L4 - Muscle Flashcards
Built-in heart rhythm
Autorhythmicity - regulated through a system of pacemakers
Muscle tissue composition
Elongated cells: muscle cells/muscle fibres/myocytes
Muscle tissue mechanism
Use energy from hydrolysis of ATP to generate force
ATP
Adenosine triphosphate
Muscle tissue function
- produce body movements
- maintain posture (stabilising body positions)
- generate heat
- protection
- storing/moving substances within body (peristalsis - smooth muscles, pump blood - cardiac muscles)
Types of muscle tissue
Skeletal, cardiac, smooth
Skleteal muscle features
~650 named skeletal muscles in body
Skeletal muscle control
voluntary (contraction is under conscious control but doesn’t always require conscious control - e.g posture)
Skeletal muscle location
Attached to bones by tendons
Skeletal muscle function
motion, posture, heat, protection
Skeletal muscle examples
Stapedius, sartorius
Stapedius features
- smallest at 1.25 mm
- stabilises smallest human bone (stapes) in the ear
- changes tension (muscle tightens) to control sensitivity of hearing by altering the amount of sound vibration transmitted through eardrum
- supplied by a small branch of facial nerve
Bell’s Palsy
paralysis of nerve causes changes in facial appearance and hyperacusis (extra loud sound perception)
Sartorius features
- longest at up to 60 cm
- in the thigh and in charge of twisting to be able to see the bottom of feet
- hip: flexor, abductor, lateral rotator
- knee: flexor
Skeletal muscle structure
- Striated (alternating light and dark bands within fibres under microscope)
- relatively big, long, cylindrical, ordered cells/fibres
- Multinucleate with many peripheral nuclei pushed to the side
Connective tissue in muscle
Epimysium, perimysium, endomysium, tendons
Epimysium location
surrounds anatomical muscle (very outer layer - fibrous fascia)
Epimysium composition
dense irregular connective tissue
Epimysium function
stops muscles from sticking to other muscle
Perimysium location
around fascicles
Fasicles
a bundle of cells grouped together which can move as individual units
Perimysium composition
dense irregular connective tissue
Endomysium location
- around muscle fibres/cell
- sits outside the sarcolemma
Endomysium composition
Areolar connective tissue - mostly reticular fibres
Endomysium function
- penetrates interior of each fascicle and separates individual muscle fibres from one another
- layer for capillaries and nerves (needed due to voluntary control)
- generally, one artery and one or two veins accompany each nerve that penetrates a skeletal muscle
Tendons and aponeuroses formation
The three connective tissue layers (epimysium, perimysium, endomysium) extend beyond to form tendons (rope like) and aponeuroses (broad, flat sheet)
Muscle cell structural components
Sarcolemma, sarcoplasm, transverse (T) tubules
Sarcolemma
Actual cell plasma membrane
Sarcoplasm
Cell cytoplasm
Sarcoplasm composition
glycogen and myoglobin (red protein that binds oxygen molecules and releases them when needed)
Transverse (T) tubules
- tiny invaginations of sarcolemma
- tunnel in from surface towards centre of each muscle fibre
- filled with interstitial fluid as they are open to the outside of the fibre
- muscle action potentials travel along sarcolemma and through T tubules (quickly spreading throughout muscle fibre = all parts of muscle excited at same instant)
Sarcoplasmic reticulum
- fluid-filled system of membranous sacs
- encircles each myofibril
- relaxed form: stores calcium ions where release of these ions tiggers muscle contraction
Myofibrils features
- 2µm in diameter
- the contractile units of muscle fibres
- highly organised arrangement of myofibrils within cells cause striations
- more or less fill the sarcoplasm
- extends the muscle fibre’s entire length
(- the tubular structure made of sarcomeres)
Myofibrils composition
Myofilaments (, proteins)
Protein types in myofibrils
Contractile, regulatory, structural
Contractile protein function
Generate force during contractions
Contractile protein examples
Myosin, actin
Regulatory proteins function
Help switch contraction process on and off
Structural protein function
- keep thick and thin filaments in proper alignment
- give myofibril elasticity and extensibility
- link myofibrils to sarcolemma and ECM
Myofilament feature
