Histology of Muscular Tissue Flashcards
(24 cards)
What are the 2 types of smooth muscle?
I. Multiunit type
Found in nictitating membrane, ciliary body, iris, pilomotor
muscles and blood vessels.
II. Unitary type
Found in the walls of hollow viscera, intestine, uterus, ureters.
What are the characteristics of multiunit smooth muscle?
A. Each cell is connected to a nerve process.
B. Cells less tightly attached to one another – no direct cell
to cell
contacts (lack gap junctions). Thus reduced cell
coordinated communication.
C. Contraction dependent upon nerve supply.
What are the characteristics of unitary smooth muscle?
- In general smooth muscle cells occurs in
large sheets found in the walls of hollow
viscera, intestine, uterus, ureters. - Cells posses gap junctions and poor
nerve supply. - Function in a syncytical fashion,
contracts together eg. visceral smooth
muscles - Cells have ability of spontaneous
contraction
What is the unit of skeletal muscular contraction
Sarcomere
What results in the striated appearance of skeletal muscle
Actin filaments that slide between myosin filaments
A-band?
Dark.
Myosin + actin overlap.
Length stays the same.
Anisotropic - lacks order
I-band?
Light.
Actin. No overlap in relaxed state.
It shortens as the filaments slide past each other.
Isotropic- ordered
H-band?
Middle of A- band.
Myosin. No overlap in relaxed state.
Disappears when muscle fully contracts.
M-band/line?
Middle of sarcomere where myosin is anchored.
Contains Creatine kinase to maintain ATP for contraction
Z-line/ disk?
Z-line/disk: Boundry of sarcomere where actin is anchored. alpha actinin
Differentiate between the endomysium, perimysium and epimysium of skeletal muscles.
- Endomysium: The innermost layer, surrounding individual muscle fibres. Reticular CT.
- Perimysium: The middle layer, encasing bundles of muscle fibres called fascicles. Dense irregular collagenous CT.
- Epimysium: The outermost layer, covering the entire muscle. Dense irregular collagenous CT.
What is a characteristic of muscle cells regarding their nuclei?
Muscle cells are multinucleated and their nuclei are located at the periphery of the cell, just under the sarcolemma.
Describe the structure of the thick myofilaments.
Myofilaments are composed of myosin-II molecules made of 2 polypeptide chains, (each consisting of an alpha-helical tail and globular head) and two pairs of light polypeptide chains that associate with the globular head of each of the polypeptide chains.
What is titin?
Anchors myosin to Z-line and helps maintain A-band width. (Thick myofilaments make up length of A-band of sarcomere.)
Describe the structure of the thin myofilaments.
2 F-actin polymers/ G-actin monomers twist together in a 2x helix.
Tropomyosin lies in the groove of the helix of F-actin and covers Myosin-II binding sites on G-actin.
Troponin (striated m.) has 3 units:
1)binds to tropomyosin
2)binds to Ca2+
3)binds to actin to prevent it from binding to myosin
Nebulin- regulates actin length.
What is the function of Desmin
found at Z-lines, links adjacent myofilaments
together and attaches myofibrils to costameres (cell
membrane specializations).
Characteristics of red muscle fibres?
Doesn’t fatigue quickly
Prolonged contraction = supported
(slow - twitch fibres)
Smaller than white fibres
Extensive blood supply
Many mitochondria
Myoglobin pigment carries and stores O2
Metabolism = oxidative
Characteristics of white muscle fibres?
Fatigues quickly
X prolonged contraction
Larger than RMF
Less well vascularized
Extensive SR - Ca2+ release
Less mitochondria
Less myoglobin
Metabolism = anaerobic glycolysis
Intermediate muscle fibres
have characteristics of both red and white
fibres.
What are satellite cells in skeletal muscle cells?
spindle-shaped cells located within the basement membrane of the skeletal muscle cell. Contain one heterochromatic
nucleus and considered to be inactive myoblasts which are activated
(by injury) to regenerate muscle fibres.
What connective tissue layer is missing in cardiac muscle and why?
Epimysium - it is too tough, the heart must be able to expand
It still has an endomysium (modified –reticular and collagenous fibres) and a perimysium
What are intercalated disks?
Present in cardiac muscle. Intercalated disks are small gap junctions that allow membrane depolarization to spread to adjacent cells. This area also receives the Z-lines of terminal sarcomeres of the cell branches.
What is atrial natriuretic peptide (ANP)?
Atrial cardiac muscle contains dense granules filled with atrial natriuretic peptide (ANP), a hormone secreted by atrial myocytes in response to increased blood volume and pressure:
It stimulates kidney medullary collecting ducts to secrete sodium and water. This peptide also causes relaxation in the smooth muscle walls of blood vessels.
