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endocrine system
communicates by means of chemical messengers secreted into the blood
nervous system
employs electrical and chemical means to send messages from cell to cell
electrophysiology
study of cellular mechanisms for producing electrical potentials and currents, basis for neural communication and muscle contraction
electrical potential
a difference in concentration of charged particles between one point and another
electrical current
a flow of charged particles from one point to another
resting membrane potential
exists because of unequal electrolyte distribution between extraceullar fluid and intracellular fluid,
potassium
greatest influence on RMP, leaks out until electrical charge of cytoplasmic anions attracts it back in and equilibrium is reached
cytoplasmic anions
cannot escape due to size or charge
sodium
membrane not very permeable to, leakage of makes RMP slightly less negative
Na+/K+ pump
moves 3 Na+ out for every 2 K+ it brings in, works continuously
local potentials
changes in membrane potential of a neuron occurring at and nearby the part of the cell that is stimulated
action potential
dramatic change in membrane polarity produced by voltage-gated ion channels
trigger zone
where action potential is generated
nondecremental action potential
do not get weaker with distance
irreversible action potential
once started, goes to completion and cannot be stopped
refractory period
the period of resistance to stimulation
absolute refractory period
no stimulus of any strength will trigger AP, lasts as long as Na+ gates are open, then inactivated
relative refractory period
K+ gates still open and any effect of incoming Na+ is opposed by the outgoing K+
unmyelinated fibers
have voltage-gated channels along their entire length, can’t skip an axon, take longer
myelinated fibers
conduct signals with saltatory conduction, signal seems to jump from node to node, fast
nodes of ranvier
gaps in the myelin sheath coating on the neural axon, contain many voltage-gated ion channels
synaptic cleft
gap between neurons
neurotransmitters
molecules that are released when a signal reaches a synaptic nob that binds to a receptor on another cell and alter that cell’s physiology
acetylcholine
neurotransmitter, in a class by itself, formed from acetic acid and choline
Amino acid
neurotransmitter, include glycine, glutamate, aspartate and GABA
Monoamines
neurotransmitter, synthesized from amino acids by removing the COOH group while retaining the -NH2 (amino) group
neuropeptides
neurotransmitter, chains of 2 to 40 amino acids, stored in secretory granules, some function as hormones
gases
nitric oxide and carbon monoxide, synthesized as needed rather than stored
neuromodulators
chemicals secreted by neurons that have long term effects on groups of neurons
neuropeptides
chains of amino acids that can act as neuromodulators
axonal transport
two-way passage of proteins, organelles and other material along an axon
anterograde transport
movement down the axon away from neurosoma
retrograde transport
movement UP the axon Towards the neurosoma
kinesin
motor proteins in ANTEROGRADE transport
dynein
motor proteins in RETROGRADE transport
fast axonal transport
rate of 20 to 400 mm/day, fast anterograde and retrograde transport
slow axonal transport
0.5 to 10 mm/day, ALWAYS anterograde
neuroglia cells
protect neurons and help them function, binds neurons together
oligodendrocytes
form myelin sheaths in CNS that speed signal conduction
Ependymal cells
line internal cavities of the brain, secrete and circulate cerebrospinal fluid
microglia
wander through CNS looking for debris and damage, develop from white blood cells
astrocytes
most abundant glial cell in CNS covering brain surface and most non synaptic regions of neurons in the gray matter, form supportive framework, form blood-brain barrier, convert glucose to lactate and supply this to neurons
Schwann cells
cells that produce a myelin sheath, envelop nerve fibers in PNS
satellite cells
surround the neurosomas in ganglia of the PNS, provide electrical insulation around the neurosoma
myelin sheath
insulation around a nerve fiber, helps speed up electrical impulses
myelination
production of the myelin sheath,
neurilemma
thick, outermost coil of myelin sheath,
endoneurium
external to neurilemma, thin layer of fibrous connective tissue, insulates 1 axon
internodes
myelin-covered segments from one gap to the next
initial segment
short section of nerve fiber between the axon hillock and the first glial cell
trigger zone
the axon hillock and the initial segment, play bid role in initiating a nerve signal
nerve growth factor
protein secreted by a gland, muscle or glial cells and picked up by the axon terminals of neurons