Mechanism of touch & temperature
- 1. MECHANISM OF TOUCH TEMPERATURE & PAIN FATIMA WAHID MANGRIO fatimawahid1234@gmail.com
- 3. Posterior Column–Medial Lemniscus Pathway to the Cortex Nerve impulses for touch, pressure, vibration, and conscious proprioception from the limbs, trunk, neck, and posterior head ascend to the cerebral cortex along the posterior column–medial lemniscus pathway. The name of the pathway comes from the names of two white-matter tracts that convey the impulses: the posterior column of the spinal cord and the medial lemniscus of the brain stem.
- 4. First-order neurons in the posterior column–medial lemniscus pathway extend from sensory receptors in the limbs, trunk, neck, and posterior head into the spinal cord and ascend to the medulla oblongata on the same side of the body. The cell bodies of these first-order neurons are in the posterior (dorsal) root ganglia of spinal nerves. In the spinal cord, their axons form the posterior (dorsal) columns, which consist of two parts: the gracile fasciculus and the cuneate fasciculus .
- 5. The axons synapse with the dendrites of second-order neurons whose cell bodies are located in the gracile nucleus or cuneate nucleus of the medulla. Nerve impulses for touch, pressure, vibration, and conscious proprioception from the upper limbs, upper trunk, neck, and posterior head propagate along axons in the cuneate fasciculus and arrive at the cuneate nucleus. Nerve impulses for touch, pressure, and vibration from the lower limbs and lower trunk propagate along axons in the gracile fasciculus and arrive at the gracile nucleus.
- 6. The axons of the second-order neurons cross to the opposite side of the medulla and enter the medial lemniscus, a thin ribbon like projection tract that extends from the medulla to the ventral posterior nucleus of the thalamus. In the thalamus, the axon terminals of second-order neurons synapse with third-order neurons, which project their axons to the primary somatosensory area of the cerebral cortex.
- 8. Anterolateral Pathway to the Cortex Nerve impulses for pain, temperature, itch, and tickle from the limbs, trunk, neck, and posterior head ascend to the cerebral cortex along the anterolateral (spinothalamic) pathway. Like the posterior column–medial lemniscus pathway, the anterolateral pathway is composed of three-neuron sets.
- 9. The first-order neurons connect a receptor of the limbs, trunk, neck, or posterior head with the spinal cord. The cell bodies of the first order neurons are in the posterior root ganglion. The axon terminals of the first-order neurons synapse with second-order neurons, whose cell bodies are located in the posterior gray horn of the spinal cord.
- 10. The axons of the second-order neurons cross to the opposite side of the spinal cord. Then, they pass upward to the brain stem as the spinothalamic tract. The axons of the second-order neurons end in the ventral posterior nucleus of the thalamus, where they synapse with the third-order neurons. The axons of the third order neurons project to the primary somatosensory area on the same side of the cerebral cortex as the thalamus.
- 12. Trigeminothalamic Pathway to the Cortex Nerve impulses for most somatic sensations (tactile, thermal, and pain) from the face, nasal cavity, oral cavity, and teeth ascend to the cerebral cortex along the trigeminothalamic pathway. Like the other somatosensory pathways just described, the trigeminothalamic pathway consists of three neuron sets First-order neurons extend from somatic sensory receptors in the face, nasal cavity, oral cavity, and teeth into the pons through the trigeminal (V) nerves.
- 13. The cell bodies of these first-order neurons are in the trigeminal ganglion. The axon terminals of some first-order neurons synapse with second-order neurons in the pons. The axons of other first order neurons descend into the medulla to synapse with second order neurons.
- 14. The axons of the second-order neurons cross to the opposite side of the pons and medulla and then ascend as the trigeminothalamic tract to the ventral posterior nucleus of the thalamus. In the thalamus, the axon terminals of the second order neurons synapse with third-order neurons, which project their axons to the primary somatosensory area on the same side of the cerebral cortex as the thalamus.