spinal accessory nerve

Examples of spinal accessory nerve in the following topics:

• Accessory (XI) Nerve

  • Traditional descriptions of the accessory nerve divide it into two components: a spinal component and a cranial component.
  • 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.
  • During neurological examinations, the function of the spinal accessory nerve is often measured by testing the range of motion and strength of the aforementioned muscles.
  • Patients with spinal accessory nerve palsy may exhibit signs of lower motor neuron disease, such as atrophy and fasciculations of both the sternocleidomastoid and trapezius muscles.
  • Upon exiting the skull via the jugular foramen, the spinal accessory nerve pierces the sternocleidomastoid muscle before terminating on the trapezius muscle.

• 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.

• Function and Physiology of the Spinal Nerves

  • Spinal nerves connect the brain and spinal cord to the limbs and organs of the body.
  • The term spinal nerve generally refers to a mixed spinal nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body.
  • The spinal nerve C1 (suboccipital nerve) provides motor innervation to muscles at the base of the skull.
  • The last four cervical spinal nerves, C5 through C8, and the first thoracic spinal nerve, T1, combine to form the brachial plexus, or plexus brachialis, a tangled array of nerves, splitting, combining and recombining to form the nerves that subserve the upper limb region and upper back.
  • Manages heart control via dedicated cardiac branches of the vagus and thoracic spinal accessory nerves.

• Brief Overview of Cranial Nerves

  • Cranial nerves are the nerves that emerge directly from the brain (including the brainstem).
  • In contrast, spinal nerves emerge from segments of the spinal cord.
  • Spinal nerves emerge sequentially from the spinal cord with the spinal nerve closest to the head (C1) emerging in the space above the first cervical vertebra.
  • 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.

• Cervical Plexus

  • The cervical plexus is the plexus of the ventral rami of the first four cervical spinal nerves.
  • 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.
  • There are two additional branches that are formed by the posterior roots of the spinal nerves:

• 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.
  • They are somatic nerves.
  • These three types of nerves continue the signal of the ascending respiratory pathway from the spinal cord to stimulate the muscles that perform the movements needed for respiration.

• Branches of Spinal Nerves

  • The spinal nerves branch into the dorsal ramus, ventral ramus, the meningeal branches, and the rami communicantes.
  • Some ventral rami merge with adjacent ventral rami to form a nerve plexus, a network of interconnecting nerves.
  • Nerves emerging from a plexus contain fibers from various spinal nerves, which are now carried together to some target location.
  • The meningeal branches (recurrent meningeal or sinuvertebral nerves): These branch from the spinal nerve and re-enter the intervertebral foramen to serve the ligaments, dura, blood vessels, intervertebral discs, facet joints, and periosteum of the vertebrae.
  • This diagram depicts the course and branches of a typical thoracic spinal nerve.

• Overview of the Spinal Nerves

  • The term spinal nerve generally refers to a mixed spinal nerve that carries motor, sensory, and autonomic signals between the spinal cord and the body.
  • The spinal nerves are part of the peripheral nervous system (PNS).
  • Each spinal nerve is formed by the combination of nerve fibers from the dorsal and ventral roots of the spinal cord.
  • This is true for all spinal nerves except for the first spinal nerve pair, which emerges between the occipital bone and the atlas (the first vertebra).
  • Spinal nerves arise from a combination of nerve fibers from the dorsal and ventral roots of the spinal cord.

• Overview of the Spinal Cord

  • The spinal nerves of the thoracic region supply the thorax and abdomen.
  • The nerves of the lumbosacral spinal cord supply the pelvic region, legs, and feet.
  • Thirty-one pairs of spinal nerves (sensory and motor) branch from the human spinal cord.
  • Each spinal nerve is formed from the combination of nerve fibers from its posterior and anterior roots.
  • The spinal nerve emerges from the spinal column through the opening (intervertebral foramen) between adjacent vertebrae.

• Plexuses

  • Nerve plexuses are composed of afferent and efferent fibers that arise from the merging of the anterior rami of spinal nerves and blood vessels.
  • The brachial plexus is formed by the ventral rami of C5–C8 and the T1 spinal nerves, and lower and upper halves of the C4 and T2 spinal nerves.
  • The sacral plexus is formed by the ventral rami of L4-S3, with parts of the L4 and S4 spinal nerves.
  • The coccygeal plexus serves a small region over the coccyx and originates from S4, S5, and Co1 spinal nerves.
  • The lumbar plexus is comprised of the ventral rami of the lumbar spinal nerves (L1–L5) and a contribution from thoracic nerve (T12).