sensory root

Examples of sensory root in the following topics:

• Trigeminal (V) Nerve

  • The ophthalmic and maxillary nerves are purely sensory.
  • 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.
  • From the trigeminal ganglion, a single large sensory root enters the brainstem at the level of the pons.
  • Immediately adjacent to the sensory root, a smaller motor root emerges from the pons at the same level.
  • Schematic illustration of the trigeminal nerve (labeled Sensory root above) and the structures it innervates in the face and mouth.

• Parasympathetic (Craniosacral) Division

  • Each has three roots entering the ganglion (motor, sympathetic, and sensory roots) and a variable number of exiting branches.
  • The motor root carries presynaptic parasympathetic nerve fibers (general visceral efferent fibers) that terminate in the ganglion by creating a synapse for the postsynaptic fibers traveling to target organs.
  • The sympathetic root carries postsynaptic sympathetic fibers (general visceral efferent fibers) that traverse the ganglion without creating a synapse.
  • The sensory root carries general sensory fibers (general somatic afferent fibers) that also do not create a synapse in the ganglion.
  • Some ganglia also carry special sensory fibers (special visceral afferent) for taste sensation.

• Sensory-Somatic Nervous System

  • The sensory-somatic nervous system is composed of cranial and spinal nerves and contains both sensory and motor neurons.
  • Sensory neurons transmit sensory information from the skin, skeletal muscle, and sensory organs to the central nervous system (CNS).
  • The sensory neuron cell bodies are grouped in structures called dorsal root ganglia .
  • Motor neurons have cell bodies in the ventral gray matter of the spinal cord that project to muscle through the ventral root.
  • The cell bodies of sensory neurons are located in dorsal root ganglia.

• Overview of the Spinal Cord

  • Thirty-one pairs of spinal nerves (sensory and motor) branch from the human spinal cord.
  • The posterior root is the sensory (afferent) root that carries sensory information to the brain from other areas of the body.
  • The anterior root is the motor (efferent) root that carries motor information to the body from the brain.
  • The swelling found in the posterior root is the posterior (dorsal) root ganglion, which contains the cell bodies of sensory neurons.
  • In addition, the cauda equina extends to sensory innervation of the perineum.

• Spinal Cord Grey Matter and Spinal Roots

  • These ganglia contain cell bodies of sensory neurons.
  • Axons of these sensory neurons travel into the spinal cord via the dorsal roots.
  • The nerve endings of dorsal root ganglion neurons have a variety of sensory receptors that are activated by mechanical, thermal, chemical, and noxious stimuli.
  • The presence of these channels in the dorsal root ganglion gives reason to believe that other sensory neurons may contain them as well.
  • These channels are found predominantly in smaller sensory neurons in the dorsal root ganglion cells and are activated by higher pressures, two attributes that are characteristic of nociceptors.

• Somatic Sensory Pathways

  • The somatosensory pathway is composed of three neurons located in the dorsal root ganglion, the spinal cord, and the thalamus.
  • The first always has its cell body in the dorsal root ganglion of the spinal nerve.
  • Like other sensory areas, there is a map of sensory space called a homunculus at this location.
  • Sensory nerves of a dorsal root ganglion are depicted entering the spinal cord.
  • The formation of the spinal nerve from the dorsal and ventral roots.

• Sensory and Motor Tracts

  • The spinothalamic tract is a sensory pathway originating in the spinal cord.
  • Somatosensory organization is divided into the dorsal column–medial lemniscus tract (the touch/proprioception/vibration sensory pathway) and the anterolateral system, or ALS (the pain/temperature sensory pathway).
  • Both sensory pathways use three different neurons to get information from sensory receptors at the periphery to the cerebral cortex.
  • These neurons are designated primary, secondary, and tertiary sensory neurons.
  • In both pathways, primary sensory neuron cell bodies are found in the dorsal root ganglia, and their central axons project into the spinal cord.

• Autonomic Ganglia

  • Autonomic ganglia are clusters of neuron cell bodies that transmit sensory signals from the periphery to the integration centers in the CNS.
  • The dorsal root ganglia lie along the vertebral column by the spine and develop in the embryo from neural crest cells, not neural tube.
  • A dorsal root ganglion (or spinal ganglion) is a nodule on a dorsal root of the spine that contains the cell bodies of nerve cells (neurons) that carry signals from the sensory organs towards the appropriate integration center.
  • The axons of dorsal root ganglion neurons are known as afferents.
  • The nerve endings of dorsal root ganglion neurons have a variety of sensory receptors that are activated by mechanical, thermal, chemical, and noxious stimuli.

• General Organization of the Somatosensory System

  • In the periphery, the primary neuron is the sensory receptor that detects sensory stimuli like touch or temperature.
  • The cell body of the primary neuron is housed in the dorsal root ganglion of a spinal nerve or, if sensation is in the head or neck, the ganglia of the trigeminal or cranial nerves.
  • At this location there is a map of sensory space referred to as a sensory homunculus. 
  • Periphery: Sensory receptors (i.e., thermoreceptors, mechanoreceptors, etc.) detect the various stimuli.
  • Image representing the cortical sensory homunculus.

• Somatic Sensory Pathways to the Cerebellum

  • A sensory system is a part of the nervous system responsible for processing sensory information.
  • A sensory system consists of sensory receptors, neural pathways, and the parts of the brain involved in sensory perception.
  • Commonly recognized sensory systems are those for vision, hearing, somatic sensation (touch), taste, and olfaction (smell).
  • Proprioceptive information is taken to the spinal cord via central processes of the dorsal root ganglia (where first order neurons reside).