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Structure & Function of Cells in the Nervous System
Transcript of Structure & Function of Cells in the Nervous System
2 K+ in
high levels of sodium in extracellular space
high levels of potassium in intracellular space ACTION POTENTIAL ACTION POTENTIAL Saltatory Conduction Graded Potentials Glial Cells not neurons, but very important in supporting neurons in many ways
10X more glial cells than neurons!
gliomas: brain tumors not in the picture: radial glia THE NEURON What are the forces at play that make an action potential possible? Concentration Gradient Electrostatic Pressure Important Ions:
-calcium Ca++ (Ca2+)
-chloride Cl- like a rubber band ready to snap... absolute refractory period: an action potential is NOT possible because the sodium gates will not re-open
relative refractory period: an action potential is possible, but it requires a stronger stimulus All-or-None Law: an action potential will either fire, or not fire
So how action potentials are measured is through the frequency and pattern of firing oligodendrocytes: myelin in the CNS
Schwann cells: myelin in the PNS multiple sclerosis: demyelination
there are no Na+ gates underneath, so the signal cannot be propagated along the axon Can release a neurotransmitter without an action potential
How is this possible? Very small neurons, with short (or none) axons or dendrites - so the signal does not need to travel very far, and thus does not degrade
Unlike action potentials, more stimulation = more neurotransmitter release (NOT all-or-nothing)
Occurs in receptor cells (e.g. retina, cochlea) The Synapse 1) voltage-dependent Ca++ gates open
2) vesicles fuse to membrane and release NT into synaptic cleft
3) NT binds to specific receptor site on post-synaptic cell and causes either an EPSP or IPSP in post-syanptic cell
4) NT is then broken down via enzymatic degradation or re-uptaken back into pre-synaptic cell What determines if there will be another action potential on the post-synaptic neuron? Summation: adding thousands of input (both excitatory and inhibitory) together; if threshold is reached, another action potential will fire
___________ summation occurs that a single synapse that is repeatedly active.
___________ summation involves multiple synapses that are active simultaneously. ionotropic receptors metabotropic receptors Neurotransmitters neurotransmitters - effect nearby neurons
neuromodulators - affect many cells over a long distance; modify cells' sensitivity/responsiveness to NT (e.g. caffeine!)
hormones - circulating through the blood glutamate: most common excitatory NT
memory storage, perception, schizophrenia
GABA: most common inhibitory NT
sleep; deficiencies: epilepsy, anxiety (Valium)
acetylcholine (Ach): muscle movement, arousal in brain
Alzheimer's: acetylcholinesterase inhibitors
serotonin (5-HT): sleep, mood regulator
deficiencies: depression (SSRIs)
dopamine, norepinephrine, and epinephrine (adrenaline): movement, arousal, reinforcement (reward)
deficiencies: depression, movement disorders (Parkinson's)
Substance P: released from pain receptors
endorphins: pain suppression, reward; runner's high
hormones: testosterone, estrogen, oxytocin, etc. How to alter the message of neurotransmitters... agonist - increase the effects of a NT
antagonist - decrease the effects of a NT
receptor sites can be blocked by drugs that mimic NTs (e.g. marijuana and hashish mimic cannabinoid neurotransmitters)
increase number of dendritic spines, which increases the number of receptor sites (e.g. learning!)
NT components: kinesin molecules, precursors (L-dopa) THE END - PHEW! Just as a reminder...the first MIDTERM is one week from Tuesday.
If you are having trouble with Homework 1, need help labeling the brain, or need further details on what has been covered so far in class, please come to my office hours :)
Don't forget: prezi.com/user/lfyomeuvi1m4 if you want to look at these presentations again THE CELL ribosomes, mitochondria, membrane (phospholipid bilayer)