MSCT Week 2: Skeletal Muscle Flashcards
Types of muscle
3 Listed
- skeletal muscle
- Cardiac Muscle
- Smooth Muscle
In all three types of muscle, energy from ____________________________ is transformed into _________________ energy.
- The hydrolysis of ATP
- Mechanical
Skeletal muscle Cell Properties
3 Listed
- elongated
- multi-nucleated
- grouped in bundles surrounded by connective tissue sheaths that extend from proximal origin to distal attachment
Identify
Epimysium description
is a dense connective tissue that surrounds the entire muscle and is synonymous with the deep fascia
Perimysium Description
2 Listed
- is the connective tissue that surrounds a group of fibers to form a fascicle.
- it conveys the large blood vessels and nerves into the muscle
Endomysium Description
a delicate connective tissue which surrounds individual muscle fibers.
Identify
Identify fiber type
- Type II fast-twitch is light colored
- Type I slow-twitch is dark colored
Type I muscle fibers AKA
Slow-Twitch
Type II Muscle Fibers AKA
Fast-Twitch
Type I muscle fibers are more efficient for and are primarily used for?
slow twitch/red muscle fibers are more efficient over long periods of time and mainly used for postural maintenance or endurance exercise.
Type I muscle fiber speed of contraction and innervation
the speed of contraction is low and there are large motor units in the muscle (large numbers of muscle fibers are innervated by a single neuron
Type I muscle fiber ATP generation and contents
ATP is generated through oxidative phosphorylation and the cells contain high levels of myoglobin
Type II Muscle Fibers are better for? But can?
better for short bursts of speed although they fatigue more quickly
Type II Muscle Fibers AKA
Fast Twitch/White
Type II Muscle Fibers ATP Generation and Contents
ATP is generated by anaerobic glycolysis and the cells contain high levels of glycogen
Type II Muscle Fibers Speed of Contraction
The speed of contraction is high
Type II Muscle Fibers Innervation and motor units
There are small motor units in the muscle and small numbers of muscle fibers are innervated by a single neuron
Skeletal muscle cells are formed in the embryo by
the fusion of myoblasts that produce a postmitotic, multinucleated myotube
Myotube size
The myotube matures into a long muscle cell with a diameter of 10 to 100um and a length of up to many centimeters
The individual fibers of the sartorius muscle may reach up to what in length?
60 cm in length
The plasma membrane of muscle cells is referred to as the?
Sarcolemma
The sarcolemma is surrounded by a?
Basal Lamina
The sarcolemma invaginates finger-like projections to form the?
Transverse Tubule System (T-Tubules)
T-Tubules function
T-Tubules make contact with the sarcoplasmic reticulum and transmit the depolarization signal deep into the muscle cell
What is the Sarcoplasmic reticulum?
an internal membrane network that has no connection with the extracellular space
The Sarcoplasmic Reticulum junctions with T-Tubules forms membrane structures called?
Triads
The Sarcoplasmic Reticulum function
The SR is a site of intracellular Ca2+ storage and release, important in the regulation of muscle contraction
About 80% of the cytoplasm of muscle cells is occupied by?
