QS Study

The sensation of pain and temperature is mediated through the lateral spinothalamic tract of the spinal cord. The lateral spinothalamic tract transmits pain and temperature. The somatosensory systems transmit information about the tactile world and the body’s position in that world to consciousness.

The pathway of pain and temperature is as follows.

(1) Receptors:

  1. Receptors for pain are free nerve endings.
  2. Receptors for cold sensation is the end bulb of Krause and for heat is Golgi – Mazzoni.

(2) The first order neuron:

The first order neuron is located in the dorsal nerve root ganglia. The processes of these neurons form sensory nerves which carry sensation from the receptors to the spinal cord where they synapse with the second order neurons. The axon of these neurons are small diameter, thinly myelinated (Aδ fibers) and unmyelinated (C fibers), and are thus slowly conducting.

(3) The second order neuron:

The second order neuron is located in the gray matter of the spinal cord. Their axons from the lateral spinothalamic tract. This track is crossed. It ascends through the lateral white column of the spinal cord to enter the brainstem where it is referred to as the spinal lemniscus. Finally, the track passes through the subthalamus to end in the thalamus. This tract ascends through the spinal cord, medulla, pons, and midbrain to the thalamus.

(4) The third order neuron: The third order neuron is the posterolateral ventral nucleus of the thalamus. Fibers arising in this nucleus pass through the internal capsule and the corona radiata to reach the somatosensory area of the cerebral cortex. Most of the spinothalamic tract fibers terminate upon third-order neurons in the ventral posterolateral (VPL) nucleus of the thalamus.

(5) Fourth-Order Neurons: Layer IV Neocortical neurons of Primary Somatosensory Cortex (Brodmann’s areas 3, 1, and 2).

Pathway of Pain and Temperature 1

Flowchart: Pathway of pain & temperature.

  • Sensory receptors for pain and temperature.
  • Peripheral nerves conduct the sensation.
  • Sensation comes to the first order neurons located in dorsal root ganglia.
  • Passes to the synapse.
  • Then it is carried to the second order neuron located in the lateral spinothalamic tract.
  • Decussation of fibers.
  • Passes to brainstem as spinal lemniscus Sensation passes to the third order neuron in the thalamus.
  • Through the internal capsule.
  • Sensation reaches the somatosensory area of the cerebral cortex.
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