Muscle Flashcards
What is found in the muscle tissue…
- muscle cells (myocytes, myofibers)
- stem cells (satellite cells)
- nerve supply
- somatic motor (for voluntary muscles)
- visceral motor (for involuntary muscles)
- sensory
- excitable plasma membranes
- connective tissue
- blood vessels, lymphatics
What is found in non-muscle contractile tissue…
- myoepithelial cells
- glandular tissues
- myofibroblasts
- wound healing
Classification of muscles
1) Skeletal (striated)
- voluntary muscles associated with skeletal movement
- biceps brachii, trapezius, deltoid etc.
1a) Visceral (striated)
- voluntary visceral muscles
- upper esophagus, pharynx, tongue, etc.
2) Cardiac (striated)
- under autonomic (sympathetic/
- parasympathetic) control
3) Smooth (non-striated)
- wide distribution
- gut, bronchioles, blood vessels, ureter, gall bladder, etc.
- under autonomic (sympathetic/parasympathetic) control
myo…, sarco…, …mysium
…mysium (flesh)
Muscle
Sarcolemma
plasma membrane + external lamina
Sarcoplasma
cytoplasm
Sarcoplamic Reticulum
smooth ER
myofiber
AKA myocyte = muscle cell
Skeletal Muscle Characteristics
- striated
- voluntary*
- long unbranched muscle fibers
- continuous external lamina
- no cell-cell gap junctions
- rich CT investments:
- surrounding entire muscle
- surrounding muscle fascicles
- surrounding muscle fibers
- multinucleated (true syncytium)
*atypical muscles (usually involuntary, but otherwise is voluntary:
- lower pharynx
- diaphragm, etc
The labeled …mysiums are all continuous with tendons
Skeletal muscle fibers - describe the cells
multinucleated, giant cells
(range from ~1mm (stapedius) to >1m (sartorius)
ID the tissue
skeletal muscle
longitudinal section
ID the tissue
skeletal muscle
cross section
myofibrils
cytoplasmic collection of sarcomeric units surrounded by the sarcoplasmic reticulum and other organelles; the sarcomere’s A and I bands in adjacent myofibril are in register, thus giving the muscle its characteristic striated appearance
packed with myofilaments; myofilaments consist of repeating sarcomeres
Muscle cells are packed with myofibrils
endomysium
between lateral cell boundaries
delicate layer (made from Type III collagen) that surrounds each individual myofiber and contains reticular fibers
Myofilaments
myofibrils are composed of myofilaments which consist of actin and myosin
During muscle contraction, what happens to the different bands
- sarcomere shortens (Z-lines
- move together)
- neither thin (actin) nor thick
- (myosin) filaments shorten
- A band width does not change
- I band narrows
- H band narrows
I band - Isotropic
A band - Anisotropic
H band - Ger. Heller (“bright”)
M line - Ger. Mittel (“center”)
Z line- Ger. Zwishen (“between” the I bands)
Excitation-contraction coupling: Skeletal muscle
Regulated by Ca2+
- two sarcomere/t-tubule triads
- continuous, enlarged SER cisterna
- propagate depolarization into cell
- stimulate calcium release from SR
dystrophin complex
Contractile proteins are linked to the ECM via the dystrophin complex
Dystrophin connects actin to plasma membrane
Muscular dystrophy
dystrophin deficiency:
- mechanical failure
- hypercalcemia leading to increased osmosis, mitochondrial rupture
Skeletal muscle fiber types
red: (slow-twitch) many mitochondria, myoglobin & oxidative enzymes (aerobic)
(these can contract for long periods without fatigue)
white: (fast-twitch) fewer mitochondria & oxidative enzymes (anaerobic)
(these are quick to fatigue)
motor unit density
The ratio of neuro-muscular junctions will change depending on the function of the tissue
coarse control, neuron:muscle fibers = 1:1000’s
fine control, neuron:muscle fiber = ~1:3
Sensory perception
provide proprioceptive information and mediate stretch reflex
a. muscle spindle
b. golgi tendon organs
Muscle spindle
one type of sensory fiber
provide proprioceptive information and mediates stretch reflex
golgi tendon organ
one of the sensory fibers
proprioception and inhibition reflex (protection from overstretching)
Cardiac muscle characteristics
- involuntary
- (sympathetic/parasympathetic)
- striated
- long branched muscle fibers:
- formed by end to end cell fusion via specialized cell-cell junctions
- discontinuous external lamina
- many gap junctions
- cells often binucleate
- has intrinsic capability to beat
ID tissue type
Cardiac muscle, longitudinal view
Cartoon diagram of cardiac muscle (no question)
ID tissue type
Cardiac muscle, cross section view
- note stippling in cytoplasm (myofibrils)
- note central location of nucleus (when visible)
intercalated discs
Cardiac cell-cell junctions
