Somatic Sensory Pathways

Posterior Column Pathway

2 parts: Cuneate fasciculus & gracile fasciculus -Cuneate Fasciculus: touch, pressure, vibration, and conscious proprioception from upper limbs, upper trunk, neck, and posterior head -Gracile Fasciculus: touch, pressure, vibration from lower limbs and trunk Axons of first-order neurons from one side of body from posterior column on same side and end in MEDULLA, where they synapse w/ dendrites and cell bodies of the second-order neurons. Axons of second-order neurons decussate, enter medial lemniscus on opposite side, and extend to THALAMUS. Third-order neurons transmit nerve impulse from thalamus to primary somatosensory cortex on side opposite the site of stimulation.

Third-order neurons

Conduct impulses from the thalamus to the primary somatosensory area of the cortex on the SAME side

Second-order neurons

Impulses from brain stem and spinal cord to the thalamus. Axons of second-order neurons DECUSSATE (cross over to OPPOSITE side) in brain or spinal cord before ascending to the ventral posterior nucleus of the thalamus *all somatic sensory info from one side of the body reaches the thalamus on the OPPOSITE side*

Anterolateral Pathway "Spinothalamic"

Pain, cold, warmth, itch, and tickle from the limbs, trunk, neck and posterior head -Axons of first-order from one side of body synapses with dendrites and cell bodies of second-order neurons in posterior gray horn on same side of body. Axons of second-order neurons decussate, enter spinothalamic tract on opposite, and extend to THALAMUS. Third-order neurons transmit nerve impulse from THALAMUS to primary somatosensory cortex on side opposite the site of stimulation

Anterior and Posterior Spinocerebellar

Proprioceptors in trunk and lower limb of one side of body to same side CEREBELLUM. Proprioceptive input informs CEREBELLUM of actual movements, allowing it to coordinate, smooth, and refine skilled movements and maintain posture and balance.

Relay Station

Region w/in the CNS where neurons synapse with other neurons that are a part of a particular sensory or motor pathway

Somatic Sensory Pathways

Relay info form the somatic sensory receptors just described to the primary somatosensory area in the cerebral cortex and to cerebellum. The pathways to the cerebral cortex consists of thousands of sets of three neurons: 1st, 2nd, and 3rd order neurons

Trigeminothalamic Pathway

Touch, pressure, vibration, pain, cold, warmth, itch, tickle from face, nasal cavity, oral cavity, and teeth. -Axons of first-order neurons from one side of head synapse w/ dendrites and cell bodies of second-order neurons in PONS and MEDULLA on same side of head. Axons of second-order neurons decussate, enter trigeminothalamic tract on opposite side, and extend to THALAMUS. Third-order neurons transmit nerve impulse from thalamus to primary somatosensory cortex on side OPPOSITE the site of stimulation

First-order neurons

impulses from somatic receptors into the brainstem or spinal cord. face, mouth, teeth, eyes, somatic sensory impulses propagate along cranial nerves into the brainstem neck, trunk, limbs, posterior aspect of head, somatic sensory impulses propagate along spinal nerves into the spinal cord