Muscle (Physiology and Histology) Flashcards
What are the 3 types of muscle?
-Skeletal
-Cardiac
-Smooth
What are the features of skeletal muscle?
-Voluntary
-Striated
-Many nuclei on the periphery of the cell
What are the features of cardiac muscle?
-Nonvoluntary
-Striated
-Once centrally located nuclei
-smaller/shorter cells
What are the features of smooth muscle
-Involuntary
-Non striated
-one centrally located nucleus
What are the 4 functional characteristics of skeletal muscle?
-Excitability
-Contractility
-Extensibility
-Elasticity
Describe the structure of the sarcomere
the contractile unit of the myrofibril
-I band
-A band
-Z disc
-H zone
-M line
What is the sarcolemma?
The membrane of a muscle cell
Explain the sliding filament model of contraction
actin has myosin binding sites that are covered by tropomyosin which are held in place by troponin. Once Ca moves into the cell, troponin moves, allowing tropomyosin to move. Once ATP bind to the myosin, it can bind to actin. The power stroke occurs (contraction), once ATP bind to myosin again, it unbind actin.
Explain signal transmission at a neuromuscular (skeletal) junction
-Signal travels down axon
-Reaches motor end plate
-Acetylcholine vesicles release and bind to receptor on postsynaptic cell
-depolarizes cell
-signal travels down t tubule of postsynaptic cell
-activates DHPR, which activates RyR
-RyR opening allows Ca to flow out of SR into intracellular space
-Ca initiates troponin movement
What are the 7 problems that can occur at the neuromuscular junction?
-Synaptic fatigue
-Hypocalcemia
-Denervation hypersensitivity
-Botulinum toxin
-Alpha toxin
-Myasthenia gravis
-Nerve gas
What is titan?
the molecular spring of the sarcomere
What are the proteins that anchor titan to the M band?
Myomesin and M-protein
What is the major neurotransmitter of the peripheral nervous system?
Acetylcholine
What are the 3 phases of a muscle twitch?
-Latent
-Period of contraction
-Period of relaxation
What is the order of motor neuron recruitment?
-Motor 1: slow oxidative
-Motor 2: fast oxidative
-Motor 3: fast glycolytic
What is the term for complete contraction?
fused tetanus
When does fused tetanus occur?
at complete contraction when ALL motor neurons are recruited
What are the differences between smooth muscle and skeletal
-Dense bodies (similar to z discs) which connect to other cells
-No t tubules, instead the sarcolemma has calveoli
-No neuromuscular junction
-Can propagate signal through gap junctions
What are calveoli?
invaginations of the smooth muscle sarcolemma that contain a high density of Ca channels
How do neurotransmitters reach the postsynaptic cell of smooth muscle?
Multiple varicosities release neurotransmitter across a wide synaptic cleft
What accounts for longer lasting contraction effects of smooth muscle?
alot of metabotropic receptors
Define isotonic contraction
-Concentric/eccentric contraction
Define isometric contraction
z discs stay in place but actin and myosin are bound
Why are type I (slow oxidative) muscle fibers so dark?
They have alot of myoglobin to use in aerobic mechanisms
List 4 histological features of skeletal muscle
-long unbranched fibers
-continuous basement membrane around each fiber
-no cell-cell communication
-nuclei pushed out to periphery
What is a satellite cell?
a skeletal muscle nucleus that contains stem cells
What is the difference between epimysium, perimysium, endomysuim?
-Epimysium: dense irregular CT around muscle belly
-Perimysium:CT that creates fascicles
-Endomysium: loose CT, mostly reticular fibers that surround in between individual muscle fibers
What CT continues into muscle tendon?
epimysium
What are intrafusal fibers?
specialized muscle fibers in the muscle spindle
What is the muscle spindle?
a sensory organ in the muscle that relays information about where the muscle is in space
What is the role of the tendon organ?
Located within tendons, attached to the epimysium that conveys stretch information
What are the 3 main histologic differences between skeletal and cardiac muscles?
cardiac is shorter/branched, has intercalated discs, and one central nucleus
What is an intercalated disc?
Where cardiac muscle cells fuse
What helps cardiac muscle with coordinated contraction?
gap junctions
Where do cardiac muscle gap junctions typically sit?
intercalated discs
True/False: cardiac muscles have an epimysium
False
Name 3 specialized myocytes of the heart
SA node, AV node, purkinje fibers
What are Purkinje fibers?
Specialized myocytes that are conducting fibers of the heart
What muscle type has limited CT (endomysium)?
smooth muscle
