Function of Muscles Flashcards
What are the main functions of muscle?
Allow movement Stabilise joints Provide static support Storage of substances Movement of substances Gives form to the body Thermogenesis Communication
What does a fixator do?
These steady proximal parts of the limb through isometric contraction while movements are occurring in distal parts
What does a synergist do?
It completes the action of the prime mover. It can act directly on as a weal/less mechanical advantaged component of the same movement or indirectly by serving as a fixator to an intervening joint
What is reflextive contraction?
Automatic activity of the muscle e.g. Respiratory movements of the diaphragm
What is tonic contraction?
The constant slight contraction of the muscles (muscle tone) when a person is conscious
What are the two main types of phasic contraction?
Isotonic -muscle changes in length in relationship to the production of movement
Isometric - muscle length remains the same no movement occurs but muscle tension is increased above tonic levels
What are the two types of isotonic contraction?
Concentric - movement occurs as a result of muscle shortening
Eccentric - movement occurs as a result of muscle lengthening
What is the name of nerves which can generate action potentials in muscles?
Motor neurons / somatic efferent neurons
Where are the cell bodies of somatic efferent nerves located?
The brainstem and spinal chord
What chemical is contained in the vesicles of the end of motor neurons?
Acetylcholine
What is the name of the region of the sarcolemma which lies directly below the terminal portion of the axion?
The motor end plate
What is the name of the entire component comprised of axon terminal and motor end plate?
Neuromuscular junction
What events lead to the release of acetylcholine into the extracellular cleft?
The motor neuron reaches the end of the axon terminal, depolarises the pm to open voltage gated calcium ion channels. Calcium ions flood into the axon terminal and bind to proteins on the membranes of vesicles containing acetylcholine. These vesicles with the neuronal membrane to allow acetylcholine to be release into the extracellular cleft.
Following release of acetylcholine into the extracellular cleft what events leads to the contraction of the muscle?
ACh diffuse across the extracellular cleft and binds to nicotinic receptors on the muscle fibre. This opens an ion channel allowing the movement of sodium and potassium ions. Sodium moves in faster than potassium moves out resulting in a local depolarisation. This depolarisation triggers the response of the muscle by causing the release of calcium.
What enzyme breaks down ACh?
Acetylcholinesterase
Following the generation of a T-tubule action potential what happens to result in contraction?
Calcium ions are released from the terminal cisternae if the sarcoplasmic reticulum and bind to troponin. This alters the conformation of tropomin so that it no longer holds tropomyosin in a blocking position. Thus, myosin becomes free to bind to actin and the sliding-filament mechanism can ensue to cause muscle contraction.
How is contraction terminated?
By the removal of calcium ions which is achieved by lowering cytosol calcium concentration by actively transporting calcium back into the sarcoplasmic reticulum via calcium ion ATPAses
During muscle contraction the sarcomere stays at constant length whilst the thick and thin filaments shorten. T/F?
False - the sarcomere shortens but the length of the thick and thin filaments stays constant
What are the four stages of the sliding-filament mechanism?
Actin binding
Cross-bridge movement
Cross-bridge dissociation from actin
ATP hydrolysis
Describe the actin binding stage of the sliding-filament mechanism.
High-energy myosin binds to the actin filament
Describe the cross-bridge movement stage of the sliding-filament mechanism.
The myosin head pivots, releasing ADP and Pi (from the previous ATP hydrolysis). This generates a force which pulls the thin filament towards the centre of the sarcomere
Describe the cross-bridge dissociation from actin stage of the sliding-filament mechanism.
A new ATP molecule binds to the ATP binding site on the myosin head causing it to detach from actin
Describe the ATP hydrolysis stage of the sliding-filament mechanism.
The binding side of ATP to myosin acts as an ATPase and splits ATP into ADP and Pi which remain bound to myosin.
All cross-bridges undergo movement simultaneously. T/F?
False
How does the sliding-filament mechanism work for eccentric contraction.
It works in the same way as for concentric contraction but the cross-bridges pull the thin filament back towards the Z line instead in order to lengthen the sarcomere
What is a twitch contraction?
The mechanical response of a muscle to a single action potential
What is the latent period?
It immediately follows the action potential and is a period where the processes of the excitation-contraction coupling pathway are occurring before the tension in the muscle fibres starts to increase
What is the name if the time interval between the end of the latent period and the time of peak tension?
Contraction time
What does the lengthen of time of twitch contraction depend on?
How long the cytosolic calcium ion concentration remains elevated and how long it takes cross-bridges to complete their cycle following the removal of calcium ions.
Isometric twitch contractions last longer than that of isotonic contractions. T/F?
True
What is summation (in terms of muscle)?
The increase in muscle tension from successive action potentials occurring during the phase of mechanical activity
When can a tetanus occur?
When a muscle undergoes successive stimulations
When does an unfused tetanus occur?
When a muscle is stimulated after the absolute refractory period but before it can relax
What is the absolute refractory period?
The period immediately following the firing of a nerve fibre when it cannot be stimulated no matter how great the stimulus applied
What is the relative refractory period?
The period shortly after the firing of a nerve fibre when a partial repolarisation has occurred and a greater than normal stimulus can stimulate a second response.
