Intro to skeletal muscle

Question 1

What is skeletal muscle tissue?

Answer 1

• Skeletal : Attach and move skeleton
• 40% of body weight
• Fibres are multinucleate cells
• Cells with obvious striations
• Contractions are voluntary

Question 2

What is cardiac tissue?

Answer 2

• Wall of the heart
• Striated walls
  -Involuntary contractions

Question 3

What is smooth tissue?

Answer 3

• Walls of hollow organs
• Lack striations
• Involuntary contractions

Question 4

What are the functions of skeletal muscle tissue?

Answer 4

• Designed to contract
• Generate mechanical force
• Heat generation (shivering, involuntary contractions etc)
• Locomotion/ external movements

Question 5

Descrive how skeletal muscle is connected to the skeleton

Answer 5

• connected via tendons
• attached to immobile bone at one end (origin)
• Other end attached to insertion (moveable bone)
• Non-contractile parts (elastic elements) of the muscle and tendons are stretched before tension where attachment occurs
• Contracting muscles - typically pull on attachment points to move insertion toward origin
• Elastic elements allow muscle to elastically recoil back to its original resting length when contraction is completed
• Antagonistic (Synergistic) pairs
• Contraction of one does the opposite to counterpart (biceps and triceps)

Question 6

What are myofibres?

Answer 6

• Elongated cells
• Arranged parallel to one another and bundled by connective tissue into fascicles

Question 7

What are sacrolemma?

Answer 7

cell membrane
- Striated (banded)

Question 8

What are the different components of skeletal muscle in connective tissue (layers) ?

Answer 8

• Superficial fascia = loose connective tissue underlying skin
• Deep fascia = dense connective tissue around muscle
• Epimysium - surrounds whole muscle
• Perimysium - surrounds bundles (fascicles) of muscle cells
• Endomysium - separates individual muscle cells
• Connective tissue layers extend beyond muscle bellly to form the tendon = aponeuroses and MTJ

Question 9

What are myofibrils?

Answer 9

• Long bundles of protein, made up of thick and thin filaments
• myofilaments arranged in sacromeres
• Repeated units
• From one Z disc to the next
• Thick filaments ar center, thin filaments at either end attached to the z-discs
• I band near either end - only thin myofilaments
• A band at midsection - thick filaments
• H zone at centre - only thick fialments (no overlap with thin)

Question 10

What is myosin?

Answer 10

• composes thick filaments
• held in place by the M line proteins

Question 11

What is Actin?

Answer 11

• Composed thin filaments alongside troponin and tropomyosin
• Myosin-binding site on each actin molecule - covered by tropomyosin in relaxed muscle
• Thin filaments held in place by Z lines. From one Z line to the next = sacromere

Question 12

What is the sliding filament mechanism?

Answer 12

• Movement of thin filaments over thick
• sacromere shorterning
• Thick filaments = stationary; thin are dragged over thick
• length of the filaments do not change

Question 13

What is the anatomy of a nerve-muscle

Answer 13

• extensive blood supply for every muscle
• Specialised nerve cell = motor neuron = associated with muscles- every muscle fibre receieves innervation from a nerve

Question 14

What events link muscle excitation / action potentials to muscle contraction (cross bridge cycling)?

Answer 14

• Action potential - propagates down the sacrolemma
• Transverse tubules conduct AP into the cell’s interior
• Ca 2+release channels open in Sarcoplasmic reticulum

Question 15

How are muscle contractions activated by action potentials?

Answer 15

• APs induce the release of Ca 2+ into the sarcoplasm
• When Ca 2+ binds to troponin on thin filament, troponins changes
• Shifts tropomyosin off myosin binding sites
• Enables myosin to bidn to actin

Question 16

What is Cross-bridge cycling?

Answer 16

Cross-bridge
Cycling
Myosin head binds to actin
Power Stroke
— Globular head bends
toward center of
sarcomere
— thin filaments pulled
toward center of sarcomere
- Cross bridge link broken and head unbends
- Myosin binds to next actin molecule on the thin filament
- Repeats, shortening length of the sarcomere

Question 17

What are contractile properties?

Answer 17

• Twitch = single contraction and relaxation of a muscle in response to a single bried stimulus
• Strength of twitch contraction can be modifed
  In vitro (isolated) - increasing stimulus strength induces large numbers of myofibres to contract
  In vivo ( in the body) - activation of additional motor units (motor unit recruitment) increases contraction strength
• Henneman’s size principle motor units - genrally recruited in order of smallest to largest (fewest fibres to most fibres ) as contraction increases

Question 18

What is the length-tension relationship?

