15.7 - Structure of skeletal muscles Flashcards
What are muscles?
They are effector organs that respond to nervous stimulation by contracting and bring about movement
What are the three types of muscles?
- Caradiac muscle
- Smooth muscles
- Skeletal muscles
Where is cardiac musclles found?
Exculisvely in the heart
Where is smooth muscle found?
In the walls of the blood vessels and the gut
Are cardiac and smooth muscles under consciously control?
No
What is skeletal muscles makes up?
The bulk of the body muscles in vertebrates
It is attached ti the bone and acs under voluntary ,conscious control
What are indidvual muscles made up of?
Millions of tiny muscle fibres called myofibrils
Properties of myofibrils
- Themseleves do not product any fcrce but collectively they can be just as powerful
What is sacroplasm?
Muscles have different structure
Separate cells become fused intomuscle fibres
Share nuclei and cytoplasm - sacropplasm
Within sacroplasm there is a high cocnentration of mitochondria and endoplasmic recticulm
What is muofibrils made up of?
- Actin is a smaller and tihinner consists of two strands around each other
- Myosin - thicker has long rod shaped tails and heads that project to one side
Why od myofirils appear stripped?
- Due to their alternating light-coloured and dark coloured bands
- Light bands are I bands (isotrophic bands) - appear light and thick and thin filaments do not overlap
- Dark bands are A bands (anisotrophic bands) They appear dark as thick and thin filaments overlap
- A - H zone
- Centre of I iZ=line
What is sacromere?
Distance between adjacent Z lines
Muscle contratcs sacromeres shorten and pattern of light and band changes
What is tropomyosin?
Forms fibrous strand on actin filament
What are the twp types of muscle fibres?
- Slow-twitch fibres
- Fast-twitch fibres
What is slow-twitch muscles fibres used for?
- Contract more slowly than fast twitch
- Porivde less powerful contractions but over long-period
- Adapted to long-period edurance
- Much more common in calf muscle
- Suited for aerobic respiration to avoid build up of lactate acid cause them to function less
Adaptations of slow-twitch fibres?
- A large store of myoglobin (red molecule stores oxygen and accounts for red colour)
- Rich supply of blood vessels to deliver oxygen and glucose for aerobic respiration
- Numerous mitochondria to produce ATP
What is fast-twitch fibres?
- Contract more rapidly and produce powerful contractions only for a short period
- Intesense exercise
- More common in muscles for short burts of activity
What is adaptations of fast-twitch fibres?
- Thicker and more numerous mysoin filaments
- High concentration of glycogen
- High concentration of enzymes involved in anaerobic respiration provides ATP rapidly
- A store of phodphocreatine a molecule rapidly generate ATP from ADP in anaerobic conditions and provide enery for muscle contractions
Similarities between nueromuscular junction and cholingeric synpase?
- Neurotransmitter transmitted in diffusion
- Receptors that are binding on neurotransmitter cause influx of sodium ions
- Use sodium-potassium pump to repolarise axon
- Use enzymes to break down neurotransmitter
Differences in neurmuscular junction
- Only exictoary
- Only links neurones to muscles
- Only motor neurones involved
- Action potential ends here
- Acetlycholine binds to receptor of membrane of muscle fibre
Differences in cholingernic synpase
- May be excitatory or inhibitory
- Links neurones to neurones to other effector neurones
- Motor ,sensory and intermediate involved
- A action potential may be produced along another neurone
- Acetlycholine binds on receptor on membrane of post synaptic membrane
