Anatomy and Microanatomy of Muscle Flashcards
What are the four types of tissue?
- connective
- muscle
- nerve
- epithelial
What are the four properties of muscles?
- contractibility
- excitability
- extensibility
- elasticity
What is Contractibility?
ability of muscle cells to forcefully shorten and generate pulling force
What is Excitability?
ability to respond to a stimulus, from a motor neuron or a hormone
What is Extensibility?
ability of a muscle to be stretched
What is Elasticity?
ability to recoil to the muscle’s original size after being stretched
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
What is a skeletal muscle composed of?
From Out to In
Muscle - Group of Fascicles
Fascicle
Muscle Fibre
Myofibril
+Connective tissue
What are Myoepithelial cells?
Expel secretions from glands
What are Myofibroblast cells?
Secrete collagen in the process of healing and repair
What are Pericytes?
Cells that surround blood vessels of muscels.
What is the Epimysium?
Connective tissue surrounding the whole muscle
What is the Perimysium?
Connective tissue around fascicles
What is the Endomysium?
Connective tissue around individual muscle fibres.
Describe a skeletal muscle cell anatomically
long, cylindrical unbranched multinucleate contractile cell
How are the skeletal muscle cells arranged?
In 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 (Mainly Actin)
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
Where are the T-Tubule systems found?
At the junction of A and I bands
Describe the sliding filament mechanism
- myosin heads hydrolyse ATP and become reorientated and energised
- myosin heads bind to actin forming crossbridges when Pi group is released
- Myosin heads rotate towards the centre of the sarcomere (power stroke) upon release of ADP
- 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 to the sarcomere during contraction?
- I band and H zone shorten
- Z lines become closer together
What is the efferent to muscles?
Motor nerves
What is a motor unit?
A number of muscle fibres innervated by one motor neurone
What is the neuromuscular junction?
structure where the motor neurone communicates with the skeletal muscle fibre
What are the parts of the NMJ?
Axonal terminal
Motor end plate
Separated by synaptic cleft
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?
Slow Twitch
- red oxidative fibres
- many mitochondria
- abundant myoglobin
- mainly gets energy from aerobic oxidative phosphorylation
- adapted for slow continuous contractions over prolonged periods (Posture)
What is the structure and function of IIA?
Fast/Intermediate Twitch
- 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 (athletics)
Structure and function of IIB?
Fast Twitch
- glycolytic fibres
- few mitochondria
- few myoglobin
- abundant glycogen
- mainly gets energy from glycolysis
- adapted for rapid contractions but fatigue quickly (Eye muscles and Digits)
What are the different ways to organise muscle fasciculi?
- parallel fasciculi
- covergent fasciculi
- pennate fasciculi
- circular fasciculi
What are some skeletal muscle clinical correlations?
Myasthenia Gravis
Duchenne Muscular Dystrophy
What is Myasthenia Gravis?
a chronic autoimmune neuromuscular disorder
causes weakness of skeletal muscle due to a lack of nAChRs at the NMJ since they’re blocked by Abs
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 are some smooth muscle clinical correlations?
Multisystemic Smooth Muscle Dysfunction Syndrome
Generalised weakness and poor functioning of smooth muscle
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
What control the cardiac muscle contractions?
Pacemakers SA and AV nodes
How does myocardium contraction work?
Cells have slow leak of Ca ions from SR
Automated contractions modulated by SA/AV and hromones
What is the functional Syncytium of cardiac muscle?
Intercalated discs for electrical and mechanical coupling with the adjacent cell.
What is special about cardiac muscels structure?
Has branching myofibrils and a T-tubule system.
What are some Cardiac muscle clinical correlations?
Angina Pectoris marked by Ischemia of cardiac muscle
Myocardial infarction
Arrhythmias
Myocarditis
Myocardial fibrosis
What is Ischemia?
an inadequate blood supply to an organ or part of the body, especially the heart muscles.
What is an arrhythmia?
Abnormal heart rhythm
What is Myocarditis?
Inflammation of cardiac muscle
What is Myocardial Fibrosis?
excess ECM from fibroblasts causing scarring and damage.
