dorsal nerve cord

Examples of dorsal 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.
  • The nerve cord found in most chordate embryos develops into the brain and spinal cord, which comprise the central nervous system.
  • In chordates, four common features appear at some point during development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.

• Chordates and the Evolution of Vertebrates

  • Adults only maintain pharyngeal slits and lack a notochord, a dorsal hollow nerve cord, and a post-anal tail.
  • Members of Cephalochordata possess a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail in the adult stage.
  • (b) The larval stage of the tunicate possesses all of the features characteristic of chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.
  • (c) In the adult stage, the notochord, nerve cord, and tail disappear.
  • Adult lancelets retain the four key features of chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.

• Phylum Chordata

  • A notochord, or a longitudinal, flexible rod between the digestive tube and the nerve cord .
  • A dorsal nerve cord which develops from a plate of ectoderm that rolls into a tube located dorsal to the notochord.
  • Other animal phyla have solid nerve cords ventrally located.
  • A chordate nerve cord splits into the central nervous system: the brain and spinal cord.
  • While tunicates are invertebrates and may seem very different from the more familiar members of Chordata, the tunicate larva possesses both a notochord and a dorsal nerve cord, although both are lost in adulthood.

• 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.
  • Each spinal nerve is formed by the combination of nerve fibers from the dorsal and ventral roots of the spinal cord.
  • The dorsal roots carry afferent sensory axons, while the ventral roots carry efferent motor axons.
  • The dorsal ramus contains nerves that serve the dorsal portions of the trunk; it carries visceral motor, somatic motor, and somatic sensory information to and from the skin and muscles of the back (epaxial muscles).
  • Spinal nerves arise from a combination of nerve fibers from the dorsal and ventral roots of the spinal cord.

• Spinal Cord Grey Matter and Spinal Roots

  • The grey matter of the spinal cord contains neuronal cell bodies, dendrites, axons, and nerve synapeses.
  • The cord has grooves in the dorsal and ventral sides.
  • Each segment of the spinal cord is associated with a pair of ganglia, called dorsal root ganglia, which are situated just outside of the spinal cord.
  • Axons of these sensory neurons travel into the spinal cord via the dorsal roots.
  • Dorsal roots and ventral roots come together and exit the intervertebral foramina as they become spinal nerves.

• Autonomic Ganglia

  • A dorsal root ganglion (or spinal ganglion) is a nodule on a dorsal root of the spine that contains cell bodies of nerve cells (neurons) that carry signals from sensory organs towards the appropriate integration center.
  • Unlike the majority of neurons found in the central nervous system, an action potential in dorsal root ganglion neuron may initiate in the distal process in the periphery, bypass the cell body, and continue to propagate along the proximal process until reaching the synaptic terminal in the dorsal horn of the spinal cord.
  • The nerve endings of dorsal root ganglion neurons have a variety of sensory receptors that are activated by mechanical, thermal, chemical, and noxious stimuli.
  • They contain approximately 20,000–30,000 nerve cell bodies and are located close to and on either side of the spinal cord in long chains.
  • Preganglionic nerves from the spinal cord synapse end at one of the chain ganglia and the postganglionic fiber extends to an effector, typically a visceral organ in the thoracic cavity.

• 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).
  • Axons and cell bodies in the dorsal (facing the back of the animal) spinal cord convey mostly sensory information from the body to the brain.
  • 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.

• Sensory-Somatic Nervous System

  • Spinal nerves transmit sensory and motor information between the spinal cord and the rest of the body.
  • The sensory neuron cell bodies are grouped in structures called dorsal root ganglia .
  • Each sensory neuron has one projection with a sensory receptor ending in skin, muscle, or sensory organs, and another that synapses with a neuron in the dorsal spinal cord.
  • The cell bodies of sensory neurons are located in dorsal root ganglia.
  • The cell bodies of motor neurons are found in the ventral portion of the gray matter of the spinal cord.

• Overview of the Spinal Cord

  • 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 swelling found in the posterior root is the posterior (dorsal) root ganglion, which contains the cell bodies of sensory neurons.
  • The cauda equina ("horse's tail") is the name for the collection of nerves in the vertebral column that extends beyond the cord.

• Somatic Sensory Pathways to the Cerebellum

  • The ventral and dorsal spinocerebellar tracts convey proprioceptive information from the body to the cerebellum.
  • The dorsal spinocerebellar tract does not decussate, or cross sides, at all through its path.
  • The axon runs via the fila radicularia (nerve rootlets) to the dorsal horn of the gray matter.
  • Axons first cross midline in the spinal cord and run in the ventral border of the lateral funiculi.
  • Proprioceptive information is taken to the spinal cord via central processes of the dorsal root ganglia (where first order neurons reside).