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M101 > W6 Nervous systems: Muscular Contractions > Flashcards

W6 Nervous systems: Muscular Contractions Flashcards

1
Q

Events during a muscle twitch after single
nerve activation

A

Latent period:
Motor end-plate depolarisation
Depolarisation (AP) transmitted down T tubules
Ca2+ channels open in SR
­ [Ca2+] in the sarcoplasm
Ca2+ binds to troponin revealing myosin binding site on actin

Contraction:
Myosin binds to actin, moves (power stroke, ADP ejected), releases (new ATP binds) and reforms many times causing sarcomeres to shorten.

Relaxation:
Ca2+ actively transported back into SR
Troponin-tropomyosin complex blocks myosin binding
Muscle fibre lengthens passively (relaxation)

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2
Q

What is a motor unit?

A

1 motor neuron & its muscle fibres

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3
Q

The all or nothing principle

A
  • The skeletal muscle fibre/motor unit either operates or it does not
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4
Q

Threshold

A
  • If the threshold stimulus for a nerve is reached and the threshold for muscle contraction is reached, the muscle fibre will contract, otherwise it will not.
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5
Q

Recruitment

A
  • The greater the force of contraction needed, the more motor units
    (one nerve and its associated innervated muscle fibres) are
    required. Each motor unit operates in an all or none fashion.
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6
Q

Why does skeletal muscle contraction require a steady supply of ATP? (3 processes)
-not respiration

A

Contraction (cross bridge forming and release)
Relaxation (pump Ca2+)
Restore Na+ and K+ after AP

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7
Q

What are the 2 types of skeletal muscle fibre?

A

Slow twitch
Fast twitch

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7
Q

What are the sources of ATP in skeletal muscles?

A

Phosphocreatine - A source of ATP
*Carbohydrates
*Aerobic metabolism : producing about 30 ATP for each molecule of glucose
*Anaerobic glycolysis : glucose is metabolized to
lactate/lactic acid with a yield of only 2 ATP per
glucose
Lack of ATP not thought to contribute to muscle fatigue – comes from other changes in the exercising muscle

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8
Q

What are the features of Cardiac muscle?
(organisation?)

A
  • Only found in the heart
  • Striated
  • Organized into sarcomere with same banding organization
  • Muscle fibres are shorter and usually contain only one nucleus
  • Connected by intercalated discs* Gap junctions and desmosomes
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9
Q

Cardiac muscle has gap junctions and desmosomes. What are the definitions of these?

A

Gap Junctions: channels between adjacent cardiac muscle fibres * allow depolarizing current to flow from one cardiac muscle cell to the next
* quick transmission of action potentials and the coordinated contraction of the entire heart
* contract in a wave-like pattern so that the heart can work as a pump.

  • Desmosome anchors the ends of
    cardiac muscle fibres together
  • cells do not pull apart during contraction
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10
Q

Smooth muscle contraction process:
(6 steps)

A
  1. External Ca2+ ions enters cell (opened calcium channels in the sarcolemma released from SR)
  2. Bind to calmodulin
  3. Ca2+ / calmodulin complex then activates an enzyme called myosin (light chain) kinase (MLCK)
  4. MLCK in turn, activates the myosin heads by phosphorylating them (converting ATP to ADP and Pi, with the Pi attaching to the head)
  5. The heads can then attach to actin-binding sites and pull on the thin filaments. Causes fibre to contract
  6. Muscle contraction continues until ATP-dependent calcium pumps actively transport Ca2+ out of the cell. * low concentration of calcium remains to maintain muscle tone.
    -Important around blood vessels.
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11
Q

Smooth Muscle compared to
Skeletal- Similarities and Differences:

A

Similarities
* Force - actin - myosin crossbridge / sliding filaments.
* Contraction (cross bridge movements) initiated by an increase in free cytosolic Ca2+
21

Differences
* Layers of smooth muscle may run in several directions
* Contract and relax much more slowly
* Less energy to generate amount of force
* Controlled by the autonomic nervous system
* Most of calcium comes from outside cell
* No T-tubules
* No troponin in actin filaments – use calmodulin
* In skeletal muscle target for calcium is actin: in smooth muscle
target for calcium is myosin

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12
Q

Differences between slow and fast twitch

A

Slow:
- Slow contraction
- Aerobic metabolism
- Fatigue-resistant and well suited

Fast-twitch
- Rapid contraction
- Use anaerobic metabolism
- Activated in short-term sprint or any short-lived “burst” activity

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13
Q

Antagonistic muscle groups function:

A

Move bones in opposite directions
Contraction can pull on a bone
Cannot push a bone away (other groups exist)

e.g. triceps muscles contracts, biceps muscle relaxes
Flexion- moves bones closer together
Extension- moves bones away from each other

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14
Q

Disorders

A
  • Muscle cramp
  • hyperexcitability of somatic motor neurons- motor unit go into a state of painful sustained
  • Overuse/ fatigue
  • Disuse atrophy
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15
Q

What are gap junctions?

A

Channels between adjacent cardiac muscle fibres

16
Q

What are desmosomes?