do not extend the length of the muscle fibre (arranged in compartments - sacromeres)
Types of myofilaments
Thin filament, thick filament
Thick filament size
- twice the thin filaments: 16 nm diam
- 1-2 µm long
Thick filament composition
Myosin protein
Thin filament size
- 8 nm diam
- 1-2 µm long
Thin filament composition
Mostly actin protein
Sarcomere features
- basic functional unit of myofibril
- coordinated but independent contractions
Sarcomere components
A band, I band, H zone, M line, Z discs, Titin filaments, Zone of overlap
A band
- dark (due to thick filaments), middle of sarcomere
- contains all thick filaments (including overlap)
I band
- lighter, less dense area
- ONLY thin filaments and NO thick filaments (spans between end of one thick filament to another - doesn’t include overlap zone)
- one Z disc passes through centre of each I band
H zone
- narrow region in centre of each A band
- ONLY thick filaments and NO thin filaments (spans between ends of overlap zones)
Zone of overlap
- where thin and thick filaments overlap (to different degrees depending on state of contraction)
- 2 thin filaments for every thick filament
M line
- middle of sarcomere/H zone
- contains protein discs that orientate/line up and hold thick filaments together
Z discs
- narrow, plate-shaped regions of dense material
- passes through centre of I band
- located between sarcomeres: separates and defines sarcomere units
- made of actinin proteins that link filaments of adjacent sarcomeres (thin filaments are anchored to Z discs)
Titin filament
- links Z disk to M line
- provides resisting tension on I band (like a molecular spring)
Cardiac muscle control
Involuntary
Cardiac muscle location
Heart wall
Cardiac muscle function
Pumps blood to all parts of body
Cardiac muscle structure
- Striated fibres (like skeletal): sarcomere structure
- Branched
- Single central nucleus (occasionally two)
- Fibres join end-to-end through intercalated discs
Intercalated discs function
- allows coordinated activity by linking different muscles together to result in walls contracting in an ordered way when pumping blood
Intercalated discs junctions
Desmosomes, gap junctions
Desmosomes in intercalated discs
- bind intermediate filaments
- provide adhesion (hold fibres together) in contraction
- strengthen, structure
Gap junctions in intercalated discs
- communication (electrical signals)
- coordinated, rapid conduction
Smooth muscle control
Involuntary
Smooth muscle location
- walls of hollow internal structures
- structures where diameter size needs to change (intestines - peristalsis, blood vessel walls - constriction, iris of eye, reproductive - uterus. digestive - gallbladder/respiratory - airways to Lungs/urinary - bladder, skin erector pili - Controls direction of hair, stomach)
Smooth muscle function
- motion (constriction of blood vessels, airways, propulsion of foods through gastrointestinal tract, contraction of urinary bladder/gallbladder)
Smooth muscle structure
- non-striated (smooth)
- short, small, spindle-shaped (about 30-200 µm long, 3-8 µm thickest in middle)
- single, central nucleus
- bundles of thin and thick filaments in unordered way
Smooth muscle shape advantage
- conducive to going around circular/hollow organs as they can pack easily together which results in a more efficient contractile process when changing the diameter of the inner lumen (inside space of tubular structures)
Thin filaments in smooth muscle
Attach to dense bodies
Dense bodies
Major protein actinin
- functionally similar to Z discs as contractile apparatus spans between dense bodies)
Intermediate filaments in smooth muscles
Also connect dense bodies
- non-contractile elements (rigid rods)
Intermediate filament function in smooth muscles
During contraction, tension is transmitted to the intermediate filaments and the cell widens/twists about these stable rods as it contracts/squishes
Junctions in smooth muscle
Gap junctions
Gap junctions in smooth muscle
Connect many individual fibres
Smooth muscle cells with gap junctions
Powerful contractions due to fibres contracting in unison
E.g gut
Smooth muscle cells without gap junctions
Individual contraction like skeletal muscles
E.g iris of eye
Tendon composition
Dense regular tissue
Tendon function
Attaches to bone
Tendon example
Achilles (calcaneal) tendon
Intercalated discs
transfer thickenings of plasma membrane unique to cardiac muscle
