18.4:
Overview of Somatic Sensory Pathways
The somatic sensory pathways transmit impulses from sensory receptors to the cerebral cortex or the cerebellum.
These pathways are composed of bundles of nerve fibers called tracts arranged on opposite sides of the spinal cord. Each tract is composed of axons that originate and terminate at the same destination.
There are three major somatic sensory pathways.
The posterior column-medial lemniscus pathway transmits impulses for fine touch, vibration, and proprioception.
The spinothalamic pathway conducts impulses for pain, temperature, and crude touch.
Both of these pathways terminate in the primary somatosensory cortex and contribute to conscious perception.
The spinocerebellar pathway carries proprioceptive impulses that are not consciously perceived. This is because this pathway does not reach the cerebral cortex but instead terminates in the cerebellum.
The somatosensory pathways start with first-order neurons that transmit impulses from receptors to the spinal cord or brainstem.
Then, second-order neurons carry the impulse to the cerebellum or thalamus.
Finally, third-order neurons conduct impulses from the thalamus to the primary somatosensory area of the cerebral cortex.
18.4:
Overview of Somatic Sensory Pathways
Somatic sensory or somatosensory pathways refer to the neural pathways that carry information related to touch, pressure, pain, temperature, and proprioception from the skin, muscles, tendons, and joints to the brain. These pathways involve several stages of processing and integration of sensory information.
The somatosensory system is divided into three main pathways: the dorsal (or posterior) column-medial lemniscus, spinothalamic (or anterolateral), and spinocerebellar pathways.
The dorsal column-medial lemniscus pathway transmits information related to proprioception, fine touch, and vibration sensation. It starts with the primary sensory neurons in the spinal cord, which synapse with secondary sensory neurons in the dorsal column nuclei in the medulla oblongata. The axons of the secondary neurons then cross over to the opposite side of the brainstem and ascend through the medial lemniscus to the thalamus, where they synapse with tertiary sensory neurons. The tertiary sensory neurons then project to the primary somatosensory cortex, where the information is processed and integrated.
The spinothalamic pathway transmits information related to pain, temperature, and crude and coarse touch sensations. It starts with the primary sensory neurons, which conduct information from the periphery to the spinal cord. These neurons then synapse with secondary sensory neurons, which cross over to the opposite side of the spinal cord and ascend through the spinothalamic pathway to the thalamus, where they synapse with tertiary sensory neurons. The tertiary sensory neurons then project to the primary somatosensory cortex, where the information is processed and integrated.
The spinocerebellar pathway is a neural pathway that carries sensory information related to proprioception from the muscles and joints to the cerebellum that overall helps in motor coordination and control. Unlike other somatosensory pathways, the spinocerebellar pathway does not involve conscious perception of sensory information.