Anatomy & Physiology I
Unit Seven
Nervous System Function
The general
purpose of the
nervous system is to
coordinate the
function of all
body cells and
maintain homeostasis
Nervous System Function
Integrating
Center
Sensor
Stimulus
Effectors
Response
Anatomy of the Human Nervous System
Anatomy of the Human Nervous System
Anatomy of the Human Nervous System
Neuron – a nerve cell
Nerve – a bundle of neuron axons
wrapped in fibrous connective
tissue
Ganglion – a mass of neuron cell
bodies found in the PNS
Anatomy of the Human Nervous System
Neuron Properties and Classes
Neuron properties:
~ excitability – respond to stimuli
~ conductivity – sending electrical
impulses
~ secretion – release of
neurotransmitters
Neuron Properties and Classes
Neuron classes:
~ afferent (sensory) neurons
* detect a variety of stimuli and
send messages to the CNS
Neuron Properties and Classes
Neuron classes:
~ interneurons
* found only in the CNS
* receive signals from afferent
neurons
* carry out integrative functions
* approximately 90% of all
neurons
Neuron Properties and Classes
Neuron classes:
~ efferent (motor) neurons
* send messages from CNS to
effectors (muscles or glands)
in response to stimuli
Neuron
Properties and
Classes
Neuron
Structure
Neuron Structure
Neuron Structure
Neuroglia
Neuroglia - support cells that aid in
the functions of neurons
> four types are found in the CNS
* astrocytes
* oligodendrocytes
* microglia
* ependymal cells
Neuroglia
Neuroglia
Neuroglia - support cells that aid in
the functions of neurons
> two types are found in the PNS
* Schwann cells
* satellite cells
Action Potentials
Resting membrane
potential:
+ polarization of
neuron due to
differences in
external & internal
ion
concentrations
Action Potentials
Action Potentials
Action potential:
+ a nerve
(electrical)
impulse
+ generated by
chemically
mediated
channels
Action Potentials
Action Potentials
Action Potentials
Action Potential
Propagation
Refractory
Period and
Action Potential
Conduction
Action Potential
Propagation
Saltatory conduction
Action
Potent
ial
Gener
ation
The Neural Synapse
A synapse is junction at the end of a
neuron axon where it stimulates another
cell by way of chemical messengers
called neurotransmitters
The Neural Synapse
The most common synapse types are:
~ neural synapse – junction
between one neuron and
another
~ myoneural synapse – junction
between a neuron and a
muscle cell
The Neural Synapse
The Neural Synapse
Presynaptic
membrane
Postsynaptic
membrane
Synaptic
cleft
The Neural Synapse
Neurotransmitters are chemical
messengers that are released by an axon
presynaptic membrane
Some neurotransmitters will excite
postsynaptic membranes while others
will inhibit them
Neurotransmitters
Neurotransmitter classes:
+ acetylcholine
+ amino acids
+ monoamines
+ neuropeptides
Neurotransmitters
Acetylcholine:
+ released in myoneural
synapses & in most ANS
synapses
+ excites skeletal muscle
+ inhibits cardiac muscle
+ excites & inhibits smooth
muscle and glands depending
on location
Neurotransmitters
Amino acids:
+ four types that excite or
inhibit activity in the CNS
+ excitatory – glutamate
& aspartate
+ inhibitory – glycine & GABA
(gamma
aminobutyric
acid)
Neurotransmitters
Amino acids:
+ glutamate is the principle
excitatory neurotransmitter
of the brain, while aspartate
is the principle one in the
spinal cord
Neurotransmitters
Amino acids:
+ GABA is the most common
inhibitory neurotransmitter
in the brain, while glycine is
the most common in the
spinal cord
Neurotransmitters
Monoamines:
+ found mainly in the brain, but
also in the spinal cord and
ANS
+ can exhibit excitatory or
inhibitory effects depending
on location
Neurotransmitters
Monoamines:
+ catecholamines are a group of
commonly known
monoamines
~ norepinephrine is found
in the brain, spinal cord &
ANS causing excitation &
inhibition
Neurotransmitters
Monoamines:
+ catecholamines are a group of
commonly known
monoamines
~ epinephrine is found
in the brain & spinal cord
causing excitation &
inhibition
Neurotransmitters
Monoamines:
+ serotonin is found in the CNS
and is secreted by platelets
+ its effects are usually
excitatory
Neurotransmitters
Monoamines:
+ histamine is found in the
brain and is secreted by
basophils
+ its effects are as a potent
vasodilator
Neurotransmitters
Neuropeptides:
+ found mainly in the CNS, but
also in the digestive tract
+ they are mainly inhibitory in
nature, playing major roles in
pain suppression and
digestion
Neurotransmitters
Neuropeptides:
+ beta endorphin suppresses
pain and fatigue
+ cholecystokinin (CCK)
suppresses appetite and aids
in digestion
The Neural
Synapse
Cholin
ergic
The Neural
Synapse
Adrene
rgic
Postsynaptic Response
As has been noted, postsynaptic responses
can be excitatory or inhibitory
Neurotransmitters that elicit an excitatory
response do so by producing excitatory
postsynaptic potentials (EPSPs)
Postsynaptic Response
Neurotransmitters that elicit an inhibitory
response do so by producing inhibitory
postsynaptic potentials (IPSPs)
Both EPSPs and IPSPs are necessary for
proper function in the nervous system
Postsynaptic Response
Postsynaptic Response
Postsynaptic Response
Summation is the
process of adding
up postsynaptic
potentials &
responding to
their net effect
Postsynaptic Response
Postsynaptic Response
Summation can
occur in two
ways:
~ temporal
~ spatial
Postsynaptic Response
Postsynaptic Response
Anesthetics (without sensation):
# most work by activating
inhibitory receptors
# others work by decreasing
membrane permeability to
Na+
Postsynaptic Response
Proprioception is subconscious perception
of the position and movements of the body
It results from the input from
proprioceptors (receptors in muscles,
tendons & joints) and the vestibular
apparatus of the inner ear