Nervous Regulation Chapter 14

I. Regulation is the life function by which organisms coordinate and control their own life activities to maintain life. Regulation includes both nerve control (animals only) & chemical control (all organisms).

A. Nerve control- nerve control depends mainly on the functioning of the neurons (nerve cells).

1. Stimulus is any change that occurs in the external or internal environment of an organism which initiates an impulse.
ex): light, sound & chemical change
2. Impulse - an electro-chemical charge generated along a neuron
3. Response is a reaction to a stimulus

a. Receptors- structures specialized to detect only 1 type of stimuli
ex.) Eye for light, ears for sound, skin for touch, nose for smell, tongue for taste

b. Effectors- organs of response such as muscles or glands

1. Stimulus activates a receptors
2. Receptors trigger impulse in a nerve pathway
3. Impulse is received by effectors which respond

B. Structure of NEURON

Neuron- A cell specialized for the transmission of nerve impulses from place to place in the body. It is composed of:

1) DENDRITES- fibers which detect the stimulus and generate impulses toward the CYTON.
2) CYTON- cell body containing the nucleus.
3) AXON- a fiber that transmits the impulse away from the CYTON toward the terminal branches
4) MYELIN SHEATH- layers of white, fatty substances produced by Schwann cells that surround some axons
5) TERMINAL BRANCHES- ends of the axons which secrete neurotransmitters (consists of synaptic knobs)

C. Synapse is a junction between adjacent neurons or between neurons and effectors

D. Neurotransmitters are special chemicals, produced and secreted by the neuron's synaptic knob (located at a terminal branch) that serves to carry impulses from 1 neuron to the next.
ex) acetylcholine

E. Types of Neurons (nerve cells) nerves are bundles of axons or dendrites that are bound together by connective tissue.

1. Sensory Neurons- carry impulses from receptors toward the spinal cord and brain (longest)
2. Interneurons-(also called associative neurons) carry impulses from one neuron to another in the brain and spinal cord (short)
3. Motor Neurons- carry impulses from the brain and spinal cord to the effectors.

How a Nerve Impulse is sent through a neuron...

II. Resting Neuron

A. Transmission of nerve impulse is made possible by a difference in electrical charge between the outer (+) and inner (-) nerve cell membrane.
B. Nerve cell membrane has an active transport (energy) mechanism that pumps sodium ions out of the cell and potassium ions into the cell (sodium pump) that makes the outside of the nerve cell membrane positive and the inside negative.
C. In its resting state, potassium ions can move freely into and out of the cell but sodium ions can only move out of the cell.

III. Nerve Impulse

A. As an impulse is carried in a neuron, sodium ions can readily diffuse back into the cell from the outside causing a reversal of polarity (the outside becomes negative and the inside becomes positive.)

B. This reversal of polarity occurs in a small area of the membrane where the impulse is.
C. Once the impulse passes, sodium ions pass from the inside back to the outside and the polarity is returned back to that of the resting neuron.

IV. Transmission at the synapse

A. During impulse (electrical energy), a neurotransmitter, acetylcholine and norepinephrine, is released into the synaptic cleft (space between 2 neurons).
B. The electrical impulse is now converted into a chemical response which stimulates the adjoining neuron to receive the transmitted impulse.
C. Once the impulse has been transmitted, cholinesterase break down the acetylcholine to clear the way for new signals.

V. Adaptation in Animals (these are listed from simplest to complex)

A. Protozoa- have no true nervous system. Responds to food, light, & chemicals.

B. Hydra- the hydra possesses a nerve net composed of modified neurons (neurofibrils). There is no central nervous system and impulses may travel in either direction over the neuron.

C. Earthworm- the nervous system of the earthworm consists of primitive brain composed of fused ganglia, a ventral nerve cord, and peripheral nerves. The presence of this central nervous system permits impulses to travel over definite pathways from receptors to effectors.

D. Grasshopper- the grasshopper's nervous system is similar to that of an earthworm. The grasshopper possesses sensory organs which include eyes, tympana, and antenna.

E. Human- the human central nervous system consists of a highly developed brain and dorsal nerve cord (found in all chordates) which permit impulses to travel over definite pathways. There is also many highly developed receptors. One disease (caused by a virus) associated with the destruction of nerve cells is polio.

Biology Trivia

1. What is the basic unit of the brain? answer

2. What two organisms (that we studied) have the most similarities within their nervous systems? answer

3. Chemicals produced by the ends of neurons and secreted into synaptic spaces are answer

4. What is a ganglion (gang lee un)? answer

return to Mr. Via's syllabus