Transcript Types of neurons

Neurons and Synapses
Types of Neurons
Sensory
Motor
Interneurons
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Sensory Neurons
INPUT From sensory organs to the
brain and spinal cord.
Drawing shows a
somatosensory
neuron
Brain
Sensory
Neuron
Spinal
Cord
Vision, hearing,
taste and smell
nerves are cranial,
not spinal
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Motor Neurons
OUTPUT From the brain and spinal
cord To the muscles and glands.
Sensory
Neuron
Brain
Spinal
Cord
Motor
Neuron
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Interneurons
Interneurons
carry
information
between other
neurons only
found in the
brain and
spinal cord.
Brain
Sensory
Neuron
Spinal
Cord
Motor
Neuron
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Structures of a neuron
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The cell body
Contains the cell’s Nucleus
Round, centrally
located structure
Contains DNA
Controls protein
manufacturing
Directs metabolism
No role in neural
signaling
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Dendrites
 Information
collectors
 Receive inputs
from neighboring
neurons
 Inputs may number
in thousands
 If enough inputs
the cell’s AXON
may generate an
output
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Dendritic Growth
 Mature neurons
generally can’t
divide
 But new dendrites
can grow
 Provides room for
more connections
to other neurons
 New connections
are basis for
learning
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Axon
The cell’s output
structure
One axon per cell,
2 distinct parts
tubelike structure
branches at end
that connect to
dendrites of other
cells
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Myelin sheath
 White fatty casing
on axon
 Acts as an electrical
insulator
 Not present on all
cells
 When present
increases the speed
of neural signals
down the axon.
Myelin Sheath
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How neurons communicate
Neurons communicate by means of an
electrical signal called the Action
Potential
Action Potentials are based on
movements of ions between the
outside and inside of the cell
When an Action Potential occurs a
molecular message is sent to
neighboring neurons
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Ion concentrations
Outside of Cell
K+
Na+
Cl-
Cell Membrane in resting state
K+
Na+
Cl-
A-
Inside of Cell
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The Cell Membrane is SemiPermeable
K+
Na+
Cl-
Outside of Cell
Cell Membrane at rest
K+
Na+
- 70 mv
ACl-
Inside of Cell
Potassium (K+)
can pass through
to equalize its
concentration
Sodium and
Chlorine cannot
pass through
Result - inside is
negative relative
to outside
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Resting Potential
 At rest the inside of the cell is at -70 microvolts
 With inputs to dendrites inside becomes more positive
 if resting potential rises above threshold an action
potential starts to travel from cell body down the axon
 Figure shows resting axon being approached by an AP
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Depolarization ahead of AP
 AP opens cell membrane to allow sodium (NA+) in
 inside of cell rapidly becomes more positive than
outside
 this depolarization travels down the axon as leading
edge of the AP
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Repolarization follows
 After depolarization potassium (K+) moves out
restoring the inside to a negative voltage
 This is called repolarization
 The rapid depolarization and repolarization produce a
pattern called a spike discharge
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Finally, Hyperpolarization
 Repolarization leads to a voltage below the resting
potential, called hyperpolarization
 Now neuron cannot produce a new action potential
 This is the refractory period
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Neuron to Neuron
 Axons branch out
and end near
dendrites of
neighboring cells
 Axon terminals are
the tips of the
axon’s branches
 A gap separates the
axon terminals from
dendrites
 Gap is the Synapse
Dendrite
Axon
Cell
Body
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Synapse
 axon terminals
contain small
storage sacs
called synaptic
vesicles
Sending
Neuron
Axon
Terminal
Synapse
vesicles contain
neurotransmitter
molecules
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Neurotransmitter Release
 Action Potential causes vesicle to
open
 Neurotransmitter released into
synapse
 Locks onto receptor molecule in
postsynaptic membrane
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Locks and Keys
 Neurotransmitter
molecules have
specific shapes
 Receptor molecules have
binding sites
 When NT binds to
receptor, ions enter
positive ions (NA+ )
depolarize the neuron
negative ions (CL-)
hyperpolarize
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Some Drugs work on
receptors
 Some drugs are
shaped like
neurotransmitters
 Antagonists : fit the
receptor but poorly
and block the NT
e.g. beta blockers
 Agonists : fit
receptor well and
act like the NT
e.g. nicotine.
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Glial cells function
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Metabolism and Synthesis in a Neuron
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Neuronal Differentiation
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 In the developing brain, a neuron depends on
molecular signals from other cells, such as
astrocytes, to determine its shape and
location, the kind of transmitter it produces,
and to which other neurons it will connect.
These freshly born cells establish neural
circuits - or information pathways connecting
neuron to neuron - that will be in place
throughout adulthood.
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