Cellular Anatomy of CNS Flashcards
what are the cells of nervous tissue
- neurons (nerve cells)
- neuroglia (astrocytes, oligodendrocytes, microglia)
- ependymal
what are neurons
comminication network
excitable
receptive to stimuli
conduct impulses
what are neuroglia
supportive cells
regulate environment
help neurons function
immune function
what are ependymal cells
specialized epithelial cells
involved in CSF production
what are the parts of the neuron
- cell body
- dendrite
- axon
- axon terminal
what are the features of the neuron cell body
supply centre of neurons
contain nucleus and cytoplasmic organelles
nissi body has concentration of ribosomes for protein synthesis
what are the features of dendrites
processes that ramify from the other cell body
provide large surface area for contact with other neurons
wgat are axons
a prominent dendrite extends from the cell body
what are the axon terminals
point of synapse
contact with other neurons
communicate by chemicals
what are the morphological variations of neurons
- multipolar
- bipolar
- unipolar
- pseudounipolar
what are mutlipolar neurons
several dendrites
most dominate type
throughout the brain and spinal cord
single axon
what are bipolar neurons
one main dendrite receiving stimuli
one axon delivering impulse to target site
olfactory, inner ear and retinal
what are unipolar neurons
sensory neurons
short extension from cell body
one dendrite and one axon
fused together
what are pseudounipolar neurons
begin as bipolar and fuse with development to give the unipolar neuron
what are the functional classification of neurons
- sensory or afferent neurons
- motor or efferent
- interneurons
what are sensory or afferent neurons
receive sensory input directly (dendrites) or from adjacent cells
conveys sensory stimuli as impulse (action potential) to the CNS via cranial or spinal nerves
mostly unipolar
what are motor or efferent neurons
convey impulse from CNS to target (muscle, glands) via cranial or spinal nerves
mostly multipolar
what are interneurons
located with CNS
connection between sensory and motor
mostly multipolar
what are olfactory cells
detect odour on chemical receptors on bipolar neurons
chemoreceptors are located on cilia that project from dendrites
cilia covered by mucs from supporting cells and olfactory glands
required to solubilize the odour for receptor association
what are the types of sensory neurons
- meissners corpuscles: touch receptor, mass of dendrite ending
- merkel: touch, free nerve endings
- pacinian: pressure, laminated capsules
- nociceptor: pain, free nerve endings
what are the most abundant neuron in the CNS
multipolar neurons
what are the types of multipolar neurons
- dendritic tree
- purkinje neuron
- pyramidal neuron
what are dendritic tree neurons
pattern can vary
greatly enhances number of synapses
dendritic spine can alter and gives a level of plasticity
what are the features of purkinje neurons
found in cerebellum
controls gait
what are the features of pyramidal neuron
found in cortex
thought processing
what is a depolarizing graded potential
makes the membrane less polarized
inside is less negative
reduced potential difference between the inside and outside of the membrane
what is hyperpolarized graded potential
makes the membrane potential more polarized
inside is more negative
greater potential difference between inside and outside
what are the effects of myelin
- insulates segments of the axons (internodes) –> nodes of ranvier is gap between internodes, has high concentration of ion channels
- action potential jumps (saltatory conduction)
- greatly enhances speed of conductance
- reduced the need for large diameter axons
what are the variable arrangements of neuron connections
- simple series circuit
- divergent series
- convergent series
- reverberating
- parallel after discharge
what are simple series circuit
single presynaptic (before synapse) stimulates a single postsynaptic (after synapse)
ex. reflex arc
what are divergent series
single presynaptic stimulates several post synaptic
ex. nerve impulse from a single neuron can influence many spinal neurons for complex movement
what are convergent series
several neurons stimulate single neuron
ex. a neuron that connects to a specific neuromuscular junction recieves input from many cells in the brain
what are reverberating circuit
feedbacks to stimulate neurons at early points in cascade
thought to be involved in memory formation
what are parallel after discharge circuits
different number of neurons in a cascade that converge on a common neuron
ex. complex cognitive processing such as math
what does the gray matter in the brain contain
neuronal cell bodies
dendrites
astrocytes
neurons arranged in specific layers and form complex networks
what does the white matter contain
myelinated axons
oligodendrocytes
microglia
what is the spinal cord composed of
gray and white matter
how is the organization of the spinal cord different from the brain
white matter on outside with gray matter forming a horn
what does gray matter in the spinal cord contain
cell bodies and dendrites
sensory neuron input (cell body in ganglion) in dorsal nerve root
interneuron mediator
motor output from ventral nerve root
connects to ascending (sensory) and descending (motor) white matter tracks
how is white matter organized in the spinal cord
tracks of myelinated axons
arranged into specific bundles called tracts
how is the PNS organized
arranged in bundles of nerve fibres
