Question

Types of Muscle Contractions

You are carrying a case of 24 bottles of water up the stairs to your third-story apartment. What type of contraction are the muscles in your arms experiencing?

A)Isotonic

B)Eccentric

C)Passive

D)Isometric

Effect of Neurotransmitter at the Neuromuscular Junction

A drug was developed and approved for the treatment of numerous disorders of muscle stiffness and muscle spasms. The cosmetic use of this drug is to temporarily reduce forehead frown lines. This new drug works by blocking the release of the neurotransmitter at the neuromuscular junction. Which neurotransmitter is blocked?

A) Dopamine

B)Epinephrine

C)Endorphin

D)Acetylcholine

Part E

Malignant hyperthermia causes a high demand for ATP within the muscle cells. Which of the following ATP-consuming events causes skeletal muscles to relax?

A) active transport of Ca²⁺  back into the terminal cisterns

B) diffusion of Ca²⁺ into the extracellular fluid

C) binding between the myosin head and actin

D) action of the Na⁺/K⁺ pump

Answer 1

1). Type of muscle contraction: isometric.

Since no movement is involved with the action of carrying case of water bottle it is isometric. Isotonic contractions involve change in the length of muscle fibres due to flexion and extension of forearm. Whereas in the above mentioned work only the case is carried wich is not associated with flexion or extension of forearm .no movement is associated with forearm. Hence the contraction here is isometric , Where only tension develops in muscle fibres of biceps .

2). Neurotransmitter blocked is : ACETYLCHOLINE.  

Acetylcholine acts at nicotine receptors in neuromuscular junction, this causes voltage gated sodium channels to open which causes depolarization and calcium channels are also opened which causes muscle contraction. Acetylcholine is released by parasympathetic nervous system . At nmj it is released and causes contraction of muscles . Other neurotransmitters like endorphins, dopamine, epinephrine has nothing to do with skeletal muscle stiffness, because skeletal muscle contractions and relaxation are only controlled by parasympathetic nervous system.  

3). ATP consuming events that cause skeletal muscle relaxation: active transport of calcium back to terminal cistern .

It is one of the main cause for skeletal muscle relaxation. Talking about contraction action potential travel through t tubules causing depolarization, which allow ryanodine receptors in sarcoplasmic reticulum to open , causing calcium release increasing the intracellular calcium level, this calcium binds with troponinC , so tropomyosin is pushed away and the active site of actin is available for myosin attachment, ATP is consumed and broken down by atp myosin head, which cause binding of myosin head to actin . This result in skeletal muscle contraction. When action potential drops calcium is taken back into terminal cistern through ATP requiring active process. So calcium level drops causing relaxation .