Muscular physiology 2

Question 1

isotonic contractions

Isometric contractions

phases of contractions- tension and shortening
isometric tension

isotonic shortening

Answer 1

Isotonic contractions - Create force / move load Concentric - shortening
Eccentric - lengthening

Isometric contractions
Create force without
moving a load

• • • • • Isometric tension
          No visible shortening, Increasing tension, Length is constant. internal pulling on myosin START OF THING, CAN’T MOVE UNTI TENSION IS GREAT ENOUGH. can’t overcome the load, release the tension and no movement
• • • • Isotonic shortening
        Visible shortening
        Tension constant

Question 2

Muscle twitch, AP is sent down and there is a delay

what is the delay, and what is happening during,
what is it building up, and what happens the greater the load gets

slight delay of AP and contraction

buildup of tetanus
4 steps of tetanus

Answer 2

A single contraction-relaxation cycle
Latent period = time between AP and contraction(rest time)
————————–
time for the AP to move down the neurons and muscle, down into the t tubules
Time for excitation-contraction coupling
BUILD UP OF ISOMETRIC TENSION
As the load increases, latent period gets longer
——————————
if AP gets sent more and more frequently, no time for tension to be let go of, cross bridges get stuck and force increases.
Tetanus
High frequency of action potentials
Ensures that no relaxation occurs during a
sustained contraction.

Twitch, summation, unfused, fused

Question 3

Motor unit summation

more load, what occurs(latent, tension, contraction distance)
slip back, recycling, velocity

what if tension can’t overcome the load

Answer 3

↑ Voltage
↑ # fibres stimulated
↑ contraction size

Recruited with increased load
More fibres contracting
More force
————————-
↑ Load
MORE tension needed
Longer latent period
↓ contraction distance (fewers cross bridges left to make visible isotonic contraction)

Back-slippage(pull along actin, or too much force and slip back along cross bridges)
Slower cross-bridge recycling
↓ contraction velocity
——————————
isometric tension cannot overcome to make isotonic occur,

Question 3

What determines muscular force

Answer 3

Larger motor units can produce more force
Muscle fibre diameter
actin and myosin cross-bridges
Muscle fibre length
Length–tension relationship

Question 4

Muscle fibre types

what colour are oxidative fibres
and glycolytic
and why? think of a turkey

Answer 4

Slow Oxidative (type I)
Fast oxidative (IIa)
Fast Glycolytic (IIb)
Based on fuel source and contraction type

Slow Oxidative Fibres (type I)
Slow cross-bridge cycling
Uses oxidative metabolism for energy. Myoglobin, mitochondia, high blood flow
“Red fibres”
Low intensity – high endurance

Fast oxidative fibres (IIa)
Faster cross-bridge cycling
Higher intensity but lower endurance
Fast Glycolytics (IIb)
Use glycolysis for energy
* Anaerobic
Highest intensity but lowest endurance
“emergency fibres”
“white fibres”

Where are the oxidative (red/aerobic) fibres?
In the legs (they run around all day) – dark meat

Where are the glycolytic (white / anaerobic) fibres?
In the breast – they don’t fly so they don’t use these
muscles unless stressed (eg. You’re trying to catch it –
they flap) – white meat

Question 5

Muscle fatigue
what is it due to

aerobic exercise effects(when you increase your fitness)

resistance exercise effects,
fast contractions at higher load

Answer 5

Depends on oxidative ability
Due to
- Increased lactic acid
- Decreased ATP
- Increased wastes
- Ca2+ changes
- not enough Ach
=———————————
Glycolytic fibres convert to oxidative
- More mitochondria
- Increased blood flow
- More myoglobin
- More glycogen
- Fast Oxidative increase their endurance levels
———————————–
More actin and myosin within the muscle fibres
Increase diameter (“bulk up”)
Muscle cells don’t divide (G0) – so fibres get bigger but don’t increase in #

build up endurance in the muscle

Question 6

effects of exercise, short term and long term

what does testosterone do

Answer 6

Short-term effects:
- - increased blood supply
- - increased temp
- - increased lactic acid and wastes
Long term effects:
- - more maintained blood flow to muscles
- - larger muscle fibre diameter
- - more mitochondria
- - conversion of fast glycolytic fibres to fast oxidative fibres.
- - More actin / myosin

TESTOSTERONE increases # of actin and myosin filaments, cardiac hypertrophy

Question 7

protective mechanisms in the muscle

muscle spindles

Answer 7

Stretch receptor reflex
- - Prevents over-stretch of the muscle
- - Triggers a reflex contraction
Golgi Tendon organ reflex
- - Prevents over-contraction (and stretch of
tendon)
- - Triggers a reflex relaxation
- - E.g. muscle failure with high load

Increased Load
Stretches spindle
Triggers reflex
Increased contraction strength

Question 8

Strains

Answer 8

Strain
Overstretching injury of muscle
* Damage to actin and myosin
* Muscle stiffness
Treatment:
* Rest / Analgesics
* Anti-inflammatories