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Transcript
What Makes Us Human?
The Psychological Answer
Neural Transmission
Key Terms
• Dendrite
– the bushy, branching
extensions of a neuron
that receive messages
and conduct impulses
toward the cell body
Key Terms (Cont’d)
• Axon
– the extension of a
neuron, ending in
branching terminal
fibers, through which
messages are sent to
other neurons or to
muscles or glands
Key Terms (Cont’d)
• Myelin [MY-uh-lin] Sheath
– a layer of fatty cells
that encase the fibers
of many neurons in
segments
– Speeds up the
transmission of neural
impulses
Key Terms (Cont’d)
• Synapse [SIN-aps]
– junction between the
axon tip of the sending
neuron and the
dendrite or cell body of
the receiving neuron
– tiny gap at this junction
is called the synaptic
gap or cleft
Key Terms (Cont’d)
• Neurotransmitters
– chemical messengers
– released by the sending
neuron
– travel across the synapse
and bind to receptor sites
on the receiving neuron
(determining whether or
not to generate a neural
impulse)
Cell Body
•
•
•
•
Cell body
Otherwise known as a soma
Contains nucleus
Produces and packages neurotransmitters
Neurons
• Neuron
– the basic building block of the nervous system
– Send messages electrochemically –
chemicals cause an electric signal
Action Potential
• Chemicals in the body are ions (electrically
charged)
• Two important ions in the nervous system
– sodium (Na) and potassium (K)
Action Potential (Cont’d)
• nerve cells are surrounded by a semipermeable membrane (allows some ions
to pass through and blocks the passage of
other ions)
Resting Membrane Potential
• Neurons that aren’t sending signals are "at
rest"
• At rest – (relatively) more sodium ions
outside the neuron and more potassium
ions inside that neuron
Action Potential
• An action potential occurs when a neuron
sends information down an axon, away from the
cell body
• Action potentials are caused by an exchange of
ions across the neuron membrane.
• The action potential is an explosion of electrical
activity that is created by a depolarizing current
Action Potential (Cont’d)
• When depolarization reaches a certain
amount (threshold) a neuron will fire an
action potential
• If the neuron does not reach critical threshold
level, then no action potential will fire
Action Potential
Action Potential (Cont’d)
• All action potentials are the same size.
• The neuron either does not reach the
threshold or a full action potential is fired this is the "ALL OR NONE" principle.
Action Potential (Cont’d)
• During an action potential sodium ions rush into
the neuron.
• Because sodium has a positive charge, the
neuron becomes more positive and becomes
depolarized
Action Potential (Cont’d)
• Potassium rushes out of the cell, reversing
the depolarization.
• At about this time, sodium channels start
to close - causing the action potential to go
back – repolarization
Part Two: The Synapse
The Synapse
• Information from one neuron flows to
another neuron across a synapse
• The synapse contains a small gap
separating neurons
The Synapse
•
The synapse consists of:
1. a presynaptic ending that contains
neurotransmitters, mitochondria and other cell
organelles,
2. a postsynaptic ending that contains receptor sites
for neurotransmitters and,
3. a synaptic cleft or gap between the presynaptic and
postsynaptic endings
An Example
Neurotransmitter Mobilization and
Release
• At the synaptic terminal (the
presynaptic ending), an
electrical impulse will trigger
the migration of vesicles
containing
neurotransmitters toward
the presynaptic membrane
Neurotransmitter Mobilization and
Release (Cont’d)
• The vesicle membrane will fuse with the presynaptic
membrane releasing the neurotransmitters into the
synaptic cleft
• Neurons can contain and release more than one kind of
neurotransmitter
• The neurotransmitter molecules then diffuse across the
synaptic cleft where they can bind with receptor sites on
the postsynaptic ending to influence the electrical
response in the postsynaptic neuron
Diffusion of Neurotransmitters
Across the Synaptic Cleft
Neurotransmitters
• Communication of information between
neurons is accomplished by movement of
chemicals across a small gap called the
synapse.
• Chemicals, called neurotransmitters, are
released from one neuron at the
presynaptic nerve terminal.
Neurotransmitters
• Neurotransmitters then cross the synapse
where they may be accepted by the next
neuron at a specialized site called a receptor
• The action that follows activation of a
receptor site may be either depolarization (an
excitatory postsynaptic potential) or
hyperpolarization (an inhibitory postsynaptic
potential)
Neurotransmitters
• A depolarization makes it MORE likely that
an action potential will fire; a
hyperpolarization makes it LESS likely that
an action potential will fire.