Muscle Tissue Flashcards
Key feature of muscle tissue
Contractility
Muscle tissue components
Structural/Microfibrillar proteins: Actin and myosin
Sarcolemma: the muscle cell membrane and sarcoplasm is the cytoplasm.
Muscle fiber is synonymous with _____
Muscle cell
Types of muscle tissue
Skeletal muscle, Cardiac muscle, Smooth muscle
Skeletal muscle
Large, elongated, multinucleated fibers.
Strong, quick, voluntary contractions.
Cardiac muscle
Irregular branched cells bound together
longitudinally by intercalated discs.
Strong, involuntary contractions.
Smooth muscle
Grouped, fusiform cells.
Weak, involuntary contractions.
Skeletal muscle fibers, striations, and location of nuclei
Fibers: Single multinucleated cells
Striations: Present
Location of nuclei: Peripheral, adjacent to sarcolemma
Cardiac muscle fibers, striations, and location of nuclei
Fibers: Aligned cells in branching arrangement
Striations: Present
Location of nuclei: Central
Smooth muscle fibers, striations, and location of nuclei
Fibers: Single small, closely packed fusiform cells
Striations: Absent
Location of nuclei: Central, at widest part of cell
Skeletal muscle connective tissue organization, major locations, and key function
Connective tissue organization: Endomysium, perimysium, and epimysium
Major locations: Skeletal muscles, tongue, diaphragm, eyes, and upper esophagus
Function: Voluntary movements
Cardiac muscle connective tissue organization, major locations, and key function
Connective tissue organization: Endomysium; subendocardial and subpericardial CT layers
Major locations: Heart
Function: Automatic (involuntary) pumping of blood
Smooth muscle connective tissue organization, major locations, and key function
Connective tissue organization: Endomysium and less-organized CT sheaths
Major locations: Blood vessels, digestive and respiratory tracts, uterus, bladder, and other organs
Function: Involuntary movements
Skeletal muscle efferent innervation, contractions, cell response to increased load, and capacity for regeneration
Innervation: Motor
Contractions: All-or-none, triggered at motor end plates
Response to increased load: Hypertrophy
Regeneration: Limited, involving satellite cells mainly
Cardiac muscle efferent innervation, contractions, cell response to increased load, and capacity for regeneration
Innervation: Autonomic
Contractions: All-or-none, intrinsic (beginning at nodes of conducting fibers)
Response to increased load: Hypertrophy
Regeneration: Very poor
Smooth muscle efferent innervation, contractions, cell response to increased load, and capacity for regeneration
Innervation: Autonomic
Contractions: Partial, slow, often spontaneous, wavelike, and rhythmic
Response to increased load: Hypertrophy and hyperplasia
Regeneration: Good, involving mitotic activity of muscle cells
Epimysium
The dense connective tissue that encloses the entire skeletal muscle. It is continuous with fascia and the tendon binding muscle to bone
Perimysium
A thin but dense connective tissue layer that surrounds a fascicle
Endomysium
Delicate connective tissue that surrounds individual muscle fibers
Skeletal muscle development
Skeletal muscle begins to
differentiate when mesenchymal cells
called myoblasts fuse to make longer, multinucleated tubes called
myotubes. They synthesize proteins that make up myofilaments.
As myotubes continue differentiating, the nuclei are moved outward against
the sarcolemma.
Some of the cells do not fuse and differentiate but remain as a group of mesenchymal cells called muscle satellite cells located on the external
surface of muscle fibers. These cells proliferate and produce new muscle
fibers following muscle injury.
Hypertrophy
Tissue growth by an increase in the diameter of individual muscle fibers (muscle cells)
Hyperplasia
Tissue growth by increase in the number of
cells. Common in smooth muscle, whose cells have not lost the ability to divide by mitosis.
Myotendinous junctions
The site of connection between tendon and muscle.
The connective tissue layers (epimysium, perimysium, and endomysium) are continuous with the connective tissue of a tendon at this junction
Myoblasts
Mesenchymal cells that eventually become skeletal muscle.
These fuse to make longer, multinucleated tubes called myotubes
Myofibrils
Cylindrical bundles of thick and thin myofilaments
that fill the sarcoplasm (most of each muscle fiber).
Thick myofilaments: Myosin
Thin myofilaments: Actin & two others
Striations
Alternating light and dark bands of the skeletal
muscle fibers.
A bands
The dark bands on the myofibrils
Overlap between actin and myosin
I bands
The light bands on the myofibrils.
Contains actin and titin
H zone
a lighter region in the middle that bisects the A band.
No overlap between actin and myosin
Z disc
A dark transverse line that bisects each I band.
Sarcomere
The repetitive functional subunit of the fiber, which extends from Z disc to Z disc.
Myosin filaments
Thick; they occupy the A band at the middle region of the sarcomere.
Actin filaments
Thin and helical, and run between the thick
filaments.
The thin filaments have two associated regulatory
proteins: Tropomyosin Troponin
Sarcoplasmic Reticulum
Skeletal muscle fibers are composed mainly of myofibrils. Each myofibril extends the length of the
fiber and is surrounded by parts of the sarcoplasmic reticulum.
The main function of the
sarcoplasmic reticulum is to store Ca2+.
The sarcolemma has deep invaginations called T-tubules
Nerve bundle
The terminal axonal twigs, and the motor end plates
on striated muscle fibers
Muscle contraction steps
- Nerve impulse stimulates acetylcholine release across the synapse, which causes a muscle impulse (membrane depolarization),
- Ca2+ release from terminal cisternae into the sarcoplasm
- Ca2+ binding to troponin causes tropomyosin to change shape and allow the myosin heads to bind the actin subunits, forming cross bridges between thick and thin filaments.
- The myosin heads then pivot as ATP releases energy, which pulls the
thin filaments along the thick filaments.
- As long as Ca2+ and ATP are present, a contraction cycle ensues in which myosin heads repeatedly attach, pivot, detach, and return, causing the filaments to slide past one another, shortening the sarcomere.
5. When the membrane depolarization ends, Ca2+ is again sequestered, ending contraction and allowing the sarcomeres to lengthen as the muscle relaxes.
Which region “disappears”
during contraction?
I band and H zone
Myasthenia gravis
an autoimmune disorder that involves circulating antibodies against proteins of acetylcholine receptors. This interferes with acetylcholine activation of their receptors, leading to periods of skeletal muscle weakness.
The extraocular muscles of the eyes are commonly the first affected.
Dystrophin
A large actin-binding protein located inside
the sarcolemma that is involved in the functional
organization of myofibrils.
Muscle spindles
Functions the stretch receptors
Have afferent sensory and
efferent motor nerve fibers associated with the
intrafusal fibers, which are modified muscle fibers.
Slow, Oxidative Fibers (Type 1) mitochondria, capillaries, myoglobin content, and glycogen content
Mitochondria: Numerous
Capillaries: Numerous
Myoglobin content: High (red fibers)
Glycogen content: Low
Fast, Oxidative-Glycolytic Fibers (Type 2a) mitochondria, capillaries, myoglobin content, and glycogen content
Mitochondria: Numerous
Capillaries: Numerous
Myoglobin content: High (red fibers)
Glycogen content: Intermediate
Fast, Glycolytic Fibers (Type 2b) mitochondria, capillaries, myoglobin content, and glycogen content
Mitochondria: Sparse
Capillaries: Sparse
Myoglobin content: Low (white fibers)
Glycogen content: High
