Anatomy and Microanatomy of Muscles Flashcards
What are the four types of tissue?
- connective
- muscle
- nerve
- epithelial
What are the four properties of muscles?
- contractibility
- excitability
- extensibility
- elasticity
What are the functions of muscles?
- movement
- maintenance of posture
- respiration and digestion
- heat generation
- communication
- constriction of organs and blood vessels
- pumping blood
- protection
What are the three types of muscle?
- smooth
- cardiac
- skeletal
Describe skeletal muscles
- striated
- somatic
- voluntary
- attached indirectly or directly to bone
What is fascicle?
a group of muscle fibres/cells
What is a muscle fibre?
groups of myofibrils
Where is perimysium found?
wrapped around fascicles
Where is endomysium found?
wrapped around individual fibre
Where is epimysium found?
surrounding a muscle
Describe a muscle cell anatomically
long, cylindrical unbranched multinucleate contractile cell
How are the muscle cells arranged?
parallel
Can muscle cells be regenerated if damaged?
yes by proliferation and differentiation of stem cells
What is the myofibril composed of?
longitudinal myofilaments
- actin
- myosin
Is actin thin or thick?
thin
What is the M line?
the line in the middle of the sarcomere
What is the A band?
the length of the thick filament (myosin)
What is the I band?
the space between thick filaments
What is the Z line?
lines that separate sarcomeres
What does myosin consist of?
heavy chain tail
light chain head
What does actin consist of?
- tropomyosin
- troponin (Ca binding site)
What is the T tubule system?
a transverse extension of sarcolemma around each myofibril
Describe the sliding filament mechanism
- myosin heads hydrolyse ATP and become reorientated and energised
- myosin heads bind to actin forming crossbridges
- Myosin heads rotate towards the centre of the sarcomere (power stroke)
- As myosin heads bind ATP the cross bridges detach from actin
Describe how muscle contraction occurs?
- sarcolemma becomes depolarised
- rapid dissemination by T tubule system
- Release of Ca^2+ ions from terminal cisternae into sarcoplasm surrounding myofilaments
- Ca^2+ ions bind to troponin which changes shape, moving tropomyosin on actin to reveal actin binding sites
- Myosin head attaches to form cross bridge
- pivots and slides thin filament towards the sarcomere centre which causes a muscle contraction
What happens during contraction?
- I band and H zone shorten
- Z lines become closer together
Are multiple muscle fibres innervated by one motor neurone?
yes
What is a neuromuscular junction?
structure where the motor neurone communicates with the skeletal muscle fibre
Describe the structure of a muscle bundle
Muscle bundle made up of many fascicles, made up of many muscle fibres, made up of many myofibrils
Describe what happens when an impulse travels down a neutron axon terminal
- nerve impulse runs down to synaptic cleft
- Acetylcholine neurotransmitters are released and attach to ACh receptors in the sarcolemma
- Action potential is propagated down the sarcolemma and T-tubules
- Action potential triggers the release of calcium ions from the terminal cisternae of the sarcoplasmic reticulum
- Calcium binds to troponin to change the shape of the tropomyosin active site to allow myosin cross bridges to attach. Myosin pulls on actin. filament, causing a muscle contraction
What are the afferents from muscles?
- golgi tendo organs
- muscle spindles
What is the role of the golgi tendon organs?
To detect changes in the tension within tendons (proprioceptors). Inhibits motor nerve activity if there is excessive tension
What is the role of muscle spindles?
-Sensory recepters/proprioceptors that detect change in length and stretch of muscles
What are the three types of muscle fibres?
- type I
- type IIA
- type IIB
What is the structure and function of type I fibres?
- red oxidative fibres
- many mitochondria
- abundant myoglobin
- mainly gets energy from aerobic oxidative phosphorylation
- adapted for slow continuous contractions over prolonged periods
What is the structure and function of IIA?
- oxidative glycolytic fibres
- many mitochondria
- reasonable amount of myoglobin
- contains glycogen
- energy source = both oxidative phosphorylation and anaerobic glycolysis
- adapted for rapid contractions and short bursts of activity
Structure and function of IIB?
- glycolytic fibres
- few mitochondria
- few myoglobin
- abundant glycogen
- mainly gets energy from glycolysis
- adapted for rapid contractions but fatigue quickly
What are the different ways to organise muscle fasciculi?
- parallel fasciculi
- covergent fasciculi
- pennate fasciculi
- circular fasciculi
What is myasthenia gravis?
a chronic autoimmune neuromuscular disorder
causes weakness of skeletal muscle
What is muscular dystrophy?
genetic disorder which causes breakdown of skeletal muscle
Describe smooth muscle anatomically
- non-striated, visceral, involunary
- small elongated cells with tapered ends
- single central nucleus
- cells arranged in sheets or bundles
- supporting collagenous tissue between cells
- contract or stretch
Describe the contractions of smooth muscle
- continuous contraction of low force
- can contract independent of innervation
- contractions are modulated by autonomic nervous system, hormones and local metabolites
Do smooth muscles have T tubules?
no they have gap junctions (also don’t have a sarcomere)
What is the structure of a smooth muscle cell?
- contractile proteins (actin and myosin) arranged in a criss-cross lattice
- they are inserted to anchoring points along with desmin-intermediate filaments and cell membrane
How does the sliding filament work in smooth muscles?
calcium calmodulin complex (calcium from cytoplasm) activates enzyme myosin light chain kinase which phosphorylates myosin and binds to actin for filament sliding contraction
What is cardiac muscle structurally and functionally an intermediate to and why?
- skeletal and smooth
- contractions are strong and use a lot of energy
- contractions are continuous and inherently contractile (involuntary)
Describe a cardiac muscle cell
- long cylindrical
- one or two nucleus usually central
- striated
- intercalculated disks
- supported by delicate collagenous tissue with rich capillaries
