Muscle 2 Flashcards
What are muscles made up of?
Many single fibers
What is a single skeletal muscle cell also called?
A muscle fiber
What is the shape of a single skeletal muscle fiber?
More or less cylindrical with an elongated shape
What does each muscle fiber end in?
Tendons made up of fibrous inelastic tissue composed largely of collagen
How are skeletal muscles attached to bone?
By tendons
What do skeletal muscle fibers contain within them?
Smaller subunits arranged in bundles called rods or myofibrils
What are myofibrils found within?
Skeletal muscle cells
How are muscle fibers formed?
During development, undifferentiated or mononucleated cells called myblast that fuse into a single cylindrical muscle fiber
Why are skeletal muscles multinucleated?
Because they form from the fusion of multinucleated myoblasts into one muscle fiber
Why is it important for skeletal muscles to be multinucleated?
For gene expression and to meet the high protein synthesis requirements of muscle
What is each muscle fiber made of?
Many myofibrils that have a specialized intracellular structure
What are myofibrils that are found in skeletal muscle cells made of?
Thick and thin filaments
What are Cytoskeletal elements?
The thick and thin filaments that make up myofilaments
What are thick and thin filaments made up of?
Proteins myosin and actin
How are muscle fibers arranged in a whole muscle?
In functional units called motor units
What is a motor unit?
All the muscle fibers that a single motor nerve innervates
What is the number of muscle fibers controlled by a single motor axon determined by?
The dexterity of the movement controlled
What is the motor unit like in Gross movement?
One nerve controls hundreds of muscle fibers (ie. Posture)
What is a motor unit like in Fine movements?
1 nerve controls 5-6 muscle fibers ex. Changing eye position
Which nervous system is skeletal muscle innervated by?
The somatic nervous system
What is the Neuromuscular Junction?
The area where the somatic nervous system meets the musculature
What are nerve cells and muscle cells separated by?
The synaptic cleft or synapse
What is the Motor Endplate?
The area of little muscle directly below the synaptic terminal
How does an action potential work in skeletal muscles?
An action potential travels down the motor neuron causing depolarization of the synaptic terminal causing opening of the voltage gated calcium channels. Calcium rushes into the synaptic terminal of the of the motor neuron causing the synaptic vesicle to fuse with the membrane and acetylcholine to be released into the synaptic cleft. Acetylcholine binds to ion channels allowing sodium to enter. The sodium causes voltage gated sodium channels to open and allow more sodium to enter the muscle fiber and a muscle fiber action potential is initiated
What does the action potential of a muscle membrane move down?
Structures called T tubules
What does each muscle cell need in order to contract?
To be stimulated by a process of a motor neuron
What does a functional unit of a motor system represent?
The smallest increment of force that can be generated
Is it possible to contract just one motor cell?
No
What is the functional unit of the motor system?
A motor neuron, its axon and all the muscle fibers it activated
What are Cross Striations?
The alternating light and dark bands seen in skeletal muscle
What do Cross striations span?
The full length of the muscle fiber
What do thick filaments interdigitate between?
The thin filaments
What does the A band of muscle contain?
The overlapping portion of thick and thin filament
What does the H zone contain?
Only thick filaments
What is the M line?
The center line that thick filaments are anchored on
What does the I band contain?
Only thin filaments
What is the Z line?
The anchor for titin and thin filaments
Where does a Sarcomere span?
From Z line to Z line
What does titin connect to?
Thick filaments and the Z line
What is the distance from Z line to Z line known as?
The sarcomere
What is the functional unit of skeletal muscle?
The Sarcomere
What is the functional unit of any organ?
The smallest unit component that can perform all the functions of that organ
How does a muscle grow and increase in length?
By adding new sarcomeres to the myofibril
Are the I bands light or dark regions?
Light regions
How big is the distance from Z line to Z line?
About 2-3 micrometers
What can you see if you look at a myofibril under magnification?
The myofilaments
What are the two types of myofilaments?
Thick filaments and thin filaments
What are Thick filaments composed of?
Myosin
What are thin filaments composed of?
Actin
What is the shape of Myosin?
Club-like shaped
What is responsible for the striated appearance of skeletal and cardiac muscle?
The highly organized sarcomeres stacked end to end
Why is smooth muscle non-striated?
Because the actin and myosin have a less regular pattern or organization
What are Myofibrils made of?
Sarcomeres stacked end to end
What is required in order for muscles to contract?
- Actin
- Myosin
- Troponin
- Tropomyosin
- ATP
- Trace Mg2+
- Ca2+
What does the presence of molecular participants in muscles allow for?
Cross bridge cycling
