; functional cells that receive and transmit information; include…

• Anterior horn cells

• Purkinje cells

• Pyramidal cells

Anterior horn cell

Neuron located in the anterior horn of the spinal cord (somatic motor neuron); very large with irregularly shaped soma

Purkinje cell

Neuron located in the cerebellum; very large and “basket-like” appearance, found on the border of the molecular and granular layer

Pyramidal cell

Neuron located in the cerebral cortex (cerebrum); cell body has a triangular shpe

Axon

A single, large process of a neuron that propagates APs away from the soma

Axon hillock

Place where axon leaves soma, devoid of Nissl substance; APs initiated here

Cell body (soma)

Part of neuron that contains the nucleus and organelles

Chromatophilic substance

“Nissl” substance/body; dark staining material found within the soma composed of ribosomes

Dendrite

Branching process that extends from the soma and transmits graded potentials to the soma

Node of Ranvier

Bare region on myelinated axons (void of myelin); APs propagated here

Synaptic knobs

Swellings on the ends of axons that form synapses with either another neuron or an effector organ

Telodendria

Axon terminals; branches at the end of axons, each process has a synaptic knob

Glial cells

Smaller and more numerous “support cells”; include…

• Schwann cells

• Satellite cells

• Oligodendrocytes

• Ependymal cells

• Astrocytes

• Microglia

Schwann cells

Large glial cells in the PNS that produce myelin; it takes many Schwann cells to myelinate a single axon

Satellite cells

Small glial cells in the PNS that provide general support (protection, structural support, nutrients)

Oligodendrocytes

Glial cells in the CNS that produce myelin; one oligodendrocyte can myelinate multiple axons

Ependymal cells

Glial cells in the CNS that line the ventricles of the brain and produce cerebral spinal fluid

Astrocytes

Star-shaped glial cells in the CNS between neurons and blood vessels that regulate nutrient transfer and create the blood brain barrier

Microglia

Small glial cells in the CNS that are phagocytic and remove bacterial debris and wastes

What is the order of structure of peripheral nerves?

Axons → fascicles → nerves (bundled by CT sheaths)

Epineurium

Nerve CT covering that surrounds an entire peripheral nerve

Perineurium

Nerve CT covering that surrounds a fascicle (a group of axons)

Endoneurium

Nerve CT covering that surrounds an individual axon