peripheral nervous system and neuromuscular junction

Question 1

define neuromuscular junction

Answer 1

a specialised synapse between a motor neuron and a muscle fiber

Question 2

synapse structure and arrangements

Answer 2

basic structure is similar throughout the nervous system, arrangements can be simple or complex

Question 3

synapse contact ratio

Answer 3

ranges from 1:1 for muscle to 1000:1 in CNS

Question 4

standardised synapse diagram

Answer 4

diagram from slide 3

Question 5

neuromuscular junction diagram

Answer 5

diagram from slide 4

Question 6

why is the muscle membrane highly folded with junctional folds

Answer 6

increases SA so more neurotransmitter receptors and enzymes which break down neurotransmitter

Question 7

why is structure of neuromuscular junction specialised

Answer 7

incorporates distal axon terminal and muscle membrane allowing for the unidirectional chemical conmunication between peripheral nerve and muscle

Question 8

what are the 3 main structures of the neuromuscular junction

Answer 8

presynaptic nerve terminal, synaptic cleft and postsynaptic endplate region on muscle fibre

Question 9

what is the neurotransmitter for voluntary striated muscle

Answer 9

acetylcholine

Question 10

organisation of motor neurones

Answer 10

upper (within brain) and lower (brain stem if going to face and spinal cord for rest of body)

Question 11

how is 1:1 motor neurone:muscle fibre ratio achieved

Answer 11

although mixture of muscle fibres innovated by many motor neurones, each muscle fibre only receives innovation from one branch of a single motor neurone through selective inhibition

Question 12

clinical significance of 1:1 motor neurone:muscle fibre ratio

Answer 12

important in injury as regrowth of nerves to muscles permits innovation of muscle fibres from more than one neurone; produces different signal to an uninjured motor neurone, so shows nerve injury

Question 13

physiology of neuromuscular junction (7 steps)

Answer 13

action potential opens voltage-gated Ca2+ channels → Ca2+ enters → exocytosis of vesicles through SNARE protein binding → acetylcholine diffuses into cleft → binds to receptor cation channel and opens it → local current flow and action potential triggered and spreads along sarcolemma down T-tubules → acetylcholine broken down

Question 14

what causes miniature end-plate potentials

Answer 14

caused at rest when individual vesicles release acetylcholine at a very low rate

Question 15

what is present in sarcoplasm

Answer 15

myoglobin and mitochondria

Question 16

muscle structure

Answer 16

sarcomere → myofibril → myofibre → muscle fibre

Question 17

types of isotonic contraction

Answer 17

concentric and eccentric

Question 18

concentric

Answer 18

generate force and muscle gets shorter

Question 19

eccentric

Answer 19

generate force and muscle gets longer

Question 20

disorders of neuromuscular junction

Answer 20

botulism, myasthenia gravis (MG), Lamert-Eaton myastenic syndrome (LEMS)

Question 21

botulism

Answer 21

botulinum toxin produces irreversible disruption in acetylcholine exocytosis, causing paralysis

Question 22

myasthenia gravis: pathophysiology

Answer 22

autoimmune disease where antibodies directed against acetylcholine receptor

Question 23

myasthenia gravis: clincial consequences

Answer 23

fatigable weakness, effects ocular, bulbar, respiratory or limb muscles

Question 24

myasthenia gravis: treatment

Answer 24

antibodies in blood removed via plasma exchange

Question 25

Lamert-Eaton myastenic syndrome (LEMS): pathophysiology

Answer 25

autoimmune disease caused by antibodies directed against voltage-gated Ca2+ channels

Question 26

what is Lamert-Eaton myastenic syndrome (LEMS): what is it associated with

Answer 26

lung cancer