Lecture 12 Flashcards
Which muscle type is striated and voluntary?
Skeletal mm
Skeletal mm fibers develop enbryologically from what?
myoblasts: mononucleated cells that fuse into long fibers which become peripheral and multinucleated.
Which muscle type is visceral or involuntary?
Smooth mm.
Which muscle type is smooth and not striated?
smooth mm… duh!
What muscle types are multinucleated ?
smooth mm.
What muscle types are mononucleated AND striated?
cardiac mm.
Branchiomeric mm is associated with ….
pharyngeal arches
describe branchiomeric mm
associated with pharyngeal arches
somewhat of a transition between smooth and striated
innervated by cranial nerves
what innervates the branchiomeric muscles?
cranial nerves
Voluntary muscle:
- muscle whose action is normally controlled by an individual’s will;
- mainly skeletal muscle, composed of parallel bundles of striated, multinucleate fibers.
Involunary muscle:
• a muscle that contracts without conscious control and found in walls of internal organs such as stomach and intestine and bladder and blood vessels (excluding the heart)
Origin (proximal attachment:)
usually proximal, may be fixed with regard to movement
Insertion (distal attachment)
usually distal, Usually more moveable
Tendons:
attachments between muscle fibers and bone
what are tendons made from?
dense collagenous connective tissue
Tendons are surrounded by…
peritendineum
Tendons are poorly/richly vascularized.
POORLY! Think about how long it takes to heal a sprained ankle!
Aponeuroses:
flat, fan shaped tendons, typically giving rise to other tendons
- Describe the gross hierarchical organization of a skeletal muscle, including the connective tissue partitions that subdivide the muscle.
Myofilament, myofibril, myofiber, Fascicle, Muscle
What are the two types of myofilament:
myosin and actin
which are the thick filaments
myosin
which are the thin filaments:
actin
Myofilaments are organized into
sarcomeres
What is a myofibril?
chain of sarcomeres
What is a myofiber?
bundle of myofibrils
Referred to as a muscle cell
Each fiber formed from may fused myoblasts
Endomysium
surrounds each muscle fiber
Lies outside the sarcolemma (cell membrane)
Perimysium
surrounds each fascicle
Epimysium
surrounds each muscle, becomes continuous with tendons, attached to periosteum
- Describe the microscopic organization of the sarcomere and changes that occur when the sarcomere shortens during contraction.
Sarcomere Arrangement
o Myosin and actin filaments are organized into cylindrical units that are aligned end-to-end to form the myofibrils.
o Each cylindrical unit is called a sarcomere.
o A myofibril is, therefore, a chain of sarcomeres.
Sarcomere structure:
•Z-lines:
• Separate adjacent sarcomeres in a fibril
• Composed of Z-actin
• Anchor actin filaments
• Located at each end of a sarcomere
•I-bands:
• Located on either side of Z-line and A-band
• Make up ends of sarcomere
• Composed entirely of actin
• Width changes during contraction
•A-bands:
• Located between two I bands in middle of sarcomere
• Composed of both actin and myosin
• Represents length of myosin chains
• Does not change width during contraction
•H-band:
• In middle of each A-band
• Composed entirely of myosin
• Band width changes during contraction
Dark, slow fibers
fatigue resistent, contract slowly, oxidative phosphorylation, large # mito, high myoglobin, low ATPase concentration
Light, Fast fibers
white, fatigue easy contract rapidly (fast twitch), rely on glycolysis, small number of mitochondria, low concentration of myoglobin, high concentration of ATPase.
Where are phasic fibers found?
all vertebrate groups
Do phasic fibers propagate an action potential?
no
Which types of fibers are not multiply innervated?
phasic
where would we find tonic fibers?
non-mammalian vertebrates
Describe where tonic fibers are used:
slow, sustained postural activities. Single nerve cell innervates many fibers (motor unit) but each fiber is innervated by more than one nerve cell.
Contract slowly
DO NOT PROPAGATE AN AP
Describe an isometric contraction
length does not change
describe an isotonic contraction
length of mm does change
Concentric
shorter
eccentric
longer
Describe a motor unit and its relation to “all or none”
- A single nerve cell (neuron) may innervate from a few to several hundred myofibers.
- A neuron and the myofibers it innervates constitute a motor unit.
- When a neuron fires, all the myofibers in the motor unit contract.
- All-or-none really refers to a motor unit.
