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