Nervous Tissue

Ch. 17, p257

Nervous Tissue

• Neurons• Neuroglia

– CNS:• Astrocytes• Oligodendrocytes• Microglia• Ependymal Cells

– PNS:• Schwann Cells• Satellite Cells

Neuron Anatomy• Cell body (aka: perikaryon= cyton

=soma)– single, central nucleus with

large nucleolus, cell organelles

• Dendrites– for receiving signals, conduct

impulses toward the cell body• Axon

– for sending signals, conduct impulses away from the cell body to effectors

– Covered by lipid myelin

Myelin

Myelin Sheath Formation

• Myelination begins during fetal development, but proceeds most rapidly in infancy.

Myelin Sheath• Insulating layer around a nerve fiber

• 20% protein & 80 % lipid (looks white)• In PNS, hundreds of layers wrap axon

– the outermost coil is schwann cell (neurilemma)• In CNS, no neurilemma• Nodes of Ranvier

– Gaps between myelin segments• Initial segment (area before 1st schwann cell) & axon hillock

form trigger zone where signals begin

Axon Nerve Impulse Conduction Speed

Myelinated - 300MPH Unmyleinated - 2 MPH

Neuron Classification• Unipolar Neuron

– Single process from cell body that is divided into axon and dendrite

– Conduct impulses toward CNS, sensory neurons

• Bipolar Neuron– One dendrite and one

axon– Occurs in retina of eye

• Multipolar Neuron– Multiple dendrites, one

axon– Carry impulses away from

CNS, Motor Neurons

Neuron Model

                                                                                                                                                                         

                                                                                                                                                                                                                                                                           

Neuron Model

Pre

Anatomy of the Brain and Cranial Nerves

Ch. 19, pg. 279