The Somatosensory and Motor Pathways Flashcards
Characteristic of neural pathways when they cross from one side of the CNS to the other at some point along their journey.
Decussation
Characteristic of neural pathways when they consist of two or three neurons that contribute to successive tracts of the pathway.
Relay
Characteristic of neural pathways where they exhibit a precise spatial relationship among the tract fivers that reflect orderly mapping of the body.
Somatotopy
Characteristic of neural pathways where they are paired on the right and left with a member of the pair present on each side of the spinal cord or brain.
Symmetry
Neurons of the ascending pathway whose cells bodies reside in a ganglion. Conduct impulses from the cutaneous receptors of the skin and from proprioceptors to the spinal cord or brain stem.
First-Order Neurons
Neurons of the ascending pathway whose cell bodies reside in the dorsal horn of the spinal cord or in the medullary nuclei. Transmit impulses to the thalamus or cerebellum.
Second-Order Neurons
Neurons of the ascending pathway that have cell bodies in the thalamus. Relay impulses to the somatosensory cortex of the cerebrum.
Third-Order Neurons
Formed by the paired tracts of the dorsal white column (fasciculus cuneatus and fasciculus gracilis) and the medial lemniscus.
Dorsal Column-Medial Lemniscal Pathways
Location of neurons in the Dorsal Column-Medial Lemniscal Pathways
First-order neurons enter the dorsal root of the spinal cord, then enter the dorsal white column on the same side without synapsing. The synapse with second-order neurons occurs. in the nucleus cuneatus and nucleus gracilis in the medulla. These fibers cross over and ascend in the medial lemniscus to the thalamus, where they synapse with third-order neurons. Thalamic neurons then transmit impulses to the somatosensory cortex.
Function of Dorsal Column-Medial Lemniscal Pathways
Transmits sensory impulses from general sensory receptors of the skin and proprioceptors, which are interpreted as discriminative touch, pressure, and limb and joint position.
Arises in the medulla and terminates int eh thalamus.
Medial Lemniscus
Consists of the lateral and ventral spinothalamic tracts. Located in the lateral and ventral white columns.
Spinothalamic Pathways
Location of neurons in the Spinothalamic Pathways
First-order neurons enter the dorsal root of the spinal cord and synapse with second-order neurons in the dorsal horns. Fibers cross to the opposite side before ascending. Synapse with third-order neurons in the thalamus. Thalamic neurons then convey impulses to somatosensory cortex.
Function of the Spinothalamic Pathways
Transmits impulses concerned with pain, temperature, crude touch, and pressure to opposite side of brain for interpretation by somatosensory cortex.
Consists of the ventral and dorsal spinocerebellar tracts. Convey information to the cerebellum.
Spinocerebellar Pathway