Muscle (Exam II) Flashcards
What is a sarcoplasm, sarcolemma and sarcoplasmic reticulum?
Sarcoplasm - cytoplasm of muscle cells
Sarcolemma - plasma membrane of muscle cells
Sarcoplasmic Reticulum - highly specialized smooth endoplasmic reticulum of a muscle cell that regulates calcium flow.
What does sarcoplasm contain?
Myoglobin and glycogen.
List some important characteristics of Skeletal Muscles
Multiple, peripherally located nuclei (hyolemmal nuclei)
Striations are seen when cut in longitudinal section
Voluntary muscles
How is skeletal muscle formed?
Derived from mesoderm. Mesenchymal cells (myoblasts) align and fuse together forming multinucleated tubes called Myotubes. Myotubes differentiate forming functional myofilaments and the nuclei are displaced against the membrane.
How are satellite cells formed?
Cells that do not differentiate and remain as mesenchymal cells are called satellite cells or myosatellite cells.
Describe the breakdown of a muscle belly (the different components).
Muscle –> Muscle Fasicles –> Muscle Fibers –> Muscle Fibrils –> Myofilaments
What is epimysium, perimysium and endomysium?
Epimysium - surrounds muscles (dense irregular CT layer)
Perimysium - surrounds muscle fasicles (dense CT)
Endomysium - surrounds muscle fibers (myofibers) (reticular fibers CT)
What are myofilaments? How can you see them?
Myosin and Actin - contractile elements
Only seen in Electron Microscopy
What is the A-band, I-band, H-zone, Z-line, M-line, Sarcomere?
A-band - Dark Band - myosin and potentially actin
I-band - Light Band - actin only (thin)
H-zone - Myosin only
M-line - middle line, where myosin is anchored
Z-line - where actin is anchored
Sarcomere - smallest contractile element of skeletal muscle from Z-line to Z-line.
What covers the myosin binding sites on actin until contraction?
Tropomyosin
What is G actin vs. F actin?
G actin - disassembled components of actin thin filament
F actin - assembled components of thin filaments (troponin and tropomyosin)
Describe the steps of muscle contraction
- Binding of calcium to troponin C (TnC)
- Conformational change in tropomyosin, exposes the myosin binding site on actin.
- Myosin head binds to actin - ATP –> ADP as myosin head moves.
- Actin slides over myosin
- Shortening of entire muscle fiber
What is a transverse tubule?
T-tubule.
Deep invagination of the sarcolemma - only found in skeletal and cardiac muscle.
Invaginations allow depolarization of membrane to quickly penetrate the interior of the cell allowing Calcium release from the sarcoplasmic reticulum.
What are the 2 types of skeletal muscle fiber types?
Type I - Red Muscle - Slow Twitch
Type II - White Muscle - Fast Twitch
Describe Type I, “Red”, Slow Twitch Muscle.
Dark color. Rich in myoglobin - to help transfer O2, accounts for dark color. Aerobic metabolism - fatigue resistant. High fat, low glycogen content. Many mitochondria.
Describe Type II, “White”, Fast Twitch Muscle
Anaerobic metabolism - more prone to fatigue.
Low fat, high glycogen.
Less myoglobin and a few mitochondria
List some important characteristics of Cardiac Muscle
Single cell with one central nucleus.
Cross striated.
Has intercalated discs - gap junctions, desmosomes
Has sarcoplasmic reticulum
Has many mitochondria - aerobic - requires a lot of O2
What are intercalated discs?
Attach cardiac muscle cells to each other providing strength and the ability to function as a syncytium.
Consist of:
Transverse Elements: anchor, desmosome (Fascia adherens, macula adherens), serve for strong attachment
Longitudinal Elements: communication, gap junction with ion channels, propagate electrical impulse.
What are the 2 types of cardiomyocytes?
Contractile - bulk of myocardium - red
Conductile - purkinje fibers - pale pink - bigger, no cross striations, sometimes 2 nuclei
What are purkinje fibers?
Modified cardiac muscle cells with 1 or 2 nuclei, myofibrils are sparse and restricted to periphery of cell
They are arranged in groups, cells are bigger and paler than contractile cardiac muscle cells
Describe the important characteristics of smooth muscle cells.
Single, centrally located nucleus. No striations, no myofibrils. Actin and myosin are still present but are not ordered (no Sarcomere) Cytoplasmic dense bodies represent anchors for myofilaments Desmosomes and gap junctions No T-tubules, No Sarcoplasmic reticulum PSNS and SNS innervation Contraction is involuntary.
Where is single (unitary) smooth muscle found? How do they work? What is their innervation like?
It is found in visceral organs.
Cells behave like a syncytium - contracting in a network
Sparse nerve innervation but cell communicate via multiple gap junctions - pass on quickly, cells behave like a network
Where is multi-unit smooth muscle found? How does it work? What is the innervation like?
Found in iris of eye.
More precise contraction.
Individual innervation of each myocyte.
Lack of gap junctions - they function individually
What are some of the functions of smooth muscle cells?
Peristalsis
Vascular dynamics (constriction and dilation)
Propulsion (urinary bladder, uterus)
Secretion (minor role)
What are the three tunics of luminal organs?
Tunica Mucosa (mucous membane) Tunica Submucosa Tunica Muscularis (1 - innermost circular layer (longitudinal section), 2 - outer longitudinal layer (cross section))
What are dense bodies (or electron dense bodies)?
Serve as attachment sites for myofilaments - cytoplasm contains numerous myofilaments
What happens to the nucleus in the contracted state of a smooth muscle cell?
Adopts corkscrew appearance.
What are myoepithelial cells? Can they be stimulated by hormones? What is another name for them? What is their germ layer origin? Where are these cells located?
Contractile cells but NOT muscle. But DO contain actin and myosin - similar to smooth muscle.
Can be stimulated by hormones.
Basket cells - have basket shape.
Of ectodermal origin (not mesoderm like muscle).
Located in salivary/mammary/lacrimal glands.
What are myofibroblasts?
Role in wound contraction - scars contracting down.
What are the 2 types of non-muscular contractile cells?
Myoepithelial cells.
Myofibroblasts.
Can skeletal muscle repair?
Has limited regeneration capacity.
Satellite cells - can respond to injury in skeletal muscle - they are positioned between basal lamina and sarcolemma of muscle cells.
Satellite cells retain their mitotic potential and thus can accomplish some repair.
Fibroblasts also form connective tissue (scar tissue) as part of the repair process.
Can smooth muscle repair?
Has limited regeneration. In addition to some mitotic activity, new smooth muscle cells ma be derived from pericapillary mesenchymal cells.
Can cardiac muscle repair?
NO they lack the ability to regenerate - scar tissue formation only
