Lecture 12 Flashcards
What type of neuron acts on skeletal muscle cells? How does it do so? What signal change occurs? Where does the neuron come from?
A motor neuron sends an action potential down its action potential to the muscle fiber and reaches the neuromuscular junction, there it releases neurotransmitter due to the influx of Ca2+ ions into the synaptic knob. This causes depolarisation of the muscle fibre which triggers contraction by release of Ca2+ ions from the sarcoplasmic reticulum. The signal changes from electrical to chemical to electrical at the neuromuscular junction. The motor neuron comes from the spinal cord, the signal comes from the brain.
What material insulates the axon of a neuron?
Myelin sheath(a fatty white substance).
Why is Ca2+ important for contraction?
In its standard state the myosin heads can’t bind with the myosin binding sites on the actin due to tropomyosin covering them, this tropomyosin is held in place by troponin. Ca2+ binds with this troponin, causing the tropomyosin to change shape and reveal the binding sites, allowing the myosin heads to bind to the binding sites and pull the actin Z lines closer together (contraction).
What is the sliding filament theory?
The sliding filament theory refers to the pulling of the Z lines of actin closer by myosin heads and as such contracting the muscle.
What is a motor unit?
A motor unit is a motor neuron, axon, all branches and all the muscle fibres it innervates. The size of which can vary.
What levels of force can a motor unit produce?
All or none.
What does the force of contraction in a whole muscle depend on?
The length, number and arrangement of the muscle fibers and the size (amount of muscle fibres controlled), number (amount employed) and rate of action potential firing of the motor units.
Also depends on the muscle attachment site.
What parts make up the anatomical levers in our body?
Bones = the lever
Joint = the pivot or fulcrum
Muscle contraction = the pull
Load = external (e.g weight of held object) or internal (e.g weight of bone)
What does the muscle attachment site primarily determine?
The class of the lever which it acts as.
What are the three lever types in the body?
First: stabilises joint position (muscle acts on the opposite side of the joint to the object)
Second: effective at overcoming loads (muscle acts further from the joint on the same side as the object in the opposite direction).
Third: gives a large range of movement and speed at the cost of effectiveness (muscle is on the same side of but closer to the joint than the object and the force is in the oipposite direction).
What are the types of muscle action and what do they mean?
Concentric: muscle is active, develops tension and causes a change in joint position and the shortening of the muscle.
Isometric: muscle is active, develops tension but there is no change in either joint position or muscle length.
EccentricL muscle is active, develops tension, causes a change in joint position and lengthens muscle.
What are the types of muscle role and what do they mean?
Agonist: Acts concentrically when the task is succeeding and is the causer of the desired movement.
Antagonist: acts eccentrically when the task is succeeding and opposes the movement change.
Stabiliser: a muscle which acts to keep the joint still, this will always be isometric action
Neutraliser: a muscle which eliminates an unwanted movement possibly caused by another muscle.
