Which muscle type is involved in swallowing, and in what sequence?

Correct answer: C. Skeletal muscle first, followed by smooth muscle

• A. The oral and pharyngeal phases are voluntary and striated — swallowing cannot be initiated by smooth muscle.
• B. This reverses the anatomy. The oral and pharyngeal phases come FIRST and are skeletal; smooth muscle takes over distally.
• C. CORRECT. Swallowing begins under VOLUNTARY control with SKELETAL muscle — the tongue, soft palate, pharyngeal constrictors and the upper third of the oesophagus are all striated. As the bolus descends, control transitions to SMOOTH muscle: the middle third of the oesophagus is mixed, and the lower third is entirely smooth muscle under involuntary autonomic (myenteric plexus) control. So the correct sequence is skeletal → smooth.
• D. This ignores the oesophagus. Only the upper third is skeletal; the lower third is unequivocally smooth muscle.

Note: The three phases: ORAL (voluntary, skeletal), PHARYNGEAL (involuntary reflex but still skeletal muscle, ~1 second, airway protected by laryngeal elevation and epiglottic closure) and OESOPHAGEAL (involuntary, transitioning skeletal to smooth). Afferent limb is CN IX and X; the swallowing centre is in the medulla.