muscles mw %% (+ Flashcards
1
Q
Muscle
A
- Generate force & movement
- Allow us to express & regulate ourselves
- 3 types – skeletal, smooth & cardiac
- Another type of excitable tissue
2
Q
Types of Muscle
A
- Striated: Skeletal (voluntary muscles, diaphragm) and Cardiac (heart).
- Smooth: blood vessels, vas deferens (the duct which conveys sperm from the testicle to the urethra), airways, uterus, GI tract, bladder etc.
3
Q
Skeletal Muscle
A
- Skeletal muscle cell = muscle fibre
- Multinucleate
- Form in utero from mononucleate myoblasts
- Increase fibre size during growth
- Myoblasts do not replace cells if damaged
4
Q
Features of skeletal Muscle
A
- Muscles are bundles of fibres encased in connective tissue sheaths
- Attached to bones by tendons
- Cells replaced after injury by satellite cells
- Satellite cells differentiate to form new muscle fibres
- Other fibres undergo hypertrophy to compensate
- Muscle will never completely recover
5
Q
Contraction: Sliding Filaments
A
6
Q
Myosin Cross-Bridge pic
A
7
Q
The Cross-Bridge Cycle pic
A
8
Q
Troponin, tropomyosin + Ca2+
A
- Tropomyosin partially covers myosin binding site
- Held in blocking position by troponin
- Co-operative block
- Calcium binds to troponin
- Troponin alters shape – pulls tropomyosin away
- Remove calcium – blocks sites again
9
Q
Muscle Mechanics definitions
A
- Force exerted by muscle = TENSION
- Force exerted on muscle = LOAD
- Contraction with constant length = ISOMETRIC (e.g. weightlifting)
- Contraction with shortening length = ISOTONIC (or concentric) (e.g. running)
- Contraction with increasing length = LENGTHENING (e.g. sitting down)
10
Q
Twitch Contractions
A
- Single AP to Muscle fibre to TWITCH.
- Latent period is time before excitation contraction starts
- Contraction time occurs between start of tension and time when we have peak tension
- Contraction time depends on [Ca2+]
- Isometric has shorter latent period, but longer contraction event
- As load increases, contraction velocity and distance shortened decreases,
11
Q
Tetanus
A
•Tetanic tension greater than twitch tension since [Ca2+] never gets low enough to allow troponin/tropomyosin to re-block myosin binding sites.
12
Q
Tetanic tension definition
A
- A sustained muscle contraction evoked when the motor nerve that innervates a skeletal muscle emits action potentials at a very high rate.
- During this state, a motor unit has been maximally stimulated by its motor neuron and remains that way for some time.
- This occurs when a muscle’s motor unit is stimulated by multiple impulses at a sufficiently high frequency.
- Each stimulus causes a twitch. If stimuli are delivered slowly enough, the tension in the muscle will relax between successive twitches.
- If stimuli are delivered at high frequency, the twitches will overlap, resulting in tetanic contraction.
13
Q
Fused and unfused tetanus
A
- A tetanic contraction can be either unfused (incomplete) or fused (complete).
- An unfused tetanus is when the muscle fibers do not completely relax before the next stimulus because they are being stimulated at a fast rate; however there is a partial relaxation of the muscle fibers between the twitches.
- Fused tetanus is when there is no relaxation of the muscle fibers between stimuli and it occurs during a high rate of stimulation.
14
Q
Length-Tension Relationship
A
- Less overlap of filaments = less tension
- Too much overlap = filaments interfere with each other
- Muscle length for greatest isometric tension = OPTIMAL LENGTH (lo)
15
Q
Flexors and Extensors
A
- Movement around a limb requires 2 antagonistic groups of muscles.
- 1 flexes, the other extends(straightens)
- Muscles arranged in lever systems
- Muscles exert far more force than the load they support.
17
Q
Fatigue
A
- Repeated muscle stim leads to muscle fatigue
- Depends on fibre type, length of contraction and fitness of individual
- Fatigue prevents muscles using up vast amounts of ATP, which would cause rigor (i.e. muscles would not be able to activate new X-bridge cycles)
27
Q
Smooth muscle
A
- No striations
- Innervated by ANS, not somatic NS
- Has a X-bridge cycle and uses Ca2+
- Filaments and excitation-contraction coupling are different
- Exists in hollow organs (e.g. GI tract, uterus, airways, ducts)
28
Q
Smooth muscle features
A
- Spindle-shaped (2-10mm diameter)
- Mononucleate and divide through life
- Thick myosin and thin actin filaments, like skeletal muscle
- However, filaments arranged diagonally across cells and are anchored to membranes and cell structures by dense bodies (like Z-lines)
- Filaments still slide together to contract cell
