Muscles Flashcards
Explain what happens when a muscle contracts
A motor neurone is stimulated by the brain and spinal cord and action potential (a process where the nerve cell is a negative charge and for the impulse to move don the cell it needs to be turned into a positive charge) arrives at the neuromuscular junction. Action potential passes down to the neuromuscular junction. The neuromuscular junction is a chemical synapse where the motor neuron transmits signals to muscle fibre to initiate a contraction. Acetylcholine (ACh) is released and binds to receptors which open sodium channels which lead to an action potential in the sarcomere.
The excitation causes the release of calcium from the sarcoplasmic reticulum into the muscle which is needed for binding. Calcium attaches to the troponin sites which is important as it opens up the attachment sites for the myosin to attach to the actin. The calcium floods into the sarcomere attaching to the troponin sites and allowing the actin and myosin to bind. The actin and myosin cross-bridges to bind and contract using the ATP store.
The muscle then contracts via the sliding filament theory.
What is the sliding filament theory - Explain
- The sliding filament theory describes the mechanism that allows the muscle to contract.
- When signalled by a motor neuron in the skeletal muscle, fibres contract. The sliding happens when calcium is released and attached to the troponin which allows the myosin to bind to the actin which pulls the actin filament causing it to slide across the thick myosin filament.
- The overall process shortens the sarcomere structure but does not change the actual length.
What can stop a muscle contraction? (4 things)
- Energy system fatigue – no more ATP left in the muscle cell to use
- Nervous system fatigue
- Voluntary nervous system control
- Sensory nervous system information
What is energy system fatigue in muscles?
no more ATP left in the muscle cell to use – (energy source has gone) meaning muscle cannot contract.
What is Nervous system fatigue (muscles)?
The nervous system isn’t able to create impulses sufficiently or quickly enough to maintain the stimulus and cause calcium to release.
What is Voluntary nervous system control (muscles)?
The nerve that tells the muscle to contract stops sending that signal because the brain tells it to, so no more calcium ions will enter the muscle cell and the contraction stops. (pick up something from the floor, but you decide not to pick it up, it will tell the brain not to contract the muscle to pick it up)
Sensory nervous system information:
e.g a sensory neuron (nerves that detect stimuli like pain or how heavy something is) provides feedback to the brain indicating that a muscle is injured while you are trying to lift a heavy weight and consequently the impulse to that muscle telling it to contract is stopped.
What are the sensory nerves that supply the muscles? (3 types)
Muscle spindles
Golgi tendon organs
Free nerve endings
What is the role of muscle spindles?
- Help to bring about the proprioceptors sense ( your body’s ability to sense movement, action, and location. It’s present in every muscle movement you have).
- Act as a stretch receptor controlling the length of a muscle. If it gets too long, it brings on a contraction to shorten muscle back again. E.g. a reflex hammer – a contraction occurs if you hit the quadriceps tendon and the contraction occurs in the quads – it causes the tendon to pull on the muscle and for the muscle to lengthen. In response to the body from stretching it too far, you get a contraction of the quad and which creates an extension movement.
- Contraction – reflex hammer
What is the role of Golgi tendon organs
- Proprioceptors (brings back)
- Sensitive to change in the muscle tension; as the muscle contracts the nerve fibres are compressed triggering a stimulus.
- Monitors extent of a muscle contraction and the force exerted (if force s too much – to stops or reduces the muscle contraction)
Inhibition of muscle
What is the difference between muscle spindles and Golgi tendon organs?
- Spindles control the length
2. Golgi tendon organs control tension
What is the role of Free nerve endings
Scattered throughout the muscle belly and more densely in the myotendinous junction
Help to mediate pain.
Include:
Mechanoreceptors (respond to pressure, active contraction, muscle lengthening
Contraction sensitive
Nociceptors – pain mediators
Differentiate the differences between muscle contractions;
Muscle tone
Isotonic
Isometric
- Muscle tone - Constant tension by muscles for long periods of time / acting against gravity.
- Isotonic (change in the muscle length but tension is constant - dynamic)
- Isometric - Tension occurs but no change in length (e.g. holding the dumbbell)
External force = internal force
Postural muscles of the body
No external movement (static)
What are the 2 types of isotonic contractions?
Concentric - muscle shortens (e.g. flexion using dumbbell)
Eccentric - muscle extends/lengthens
What affects the strength of contraction (3 points)
Recruitment
Type
Age
