Nervous Tissue Flashcards
What is a neuron? What do they constitute? What are they located?
structural and functional unit of nervous system
constitute: most sensory receptors, conducting pathways, and integration centers
in CNS
What is nervous tissue consisted of?
neurons and supporting cells (non-conducting)
What do supporting cells provide? What are there categories?
physical support and protection, electrical insulation, metabolic exchange
neuroglia in CNS, Schwann cells in PNS, and satellite cells in ganglia
What is a defining characteristic of neurons?
terminally differentiated, do not divide, although regeneration of axon is possible
What is a soma?
cell body - contains nucleus, surrounded by cytoplasm = perikaryon
What are Nissl substance, neurilemma, and melanin, lipofuscin?
nissl = rER
neurilemma = plasma membrane surrounding cell
melanin and lipofuscin = age pigment within cell body
What are some characteristics of neurons?
1 or more dendrites - highly branched neuron processes
receive stimuli from other neurons or environment (Afferent)
single axon - transmits stimuli to other neurons or effector cells (Efferent)
axons arise from axon hillock, terminates in distal swelling called terminal bouton
What is axonal transport? What are the types?
movement of products down axon
slow axonal transport carries cytoskeletal elements; fast carries membrane-bound organelles
anterograde transport = from cell body down axon = uses kinesin
retrograde transport = from axon to cell body = uses dynein
What are the basic neuron types?
multi-polar neuron: most common, several dendrites (motor neuron)
bipolar: single dendrite opposite axon
unipolar: no dendrites on soma, axon only (sensory neuron)
pseudo unipolar: single dendrite and axon fuse; soma off to one side (dorsal root ganglia)
What is the physiology of the nervous conduction?
sodium and chloride higher outside cell
potassium higher inside cell
due to Na-K pumps in neuron cell membrane, Na pumped out and K pumped in. net = -80 resting membrane potential inside cell
What does an action potential do in the cell body?
“all or none” response
arises in cell body as a result of efferent stimulus
causes region of plasma membrane to depolarize
voltage gated Na channels open and sodium rushes into cell
voltage gated K leak channels open and K rapidly leaks out of cell
causes reversal of resting potential (goes to zero)
membrane loses polarity = becomes depolarized
Na channels close and refractory period begins, then K channels close and membrane repolarizes
action potential then conducted to effector cell at synapse via neurotransmitter
What are neuromuscular junctions?
specialized junctions between neurons or between neuron and effector cell
each synapse unidirectional and response to stimulis may be either excitatory or inhibitory
What is entrainment?
more a pathway is used = easier it is to access
What is the terminal bouton separated from effector cells by?
synaptic cleft
What does the terminal bouton contain?
mitochondria and membrane bound synaptic vesicles containing neurotransmitters
Signaling molecules release from:
diffuse across synaptic cleft and do what?
pre-synaptic membrane
bind to receptor molecules on post-synaptic membrane
What neurotransmitters are used in the CNS? PNS?
CNS = GABA, dopamine, serotonin
PNS = acetylcholine and norepinephrine
What is the ANS divided into? What do those divisions use?
sympathetic = norepinephrine as excitatory neurotransmitter (adrenergic)
parasympathetic = promotes relaxation using acetylcholine as excitatory neurotransmitter (cholinergic)
What does the peripheral nervous tissue contain? Where are the cell bodies located?
contains afferent and efferent fibers of either somatic or auntonomic nerves
cell bodies of peripheral nerves located in CNS or in ganglia
What is a peripheral nerve?
bundle of axons or fascicle
What are Schwann cells derived from? What do they do?
neural crest associated with axons
provide metabolic support and electrical insulation
nuclei along length of axon belong to Schwann cells
In non-myelinated nerves where do axons lie?
in channels with Schwann cell, surrounded by single layer of neurilemma from Schwann cell
(PNS)
What are myelinated nerves?
insulated by many concentric layers of plasma membrane from many Schwann cells
What is the sheath of Schwann?
consists mostly of cell membrane forms myelin sheath = axon
many axons bound together in fascicle form nerve
