Neurones And Neuroglia Flashcards
what is the functional unit of the nervous system
neurons
Briefly describe neurons
excitable and can carry electrical signals. they are organised in circuits or networks that encode information for all conscious and non-conscious information in the CNS
what supports and protects the neurons
glial cells
ratio of glia to neurons?
10:1
Briefly describe glial cells
support and protect neurons. They have sorter processes. provide nervous system stem cell pool
provide a barrier between compartments. participate in neuronal activity. participate in metabolic assistance
provide the immune response to iflammation and injury to the NS
describe dentrites
short processes arising from the cell body
may contain dentritic spines
site of synaptic contacts
describe the cell body
houses the nucleus
site of protein, hormone and neurotransmitter production
gives rise to a single axon
other names for the cell body
perikaryon, soma
describe the axon
long, cylindrical and slender process, axon hillock and initial segment
axolemma (plasma membrane), axoplasm (cytoplasm)
myelinated or unmyelinated
describe the synapse
presynaptic terminal
synaptic cleft
post synaptic terminal
brief overview of metabolism and synthesis in neurons
cell body is the site of energy generation and synthesis
axonal transport - vesicles (fast axonal transport to terminal, retrograde to cell body)
electrical depolarisation
what is the resting membrane potential of neurons
-70mV
resting membrane potential of smooth muscle cell
-40mV
what is the resting membrane potential of cardiac cell
-90mV
How is the difference between the electrical charge inside the cell and outside the cell maintained
At rest K is higher than Na in the cell
Na leaks in
K leaks out
Na/K ATPase pumps out 3 Na in exchange for 2K pumped in
what leads to a change in membrane potential?
change in ion permeability
describe graded potentials
incoming signals and vary in strength
they lose strength over distance
slower than APs
Excitatory (EPSPs)
Inhibitory (IPSPs)
describe action potentials
travel very rapidly over longer distances
what are the 2 types of electrical signals
graded potentials and action potentials
net movement of ions does what to the cells
depolarises or hyperpolarises the cell
3 examples of gated ion channels
mechanically gated channels, voltage-gated, chemically gated
what happens when graded potentials travel to the trigger zone
subthreshold - too weak; no generation of AP
suprathreshold - generate AP
excitatory signal at trigger zone
depolarises, reduces threshold
inhibitory signal at trigger zone
hyperpolarises, increases threshold
describe the steps of an action potential
resting membrane potential, depolarising stimulus, membrane depol to threshold, colt gated Na channels open and Na enters the cell. Vol gated K channels open slowly; Rapid Na entry depol cell; Na channels close and slower K channels open; K moves from cell to extra cellular fluid; K channels remain open and K leaves cell, hyperpolarising; K close; cell returns to resting potential
what are the 2 types of summation
temporal or spatial
describe temporal summation
intense stimulation by ONE presynaptic neuron
EPSPs spread from ONE synapse to trigger zone
Post synaptic neuron fires
Describe spatial summation
SImultaneous stimulation by several presynaptic neurons
EPSPs spread from several synapses to trigger zone
Postsynaptic neuron fires
List 4 neuron types
pseudounipolar neurons
bipolar neurons
multipolar neurons
anaxonic neurons
describe pseudounipolar neurons
found mainly in spinal ganglia
single process arises from the cell body and divides into 2 brances
one projects to the periphery and the other projects to the CNS. information collected from the terminals of the peripheral branch is transmitted to the CNS via the terminals of the other branch, bypasses the cell body
signals relayed from the receptor to the CNS without being modified
describe bipolar neurons
have 2 processes - which arise from an elongated cell body
one process ends in dendrites, the other an axon
integrate multiple inputs and then pass that modified, processed information onto the next neuron in the chain
where are bipolar neurons mainly found
in the retina and olfactory epithelium
