accessory nerve

Examples of accessory nerve in the following topics:

• Accessory (XI) Nerve

  • The accessory nerve (cranial nerve XI) controls the muscles of the shoulder and neck.
  • The accessory nerve (cranial nerve XI) controls the sternocleidomastoid and trapezius muscles of the shoulder and neck.
  • Unlike the other 11 cranial nerves, the accessory nerve begins outside the skull.
  • Due to its unusual course, the accessory nerve is the only nerve that enters and exits the skull.
  • Therefore, in contemporary discussions of the accessory nerve, it is common to disregard the cranial component when referencing the accessory nerve and assume reference to the spinal accessory nerve.

• Brachial Plexus

  • The brachial plexus is formed by the four lower cervical spinal nerves and the first thoracic spinal nerve.
  • The brachial plexus is a network of nerve fibers that run from the spine that are formed by the ventral rami of the lower four cervical and first thoracic nerve roots (C5–C8, T1).
  • It is a collection of nerves passing through the cervico-axillary canal to reach the axilla and innervate the brachium, the antebrachium, and the hand.
  • The brachial plexus is responsible for cutaneous and muscular innervation of the entire upper limb, with two exceptions: the trapezius muscle is innervated by the spinal accessory nerve (CN XI) and an area of skin near the axilla is innervated by the intercostobrachial nerve.
  • Five roots: The five anterior rami of the spinal nerves, after they have given off their segmental supply to the muscles of the neck.

• Cervical Plexus

  • There is anastomosis with the accessory nerve, hypoglossal nerve, and sympathetic trunk.
  • The lesser occipital nerve, or small occipital nerve, is a cutaneous spinal nerve that arises between the second and third cervical vertebrae, along with the greater occipital nerve.
  • The great auricular nerve originates from the cervical plexus and is composed of branches from spinal nerves C2 and C3.
  • The supraclavicular nerves (descending branches) arise from the third and fourth cervical nerves.
  • The phrenic nerve (C3–C5, but primarily C4) is a nerve that originates in the neck and passes down between the lung and heart to reach the diaphragm.

• Brief Overview of Cranial Nerves

  • Cranial nerves are the nerves that emerge directly from the brain (including the brainstem).
  • The terminal nerves, olfactory nerves (I) and optic nerves (II) emerge from the cerebrum or forebrain, and the remaining ten pairs arise from the brainstem, which is the lower part of the brain.
  • The optic nerve (II): This nerve carries visual information from the retina of the eye to the brain.
  • The spinal accessory (XI): This nerve controls specific muscles of the shoulder and neck.
  • The hypoglossal nerve (XII): This nerve controls the tongue movements of speech, food manipulation, and swallowing.

• Function and Physiology of the Spinal Nerves

  • The spinal nerve C1 (suboccipital nerve) provides motor innervation to muscles at the base of the skull.
  • These include the greater occipital nerve that provides sensation to the back of the head, the lesser occipital nerve that provides sensation to the area behind the ears, the greater auricular nerve, and the lesser auricular nerve.
  • The phrenic nerve arises from nerve roots C3, C4, and C5.
  • Manages heart control via dedicated cardiac branches of the vagus and thoracic spinal accessory nerves.
  • PNS nerves are involved in the erection of genital tissues via the pelvic splanchnic nerves 2–4.

• Neural Mechanisms (Cortex)

  • The processes that drive its functions aren't fully understood, but it works by sending signals to the spinal cord, which sends signals to the muscles it controls, such as the diaphragm and the accessory muscles for respiration.
  • The phrenic nerves: The nerves that stimulate the activity of the diaphragm.
  • They are autonomic nerves.
  • It is a major autonomic nerve.
  • They are somatic nerves.

• Fibrous Joints

  • These joints have a synovial cavity and are united by the dense irregular connective tissue that forms the articular capsule normally associated with accessory ligaments.
  • It also pumps blood and lymph from the periodontal membrane into the dental veins and lymph channels and stimulates sensory nerve terminals in the membrane to send signals to the brain centers that control the muscles of mastication.

• Proprioceptor Regulation of Breathing

  • When the lungs are inflated to their maximum volume during inspiration, the pulmonary stretch receptors send an action potential signal to the medulla and pons in the brain through the vagus nerve.
  • The pneumotaxic center of the pons sends signals to inhibit the apneustic center of the pons, so it doesn't activate the inspiratory area (the dorsal medulla), and the inspiratory signals that are sent to the diaphragm and accessory muscles stop.
  • As the Hering–Bauer reflex uses the vagus nerve as its neural pathway, it also has a few cardiovascular system effects because the vagus nerve also innervates the heart.
  • During stretch receptor activation, the inhibitory signal that travels through the vagus nerve is also sent to  the sinus-atrial node of the heart.
  • The vagus nerve is the neural pathway for stretch receptor regulation of breathing.

• Male Reproductive Anatomy

  • In the male reproductive system, the scrotum houses the testicles or testes, providing passage for blood vessels, nerves, and muscles related to testicular function.
  • Semen is a mixture of sperm and spermatic duct secretions (about 10 percent of the total), along with fluids from accessory glands, that contribute most of the semen's volume.
  • The bulk of the semen comes from the accessory glands associated with the male reproductive system, including the seminal vesicles, the prostate gland, and the bulbourethral gland .
  • An orgasm is a two-stage process: first, glands and accessory organs connected to the testes contract; second, semen (containing sperm) is expelled through the urethra during ejaculation.

• Trochlear (IV) Nerve

  • The trochlear nerve (cranial nerve IV) is a motor nerve that innervates a single muscle: the superior oblique muscle of the eye.
  • The trochlear nerve (cranial nerve IV) is a motor nerve that innervates a single muscle: the superior oblique muscle of the eye.
  • The trochlear nerve is unique among the cranial nerves in several respects.
  • Other than the optic nerve (cranial nerve II), it is the only cranial nerve that decussates (crosses to the other side) before innervating its target.
  • Lesions of all other cranial nuclei affect the ipsilateral side (except of course the optic nerve, cranial nerve II, which innervates both eyes).