A&P Chapter 16.3 - Somatic Sensory Pathways

Primary somatosensory area

A region of the cerebral cortex posterior to the central sulcus in the postcentral gyrus of the parietal lobe of the cerebrum that localizes exactly the points of the body where somatic sensations originate.

Posterior column

Consists of two tracts: (1) cuneate fasciculus, which conveys nerve impulses for touch, pressure, vibration, and conscious proprioception from upper limbs, upper trunk, neck, and posterior head, and (2) gracile fasciculus, which conveys nerve impulses for touch, pressure, and vibration from lower limbs and lower trunk. Axons of first-order neurons from one side of body form posterior column on same side and end in medulla, where they synapse with dendrites and cell bodies of second-order neurons. Axons of second-order neurons decussate, enter medial lemniscus on opposite side, and extend to thalamus. Third-order neurons transmit nerve impulses from thalamus to primary somatosensory cortex on side opposite the site of stimulation

Anterior and posterior spinocerebellar

Convey nerve impulses from proprioceptors in trunk and lower limb of one side of body to same side of cerebellum. Proprioceptive input informs cerebellum of actual movements, allowing it to coordinate, smooth, and refine skilled movements and maintain posture and balance.

Spinothalamic

Conveys nerve impulses for pain, cold, warmth, itch, and tickle from limbs, trunk, neck, and posterior head. Axons of first-order neurons from one side of body synapse 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 side, and extend to thalamus. Third-order neurons transmit nerve impulses from thalamus to primary somatosensory cortex on side opposite the site of stimulation.

Trigeminothalamic

Conveys nerve impulses for touch, pressure, vibration, pain, cold, warmth, itch, and tickle from face, nasal cavity, oral cavity, and teeth. Axons of first-order neurons from one side of head synapse with 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 impulses from thalamus to primary somatosensory cortex on side opposite the site of stimulation.

spinocerebellar tracts

Somatic sensory impulses reach the cerebellum through this.

trigeminothalamic pathway

impulses for most somatic sensations—tactile, thermal and pain—from the face, nasal cavity, oral cavity and teeth

anterolateral (spinothalamic) pathway

impulses for pain, temperature, itch, tickle and posterior head

First-order neurons

impulses from somatic receptors to the brain stem or spinal cord.

Second-order neurons

impulses from the brain stem and spinal cord to the thalamus.

posterior column-medial lemniscus pathway

impulses from the limbs, trunk, neck and posterior head

Third-order neurons

impulses from the thalamus to the primary somatosensory area of the cortex on the same side.

Postcentral gyri

located on both parietal lobes of the brain are the sites for the primary somatosensory area.

Somatic sensory pathways

relay information from the somatic sensory receptors just described to the primary somatosensory area in the cerebral cortex and to the cerebellum