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Nervous System
q
Acts to allow
communication between cells/tissues of body.
q
Like a
computer or telephone network with a complex central control.
q
Divided into 2
General Systems:
o
Central
Nervous System (CNS)
– Command & Control rgion
§
Usually
involve Brain & Spinal Cord
o
Peripheral
Nervous System (PNS)
q
Composed of
generalized nerve cells called Neurons
General
Structure of a Neuron
q
Neurons are
composed of the following Structures
o
Cell
Body: contain
majority of cell’s cytoplasm & organelles.
o
Dendrites:
Extensions which generally serve in the reception of nerve signals
o
Axons:
Long fibers used to transmit nervous impulses.
§
Often
surrounded by Schwann Cells (PNS) or oligodendrocytes
(CNS) which coat axons with a Myelin sheath
·
Insulates
axons and speeds nerve impulses as impulses jump from the Nodes
of Ranvier.
§
End at Synaptic
terminals. At the Synapses which are small
spaces between adjacent nerve or effector cells.
q
There are
several forms of neurons: Some common types:
o
Sensory
Neurons: Carry sensory information from receptors to the CNS
o
Motor Neurons:
Carry nerve impulses to effector cells/tissues
o
Interneurons:
Integrate sensory & motor neurons.
Neural
Function:
Neurons
function through transmission of a propagating wave of electrochemical
potential. This is produced by
diffusion of Na+ and K+ ions across a neuron’s
membranes.
q
In resting
membrane potential there is an excess of K+ on the inside of
the cell, and an excess of Na+ on the outside.
q
When
stimulated, the cell allows the diffusion of ions through it’s membranes
through gated ion channels.
K+ , and Na+ This changes the potential across the
membrane and is the basis of the electrochemical impulse.
Once stimulated, this reaction propagates down the axon.
q
Sodium and
potassium concentrations are then restored through the sodium-potassium
pump (see active transport systems)
q
This can be
accelerated as neural impulses can “jump” across the nodes
of ranviers
q
Nerve impulses
continue along axons until they reach the synaptic
terminals.
q
Synaptic
terminals end in close proximity to another neuron or an effector cell, and is
separated by a region called a synapse.
q
When the nerve
impulse reaches the terminus, chemical messengers called neurotransmitters
are released from synaptic vesicles into the
synapse. These stimulate neuroreceptor
proteins in the adjacent cell, and the signal is propagated to the next
cell.
The
synapse
Neurotransmitter function
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Mr.Stanley
Last updated: 03/11/2004
