| Sacral spinal nerve | |
|---|---|
 The plan of the lumbosacral plexus | |
| Details | |
| Identifiers | |
| Latin | nervi spinalis |
| FMA | 6426 |
| Anatomical terminology | |
The sacral spinal nerve 4 (S4) is a spinal nerve of the sacral segment. [1]
It originates from the spinal column from below the 4th body of the sacrum
S4 supplies many muscles, either directly or through nerves originating from S4. They are not innervated with S4 as single origin, but partly by S4 and partly by other spinal nerves. The muscles are:
The peripheral nervous system (PNS) is one of two components that make up the nervous system of bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside the brain and the spinal cord. The main function of the PNS is to connect the CNS to the limbs and organs, essentially serving as a relay between the brain and spinal cord and the rest of the body. Unlike the CNS, the PNS is not protected by the vertebral column and skull, or by the blood–brain barrier, which leaves it exposed to toxins.
The pudendal nerve is the main nerve of the perineum. It is a mixed nerve and also conveys sympathetic autonomic fibers. It carries sensation from the external genitalia of both sexes and the skin around the anus and perineum, as well as the motor supply to various pelvic muscles, including the male or female external urethral sphincter and the external anal sphincter.
The autonomic nervous system (ANS), formerly referred to as the vegetative nervous system, is a division of the nervous system that operates internal organs, smooth muscle and glands. The autonomic nervous system is a control system that acts largely unconsciously and regulates bodily functions, such as the heart rate, its force of contraction, digestion, respiratory rate, pupillary response, urination, and sexual arousal. This system is the primary mechanism in control of the fight-or-flight response.
The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system.
A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the corresponding cervical, thoracic, lumbar, sacral and coccygeal regions of the spine. There are eight pairs of cervical nerves, twelve pairs of thoracic nerves, five pairs of lumbar nerves, five pairs of sacral nerves, and one pair of coccygeal nerves. The spinal nerves are part of the peripheral nervous system.
The anal wink, anal reflex, perineal reflex, or anocutaneous reflex is the reflexive contraction of the external anal sphincter upon stroking of the skin around the anus.
The external sphincter muscle of male urethra, also sphincter urethrae membranaceae, sphincter urethrae externus, surrounds the whole length of the membranous urethra, and is enclosed in the fascia of the urogenital diaphragm.
A nerve plexus is a plexus of intersecting nerves. A nerve plexus is composed of afferent and efferent fibers that arise from the merging of the anterior rami of spinal nerves and blood vessels. There are five spinal nerve plexuses, except in the thoracic region, as well as other forms of autonomic plexuses, many of which are a part of the enteric nervous system. The nerves that arise from the plexuses have both sensory and motor functions. These functions include muscle contraction, the maintenance of body coordination and control, and the reaction to sensations such as heat, cold, pain, and pressure. There are several plexuses in the body, including:
The posterior cutaneous nerve of the thigh is a sensory nerve of the thigh. It is a branch of the sacral plexus. It supplies the skin of the posterior surface of the thigh, leg, buttock, and also the perineum.
The lumbar nerves are the five pairs of spinal nerves emerging from the lumbar vertebrae. They are divided into posterior and anterior divisions.
The perforating cutaneous nerve is a cutaneous nerve of the sacral plexus that provides sensory innervation to the skin of the buttocks.
Pelvic splanchnic nerves or nervi erigentes are splanchnic nerves that arise from sacral spinal nerves S2, S3, S4 to provide parasympathetic innervation to the organs of the pelvic cavity.
The ventral ramus is the anterior division of a spinal nerve. The ventral rami supply the antero-lateral parts of the trunk and the limbs. They are mainly larger than the dorsal rami.
Sacral nerve stimulation, also termed sacral neuromodulation, is a type of medical electrical stimulation therapy.
The external sphincter muscle of female urethra is a muscle which controls urination in females. The muscle fibers arise on either side from the margin of the inferior ramus of the pubis. They are directed across the pubic arch in front of the urethra, and pass around it to blend with the muscular fibers of the opposite side, between the urethra and vagina.
The sacral spinal nerve 5 (S5) is a spinal nerve of the sacral segment.
The sacral spinal nerve 3 (S3) is a spinal nerve of the sacral segment.
The sacral spinal nerve 2 (S2) is a spinal nerve of the sacral segment.
The sacral spinal nerve 1 (S1) is a spinal nerve of the sacral segment.
The ciliary ganglion is a parasympathetic ganglion located just behind the eye in the posterior orbit. Three types of axons enter the ciliary ganglion but only the preganglionic parasympathetic axons synapse there. The entering axons are arranged into three roots of the ciliary ganglion, which join enter the posterior surface of the ganglion.
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