Made up of end-to-end juctions (uses fascia adherens and desmosomes) and lateral cell-cell junctions (uses gap junctions and desmosomes and is discontinuous basal lamina)
Excitation-contraction coupling: Cardiac Muscle
Regulated by Ca2+
- one T-tubule/sarcomere: Diad rather than triad
- discontinuous, anastomosing cisterna
- T-tubules situated at Z-bands
- SER does not encircle myofibrils
therefore, less efficient than skeletal muscle but cell-autonomous contractility and a functional syncytium (gap junctions) compensate
Specialized myocardial cells
Endocrine cells
Purkinjee fibers (specialized conducting cells)
Endocrine cells
type of specialized myocardial cell
- ANF (Atrial Natriuretic Factor) – vasodilator
- released in response to high BP, high Na+, angiotensin II
- predominantly in atria
Purkinjee Fibers
Specialized conducting cells
- rich in glycogen
- conduct impulses
Smooth muscle characteristics
- non-striated
- involuntary
- unfused, spindle-shaped cells (20-500mM)
- central nucleus
- discontinuous external lamina
- many gap junctions
- widely distributed:
- hollow organs (GI tract, blood vessels, bladder etc.), skin (arrector pili)
- no true sarcomeres
ID tissue type
Smooth muscle
Excitation-contraction coupling: Smooth Muscle
1) electrical, via gated Ca2+ channels
- atypical neuromuscular junction:
- neurotransmitters released at 10-200m from muscle = slow excitation
2) mechanical
* stretching stimulates mechano-sensitive ion channels (“myogenic” response)
3) hormonal
* e.g. oxytocin stimulates uterine contractions
Doesn’t have t-tubules; caveolae replace T tubule system because deep penetration not needed
caveolae
replace T tubule system in smooth muscle
Skeletal Muscle Repair
Satellite cell activation
- disease (e.g. muscular dystrophies)
- damage (e.g. excessive weight training)
(although most increased muscle mass during normal training is due to hypertrophy not hyperplasia)
Cardiac Muscle Repair
Some satellite cell activation????
- limited mitosis is possible
- most repair is fibrotic (scar tissue)
Smooth Muscle Repair
Actively proliferates in response to:
- damage
- physiological needs (e.g. uterine expansion during pregnancy)
Skeletal muscle examples
biceps brachii, trapezius, deltoid etc.
Visceral muscle: upper esophagus, pharynx, tongue, etc.
Cardiac muscle examples
main tissue in the walls of the heart
Smooth muscle examples
gut, bronchioles, blood vessels, ureter, gall bladder, etc.
Epimysium
outermost CT capsule that contains the bundles of myofibrils arranged into fascicles
dense connective tissue sheath (made from type I collagen) on the external surface of the muscle, which is continuous with the tendons that attach the muscle to bones. The epimysium is synonymous with deep fascia in gross anatomy and will frequently be named according to the muscle it covers, such as brachial and crural fascia for the arm and leg muscles, respectively
Perimysium
(Made from type I collagen) surrounds groups of fibers and
organizes them into fascicles
Sarcomere
Sliding filament mechanism for muscle contraction
- sarcomere shortens (Z-discs move together)
- neither thin (actin) nor thick (myosin) filaments shorten
- A band width does not change
- I band narrows
- H band narrows
ID the tissue
Cardiac Muscle
ID the tissue
Cardiac muscle cross section
- note stippling in cytoplasm (myofibrils)
- note central location of nucleus (when visible)
ID the tissue
cardiac muscle, longitudinal view
Note: intercalated disc
ID the tissue
Purkinje fibers
- rich in glycogen, which is what gives them the pale appearance
- conduct impulses
- contractile, but not thought of that way
Endocardium is at the top of the picture
Cardiac muscle below
Dense bodies
Dense bodies are the z-disc (line) equivalent in smooth muscles
ID the tissue
Smooth muscle
note the dense bodies
T-Tubules
perpendicular invaginations of the sarcolemma
Once depolarized, impulses travel from the sarcolemma into the musclefiber through T tubules
Not found in all muscles; they are found in large cells in order to propegate action potential
Not needed in smooth muscle; caveolae replace T tubule system in smooth muscle
ID the tissue
Smooth muscle cross-section
Note gap junctions (arrows) – in these locations the external lamina is absent
ID the tissue
Skeletal and smooth muscle
Leiomyomas
Fibroids - smooth muscle tumors almost exclusively found in the uterus
ID the tissue
skeletal muscle - longitudinal section
ID the tissue
skeletal muscle - cross section
ID the tissue
Skeletal
ID the tissue
Cardiac
ID the tissue
Smooth
ID the tissue
Skeletal - cross section
ID the tissue
Smooth muscle - cross section
ID the tissue
Cardiac - cross section
Comparison of muscles (no question)
Smooth muscle vs. dense, regular CT of a tendon