nerves enclosed in 3 layers
what are the 3 layers that enclose nerves in the PNS
- epineurium
- perineurium
- endonurium
schawnn cells myelinate axons in the PNS
what is the epineurium
thick, tough connective tissue
what is the perineurium
tough CT surrounding bundle
what is the endonurium
loose delicate CT
surrounds each axon
how many schawnn cells per axon
1 cell per axon
what are the labels
what are the cells that support the cells of the CNS
- astrocytes
- oligodendrocytes
- microglia
what are astrocytes and their function
star shaped
protoplasmic (gray) and fibrous (white)
involved in blood brain matter and remove neurotransmitters from synaptic cleft
what are oligodendrocytes and their function
found mainly in white matter
smaller than astrocytes
produce myelin around axons
what are microglia
ovoid shape
change morphology on activation
resident immune cells, remove debris + bacteria (lipid laden macrophages gitter cells)
what are the structures
what are the important roles astrocytes play
associates with blood vessel to form barrier –> association with pericytes to regulate gene expression
reactive in many neurodegenerative disorders and extend processes
produce trophic substances and can upatake glutamate and potassium
can form scar tissue to block formation of neuronal tracks (spinal cord injury)
what is the blood brain barrier and the blood CSF barrier
CNS needs a consistent environment
cannot be subjected to gross fluctuations of ionic chemical and hormonal levels
energy source needs replenished and waste needs to be removed
what is the function of the choroid plexus
produces CSF
lateral, third and 4th ventricle
CSF enters subarachnoid space –> between pia and arachnoid meninges
then enters spinal canal –> circulates around the CNS
what are ependymal cells of the choroid plexus
cuboidal or columnar epithelial cells
line the vesicles of the brain and spinal cord
ciliated to regulate CSF movement and turnover
what is the funciton of ependymal cells of the choroid plexus
ependymal tight junction
act to filter blood
CSF is clear solution
how is CSF absorbed
in arachnoidal villus into venous sinus
what are arachnoid villi
project into the sinus through the dura matter (grouped arachnoid villi termed arachnoid granulations)
what are arachnoid villi covered in
thin layer of epithelium from sinus
what occurs when pressure in subarachnoid space is higher than sinus
CSF moves into sinus
higher pressure closes the tubules of the arachnoid villa
what can abnormality of arachnoid villi lead to
abnormality in regulation can lead to hydrocephalus
how does communication via neurotransmitters (NT) occur
synaptic cleft –> gap between presynaptic and postsynaptic membranes
APs can’t jump the cleft –> NT cause either excitatory or inhibitory gradient on postsynaptic sites
what are excitatory NTs
depolarizes post synaptic membranes so resting potential nearer the threshold for AP
excitatory postsynaptic potential (EPSP)
ex. glutamate, aspartate
stimulate influx of +ve ions or efflux of -ve ions
what are inhibitory NTs
hyperpolarization of post synaptic membrane so resting potential further from threshold
inhibitory postsynaptic potential (IPSP)
GABA, glycine
stimulates influx of -ve ions or efflux of +ve ions
what are the events at the synapse (7)
- nerve impulse travels along axon to the presynaptic terminal
- impulse causes depolarization that activates and opens calcium channels
- calcium activates a series of protein events on synaptic vesicles (proteolytic and phosphorylation events)
- synaptic vesicles fuse with membrane and release the NTs into synaptic cleft
- Nts bind to receptors on postsynaptic membrane ion channels (dendrites)
- initates post synaptic depolarization
- clearance of NTs from the synaptic cleft occurs by various methods (diffusion, enzymatic breakdown, reabsorption)
what are ionotropic receptors
ligand binding site
ligand modulates opening
probablity and ion flux
GABA
what are metabotropic receptors
has a ligand binding site
couples to a G protein site
production of 2nd messenger modulates ion channels
alters opening probability
ex. acetylcholine
what are the classes of neurotransmitters
- amino acids
- monoamines
- soluble gases
- acetylcholine
(excitatory, inhibitory, both)
what are the features of glutamate
simple amino acid
excitatory transmitter in CNS
what is NMDA
a subtype of glutamate receptor
what is a feature of NMDA
has a pore containing a Mg2+ binding site –> binding block the channel and is removed following depolarization
what is GABA
g-aminobutyric acid
inhibitory NT
how is GABA generated
by conversion of glutamate by GAD
what are the two types of receptors
- GABA A: ionotropic, located post synaptically and permeable to Cl- ions
- GABA B: metabotropic, located pre and post synaptically and modulated calcium and potassium channels
what are biogenic amines
removal of carboxy groups of certain amino acids generate biogenic amines
most act via metabotropic receptors
what is a class of biogenic amines
catecholamines
norepinephrine, epinephrine, dopamine
what are the receptors of acetylcholine
ionotropic (nicotine) and metabotropic (muscarinic)
mainly excitatory
what are purines
ATP and adenosines
ATP acts on P2 ionotropic receptors and can be excitatory
adenosines: A1-3 receptors
what is nitric oxide
lipid soluble free radical
no receptor, passes membrane by diffusions
influences blood pressure
what are neuropeptides
G-protein coupled receptors
powerful analgesics
