MLT GlobePhysiology: Muscle physiology
11 Physiology MCQs on Muscle physiology with answers and explanations.
Based on conscious control, muscle activity is classed as:
Skeletal muscle is under voluntary control, while cardiac and smooth muscle are involuntary. Sympathetic and parasympathetic are divisions of the autonomic nervous system, not types of muscle action.
Which statement about skeletal muscle is FALSE?
Skeletal muscle is voluntary and striated; Ca2+ binding to troponin C moves tropomyosin to allow cross-bridging. Calmodulin regulates smooth, not skeletal, muscle.
On an electron micrograph of muscle, the segment from one Z disc to the next is the contractile unit known as the:
A sarcomere spans Z line to Z line and shortens during contraction. The H zone and A band lie within it, and a myofibril is a chain of sarcomeres.
Which structure is part of a muscle fibre's contractile unit rather than of a chemical synapse?
A synapse consists of the presynaptic terminal, the synaptic cleft and the postsynaptic membrane. The sarcomere is the repeating contractile unit of striated muscle.
Under the microscope, which feature identifies skeletal muscle fibres?
Skeletal fibres are long, unbranched, striated and multinucleate with nuclei at the edge. Branching with intercalated discs is cardiac; spindle cells without striations are smooth muscle.
Release of which ion from the sarcoplasmic reticulum allows myosin heads to bind actin in skeletal muscle?
Ca2+ released from the sarcoplasmic reticulum binds troponin C, shifting tropomyosin off actin's binding sites so cross-bridges can form. Sodium triggers the action potential, not cross-bridge binding.
Which neurotransmitter crosses the skeletal neuromuscular junction to trigger muscle contraction?
Motor neurones release acetylcholine, which binds nicotinic receptors on the motor end plate. Myasthenia gravis antibodies target these receptors.
Inward extensions of the sarcolemma that carry the action potential deep into a muscle fibre are the:
Transverse tubules are sarcolemmal invaginations lying next to the terminal cisternae of the sarcoplasmic reticulum, which store and release calcium but are separate internal membranes.
In a sarcomere, where are the thin actin filaments anchored?
Thin filaments attach to the Z discs and extend toward the centre; thick myosin filaments are held at the M line. The I band contains only actin.
Holding a heavy bag still with the elbow bent involves a contraction in which muscle tension rises but length stays the same. This is:
In isometric contraction tension develops without shortening. In isotonic contraction the muscle changes length under a roughly constant load.
At the neuromuscular junction, acetylcholine opens a receptor that is itself a cation channel. Which receptor type is this?
Nicotinic receptors are ligand-gated ion channels that open directly on binding acetylcholine. Adrenergic, H2 and muscarinic receptors are G-protein coupled.