6.1 - Lecture - Muscle Flashcards
Endomysium
- Sounds fibers
- immediately surrounds muscle fibers - primary reticular fibers
- transmit force laterally within muscle
Perimysium
- Surrounds fasicles
- recognizable for its major blood vessels found in its thicker CT layer
Epimysium
- Connects fasicles
- Surrounds muscle as a whole
- connects body of muscle to tendon (dense regular CT connecting muscle to bone)
Myotubes
- early myofibers
- they are smaller and still have centrally located nucleus and free cytoplasm
Cardiac Myocyte
- basic unit of cardiac muscle - can have primary nuclei (often just 1)
- joined at the ends by fascia adherens (adhering plate)
- have gap JXN along membranes between adjacent cardiomyocytes - allows for contraction in unison
- have intercalated discs
- sarcoplasmic cone - cytoplasmic space devoid of myofibrils (b/c they bend around central nucleus): filled with mitochondria and cellular organelles
- dyads
Striated Muscle
- general term for muscle in which actin and myosin is organized into parallel bundles of myofibrils
- subtypes : Cardiac muscle and skeletal muscle
Skeletal Muscle
- subtype of muscle typically found connected to bones - generally generates force under direct command of NS
Sarcolemma
cell membrane of a muscle cell
Myofiber
= basic unit of skeletal muscle - bound by sarcolemma
- different from muscle cell because develops from union of several myocytes in order to form syncytium (cells sharing one outer membrane + common cytoplasm)
Myocyte
= muscle cell
Satellite Cells
= adult myocytes persisting outside the cell membrane of the myofiber, but still inside of the external membrane
Describe the parallel arrangement of skeletal muscle
- Adjacent myofibers that travel in the same direction form fasicles - the basic unit of muslce from an anatomical perspective
- within 1 myofiber there are numerous distinct unit of myofibrils containing orderly parallel arrangements of my filaments (thin filament actin and thick filament myosin)
Fascicle
- the basic unit of muscle from an anatomical perspective
- formed by adjacent myofibers that travel in the same direction
Myofibrils
- the numerous distinct units forming one myofiber
- each contains orderly parallel arrangements of myofilaments
Myofilaments
- thin filament actin
- thick filament myosin
Sarcomeres
- repeating organized units within myofibrils
- within a sarcomere actin and myosin are held in an orderly hexagonal packing by structural proteins
Alpha-actinin
- one of the structural proteins of a sarcomere
- holds actin
- forms the Z-line
- arranged perpindicular to the myofilaments
Myomesin and C-protein
- structural proteins of a sarcomere
- holds myosin
- forms the M-line
- arranged perpindicular to the myofilaments
Nebulin and titin
- structural proteins of a sarcomere
- run in the parallel direction with the myofilaments
- binds actin to the alpha-actinin of the Z-line
Troponin and tropomyosin
- regulate the binding of actin and myosin
A-band
- formed by thick myosin molecules
I-band
- formed by the absence of myosin
- will change with contraction
H-band
- formed by the absence of actin at the center of the sarcomere
- will change with contraction
Costameres
= intermediate filaments
- bind adjacent myofibrils to the cell membrane
- a clinically important protein that is part of this = dystrophin
Dystrophin
- A clinically important protein that is included in the costmeres (intermediate filaments that connect to the cell membrane and myofibrils)
What are the three types of skeletal muscle
Type I = Red
Type IIa = intermediate
Type IIb = white
- each muscle has a characteristic ratio of the three, which may change through exercise or disease state
Type I fibers
- slow contracting
- non-fatiguing
- aerobic fibers
- mainly derive energy from oxidative metabolism
Type IIa
- have properties intermediate to types I and IIb
Type IIb
- fast contracting
- easily fatiguing
- anerobic
- mainly derive energy from glycolytic pathways
External membrane
- analogous in structure to basement membrane of the epithelia
- separates skeletal muscle fibers from the surrounding CT
Endomysium
- CT connected to the external membrane
Perimysium
- surrounds each fascicle
- is thicker, tube-shaped layer of CT (compared to endomysium)
Epimysium
= CT fascia that binds the anatomical form of the muscle to the surrounding tissues
- is external to the perimysium
Cardiac muscle
= type of striated muscle specific to the heart
- specialized to support rhythmic contraction
- cardiac myocytes are smaller than skeletal muscle myofibers
- typically larger than smooth muscle myocytes
- one or sometimes two nuclei - centrally located
- arrangement of myofilaments, myofibrils, sarcomeres is identical to skeletal muscle
- have sarcoplasmic cone (space without myofilaments - filled with mitochondria and other organelles)
- adjacent myocytes are connected by gap jxns and bound physically by fascia adherens (which creates intercalated disc pattern in LM)
Sarcoplasmic Cone
- space devoid of myofilaments
- created due to the central nucleus in cardiac myocytes
- filled with mitochondria and other organelles
- only in cardiac myocytes
Fascia adherens
- physical connection between adjacent cardiac myocytes
- usually longitudinally physically binding them?
- only in cardiac myocytes?
Intercalated disc
- specific to cardiac myocytes?
= the name for the pattern created by the appearance of the fascia adherens in the LM
Purkinje Fibers
= modified cardiac myocytes
- contain fewer myofilaments
- run in characteristic anatomical pathways in the subendocardium
- deliver electric potentials to cardiac muscle
Smooth muscle
= evolutionarily oldest muscle
- consists of fibroblast-like cell that expresses myosin
- an involuntary muscle
- forms layers in many organs such as the GI, Bladder, uterus, prostate
What are the two types of smooth muscle
Unitary
Multiunit
Unitary Smooth muscle
- smooth muscle acts as one mechanical unit
- transmitting signals from relatively few axons among cells via gap JXNs
(ratio of axons - cells is greater than 1/10?)
Multiunit Smooth Muscle
- Contains closer to a 1:1 ratio of axons to muscle cells
- allows for finer, graded control in places where it is needed (i.e. Iris)
Random fact about smooth muscle cells in the uterus from the syllabus (p.114)
Smooth muscle cells in the uterine myometrium are hormonally responsive and grow up to 200 microns in length during pregnancy
NMJ
- a specialized structure joining a motor nerve axon with a muscle
- is most specialized in skeletal muscle
- also exists in rudimentary form in smooth muscle
Junctional folds
- local invaginations of the sarcolemma underneath the point of contact with the axon
- designed to increase surface area + the number of Ach Receptors present
Muscle spindles
= sensory structures in muscle designed to sense the position and state of stretch of the muscle
- composed of modified muscle fibers (bag and chain fibers)
Bag and Chain fibers
= modified muscle fibers that compose the muscle spindles
- FXN in sensing stretch of the muscle
- sensory fibers originate at the surface of the bag and chain fibers to sense stretch
- motor fibers (including gamma motor neurons) innervate the bad and chain fibers to alter their sensitivity
Gamma motor neurons
- unique motor fiber that innervates the bag and chain fibers comprising the muscle spindles
- FXN: alter the sensitivity of the bag and chain fibers
Golgi Tendon Organ
- functionally similar structure to the muscle spindles
- positioned between the muscle fibers and their connected tendon (i.e. in parallel with the muscle fiber)
- primarily associated with reflexive responses of the muscles
