GROSS ANATOMY

Detailed explanation-1: -Sacral parasympathetic outflow arises from the S2 to S4 segments of the spinal cord and via the pelvic splanchnic nerves innervates the smooth rectal muscles, the bladder detrusor, the internal urethral sphincter and the reproductive organs (Hamill et al., 2012).

Detailed explanation-2: -Some parasympathetic fibers leave the spinal cord between S2 and S4. The sclera is thickest over the posterior part of the eye. Receptors in the semicircular canals are stimulated when the stapes vibrate. Both the lens and the cornea are devoid of sensory nerve fibers.

Detailed explanation-3: -The pelvic splanchnic nerves (also called nervi erigentes) are the preganglionic parasympathetic nerve fibers that arise from the anterior rami of spinal nerves S2-S4 and freely distribute across the abdominal and pelvic cavities to innervate the abdominopelvic viscera.

Detailed explanation-4: -The parasympathetic nervous system consists of nerves originating either from the brain or sacral region of the spinal cord (right side of Figure 1) that project to ganglia usually located either near or in end organs.