The Somatosensory and Motor Pathways

Question 1

Characteristic of neural pathways when they cross from one side of the CNS to the other at some point along their journey.

Answer 1

Decussation

Question 2

Characteristic of neural pathways when they consist of two or three neurons that contribute to successive tracts of the pathway.

Answer 2

Relay

Question 3

Characteristic of neural pathways where they exhibit a precise spatial relationship among the tract fivers that reflect orderly mapping of the body.

Answer 3

Somatotopy

Question 4

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.

Answer 4

Symmetry

Question 5

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.

Answer 5

First-Order Neurons

Question 6

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.

Answer 6

Second-Order Neurons

Question 7

Neurons of the ascending pathway that have cell bodies in the thalamus. Relay impulses to the somatosensory cortex of the cerebrum.

Answer 7

Third-Order Neurons

Question 8

Formed by the paired tracts of the dorsal white column (fasciculus cuneatus and fasciculus gracilis) and the medial lemniscus.

Answer 8

Dorsal Column-Medial Lemniscal Pathways

Question 9

Location of neurons in the Dorsal Column-Medial Lemniscal Pathways

Answer 9

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.

Question 10

Function of Dorsal Column-Medial Lemniscal Pathways

Answer 10

Transmits sensory impulses from general sensory receptors of the skin and proprioceptors, which are interpreted as discriminative touch, pressure, and limb and joint position.

Question 11

Arises in the medulla and terminates int eh thalamus.

Answer 11

Medial Lemniscus

Question 12

Consists of the lateral and ventral spinothalamic tracts. Located in the lateral and ventral white columns.

Answer 12

Spinothalamic Pathways

Question 13

Location of neurons in the Spinothalamic Pathways

Answer 13

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.

Question 14

Function of the Spinothalamic Pathways

Answer 14

Transmits impulses concerned with pain, temperature, crude touch, and pressure to opposite side of brain for interpretation by somatosensory cortex.

Question 15

Consists of the ventral and dorsal spinocerebellar tracts. Convey information to the cerebellum.

Answer 15

Spinocerebellar Pathway

Question 16

Location of neurons in the Spinocerebellar Pathways

Answer 16

First-order neurons enter the dorsal root of the spinal cord and synapse with second-order neurons in the dorsal horn on the same side of the cord. Fibers ascend without crossing and terminate in the cerebellum . (No third-order neurons.)

Question 17

Function of the Spinocerebellar Pathways

Answer 17

Transmits impulses from trunk and lower limb on the same side of the body to the cerebellum for subconscious proprioception.

Question 18

Consists of the pyramidal cells of the motor cortex and the neurons of subcortical motor nuclei.

Answer 18

Upper Motor Neurons

Question 19

Consists of ventral horn motor neurons. Directly innervate the skeletal muscles.

Answer 19

Lower Motor Neurons

Question 20

Send impulses through the brain stem to the spinal cord without synapsing. Consists of the lateral and ventral corticospinal tracts.

Answer 20

Pyramidal Tracts

Question 21

Location of neurons in the lateral corticospinal tracts

Answer 21

Pyramidal cells of motor cortex of the cerebrum cross over in pyramids of the medulla. Descend along the lateral white column. Synapse with lower motor neurons in the ventral horn.

Question 22

Location of neurons in the ventral corticospinal tracts

Answer 22

Pyramidal cells of motor cortex cross over in the spinal cord. Descend along the lateral white column. Synapse with lower motor neurons in the ventral horn.

Question 23

Function of pyramidal tracts

Answer 23

Transmite motor impulses from cerebrum to spinal cord motor neurons which activate skeletal muscles on opposite side of the body. A voluntary motor tract.

Question 24

Includes all motor pathways that are not pyramidal. Multisynaptic. (Name the tracts.)

Answer 24

Indirect Pathways. (Includes reticulospinal tracts, vestibulospinal tracts, rubrospinal tracts, and tectospinal tract)

Question 25

Location of neurons in reticulospinal tracts

Answer 25

Originates in the reticular formation of the brain stem. Includes both crossed and uncrossed fibers. Descends along the medial and lateral white columns. Synapse with lower motor neurons in the ventral horn.

Question 26

Function of the reticulospinal tracts

Answer 26

Transmits impulses concerned with muscle tone and many visceral motor functions. May control most unskilled movements.

Question 27

Location of neurons in vestibulospinal tracts

Answer 27

Originates in the vestibular nuclei in the medulla of the brain stem. Fibers descend without crossing. Descends along the ventral white columns. Synapse with lower motor neurons in the ventral horn.

Question 28

Function of the vestibulospinal tracts

Answer 28

Transmits motor impulses that maintain muscle tone and activate ipsilateral limb and trunk extensor muscles and muscles that move the head. Helps maintain balance during standing and moving.

Question 29

Location of neurons in rubrospinal tracts

Answer 29

Originates in the red nucleus of the midbrain of the brain stem. Fibers cross to the opposite side just inferior to the red nucleus. Descends along the lateral white columns. Synapse with lower motor neurons in the ventral horn.

Question 30

Function of the rubrospinal tracts

Answer 30

Transmits motor impulses concerned with muscle tone of distal limb muscles (mostly flexors) on opposite side of the body.

Question 31

Location of neurons in tectospinal tracts

Answer 31

Originates in the superior colliculus of the midbrain of the brain stem. Fibers cross to the opposite side of the spinal cord. Descends along the lateral white columns. Synapse with lower motor neurons in the ventral horn.

Question 32

Function of the tectospinal tracts

Answer 32

Turns head so eyes can follow a moving object.