In anatomical position, the palms of the hands are pronate.

 

Choice A reason: A meatus is a canal-like passageway through bone, such as the external auditory meatus in the skull. It does not describe a rounded projection.

Choice B reason: A foramen is a hole or opening in a bone that allows the passage of nerves and blood vessels. It is not a projection.

Choice C reason: A condyle is a rounded articular projection that typically forms part of a joint. It allows for smooth articulation with another bone, making it the correct answer.

Choice D reason: A fossa is a shallow depression in a bone, often serving as an articular surface or for muscle attachment. It is not a projection.

Choice A reason: Myosin heads pulling actin toward the center of the sarcomere is the core mechanism of cross-bridge cycling. This interaction shortens the sarcomere and generates muscle contraction. ATP binding and hydrolysis drive the cycle of attachment, power stroke, and detachment.

Choice B reason: Thick filaments do not shorten during contraction. Instead, thin filaments slide past the thick filaments as the sarcomere shortens. The filaments themselves remain the same length.

Choice C reason: Actin and myosin do not lengthen during contraction. They maintain their structural integrity while sliding past each other through repeated cross-bridge interactions.

Choice D reason: Z discs define the boundaries of a sarcomere and move closer together during contraction, but they do not slide over myofilaments. Their movement is a result of filament sliding, not a direct action.

Choice E reason: Titin is a structural protein that contributes to passive elasticity and sarcomere stability. It does not actively shorten or participate in the cross-bridge cycle