nerve cord

Examples of nerve cord in the following topics:

• Characteristics of Chordata

  • Animals in the phylum Chordata share four key features: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.
  • It is located between the digestive tube and the nerve cord, providing skeletal support through the length of the body.
  • The dorsal hollow nerve cord derives from ectoderm that rolls into a hollow tube during development.
  • In contrast to the chordates, other animal phyla are characterized by solid nerve cords that are located either ventrally or laterally.
  • The nerve cord found in most chordate embryos develops into the brain and spinal cord, which comprise the central nervous system.

• 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.
  • In the human, 31 pairs of spinal nerves (sensory and motor) branch from the spinal cord.
  • Each spinal nerve is formed from the combination of nerve fibers from its posterior and anterior roots.
  • The cauda equina ("horse's tail") is the name for the collection of nerves in the vertebral column that extend beyond the cord.

• 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 Olfactory Nerve (I)-The olfactory nerve is instrumental for the sense of smell, it is one of the few nerves that are capable of regeneration.
  • The Abducens Nerve (VI)- The abducens nerve is a motor nerve that innervates the lateral rectus muscle of the eye, which controls lateral movement.

• 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.

• Function and Physiology of the Spinal Nerves

  • Spinal nerves connect the brain and spinal cord to the limbs and organs of the body.
  • The peripheral nervous system (PNS) consists of the nerves and ganglia outside of the brain and spinal cord.
  • 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 phrenic nerve arises from nerve roots C3, C4, and C5.
  • If the spinal cord is transected above C3, then spontaneous breathing is not possible.

• Sensory-Somatic Nervous System

  • Each cranial nerve has a name .
  • Spinal nerves transmit sensory and motor information between the spinal cord and the rest of the body.
  • Motor neurons have cell bodies in the ventral gray matter of the spinal cord that project to muscle through the ventral root.
  • These neurons are usually stimulated by interneurons within the spinal cord, but are sometimes directly stimulated by sensory neurons.
  • The cell bodies of motor neurons are found in the ventral portion of the gray matter of the spinal cord.

• Accessory (XI) Nerve

  • The accessory nerve is designated the 11th of 12 cranial nerves and it controls the muscles of the shoulder and neck.
  • Unlike the other 11 cranial nerves, the accessory nerve begins outside the skull.
  • In fact, most of the fibers of the nerve originate in neurons situated in the upper spinal cord.
  • Due to its unusual course, the accessory nerve is the only nerve that enters and exits the skull.
  • However, more modern characterizations of the nerve regard the cranial component as separate and part of the vagus nerve.

• Overview of the Spinal Nerves

  • 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 spinal nerve is formed by the combination of nerve fibers from the dorsal and ventral roots of the spinal cord.
  • The posterior distribution of the cervical nerves includes the suboccipital nerve (C1), the greater occipital nerve (C2) and the third occipital nerve (C3).
  • The subcostal nerve comes from nerve T12, and runs below the twelfth rib.
  • Spinal nerves arise from a combination of nerve fibers: the dorsal and ventral roots of the spinal cord.

• 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 running from the spine and formed by the ventral rami of the lower four cervical and first thoracic nerve roots (C5-C8, T1) .
  • The brachial plexus is divided into roots, trunks, divisions, cords, and branches.
  • These six divisions will regroup to become the three cords.
  • The cords are named by their position with respect to the axillary artery: The posterior cord is formed from the three posterior divisions of the trunks (C5-C8,T1), the lateral cord is the anterior divisions from the upper and middle trunks (C5-C7), and the medial cord is simply a continuation of the anterior division of the lower trunk (C8,T1)

• Trigeminal (V) Nerve

  • The trigeminal nerve is the fifth cranial nerve and it is responsible for sensation and motor function in the face and mouth.
  • The trigeminal nerve is the fifth cranial nerve, and it contains both sensory and motor fibers.
  • The trigeminal nerve is the largest of the cranial nerves.
  • Its name, "trigeminal," meaning "three twins," is derived from the fact that each nerve, one on each side of the pons, has three major branches: the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3) .
  • The trigeminal ganglion is analogous to the dorsal root ganglia of the spinal cord, which contain the cell bodies of incoming sensory fibers from the rest of the body.