Nervous System = Communication Function: Receives Stimuli
Interprets information Causes a response -Controls and coordinates
bodily functions -Controls and coordinates bodily functions
-Responds to stimuli (inside or outside the body) -Responds to
stimuli (inside or outside the body)
Slide 5
What is the basic functional unit of the nervous system?
Neuron! What does the neuron do? Carries messages throughout the
body How does it carry the messages? By conducting electrical
signals What are these signals called? Nerve impulses!
Slide 6
What does a neuron look like?
Slide 7
Neuron Anatomy Three parts to a NEURON: 1.Cell body: Large,
central portion of the neuron where all organelle are located What
is its job? Interpret incoming signals Cell Body
Slide 8
Neuron Anatomy 2. Dendrites: Short, highly branched fibers what
is its job? Carries impulses toward the cell body Referred to as
the afferent process Dendrites
Slide 9
Neuron Anatomy 3. Axon: Long, slightly branched fiber What is
its job? What is its job? Carry impulses away from the cell body
Carry impulses away from the cell body Referred to as the efferent
process Referred to as the efferent process
Slide 10
The Axon Axon Terminals Axon Hillock fiber
Slide 11
Neuron Anatomy Additional Parts of a Neuro n Dendrite Cell body
Axon terminal Myelin sheath Nodes of Ranvier Axon Nucleus Structure
of a Typical Neuron
Slide 12
Neuron anatomy What do you remember ? 3 1 2 4 5 6 7 dendrites
nucleus Cell body axon Nodes of Ranvier Myelin sheath Axon
terminals Direction of impulse
Slide 13
Three Types of Neurons II. Motor Neurons: Carry impulses to
muscles and glands Cause a response to some stimuli III.
Interneurons: Connect sensory and motor neurons Allow for quick
response (reflex action)
Slide 14
Three types of neurons
Slide 15
Neurons What is grey matter? Collective cell bodies and
dendrites of all neurons Collective cell bodies and dendrites of
all neurons What is white matter? Myelinated nerve fibers
Myelinated nerve fibers Axons of all neurons Axons of all neurons
Can be approximately one meter in length Can be approximately one
meter in length White matter Gray matter
Slide 16
What is a Nerve? Bundle of axons held together by connective
tissue. What color is a nerve? White!Why? Because axons are white
matter and they compose nerves
Slide 17
How are nerves held together? Connective tissue What is this
connective tissue called? tissue called? Neuroglial cells (nerve
glue) Approximately half of the volume of the brain is composed of
neuroglial cells Most brain tumors develop in mesoglial cells NOT
neurons
Slide 18
What do neuroglial cells do? Support the axons Insulate the
electrical impulses Like electrical tape insulates electric wires
this prevents leaking of electric signals
Slide 19
An example of a neuroglial cell Schwann cell This wraps around
the axon in multiple layers It is composed of a fatty material
called Myelin Regular breaks in the myelin sheath are called Node
of Ranvier
Slide 20
Impulse speed Some neurons are fast, good conductors of
impulses Other neurons are slow, poor conductors of impulses What
distinguishes these two types? 1. Diameter of the axon 2.
Myelination Fastest axons have a large diameter and are myelinated.
How much faster? Up to 100 times faster! (Reflexes are this
type)
Slide 21
The Nerve Impulse How are messages (impulses) carried by the
nervous system? As electrical and chemical signals. How does the
impulse develop? Charged particles (ions) move across the cell
membrane A neuron is ready to transmit an impulse when it is in the
resting state. Resting membrane potential is -70 mV
Slide 22
Resting Membrane Potential The inside of the cell has a
negative charge as compared to the outside of the cell membrane.
How does this charge difference develop? There are more Na +
(sodium) ions outside and fewer K + (potassium) ions inside.
Slide 23
The Nerve Impulse How does the impulse begin? The neuron is
stimulated by another neuron or by stimuli from the
environment.
Slide 24
The Nerve Impulse If the stimulus is strong enough, it reaches
threshold level. This stimulates an impulse. If the stimulus is not
strong enough, no impulse occurs (all-or- none principal)
Slide 25
The Nerve Impulse What happens if threshold is reached? An
action potential (nerve impulse) begins What is an action
potential? Rapid reversal of membrane potential in response to a
stimulus How does this happen? Sodium channels open allowing Na +
to flood into the cell. The membrane potential rises to +30 mV
(rising phase) as inside of cell becomes more positive
Slide 26
The Nerve Impulse Please, please, tell us what happens next
When the membrane potential reaches +30 mV, the sodium channels
close. Potassium channels open and K + flows out of the cell. This
causes the membrane potential to become more negative again
(falling phase).
Slide 27
The Nerve Impulse Na + channels close K + leaves cell K +
channels open, K + begins to leave cell Na + channels open, Na +
enters cell K + channels close Excess K + outside diffuses away
Threshold of excitation Membrane potential (mV) +50 0 -70 1 2
3
Slide 28
Slide 29
The Nerve Impulse
Slide 30
Action potential Resting state Threshold Failed initiations
Refractory period Time (ms) Voltage (mV) Depolarization
Repolarization 0 1 2 3 4 5 +40 -55 -70 0 Stimulus
Slide 31
The Nerve Impulse What happens when the action potential passes
down the axon? The resting potential is restored via the
sodium/potassium pump. Now the membrane is ready to transmit
another impulse. extracellular fluid cytoplasm Na + ATP ADP
K+K+
Slide 32
The Nerve Impulse An action potential only moves in one
direction down the axon. From axon hillock, thru axon fiber to the
axon terminal. The action potential is regenerated at each Node of
Ranvier down the length of the axon.
Slide 33
The Nerve Impulse What happens when the impulse reaches the
axon terminal? It must pass thru the synapse. What is a synapse? It
is the gap between two neurons, or between a neuron and organ
(effector). Why is there a gap? So the neurons dont short each
other out!!
Slide 34
The Synapse How do neurons pass the impulse across the synapse?
Using chemicals called neurotransmitters What do neurotransmitters
do? Stimulate the dendrites of other neurons or membranes of other
cells. If a dendrite is stimulated, it sends its message to the
cell body and the message is passed on If a muscle or gland is
stimulated, a reaction occurs in that organ.
Slide 35
The Synapse
Slide 36
synaptic vesicles Axon of presynaptic cell neurotransmitters
receptors for neurotransmitters receptors for glycoprotein synaptic
cleft Glycoprotein (ligands) Model of the Synapse
Slide 37
The Synapse
Slide 38
Neuron Smear: Identification: Note distinctive shape of neuron,
with long processes (dendrites and/or axons, 5) extending out from
main cell body. Features to Know: The large, irregularly shaped
cell body (3) contains a darker nucleus (2), which contains an even
darker-staining nucleolus (1). The large, irregularly shaped cell
body (3) contains a darker nucleus (2), which contains an even
darker-staining nucleolus (1). There are also numerous supporting
glial cells, though only their small dark nuclei (4) are easily
seen. There are also numerous supporting glial cells, though only
their small dark nuclei (4) are easily seen.