Flashcards in Muscle Physiology 2 Deck (50):
What are the three types of muscle tissue?
Give a brief description of skeletal muscle
Multinucleate, striated (striped), voluntary muscle
Give a brief description of cardiac muscle
Mononucleate, striated, involuntary muscle
Has intercalated discs
Give a brief description of smooth muscle
Mononucleate, non-striated, involuntary muscle
What is the primary function of skeletal muscle?
To move bones around joints.
What is skeletal muscle composed of?
Hundreds to Thousands of muscle fibres.
What are tendons made up of?
Three membranes: epimysium, perimysium, endomysium
What does skeletal muscle shortening correlate with?
Describe each muscle fibre in skeletal muscle
Made of single cells
Contains filaments of actin and myosin
Seen as striations (dark bands and short bands)
What is skeletal muscle attached to?
What are body movements coordinated by?
Contraction of prime movers (and synergists) and relaxation of antagonistic muscles
What are prime movers and synergists?
The muscles doing the moving.
Do muscles push or pull?
What are antagonistic muscles?
The muscle of a pair that is relaxing.
What is adduction?
The movement of a muscle that brings the muscle closer.
What is abduction?
The movement of a muscle that moves the muscle further away.
What physiological component is the reason we have control over the power of our movements?
What is a motor unit?
A motor unit is a group of muscle fibres that all get their signals from the same motor neuron. All the fibres get signals from one neuron so they act as a group.
Where are big units found?
In areas that do not need to make delicate movements.
What are fine movements controlled by?
Small motor units. They have fewer muscle fibres per motor neuron.
What are graded potential responses affected by?
Both the frequency and the strength at which they are stimulated.
How does a body increase the force of a muscle?
By increasing the frequency at which motor neurons are firing.
What is muscle force a product of?
How many myosin heads are bound to actin in each sarcomere. More calcium means more available binding sites. More frequent activation means ever more calcium, since it can't all be pumped away.q
When does the relaxation period of body movements occur?
When calcium is pumped back into the sarcoplasmic reticulum.
What does the body determine frequency (and thus grade) of force in muscle movements?
Using a site principle.
What does the tension of skeletal muscle depend on?
The number of cross bridges, which is dependent on the degree of overlap between thick and thin filaments.
What are the two main ways to classify contractions?
Describe isotonic contraction
Muscle length shortens to move a load (e.g. squat)
Describe isometric contraction
There is tension in the muscle, but no change in muscle length (e.g. a plank)
What is a twitch?
A single contraction from a single stimulation.
What are the two types of twitch fibres?
Slow twitch fibres
Fast twitch fibres
Describe slow-twitch fibres.
Less powerful, but fatigue slowly – fewer myofibrils, more mitochondria and myoglobin
Describe fast-twitch fibres.
Powerful but fatigue fast – lots of myofibrils, few mitochondria
Reach peak contraction quickly.
Describe a single twitch
A single action potential
Divided into the Latent, Contraction and Relaxation Periods
Describe the latent period of a single twitch.
Beginning phase: short
Describe the contraction period of a single twitch.
Cross-bridges form, sarcomeres change length
Describe the relaxation period of a single twitch.
Longest phase. Calcium is reabsorbed.
Treppe is an increase in peak tension with each successive stimulus delivered shortly after the completion of the relaxation phase of the preceding twitch.
Describe Wave Summation.
Wave summation occurs when successive stimuli arrive before the relaxation phase has been completed.
Describe Incomplete tetanus.
Incomplete tetanus occurs if the stimulus frequency increases further. Tension production rises to a peak, and the periods of relaxation are very brief.
Describe complete tetanus.
During complete tetanus, the stimulus frequency is so high that the relaxation phrase is eliminated; tension plateaus at maximal levels.
What is a motor unit?
The name given to a somatic motor neuron and its muscle fibers that function together.
There is one axon terminal on each fibre
Each motor neuron has terminals on many fibres.
How is tension determined?
Tension is the sum of all the fibres that are stimulated/contracted at the same time.
Where is smooth muscle found?
Walls of hollow organs
How is smooth muscle arranged?
Arranged in layers (longitudinal) or around (circular) lumen
What allows motor units to function together?
The fact that there is one axon terminal on each fibre.
Describe Smooth Muscle
Cells are spindle shaped
Has one central nucleus
No striations (the myofilaments not lined up)
Involved in involuntary movements within organs
Describe smooth muscle contractions
Calcium ions in extracellular fluid and sarcoplasmic reticulum
Not organized into sarcomeres like skeletal muscle
Thin filaments anchored to dense bodies
Act independent of other smooth muscle cells
Not always innervated my motor units
Describe Cardiac Muscle
Located in the walls of the heart (only)
Cells are connected to each other and form a network
Cells are branched
Has one central nucleus
Striated myofilaments lined up
Involuntary – muscle contracts rhythmically; set by pacemaker