Muscle Flashcards
Morphology and Function of skeletal muscle
Striated and voluntary
3 Types of muscle
Skeletal, cardiac, smooth
Morphology and function of cardiac muscle
Striated and involuntary
Morphology and function of smooth muscle
Non-striated and involuntary
What is sarcoplasm?
The cytoplasm of a muscle cell
What is the sarcolemma?
The cell boundary of a muscle cell
Describe the structure of skeletal muscle on macroscopic level
Sarcolemma surrounds a myofibril. Myofibrils are separated from one another by the endomysium. Perimysium contains bundles of myofibrils. Epimysium covers the whole of the muscle.
In order: Epimysium, Endomysium, Perimysium from unit to whole muscle
Endomysium to perimysium to epimysium
Describe the morphology of skeletal muscle
Long (up to 0.3 m), cylindrical multinucleate cells surrounded by external lamina
What are satellite cells in skeletal muscle?
Residual myoblasts still located in mature muscle.
Describe skeletal response to damage
Typically dies. Macrophages clean up and satellite cells proliferate and replace the fiber
How do skeletal muscle fibers form?
Fusion of myoblasts
Where are nuclei of skeletal muscle cells typically found?
Periphery of the cells
Describe communication between cells in skeletal muscle
Each fiber is an island. Single site of innervation. Don’t communicate between fibers.
More force in motion results from recruitment of?
More fibers
Describe the sarcoplasm in skeletal muscle
Filled with cylindrical myofibrils. Striations reflect organization of thick and thin filament bands in the muscle
What is a sarcomere?
The contractile unit of the myofibril and is marked by the z disks in muscle
Light bands in muscle are also known as?
I bands
Dark bands in muscle are also known as?
A bands
What bisects the I bands?
Z disk
What is the band where actin and myosin overlap?
A band
Where in the A band is there no actin?
H band (only myosin)
I band has only what type of cytoskeleton?
Actin
What is desmin?
Anchors myofibril to myofibril (contract together)
What is the function of alpha-actinin and nebulin?
Bind actin to the Z disk
What is the function of titin?
Binds myosin to the z disk
What is thicker actin or myosin?
Myosin
Describe the mechanism of the sliding filament theory of contraction for muscle
In absence of ATP actin and myosin associate. ADP and P present on myosin are released allowing for the power stroke of myosin on the actin filament. ATP bids to the S1 fragment on myosin causing the S1 subsegment to reset with ADP and P
In the power stroke of muscle contraction what happens?
Actin is pushed toward center of the sarcomere when ADP and P are released from myosin.
Contraction does what to the sarcomere?
Pulls the z disks together decreasing the width of the H and I bands.
What does the H band look like in fully contracted muscle
Disappears
Describe regulation of muscle contraction
Troponin (attached to tropomyosin) in actin prevents the binding of the crossbridge head on myosin when relaxed. In presence of Ca+2, troponin changes shape allowing for myosin and actin interaction
Troponin is associated with which myrofibril?
Actin
The connection between actin and myosin is made from whom to whom?
Myosin head walks on actin (towards the + end)
What is a T-tubule?
A deep invagination of the sarcolemma in muscle found only in skeletal and muscle cells. Allows signals to be transmitted to the interior very quickly.
What is a triad in skeletal muscle?
T tubules overlap between A and I bands of sarcomeres and connect with terminal pairs of sarcoplasmic reticulum (located near Z disk)
T tubule is short for
Transverse tubule (deep into muscle)
Function of sarcoplasmic reticulum in muscle?
Ca+2 release mediated by ryanodine receptors. Ca+2 uptake mediated by Ca+2 ATPase
Two types of skeletal muscle fibers
Type I - Red/Slow twitch
Type II - White/Fast Twitch
Where would Type I skeletal muscle be found? Type II?
Leg muscle; Breast muscle
Type I/II skeletal muscle vascularization
Type I has rich vascular supply
Type II has poorer vascular supply
Type I/II Fiber diameter
Type I is smaller and weaker in contraction
Type II is larger and stronger in contraction
Type I/II contraction speed
Type I is slow and resistant to fatigue
Type II is fast and easily fatigued
Type I/II Myoglobin
Type I is rich in myoglobin
Type II is poor in myoglobin
Type I/II Mitochondria
Type I is numerous
Type II is few
Type I/II enzymes
Type I rich in oxidative enzymes
Type II poor in oxidative enzymes
Type I/II sarcoplasmic reticulum
Type I not extensive
Type II extensive
Type I/II innervation
Type I has small diameter nerve fibers
Type II has large diameter nerve fibers
Staining for succinate dehydrogenase will show what?
Fiber types in muscle (dark are Type I (oxidative) and light are Type II (glycolytic))
T or F: Innervation can determine the skeletal muscle fiber type
T
T or F: Damage to the motor neuron can potentially lead to change of skeletal muscle type
T, depends on muscle innervation
T or F: There are intermediate fiber types between Type I and Type II
T (look darkish)
Type I skeletal muscle use what energy source?
Oxidative (Fat)
Type II muscle fibers use what energy source?
Glucose
What is dystrophin?
A connection protein between the inside and outside world in muscle fibers. Loss leads to susceptibility to damage
Duchenne muscular dystrophy is?
Affects young boys only. Tend to have centrally located nuclei, immature cells. Don’t function well.
Describe the muscle spindle
Used for proprioception. Two types of spindle cells: nuclear bag fiber and nuclear chain fiber. Group II sensor fibers and Group Ia afferent fibers detect motion and static gamma motor neurons move with the muscle
Where is the muscle spindle located?
Bag around the external capsule
Characteristics of cardiac muscle
Contract sponateously, branched and connected by intercalated disks, one (sometimes two) central nucleus, glycogen granules, striated but less defined as skeletal muscle, does not regenerate
How are cardiac muscle cells connected?
Intercalated disk in the I band. Fascia adherens with lots of gap junctions with actin interactions
What are Purkinje fibers? Characteristics?
Translate pace maker signals through the heart. Very few myofibrils and have large diameter cells full of glycogen.
What are atrial granules?
Filled with atrial natriuretic peptide to lower blood pressure by increasing sodium excretion and relaxing the blood vessel smooth muscle.
Nuclei of smooth muscle location?
Centrally located
T or F: Smooth muscle is connected by gap junction
T
What are dense bodies?
Linked network of actin, desmin, and vimentin filaments to distribute strain during contraction of smooth muscle
