Introductory Physiology- Course Notes

Nervous System

Why?

Guide the actions of body systems so they work together harmoniously

Goal = homeostasis (keeping bodily processes at fairly constant levels)

Guide actions of the whole body so that it interacts with the environment appropriately

What is involved?

1. sensor

means of

getting

information

from 1  2

2. control center

means of

getting

information

from 2 3

3. effector ( way of responding)

A muscle or a gland

Basic Unit - a cell called a neuron

extraordinary cells- functional units for:

 sensation

 communication

 control

 memory

 consciousness

Structure of a neuron

1. Dendrites — receive input from other neurons

 Message begins here and is conducted toward cell body

2. Cell body — maintains cell and receives input

3. Axon — conducts impulse away from cell body its ending release a chemical that

may

 Start impulse in next neuron

 Cause muscle to contract

1

Myelinated axons:

Where are they found?

- most in peripheral nervous system some in central nervous system

What are they?

- the axon is enclosed in a sheath

How are they formed?

- special cells wrap around the axon, Schwann cells (if outside central nervous

system)

- the sheath is many layers of myelin- a material derived from the Schwann cell

membrane

-nodes of Ranvier - gaps in myelin sheath between Schwann cells

Functions of myelin sheath:

1. increase rate of conduction - up to 100X

-called saltatory conduction

-impulse "jumps" from node to node

2. assist in repair of damaged neuron by providing tube to grow through

3. insulation- to prevent short circuiting between axons











Multiple Sclerosis

degeneration + disappearance of myelin covering nerve fibers in brain + spinal cord

strikes young adults- age 20-40

cause unknown- might be measles virus , gene for susceptibility

attacks of paralysis, numbness, blurred vision, etc. alternate with periods of relative

normalcy

no known cure

Functional Classification...