Muscle Contraction Lab Report

Thato’s muscle had remained unused for 6 weeks. Once the cast is removed and he steps down from the examination table, his muscle begins to contract. Due to this 6 week period of rest, the muscles initial strength of contraction may be significantly low as compared to its strength a few minutes later. The strength of contraction of his muscle increases to a plateau, which is termed the staircase effect. Due to his muscles low initial strength of contraction, Thato loses his balance and falls.

1.2 Yes, skeletal muscles can contract without shortening. Isometric muscle contraction is when the muscle does not shorten during contraction. Hence, the muscle contracts against a force transducer without decreasing the muscle length.

Question 2
In co-transport:
Due to the large concentration gradient of sodium ions across a cell membrane, sodium ions outside the cell membrane are constantly trying to diffuse to the interior.
By means of a coupling mechanism, sodium ions are able to pull other substances along with them through a cell membrane. A carrier protein situated in the cell membrane serves as an attachment point for the co-transport of the sodium ion as well as the other substance. Once attached, both the sodium ion and the other substance are transported to the interior of the cell together. This is due to the diffusion energy gradient of the sodium ion.

Examples of co-transport:
Sodium-glucose co-transport mechanism
The sodium ion and glucose both attach to the exterior side of the carrier protein. Once attached, a conformational change occurs, and the sodium ion and glucose are transported to the interior of the cell together. Transport is made possible by energy from the sodium ion due to a large concentration gradient.

Sodium co-transport of amino acids
This occurs in the same manner as that of glucose, except that a different set of transport proteins are
used.

In counter-transport:
As in co-transport, due to the large concentration gradient of sodium ions across a cell membrane, sodium ions outside the cell membrane are constantly trying to diffuse to the interior. However, in counter-transport, the substance to be transported is located at the interior of the cell, and must be transported to the exterior. Therefore, the sodium ion attaches to the exterior projection of the carrier protein, and the substance to be counter-transported, to the interior projection. Once both are attached, a conformational change takes place, and the other substance moves to the exterior of the cell, due to the energy released by the sodium ion moving to the interior.

Examples of counter-transport:
Sodium-calcium counter-transport
Both the sodium ion and the calcium ion are attached to the carrier protein. Due to energy from the sodium ion, it moves to the interior of the cell, and the calcium ion, to the exterior.

Sodium-hydrogen counter-transport
This occurs in the same manner as that of sodium-calcium counter-transport.

Question 3

The sodium-potassium pump refers to a transport process which pumps sodium ions through the cell membrane to the exterior of the cell, whilst simultaneously pumping potassium ions from the exterior of the cell to the interior.

One of the most important functions of the sodium-potassium pump is to control cell volume. Large numbers of proteins and other organic molecules are situated inside the cell. Most of these are negatively charged, and automatically attract large amounts of sodium, potassium, and other positive ions. All of these molecules and ions cause osmosis of water inside the cell. Therefore, without proper function of the sodium-potassium pump, most cells of the body would swell indefinitely until they burst.

Question 4

• There is slow cycling of the myosin cross-bridges in smooth muscle as compared to skeletal muscle. In contrast, the fraction of time that the cross-bridges remain attached to actin filaments is far greater in smooth muscle as compared to skeletal muscle.
• There is a lot less energy required to sustain the same tension of contraction in smooth muscle as compared to that of skeletal muscle.
• There is slow onset of contraction and relaxation of smooth muscle (1-3 seconds) as compared to a single contraction of an average skeletal muscle.
• The maximum force of contraction of smooth muscle is generally greater than that of skeletal muscle.
• A latch mechanism allows for prolonged holding of contraction of smooth muscle. Therefore, energy required for prolonged holding of contraction of smooth muscle is far less as compared to sustained skeletal muscle contraction.