Intro to skeletal muscle Flashcards
(33 cards)
1
Q
What is skeletal muscle tissue?
A
- Skeletal : Attach and move skeleton
- 40% of body weight
- Fibres are multinucleate cells
- Cells with obvious striations
- Contractions are voluntary
2
Q
What is cardiac tissue?
A
- Wall of the heart
- Striated walls
-Involuntary contractions
3
Q
What is smooth tissue?
A
- Walls of hollow organs
- Lack striations
- Involuntary contractions
4
Q
What are the functions of skeletal muscle tissue?
A
- Designed to contract
- Generate mechanical force
- Heat generation (shivering, involuntary contractions etc)
- Locomotion/ external movements
5
Q
Descrive how skeletal muscle is connected to the skeleton
A
- 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)
6
Q
What are myofibres?
A
- Elongated cells
- Arranged parallel to one another and bundled by connective tissue into fascicles
7
Q
What are sacrolemma?
A
cell membrane
- Striated (banded)
8
Q
What are the different components of skeletal muscle in connective tissue (layers) ?
A
- 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
9
Q
What are myofibrils?
A
- 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)
10
Q
What is myosin?
A
- composes thick filaments
- held in place by the M line proteins
11
Q
What is Actin?
A
- 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
12
Q
What is the sliding filament mechanism?
A
- Movement of thin filaments over thick
- sacromere shorterning
- Thick filaments = stationary; thin are dragged over thick
- length of the filaments do not change
13
Q
What is the anatomy of a nerve-muscle
A
- extensive blood supply for every muscle
- Specialised nerve cell = motor neuron = associated with muscles- every muscle fibre receieves innervation from a nerve
14
Q
What events link muscle excitation / action potentials to muscle contraction (cross bridge cycling)?
A
- Action potential - propagates down the sacrolemma
- Transverse tubules conduct AP into the cell’s interior
- Ca 2+release channels open in Sarcoplasmic reticulum
15
Q
How are muscle contractions activated by action potentials?
A
- 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
16
Q
What is Cross-bridge cycling?
A
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
17
Q
What are contractile properties?
A
- 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
18
Q
What is the length-tension relationship?
A
- 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
19
Q
Wnat are the types of muscle contraction?
A
- 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
20
Q
What is an isometric contraction?
A
- Muscle does not shorten,remains at the same length
- Force generated by the contraction is equal to the load applied
21
Q
What are isotonic contractions?
A
- Muscle changes length
22
Q
What are concentric contractions?
A
- Force generated is greater than load applies
- Muscle shortens as it contracts
23
Q
What are eccentric contractions?
A
- Force generated is less than load applied
- Muscle lengthens even though it is contracting
24
Q
What do muscle contraction require?
A
- ATP
- Cross bridge cycling
-Ca 2+ pump activity
Sources available: - cytosolic ATP
- Phosphocreatine (PCr)
- Aerobic respiration (oxidative phosphorylation)
- Anaerobic respiration (fermentation)
25
Describe ATP and Creatine Phosphate in muscle
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
26
What is anaerobic respiration?
- 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
27
What is aerobic respiration?
- 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
28
How is skeletal muscle developed and regenerated (via postmitotic nuclei) ?
- where are they located?
-Adult SKM fibres have 100-1000s of postmitotic nuclei that are located at the periphery of the fibres
29
What are satellite cells?
Active in young growin.. and ... in older muscles
Donate ... into growing...
Repair...
- active in young growing muscle and quiescent in older muscles
- donate myonuclei into growing muscle fibres
- Satellire cells - repair muscle damage
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)
- 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
31
What are the two ways that muscle tissue can grow?
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
32
What are the two possible outcomes of hypertrophy?
Hypertrophy with ... dilution
(increase in nuclear number)
DNA: ... is kept ... during hypertrophy
- Hypertrophy with DNA dilution (only protein synthesis)
- Mechanism for increase in nuclear number
- DNA - to muscle volume is kept constant during hypertrophy
33
What is the role of satellite cells in hypertrophy?
- Satellite cell proliferation and differentation
- Hypertrophy stimulus
- Nucleus donated by satellte cell
- Fusion of some satellite cells with muscle fibres
