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The Neuron
Inter-workings of the Brain
Drill #22
• Draw the neuron.
• Label it correctly with the following
parts:
– Soma
– Dendrites
– Axon
– Myelin Sheath
– Terminal Buttons
• Write the function of each of the parts
Neural Impulse
• NEURAL IMPULSES are
complex electrochemical
reactions involving IONS
– electrically charged
atoms that flow back and
forth across the cell
membrane
– Positively charged ions –
sodium & potassium
– Negatively charged ions chloride
• Positively & negatively
charged ions DO NOT
travel at the same rate
– This leads to a slightly
higher concentration of
negatively charged ions
inside the cell
Resting vs. Action Potential
Alan Hodgkin & Andrew Huxley
• Resting Potential
– when a neuron is at its
stable, negative
charge
– When it is inactive
• Action Potential
– A very brief shift in a
neuron’s electrical
charge that travels
along an axon – a
voltage spike occurs
• This occurs when
channels open up,
briefly allowing
positively charged
sodium ions to rush in
Absolute Refractory Period
&
The All or None Law
• Absolute Refractory
Period
– The minimum amount
of time after an action
potential during which
another action
potential CANNOT
begin
• All or None Law
– Think of a Neuron like
a gun – you cannot
half-fire a gun
– Either the neuron fires,
or it doesn’t
– Action potentials are
all the same size –
weaker stimuli do not
produce smaller action
potentials
**Neurons can convey information about the strength
of a stimulus by varying the rate at which they fire**
The Synapse
• Where neurons meet
• Synaptic Cleft – an
infinitely small gap
between the terminal
buttons of one neuron &
the cell membrane of
another neuron
– Signals have to jump this
gap to communicate
– Presynaptic Neuron
• Sends the signal
– Postsynaptic Neuron
• Receives the signal
NeuroTransmitters
Chemicals that transmit information
from one neuron to another –
fundamental to behavior & play a key
role in everything from muscle
movement to mood and mental health
Common Neurotransmitters &
Their
Functions
• Acetylcholine
(can be stimulated by nicotine)
– Activates motor neurons controlling skeletal muscles
– Regulates attention, arousal, and memory
• Dopamine (Cocaine & amphetamines elevate Dopamine activity)
– Control of voluntary movement & pleasurable emotion
– Overactivity is associated with Schizophrenia
• Norepinephrine (Cocaine & amphetamines elevate NE levels)
– Modulation of mood & arousal
• Serotonin (Prozac & antidepressants affect Serotonin levels)
– Regulation of sleep, eating & aggression
– Abnormal levels contribute to depression & OCD
• GABA (Valium & anti-anxiety drugs work at GABA synapses)
– Seem to produce only inhibitory postsynaptic potentials
– Regulation of anxiety in humans & plays a role in seizures
• Endorphins (resemble opiate drugs in structure & effects)
– Pain relief & pleasurable emotions
Receiving Signals
• Postsynaptic Potentials
(PSP)
– Voltage change at the
receptor site on a
postsynaptic cell
membrane
• DO NOT follow the All or
None Law
• Vary in size and increase
or decrease probability
of a neural impulse
• Excitatory PSP
– A positive voltage shift that
increases likelihood that
the postsynaptic neuron
will fire action potentials
• Inhibitory PSP
– A negative voltage shift that
decreases the likelihood
that the postsynaptic
neuron will fire action
potentials
The Reuptake Process
• A process in which
neurotransmitters are
sponged up from the
synaptic cleft by the
presynaptic
membrane