Muscles&

Physical Activity

updated 2012

Muscle Tissue: produces movement:-

• For – breathing– For distributing -

• BLOOD• FOOD SUBSTANCES• fluids

– For maintaining posture– For moving the body– For producing heat

• For – breathing– For distributing -

• BLOOD• FOOD SUBSTANCES• fluids

– For maintaining posture– For moving the body– For producing heat

Types of Muscle

• Cardiac Muscle– Striated INVOLUNTARY muscle, found only in the heart

• Skeletal Muscle- Striated VOLUNTARY muscle

• Smooth Muscle types-1. Organ muscle (VISCERAL – e.g. walls of the GI

system, bladder,

• Single unit-Lots of muscle cells working as a• Or • Multiunit unit -cells i.e:- Arector pili & tunic media

working in specific areas rather than the entire unit

• Cardiac Muscle– Striated INVOLUNTARY muscle, found only in the heart

• Skeletal Muscle- Striated VOLUNTARY muscle

• Smooth Muscle types-1. Organ muscle (VISCERAL – e.g. walls of the GI

system, bladder,

• Single unit-Lots of muscle cells working as a• Or • Multiunit unit -cells i.e:- Arector pili & tunic media

working in specific areas rather than the entire unit

Skeletal Muscle Focus

Action

POWER TO MOVE

KEY FEATURESInserts and origins

Origin- a fixed point

Insertion - a movable point

Muscle attachment to bone- via tendons

Skeletal Muscle

Muscle Anatomy Belly = main part of muscle

Epimysium = connective tissue coveringFascicles = within epimysium

Perimysium covers fascicles. They contain Myofibrils = single muscle fibres, within endomysium

The organisation of Muscle

Myofibrils

• MYOFIBRILS - a straight, unbranched pattern• Regular Striped appearance• Multi nucleated cells with many Mitochondria -

– Allowing power & energy to move

Sliding Filament Hypothesis

•Acetylcholine- the neurotransmitter runs through

T tubulesT tubules

•Calcium ions attach to regulatory proteins THEN

ACTIN & MYOSIN to link up THEN

The linkup point - A CROSSBRIDGE is fuelled by ATP & it pulls one strand over the other

This shortens the myofibril 1 2

T Tubule Entry point for Acetylcholine

T TUBULESSarcoplasmic reticulum

Animation 2

1. Action potential causes Ca++ release from S.R.

2. Ca++ binds to Troponin

3. Troponin moves Tropomyosin

4. Tropomyosin uncovers myosin binding site on Actin

5. Myosin binds to Actin

6. ATP acts- "rachet“fibres along

•Myosin pulls actin chain along >>>> one direction Sarcomere shortens (Z discs move closer together)

When the Whole fibre shortens Contraction!

Calcium restored to the Sarcoplasmic Reticulum Relaxation!

RECAP• Within a myofibril there are sheaths of

thin and thick filaments.

• The thin filaments are made up of ACTIN with Troponin & Tropomyosin

• Thick filaments are made up of MYOSIN

• Contraction is caused as thin filaments are pulled telescopically over actin

Animation 3

Cycle of contraction and relaxation

Potential for contraction

Lots of muscle fibres contracting

together – summation of

twitch

Energy now depleted & CA+

+ has moved back to the SR

AEROBIC MUSCLE types

•Slow metabolic fibres-

•Fast metabolic fibres –

•Both have lots of myoglobin packed with oxygne

Both produce energy from glucose & oxygen

Slow oxidative fibres

•Produce energy from glucose & Oxygen

•smallest slow twitch fibresvery fatigue resistant

work aerobically by generation of ATP

have many mitochondria

produce slow contractions

Fast oxidative fibres

• Produce energy from glucose & Oxygen

• intermediate fibres fatigue resistant work aerobically by generation of ATP

have many mitochondria

produce fast contractions

Anaerobic fibresFast glycolytic (Breakdown Glycogen)

fibres largest fibres they fatigue easily

have low myoglobin & few mitochondria

have high levels glycogen generate ATP anaerobically produce strong, fast contractions

Case Study

• Jeff wants to prepare himself for race for life

• He is quite slim and has a limited muscle mass

• What would you urge him to do to prepare for the race?

