Muscle Tissue Flashcards
4 basic tissues of the body:
Epithelium, connective tissue, muscle tissue, nervous tissue
Muscle cells contract to produce movement needed for:
Locomotion, propulsion, and pressure regulation
Other names for muscle cells
Myocytes and myofibers (cell and fiber are used interchangeably)
What shape are muscle cells and where do they originate?
Spindle-shaped and originate from the mesoderm (myoblasts)
Myotubes
Multinucleated tubes of mesenchymal cells that have aligned and fused together
Myofilaments
Differentiated myotubes; the nuclei are displaced against the plasma membrane
Satellite cells
Undifferentiated mesenchymal cells that function in muscle repair
Sarcoplasm
Cytoplasm of muscle cells, contains glycogen and myoglobin
Sarcolemma
Plasma membrane of the muscle cell
Sarcoplasmic reticulum
The highly specialized smooth ER of a muscle cell (regulates calcium flow)
How much of the body weight is made up of skeletal muscle?
50%
T/F: Skeletal muscles are involuntary muscles.
False - voluntary
Epimysium
The dense irregular connective tissue layer that surrounds muscles
Fascicles
Many smaller bundles that make up a whole muscle; composed of myocytes and myofibers
Perimysium
Surrounds fascicles; dense connective tissue
Myofibrils
Cylindrical bundles contained in myofibers
Myofilaments
Smaller bundles found in myofibrils; composed of actin and myosin - contractile proteins and tropomyosin - regulatory proteins
Endomysium
Reticular fibers surrounding individual myocytes
Describe the components of the I and A bands.
I band - actin only A band - actin and myosin overlap
Sarcomere
Contractile or functional unit of the myocyte; includes all elements from Z line to Z line; at full contraction, Z lines (discs) will be drawn closer to each other
Z-line
A protein disc that bisects the I band; actin filaments are anchored here
Sliding filament model
Each sarcomere shortens –> myofilament length is constant –> I band shortens, almost disappears –>thin filaments slide past thick filaments
Summation of all sarcomere shortening produces contraction of the muscle cell
Steps in muscle contraction
- Binding of calcium to troponin C
- Conformational change in tropomyosin, exposing the myosin-binding site on actin
- Myosin head binds to actin; ATP –> ADP moving myosin head
- Bound thin filaments slide over thick filaments
- Shortening of entire muscle fiber
T-tubules (transverse tubules)
A deep invagination of the sarcolemma (plasma membrane) only found in skeletal and cardiac muscle cells; these invaginations allow depolarizaton of the membrane to quickly penetrate to the interior of the cell allowing calcium release from the sarcoplasmic reticulum
Sarcoplasmic reticulum
Equivalent to the endoplasmic reticulum but seen in smooth and striated muscle; stores and releases calcium ions to initiate contractions
Identify and describe each numbered structure
1) Myofibrils, made of myosin and thin actin myofilaments
2) Sarcoplasmic reticulum, stores and releases calcium
3) Terminal cisterna, expanded ends of sarcoplasmic reticulum
T) Transverse T-tubule, deep tubular finger-like invaginations of sarcolemma (plasma membrane) of skeletal muscle cell create anastomosing network of tubules
Describe Type 1 skeletal muscle fibers
- “red muscle”
- slow twitch
- dark color - rich in myoglobin which accounts for dark color
- aerobic metabolism –> fatigue resistant
- high fat, low glycogen content
- many mitochondria
- myoglobin - to help transfer oxygen
Describe Type 2 skeletal muscle fibers
- “white muscle”
- fast twitch
- anaerobic metabolism –> more prone to fatigue
- low fat, high glycogen content
- less myoglobin and a few mitochondria
Describe cardiac muscle
- cardiomyocyte = myocardiocyte = cardiac myocyte
- single cell with one central nucleus
- cross striated
- has intercalated discs
- gap junctions
- desmosomes
- has sarcoplasmic reticulum
- has many mitochondria (up to 20% cell volume) - requires a lot of O2
Intercalated discs
Attach cardiac muscle cells to each other, providing strength and the ability to function as a syncytium
- a true syncytium is a multinucleated cell (i.e. skeletal muscle cell)
- consist of
- transverse element
- anchor
- desmosome - fascia adherens and/or macula adherens
- serve for strong attachment
- longitudinal element
- communication
- gap junction (nexus) with ion channels
- propagate electric impulse
- transverse element
Identify the components of the intercalated disc
- macula adherens
- gap junction
- fascia adherens
Atrial myocardium
Atrial muscle cells contain membrane bound granules that are especially numerous at the right atrium; atrial granules have an endocrine function due to the presence of ANF/ANP
Name and describe the two types of cardiomyocytes
- contractile - red
- conductile - pale pink
Purkinje fibers
Modified cardiac muscle cells with 1-2 nuclei, myofibrils are sparse and restricted to periphery of cell; arranged in groups, cells are bigger and paler than contractile cardiac muslce cells
Describe smooth muscle cells
- single centrally located nucleus
- no striations
- no myofibrils!
- actin and myosin myofilaments are present but are not ordered
- cytoplasmic dense bodies represent anchors for myofilaments (like Z bodies)
- desmosomes and gap junctions
- no T-tubules and sarcoplasmic reticulum is poorly developed
- spindle shaped (fusiform) cells surrounded by a basal lamina and reticular fibers
- parasympathetic and sympathetic innervations
- contraction involuntary
Single unit (unitary) smooth muscle
- found in visceral organs
- cells behave like syncytium contracting in a network
- sparse nerve innervation but cells communicate via multiple gap junctions
Multi-unit smooth muscle
- found in iris of eye
- precise contraction
- individual innervation of each myocyte
- lack of gap junctions, function individually
Functions of smooth muscle
- peristalsis - wave-like contractions
- vascular dynamics - contraction alters blood flow and important in blood pressure
- propulsion
- secretion (minor role)
Dense bodies
The smooth muscle equivalent of Z discs of skeletal and cardiac muscle; note cigar-shaped nucleus
Innervation of smooth muscle
- Innvervated by ANS (sympathetic and parasympathetic system)
- allows stimulation (fast & slow) and inhibition of muscle cells
- acetylcholine, norepinephrine, epinephrine are common neurotransmitters
Myoepithelial cells
- contractile non-muscle cells
- ectodermal origin
- contain actin/myosin
- similar to smooth muscle
- can also be stimulated by hormones (mammary gland)
- basket-like shape –> known as basket cells
- location: salivary/mammary/lacrimal (crying) glands
Satellite cells
Skeletal muscle has limited regeneration capacity, and these cells retain mitotic potential and thus can accomplish some repair; positioned between basal lamina and sarcolemma of muscle cell; fibroblasts also form connective tissue (scar) as part of the repair process
Muscle regeneration
- cardiac muscle cells lack the ability to regenerate
- smooth muscle regeneration is limited; in addition to some mitotic activity, new smooth muscle cells may be derived from pericapillary mesenchymal cells
- in all muscle types, repair is completed by scar tissue formation
