Nervous Tissue Flashcards
Neurons
Structural & functional unit of nervous system
what do neurons consists of and its location?
- Neurons constitute most sensory receptors, conducting pathways, & integration centers
- All neurons terminally differentiated (Go); do not divide, regeneration of axons possible
- location: in CNS
2 basic cell types of nervous tissue?
- neurons
2. supporting cells (non-conducting)
supporting cells
physical support & protection, electrical insulation, metabolic exchange
3 categories of supporting cells
- neuroglia in CNS
- Schwann cells in PNS
- satellite cells in ganglia
Soma
cell body—contains nucleus, surrounded by perikaryon
perikaryon
cytoplasm surrounding the nucleus in the soma
Nissl substance
rER
Neurilemma
plasma membrane surrounding cell
melanin, lipofuscin
age pigment within cell body
Neuron characteristics
- dendrites
- axon
- cell body
dendrites
highly branched neuron processes, receive stimuli from other neurons or environment (afferent)
single axon
transmits stimuli to other neurons or effector cells (efferent)
axon hillock
axon arises from
terminal bouton
terminates in distal swelling of axon
axonal transport
Movement of products down axon
slow axonal transport
carries cytoskeletal elements
fast axonal transport
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? (4)
- multi-polar neuron
- bipolar
- unipolar
- pseudounipolar
multi-polar neuron
- most common
- several dendrites
- (e.g., motor neurons, interneurons)
Bipolar
single dendrite opposite axon (e.g., receptor neurons of retina)
Unipolar
no dendrites on soma, axon only (eg. sensory axons)
Pseudounipolar
single dendrite & axon fuse; soma off to one side (e.g., dorsal root ganglia)
Physiology of nervous conduction
- [Na+] & [Cl-] higher outsidecell
- [K+] higher insidecell
- Due to Na-K pumps in neuron cell membrane, Na pumped outside cell, K inside => + charge outside, —charge inside => ~ net –80 uv resting membrane potential inside cell
- Action potential–“all or none” response
- Arises in cell body as a result of an afferent stimulus•Causes region of plasma membrane to depolarize
- Voltage gated Na channels open & Na rushes into cell
- Voltage gated K leak channels open & K rapidly leaks out of cell
- —cell’s electrical potential neutralized (goes to zero, or slightly +) —i.e., membrane loses its polarity, or becomes “depolarized”
Causes reversal of resting potential
cell’s electrical potential neutralized (goes to zero, or slightly +) —i.e., membrane loses its polarity, or becomes “depolarized”
Refractory period
- Na channels close & can’t reopen for 1-2 msec
- where N is unresponsive to stimuli
Absolute refractory period
where response to stimulus impossible
Relative refractory period
where only a very strong stimulus can initiate depolarization
What happens after Na channels close…?
voltage gated K channels also close; membrane repolarizes, ends refractory period
“wave of depolarization”
Opening & closing of Na & K channels in “domino effect” along axon => change in electrical potential of membrane which travels down axon
neurotransmitter
Action potential then conducted to effector cell at synapse
Neuromuscular junctions
Specialized junctions between neurons or between neuron & effector cell
Synapses
each synapse is unidirectional; response to a stimulus either excitatory or inhibitory
Entrainment
more a pathway is used, easier it is to access
Terminal bouton
- separated from effector cell by synaptic cleft
- Contains mitochondria & membrane bound synaptic vesicles containing chemical neurotransmitters
pre synaptic membrane
signaling molecules released
post synaptic membrane
- Diffuse across synaptic cleft, bind to receptor molecules
- Vesicles on post-synaptic membrane contain hydrolytic & oxidative enzymes—e.g., acetylcholinesterase; MAO
what 2 neurotransmitters are used in PNS
Acetylcholine& norepinephrine (adrenaline)
Automatic Nervous System is divided into what?
- sympathetic
2. parasympathetic
Sympathetic
“fight or flight” response
•Uses noradrenaline (nor-epinephrine) as excitatory neurotransmitter (adrenergic)
Parasympathetic
promotes relaxation
Uses acetylcholineas excitatory neurotransmitter (cholinergic)
Inactivate neurotransmitters between consecutive impulses
prevent continuous stimulation (e.g., tetany)
Peripheral Nervous Tissue
- Contains afferent &/or efferent fibers (axons) of either somatic (voluntary) or autonomic (involuntary) Nn
- Cell bodies located in CNS or in ganglia
peripheral nerves
bundle of axons, or fascicle
Schwann cells
- provide structural & metabolic support
- derived from neural crest associated with axons provide metabolic support & electrical insulation
- Nuclei along length of axon belong to Schwann cells
In PNS, all neurons enveloped by…..?
Schwann cells
In non-myelinated neurons….
several axons lie in channels within Schwann cell, surrounded by single layer of neurilemma from Schwann cell
Myelinated neuron
- insulated by many concentric layers of plasma membrane from many Schwann cells
- Many axons bound together in fascicle form nerve
sheath of Schwann
consists mostly of cell membrane—forms myelin sheath~ axon
nodes of raniver
- Gaps in myelin sheath between adjacent Schwann cells
- responsible for rapid “saltatory” conduction
- Membrane depolarization occurs only at nodes
oligodendrocytes
- myelinated Nn in CNS sheathed by cells
- One oligodendrocyte surrounds several Nn with >1 layer of plasma membrane
Rate of conduction
diameter of axon, myelin also increase conduction rate
Peripheral Nervous Tissue
Individual axon and Schwann cells surrounded by loose connective tissue endoneurium
perineurium
- surrounds multiple axons organized into bundles (fascicles)
- cells of perineurium unique
what plays a role in axon regeneration
Exhibit epithelioid & myoid features
epineurium
Larger Nn containing several fascicles surrounded by additional layer of connective tissue
what do blood vessels tend to follow?
epi and perineurium
In ANS, two neurons connect CNS to____
preganglionic & postganglionic neurons
Preganglionic(= presynaptic) neurons
- cell bodies in gray matter of brain & cord in CNS
- will synapse with post ganglionic
postganglionic (= postsynaptic) neurons
cell bodies located in ganglia
Ganglia
discrete aggregations of postsynaptic neuron cell bodies located outside the CNS
neural crest
where embryologically are derived, like all peripheral neurons
In the ganglia, each cell body (soma) are surrounded by what?
satellite cells
satellite cells
derived from neural crest—provide structural & metabolic support
location of gangila in sympathetic and parasympathetic
sympathetic ganglia: the parallel vertebral column
parasympathetic: ganglia lie in or near effector organ
Sympathetic ganglia include what? (2)
include prevertebral & paravertebral ganglia
prevertebral ganglia location
anterior to spine—e.g., celiac & mesenteric plexi
part of sympathetic ganglia
paravertebral ganglia location
1’ in sympathetic trunk
part of sympathetic ganglia
Parasympathetic ganglia location
located in or near effector organ e.g., between smooth Mm layers of gut wall—
