Tissues and Cells of the Nervous System: A & P Exam 3

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