Muscle Flashcards
Describe muscle cells.
-Special cells that contract to produce movement for:
>locomotion
>propulsion
>pressure regulation
-also known as myocytes & myofibers
-spindle shaped
-originate in mesoderm (from myoblasts)
Define sarcoplasm, sarcolemma, & sarcoplasmic reticulum.
- Sarcoplasm = cytoplasm that contain:
-glycogen
-myoglobin - Sarcolemma = plasma membrane
- Sarcoplasmic membrane = smooth ER
-regulates calcium flow
-seen in smooth & striated muscle
Muscle classification.
Describe the histology of skeletal, cardiac, and smooth muscle.
Describe where you would find skeletal muscle.
-voluntary sphincters in GI tract, urinary system, esophagus, tongue
Describe skeletal muscle development.
- Mesenchymal cells (myoblasts) fuse together to form multinucleated tubes = myotubes
- Myotubes differentiate to form myofilaments & the nuclei are against the PM
- Some cells dont differentiate & stay as mesenchymal stem cells = satellite cells (help with muscle repair)
Describe skeletal muscle organization.
-muscles surrounded by dense irregular CT = epimysium (fascia)
-whole muscle made of smaller bundles = fascicles (surrounded by perimysium)
-myofibers contain myofibrils which contain myofilaments
Cross section of striated muscle (picture)
-endomysium = individual myocytes surrounded by reticular fibers
Describe myofibers VS myofibrils.
- Myofibers [composed of myofibrils] = multinucleated cells with peripheral nuclei (hypolemmal)
- Myofibrils = bundles of repeating contractile proteins called myofilaments (striations)
>thick myosin & thin actin = contractile proteins
>tropomyosin = regulatory protein
Cross section VS longitudinal skeletal muscle (picture)
striations can be seen
Describe the striations in myofibrils.
- A band = dark (actin & myosin)
-thick & thin filaments overlap - I band = pale (actin)
*I band bisected by protein disk = Z line
*Actin filaments anchored onto Z line
Describe the sarcomere.
-contractile functional unit of myocyte
-sarcomere includes all elements in between each Z line
-at contraction Z lines (discs) are closer
Describe what happens during muscle contraction.
-motion is based on conversion of ATP to mechanical energy
-each sarcomere shortens
-during contraction actin filaments slide over the myosin filaments = shorten I band
-myofilaments are held in place in the myofibril by other proteins (desmin, tropomyosin, troponin) length is constant
Describe the muscle contraction steps.
- Binding of Ca to TnC
- Change in tropomyosin = exposes myosin binding site
- Myosin head binds to actin: ATP -> ADP moving myosin head
- Bound thin filaments slide over thick filaments
- Shortening of muscle fiber
Describe the transverse tubule system.
- Myofibrils
- SR
- Terminal cisterna = expanded ends of SR
- Transverse T tubule = deep tubular finger like invaginations of sarcolemma (PM) in skeletal & cardiac muscle
Describe T tubules.
-allow depol of membrane to penetrate interior of cell = Ca release from SR
Describe the physiologic skeletal muscle classifications.
- Rates of contraction (fast/slow)
- Rates of fatigue (fast/slow)
- Types of metabolism (oxidative, glycolytic, mixed)
Describe type 1 muscles.
“Red”
-slow
-dark = myoglobin (transfers O2)
-aerobic metabolism = fatigue resistant
-high fat, low glycogen
-many mitochondria
EX: postural & pectoral muscles
Describe type 2 muscles.
“White”
-fast
-anaerobic metabolism = prone to fatigue
-low fat, high glycogen
-less myoglobin & mitochondria
1. Type 2A (intermediate) = mixed oxidative-glycolytic, slow fatigue
2. Type 2B = fast contracting, fast fatigue, glycolytic (depend on glycogen for energy)
Skeletal muscle summary (picture)
Describe cardiac muscle.
-single cell with a central nucleus
-cross striated
-intercalated discs: gap junctions & desmosomes
>function as a syncytium
-SR
-many mitochondria
-requires O2
Describe intercalated discs.
- Transverse element
-anchor
-desmosomes = fascia adherens/macula adherens
-strong attachment - Longitudinal element
-communication
-gap junctions (nexus) with ion channels
-propagate electric impulse
Describe the 2 types of cardiomyocytes.
- Contractile = red
- Conductive = pale pink
>purkinje cell = neuronal cell bodies in cerebellar
>purkinje fiber = modified cardiac muscle fiber in subendothelial tissue
—conduct impulses through heart
—form cardiac nodes
Describe purkinje fibers.
-1 or 2 nuclei
-sparse myofibrils (periphery only)
Describe smooth muscle cells.
-single central nucleus
-no striations
-no myofibrils
-myofilaments (not ordered)
>cytoplasmic dense bodies = anchors for myofilaments (like Z bodies)
-desmosomes & gap junctions
-no T-Tubule
-SR poorly developed
-involuntary
-ANS innervation
-spindle shaped (fusiform) surrounded by basal lamina & reticular fibers)
Describe single (unitary) smooth muscle.
-found in visceral organs
-syncytium
-sparse nerve innervation
-communicate via gap junctions
Describe multi-unit smooth muscle.
-found in iris
-precise contraction
-individual innervation of each myocyte
-lack gap junctions
-function individually
Describe the function of smooth muscle.
- Peristalsis = contractions (EX. GI tract)
- Vascular dynamics = contraction alters blood flow
- Propulsion = urinary bladder, uterus
- Secretion
Describe the tunica muscularis of the luminal organs.
Describe myoepthelial cells.
-ectodermal origin
-actin/myosin
-similar to smooth muscle
-stimulated by hormones (mammary gland)
-basket cells
-location: salivary, mammary, lacrimal glands
-contractile non-muscle
Describe satellite cells.
-between basal lamina (intact) & sarcolemma
-mitotic potential
-fibroblasts form CT (scar tissue)
-cardiac muscle can’t regenerate
-new smooth muscle derived from pericapillary mesenchymal cells