what is the most common type of neuron in the CNS
Multipolar
describe multipolar neurons
possesses 3 or more dendrites which branch off directly from the cell body
have a single long axon issuing from the axon hillock
describe anaxonic neurons
has only dendrites and no apparent axon can be determined
what powers fast anterograde transport
Kinesin motors power anterograde transport (to synapse)
use ATP hydrolysis to walk toward plus-end. numerous kinesin-related proteins
what powers fast retrograde transport
cytoplasmic dynein
uses ATP hydrolysis to walk minus end 50-200mm/day
what exploits Cytoplasmic Dynein
viruses eg herpes simplex virus, rabies virus, polio
what do the head of motors walk along
microtubules
what determined cargo specificity
tail of motor protein
what do neuroglia cells maintain
appropriate environment and provide structural support for normal neuronal functions
what are the classification groups of neuroglia
astrocytes, oligodendrocytes, microglia, polydendrocytes, ependymal cells, satellite cells, schwann cells
what is the tripartite synapse
Glutamate activates class1 metabotropic receptors; calcium release from astrocytes; resulting in release of gliotransmitters, modulate neuronal function; play a role in the regulation of local microcirculation in the brain
describe astrocytes
largest glial cell, stellate appearance, centrally located nuclei; processes make contact with thousands of neurons, form end feet on blood vessels, shuttle excess ions, pick up glucose and metabolites from vasculature and carry them to neurons, major role in tripartite synapse
what are the types of astrocytes
Fibrous (white matter)
Protoplasmic (grey matter)
Muller cells (retina)
describe oligodendrocytes
myelinating cell within the CNS
smaller than astrocytes with fewer processes, can myelinate multiple axons
describe microglia
smallest of all glial cells
derived from monocyte-macrophage lineage, immune cells of the CNS, activated by inflammatory markers, phagocytotic
describe polydendrocytes
stem cell pool, recruited as oligodendrocyte precursors in remyelination, can provide link between neuronal signalling network and glial cells
describe ependymal cells
epithelial cells that separate CSF from tissue
describe satellite cells
similar to schwann
found in sensory, sympathetic, parasympathetic ganglia
describe schwann cells
myelinating cells of the PNS, one schwann cell per axon. at neuromuscular junction can take up excessive neurotransmitter
describe myelination in the PNS
axon comes into contact with the schwann cell which then rotates around the axon
as the schwann cell wraps around the axon, the cytoplasm becomes progressively reduced and the inner layers of the plasma membrane come into contact and fuse together
describe myelination in the CNS
oligodendrocytes myelinate axons in the CNS. broad flat processes wrap about CNS axons, but the cell bodies do not surround the axons,
no neurolemma is formwed
little regrowth after injury is possible due to the lack of a distinct tube or neurolemma
what is white matter
myelinated processes
what is grey matter
nervel cell bodiues, dendrites, axon terminals, bundles of unmyelinated axons and neuroglia
how does myelination in the CNS differ from the PNS
oligodendrocytes myelinate up to 50 axons each, not just 1
the myelin in oligodendrocytes has a different biochemical composition
describe multiple sclerosis
autoimmune disorder causing disruption of myelin sheaths in CNS
sheaths becomes scars or plaquies, appears between ages 30 and 40. 2x more in women
symptoms of MS
muscular weakness, abnormal sensations or double vision
remissions and relapses result in progressive, cumulative loss of function
What is Guillan-Barre Syndrome
disease of the PNS involving an acute inflammatory, autoimmune attack on myelinated peripheral nerve fibres
potentially fatal neurological emergency and can lead to paralysis or death
symptoms of Guillan-Barre Syndrome
weakness
loss of tendon reflexes
high spinal fluid protein without extra cells (albuminocytologic dissociation)
what is Charcot-Marie-Tooth Disease
an inherited disorder of the PNS involving myelination
signs and symptoms of CMT
pes cavus, distal wasting, weakness of intrinsic hand muscles, hypertrophy of the greater auricular nerve