myofibrils surrounded by ATP-producing mitochondria, the SR, and T-tubules
Myofibrils filaments
- Thin filaments containing Actin
- Thick filaments composed of Myosin
Sarcomeres
the myofibrils are organized into repeating contractile elements called Sarcomeres
Sarcomerre unit width
2.2um
Identify
Sarcomere: Z-Lines
- Define the boundaries of each sarcomere
- contains the actin-binding protein alpha-actinin
Sarcomere: I-band
- Composed exclusively of actin thin filaments
- Width decreases during contraction
Sarcomere: A-band
- Composed of overlapping thick and thin filaments
- width remains constant during contraction
Sarcomere: H-Band
- The central region of the A band which contains only thick filaments
- Width decreases during contraction
Sarcomere: M-Line
- Middle of the H band
- Overlapping tails of thick filaments
Identify
Thin filaments components and actions
7 listed
- Thin filaments are composed of G-actin monomers that bind to each other forming a double-stranded and twisted F-actin filament
- Each G-actin monomer displays a binding site for myosin resulting in many regularly-spaced myosin binding sites per F-actin filament
- F-actin forms a complex with the proteins tropomyosin and the troponin complex (I, T, and C)
- Tropomyosin consists of two polypeptides twisted around each other running in the groove formed by the F actin filaments
- Tropomyosin binds to troponin-T of the Troponin complex
- The other components of the troponin complex are Troponin-I which inhibits the binding of myosin to actin and troponin-C that binds Ca2+
- Nebulin extends from the Z-line along the length of the thin filament and acts as a stabilizer of thin filament length
Identify
Thick Filaments components and action
6 Listed
- Thick Filaments are composed of myosin that consists of two identical heavy chains and two pairs of light chains
- each heavy chain consists of a globular head, containing a binding site for actin and an ATPase domain, and a long α-helical coiled tail that enables several myosin molecules to self-assemble into a bipolar aggregate or filament
- The globular head and tail are separated from one another by a movable hinge region
- The binding and hydrolysis of ATP at the myosin head affects the interaction of myosin with actin and causes conformation changes in the protein and movement at the hinge joint
- The myosin light chains play a role in regulating activity of the myosin head and the other protein associated with the thick filament is the molecule titin
- Titin is a very large protein that extends from the Z-line to the center of the sarcomere and functions to control the assembly of the thick filaments and provides elasticity to the sarcomere
Identify
Skeletal muscle contracts and generates tension by?
- sliding of the thick and thin filaments toward the center of the sarcomere
- the length of the thick and thin filaments does not change during contraction
- the length of the sarcomere decreases because the thick and thin filaments slide past one another causing the Z-lines to move closer together and the width H band and I band to decrease
explain skeletal muscle contraction
The sliding of filaments and the generation of tension is facilitated by?
the conformational changes in the myofibrillar proteins through the binding and hydrolysis of ATP and the release and binding of intracellular Ca2+
Single cycle of muscle contraction
5 Listed
- ATP binds to the myosin head causing the dissociation of myosin from the actin thin filament
- ATP is hydrolyzed by the myosin head ATPase causing a conformational change in the myosin and movement at the hinge such that the angle between the head and tail increases. This lines up the head with a new myosin binding site on the thin filament
- The myosin head attaches to the thin filament
- The binding of myosin causes the release of Pi and a conformational change in the myosin and movement at the hinge such that the angle between the head and tail decreases. This causes a sliding of the thin filament toward the center of the sarcomere.
- ADP is released from the myosin head and the cycle begins anew
Describe the cross-bridge cycle
Muscle Cell Depolarization
6 Listed
- Depolarization spreads from the sarcolemma to the T-tubules, which transport the signal to the interior of the muscle cell
- The depolarization of the T-Tubule is sensed by an L-type Ca2+ channels in the membrane of the T Tubule that induces the opening of ryanodine-sensitive Ca2+channels in the membrane of the sarcoplasmic reticulum
- Calcium stored in the SR is released into the cytoplasm of the muscle fiber increasing the resting level of Ca2+ from 10-7 to 10-5 mM
- Ca2+ binds to Troponin-C causing a conformational change in the whole troponin complex
- The change in troponin alters the conformation of tropomyosin and leads to uncovering of the myosin-binding sites on actin allowing the thick filament head to bind to actin
- A Ca2+ dependent ATPase mediates the return of Ca2+ into the SR during relaxation and a lowering of the cytoplasmic Ca2+ levels
Describe muscle cell depolarization
Each skeletal muscle fiber is innervated by _______________.
An axon of a motor neuron
The motor neuron axon interacts with a muscle fiber via the _____________________.
Motor end plate or neuromuscular Junction
Neuromuscular Junction AKA
Motor End Plate
Neuromuscular junction: Contraction
5 listed
- Contraction begins with the release of acetylcholine from synaptic vesicles in the motor neuron end plate
- Acetylcholine binds to a receptor on the muscle sarcolemma and causes a depolarization of the cell membrane
- The action potential spreads from the sarcolemma and causes a depolarization of the cell membrane
- The action potential spreads from the sarcolemma to the T tubules, which transmits the signal to the interior of the muscle cell to cause the release of calcium from the SR
- The activity of acetylcholine is eliminated through the action of the enzyme acetylcholinesterase that is present within the basal lamina of the synaptic cleft
Identify
Identify
A Motor unit is?
