Sarcoplasmic Reticulum and Transverse Tubules

Question 1

What is the sarcoplasmic reticulum?

Answer 1

A loose network of flattened tubules which surround myofibrils. Resembles SER. Acts as a store for Ca2+

Question 2

What are transverse (T) tubules?

Answer 2

They are deep invaginations of the sarcolemma

Question 3

What is the terminal cisternae and where are they found?

Answer 3

Expanded parts of the SR, 2 are found at either side of a T tubule. Referred to as a triad

Question 4

In resting muscle fibres, do the terminal cisternae contain a high or low concentration of Ca2+?

Answer 4

High. They’re actively pumped from the surrounding sarcoplasm by pump proteins

Question 5

When does the contraction process begin?

Answer 5

When an action potential travels down the T tubules and opens protein channels in the terminal cisternae.
Ca2+ ions diffuse out of the open channels and bind to proteins in nearby sarcomeres