nerve and muscle Flashcards
what does the CNS consist of?
the brain (forebrain, midbrain and hindbrain) spinal cord (31 segments)
what are the subunits of the PNS?
autnomic nervous system
somatic nervous system
what does the ANS do?
involunatry nervous system split into symapthetic and parasympathetic nervous system
what does the somatic nervous system do?
voluntaery nervous system,
has somatic, efferent motor neurones
innervates and contols voluntary, striated msucles and has sensory afferent neurones
what does the sympathetic nervous system do?
fight or flight response
what does the parasympathetic nervous system do>
rest and digest response
what are glial cells?
support cells of neurones
what do gial cells do?
regulate neurone metabolism and function
repari and recover them from njury
regulate blood - brain barriers
destroy pathogens and remove dead neurones
give examples of glial cells in the PNS?
satellite cells and schwann cells
give examples of glial cells in the CNS
epideymal cells
oligodendrocytes
ostrocytes
microglia
describe the myelination of axons
olgiodendrocytes in the CNS
schwann cells in the PNS
wrap around the axon in spiral of concentric layers of fatty myelinated membrane
insulation for axons to aid impulse transmission
the gaps between the adjacent cells are called the nodes of ranvier
how are nerve fibres classified?
based on their diameter and conduction velocity
one classifcation system refers to motor fibres and non-msucle sensory neurones, A, B, C
another refers to sensory fibres from muscles - I,II,III,IV
describe the pathway of sensory info from the PNS to the CNS
through somatic sensory neurones to dorsal root
to interneurons
describe the pathway of sensory info from the CNS to PNS
from CNS to ventral root to somatic motor neurone
what are some differences between somatic and autonomic pathways?
somatic has sensory and motor pathways, autonomic only has motor pathways
somatic controls msucles and movement, autonomic controls internal organs and glands
somatic has no subdiivisons where as autonomic is split into symapthetic and parasympathetic
how are sensory receptors classified?
classified based on location and stimulus
where are muscle spindles found, what stimulates them?
found in skeletal muscle.
stimulated by stretch
where are pancian corpuscles found and what stimulates them?
deep in dermis, tendons, joints and genetalia
vinbrations, deep pressure
where are meissners orkrauses bulbs found and what stimulates them?
oral muscus, lips, genetalia, fingertips
touch, light vibration
what are refuni organs foudn and what stimulates them?
deep in dermis, ligaments, joint capsule
stretch and deep pressure
state the order in the spinal reflex pathway
sensory receptor sensory neurone integration centre motor neurone effect
how is action potential generated?
Na+ channels open and Na+ enters the cell. this causes the membrane potential to rise towards zero
if the threshold potential is reached, voltage gated Na+ channels open and more Na+ flows into cell action potential spike
Na+ channels close when Na+ equilibrium potential is reahced. voltage gated K+ channels open and K+ flows out of the cell = membrane potential reverses
K+ ions continue to flow out of cell while Na+ channels close and hyperpolrisation results
how is impulse conducted along a myelinated neurone?
nodes of ranvier are the only area where current can pass through the membrane, so the only area where the membrane can depolarise
the impulse travels in jumps not in slow flow
describe the spinal reflex pathway from muscles
stretching of the muscle stretches muscle spindle = increased discharge of the sensory enrves
this results in increased firing of motorneurone and the muscle contracts
what are the 2 types of synapses?
electrical and chemical
how does an electrical synapse work?
direct passage of current via ions through gap junctions
formed by interlocking connexon channels of adjacent neurones
how do chemical synapses work?
release of vesicles contraining chemical transmitter which has an effect on receptors on a target cell
describe chemical transmission across a synapse
action potential arrives at the synaptic terminal causing depolarisation
voltage gated Ca2+ chennels are opened by depolarisation and Ca2+ ions rush into the terminal
rise in Ca2+ causes vesicles to move to active zone and undergo fusion with the membrane and release contents by exocytosis
transmitter bidns to post synaptic receptors and ion channels open - excitation (EPSP) or inhibition (IPSP) occurs
what are the 2 types of receptor in synapses?
ionotropic receptors
metabotropic receptors
what are ionotropic receptors
a cluster of similar subunits forming ion channels that depolarise or hyperpolarise the presynaptic cell (fast response)
what are metabotropic receptors?
