Nervous System Tissue

I. Neurons

A. Function: conduct impulses from one part of body to another

B. Structure:

1. cell body: nucleus, nucleolus, cytoplasm, organelles

2. dendrites: highly branched cytoplasmic process, it conducts to cell body. dendro=tree

3. axon: elongated cytoplasmic process.

a. axon collateral=branches off of main axon

b. axon terminals= end of axon which branches into many fine filaments.

c. synaptic end bulb= bulb like sacs at the teminal end of axon.

d. synaptic vessicles= in synaptic end bulb. Contains neurotransmitters.

4. myelin sheath aka neurolemmocyte

a. myelinated axon = cell wraps many times around axon, the cytoplasm and nucleus are in the outermost layer of sheath.

b. unmyelinated axon= still has wrapping with a different type of cell.(found in CNS)

c. Function:

i. to increase speed of impulse

ii. insulate and maintain axon

d. structures

i. nodes: spaces between neurolemocyt. This is where the impulse actually travels-from node to node.

ii. neurolemma: nucleated, cytoplasmic layer of cell

5. oligodendrocyte

a. function:

i. maintain central nervous system neurons

ii. absence of neurolemma

iii. pathology damage to this tissue is permanent due to the lack of neurolemma cells. Regeneration is not possible.

6. Growth and development

a. sheaths are laid down during fetal development. So coordination is poor in infancy.

II. Types of neurons

A. functional types

1. motor (efferent): carry impulses away from central nervous system CNS

2. sensory (afferent): from receptor to CNS

3. Interneurons: multipolar, unmyelinated, connect neurons

B. of brain

1. pyramidal cells: multipolar, found in cerebral cortex

2. purkinje cells: multipolar, found in cerebellum

C. structural types

1. multipolar: cell body at one end and dendrites at other end

2. unipolar: cell body with one axon

3. bipolar: cell body with axon extending either direction