Muscle Tissue Flashcards
Individual muscle cells are enveloped by ____
External lamina
Order of CT wrapping in skeletal muscle from big to small
. Epimysium (deep fascia)
. Perimysium (around fascicles)
. Endomysium (around muscle fiber)
Muscle fiber diameter and length
10-100 um in diameter
1mm-30cm in length
Embryology go muscle cell
. Myoblasts (progenitor cells) aggregate and fuse for multinucleated myotubes
. Myoblasts that don’t fuse become satellite cells (stem cells for skeletal muscle)
Myofibril
. Parallel array of cytoplasmic filaments within each muscle fiber
. Formed by thick myosin filaments and thin actin filaments
Sarcomeres
. Contractile units
. Consists of dark A band (anisotropic) and light I band (isotropic)
.Forms numerous junctions folds in region of neuromuscular junction
Myosin and actin organization in sarcomeres
. Myosin heads project from thick filaments to actin binding to acting forming transient bridges and ATP to catalyze energy release
. Actin associated w/ troponin and tropomyosin
Z discs
. Separate sarcomeres by divine I band
. Has alpha-actinin that attaches to thin filaments in I bands
T/F In I bands the thin filaments don’t overlap w/ thick elements
T
H zone
Center of A band void of any filaments
M line
Middle of H zone
How skeletal muscle contraction happens on microscopic level
. Sliding movement between thick and thin filaments
. Myosin head groups bind to actin then generate movement and pull thick filaments over the thin filaments shortening length of sarcomeres
. Energy generated by ATP hydrolysis by myosin heads
Sarcoplasm
. Cytoplasm of the muscle fiber
. Mitochondria and cisterna of sarcoplasmic reticulum (SER) in between fibrils
Sarcoplasmic reticulum
. Specialized for Ca sequestration and release (essential in muscle contraction)
Terminal cistern
. A-I Junction of each sarcomeres where tubules of SER coalesce to make larger tube
Transverse/T tube
. Deep invagination of the sarcolemma
. 2 terminal cisterns of SER contact this forming triad
What occurs at triad of skeletal muscle?
. Depolarization of sarcolemma from action potential causes Ca release from SER leading to muscle contraction
What are voluntary muscle innervated by?
Peripheral nervous system
nerve pathway to Neuromuscular junctions
. Myelinated motor nerves of PNS branch w/in perimysium to give rise to unmyelinated nerve terminals that pass via endomysium forming junctions w/ individual muscle fiber
Motor end plate
. Dilated terminal formed by axonal branch
. Located in trench on surface fo muscle fiber
. Contain Ach
. Only one per muscle fiber
Motor unit
. Group of muscle fibers innervated by single spinal nerve branches
. small in precisely controlled muscles
. Can have more than 100 fibers in muscles w/ less precision
Muscle spindles
. Stretch detectors part of muscle proprioception system by detecting changes in length of the surrounding extrafusal muscle fibers caused from body movement
. Sensory nerves relay info from spindle to spinal cord
Intrafusal fibers
. 2 mm long thin muscle fibers encapsulated by modified perimysium
. Get wrapped by several sensory nerve fibers that have penetrated muscle spindle
Type I skeletal muscle
. Aerobic, slow, oxidative
. Small fibers
. Slow contractions for long periods of time but resistant to fatigue (true back muscles)
. Major source ATP is oxidative phosphorylation
. Numerous mitochondria
. High density of surrounding capillaries
. High levels myoglobin
. Low glycogen content
Type IIa skeletal muscles
. Fast intermediate oxidative-glycolytic fibers
. Medium fibers
. Fast constrictions, less resistant to fatigue than type I
. Major source ATP is oxidative phosphorylation
. Numerous mitochondria
. High density surrounding blood capillaries
. High levels myoglobin (red fibers)
. Intermediate glycogen content
Type IIb skeletal muscle fibers
. Fast, white glycolytic . Large fibers . Fast contractions, suspect I’ll to fatigue . Capable of fast, precise movements . ATP source anaerobic glycolysis . Sparse mitochondria . Lower density of surrounding blood capillaries . Low myoglobin levels (white fibers) . High glycogen content
