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1.During a clinical examination, a neurologist tests a patient's muscle tone and reflexes. Which component of the motor system is primarily assessed by these tests? (1 Point) Basal ganglia Cerebellum Lower motor neurons Upper motor neurons 2.Which of the following components are found in a muscle spindle? (1 Point) Alpha motor neuron and gamma motor neuron Extrafusal muscle fibres connected to the afferent and efferent nerve fibres Intrafusal muscle fibres connected to afferent and efferent nerve fibres Stretch receptors and tension receptors 3.A patient with hypocalcaemia exhibits muscle cramps and spasms. How does calcium deficiency affect muscle contraction? (1 Point) Decreases ATP production in muscles Impairs binding of calcium to troponin Inhibits action potential generation in motor neurons Reduces acetylcholine release at the neuromuscular junction 4.A patient with poliomyelitis shows severe muscle weakness in the limbs. Which type of lower motor neuron is primarily affected in this condition? (1 Point) Alpha motor neurons Beta motor neurons Gamma motor neurons Sensory neurons 5.What is “motor system” with respect to body movement? (1 Point) The afferent signals to the motor cortex involved in specific movement The muscles and bones involved in specific movement The parts of the nervous system involved in reflexes that control movement. The parts of the nervous system involved in transmitting impulses to the muscle

Here are the answers with explanations:
1. Which component of the motor system is primarily assessed by muscle tone and reflex tests?
✅ Upper motor neurons
Muscle tone and deep tendon reflexes are primarily mediated by the upper motor neuron (UMN) system. UMN lesions cause increased tone (spasticity) and hyperreflexia, while lower motor neuron lesions cause flaccidity and hyporeflexia. Testing tone and reflexes tells the clinician about the integrity of the corticospinal (UMN) pathway.
2. Which components are found in a muscle spindle?
✅ Intrafusal muscle fibres connected to afferent and efferent nerve fibres
Muscle spindles contain intrafusal fibres (as opposed to extrafusal fibres, which make up the bulk of the muscle). They are innervated by:
  • Afferent fibres (Ia and II sensory axons) that detect stretch
  • Efferent gamma motor neuron fibres that set spindle sensitivity
3. How does calcium deficiency affect muscle contraction in hypocalcaemia?
✅ Impairs binding of calcium to troponin
Muscle contraction requires Ca²⁺ to bind troponin C, which displaces tropomyosin and exposes actin binding sites for myosin cross-bridge cycling. In hypocalcaemia, insufficient Ca²⁺ is available for this step. Paradoxically, hypocalcaemia also increases neuronal membrane excitability (causing tetany/spasms) because Ca²⁺ normally stabilizes voltage-gated Na⁺ channels - but the direct intracellular mechanism of impaired contraction is the troponin-binding failure.
4. Which type of lower motor neuron is primarily affected in poliomyelitis?
✅ Alpha motor neurons
Poliovirus selectively destroys alpha motor neurons in the anterior horn of the spinal cord. Alpha motor neurons directly innervate extrafusal (force-generating) muscle fibres, so their destruction leads to flaccid paralysis, muscle wasting (atrophy), and loss of reflexes in the affected limbs.
5. What is the "motor system" with respect to body movement?
✅ The parts of the nervous system involved in transmitting impulses to the muscle
The motor system encompasses all neural components responsible for generating and transmitting motor commands - from the motor cortex, basal ganglia, cerebellum, brainstem, spinal cord, and ultimately the motor neurons that deliver impulses to muscles. It is distinct from the musculoskeletal system (muscles/bones) and from purely afferent/sensory pathways.
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