11/21/2014 Microscopic Anatomy Muscle Ira Ames Flashcards
General characteristics of smooth muscle
- not striated
- innervated by autonomic nervous system (involuntary)
- slow contracting
- found in the walls of hollow viscera and blood vessels (regulates lumen size)
- capable of regeneration after injury
(smooth & skeletal muscle cells, pericytes, bone marrow stem cells)
Histological appearance of smooth muscle
- fibers (cells)
a. elongated and tapered
b. average length about 200μm
c. average diameter about 5 μm
d. single nucleus - spindle shaped
- located in middle of cell
- diffuse chromatin
e. eosinophilic cytoplasm (sarcoplasm)
f. arranged in bundles or sheets - held together by connective tissue
- staggered arrangement of fibers
- cell boundaries are difficult to observe with a light microscope
General characteristics of skeletal muscle
- innervated by cerebrospinal nerves (voluntary)
- rapidly contracting
- cross striated
- makes up the somatic musculature
- capable of regeneration after injury
Histological characteristics of skeletal muscle (1)
- connective tissue
a. epimysium (dense irregular connective tissue) - surrounds entire muscle
b. perimysium (loose connective tissue) - divides muscle into fascicles (bundles)
c. endomysium (reticular fibers) - surrounds individual muscle fibers
d. integrates action of contractile units
e. supports blood vessels and nerves
Histological characteristics of skeletal muscle (2)
- fibers (cells)
a. long and cylindrical
b. average length about 20 mm
c. average thickness about 50 μm
d. multinucleated - elongated nuclei
- peripheral
- diffuse chromatin
e. cross striated (due to presence of myofibrils) - A band (dark)
- I band (light)
- Z line (disc)
(a) cross linking of thin myofilaments
(b) transmission of force
(c) signal transduction
(d) interface between contractile apparatus and cytoskeleton - H band (lacks thin filaments)
- M line (site of lateral connections between adjacent thick filaments)
f. sarcomere - portion of a myofibril between 2 adjacent Z lines
- unit of contraction
- regularity of structure maintained by titin
(a) giant muscle protein
(b) extends from M line to Z disc
(c) attaches thick filaments to Z disc
(d) acts as a passive elastic element
Histological characteristics of skeletal muscle (3)
- satellite cells
a. present in low frequency in adult muscle
b. mono nucleated
c. lie between basal lamina and sarcolemma of skeletal muscle fiber
d. scanty cytoplasm - few mitochondria
- few free ribosomes
- endoplasmic reticulum and Golgi apparatus are poorly developed
- lack lysosomes and myofilaments
e. chromatin tends to clump at inner face of nuclear membrane
f. are a heterogeneous population of cells
g. exist in a reversible quiescent state
h. responsible for skeletal muscle regeneration
i. time frame of skeletal muscle regeneration - activation (2 hrs.)
- proliferation (2-3 days)
- restoration (2 weeks)
j. other cells that may participate in skeletal muscle regeneration - muscle derived stem cells
- bone marrow stem cells
- blood vessel associated progenitors
(a) mesangioblasts
(b) pericytes
k. satellite cell population is not static - increases upon injury and after exercise
- decreases with age
Classification of skeletal muscle fibers (based upon structure, function, & histochemical reactivity
a. red fibers (TYPE I)
(1) small diameter
(2) high myoglobin content
(3) numerous mitochondria
(4) fatigue resistant
(5) derive energy from oxidative-phosphorylation
(6) contract relatively slowly (postural function)
b. white fibers (TYPE IIB)
(1) greater diameter
(2) low myoglobin content
(3) fewer mitochondria
(4) readily fatigued
(5) derive energy from anaerobic glycolysis
(6) sudden contraction
c. intermediate fibers (TYPE IIA)
(1) intermediate size, myoglobin content and number of mitochondria
(2) fatigue resistant
General characteristics of cardiac muscle
- innervated by autonomic nervous system
- rapidly contracting
- cross striated
- makes up wall of heart
- capable of regeneration after injury??
Histological characteristics of cardiac muscle
- fibers (cells)
a. branch and anastomose
b. average length about 100 μm
c. average diameter about 10 μm
d. single nucleus
- spindle shaped
- centrally placed
- diffuse chromatin
e. cross striations not as distinct as those in skeletal muscle
f. intercalated discs
- interface between adjacent cardiomyocytes
- occur at level of Z lines
- presence of gap junctions and adhering junctions (desmosomes and intermediate junctions)
- functions
(a) mechanical attachment between cells (zonula & macula adherens)
(b) transmission of electrical & chemical stimuli (gap junctions)
g. presence of secretory granules
- can be observed in atrial musculature
- contain atrial natriuretic factor (ANF)
(a) released in response to wall stretch
(b) plays a role in regulation of cardiovascular homeostasis by
controlling water & electrolyte balance and blood pressure
h. regenerative capacity ???
- cardiac muscle stem cells
- bone marrow stem cells
- umbilical cord, embryonic, and induced pluripotent stem cells (IPSC)
General characteristics of Purkinje fibers
- modified for conduction
a. responsible for the final distribution of the electrical stimulus to the myocardium - found in interventricular septum of heart
Histological differences between Purkinje fibers and cardiac muscle fibers
- larger fibers
- myofibrils are displaced toward periphery of fibers
- richer in glycogen (present in center of cells)
- intercalated discs are rarely observed
- have variable and unusual shapes
Examples of disease processes that affect skeletal muscle
Focal lesions due to trauma, inflammation or circulatory disturbances
Generalized diseases of muscle that affect skeletal muscle (1)
a. muscular dystrophies
(1) characterized by progressive muscular weakness and wasting
(2) believed to be due to an intrinsic defect in the muscle itself
(3) Duchenne type
(a) inherited as a sex-linked recessive
(b) almost exclusively found in males
(c) begins at about the age of 5
(d) patient often dies in adolescence
Generalized diseases of muscle that affect skeletal muscle (2)
b. polymyositis
(1) acute progressive disease that usually begins in adult life
(2) early signs include muscular weakness and tenderness
(3) may be rapidly fatal
Generalized diseases of muscle that affect skeletal muscle (3)
c. neurogenic atrophy
(1) secondary to a neurological problem
(2) most common cause is motor neuron disease
- anterior poliomyelitis
- amyotrophic lateral sclerosis (ALS)
