unit 12

neurons and impulses

nervous system

nervous system

controls and coordinates functions throughout the body, responds to internal and external stimuli

neuron

the impulse-sending cell of the nervous system

central nervous system

brain and spinal cord

peripheral nervous system

sensory receptors, sensory organs, nerves (motor and sensory)

motor neurons

somatic system and autonomic system

somatic system

under conscious control

autonomic system

not under conscious control; automatic, made up of sympathetic and parasympathetic systems

sympathetic system

stressful, tends to “increase”

parasympathetic system

relaxing, tends “decrease”

types of neurons (based on which direction they send their impulse)

sensory, motor and interneurons

sensory/afferent neurons

carry impulse from the sense organs to the spinal cord and brain

motor/efferent neurons

carry impulses from brain and spinal cord to muscles and glands

interneurons

connect sensory and motor neurons and send impulses between them

cell body

body of the neuron, contains the nucleus, most of the cytoplasm, and is the site of cell metabolism

dendrite

branched extensions that receive impulses and send the toward the cell body

axon

long, branched extensions that carries impulse away from cell body; ends at synaptic knobs

myelin sheath

insulating sheath around axon, produced by Schwann cells in PNS, produced by oligodendrocytes in CNS, spaces between them are the Nodes of Ranvier; allows for a more rapid actions potential to occur

the impulse

caused by a change in charge by changing the levels of sodium and potassium across a membrane

formation of the resting potential

3 sodium ions pumped out of the neuron & 2 potassium pumped into the neuron, ions leak back across but this occurs slowly, a gradient of S and P is built up across the membrane, a negative charred builds up inside of the neuron

threshold

the minimum level of stimulus to activate a neuron

absolute refractory period

time after an impulse the neuron will not “fire” no matter how stimulated it is (ions are at equilibrium), sodium potassium pump pushes ions back to the correct side

relative refractory period

time after an impulse the neuron will fire with stimulus, amount of stimulus required decreases as neuron goes towards complete recovery, ion gradient is building back to resting potential

neurotransmitters

norepinephrine, epinephrine, serotonin, dopamine, endorphins, acetylcholine, GABA (gamma aminobutyric acid)

norepinephrine & epinephrine

fight or flight responses, charges up your body

serotonin

sleep and arousal, learning, involved in depression prevention

dopamine

sleep, mood, attention, learning and motor skills, too much linked to schizophrenia, too little is linked to Parkinson’s disease, most addictive drugs are affection synapses that involve the neurotransmitter dopamine, involved in pleasure in pain and suppression (thus drug addiction)

endorphins

linked to pain suppression

acetylcholine

required for neuron-to-muscle function, involved in REM sleep and dreaming

GABA ( gamma aminobutyric acid)

inhibitory neurotransmitter