Neuromuscular commuication Flashcards
What type of tissues are nerve and muscle tissue?
Excitable tissue
What does it mean by ‘excitable’ tissue?
They can undergo rapid changes in their membrane potentials due to a stimulation
What do excitable tissues change their resting potentials into and what does this aid with?
Into electrical signals that aid in cellular communication
What are the above signalling events mediated by?
By ion channels
What does the PNS do?
Carries information in and out of the CNS
What muscle does the somatic system carry information to?
Skeletal muscle
Is the autonomic system voluntary or involuntary?
Involuntary
Where do ventral roots come from?
Spinal cord
Where does the information come from in the ventral roots?
From motor neurons
What type of nerves are present in the PNS?
Mixed spinal nerves
What are mixed spinal nerves?
Nerves that send motor, sensory and autonomic signals
When do muscle fibres have to contract and why?
At the same time to reach the maximum contraction of muscle
Can a motor neuron contract multiple muscle fibres at the same?
Yes
What decides the size of the motor neuron?
The amount of muscles a motor neuron connects
How do ventral roots form?
Axons of lower motor neurons bundle together to form ventral roots
How is the spinal nerve formed?
By the joining of the ventral root and dorsal root
Why are central horns swollen in certain areas of the spinal cord?
To accommodate large numbers of motor neurons – segments C3-T1 (arms) and L1-S3 (legs)
What is muscle enclosed in?
In connective tissue sheath
What forms at the end of muscle?
Tendons
What is each muscle fibre innervated by?
A single axon branch from the CNS
What is each muscle fibre made up of?
Myofibrils
What is the sarcolemma?
The cell membrane that encloses each muscle cell
What is the endomysium?
Connective tissue that wraps each individual muscle fibre.
What is the perimysium
Connective tissue that wraps bundles of muscle fibres - the “bundles” being known as fasicles.
What is the epimysium
The connective tissue that wraps the whole muscle.
What is fascia (or deep fascia)?
A layer of thickened connective tissue that covers the entire muscle and is located over the layer of epimysium.
What does skeletal muscle require to contract?
Stimulation by the nervous system
Where do skeletal muscle communicate?
At the neuromuscular junction (NMJ)
What happens at the neuromuscular junction?
- Impulse (action potential) travels down nerve
- Reaches NMJ and causes chemical transmitter (acetylcholine) to be released which triggers muscle contraction
What is the motor unit?
The motor neuron and all the muscle fibres it innervations
What is skeletal muscle supplied by?
The efferent arm of the somatic nervous system (S.N.S.)
What is the process of the synaptic transmission?
Complex signaling from higher centres leads to synaptic transmission to lower motor neuron cell bodies that arise in the ventral horn of the spinal cord.
How many fibres are there from the cell body to the muscle?
One
What types of activity is motor neuron activity?
- Cholinergic
- Nicotinic
- Excitatory
What is the pathway of the central control of motor activity?
Motor → Basal ganglia → Cerebellum → Brain stem
What is the space between the terminal button and the motor end plate called?
The cleft
Where do terminal boutons fit into?
Shallow depressions of the sarcolemma of individual muscle fibres.
What is the term for postsynaptic part of NMJ?
The motor end plate
Where and how is excitatory signal sent?
From the terminal button to the motor end plate using acetylcholine via the nicotinic receptor.
What is a specialised site on a muscle cell, where an αlpha-motorneuron forms a synapse called?
Neuromuscular junction
What are alpha motor neurons?
Lower motor neurons that control muscle contraction involved in voluntary movement.
How many neuromuscular junctions are there per muscle cell?
1
What are the main players to induce contraction of muscle fiber?
Sodium, potassium, chlorine, calcium
Give a summary of events
- An action potential in a motor neuron is propagated to the axon terminal.
- This local action potential trigger the opening of voltage-gated Ca2+ channels and the subsequent entry of Ca2+ into the terminal button.
- Ca2+ triggers the release of acetylcholine (ACh) by exocytosis from a portion of the vesicles.
- ACh diffuses across the space seperating the nerve and muscle cells and binds with receptor-channels specific for it on the motor end plate of the muscle cell membrane.
- This binding brings about the opening of these non-seletive cation channels, leading to a relatively large movement of Na2+ into the muscle cell compared to a smaller movement of K+ outward.
- The result is an end-plate potential. Local current flow occurs between the depolarized end plate and the adjacent membrane.
- This local current flow opens voltage-gated Na+ channels in the adjacent membrane.
- The resultant Na+ entry reduces the potential to threshold, initiation an action potential, which is propagated throughout the muscle fiber.
- ACh is subsequently destroyed by acetylcholinesterase, an enzyme located on the motor end-plate membrane, terminating the muscle cell’s response
What is muscle fibre made up of?
Myofibrils
What are myofibrils
Cylinders with regular pattern
What is the appearance of muscle fibres and why?
Striated appearance due to presence of sarcomeres
What are muscle fibres composed of (repeating)?
Repeating arrays of filament
What is thick filament composed of?
Myosin
What is thin filament composed of?
Actin
What does increasing extent of overlap between thick and thin filaments cause?
The shortening of sacromere
What is the sacromere regulated by? check
Regulated by cytosolic Ca2+
Give two examples of immune driven neuromuscular disease arising from divergent aetiologies.
- Myasthenia
- Myasthenia gravis
