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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 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
Resting vs. Action PotentialAlan Hodgkin & Andrew Huxley
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