Principles of the Sensory System

Question 1

What is a primary neuron?

Answer 1

Where our sensations begin.

Question 2

Define transduction

Answer 2

The conversion of stimulus energy into a change in membrane potential

Question 3

Describe the labeled line code

Answer 3

Modality is represented by the activity of specific receptors and the CNS pathways to which they’re connected

Question 4

Discuss synesthesia

Answer 4

Cross wiring of circuits in the CNS during development. Allows people to experience colors in response to sounds.

Question 5

How is stimulus intensity encoded?

Answer 5

1. Frequency code
2. Population code
   - Stimulus intensity is encoded by the number of activated receptors.

Question 6

How is stimulus location encoded?

Answer 6

Spatial distribution of sensory neurons activated by a stimulus.

Question 7

Define adaptation

Answer 7

A decrease in receptor firing during constant stimulation. There are slow and fast adapting receptors

Question 8

What are Exteroceptors? Proprioceptors? Visceroceptors?

Answer 8

1. Exteroceptors - endings located in the skin. These receptors respond to external stimuli like touch, pressure, pain and temperature.
2. Proprioceptors - in muscles, tendons and joints. These receptors provide afferent information for reflex adjustments of muscle tension and for awareness of position and movement.
3. Visceroceptors - located in mesentery and hollow organs. They respond to internal stimuli like bowel and bladder distension. They’re involved in visceral reflexes and mediate sensations of fullness and discomfort

Question 9

Describe the Proprioceptive sense organs

Answer 9

These receptors are in muscles, tendons and joint capsules. There are 3 types: Muscle spindles, Golgi tendon organs and Ruffini endings.

Question 10

Discuss Muscle spindles

Answer 10

Organized in parallel muscle fibers and signal muscle length and rate of change of muscle

Question 11

Discuss Golgi tendon organs

Answer 11

Located at the junction of muscle and tendon. Signal for muscle tension and amount of force generated by contraction

Question 12

Discuss Ruffini endings

Answer 12

Found in joint capsules. Respond to static limb position and movement. Important fro balance, posture and limb movement.

Question 13

Discuss first-order DC-ML sensory fibers

Answer 13

Enter spinal cord and ascend in the dorsal columns to the gracile and cuneate nuclei in the brainstem.

Question 14

Discuss second-order DC-ML sensory fibers

Answer 14

Cross to the contralateral medulla via internal arcuate fibers and form the medial lemniscus. This ascends through the medulla and midbrain before terminating in the ventral posterolateral nucleus of the thalamus.

Question 15

Discuss third-order DC-ML sensory fibers

Answer 15

Neurons project through the internal capsule to the postcentral gyrus of the parietal lobe (Somatosensory cortex)

Question 16

What are the 4 proprioceptive tracts?

Answer 16

Lower limbs: Dorsal and Ventral spinocerebellar tracts

Upper limbs: Rostral and Cuneocerebellar tracts

Question 17

Whats the danger of lesions in the spinocerebellar pathways?

Answer 17

Ataxias; lack of coordination during walking

Question 18

Discuss lesions in the DC-ML pathway

Answer 18

A complete transverse lesion will produce bilateral effects. A Unilateral lesion (Brown-Sequard syndrome) will produce ipsilateral impairment.