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Anatomy & Physiology > 6: Muscle > Flashcards

6: Muscle Flashcards

1
Q

What is muscle?

A

Muscle is a highly specialised tissue that can contract and shorten its length with force. When anchored to other structures, the muscle causes the other structures to move too

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2
Q

What are the general roles of muscles?

A

The roles of the muscle include:

  1. Movement and maintenance of posture
  2. Respiration
  3. Production of body heat
  4. Communication
  5. Constriction and dilation in organs and vessels
  6. Heart beat
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3
Q

Describe the structure of smooth muscle:

A
  • Smooth muscle doesn’t have highly structured neuromuscular joints
  • It has nerve fibres with many swellings that release neurotransmitters
  • It as no striations
  • It has no sacromeres
  • Actin filaments are thin
  • Myosin filaments are thick
  • Less well developed sacrophagi cells than skeletal muscles
  • Doesn’t retain such significant amounts of calcium as skeletal muscle
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4
Q

What is the function of smooth muscle?

A

Smooth muscle has long contract/relax cycles and can maintain contractile tension for long periods of time and create powerful contractions

It is found in the walls of hollow organs, blood vessels and glands. It’s action is involuntary, activated when neurotransmitters open calcium channels in the cell membrane to allow it to enter. When the calcium is transported back out of the cell, the contraction ends

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5
Q

What are the types of muscle?

A

The types of muscle are:

  1. Smooth muscle
  2. Cardiac muscle
  3. Skeletal muscle
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6
Q

Describe the structure of cardiac muscle:

A
  • Cardiac muscle has similar striated structure to skeletal muscle
  • It contracts using a similar mechanism
  • Cells are short and branched
  • Cells are interconnected via intercalated discs, allowing ions to pass from cell to cell
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7
Q

What is the function of cardiac muscle?

A

Cardiac muscle is only found in the heart and acts involuntarily. Some cells are self-excitable, activating the whole heart to contract auto rhythmically

Cardiac muscle has a long refractory period, where it cannot be stimulated again. This prevents interfering contractions that would disrupt the heart’s cycle and pumping action

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8
Q

Describe the structure of skeletal muscle:

A
  • Attached to bones via tendons at origins (moves the least) and insertions (moves the most)
  • Striated structure due to myofibril protein arrangement
  • Each muscle cell has the components of a normal cell, but with different names
  • Cells have multiple nuclei
  • Cells are rich in mitochondria and glycogen for energy
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9
Q

What is the plasma membrane called in skeletal muscle?

A

The plasma membrane is called the sacrolemma in skeletal muscle

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10
Q

What is the cytoplasm called in skeletal muscle?

A

The cytoplasm is called the sarcoplasm in skeletal muscle

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11
Q

What is the endoplasmic reticulum called in skeletal muscle?

A

The endoplasmic reticulum is called the sarcoplasmic reticulum in skeletal muscle

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12
Q

What are the layer’s of skeletal muscle membrane?

A

The layers of skeletal muscle membrane in order from outer to inner are:

  1. Epimysium
  2. Perimysium
  3. Endomysium
  4. Muscle cells
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13
Q

Describe the epimysium in skeletal muscle:

A

The epimysium is the outermost layer of skeletal muscle. It is made up of dense fibrous connective tissue and encloses the whole muscle

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14
Q

Describe the perimysium in skeletal muscle:

A

The perimysium is the layer below the epimysium. It encloses a bundle of muscle cells called fascicles. The perimysium is made up of connective tissue

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15
Q

Describe the endomysium in skeletal muscle:

A

The endomysium is within the perimysium of skeletal muscle. It fills the spaces between muscle cells in the bundle. It is made of loose connective tissue

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16
Q

Describe muscle cells within skeletal muscle membrane:

A

Muscle cells in the skeletal membrane are packed with myofibrils (mainly actin and myosin). They’re arranged into a repeating structure called a sacromere.

Sacromeres join end to end to create myofibrils running the length of the muscle cell

Different arrangements of muscle cells on the tendon produce different shaped muscles. The shape can determine the relative strength of the muscle

17
Q

What is the function of skeletal muscle?

A
  • Skeletal muscle works in groups acting together as synergists
  • Contracts when actin and myosin increase their overlapping
  • Causes the shortening of each sacromere. These combined movements create gross shortening of muscles (20%)
  • Returning to its resting length requires gravity or a muscle acting in the opposite direction
18
Q

What is a prime mover in skeletal muscle?

A

The prime mover is the synergist that makes the major contribution

19
Q

What is the fixator in skeletal muscle?

A

The fixators are the muscles that help to support the synergist prime mover

20
Q

What is an antagonist in skeletal muscle?