A

Anchors the ends of cardiac muscle fibres
- cells do not pull apart during contraction

17
Q

Functions of gap junctions in the heart? (3)

A
  • Allow depolarising current to flow from one cardiac muscle cell to the next.
  • Quick transmission of action potential and the coordinated contraction of the entire heart
  • Contract in a wave-like pattern so that the heart can work as a pump
18
Q

Cardiac muscle

A
  • Only found in the heart
  • Striated
  • Organised into sarcomere with same banding organisation
  • Muscle fibres are shorter, usually contain only one nucleus
  • Connected by Intercalated discs (gap junctions and desmososmes)
19
Q

Heart:Pacemaker function

A
  • Contractions of the heart (heartbeats) are controlled by specialised cardiac muscle cells called pacemaker (SAN)
  • Pacemaker cells respond to signals from the autonomic nervous system (ANS) to speed up or slow down the heart rate.
  • Also responds to various hormones that modulate heart rate to control blood pressure.
  • Heart also has uniquely shaped action potential (contractile cells)
20
Q

Recruiting motor units by increasing stimulus intensity

A
  • Controls the force of contraction (in absence of internal changes, such as fatigue,
    fibres will contract ‘fully’ each time).
  • The more motor units the bigger the twitch
21
Q

Differences between Slow Twitch and Fast twitch

A

Fibre diameter: Slow twitch (Red muscle)= Smallest
Fast twitch O (Red muscle) = Medium
Fast twitch G (Red muscle) = Large

Contraction time: ST= Slow
FT O = Fast
FT G = Very fast

22
Q

Control of Contraction force

A
  • As stimulus increases more neurones
    with higher thresholds begin to fire
  • Fast twitch fibres
  • Generate more force but fatigue
    more quickly
  • All muscles in 1 motor unit are same type
  • Muscle as a whole made of multiple motor units of different types
  • Weak stimulus: activates only neurons with low threshold of activation
  • Slow twitch fibres (minimal force)
  • Force – result of number of motor units and type of muscle fibres
23
Q

How do we move ?
(Bone and Joint movement)

A
  • Origin (bone): does not move
  • Insertion (bone): the point that moves
  • Bones & joints : levers and fulcrums on which muscles exert force to move or resist a load
24
Q

Smooth muscle fibres

A
  • Lack striations – tissue appears uniform/bright
  • Small, spindle-shaped cells with a single nucleus
  • Have actin and myosin contractile proteins, and
    generate force through thick and thin filaments
  • Thin filaments are anchored by dense bodies
  • Filaments occur in parallel with each other, but run
    obliquely
  • therefore get contraction in different directions
25
Q

Smooth Muscle

A
  • More variable than skeletal
  • Located
  • Blood vessel walls
  • Walls of GI tract / associated organs
  • Urinary system (walls of bladder and ureters)
  • Respiratory system (airway passages)
  • Reproductive system (both females and males), and
  • Ocular muscles (eye).
  • Some alternate between contraction and relaxation
    (phasic smooth muscle)
  • Some continuously contracted (tonically contracted)
26
Q

Which protein is not involved in skeletal muscle contraction?
Troponin, myosin, tropomyosin, Actin, calmodulin

A

Calmodulin-involved with smooth muscle

27
Q

What are the steps of Smooth Muscle Contraction? (6)

A
  1. External Ca2+ ions enters cell (opened calcium channels in the sarcolemma released from SR)
  2. Bind to calmodulin
  3. Ca2+ / calmodulin complex then activates an enzyme called myosin (light chain) kinase (MLCK)
  4. MLCK in turn, activates the myosin heads by phosphorylating them (converting ATP to ADP and Pi, with the Pi attaching to the head)
  5. The heads can then attach to actin-binding sites and pull on the thin filaments. Causes fibre to contract
  6. Muscle contraction continues until ATP-dependent calcium pumps actively transport Ca2+ out of the cell.
    * low concentration of calcium remains to maintain muscle tone.-Important around blood vessels.
28
Q

What are proprioreceptors?
Example?

A

Proprioceptors sense muscle length and activate sensory neurones (Iaaxons)
*Muscle Spindles are Proprioceptors
*Muscle spindles are specialised muscle fibres surrounded by a capsule inside skeletal muscle
* Runs parallel to muscle
* Cause a contraction

29
Q

What is the stretch reflex? (5 steps)

A
  1. Stretching of muscle stimulates muscle spindles
  2. Activation of sensory neuron
  3. Information processing of motor neuron
  4. Activating of motor neuron
  5. Contraction of muscle
30
Q

When does the stretch reflex occur?

A
  • Stretch reflex occurs when muscle proprioceptors detect the stretch and tension of a muscle
  • Send messages to the spinal cord to contract it.
  • Increase muscle tension to counter stretching
  • Allows fluidity of movement
  • Vital for bearing body weight, etc.
31
Q

What are the Golgi Tendon Organs?

A

*Proprioceptors between muscle and tendon sense tension and activate sensory neurones (type Ib)

M101 (41 decks)

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