Nerves Flashcards
What is the structure of an axon?
Initial segment- unmyelinated membrane closest to cell body. May contain undulations in membrane (axon hillcote).
Myelin sheath
Nodes of Ranvier
Internodal membrane - membrane under schwann cells inbetween the nodes of ranvier.
Axonal terminal - the end of the axon
How many action potentials are generated?
2 - one goes down axon and one goes back to cell body to say a signal has been sent
What is the structure of the peripheral nerves?
An entire nerve is ensheathed by epinureum and contains fascicles and blood vessels. A nerve fascicle is ensheathed by perineureum and contains axons. Interfascicular bands attach adjacent fascicles. A single cell axon is surrounded by endoneureum.
What are nerve fascicles?
Collection of neurones with a common origin and destination.
what do all neurones have?
1 axon and 1 cell body
What does a cell body contain?
Nucleus containing a nucleolus and encased by a perinuclear membrane.
Nissl - substance for protein synthesis
Golgi - for packaging the neurotransmitters into vesicles
What do dendrites do?
Increase SA for interactions with other cells
What are neurones with multiple dendrites, one dendrite and no dendrites called?
Multi-polar, bi-polar (have an axon too), unipolar (still have an axon)
What is grey and white matter?
grey- collection of cell bodies
white- collection of axons
what is a ganglion?
collection of cell bodies (a swelling)
What are the membranes in the CNS?
continuous with coverings of brain and spinal cord. out to in: dura mater arachnoid mater pia mater
where are sensory neurones found?
in the PNS
when is an axon said to be myelinated?
when schwann cells have wrapped themselves around in several concentric layers of plasmalemma.
what do peripheral nerve fibres consist of?
axons surrounded by a sleeve of schwann cells - neurolemma
what are the gaps in the myelin sheath and what are their function?
Nodes of Ranvier, allow for saltatory conduction as have ion channels for depolarisation
why is the myelin a good electrical insulator?
The schwann cells wrap around the axon around 100 times to ensure it doesnt come off which forms the myelin sheath. The cytoplasm of the schwann cells is extruded as the schwann cells wrap around the axon which leaves predominantly membrane around the axon that can fuse. As membranes are made up of phospholipid bilayer this leaves a predominately lipid layer around the axon which is very good at conductive insulation.
what myelinates the axons in the CNS?
glial cells called oligodendrocytes produce and maintain the coating
Do the autonomic and somatic nervous systems contain myelinated or non myelinated neurones?
A- myelinated in CNS and unmyelinated in PNS
S- all myelinated
What does a myelin sheath allow for and why is it good?
saltatory conduction and is quicker as the whole membrane doesnt have to be depolarised.
where do synaptic connections occur?
between axon terminals and cell body/dendrite or another axon
What do excitatory neurones release?
glutamate/aspartate neurotransmitter
what do inhibitory neurones release?
glycine/GABA neurotransmitter
What are the CNS and PNS in relation to each other?
A continuum of the same cell, not independent from one another
what are the brain and spinal cord encased by?
cranium and vertebral column
what is the CNS suspended in?
spinal fluid
what happens in demyelination and what is an example of a disease caused by this?
The impulse has further to travel as salutatory propagation is inhibited so they whole membrane has to be depolarised and the response is slower.
Multiple Sclerosis
What happens in multiple sclerosis?
myelin sheath replaced by scar tissue which cannot conduct and so the axon is useless
what is the function of glial cells?
support neurones, help maintain homeostasis and form myelin
what are the 5 types of glial cells? MOSSA
microglia oligodendrocytes schwann cells satellite astrocytes
what are the functions of astrocytes and where are they found?
Blood brain barrier
assist in transfer of nutrients and waste
CNS
what are the functions of oligodendrocytes and where are they found?
myelination (one cell can myelinate up to 250 axons at a time)
CNS
what are the functions of microglia and where are they found?
immune and inflammatory functions (can remove if present)
BOTH CNS and PNS
what are the functions of schwann cells and where are they found?
myelination (1 peripheral axon per cell)
PNS
what are the functions of satellites and where are they found?