A

The antagonist is the member of the syngergist that moves in the opposite direction to its “team mates”

21
Q

Describe a parallel skeletal muscle:

A

A parallel skeletal muscle is very powerful, with a small range of movement

22
Q

Describe a unipennate skeletal muscle:

A

A unipennate skeletal muscle is not as powerful as a parallel muscle, but has a larger range of movement

23
Q

Describe the sequence of skeletal muscle contraction:

A

The sequence of events that produces muscle cell contraction is:

  1. Nerve signal passes along motor nerve to neuromuscular junction where nerve and muscle cells meet
  2. Neurotransmitter is released from presynaptic membrane
  3. Acetykcholine binds to receptor on the muscle cell causing a change in voltage
  4. The voltage reaches threshold, causing an action potential release into muscle cell membrane
  5. AP moves across muscle cell surface and into muscle cell
  6. AP causes sarcoplasmic reticulum to release its calcium stores
  7. Released calcium binds to troponin, producing activated troponin
  8. Activated troponin binds to tropomyosin, causing exposure of myosin binding site
  9. Myosin now binds to actin. ATP provides energy
  10. If ATP and calcium are still present, the process repeats causing the cell to contract
  11. If nerve signals stop, Ach release stops, returning the voltage to resting level
  12. Troponin’s calcium returns to the sarcoplasmic reticulum
  13. Tropomyosin released from troponin
  14. Myosin binding sights are covered again
  15. Muscle cell is now relaxed
  16. Will return to longer resting length if gravity or an antagonist muscle acts
24
Q

Describe the length tension relationship in skeletal muscle:

A

More cross bridges forming between myosin and actin means more tension. Amount of tension from the whole muscle depends on how many muscle cells are stimulated

The force of contraction will depend on:

  1. Amount of overlap between actin and myosin- shorter cells=more overlap=higher tension
  2. Frequency of stimulation- more frequent=more calcium
25
Q

What is an insertion point in a muscle?

A

Each muscle has its insertion point which is where the muscle is working at its most efficient range

26
Q

What is tetanus in muscles?

A

Normally, muscle cells are stimulated to tetanus, which is where the tension exerted by the whole muscle is the sum of all of the switched on individual muscle cells. By controlling the number of stimulated muscle cells, the tension/force of the entire muscle can be varied

27
Q

Describe the frequency of stimulation in skeletal muscle:

A

A single nerve stimulation of a muscle cell will cause a single short contraction called a twitch. A twitch has different phases

To lengthen the duration of contraction, repeated nerve signals must be sent to the muscle. If a second is sent immediately after the relaxation of the first, the second has more tension. True for 10-15 contractions. If the second arrives before the end of the relaxation of the first, a second more powerful contraction takes place. More stimuli creates a peak in tension and tetanus. This is the state most skeletal muscles work in

28
Q

Describe the characteristics of a skeletal muscle twitch:

A

Twitch length varies, but the characteristics are the same:

  1. Latent phase- 2msecs. Time for nerve signal to activate cell. No tension
  2. Contraction phase- 15msecs. Calcium released and myosin heads move. Tension rises to peak
  3. Relaxation phase- 25msecs. Calcium decreases, actin sites recovered. Tension decreases
29
Q

What is twitch summation?

A

Twitch summation is when twitches act accumulatively. If the second stimulus arrives before the end of the relaxation period of the first, the second contraction is more powerful

30
Q

What is incomplete tetanus?

A

Incomplete tetanus is when more stimuli are given to a muscle and it can’t relax. Tension will peak, creating incomplete tetanus

31
Q

Describe motor units in muscles:

A

Each whole muscle is made up of many thousand individual cells. Nerves supplying muscles typically activate a few of these cells. This creates a muscle unit of the nerve and all the cells it activates. As the load on a muscle increases, more motor units are stimulated to help

32
Q

What is recruitment in muscle cells?

A

Recruitment is when other motor units are stimulated to help with the load on a muscle. Maximum tension occurs when every motor unit is activated to tetanus. Cells quickly run out of energy, so to sustain a contraction, different motor units can be used in rotation

33
Q

What do muscles use as the energy source for contractions?

A

Muscles use ATP as te energy source for contractions. The store of ATP in a cell is only good for a couple of seconds, after which AT has to be fold from other sources

34
Q

What limits how long a muscle can contract for?

A

The limit on how long a muscle can contract i the speed at which it can produce ATP from other stores

35
Q

What happens if a muscle runs out of metabolites, glucose or oxygen?

A

If a muscle runs out of metabolites, glucose or oxygen, it becomes reduced in capability and fatigued. Recovery from this can take days

36
Q

What are the energy stores for muscle contractions?

A

At rest, some ATP is used to make creative phosphate, which can be used as a fast energy source when ATP has run out, lasting for about 15 seconds of contraction. After this, the muscle will have to wait for ATP to be produced by glycolysis in the mitochondria. This requires oxygen, so when insufficient oxygen is available in exercise, the mitochondria can produce lactic acid as energy

37
Q

What happens when lactic acid is used in contractions?

A

Lactic acid can be used for a small amount of energy in muscle contraction. Lactic acid isn’t tolerated well by the human body, so has to be removed and metabolised by the liver, in a process requiring oxygen. This creates an oxygen debt

38
Q

What happens if the muscle runs out of metabolites, glucose or oxygen?

A

If a muscle runs out of metabolites, glucose or oxygen, it becomes reduced in capability and fatigued. Recovery from this can take days

Anatomy & Physiology (13 decks)

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