Skeletal muscle as a target for NS control Flashcards
Name some features of the Neuromuscular junction
-synaptic vesicles
-Axon terminals
-synaptic cleft
-junctional folds of the sarcolemma
-sarcoplasm of muscle fibre
-nicotinic acetylcholine receptor (nAChR’s)
What happens at the post synaptic membrane?
- depolarisation leads to graded local potential generated by opening nAChRs
-Opens Na+ channels
-Opens K+ channeles
-generates an AP
Define sarcolemma
-plasma membrane of the muscle cell
-basement membrane and endomysial connective tissue
Define Sarcoplasmic reticulum
network of tubules and sacs that are important in muscle contraction and relaxation by releasing and storing Ca2+ ions
What do voltage-sensitive tubule proteins do?
make physical contact with particular types of calcium release channels (l type) when activated changes the membrane potential which physically open channels by releasing calcium
What are the triads of the sarcoplasmic reticulum made of?
-T tubule
-terminal cisternae
What are Z disks made of?
-cytoskeleton
-actin is anchored to those Z disks which interact with myosin
Name 3 proteins in the sarcomere
-actin (thin)
-titin (largest protein in the human body)
-myosin (thick)
What is the function of titin in the sarcomere?
-helps to recoil the sarcomeres
-stabilisation of the sarcomere structure
Name the other two proteins associated with actin
-troponin
-tropomyosin
What is the difference between troponin and tropomyosin?
-troponin promotes muscle contraction
-tropomyosin blocks muscle contraction
in the prescence of calcium troponin senses and tropomyosin moves exposing binding sites
Main steps of E-C coupling
- AP travels across sarcolemma
- AP travels down T-tubes
- SR releases calcium via ryanodine sensitive channels
- Calcium ions bind to troponin
- Tropomyosin exposes active myosin binding sites on actin
- Myosin binds to actin
- ATP binds to myosin –providing energy
What are the motor units made of?
unit 1- small fibres
unit 2- medium fibres
unit 3-large fibres
-strength of muscle contraction depends on the proportion of motor units excited
Describe frequency coding
as the intensity of a stimulus increases, the frequency of action potentials increases
If muscles cant rest between AP- go into temporal summation
How do you improve the smoothness of motor actions?
1- frequency coding
2- recruit motor units with larger and larger cells
3- recruit more and more motor units
What happens during rigor mortis?
- ATP synthesis stops
- SR calcium pumps stop
- So actin /troponin complex activated
- No ATP available for cross bridge detachment
- Muscle stiffen – 3 -12 hrs to develop
- Only enzymatic breakdown of proteins can reverse this
what is sarcopenia?
muscle loss/ muscle ageing
What are some contributing factors to sarcopenia?
1-myosin production
2-mitochondrial malfunction
3-motor axon atrophy
4-atrophy of muscle fibres
What are the 2 types of spinal reflex?
-ipsilateral
-contralateral
What are the 5 components of the reflex arc?
-receptor
-sensory neuron
-integration center
-motor neuron
-effector
What is the withdrawal flexor reflex? (avoiding standing on a pin)
-doesn’t require concious input
-however the brain is involved at a later stage as there is afferent sensory input to the brain and efferent motor output
Describe the crossed extension reflex (lifting the leg)
-excited efferents to flexor muscle
-inhibited efferents to extensor muscles
-commisural interneuron carries info from one side of the brain/spine to the other by inhibiting efferents to flexor muscles and exciting efferents to extensor muscles
What is the myotatic reflex?
-contraction of a muscle in response to a change in the stretching of a muscle
(tap stimulus to knee joint)
Describe the muscle spindles
-Aka knee jerk reflex
-stretch sensitive nerve endings activated when intrafusal stretches
-group 1a and 2 fibres
-send afferent info about muscle length
-gamma motor neurons innervate intrafusal linked to alpha motor neuron activity
-gamma loop reflex distinct from myostatic
Whats the difference between 1a and 2 muscle spindle groups?
1a-primary afferent
2-secondary afferent
Describe the tedon reflex
-inverse myostatic reflex
1-tendon organ encodes tension activates interneurons
2-inhibition of extensor, activation of the flexor
what is the golgi tendon organ?
sensory receptor located near a muscle junction
decribe the integration at the interneuron in the spine
From upper motor neuron in cortex
via intergration of these factors in the interneuron of the spine
-spindle afferent
-pain afferent
-golgi afferent
goes to lower motor neuron in spines
input-output
