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Flashcards in Principles of the Sensory System Deck (18):

What is a primary neuron?

Where our sensations begin.


Define transduction

The conversion of stimulus energy into a change in membrane potential


Describe the labeled line code

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


Discuss synesthesia

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


How is stimulus intensity encoded?

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


How is stimulus location encoded?

Spatial distribution of sensory neurons activated by a stimulus.


Define adaptation

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


What are Exteroceptors? Proprioceptors? Visceroceptors?

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


Describe the Proprioceptive sense organs

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


Discuss Muscle spindles

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


Discuss Golgi tendon organs

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


Discuss Ruffini endings

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


Discuss first-order DC-ML sensory fibers

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


Discuss second-order DC-ML sensory fibers

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.


Discuss third-order DC-ML sensory fibers

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


What are the 4 proprioceptive tracts?

Lower limbs: Dorsal and Ventral spinocerebellar tracts
Upper limbs: Rostral and Cuneocerebellar tracts


Whats the danger of lesions in the spinocerebellar pathways?

Ataxias; lack of coordination during walking


Discuss lesions in the DC-ML pathway

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