Physical support to peripheral neurones
PNS
Are the somatic and autonomous nervous systems voluntary or involuntary?
s- voluntary
a- involuntary
What types of neurones does the ANS comprise of?
one pre ganglion and one post ganglion
where are the cell bodies of the pre and post ganglion neurones? what does this allow for?
one in the CNS, one in the PNS
flexibility
where do the ANS neurones exert their actions?
via smooth muscle, viscera, secretory glands, cardiac muscle
What response is the sympathetic involved in and what is the outflow called? (where are the cell bodies?)
fight/flight
thoraco-lumbar outflow (T1-L2)
What response is the parasympathetic involved in and what is the outflow called? (where are the cell bodies?)
rest and digestion
cranio-sacral outflow (cranium and S2-S4)
what are the pre/post ganglion nerve fibre length in sympathetic nervous response?
pre = short post = long
where may the sympathetic nervous system synapse?
at same level as origin (paravetebral origin)
different level to origin
not in the paravertebral chain (ones that supply the gut)
what are the pre/post ganglion nerve fibre length in parasympathetic nervous response?
pre = long (may even go into target organ as ganglion can be inside) post = short (possibly inside target organ)
how do the sympathetic and parasympathetic work together?
effects usually reciprocal
what are the functions of the sympathetic nervous system?
fight/flight diversion of blood to muscles and heart (vasoconstriction at periphery) Increase HR and BP reduce blood flow to GIT and skin Hyperventilation (bronchi dilate) increased secretion from sweat gland decreased lacrimation male ejaculation
what are the functions of the parasympathetic nervous system?
rest and digest
reduce heart rate and force of contraction (vasodilation)
promotes digestion
promotes bladder emptying
increased lacrimation (nutrition in tears)
what can happen in overactivity of the sympathetic or parasympathetic nervous systems?
S- constriction of blood vessels for too long lead to tissues at the periphery dying due to lack of O2/nutrients
P- dilated blood vessels for too long decreases blood supply and nutrients to brain so you faint.
what are the features of the somatic nervous system?
1 neurone carries output and terminated directly on effector organ. eg skeletal muscle, activated to carry out one specific task and inactive the rest of the time. can be turned off by individual.
what happens when a somatic effect is ‘turned off’ by an individual?
still minimal movement called motor tone
why is the somatic nervous system underdeveloped at birth?
so it can be programmed by the environment the individual is born into.
what are the transmitters/receptors at the pre/post ganglion neurones in the sympathetic nervous system?
pre are cholinergenic (acetyl choline)
post express nicotine receptors
post are noradrenergic (noradrenaline)
what are the transmitters/receptors at the pre/post ganglion neurones in the parasympathetic nervous system?
pre are cholinergenic (acetyl choline)
post express nicotine receptors
post are cholinergenic
How does a neurone react to being severed?
proximal segment of axon seals up to prevent leakage of cell contents therefore a nerve stump is formed.
the distal segment is cut off from nutritional support and soon dies, undergoes wallerian degeneration.
cell body puffs up with increased content and the nucleus is displaced from central position to peripheral margins (chromatolysis).
Axon usually regrows (wallerian regeneration)
what is chromatolysis?
when the nucleus of the cell body is displaced to the periphery margins.
what do afferent neurones do?
conduct/carry incoming signals from periphery to CNS (sensory neurones)
what do efferent neurones do?
conduct/carry outgoing signals from CNS to periphery (motoneurone/autonomic neurone)
what is a pre-ganglion neurone and what do they do?
neurone immediately proximal to ganglion.
bring signals to the ganglion
what is a post-ganglion neurone and what do they do?
neurone immediately distal to ganglion
carry signals away from the ganglion
what is an effector?
target organ to which the nervous system exerts its actions.
What types are nerve cells split into?
Glia (90%) and neurones (10%)