Answer 18

• Normal resting length for skeletal muscles ( sacromere ~ 2.0 micrometeres) - for generation of max tension
• If length decreased ( sacromere length < 2.0 micrometers ) - tension reduced as fluid pressure builds, thin filaments from either end of the sacromere collide

Question 19

Wnat are the types of muscle contraction?

Answer 19

• Summation : when a muscle is stimulated multiple times in rapid succession
• Complete tetanus - muscle stimulates at high frequency so that no relaxation occurs (Steady state of tension)
• In vitro - high rate of stimulation prevents muscle fibres from relaxing
• In vivo - different motor units activated in rapid succession to generate sustained contraction

Question 20

What is an isometric contraction?

Answer 20

• Muscle does not shorten,remains at the same length
• Force generated by the contraction is equal to the load applied

Question 21

What are isotonic contractions?

Answer 21

• Muscle changes length

Question 22

What are concentric contractions?

Answer 22

• Force generated is greater than load applies
• Muscle shortens as it contracts

Question 23

What are eccentric contractions?

Answer 23

• Force generated is less than load applied
• Muscle lengthens even though it is contracting

Question 24

What do muscle contraction require?

Answer 24

• ATP
• Cross bridge cycling
  -Ca 2+ pump activity
  Sources available:
• cytosolic ATP
• Phosphocreatine (PCr)
• Aerobic respiration (oxidative phosphorylation)
• Anaerobic respiration (fermentation)

Question 25

Describe ATP and Creatine Phosphate in muscle

Answer 25

ATP - limited stores (used up in a few contractions)
- Phosphocreatine (creatine phosphate)
- Storage of high energy phosphate bonds
- Used to quickly regenerate ATP from ADP
- Limited supply in cells

Question 26

What is anaerobic respiration?

Answer 26

• Glycolysis + lactate fermentation
• breakdown of glucose
• Stored as glycogen in muscle cells
• Does not require O2
  -Generates ATP quickly (faster than aerobic respiration)
• Used during intense exercise - O2 supply cannot keep up with demand
• Lactate produced - associated with muscle soreness and fatigue

Question 27

What is aerobic respiration?

Answer 27

• Occurs in mitochondria
• Requires O2 to form ATP
• Fatty acids = primary nutrient source
• Contain lots of energy, but requires O2 to release it
• Aerobic exercise - light to moderate exercise (walking, jogging, swimming)
• Max O2 uptake
• Max rate of O2 delivery to the muscles
• Max level of aerobic activity

Question 28

How is skeletal muscle developed and regenerated (via postmitotic nuclei) ?
- where are they located?

Answer 28

-Adult SKM fibres have 100-1000s of postmitotic nuclei that are located at the periphery of the fibres

Question 29

What are satellite cells?
Active in young growin.. and … in older muscles
Donate … into growing…
Repair…

Answer 29

• active in young growing muscle and quiescent in older muscles
• donate myonuclei into growing muscle fibres
• Satellire cells - repair muscle damage

Question 30

What is myogenesis?
- Reg by … reg factors
- Appear at different.. during… development
- … MRFs regulate ….. {MYOD-r Myf-5),
- Secondary MRFS regulate fusion of … and terminal differentiation (MRF4)

Answer 30

• The muscle making process
• Regulated by myogenic regulatory factors (MRFS)
• They appear at different times during muscle development
• Primary MRFs regulate determination ( MyoD or Myf-5), Secondary MRF’S regulate fusion of myoblasts and terminal differentiation (MRF4)

Somite cells to Myoblasts then Proliferation then Fusion = muscle fibres

Question 31

What are the two ways that muscle tissue can grow?

Answer 31

1. Cells can double their nuclei/DNA and contents in a process called cell cycle and then split - HYPERPLASIA - most common form of muscle growth during development
2. Adult muscle cells can also grow in size = HYPERTROPHY. Hyperplasia does not occur in adulthood. Cellular hypertrophy limited because the DNA concentration within a cell with one nucleus will be diluted due to their post-mitotic nature

Question 32

What are the two possible outcomes of hypertrophy?

Hypertrophy with … dilution
(increase in nuclear number)
DNA: … is kept … during hypertrophy

Answer 32

• Hypertrophy with DNA dilution (only protein synthesis)
• Mechanism for increase in nuclear number
• DNA - to muscle volume is kept constant during hypertrophy

Question 33

What is the role of satellite cells in hypertrophy?

Answer 33

• Satellite cell proliferation and differentation
• Hypertrophy stimulus
• Nucleus donated by satellte cell
• Fusion of some satellite cells with muscle fibres