Nervous System Notes

Nervous control depends mainly on the functioning of nerve cells. (neurons)

The nervous and endocrine gland systems interact to control and coordinate the body's responses

to changes in its environment, as well as growth, development, and reproduction.

stimulus: a change in the external or internal environment which initiates an impulse

impulse: an electro-chemical charge generated along a neuron

receptors: structures specialized to detect certain stimuli

response: a reaction to a stimulus

effectors: organs which respond to a stimulus such as muscles or glands

neuron = nerve cell (specially designed for the transmission of impulses)

(Parts of a Neuron)

cyton: cell body containing the nucleus

dendrites: cytoplasmic fibers extending from the cyton -- these have the job of detecting the stimulus and generating impulses toward the cyton

axon: the longest dendrite--carries nerve impulses away from the cyton toward the terminal

branches (endbrushes)

** All axons are covered with a fatty myelin sheath to provide electrical insulation.

terminal branches: ends of axons that secrete neurotransmitters

synapse: gap between adjacent neurons (terminal branches of one neuron and the dendrites of the next) or the gap between neuron and effecto

A Neuron Diagram

1 = dendrite

2 = cyton (cell body)

3 = axon (covered by myelin sheath)

4 = endbrushes

neurotransmitter: chemical substance which starts the transmission of the nervous impulse

How do neurotransmitters work to transmit the nervous impulse in humans?

1. A nervous impulse travels down an axon to the tips of a terminal branch.

2. The terminal branch secretes neurotransmitter into the synapse gap.

3. The neurotransmitter travels to the next neuron and causes depolarization of that neuron -- thus a new nervous impulse is started in the next neuron.

neuron: the basic cellular unit of the nervous system

Neurons may release chemicals to stimulate each other, or these chemicals may be released to stimulate a muscle or gland. An example of a muscle being stimulated by a neuron appears after the reflex path pictured in number four in the diagram.

Dynamic equilibrium results from detection and response to stimuli.

stimulus -- a change in the environment detected by an organism

response -- the organism's reaction to a stimulus

Responses involve the action of effectors.

effector -- any muscle or gland

Organisms detect and respond to change in a variety of ways at both the cellular level and the organism level.

More complex animals have a central nervous system which includes a brain and a nerve cord.

Brain: a large mass of neurons located in the cranial cavity--contains three major divisions

cerebrum: center for voluntary activity interprets sensory impulses, initiates some motor activities, and responsible for memory, thinking and reasoning

cerebellum: coordinates motor activities and aids in maintaining balance

medulla: controls involuntary activities such as breathing, heartbeat, blood pressure and peristalsis (is part of the brain stem)

2. Spinal cord: lies within, and is protected by, the vertebrae of the spinal column

-- is continuous with the brain -- coordinates activities between the brain and other body structures

-- it is also a center for reflex actions

[Peripheral Nervous System]

--is located outside the central nervous system and consists of nerves extending throughout the body

stroke: a disease resulting from a cerebral hemorrhage or a blood clot in a

cerebral blood vessel blocking blood flow to part of the brain

-- may also result from a ruptured blood vessel

** This may result in brain damage leading to partial or total paralysis.