13. The Peripheral Nervous System

How does the strength of a sensory stimulus affect the generator potential in sensory receptors?

Spatial discrimination is the ability to distinguish between and precisely identify two or more stimuli. In terms of touch, which of these body parts do you think would have the lowest degree of spatial discrimination?

Mark the following statements about the spinal cord as true or false. If a statement is false, correct it to make a true statement.

The corticospinal tracts are the main sensory tracts in the spinal cord.

The tracts of the posterior columns decussate in the ________, whereas the tracts of the anterolateral system decussate in the ________.

Which of the following statements is false?

a. The spinothalamic tracts are part of the anterolateral system.

b. Pain, temperature, and crude touch stimuli are carried by the anterolateral system.

c. Descending pathways from the brain and spinal cord can make the spinal cord less receptive to pain stimuli.

d. The thalamus serves as the 'gateway' for entry of all special sensory stimuli into the cerebral cortex, with the exception of audition (hearing).

Label the following components of the corticospinal tracts with numbers 1 through 6, with 1 being the origin of the tracts and 6 their destination.     

_____ Medullary pyramids where most fibers decussate.     

_____ Anterior horn of the spinal gray matter.     

_____ Midbrain and pons.      

_____ Upper motor neurons in the primary motor and premotor cortices.     

_____ Corona radiata and internal capsule.        

_____ Lateral funiculus of the spinal cord.

Which of the following somatic sensations is not carried by the posterior columns?

a. Tactile senses

b. Temperature

c. Proprioception

d. Stretch

Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

a. The somatic sensory division of the PNS detects sensory stimuli from the organs in the thoracic and abdominopelvic cavities.

Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

b. The somatic motor division of the PNS consists of lower motor neurons that directly innervate skeletal muscle fibers.