membrane potential - difference in charge across the membrane
- cytoplasm = negative, extracellular matrix = positive
- fixed anions - negatively charged molecules too large to diffuse out of the cell
- leak channels and sodium-potassium pump keep positively charged ions out of the cell
- equilibrium potential - point where electrical/chemical forces balance out for a certain ion
graded potentials - small changes in membrane potentials
- casued by activation of gated ion channels (can open in response to stimuli like hormones)
- chemical (ligand) gated channel - open when chemicals bind to them
- channels open >> change in membrane permeability >> different ions can get in/out
- depolarization >> membrane potential becomes less negative
- hyperpolarization >> membrane potential becomes more negative
- summation - ability of graded potentials to combine
- threshold - amount of depolarization needed to create action potential
action potential - nerve impulse once voltage-gated ion channels open
- voltage-gated ion channel - opens/closes depending on membrane potential
- Na+ gates open first, before K+ gates
- Na+ enters cell (depolarization) >> K+ exits cell (repolarization) >> possible undershoot if K+ channels stay open (hyperpolarization)
- cannot combine w/ other action potentials
- either occurs completely or none at all
- can depolarize another area of the membrane, starting a chain of action potentials
- saltatory connection - action potentials jumping from node to node in myelinated axons
- speeds up nervous transmissions
- myelinated + larger axon diamter >> fast action potential transmission
synapse - intercellular junction between dendrites and soma
- electrical synapse - uses direct cytoplasmic connections
- usually found in invertebrate systems
- chemical synapse - accounts for majority of synapses
- synaptic cleft - narrow space that separates 2 cells
- synaptic vesicles - contains neurotransmitters
- action potential at end of axon >> Ca++ channels open >> depolarization >> vesicles bind to membrane >> neurotransmitters released through exocytosis, bind to receptor proteins on other cell
- neurotransmitters recycled into cell by transporters, but most go back to cell body before being used again by vesicles
- excitatory postsynaptic potential (EPSP) - depolarization
- inhibitory postsynaptic potential (IPSP) - hyperpolarization
- synaptic integration - EPSP’s and IPSP’s working together to bring about overall effect on cell
neurotransmitters -
- dopamine - used to control body mov’ts
- deficiency causes Parkinson’s disease
- excess causes schizophrenia
- norepinephrine - adds on to the effect of epinephrine, secreted by adrenal gland
- serotonin - regulates sleep/emotion
- deficiency can cause depression
- drug LSD blocks serotonin receptors >> depression
- substance P - neuropetide that responds to pain stimuli
- pain won’t be felt w/o it
- nitric oxide - 1st gas discovered to act as regulatory molecule
- cannot be stored (diffuses through membranes)
- causes smooth muscles to relax
drugs - decreases the sensitivity of receptors, mimics the effects of neurotransmitters
- habituation - receptors lost ability to respond if exposed to constant stimulus for long time
- number of receptor proteins decrease
- blocks transporters >> excess of neurotransmitters in synapse cleft >> # of receptors decrease due to over-stimulation >> addiction
- body adjusts to conditions when drug is present >> withdrawal symptoms occur when drug no longer used
- agonist - acts like the neurotransmitter
- antagonist - blocks the receptor for a neurotransmitter
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