D4H3 Nervous System Flashcards
3 basic divisions of the nervous system
1) central nervous system
2) peripheral nervous system
3) special senses
gray matter in CNS
- consists mostly of nerve cell bodies, dendrites, and axons (together called neuropil) and glial cells
- eg: cerebral cortex, or central horns of the spinal cord
white matter in CNS
- made up of axons of the neurons in the gray matter
- eg: corpus callosum of the cerebrum, tracts of the spinal cord
3 basic cell types in the nervous system
1) neurons
2) glia and support cells
3) non-neural cells
definition of neurons
- electrically excitable cells
- highly polarized structure (dendrites, cell body/soma/perikaryon, axon)
- can communicate signals by means of action potentials propagated along long extensions (axons)
- transmit message to other neurons and other cells at special junctions called synapses by releasing neurotransmitters
cell body/soma of neurons
- neuron cell bodies w/ large, rounded nucleus w/ prominent nucleolus
- have lots of rough ER to make lots of protein
dendrites of neurons
- processes that receive stimuli from other neurons, then send the message to the cell body
- usually highly branched, like a tree (dendrite = tree)
- often covered in spines (small projections on surface); synaptic contact often happens at spines
axons of neurons
- processes that conduct action potentials away from the cell body
- arises from the cell body at the axon hillock, where action potentials are initiated
- are smooth processes (w/o spine)
axoplasmic support
- axons don’t have ribosomes (so don’t have protein synthesis)
- axoplasmic transport is a way to get cellular components from the cell body (point of synthesis) to the axon
- 2 components:
1) fast transport (mostly vesicles moving along microtubule tracks, mediated by kinesin in anterograde direction; dynein in retrograde)
2) slow transport (for larger cell components, cytoskeleton, cytoplasm)
synapses
- sites of chemical communication usually found between the end of an axon and a cell body or dendrites of another neuron
- can also be found between dendrites, between axons
glial cells
- aka “neuroglia” (= nerve glue)
- occupy the space between neurons, separating neurons from each other and from blood vessels
- 3 types of neuroglial cells in CNS:
1) astrocytes
2) oligodendrocytes
3) microglia
astrocytes (what are they/what are the basic types?)
- type of neuroglial cells in CNS
- star-shaped cells (“astro”naut in the stars)
- 2 basic types:
1) protoplasmic (in gray matter of brain and spinal cord)
2) fibrous (in white matter)
function of astrocytes
- transport materials between neurons and blood vessels
- give structural rigidity to the CNS
- regulate the composition of the extracellular space around neurons
- store energy (mainly glycogen)
- secrete growth factors
What is astrocyte cytoskeleton made up of?
astrocyte cytoskeleton is mostly microtubules and intermediate filament proteins made up of “glial-fibrillary acidic protein” (GFAP)
oligodendrocytes
- type of neuroglial cell in CNS
- most abundant in the white matter of the CNS, where they form the myelin sheaths of axons
ependymal cells (what are they?)
-epithelium-like layer lining the cavities (ventricles) of the brain and the central canal of the spinal cord (these cavities contain the cerebrospinal fluid)
Why do ependymal cells have cilia on their apical surfaces?
-cilia on surface helps to circulate the CSF (cerebrospinal fluid)
choroid plexus
- the folds of ependyma (choroidal villi) extending into the ventricles of the brain
- has many blood vessels
- is covered by cuboidal epithelium that secretes the CSF
microglia
- “micro” (small), dense, highly branched cells w/ processes covered in thornlike projections
- are migratory and phagocytic, serve a “white blood cell” type of role: “brain macrophages”
- are derived from circulatin macrophages
- more abundant after damage (so they can clear dying neurons)
meninges
-fibrous, connective tissue coverings of the CNS
- 3 layers:
1) outer dura mater
2) middle arachnoid layer (has subarachnoid space b/n arachnoid layer and pia mater, bridged by arachnoid trabeculae, filled w/ CSF)
3) inner pia mater (thin layer of tissue that coats the outer surface of the CNS, fuses w/ arachnoid trabeculae)
Nissl bodies/Nissl substance
..
why is gray matter gray?
-darker b/c made up of clusters of cell bodies
why is white matter white?
-lighter b/c made up of axons (of neurons), which have myelin, which is fatty (and fat is white)
GFAP (glial-fibrillary acidic protein)
- intermediate filament proteins
- ..?
BBB (blood brain barrier)
- due to zonula occludens between capillary endothelium cells
- restricted permeability for capillaries in the brain
- essential metabolites in blood are transported across, but other things (ex: antibiotics) kept out of brain
- certain regions of brain have permeable BBB so can “sample” blood for regulatory molecules
glymphatic system
-brain’s version of trying to do what the lymphatic system does elsewhere
…
satellite cells in PNS
- act as supportive cells around neurons
- are the glia in ganglia
- act like Schwann cells (provide wrappings)
Schwann cells
myelinate neurons
…
