nervous system~histology

Nervous System function

Sensory input, integration, and motor output

CNS components

brain and spinal cord

Peripheral nervous system (PNS)

paired spinal nerves and cranial nerves

Sensory afferent fibers

carry impulses from skin, skeletal muscles, and joints to the brain

Visceral afferent fibers

transmit impulses from visceral organs to the brain

Motor (efferent) division

Transmits impulses from the CNS to effector organs

Somatic nervous system

responsible for all conscious body movements and processing external sensory informatio

Autonomic nervous system (ANS)

Regulates smooth muscle, cardiac muscle, and

glands: Divisions – sympathetic and parasympathetic

Neurons

excitable cells that transmit electrical signals

Supporting cells

cells that surround and wrap neurons

neuroglia or glial cells

Provide a supportive scaffolding for neurons and segregate and insulate neurons

Astrocytes

Most abundant, versatile, and highly branched glial cells that support and brace neurons

Microglia function

Phagocytes that monitor the health of neurons

Ependymal cells

They line the central cavities of the brain and spinal column

Oligodendrocytes

branched cells that wrap CNS nerve fibers

Schwann cells

surround fibers of the PNS

Satellite cells

surround neuron cell bodies with ganglia

Structural units of the nervous system

Composed of a body, axon, and dendrites and long-lived, amitotic, and have a high metabolic

rate

neuron plasma membrane functions in:

Electrical signaling and Cell-to-cell signaling during development

Nerve Cell Body

Contains the nucleus and a nucleolus - Is the major biosynthetic cent

Processes

Armlike extensions from the soma

 Called tracts in the CNS and nerves in the PNS - called dendrites and axons

Dendrites of Motor Neurons

Short, tapering, and diffusely branched processes

They are the receptive, or input, regions of the

neuron

Axons: Structure

Slender processes of uniform diameter arising from

the hillock

• Long axons are called nerve fibers

Axons: Function

Generate and transmit action potentials and secrete neurotransmitters from the axonal terminals

Myelin Sheath structure

Whitish, fatty (protein-lipoid), segmented sheath around most long axons

Myelin Sheath function

Protect the axon

 Electrically insulate fibers from one another

Myelin Sheath and Neurilemma: Formation in PNS

Formed by Schwann cells in the PNS

Schwann cells:

Envelopes an axon in a trough

 Encloses the axon with its plasma membrane

 Has concentric layers of membrane that make up the myelin

sheath

Neurilemma

remaining nucleus and cytoplasm of a Schwann cell

Nodes of Ranvier

Gaps in the myelin sheath between adjacent Schwann cells

Axons of the CNS

Both myelinated and unmyelinated fibers are present

 Myelin sheaths are formed by oligodendrocytes

 Nodes of Ranvier are widely spaced

White matter

dense collections of myelinated fibers

Gray matter

mostly soma and unmyelinated fiber

Multipolar neurons

three or more processes

Bipolar

two processes (axon and dendrite)

Unipolar

single, short process

functional Sensory (afferent)

transmit impulses toward the CNS

functional Motor (efferent)

carry impulses away from the CNS

functional Interneurons (association neurons

shuttle signals through CNS pathways

which type of neuron is most abdunant ?

multipolar

which neuron type is rarest?

bipolar (dendrite and axon)

where is unipolar neurons mostly found

PNS, common in dorsal root ganglia and sensory ganglia of cranial nerves