Download The Function & Anatomy of Neurons What is a Neuron?

The Function & Anatomy
of Neurons
What is a Neuron?
It is the cell of nerve tissue that is
responsive and conducts impulses within
the Nervous System at high rates of
speed.
 They are the primary structural and
functional unit of the nervous system.

All Neurons are Made of Three
Basic Parts
Cell Body
 Dendrites
 A Single Axon

Neuron Parts
 Cell
Body- Main part of neuron, cytoplasm with
organelles, a nucleus, and a plasma membrane.
 Processes:
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Axon-Conducts impulses away from the cell body,
only one per neuron (may have side branches),
often has many small branches at terminal end.
Dendrite- Conducts impulses towards the cell
body, thin branching extensions.
Parts Continued..
Nucleus-
control center of the cell.
Neurofibrils- Cytoskeleton of the cell.
Nissl Bodies-Type of rough ER that
performs metabolic activities.
Collaterals- Side branches of axon.
Axon Hillock- Enlargement at
beginning of axon.
Parts Continued Again…
 Axon
Terminals- branching ends of
axon.
 Myelin Sheath- Insulated covering
over axon, increases impulse speed.
 Schwann Cells- Cells that wrap
around axon to make myelin
sheath.
 Nodes of Ranvier- Unmyelinated
gaps on axon.
Neurons Structures
Impulse Propagation of a
Myelinated Neuron
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The insulation provided by the myelin sheath forces the
impulse to jump the myelin to each node of Ranvier.
This speeds up the propagation and is called saltatory
conduction.
Different Types of Neurons
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Multipolar- Has many dendrites surrounding
the cell body has a single axon (CNS
Skeletal Muscle).
Bipolar-Has a single dendrite and single axon
arising from the cell body (found in eyes, ears,
nose).
Unipolar- Single nerve fiber extending from
the cell and that splits in two branches, one
extending to the spinal cord (axon), the other
to the P.N.S. (dendrite).
Neuroglia and Associated
Structures
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Neuroglia- Cell that supports and maintains neuron
structure AKA (glial cell).
Astrocytes- Star shaped cell that attaches neurons to
their blood vessels.
Oligodendrocytes- Support neurons and produce a
fatty myelin sheath around axon in CNS.
Microglia- Also called brain macrophages, engulf
and destroy microbes.
Ependymall Cells- Single layer ciliated cells that line
the ventricles of the brain and central canal of the
spinal column.
Satellite Cells- Surround cell body and aid in
controlling chemical environment.
Neurons Have Three Different
Types of Function
Sensory(Afferent)- Carry impulses from the
peripheral to the central nervous system
(unipolar).
 Association- Carry impulses between
neurons within the central nervous
system(multipolar).
 Motor(Efferent)- Carry impulses from the
central nervous system to any part of the
body capable of responding. (most are
multipolar).

Impulse Propagation
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The Neuron is at rest.
At rest the neuron has a resting membrane
potential (+ outside, - inside).
An impulse comes from the brain, another
neuron etc.
Ion channels open and move Na+ in to the cell.
This changes the balance of charges on the
neuron and causes the electrical charge on
the inside of the neuron to become more
positive.
Action Potential and the
conduction of nerve impulse
The wave of ionic reversals create the
action potential which conducts the
nerve impulse along the neuron.
 Soon after the depolarization the
membrane begins to repolarize.
 The rapid depolarization followed be
repolarization creates the Action
Potential and conducts the impulse.

Transmission of Nerve Impulse
Can happen neuron to neuron, neuron to
muscle etc.
 In nerve to nerve transmission the impulse
crosses the nerve junction (synapse).
 Presynaptic neuron that which sends the
impulse.
 Postsynaptic neuron that which receives
the impulse across the synapse.
 The impulse carries down the presynaptic
neuron to the synaptic end bulb.

Transmission of a Nerve
Impulse Continued
The postsynaptic neuron has a concaved
surface that creates a gap (synaptic
cleft) between the synaptic bulb and the
postsynaptic neuron.
 Once the impulse reaches the bulb the
synaptic vesicles of the bulb move toward
the bulb membrane.
 At the membrane the vesicles open and
release the neurotransmitters.
 These chemicals travel across the cleft
and attach to the receptor sites of the
postsynaptic membrane.

Impulse Transmission
This figure is a graphic representation of nerve to nerve impulse transmission