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Fundamentals of Physiology PM1A > Muscle physiology > Flashcards

Muscle physiology Flashcards

1
Q

Define skeletal muscle

A

Movement of bones - muscle attached to skeleton to provide support, frame and protection

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2
Q

Define cardiac muscle

A

Allow the heart to pump blood throughout the body

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3
Q

Define smooth muscle

A

Muscles of the internal organs which support the activities of the systems e.g respiratory - air flow

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4
Q

what are the cell shapes of: skeletal, cardiac and smooth muscle

A

Skeletal - elongated
Cardiac- often branched
Smooth- spindle

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5
Q

What are the striations on the 3 types of muscle

A

skeletal - visible striations
Cardiac- visible striations
smooth- no visible striations

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6
Q

what is the control of each muscle type

A

skeletal - voluntary, Calcium & troponin
Cardiac - involuntary, calcium and troponin
smooth - involuntary, Calcium & calmodulin

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7
Q

What are the functions of skeletal muscle

A

control of movement by contraction, and control of respiration.

  • Homeostatic- bone stores Calcium ions, skeletal muscle stores potassium
  • role in metabolism and temperature regulation
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8
Q

What are the ways in which skeletal muscle contracts

A

1- tissue organisation
2- excitation-contraction coupling
(excitation = nervous control of the NMJ, contraction = sliding filament model)

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9
Q

how is tissue organised in skeletal muscle

A

2 ends - attached to bones via tendons.

  1. Each muscle is surrounded by connective tissue- epimysium
  2. Within epimysium- tissue is organised into fascicles- bundles of muscle cells
  3. Connective tissue called perimysium separates individual fascicles
  4. Individual muscle cells (myofiber) in fascile are surrounded by connective tissue - endomysium
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10
Q

what are the key features of skeletal muscle (5)

A
  1. sarcolemma – plasma membrane of skeletal
  2. T-tubule - invagination of sarcolemma, extends deep into muscle fibre
  3. Sacroplasmic reticulum - surrounds each myofibril, ends near the T tubule region -called terminal cisternae
  4. Triad - region where 1 t tubule is flanked by 2 terminal cisternae
  5. myofibril - bundle of contractile filaments within muscle fibre
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11
Q

what are the 2 myofibril proteins?

A

Actin (thin filaments)
Myosin ( thick filaments)
- which give muscles striated appearance

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12
Q

what is A band in skeletal

A

quite dark, length of thick myosin filaments

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13
Q

What is I band in skeletal

A

V light region with thin actin. Length decreases during contraction

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14
Q

what is Z line in skeletal

A

bisects the I band - protein disc onto which thin filaments attach

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15
Q

what is H zone in skeletal

A

length decreases during contraction

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16
Q

What is M line in skeletal

A

Middle of the A band - region where thick filaments attach

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17
Q

What is the sarcomere? (skeletal)

A

Fundamental contractile unit region between 2 Z lines

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18
Q

what is the innervation of skeletal muscle and how does an AP arrive at the muscle?

A

It is voluntary so thus requires neurogenic innervation.

The AP travels from the spinal cord to muscle along 1 alpha-motor neuron

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19
Q

what are small and large motor units for?

A

Small - muscles requiring fine control e.g eyes

Large- muscles requiring stronger contraction e.g quadriceps

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20
Q

what needs to happen for skeletal muscle to contract?

A

Each cell must be stimulated by motor neurone process - the motor unit is the functional element of muscle contraction

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21
Q

what does the sliding filament theory require (muscle contraction)? (6)

A

ACT-4

  • ATP
  • calcium ions
  • Thin filaments
  • Thick filaments
  • Tropomyosin
  • Troponin
22
Q

what is the sequence of events that happen at the NMJ? Skeletal

A
  • APs from alpha motor neurone depolarise terminal - this opens voltage dependent calcium channels and Ca dependant vesicle fusion
  • ACh is released from nerve terminal = exocytosis. Ach diffuse across synaptic cleft to activate the nicotinic ACH receptors. - opening receptor ionophore and leading to Na influx and depolarise membrane
  • Na+ entry causes an excitatory end plate potential - these are summate and if obtain threshold they generate an AP.
  • Muscle AP spreads along sarcolemma to T tubules triggering calcium release from terminal cisternae - this triggers excitation contraction coupling.
  • Ca binds to troponin on actin fibres leading to cross bridge formation and the muscle contracts according to the sliding filament model. (ATP)
  • Ach is continuously degraded into acetate and choline by the enzyme acetylcolinesterase at the NMJ. There is a decrease sarcoplasmic [Ca] and actin-myosin interactions are inhibited an the muscles relax.
23
Q

What is excitation-contraction coupling? skeletal

A

AP travels along sarcoplasmic T tubules from the motor end plate.
- AP activates DHP, DHP activates RR by changing its conformation. Activated RR pumps calcium ions from SR into the cytosol to initiate muscle contraction

24
Q

what are the 2 important physically associated proteins in excitation contraction coupling

A
  1. Dihydropyridine receptor DHP - (l type voltage gated Ca channel) - on triads at t tubules
  2. Ryanodine receptor on the SR
25
Q

what does each actin monomer contain?

A

a single myosin binding site on the external surface (MBS)

26
Q

what are the 2 types of skeletal muscle fibres?

A

Type I, slow twitch, red

Type II, fast twitch, white

27
Q

Red skeletal fibres: where are they?
What features does it have?
What is energy production?

A

In postural muscle (surrounded by adipocytes)

  • half diameter of white fibre
  • dense with capillaries
  • rich in mitochondria and myoglobin (red)
  • low glycogen

Energy: it maintains contraction for long to sustain energy but the contraction rate is SLOW due to use of oxidative phosphorylation for energy production - hence the name ‘slow’ or oxidative’

28
Q

white skeletal fibres: where are they?
What features does it have?
What is energy production?