A motor axon and all the muscle fibers that it innervates defines a “motor unit”
Small motor units have?
fewer muscle cells innervated per axon (Type II)
Large muscles have _______ motor units
large motor units
Muscles requiring fine motor control have _________ motor units
small motor units
fiber types of a motor unit
all fibers that are part of a motor unit are of the same type
motor units and fiber type explanation
Can a muscle fiber type change?
Yes, if the innervating neuron changes from one type to another (i.e. following an injury to the nerve) or changes the signals that it produces
Following denervation myofibers undergo…
myofibers undergo atrophy, often assuming a flattened, angulated shape
Reinnervation of myofibers
restores fiber size and shape but may make a denervated myofiber part of a different motor unit and a switch in fiber type
Enlargement of motor units due to ongoing axonal or neuronal dropout or damage
in the face of ongoing axonal or neuronal damage and drop out, residual motor axons may innervate increasingly larger numbers of myofibers, leading to enlargement of motor units each comprised of a single type of muscle fiber (fiber type grouping) these large motor units are also susceptible to grouped atrophy if the innervating axon is damaged.
Identify
2 Listed
Sensory organs in skeletal muscle, tendons and joints
Proprioreceptors
Proprioreceptors
provide feedback on the contractile state of the muscle, tendon tension and position of the joint
Muscle Spindles consist of?
- Found in all human skeletal muscles and consist of 2-20 intrafusal muscle fibers and their afferent nerve endings
Muscle Spindles Function
- Stretching of the muscle, and hence enclosed spindle, stimulates the nerve ending whose sensory action potential is sensed by the spinal cord
- The appropriate motor neuron is stimulated and the stretched muscle is stimulated to contract
- At the same time, the incoming sensory neuron synapses on an interneuron in the spinal cord that inhibits the motor neuron to the antagonistic muscle allowing it to relax
Identify
Identify
The Golgi Tendon Organ function and description
2 listed
- is a bare sensory nerve ending in tendons that inhibits muscle contraction when it senses excess tension placed on the tendon by a muscle
- At the same time, it causes contraction of the antagonistic muscle group
Identify
E = Epimysium
P = Perimysium
En = Endomysium
Epimysium
Dense connective tissue that surrounds the entire muscle
Synonymous with deep fascia
Perimysium is?
Connective tissue that surrounds a group of fibers to form a fascicle
Conveys large blood vessels and nerves to muscle
Endomysium is?
Delicate connective tissue which surrounds individual muscle fibers
Identify
Type I muscle Fibers ATP is generated by?
Oxidative phosphorylation
Type I muscle Fibers glycogen content
Low
Type I muscle Fibers Myoglobin content
High
Type I muscle Fibers Utilized for what kind of activities
Endurance
Type I muscle Fibers ATPase activity and contraction speed
Low
Type I muscle Fibers Resistance to fatigue
High
Type I muscle Fibers motor unit size
Large
Type II Muscle Fibers ATP generated by?
Anaerobic Glycolysis
Type II Muscle Fibers Glycogen content
High
Type II Muscle Fibers Myoglobin content
low
Type II Muscle Fibers utilized for?
Rapid, fine movements
Type II Muscle Fibers ATPase activity and contraction speed
High
Type II Muscle Fibers Resistance to Fatigue
low
Type II Muscle Fibers Motor Unit size
small
What is this?
Sarcomere
Identify
Identify
Identify
Accessory proteins of myofibrils: Titan
Elastic protein that positions the thick filament in the sarcomere and provides elasticity to the muscle fiber
Accessory proteins of myofibrils: Nebulin
Anchors the thin filament to the Z-disc
Identify
Ca2+ binds to?
Troponin complex
Malignant Hyperthermia is caused by?
Autosomal dominant mutation in the RYR1 receptor
Malignant Hyperthermia pathology
Myasthenia Gravis is an?
Autoimmune Disease in which Antibodies are produced against Acetylcholine receptors
Myasthenia gravis pathology
muscle spindle overview
Golgi Tendon Overview
