mixed spinal nerve

Examples of mixed spinal nerve in the following topics:

• Overview of the Spinal Nerves

  • Spinal nerves, a part of the peripheral nervous system (PNS), are mixed nerves that send motor, sensory, and autonomic signals between the CNS and the body.
  • 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.
  • 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.

• 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.
  • Each pair of spinal nerves roughly correspond to a segment of the vertebral column: 8 cervical spinal nerve pairs (C1–C8), 12 thoracic pairs (T1–T12), 5 lumbar pairs (L1–L5), 5 sacral pairs (S1–S5), and 1 coccygeal pair.
  • 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.

• Classification of Nerves

  • Nerves are primarily classified based on their direction of travel to or from the CNS, but they are also subclassified by other nerve characteristics.
  • Mixed nerves contain both afferent and efferent axons, and thus conduct both incoming sensory information and outgoing muscle commands in the same nerve bundle.
  • Spinal nerves innervate much of the body and connect through the spinal column to the spinal cord.
  • Spinal nerves are assigned letter-number designations according to the vertebra where they connect to the spinal column.
  • Schematic of efferent and afferent nerve transmission to and from peripheral tissue and spinal cord.

• 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.

• Accessory (XI) Nerve

  • In fact, most of the fibers of the nerve originate in neurons situated in the upper spinal cord.
  • 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.
  • Upon exiting the skull via the jugular foramen, the spinal accessory nerve pierces the sternocleidomastoid muscle before terminating on the trapezius muscle.

• 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.

• 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).

• Dermatomes

  • A dermatome is an area of skin that is supplied by a single spinal nerve, and a myotome is a group of muscles that a single spinal nerve root innervates.
  • A dermatome is an area of skin that is supplied by a single spinal nerve .
  • A myotome is the group of muscles that a single spinal nerve root innervates.
  • Results may indicate lesions to the spinal cord nerve root, or intervertebral disc herniation that presses on the spinal nerve roots.
  • Dermatomes are areas of skin supplied by sensory neurons that arise from a spinal nerve ganglion.

• Axon Bundles

  • Nerves in the PNS are typically divided into cranial and spinal nerves.
  • There are twelve pairs of cranial nerves and thirty one pair of spinal nerves.
  • In addition, cranial nerves have descriptive names.
  • Spinal nerves innervate much of the body, and connect through the spinal column to the spinal cord.
  • They are given letter-number designations according to the vertebra through which they connect to the spinal column .