Muscle physiology Flashcards
What are the striations seen in muscle?
Actin (thin) and myosin (thick) filaments
What is a motor unit in muscle?
The motor neuron + the muscle fibre that it innervates
How is contraction stimulated in skeletal muscle?
Neurogenic stimulation
How is contraction of cardiac muscle stimulated?
Myogenic (pacemaker potential of the heart)
Is what type of muscle do you find gap junctions?
Cardiac
Is their gap junctions is skeletal muscle?
No
Is their neuromuscular junctions in skeletal muscle?
Yes
What ion is the link betweek exitation and contraction?
Contraction
Where does the calcium come from in skeletal muscle?
Sarcoplasmic reticulum
How is force of contraction increased in skeletal muscles?
Motor unit recruitment and summation of contractions
How is force of contraction controlled in cardiac muscle?
Frank starling mechanism
What is excitation contraction coupling?
The process by which the surface action potential results in activation of the contractile mechanism of the muscle fibre. An electrical stimulus is turned into a mechanical response.
What branch of the nervous system controls the movement of skeletal muscles?
Somatic
What is the functional unit of muscle called?
A sarcomere
In a muscle that requires fine precision and control will there be more or less fibres per motor unit?
Less
What is a z line is a muscle fibre?
The connection between the thin filaments of 2 adjoining sarcomeres.
How is muscle tension produced?
The sliding of actin over myosin filaments. This causes the muscle to shorten and a force to be produced which results in a movement.
How is the depolarization signal sent down to the sarcoplasmic reticulum?
Down the T tubules
Opening of which channel causes the cell to depolarize?
Na+. This causes a sodium influx
How does hyperpolarization occur?
Closure of Na+ channels and opening of K+ channels
What needs to happen to the degree of depolarization before an action potential can be fired?
Must reach threshold
What exactly is an action potential?
A transient depolarization of the cell membrane beyond the threshold potential followed by a hyperpolarization before returning to a normal resting membrane potential.
How many nerves innervate each muscle fibre?
1
Explain how calcium causes contraction in a skeletal muscle?
When muscles are resting the myosin binding sites on the actin molecule are covered. When calcium is release, it binds to troponin C which casuses a conformational change and exposes these sites. The myosin head then attaches to the actin molecule and releases a phosphate group. This then causes release of a molecule of ADP. A molecule of ATP then binds to the myosin head, causing detachment from the actin. The ATPase action of this cleaves ATP and produces energy.
Explain the relaxation of muscle
Upon repolarizing calcium is actively pumped back out and into the sarcoplasmic reticulum. This causes a drop in intracellular calcium levels and causes tropomyosin to re - cover the myosin binding sites and causes relaxation.
What two things control the degree of tension in a muscle?
- The number of fibres contracting within the muscle
2. The degree of tension developed by each contracting muscle fibre
Is the duration of the action potential shorter or longer than the degree of the resulting twitch?
Much shorter
With regard to action potentials, how is the force of contraction in muscles increased?
One AP = 1 twitch. If a second AP is fired before the muscle has fully relaxed then the second response in added to the first. As this keeps happening the degree of tension keeps increasing.
Why can you not continue to fire APs simultaneously in cardiac muscle?
Due to the long refactory time
What is meant by isotonic contraction?
Muscle tension remains constant but muscle length changes
What is meant my isometric contraction?
Muscle tension increases at a constant muscle length
When resting, is a skeletal muscle at its optimal length?
Yes
What kind of movement requires isotonic contraction
Movement of objects and active body movement
What kind of movement requires isometric contraction?
Maintaing body posture and supporting objects in fixed positions
What is the stretch reflex?
A negative feedback that resists passive change in muscle length
What tendon causes the knee jerk reaction?
Tendon of the quadriceps femoris
What are the muscle spindle sensory fibres also known as?
Intrafusal fibres
What are annulospiral fibres?
The sensory nerve endings of the intrafusal fibres
Name the three different types of muscle fibres
Slow oxidative
Fast oxidative
Fast glycolytic
Name three metabolic pathways that supply ATP to the muscle fibre
- Transfer of high energy phosphate from creatinine phosphate to ADP, creating an immediate source of ATP
- Oxidative phosphorylation (presence of oxygen)
- Glycolysis (absence of oxygen)
What type of muscle fibres are used mainly for prolonged, relatively low work aerobic activity such an maintainence of posture?
Slow oxidative
What type of muscle fibres are used in aerobic and anaerobic metabolism in prolonged, moderate activities such as jogging
Fast oxidation
What type of muscle fibres use anaerobic metabolism and are mainly used for short term high intensity activities such as jumping.
Fast glycolytic
What is the neurotransmitter at the neuromuscular junction?
Acetylcholine
