Physiology Of Muscle Contraction MCQs With Answers

Explanation
The ciliary muscle is a specific type of smooth muscle fiber found in the muscles of the eye that controls the lens. It is responsible for changing the shape of the lens to allow the eye to focus on objects at different distances. When the ciliary muscle contracts, it causes the lens to become thicker, which allows for near vision. When the ciliary muscle relaxes, the lens becomes thinner, allowing for distant vision. This muscle plays a crucial role in the eye's ability to adjust and focus on objects at various distances.

Explanation
The duration of one muscle twitch is 0.1 seconds. This is the time it takes for a muscle to contract and then relax. Muscle twitches are brief and involuntary contractions of a small portion of a muscle. They are caused by the firing of a single motor unit within the muscle. The duration of a muscle twitch can vary slightly depending on the individual and the specific muscle involved, but on average it lasts for about 0.1 seconds.

Explanation
Myosin is the correct answer because it is a contractile protein found in muscle cells. It plays a crucial role in muscle contraction by interacting with another protein called actin. Myosin molecules have a unique structure that allows them to generate force and movement by using energy from ATP. Therefore, myosin is directly involved in the contraction and relaxation of muscles, making it the contractile protein of a muscle.

Explanation
The synaptic cleft is the correct answer because it refers to the space that separates two neurons. This gap is where the transmission of signals occurs between neurons, allowing for communication and the transfer of information. The synaptic cleft plays a crucial role in the functioning of the nervous system by facilitating the transmission of neurotransmitters from one neuron to another.

Explanation
The brainstem is connected to the cerebrum, cerebellum, and spinal cord. The cerebrum is responsible for higher cognitive functions such as language, memory, and perception. The cerebellum controls coordination, balance, and motor skills. The spinal cord serves as a pathway for transmitting signals between the brain and the rest of the body. These connections allow the brainstem to regulate essential functions such as breathing, heart rate, and digestion, as well as coordinate movement and sensory information.

Explanation
A myofibril is a long, cylindrical structure that extends the entire length of a muscle fiber. It is composed of sarcomeres, which are the basic contractile units of muscles. Each sarcomere contains thick myosin filaments and thin actin filaments, which slide past each other during muscle contraction. The M-line is a structure within the sarcomere that helps anchor the myosin filaments. Therefore, the myofibril is the most likely structure to extend the entire length of a muscle fiber.

Explanation
When a muscle fiber shortens, the sarcomere, which is the basic unit of muscle contraction, also shortens. The sarcomere consists of actin and myosin filaments, which slide past each other during muscle contraction. The Z-line, on the other hand, remains stationary and acts as an anchor for the actin filaments. Therefore, the correct answer is sarcomere.

Explanation
The cerebrum is the largest part of the brain and is responsible for higher cognitive functions such as memory, language, perception, and voluntary movement. It is divided into two hemispheres and consists of various lobes, including the frontal, parietal, temporal, and occipital lobes. The cerebrum plays a crucial role in complex thinking, problem-solving, decision-making, and overall consciousness. It receives and processes sensory information from the body and controls voluntary movements.

Explanation
The correct answer is "All of the above". The stress response involves various systems in the body, including the immune system, musculoskeletal system, endocrine system, and autonomic nervous system. When the body experiences stress, the immune system releases certain chemicals to protect against potential threats. The musculoskeletal system may tense up, preparing the body for action. The endocrine system releases stress hormones like cortisol, while the autonomic nervous system controls automatic bodily functions like heart rate and breathing. Therefore, all of these systems play a role in the stress response.

Explanation
Cardiac muscle tissue cannot regenerate. Unlike skeletal muscle tissue and smooth muscle tissue, which have the ability to regenerate and repair themselves to some extent, cardiac muscle tissue lacks this regenerative capacity. This is because cardiac muscle cells, also known as cardiomyocytes, have a limited ability to divide and replace damaged cells. Therefore, any damage to cardiac muscle tissue, such as from a heart attack, can result in permanent loss of function and scar tissue formation.