ABSTRACT
To explain the innervation of the prostate, it is necessary to describe briefly the neurophysiology of continence and micturition. The bladder and urethra are innervated by three sets of nerves: the sympathetic, from T10 to L2 spinal levels, the parasympathetic, from sacral spinal segments S2 to S4, and the pudendal nerve, which carries somatic innervation from S2 to S4 (Figure 6). During bladder filling, sensory nerve endings detect progressive stretching of the bladder wall and convey information via the parasympathetic nerves to the spinal cord and brain. Increasing activity in these nerves produces a progressive reflex contraction in the bladder neck and prostatic urethra, as well as in the external urethral sphincter, thereby maintaining urinary continence. When the bladder volume reaches 300-500 ml, an awareness of the need to void develops, although true bladder contractions should not occur until a socially convenient time arrives. Voluntary voiding is accomplished as a result of a barrage of impulses down the parasympathetic nerves to the detrusor muscle. The neurotransmitter acetylcholine is released, which binds to muscarinic receptors on detrusor smooth muscle cells to produce coordinated contraction of the bladder body. At the same time, neural impulses passing down the sympathetic and pudendal motor fibers cease momentarily, thereby allowing relaxation of the normally tonically contracted, continent bladder neck, prostatic urethra and external sphincter. Bladder pressure rises, the bladder neck funnels and urine flow commences, achieving a maximum flow rate of more than 15 ml/s, with a maximum detrusor pressure of less than 40 cmH2O. Provided that the urethra is unobstructed, bladder contraction continues until emptying is complete; urethral and bladder neck tonus is then re-established and the bladder-filling cycle begins again. The main functional innervation of the prostate is through the sympathetic (noradrenergic) nervous system, although acetylcholinesterase-containing (presumably parasympathetic) and non-adrenergic, non-cholinergic nerve fibers are also present. These nerves are responsible for the maintenance of vasconstrictor tone. Sympathetic nerves control prostatic smooth muscle tone and can be modulated by α1-adrenoceptor blockers.
