nervous system Flashcards
epidymal cells
columnar/cuboidal cells contain perikaryon; lines ventricles of brain +central canal of spinal cord
some have cilia- facilitate mov of CSF
produces it in choroid plexus
joined apically, but unlike epithelial no basal lamina instead its cells are elongated and extend branching process to adj neuropil
astrocytes function
1) extend processes that associate w synapse which affect the function and plasticity
2) processes w long perivascular feet that contribute to BBB
3) regulate extracellular ionic conc
4) reg vasodilation, transporting nutrients between neuron + capillaries
5) form glial limiting membrane which lines meninges at external CNS
microglia
- origin: monocytes
- short irregular processes for white+grey matter
- size for glial cells (large, spherical and lightly stained) for microglia (small, elongated and dense- play big role in defense of mechanism of phagocytes)
- has # immunoregulatory cytokines
- mononuclear phagocyte system
- when activated by damage/ invader, retract their processes and proliferate to assume characteristic+function of antigen-presenting cells
major dense lines shown in TEM
in myelinated neurons fused protein rich on cytoplasm surface of schwann cell membrane that temporarily disappears.
Cytoplasmic surface important bc allow transient mov of cytoplasm for membrane maintenance which forms:
myelin cleft- along myelin sheath. surface separates slightly to follow movement of cytoplasm for membrane maintenance
CNS
CNS - brain and spinal cord, which are responsible for receiving and processing information+ send commands to body. axons grouped as tracts
- white matter-deep within brain+ peripheral spinal cord. lipid rich-myelin F: transmit info between neurons. (microglia, astrocyte+few neuronal bodies)
- gray matter- cerebral+cerebellar cortex +cerebral nuclei. (perikaryon+ dendrites+ astrocytes+microglia)
cerebral cortex (Sensory integration)initiate voluntary motor resp=efferent pyramidal neurons
cerebellar cortex coordinate muscle activity 3 layer 1) molecular-neuropil+ scattered cell bodies=soma 2) purkinje fibre large neurons w their dendrites 3) granular- densely packed neurons +little neuropil
CNS CT=meninges between vertebra, skull and nervous tissue. 3 layers
1) dura mater- dense irr+fibroelastic, periosteal layer of skull+ meninges layer. dura mater separated by periosteum of vertebrae by spidural space (has plexus of thin walled veins which absorb CSF by arachnoid villi+areolar CT). separated by arachnoid via subdural space. internal+external surface = simple squamous epithelium
2) arachnoid- sheet like of CT in contact w dura mater+ system of loosely arranged trabeculae (collagen+fibroblasts continuous w pia mater). Subarachnoid space (sponge-like cavity) filled CFS (cushion+prtect CNS)+ communicates w ventricles. CT avascular has vessels that penetrate. arachnoid+pia mater often form single membrane (pia-arachnoid).
3) Pia mater-innermost, mesenchymal derived cells on surface of CNS., covered by glial limitants=astrocytes barrier so cant comm w neurons. pia mater+ layer of astrocytic end feet form barrier between CNS+CSF in subarachnoid space.
PNS- cranial, spinal, peripheral nerves and ganglion cells (somatic- body mov + sensory /autonomic-involuntary heartbeat, digestion, breathing)
BBB+ choroid plexus
BBB
barrier-controls passage of substances in/out of cell.
- main component=cappilary endothelium (tightly sealed-occluden junctions. little to no transcytosis (vesicles fuse w other membrane inside to transport material within cell)
- limiting layer:perivascular astrocyte feet - envelop basal lamina of capillaries and forms BBB. forms other components that reg passage of ions.
- surrounded by basement membrane
- protect from : bacterial toxins, infectious agents and helps maintain stable ion conc in interstitial fluid.
- not found in choroid plexus, in post pituitary or region hypothalamus (where plasma components monitored).
choroid plexus
cuboidal epidymal cells. specialised tissue that projects onto 4 ventricles of brain. found where epidymal lining contacts pia mater. produced continuously + fills ventricles, subarachnoid +perivascular space +central canal of spinal cord.
- F: remove h20 from blood and release CSF (Na, Cl, K)-provide ions to CNS;arachnoid absorb mechanical shock (villi acts as main pathway for absorption of CSF back to venous circulation. No lymphatic vessels in central nervous tissue
neural plasticity
neural plasticity- differentiation_formation of new synapses to replace ones lost by injury. controlled by growth factors released neurons+glial cells=NEUTROPHINS. during embryonic development makes extra differentiation neurons which eliminated by apoptosis if don’t find correct synapse w other neurons. neuronal stem cell+projecitor cells in CNS in epidyma= supplies neurons, astrocytes + oligodendrocyte.
- astrocyte proliferate at infured site, interfear w axonal regeneration in spinal cord tracts. Greater potential for regeneration when simple peripheral n.
1) schwann de-differentiates+shed myelin coat within layer of CT+macrophage picks up debrie+ released neutrophins (promote anabolic events for axonal reg)
2) chromatolysis -axonal reg signalled by changes in perikaryon:
- cell body swell due to nissl’s body diminishing+nucleus migrates to peripheral
- axon segment close to injury degenerate (isolated from nutrients +source of protein +organelle) but grows again when nissl’s body returns + debris removed
- new schwann align to guide regrowing axon = polypeptide factor
- motor end reestablishes synaptic connection w muscle + function restored
formation of neuronal cells
NS derived from outermost layer of 3 embryonic layer-ectoderm. at third week, notochord send signal to thicken ectoderm= epithelial neural plate. lateral sides fold upward grow towards each other, fuse+form neural tube=responsible for CNS cells, neurons+some glial cells
neural crest PNS+non neural cells.
neural tube separate from ectoderm =epidermis
neural crest separate from neural epithelium= mesenchymal
AP vs impulse vs synapse
AP process for change in electrical potential of cell membrane. depolarization+hyperpolarization and then Resting P. check pic on notes
impulse is transmission of signal along nerve fibre. initiated by AP or stimulus.
chemical (NT) or electrical (ions:K, Na, Ca) both change the membrane potential=depolarization.
synapse: specialised junctions (site) between neurons to communicate+ convey impulse from pre-to postsynpatic neuron+effector cell
AP unstimulated+stimulated
*AP- generated w impulse/ in unstimulated neurons. when nerve has impulse that reaches threshold, electrical chemical process initiated in axon hillock. AP propagate along axon= depolarization (Na+K channels). - extracellular compartment along neuron= thin zone outside cell formed by enclosing glial cells-help reg ionic conc.
- unstimulated neurons- pump maintains axoplasmic Na conc 1/10 outside of cell; K greater than EC conc. makes potential electrical diff -65mV. stimulate a section of axolemma cause depolarization (na) and then return to resting potential (k) (event takes <1ms)=nerve impulse arriving at synaptic nerve ending trigger release of NT. goes across synpatic cleft to post allowing another impulse to be generated.
glial cells
Glial=non-neuronal cells Derived from projenitor cells of embryonic neural plate (neuroectoderm in mesenchyme). myelin = lipid rich lipoprotein (40% water and 60%lipoproteins). 10x more abundant in mammals. F:provide insulation+support. surround neural cell body+axons +Dendrite process occupy space between neurons. In large blood vessels in CNS have less CT, acts as substitute. support neurons+create microenvironment around cell.
- Fibre surrounding cells resemble collagen in light microscope but its neuropil (dense network of glial procc)
