Organs of the nervous
system are divided
into
•Central Nervous
System (CNS)
•Peripheral
Nervous System
(PNS)



Sensory
Integrative
Motor

Sensory functions detect changes
Sensory receptors at the end of peripheral
nerves detect changes inside/outside of the
body
2. External – light, sound touch Internal – pH
levels, oxygen/carbon dioxide
concentrations
3. Information gathered is converted to nerve
impulses of the PNS which sends the
information to the CNS
1.

Integrative functions bring sensory
information together and makes
decisions that are acted upon by using
motor function

Motor functions are responses to
sensory information
Employ peripheral nerves that carry
impulses from CNS to responsive parts
called effectors
2. Effectors are outside the NS and include
a. Muscles – contract when stimulated
b. Glands – secrete hormones when
stimulated
(glandular epithelial tissue)
1.

Neurons (nerve cells) are the functional unit;



Specialized to react to physical & chemical changes
in their surroundings and conduct nerve impulses
Neuroglia support the physiological needs of
neurons
Fig. 8-2, 8-3, 3-21 pg. 70



dendrite – provide receptive surfaces to carry
impulses toward cell body; relatively short &
highly branched
cell body – contains various organelles
axon – a single axon arises from cell body;
transmit impulses away from the cell body;
some are surrounded by specialized glia cells
called Schwann cells that form myelin sheath
http://www.viddler.com/explore/annette/vide
os/7/



motor neurons – transmit impulses form
brain to an effector (efferent neurons)
(multipolar)
sensory neurons – transmit impulses to
spinal cord & brain (afferent neurons)
(most unipolar, some bipolar)
interneurons – carry impulses from
sensor neurons to motor neurons
(multipolar)

bipoloar – only 2
nerve fibers, one
arising from either
end; found in
specialized parts of
the eyes, nose, &
ears

unipolar/monopolar
– single nerve fiber
extending from its
cell body; found in
ganglia outside the
brain or spinal cord

multipolar – many nerve fibers arising from
their cell bodies; most common type of neuron
in the brain & spinal cord (ganglia – a mass of
neuron cell bodies, usually outside the CNS)



Accessory cells – Schwann cells, astrocytes,
microglia, oligodendrocytes, ependymal (We
will discuss the functions of each of these types
of cell during the lab.)
Fill spaces, support neurons, hold nervous
tissue together; play a role in the metabolism of
glucose, help regulate K+ concentration,
produce myelin, and carry on phagocytosis
Fig. 8-3



If a neuron cell body is injured, the
neuron is likely to die
If the axon of a peripheral nerve fiber is
severed, its distal portion will die, but
the proximal portion may regenerate &
re-establish its former connections
Significant regeneration is unlikely to
take place in the CNS
Epineurium –
outermost layer;
dense and include
many collagenous
fibers
 Fasicicle – a bundle
of nerve fibers
 Perineurium – less
dense connective
tissue surrounding
fascicle
 Endoneurium – small
amount of loose
connective tissue that
surrounds individual
nerve fibers


http://www.dnatube.com/video/5035/Neuro
n-Resting-Potential

Resting Potential (-70 mvolts)
 Nerve cell is not conducting impulses
 [Na+] is greater on the outside of the cell and [K+]
is greater on the inside of the cell
 There is a large number of negatively charged ions
inside the cell which can’t diffuse out
 At rest inside stays negative because K+ can diffuse
easily out of the cell through open channels; Na+
can’t diffuse as easily into cells through “their”
protein channels
 Na+ /K+ pump (active transport) – maintains
system so equilibrium is not reached; therefore,
Na+ is always being pumped back out and K+ is
being pumped back in
Stimulation of a membrane affects its
resting potential in a local region (light,
temp., other neurons
 Membrane starts to become
depolarized (moves toward zero)
 Threshold potential is reached which
causes an action potential


http://www.dnatube.com/video/1105/Under
standing-Action-Potential-and-Nerve-Impulses





At threshold, Na+ channels open and Na+ diffuse
inward causing depolarization
About the same time K+ channels open and K+
diffuses outward, causing repolarization
This rapid change in potential is an action
potential
Many action potentials can occur before an active
transport mechanism re-establishes the original
resting potential
The propagation of actions potentials along a
nerve fiber is an impulse


Refractory Period
 A brief time (10-30 m/sec.) following the passage
of a nerve impulse when the membrane is
unresponsive to ordinary stimuli
 Membrane must return to resting potential before
it can be stimulated again
All – or – None Response
 If a nerve fiber responds at all, it responds
completely
 All impulses carried on that fiber will be of the
same strength



Frequency of action potentials – a weak stimulus
initiates only a few action potentials/sec., a strong
stimulus initiates many (upper limit because of
refractory period)
Duration of a burst of action potentials – a weak
stimulus may give rise to a short burst of pulses in
the neuron, a strong stimulus a longer burst
Number & kinds of neurons firing – The threshold
needed to initiate a nerve impulse varies from one
neuron to another. Thus a weak stimulus will cause
only a few neurons to fire, strong will fire all of these
neurons, plus others with higher thresholds.
Unmyelinated fibers conduct impulses
that travel over their entire surface
 Myelinated – impulses travel from
node to node
 Impulse conduction is more rapid on
myelinated fibers with large diameters
 http://www.youtube.com/watch?v=D
Je3_3XsBOg

Impulses usually travel from a dendrite or
cell body, then along the axon to a synapse
 Axons have synaptic knobs at their distal
ends that secrete neurotransmitters
 The neurotransmitter is released when a
nerve impulse reaches the end of an axon
and the neurotransmitter diffuses across the
synaptic cleft.
 When the neurotransmitter reaches the nerve
fiber on the distal side of the cleft, a nerve
impulse is triggered.


http://www.dnatube.com/video/261/NeuralSynapse


Reflex Arc – simplest nerve pathway
 A reflex arc usually includes a sensory neuron, a
reflex center composed of interneurons, and a
motor neuron
 Reflex arc is the behavioral unit of the nervous
system
Reflex Behavior
 Reflexes are automatic unconscious responses to
changes
 Help maintain homeostasis
 Knee jerk – 2 neurons
 Withdrawal reflexes are protective actions

http://www.youtube.com/watch?v=Y5nj3Zfe
YDQ&feature=related