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.

• Sensory-Somatic Nervous System

  • Humans have 12 cranial nerves, nerves that emerge from or enter the skull (cranium), as opposed to the spinal nerves, which emerge from the vertebral column.
  • Other cranial nerves contain a mix of sensory and motor fibers.
  • Spinal nerves transmit sensory and motor information between the spinal cord and the rest of the body.
  • Each of the 31 spinal nerves (in humans) contains both sensory and motor axons.
  • Spinal nerves contain both sensory and motor axons.

• 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.

• Spinal Cord

  • The spinal cord is a bundle of nerves that is connected to the brain and relays information from the brain to the body and vice versa.
  • Connecting to the brainstem and extending down the body through the spinal column is the spinal cord: a thick bundle of nerve tissue that carries information about the body to the brain and from the brain to the body.
  • The spinal cord is contained within the bones of the vertebral column, but is able to communicate signals to and from the body through its connections with spinal nerves (part of the peripheral nervous system).
  • Spinal cord injuries are notoriously difficult to treat because spinal nerves do not regenerate, although ongoing research suggests that stem cell transplants may be able to act as a bridge to reconnect severed nerves.
  • Researchers are also looking at ways to prevent the inflammation that worsens nerve damage after injury.

• 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).