Muscle

Question 1

what are the muscle types?

Answer 1

Skeletal: limbs, body walls opening of digestion and urinary track: striated, voluntary (static & dynamic)
Smooth: in walls of tubes, blood vessels, gut, and ureter; non-striated and involuntary
Cardiac - Heart: striated and involuntary

Question 2

What are the functions of the muscle?

Answer 2

Movement of the skeleton

Support/protect soft tissues

Posture

Guard entrance/exits

Shiver ( to regulate body type)

Question 3

what is the hierarchal structure of muscle?

Answer 3

Tendon: connects bone to muscle
Muscle tissue: Surrounded by epimysium & Contains many fascicles
Fascicles: Surrounded by perimysium & containing many muscle fibres
Muscle fibres (huge cells): Surrounded by endomysium & contains many myofibrils Blood vessels and nerves

Question 4

Describe a muscle fibre cell

Answer 4

Basic structural unit
Long mulitnucleated cylindrical cell
Thickness: 10-100 microns
Length: 1-30cm
Encased in a plasma membrane called the sarcolemma.
Muscle fibre consists of fibrils
Myofibrils consist of several sarcomere (basic unit of contraction) Actin myosin titin , nebulin - sarcomere, 1.6-2.6 um in length

Question 5

Describe a sarcomere

Answer 5

contractile unit
10k sarcomeres placed end-end
Z-line = bundary in between
Appear striped due to two proteins:
Thick filaments - myosin
Thin filaments - actin, tropomyosin and troponin
Sarcoplasmic reticulum: Organised network of tubules and sacs closely correlated with repeating patterns of sarcomeres

Question 6

What is the motor unit

Answer 6

a signle motor neuron and the muscle fibres innervated by it
When stimulated all move at once (All or nothing)
Small muscles that require fine control
Large muscles = coarse control

Question 7

Describe the sliding filament theory in muscle contraction

Answer 7

Active shortening of the sarcomere, and hence the muscle, results from the relative movement of the
actin and myosin filaments past one another while each retains its original length

Question 8

Steps involed in contraction (sliding filament theory)

Answer 8

1. Motor neuron stimulates the muscle
   at the neuromuscular junction
2. Action potential depolarises the
   muscles cell membrane
   (sarcolemma)
3. Calcium ions (Ca++) are stored in
   sarcoplasmic reticulum (SR).
   Depolarization of SR makes its
   membrane permeable for Ca++
4. Ca++ binds to troponin
5. Tropomyosin is moved away from
   myosin receptor sites
6. Contraction begins though myosin
   docking and pulling on actin.
7. Contractile activity persists until Ca++
   is pumped back to SR.

Question 9

Describe the Musculotendinous Unit

Answer 9

Tendons represent a viscoelastic component located in series with the contractile components (myofibril) of muscle
Epimysium, perimysium, endomysium and sarcolemma represent a second elastic component located in parallel with contractile components
When the parallel and series elastic components stretch during active contractionor passive extension, tension is produced and energy is stored; when they recoil with muscle relaxation, this energy is released

Question 10

Describe the mechanical response to a single stimulus

Answer 10

The mechanical response to a single stimulus (action potential - AP) of its motor nerve is
known as a twitch
Following stimulation
➢ Latency period (time required for slack in elastic components to be taken up)
➢ Contraction time (time of start of tension to peak tension)
➢ Relaxation time (time from peak tension to zero tension)
➢ Each time will depend on the make up of the muscle (10ms-100ms)
A series of AP’s can be initiated before the first
twitch is completed
➢ The mechanical response to successive stimuli are
then added to initial twitch
➢ The greater the frequency of stimulation, the
greater the tension
➢ There is max frequency by which tension in muscle
cannot increase

Question 11

Describe the types of muscle contraction

Answer 11

last type : Isokinetic
➢ A type of dynamic muscle work in which movement
of the joint is kept at a constant velocity, and hence
the velocity of the shortening or lengthening of the
muscle is constant

Question 12

what relationships do you examine in teh force production of muscle

Answer 12

➢ Length-tension relationship
➢ Length-velocity relationship
➢ Force-time relationship

Question 13

Describe the length tension relationship

Answer 13

➢ The force, or tension, that a muscle exerts varies with the length at which it is held when
stimulated
➢ In whole muscle the tension produced by both active components and passive components must be taken into account
Force generated decreases as the overlap between the actin and myosin decreases

Question 14

Describe the Load-Velocity Relationship

Answer 14

The velocity of shortening or eccentric lengthening of a muscle is related to the magnitude of the external load

Question 15

Describe the Force-time relationship

Answer 15

The force, or tension, generated by a muscle is proportional to the contraction time: the longer the contraction time, the greater is the force developed, up to the point of maximum tension.
Slower contraction leads to greater force production because time allows for the tension produced by the contractile elements to be transmitted through the parallel elastic components to tendons

Question 16

Describe the effects of muscle architecture on Force production

Answer 16

Question 17

Describe the three types of force production

Answer 17

Question 18

What are the external effects on force production in the muscle

Answer 18

➢ Prestretching
Muscle performs more work after being stretched than when it shortens from a stateof isometric tension
➢ Temperature
Increase causes increase conduction velocity across sarcolemma increasing frequency of stimulation and hence muscle force.
Rise in temperature also causes greater enzymatic activity
➢ Fatigue (not to be confused with damage accumulation)
Fatigue in muscle contracting isometrically. Prolonged stimulation occurs at a frequency that outstrips
the muscle’s ability to produce sufficient ATP for contraction.

Question 19

What are the different types of muscle injuries?

Answer 19

Contusion – bruising

Laceration – cutting

Rupture – torn in two

Ischemia – lack of oxygen

Denervation – defected motor unit (brain cant sent signals = lose control)

Question 20

Describe how disuse use of the muscle can lead to wear

Answer 20

➢ Atrophy – reduced size/number
➢ Depends on muscle type and length (Immob)
➢ Immediate mobilization – beneficial
➢ Type I fibre more prone to atrophy
➢ Elite athletes show rapid reduction in muscle
fibre capability

Question 20

Describe Muscle Constitutive Modelling

Answer 20

Mechanical models are used to describe the viscoelastic behaviour of materials. These
models use spring and dashpot elements in order to describe the mechanical behaviour of
a viscoelastic material in response to an applied force.
➢ A linear spring (k) is supposed to produce instantaneously a deformation proportional to
the load. If F is the force acting in a spring and x is the extension, then F=kx.
➢ A dashpot (c) is supposed to produce a velocity proportional to the load at any instant. If
the force F acts on a dashpot it will produce a velocity of deflection x, and F=cx
➢ Kelvin Model for Viscoelasticity: This is also known as the standard linear model. In this
model the total force is given by the sum of the force F2 from the spring and F1 from the
Maxwell element.