2
Basic Cells of the Nervous System
Neuron
•
Basic functional cell of nervous system
•
Transmits impulses (up to 250 mph)
Parts of a Neuron
•
Dendrite
– receive stimulus and carries it impulses
toward the cell body
•
Cell Body
with nucleus – nucleus & most of
cytoplasm
•
Axon
– fiber which carries impulses away from cell body
•
Schwann Cells
- cells which produce myelin or fat layer in the Peripheral Nervous System
•
Myelin sheath
– dense lipid layer which insulates the axon – makes the axon look gray
•
Node of Ranvier
– gaps or nodes in the myelin sheath
•
Impulses travel
from dendrite to cell body to axon
Three types of Neurons
o
Sensory neurons
– bring messages to CNS
o
Motor neurons
- carry messages from CNS
o
Interneurons
– between sensory & motor neurons in the
CNS
Impulses
•
A
stimulus
is a change in the environment with sufficient
strength to initiate a response.
•
Excitability
is the ability of a neuron to respond to the stimulus and convert it into a nerve impulse
•
All of Nothing Rule
– The stimulus is either strong enough to start and impulse or nothing happens
•
Impulses are always the
same strength along a given neuron
and they are
self-propagation
– once it
starts it continues to the end of the neuron in only one direction-
from dendrite to cell body to axon
•
The nerve impulse causes a movement of ions across the cell membrane of the nerve cell.
Synapse
o
Synapse
-
small gap or space between the axon of one neuron and the dendrite of another
-
the
neurons do not actually tough at the synapse
o
It is junction between neurons which uses neurotransmitters to start the impulse in the second
neuron or an effector (muscle or gland)
o
The synapse insures one-way
transmission of impulses
Neurotransmitters
Neurotransmitters
– Chemicals in
the junction which allow impulses to
be started in the second neuron