T/F Fibers fo a single motor unit don’t have to be the same type
F, they are all the same type
Hyperplasia vs. hypertrophy
Hyperplasia is increase in number of cells
Hypertrophy is increase in size of same muscle fibers
Myopathies
. Innervation of muscle is intact
. Include hereditary muscular dystrophies
. Can be result of aging, malnutrition, and immobilization
Muscle neuropathies
Innervation to muscle is lost
. Occurs in diseases caused by degeneration of motor neurons (ALS)
Myasthenia gravis
. Autoimmune is ease where autoantibodies to neurotransmitter ACh receptors in muscle cells block binding of ACh
Cardiac muscle location
. Found in myocardium of heart and at the proximal end of some large vessels entering and leaving heart
Cardiac muscle structure
. Fibers cylindrical and shorter than skeletal fibers
. Single, centrally located nucleus
. Branching to connect fibers
. Have intercalated discs
Intercalated discs
. Specialized intercellular junctions in cardiac muscle
. Appear as dark transverse lines that cross muscle cells
. Bind cardiac cells together and serve to anchor myofibrils
. Have many desmosomes and fasciae adherentes on transverse portion
. Longitudinally oriented portions have gap junctions
Functional syncytium
Quick spread of ions between cells in cardiac muscles
Cardiac cell thick and thin filaments
. Similar striated structure as skeletal muscle but branching makes it hard to see in LM
T tubules and SER in cardiac muscles
. Present but less regularly arranged
. T tubules More numerous and larger
. SER less abundant
Ca in cardiac muscle
. Slowly leaks from SER into cytoplasm after recovery from contraction
. Causes new automatic contractions independent of external stimuli
Rate of inherent rhythm in cardiac muscle is modulated by ___
. External autonomic and hormonal stimuli
T/F Mitochondria more numerous in cardiac muscle than skeletal muscle
T, 40% of cytoplasmic volume (2% of cell volume in muscle cell)
Sources of energy in cardiac muscle
. Fatty acids major source stored as triglycerides in lipid droplets present in cardiac muscle
. Glycogen often present
Difference between atrial cardiac cels and ventricle cardiac cells
. Atrial smaller w/ less T tubules than the cells of ventricles
. Release peptide hormone atrial natriuretic factor (ANF) that acts on target cells in kidney to affect Na excretion and H2O balance
Innervation of cardiac cells
. ANS and punkinje cells
Purkinje cells
. Modified cardiac cells that form pacemaker regions
. Makes coordinated contractions of myocardium as a while in each cardiac cycle
Regeneration fo cardiac cells
Don’t have satellite cells and don’t regenerate
. Dead tissue replaced w/ fibrous scar tissue
Smooth muscle cells contractions
. Continuous contractions of low force producing diffuse movements through contraction of whole muscle mass rather than of individual motor units
Smooth muscle cell structure
. Small fusiform cells linked by gap junctions
. Single Centrally located nucleus
. SER not developed and no T tubules
. Not striated
. Thick and thin filament bundles criss cross obliquely
. Actin filaments attach to alpha-actinin in dense bodies in sarcoplasmic near sarcolemma
. Desmin also attaches to alpha-actinin
Innervation of smooth muscle
. Involuntary contraction through autonomic nerves, hormones, and physiological conditions (stretch)
. Type of contraction depends on degree of autonomic innervation and density of gap junctions
Autonomic smooth muscle innervation contraction type
. Iris of the eye type
. Muscle fibers contract as small group for precise action
Peristalsis spontaneous contractions in smooth muscle
. Muscle cells generate own low level of rhythmic contraction
. ANS acts to inc. or dec. but doesn’t initiate
Regeneration of smooth muscle cells
. Capable of regeneration
. Can undergo hyperplasia (uterus during pregnancy)
