Exam #3: second part Flashcards
What process is necessary for muscle fiber activation?
Excitation-Contraction (EC)
What is the initial step of excitation contraction?
Action potential
What components of the skeletal membrane system is required to activate the contractile elements?
Transverse Tubular (T-Tubule) system Sarcoplasmic Reticulum (SR)
What is a neuromuscular junction?
An area of contact between a muscle fiber and a neuron
What are T-Tubules?
They begin as invaginations of the surface membrane- they are holes that extend deep into the muscle fibers
They invaginate and extend transversely across the long axis of the muscle fibers
The T-System conducts the activation signal from the motorneuron to the myofibrils
The system provides a means for myofibrillar activation that is much faster that would occur if activation relied on simple diffusion of molecules from cell surface
What is the sarcoplasmic reticulum?
The SR is an elaborate system of closed membranes and channels surrounding individuals myofibrils
When the muscle contracts, the longitudinal channels become shorter and wider
Function: To store and release ionized Ca into the cytosol around the myofibril
Where is calcium stored?
Terminal cisternae
How does the Sr communicate with the terminal cisternae?
The longitudinal elements of the SR communicate with the terminal cisternae at each end, which forms a highly branched network
How is the SR connected to the T system?
The “junctional feet” of the SR connects the T-system to the SR
These feet are made of two discreet protein components: RyR and DHP
What is RyR?
Ryanodine Receptor: a voltage sensing protein embedded in the SR that senses the action potential traveling across the T-system
What DHP?
Dihydropyridine: a receptor that is the calcium release channel through which the myofilament activating calcium passes
What is a triad?
A single T tubule surrounded by 2 SR tubules at each Z disk
It is the true interface between the extracellular and intracellular worlds around the muscle fiber
What are Satellite cells?
Small cells located beneath fiber basal lamina
Has no known role in normal cell function
It is like “stem cells” that have the ability to differentiate into myoblasts and form new muscle fibers
What is schwan cells?
It envelopes an axon in a trough
It then rotates around the axon enveloping it in successive layers of its plasma membrane
Eventually the schwan cell cytoplasm is squeezed from between the membranes and comes to lie just beneath the exposed portions of the schwan cell membrane.
It forms the myeling sheath
What is the first step in excitation contraction coupling?
Generation of an action potential to the peripheral nerve