A

In fat muscle- for quick action and large power production.

  • White (low myoglobin)
  • few capillaries
  • low mitochondria
  • High glycogen

Energy; Glycolysis - so they’re fast but are fatiguable.
(fast or glycolytic muscle)

29
Q

What types of contractions normal muscle activity controlled by?

A

Isometric and isotonic contractions

30
Q

what are isometric and isotonic contractions?

A

Isometric - contraction involves development of tension without any change in length

isotonic - contraction involves a change in length, no change in tension

31
Q

when does isotonic contraction occur?

A

occurs when force of muscle contraction is greater than the load. - tension constant while the length of muscle shortens to fit the load

32
Q

when does isometric contraction occur?

A

when load is greater than force of contraction so muscle length same but tension increases

33
Q

Name some acquired skeletal muscle myopathies (diseases)

A
  • inflammatory - polymyositis
  • NMJ - myasthenia gravis, lambert eaton
  • Endocrine - Cushings disease
34
Q

Name some generic skeletal muscle diseases

A

muscle dystrophy e.g Duchenne MS

Myotonic dystrophy

Ion channel diseases

35
Q

what happens when muscle contraction is ending? (i.e how do we end muscle contraction)

A

the muscle will keep contracting as long as it has ATP and Ca ions to expose the myosin binding site on actin.

  • Contraction is terminated by Ca being removed from cysotol and back into SR - involves the Ca pump - SERCA
  • Ca pumped against its [gradient] so needs energy
  • The AP stops, no more Ca released but Ca is high, so Ca binds to SERCA, which induces binding of ATP to SERCA- ATP gets hydrolysed and Ca transported.
36
Q

how are thick and thin filaments kept in order (i.e linear)?

A

Thin (actin) - by nebulin proteins

Thick - by titin proteins

37
Q

what is the length tension relationship in skeletal?

A

when all myosin heads overlap with actin filaments - this is maximum tension at optimal sarcomere length
(tension is related to the number of cross bridges that form)

38
Q

Describe excitation contraction coupling in cardiac muscle

A

Phase 2 cardiac AP, myocardial depolarisation permits Ca entry via L-type Ca channels in T tubules of sarcolemma.
- Ca entry is sensed by Rr to trigger Ca release from SR - triggers ECC
- Ca interacts with troponin-C (TN-C) causing TN-1 to uncover myosin binding site on actin to produce the force required for muscle contraction (sliding filament)
- After contraction, Ca reabsorbed into SR via SERCA pump and removed from cell via the Na+/Ca2+ exchanger or ATP dependant pump
- Ca decreases, dissociates from TN-c and the MBS on actin is inhibited.
ATP is required to unbind myosin from actin and reset sarcomere to normal length

39
Q

what is preload in cardiac muscle?

How does this affect force of contraction?

A

The pressure exerted by the left ventricle during diastole

  • Determined by the amount of blood returning to the heart (venous return).
  • Increase in preload means an increase in actin/myosin overlap, leading to increased force of contraction
40
Q

what is afterload in cardiac muscle

A

The pressure exerted by the aorta.

It determines how much force is used to generate pressure / muscle shortening

41
Q

what is contractility? how does It affect force of contraction?

A

Change in length / change in time
Provides a preload indépendant mechanism to increase force of contraction
(frank starling forces)

42
Q

What does the force of cardiac muscle contraction depend on?

A
  1. Initial muscle fibre length (set by frank starling)

2. Control of ANS - sympathetic nerves cause fibres to develop increased force from same initial fibre length

43
Q

how are smooth muscle adapted for different functions (2)?

A

single unit - coupled by gap junctions

multi unit - under neural control

44
Q

describe excitation of smooth muscle (more complex than cardiac/skeletal)

A
  • SM APs are longer and involve influx of BOTH Na and Ca ions
  • driven by Ca/2nd messenger pathways - NTs stimulate Ca release from SR (receptors linked to IP3) to allow direct ca influx
  • Hormones increase CaM to increase Ca release from SR also
  • 2nd messengers e.g NO release Ca
45
Q

whats different between smooth muscle and cardiac/skeletal actin & myosin?

A

Smooth uses actin and myosin but they aren’t arranged as regular sacromeres

46
Q

how is contraction of smooth muscle different from skeletal? (4)

A

it uses tropomyosin but lacks troponin C
no T tubule system
Contraction develops slower in Smooth but lasts longer
ATP usage is less and slower for a similar contraction in skeletal

47
Q

How does smooth muscle contract?

A

Ca acts through calmodulin to activate MLCK to phosphorylate myosin heads.
This increases myosin ATPase activity to provide energy for myosin to form cross bridges with actin (sliding filament)
NO T TUBULE SYSTEM

48
Q

how much longer are smooth muscle action potentials compared to skeletal/cardiac?

A

10-50ms

49
Q

what is the nervous control of skeletal, cardiac and smooth?

A

Skeletal - alpha motor neuron
Cardiac - autonomic neurons
Smooth - autonomic neurons

50
Q

how are each muscle activated? (Ca2+ sensor)

A

Skeletal and cardiac - troponin

Smooth - calmodulin and MLCK

51
Q

compare contraction speeds of the 3 muscles

A

Skeletal fastest
Cardiac intermediate
Smooth slowest

52
Q

How is each muscle contraction terminated?

A

Skeletal - breakdown of Ach by acetylcholinesterase
Cardiac - action potential depolarisation
Smooth - myosin light chain phosphatase

Fundamentals of Physiology PM1A (23 decks)

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