What is muscle?
contractile tissue which serves to bring about movement
What does muscles contraction and relaxation bring about?
- Body movement
- Movement of body levers
- Enables locomotion via articulations - Posture maintenance
- Stabilisation of bony levers and articulations
- Enables body position to be maintained - Body substance movement / transport / storage
- Movement and storage of digesta, blood, urine, etc within the body - Heat generation
- Conversion of ATP into muscle movement is inefficient
- Only 25%of ATP energy produces muscle movement
- Remaining 75% is converted to heat
- Heat helps maintain body temperature
- In cold environments involuntary contraction of skeletal muscle (shivering) further helps
What are the three types of muscle?
skeletal
cardiac
smooth
What is skeletal muscle?
voluntary
attached to skeleton
striated
How is muscle structured?
Fibres arranged in bundles known as fasicles
Surrounded by endomysium
Multiple bundles surrounded by perimysium
Muscle surrounded by epimysium
What are sarcomeres?
makes up muscle fibre and gives muscle a striated look
contraction occurs through sarcomeres through chemical reaction causing myosin and acts to bind and contract
How does contraction of the muscle occur?
- Contraction cycle consists of excitation phase, contraction phase and relaxation phase
- Excitation phase (aka latent period) involves stimulus arriving at the neuromuscular junction
- Stimulus is transmitted to motor end plate
- Sarcolemma depolarises
- Action potential propagated from sarcolemma to t-tubules and then sarcoplasmic reticulum
- Ca ions released into sarcoplasm
- Ca bind with troponin causing troponin-tropomyosin complex to move from actin chain
- Lasts ~ 5msec
What occurs in the Contraction Phase?
- Adenosine Trihosphate ATP on myosin head hydrolysed to Adenosine Diphosphate (ADP) and Inorganic Phosphate (P)
- Myosin head moves and attaches to actin chain
- Hydrolysed P released triggering power stroke
- Once energy used up movement stops
- ATP from sarcoplasm binds to mysoin and another power stroke triggered
- Sequence is repeated whislt [Ca ion] is high
- Lasts 20-200 msec
What occurs the the relaxation phase?
- Action potential ends
- Ca actively pumped back into the sarcoplasmic reticulum
- Takes 10-100 msec
What is the refractory period?
- This is time period where a muscle has received one stimulus to contract and cannot respond to a further stimulus
- ~ 5 msec for skeletal, ~300 msec for cardiac
- Further stimulus after the refractory period leads to increased muscle contraction (summation) – due to only partial relaxation
- Stimuli arriving at 80-100 / sec cause tetanic contraction
What are the three skeletal muscle fibre types?
Type I – slow oxidative
Type IIA – fast oxidative-glycolytic
Type IIB – fast glycolytic
•The ‘type’ refers to the form of myosin present
•The three forms of myosin have different ATPase activities and hence different contraction speeds
What is type I skeletal muscle?
- Narrow
- Least forceful
- Aerobic only
- Contain large numbers of mitochondria
- Supplied by large numbers of capillaries
- Contain large concentration of myoglobin
- Slow contractions (~ 100-200msec)
What is type IIA skeletal muscle?
- Intermediate diameter
- Intermediate forces
- Large numbers of mitochondria
- Large concentrations of myoglobin
- Supplied by large number of capillaries
- Produce ATP aerobically and anaerobically
- Faster contraction speed (<100msec)
What is type IIB skeletal muscle?
- Widest
- Produce greatest forces
- Supplied by relatively few capillaries
- Small number of mitochondria
- Low concentration of myoglobin
- High glycogen content
- Anaerobic
What is distribution of fibres within muscles determined by?
Muscle function
Genetics
Exercise and training
How does exercise effect muscle fibre types?
- Postural muscles have high type I contents
- Exercise stimulates conversion from IIA to IIB and vice versa
- Increased muscle use causes hypertrophy – due to increased nervous stimulation. More myofibrils, mitochondria and sarcoplasmic reticulum. Stronger
- Lack of use causes fibre atrophy – due to lack of stimulation causing loss of myofibrils
- Type I fibres most affected
What are the four properties of muscle tissue?
- Excitability – muscle responds to stimuli and produces action potential for movement
- Contractility - muscle responds to an action potential by producing a force
- Extensibility - ability of muscle to stretch (without damage) and still exert a force
- Elasticity - muscle always returns to its resting state (length, shape, etc.) after contraction is finished or following extension
How many muscle layers does the horse have?
4
cutaneous trunci- first layer that can spasm
superficial layer- large, broad muscles, production of locomotion
middle layer- more finer tuned movements eg; steering
deep layer- smaller and densely compact muscles that are involved in posture and stabilisation of joints
How many muscle layers does the dog have?
4
cutaneous trunci
superficial layer- large, broad muscles, production of locomotion
middle layer- more finer tuned movements eg; steering
deep layer- smaller and densely compact muscles that are involved in posture and stabilisation of joints
What does intrinsic mean?
stays within a system eg; muscle with origin and insertion in axial skeleton
What does extrinsic mean?
crosses systems eg; muscle with origin in axial skeleton but insertion in appendicular
What are the different muscle shapes?
fusiform () eg; biceps brachii
parallel I I eg; rectus abdominis
convergent V eg; latissimus dorsi
unipennate /J eg; found in limbs
bipinnate U eg; rectus femoris
Multipennate. \U/ eg; deltoid
Circular O eg; internal muscles- in digestive system
What is concentric contraction?
shortening contraction
What is isotonic contraction?
change in length with constant force
