Lecture 12-13: Muscle Flashcards
Four basic tissues of the body
- Epithelium
- Connective tissue
- Muscle tissue
- Nervous tissue
Muscle cells
specialized cells capable of contraction to produce movement needed for locomotion, propulsion, and pressure regulation
Muscle cells are also known as
myocytes and myofibers
Muscle cells are ____-shaped and originate from
- Spindle
- The mesoderm
Mesenchymal cells (myoblasts) align and fuse together forming multinucleated tubes called
myotubes
Myotubes differentiate, forming
Functional myofilaments
The nuclei are displaced against the plasma membrane
Satellite cells
Cells that don’t differentiate and remain as mesenchymal cells.
Function in muscle repair
Sarcoplasm
- The cytoplasm of muscle cells
- Contains glycogen and myoglobin
Sarcolemma
Plasma membrane of the muscle cells
Sarcoplasmic reticulum
Highly specialized smooth er of a muscle cell that regulates calcium flow
Skeletal muscle make up ___% of body weight
50
Skeletal muscle nuclei
Multiple, peripherally located nuclei
Striations in skeletal muscle are seen in myocytes when cut in
longitudinal section
Epimysium
Muscles are surrounded by this dense irregular connective tissue layer
A whole muscle is made up of many smaller bundles known as _____ surrounded by _______
fascicles
perimysium
Myofibers contain cylindrical bundles of ______ which in turn contain many smaller bundles of _________
myofibrils
myofilaments
Individual myocytes are surrounded by reticular fibers which form
the endomysium
Two myofilaments
myosin and actin
What are the contractile elements of muscles
myofibrils
What cause the striated appearance of skeletal and cardiac muscles
myofibrils
A band and I band
Functional unit of myocyte
sarcomere
At full contraction the Z lines
will be drawn closer to each other
A band
actin and myosin
I band
actin filaments
A band on a stain
- Dark
- Corresponds to the area where the thick and thin filaments overlap
- Composed of myosin and actin
I band on a stain
- Pale
- Composed only of thin actin filaments
Each I band is bisected by
- A protein disc known as the Z line
- Actin filaments are anchored into the Z line
Motion mediated by muscle cells is based on
The conversion of chemical energy (ATP) into mechanical energy by the contractile apparatus of muscle cells
During muscle contraction, actin filaments
slide over the myosin filaments which results in a shortening of the I band
Actin and myosin are held in position by
The myofibril by other proteins (desmin, tropomyosin, troponin)
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
5 steps of muscle contraction
- Bidning of Calcium to Troponin C
- Conformational change in tropomyosin, exposing the myosin-binding site on actin
- Myoisin head binds to actin; ATP->ADP moving myosin head
- Bound thin filaments slide over thick filaments
- Shortening of entire muscle fiber
T-tubule
A deep invagination of the sarcolemma only found in skeletal and cardiac muscle.
Allow depolarization of the membrane to quickly penetrate to the interior of the cell allowing Ca release from the SR
Sarcoplasmic reticulum
- Equivalent to the ER but seen in smooth and striated muscle
- Stores and releases Ca ions to initiate contractions
Terminal cisternae
Expanded ends of the SR
Type I muscle
Slow oxidative
Type 2
Fast glycolytic
Cardiomyocyte
Single cross-striated cell with one central nuclei.
- Has intercalated discs (gap junctions, desmosomes)
- Has sarcoplasmic reticulum and many mitochondria
Intercalated discs function as a ________ and
Syncytium
Attach cardiac muscle cells together, providing strength and ability to function
A true syncytium
A multinucleated cell
E.g. Skeletal muscle cell
Two elements of intercalated discs
- Transverse element
2. Longitudinal element
Transverse element of intercalated disc
- Anchor
- Desmosome - fascia adherens and/or macula adherens
- Serve as strong attachment
Longitudinal element of intercalated disc
- Communication
- Gap junction (nexus) with ion channels
- Propagate electric impulse
Atrial muscle cells contain
membrane bound granules
Where are atrial granules especially numerous?
Right atrium
Atrial granules have an endocrine function due to the presence of
Atrial Natriuretic Factor (ANF)
also known as
Atrial Natriuretic Peptide (ANP)
Two types of cardiac myocytes
- Contractile (red)
- Conductile (pale pink)
___ ____ ____ ____ form the cardiac nodes and fibers involved in impulse conduction
Modified cardiac muscle cells
Purkinje fibers
- Modified cardiac muscle cells with 1 or 2 nuclei, myofibrils ar sparse and restricted to periphery of cells
- Arranged in groups, cels arebiggere and paler than contractile cardiac muscle cells
Smooth muscle cell nucleus
Single centrally located
Are actin and myosin present in smooth muscle
Yes, but not ordered
In smooth muscle cells, cytoplasmic dense bodies
Anchors for myofilaments, like Z bodies
Do smooth muscle cells have desmosomes and gap junctions
yes
Smooth muscle Ttubules and SR
No T-tubules
SR is poorly developed
Smooth muscle shape
Spindle (fusiform)
Surrounded by basal lamina and reticular fibers
Single (unitary smooth muscle)
- Found in visceral organs
- Cells behave like syncytium contracting in a network
- Sparse nerve innervation but cell communicate via multiple gap junctions
Multi-unit smooth muscle
- In iris of eye
- Precise contraction
- Individual innervations of each myocyte
- Lack of gap junctions, function individually
4 functions of smooth muscle cells
- Peristalsis: Wave-like contractions (ex. gastrointestinal tract)
- Vascular dynamics: contraction alters blood flow and important in blood pressure
- Propulsion: urinary bladder, uterus
- Secretion
Contracted appearance of smooth muscle cells
- Oblique arrangement of actin/myosin filaments and the intermediate filament arrangement allow the entire cell to shorten up to 80%.
- Corkscrew appearance of nucleus
Innervation of smooth muscle
- Innervated by ANS
- Allows stimulation and inhibition of muscle cells
- Acetylcholine, norepinephrine, epinephrine are common neurotransmitters
Non-muscle cells
myoepithelial cells
Myoepithelial cells have what origin
Ectodermal
Do myoepithelial cells contain actin/myosin
yes
Can myoepithelial cells be stimulated by hormones?
Yes
Myoepithelial cells are also called
Basket cells (basket shape)
Where are basket cells located?
Salivary/mammary/lacrimal glands
Satellite cells
- Positioned between basal lamina and sarcolemma of muscle cell
- These cells retain mitotic potential and thus can accomplish some repair
- Fibroblasts also form connective tissue (scar) as a part of the repair process
Can cardiac muscle cells regenerate?
Nope
In addition to mitotic activity, new smooth muscle cells may be derived from
pericapillary mesenchymal ccells
All types of muscle repaid is completed by
Scar tissue formation
