Muscle Histology Flashcards
What are thin filaments composed of?
G-actin monomers that bind to each other forming a double stranded and twisted F actin filament
What are thick filaments composed of?
They are composed of myosin that consist of two identical heavy chains and two pairs of light chains.
During contraction the length of what does not change?
The length of thick and thin filaments.
What length does decrease during contraction?
The length of the sarcomere decreased-
Z lines move closer together, the width of the H and I hands decrease
Describe the first step of the cross bridge cycle.
No ATP is bound to myosin and the myosin head is tightly bound to the actin thin filament
What is the second step of the cross bridge cycle?
The binding of ATP to the myosin head produces a confirmation change in myosin protein. This results in the dissociation of myosin from the actin filament.
What is the fourth step of the cross bridge cycle?
Myosin binds to actin
What is the last step of the cross bridge cycle?
Myosin binds actin, ADO is released. There is a sliding of the thin filament toward the center of the sacromere and a return of myosin to the rigor position.
Is calcium high or low during relaxation?
Low.
Calcium returns to the SR
What is acetylcholine eliminated by?
Acetylcholinesterase present within the the basal lamina of the synaptic cleft
What is the difference between small and large motor movements?
Small motor units have fewer muscle cells innervated per axon.
Muscles requiring fine motor control have small motor units whereas large muscles used for gross/powerful movements have large motor units
Are fibers of the same motor unit the same type?
Yes they are either type 1 or type 2
What are proprioreceptors?
They provide feedback on the contractile state of the muscle, tension in tendon, and position of the joint
What do golgi tendons organs do?
They are bare sensory nerve endings in the tendon that inhibit muscle contraction when it senses excess tension placed on the tendon by a muscle
What are Z lines? What do they contain?
They define the boundary of each sacromere.
They contain actin binding protein, alpha actinin
What are I bands?
Contain actin thin filaments.
The width decreases during contraction
What is an A band?
They are composed of thick and thin filaments.
The width remains constant during contraction
What is an H band? What is it composed of?
It is the central region of the A band which only contains thick filaments.
The width decreases during contraction.
What is the M line?
Middle of the H band.
It had overlapping tails of thick filaments
What is the third step of the cross bridge cycle?
ATP is hydrolysis by the myosin head ATPase causing a further conformational change in the myosin movement at hinge, angle between head and tail increases. ADP and Pi remain bound to the myosin head. This lines up the head with a new myosin binding site on the thin filament
What happens when acetylcholine binds to a receptor on muscle sacrolemma?
Depolarization of cell membrane
Where is acetylcholine esterase located?
Basal lamina of the synaptic cleft
What are proprioreceptors? What do they do?
They are the sensory organs in skeletal muscle tendons In joints.
They provide feedback on contrile state of the muscle, the tension in the tendon, and position of the joint.
What is the muscle spindle and what does it do?
It is the sensory organ in skeletal muscle: it consists of 2-20 specialized muscle fibers and their afferent nerve endings a
Stretching stimulates afferent nerve endings which send a signal to the spinal cord, causing muscle to contract.
The afferent axons also may synapse in interneurons in the spinal cord that inhibit motor neurons to antagonistic muscles allowing them to relax
What does the perimysium convey?
Large blood vessels and nerves into the muscle
How does type 1 muscle create energy?
Oxidative phosphorylation
How are muscle cells formed in the embryo?
By the fusion of myoblasts that produce a post of mitotic multi nucleated myotube
What is the diameter and length of a muscle fiber?
10 to 100 micro meters
Up to 60 cm in length
What is Desmin anchor to and what does it do?
Anchors to the inside of the sarcolemma. And it extends from one myofibril to another
What is the function of Desmin?
Organize cytoplasm and facilitate coordinated contraction of individual myofibrils
What is a sarcomere?
A repeating contractile element made by organized myofibrils
What does the Z line contain?
Alpha actin that binds actin
What happens to I band during contraction ?
Decreases
Which two bands decrease during contraction?
I band and H band
What are thin filaments composed of?
G actin monomers that bind to each other that for a double stranded and twisted F actin
What is the sensory of skeletal muscle?
What do they do?
Muscle spindle.
Consists of 2-20 specialized muscle fibers and afferent nerve endings.
Cause muscle to contract or relax
What is the golgi tendon organ?
It is a nerve ending in tendons.
Sends signal to spinal cord-prevents over contraction.
Also can stimulate antagonistic muscle group
What is titin?
A large protein that extends from the Z line to the center of the sarcomere and functions to control the assembly of thick filaments and provide elasticity to the sacromere
What is nebulin?
It extends the Z line along the length of the thin filament and acts as a stabilizer of thin filament