Muscle contractions

• Incomplete tetanus:– Relaxation period shortens between

twitches.– Strength of contraction increases.

• Complete tetanus:– No visible relaxation between twitches.– Smooth sustained contraction.

Working with what you are born with

• Sprinter need fast twitch fibres because they reach peak tension much faster than their slow twitch counterparts.

• Gram for gram, the two types are not different in the amount of force they produce, only their rate of force production

• Endurance athletes need more slow twitch fibres.

• These fibres give up lightning contraction and relaxation velocity for fatigue resistance

Working with what you are born with

2 reasons to Train muscle1. They respond to chronic overload (training), to

minimize the disturbance caused by the training.

• more mitochondria & surrounding capillaries develop muscle ability to cope with exercise stress

2. Fibre type is a poor predictor of performance.

• many factors determine success!

• mixed fibre composition is ideal for success in a range of events

Energy for Muscle actionEnergy for Muscle action•1st stages of muscle contraction,

– Residual food i.e. protein, fat, glucose, lying around in the cell

– There is also a rise in ATP concentrations, allowing aerobic energy metabolism to continue.

•Kick start action (a sprint from starting blocks),– Creatine phosphate (anaerobic).

– 4-6 times greater than ATP but is similar to ATP.4-6 times greater than ATP but is similar to ATP.

– Loads of energy released -when the phosphate is taken from Loads of energy released -when the phosphate is taken from creatine =ADPcreatine =ADP

•Maintenance = glycogen stores and aerobic action

Smooth muscles fibres

In general, contraction & relaxation periods = slower than skeletal muscle

• Contractions are rhythmical – may last 30 seconds or more. – specialised action is suited to organs such as GI

system

Muscle repair Satellite cells• After embryonic development,

muscle progenitor cells lay dormant close to the basement membrane. In response to exercise of trauma then divide to form called myogenic precursor cells or skeletal myoblasts, which further multiple to a final stage of division fuse with muscle cells to form multinucleated myofibres.

Grand and Rudnick 2007

http://dev.biologists.org/content/134/22/3953.full accessed 19/7/2012

Damaged Muscle

Repaired Muscle

Smooth Muscle-Your ongoing work

• Do not contain sarcomeres.

• Contain > content of actin than myosin (ratio of 16:1).

• Myosin filaments attached at ends of the cell to dense bodies.

• Contain gap junctions.

Multi & Single unit muscles fibres

Where would you find multi-unit fibres?• Justify their position in relation to their

function o the tissue/organ

Where would you find single unit fibres?• Justify their position in relation to their

function o the tissue/organ

Smooth Muscle Contraction• Depends on rise in free intracellular Ca++ .

• Ca++ binds with calmodulin.

• Ca++ calmodulin complex joins with & activates myosin light chain kinase.

• Myosin heads are phosphorylated.

• Myosin head binds with actin.• Relaxation occurs when Ca++ concentration

decreases.

• Contain actin & myosin arranged in sarcomeres.

• Contract via sliding-filament mechanism..

• Adjacent myocardial cells joined by gap junctions.– AP spread through cardiac

muscle through gap junctions.

– Behaves as one unit.– All cells contribute to

contraction.

Learning Outcomes Give examples of muscle action Briefly describe the three types of muscles Describe a sarcomere. Explain the arrangement of a muscle’s molecular structure Describe the sliding filament hypothesis Describe energy sources for aerobic and anaerobic muscle action State appropriate rational for particular nourishment for patients, to maintain muscle

action Briefly explain twitch, isotonic, isometric and treppe contraction in muscle State the essential difference between slow, fast and intermediate twitch muscle in

relation to fuel, metabolism and function. Compare and contrast smooth muscle, cardiac muscle and skeletal muscle Briefly describe smooth muscle and include detail of single and multi unit muscle,

stating it application and function Describe the action potential of muscle Describe the role of Calcium in striped muscle twitch Describe the role of Calcium & Calmodulin in striped muscle twitch Describe the neuromuscular junction considering electrical and chemical

transmission of the impulse