Download The Nervous System

The Nervous System
Introduction
Two organ systems, the nervous
and endocrine systems, coordinate
organ system activity.
The nervous system provides swift
but brief responses to stimuli
The endocrine system adjusts
metabolic operations and directs
long-term changes
The Nervous System
The nervous system includes al the
neural tissue in the body.
Its anatomical divisions include the
central nervous system (CNS) (the
brain and spinal cord
And the peripheral nervous system
(PNS) (all neural tissue outside the
CNS)
Functionally it can be divided
into an afferent division which
brings sensory information to
the CNS
And an efferent division which
carries motor commands to
muscles and glands
The efferent division includes
the somatic nervous system
(voluntary control over skeletal
muscle contractions
And the autonomic nervous
system (involuntary regulation
of smooth muscle, cardiac
muscle, and glandular activity.
8-1
Cellular Organization in
Neural Tissue
There are two types of cells in
neural tissue
Neurons, which are responsible
for information transfer and
processing
Neuroglia, which provide a
supporting framework and act
as phagocytes.
Neurons
Sensory neurons: form the
afferent division of the PNS
and deliver information to the
CNS
Motor neurons: stimulate or
modify the activity of a
peripheral tissue, organ or
organ system
Interneurons: may be located
between sensory and motor
neurons; they analyze sensory
inputs and coordinate motor
outputs.
A typical neuron has a cell
body, an axon, and several
branching dendrites and
synaptic terminals
8-2
Neurons may
be described
as unipolar,
bipolar, or
multipolar
8-3
Neuroglia
Four types
Astrocytes: largest and most
numerous
Oligodendrocytes: myelinate
CNS neurons
Microglia: phagocytic white glod
cells
Ependymal: produce and help
circulate cerebral spinal fluid
8-4
Nerve cell bodies in the PNS
are clustered into ganglia.
Their axons are covered by
myelin wrappings of Schwann
cells.
8-5
Anatomical organization
In the CNS, a collection of neuron
cell bodies that share a particular
function is called a center
A center with a a discrete
anatomical boundary is called a
nucleus.
Portions of the brain surface are
covered by a thick layer of gray
matter called the neural cortex
The white matter of the CNS
contains bundles of axons, or
tracts that share common
origins, destinations and
functions.
Tract in the spinal cord form
larger groups called columns
8-6
Neuron Function:
Membrane Potential
The resting potential, or
membrane potential of an
undisturbed nerve cell, is due
to a balance between the rate
of sodium ion entry and
potassium ion loss and to the
sodium-potassium exchange
pump
Any stimulus
8-7
that affects this
balance will
alter the
resting
potential of the
cell
An action potential appears
when the membrane
depolarizes to a level known
as the threshold.
Steps include; opening of
sodium channels and opening
of potassium channels, return
to normal permeability
8-8
Propagation of an
Action Potential
In continuous propagation, an
action potential spread across
the entire excitable membrane
surface in a series of small
steps.
During saltatory propagation,
the action potential appears to
leap from node to node.
8-9
Action potential
Neural Communication
A synapse is a site where
intercellular communication occurs
through the release of chemicals
called neurotransmitters.
A synapse where neurons
communicate with other cell types
is a neuroeffector junction.
Structure of a Synapse
Neural
communication
moves from
the presynaptic
neuron to the
postsynaptic
neuron over
the synaptic
cleft
8-10
Synaptic function and
Neurotransmitters
Cholinergic synapses release
the neurotransmitter
acetylcholine (Ach)
Ach is broken down in the
synaptic cleft by the enzyme
acetylcholinesterase (AChE)
Other neurotransmitters
Norepinephrine-excites
Dopamine-inhibits
GABA -inhibits
Serotonin-inhibits
8-11, table 8-1
neurotransmitters