7-transmembrane molecule coupled to intracellular proteins that transduce a signal to cell interior (slow responses)
how does postsynaptic excitation occur?
binding of released transmitter to a ligand gated ion channel receptor cyases opening of channel pore
bidning of glutamate or acetylcholine to receptors causes influx of Na+ = EPSP, depolarising cell towards threshold potential = AP
how does postsynaptic inhibition work?
binding of GABA or glycine to their receptors causes influx of Cl- ions giving rise to an inhibitory post synaptic potential (IPSP) in post synaptic cell.
yperpolarise cell and make reaching AP less likely
mechanism of skeletal muscle contraction
Ca released by sarcoplasmic reticulum in response to depolarisation
Ca binds to TnC region on troponin
troponin changes shape, moving tropomyosin, exposing binding site on actin filament
attachment - myosin head with ATP binds actin
power stroke - mysoin head bends, ulling along the actin filament, ADP and Pi are released
What is the crossbridge theory?
myosin head is attached to actin, forming a cross bridge
inorganic phosphate generated in previous contraction cycle is released intitiating the power stroke - the mysoin head pivots and pulls actin along and ADP is released
as new ATP binds to myosin head, the crossbridge weakenns and detaches
as ATP splits to ADP and Pi, the mysoin head is energised
what are 3 factors that affect the force of muscle contraction
number of action potentials per second
amount of overlap between thick and thin filaments
number of motor units recruited
give a genetic muscle disorder
muscular dystrophy
give 2 inflammation muscle disorder
myositis
polymyalgia rheumatica
give 3 neurological msucle disorders
multiple sclerosis
myasthenia gravis
parkinsons disease
what does the motor unit consist of?
motor nerve and all muscle fibres innervated by that nerve
describe the release and reception of ACh at the NMJ
- AP arrives and depolarises terminal bouton
- opening of voltage gated Ca2+ channels
- influx of Ca2+ in synaptic bouton
- fusion of vesicles and release by exocytosis
- binding of ACh to nicotinic receptors on muscle cell membrane
- receptor activation = Na+ enters#
- membrane depolarisation
how are nicotinic receptors activated?
when 2 ACh molecules bind to it - one on each bidning site on the 2 alpha subunits
describe the breakdown of ACh
ACh is hydrolysed to choline and acetate by acetylcholinesterase - bound mainly to basal lamina
choline is taken up by nerve terminal by cotransport with Na+
vesicles become part of membrane - endocytosis, clathri coated and internalised, fuses with endosome - new vesicles formed by budding new cycle
acitic acid excreted as waste and broken down into water and carbon dioxide
state 3 types of drugs used on NMJ?
non-depolarising competitive nAChR antagonist
choline esterase inhibitors
depolarising nAChR agonist
give an example of a nondepolarising competitive nAChR antagonist drug?
tubocurarine
give 2 examples of choline esterase inhibitor drug
neostigimine and endophosim
how does tubocurarine work?
competes with ACh for nictotinic receptor sites
reversed by AChE inhibitors and hydrolysed by circulating esterases
what is neostigimine used for ?
treatment of myothenia gravis
what is endophosism used for?
diagnosis of myithenia gravis
how does succinylcholine work?
persistant depolarisation of neuromuscular junction
what is lambert eaton syndrome?`
rare autoimmune response which inhibits Ca2+ channels and thereby reducing ACh release
describe the structure of cardiac muscle
striated branched interconnected cells are smaller than skeletal cells rich in glycogen, myoglobin and mitochondria
describe the ultrastructure of cardiac muscle
each cell contains 1-2 centrally located nuclei
mitchondria comprise 30% of cell volume
intercalated discs are specialised cell-cell contacts with desmosomes acting as mechanical coupling and gap junctions allowing the spread of action potential
describe ventral action potential
depolarisation - greatly increased membrane permeability to Na
partial repolarisation - loss of Na and K conductance
plateau - slow inward flow of Ca2+ and some movement of Na
repolarisation - fall in Ca conductance and rise in K conductance - becomes negative again and NA/K pump re-establishes distribution
interva between AP when ventricular muscles are at their stable resting membrane potential
describe cardiac excitation
Action potential invades T tubules
voltage gated L-type Ca2+ channels opne in T tubule membrane
Ca2+ enters through L-type Ca channels and triggers further Ca release from sarcoplasmic reticulum
Ca binds to troponin-C and contraction proceeds in same way as muscles
what 2 hormones control autonomic regulation of heart rate
acetylcholine and noradrenaline
how does acetycholine control autonomic regulation of heart rate
via parasympathetic nerves
- stimulates vagus nerve
- decreases SA node rate
- decreases heart rate
how does noradrenaline control autonomic regulation of heart rate?
via sympathetic nerves
- increases rate of depolarisation of pacemaker cells of SA node
- develop AP at an increased rate
- increases heart rate
describe the structure of smooth muscle
2 sheets of closely opposed fibres smaller fibres than skeletal muscles spindle sahped with single central nucleus no sarcomere or t tubules more actin than myosin caveosae actin attached to dense bodies
describe the contraction of smooth muscle
- Ca binds to calmodulin (not troponin) and interacts with myosin kinase to phosphorylate myosin
- phosphorylation gives tension
- when Ca falls then Ca-calmodulin complex dissociates = inactivates myosin kinase
- cross bridgs are dephosphorylated by myosin phophatase
