Muscle Histology II Flashcards
Each myofiber is connected to a motor _______.
Neuron
What is the chemical neurotransmitter for skeletal muscle? (Full name and abbreviation)
Acetylcholine, ACh
A myofiber only contracts when stimulated by its nerve
Motor______ _____.
End Plate
At the end plate, the sarcolemma is extensively ______ to increase _______ ________.
Folded
Surface Area
What purpose does the motor end plate serve?
Provides a large surface area for millions of ACh receptors
What is a graded response with skeletal muscle?
Our muscle contractions are relatively smooth and can vary in strength as different demands are put on them. Variations in the degree of a muscle contraction are referred to as graded responses.
What does innervation ratio mean in the context of skeletal muscle?
The ratio of motor neurons to muscle fibers
What is an example of an innervation ratio for fine control?
Muscles for the eyes; 1:8 ratio
What is an example of an innervation ratio for strength an power?
Quad; 1:2,000 ratio
What is muscle recruitment?
To increase contractile power, more units are stimulated
Muscle units of a single motor unit are not clustered all together, but are dispersed throughout the _______ ______.
Whole muscle
When muscles are stimulated, this causes a _____ contraction over a wide area, not a localized twitch in a small region.
Weak
What is an advantage of multiple motor units within a muscle?
They are “able to work in shifts.” Muscle fibers fatigue when subjected to continued stimulation, and so other motor units take over while fatigued ones rest.
In muscle contraction, or the “sliding mechanism” what structures shorten?
Myofiber
Myofibrils
What defined area shortens during the “sliding” mechanism?
The sarcomere, or area from Z line to Z line
What structures do not shorter, but rather slide by each other?
Myofilaments
Crossbridging takes place between ______ and ________.
Actin
Myosin
When does crossbridging take place? When working or at rest.
When the muscle is at work.
How do myosin and actin crossbridge?
Myosin has a “head” portion that attaches to and then detaches from actin, allowing them to slide by each other
What two molecules essential for crossbridging?
ATP and Ca++
What is stored in the terminal cisternae?
Ca++
How is Ca++ put back into the terminal cisternae?
By active transport
Why is Ca++ stored in the terminal cisternae?
To assist with muscle contraction
What 3 proteins make up actin?
F actin
Tropomyosin
Troponin
What is F Actin made from?
A string of 200+ G actins
What is G actin?
A bean-shaped polypeptide with an active site
What is tropomyocin?
2 protein strands spiralled around 2 strands of F actin
What shape is tropomyosin?
Rod-shaped
Troponin is a 3 _______ complex
polypeptide
What is troponin attached to?
Tropomyosin
What is the site for Ca++ attachment in actin?
Troponin
What are the two regulatory proteins in actin?
tropomyosin
troponin
What happens when Ca++ binds to troponin?
When Ca++ is present, it binds to troponin, and this makes the tropomyosin “move away” from the active sites. It uncovers the active site on the F actin, allowing the myosin heads to attach to the F actin active sites.
So, it allows for contraction.
When myofibrils are sliding past each other, the heads of the ______ must disconnect from _____.
Myosin
Actin
Myosin is a ____-shaped protein with 2 ______.
Rod-shaped
2 heads
What two compounds are found on the heads of myosin?
ATP binding sites and ATPase
The head of myosin allows for ___________ with actin.
Crossbridging
The heads of myosin are not present in the ___ zone.
H zone
When muscle is at rest, the heads of myosin _____ attached.
aren’t
