Muscular system

What are functions of the muscular system

Muscle, posture, stabilise and heat

How do muscle function for movement

Responsible for both internal and external movement

How do muscles function for posture

Muscles continually adjust to maintain the bodies position against gravity

How do muscles function as stabilisation

Muscles pull on bones to stabilise joints

How do muscles function to generate heat

Muscles generate heat as a byproduct of contraction, which is vital for maintaining normal body temperature

What are the characteristics of muscles

Excitability

Contractility

Extensibility

Elasticity

What is excitability

Receive and respond to a stimulus

What is Contractility

Ability to contract or shorten

What is extensibility

Ability to stretch to original length

What is elasticity

Ability to resume tension after stretching

What is the fibre arrangement of a muscle

Parallel

Convergent

Pennate

Circular

What is the parallel fibre arrangement

Long parallel, strap like

Coves long distances

What is the convergent fibre arrangement

Fan shaped

Converge at insertion

Fibres will come together at one single point

What is the Pennate fibre arrangement

Short

Many fibres per unit area

What is the circular fibre arrangement

Circular fibre bands

Surrounds body openings

What are the supporting structures of the muscle

Epimysium

Perimysium

Endomysium

Fascicles

Myofibrils

Nerve supply

Blood supply

What are Epimysium

Outer layer of connective tissue that surrounds the entire muscle

What is the perimysium

Middle layer that surrounds bundles of muscle fibres called fascicles

What is the endomysium

Inner layer surrounding each individual muscle fibre

Continuous with tendons

Attach muscles to bones

Bone is moved

What are fascicles

Formed by bundled muscle fibres

Composed of myofibrils

How do muscles interact with bones

They attach to the bone

Through the origin and insertion

What is the origin

ImMoveable bone

Lies close to insertion

Where muscle starts

Origin never moves towards the insertion

What is the insertion

Moveable bone

Moves towards origin

Where muscle ends

How does the muscle interact with other muscles

Muscles can only pull, never push

Prime mover (provides major force for movement)

Synergistic (adds force to action of prime mover)

Antagonist (opposes movement, usually relaxed)

Fixation (immobile bones and/or origins

What is a lever

Rigid bar that moves on a fixed point

What is the 3 components of the lever

Fulcrum

Effort

Load

What is the fulcrum

Fixed point around which the lever moves

Usually the joint

What is the effort

Applied force used to move a resistance

What is the load

Resistance which is moved by force

What are three types of lever (FLE)

First class (fulcrum in middle)

Second class (load in middle)

Third class (effort in middle)

What are the three types of muscle tissue

Skeletal

Cardiac

Smooth

What is skeletal muscle tissue

Controlled voluntary

Produces body movement, maintains posture and generates heat

What is cardiac muscle tissue

Controlled involuntary

Contracts rhythmically to pump blood through the circulatory system

What is the smooth muscle tissue

Controlled involuntary

Moves substances, food and fluids through internal passageways and organs

What are the thick filaments

Myosin molecules

Two polypeptide chains, two globular heads

Heads contain ATP binding sites

Thick filament contain 200 myosin molecules

What are thin filaments

Actin molecules

Globular proteins linked into chains and twisted

Strengthened by tropomyosin protein strands

Contain myosin binding sites (trooping)

What are myofibrils

Banded or striated sarcomeres

Rodlike contractile elements

What are the sarcomere regions

A bands

H zone

I bands

Z disc

Titian

What is the A band

Contains the thick filaments and the zone

What is the h zone

Contains thick filaments only

What is the m line

Holds adjacent thick filaments together by accessory proteins

What is the I band

Contains the thin filaments only

Contains the z disc

What is the z disc

Thin filaments joining sarcomeres

What is the titian

Provides strength and recoil

Allows for extensibility and contraction

What occurs on the outer edge of the A band

The thick and thin filaments overlap

What is the sarcoplasmic reticulum

a specialised network inside muscle cells that acts as a storage container for calcium ions

It penetrates each muscle fibre, so the stimulus is transferred into muscle depths

What are T tubules

Elongated tubes that penetrate deep into the muscle fibre from the sarcolemma (plasma membrane)

Transfers the stimulus for contraction into the depths of the muscle

How are muscle fibres stimulated to contract (neuromuscular junctions)

1. Motor neurons bind to muscle tissue (which is separated by the synaptic cleft)

2. Nerve impulse arrives at the axonal end of a motor neuron

3. Calcium enters the axonal terminal  

4. This calcium triggers vesicle production of the neurotransmitter acetylcholine

5. Vesicles release ACh into the synaptic cleft via exocytosis 

6. Acetylcholine travels across synaptic cleft

7. Acetylcholine binds to receptors on junctional folds of the muscles fibres sarcolemma

8. This binding triggers the release of calcium ions from the SR to begin the contraction process

9. Cholinesterase then degrades the ACh in the synapse to prevent multiple impulse transmissions from a single stimulus

What are the events of excitation-contraction coupling that leads to cross bridge activity

This the sequence of events by which an electrical impulse (action potential) leads to sliding of myofilaments

1. The action potential propagates along the sarcolemma and down the t tubules

2. This causes voltage sensitive tubule proteins to change shape, which opens calcium ions to release channels in the sarcoplasmic reticulum

3. Calcium ions flow in the cytosol and bind to troponin

4. Troponin changes shape, moving tropomyosin away from the myosin binding sites on the actin filament

5. Once the binding sites are free, myosin heads can attach to actin, and the cross bridge cycle begins

What are binding sites composed of

Troponin and tropomyosin

What is sliding filament model

Describes how muscle fibres shorten

In relaxed state actin and myosin overlap slightly

During contraction, the mysosin heads bind to actin and pull the thin filaments toward the centre of the sarcomere (m line)

The filaments do not shorten, they slide past each other, increasing overlap and causing the sarcomere to shorten

I bands shorten, distance between z discs shorten, H zones disappear, A bands move closer together but do not change length

What are the steps of the cross bridge cycle

1. Calcium binds to top of troponin (actin). This moves tropomyosin out of the way and uncovers the binding site for myosin.

2. Cross bridge formation (myosin head binds to actin, phosphate is released)

3. The power stroke (Myosin head pivots and pulls actin towards the centre of the sarcomere, ADP is released)

4. Cross bridge detachment (A new ATP molecule binds to the myosin head, causing it to release the actin filament)

5. Cocking of the myosin head (ATP is broken down  into ADP and phosphate is stored back into the head ready for the next movement)