Inter-workings of the Brain 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 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) Excitatory 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