Week 2 Objective 3: Somatic Senses and Pathways

Question 1

Somatic senses: function and types (broadly)

Answer 1

collects sensory information from all over the body

types include:

1. mechanoreceptive
2. thermoreceptive
3. pain

Question 2

These include both tactile and position senses that are stimulated by mechanical displacement of some tissue of the body

Answer 2

mechanoreceptive somatic senses

Question 3

Mechanoreceptor skin receiving tactile sensibilities

Answer 3

Expanded tip endings such as Merkel’s discs

Encapsulated endings: Meissner’s corpuscle, Kraus’ corpuscles

Question 4

Mechanoreceptor deep tissue sensibilities

Answer 4

Free & expanded tip
Spray endings: Ruffini’s corpuscle
Encapsulated endings: Pacinian corpuscles

Question 5

Ascending pathways: number of neurons involved, where those are located and what they do

Answer 5

1. Primary sensory neurons: external regions to dorsal roots of spinal cord
2. Secondary neurons: make up tracts in spinal cord and brainstem
3. Tertiary neurons: from thalamus to primary cortex, travel through internal capsule

Question 6

Ascending pathways for conscious perception include

Answer 6

Spinothalamic system

medial leminiscal system

Question 7

Ascending pathways for unconscious perception include

Answer 7

spino-cerebellar
spino-olivary
spinotectal
spinorecticular

Question 8

Lateral spinothalamic tract: differences from anterior spinothalamic tract

Answer 8

Carries pain and temperature

differences

later ascends 2-3 segments before synapsing with secondary fiber; decussates through anterior gray and white commissures; carries pain and temp; tertiary fibers synapse in postcentral gyrus (somatic sensory 3, 1, 2) , tertiary fibers form PART OF THE INTERNAL CAPSULE

anterior ascends 8-10 segments before synapsing; decussates in anterior gray OR white commissures; tertiary fibers ascend THROUGH INTERNAL CAPSULE to primary sensory cortex

Question 9

Lateral spinothalamic tract: similarities to anterior spinothalamic tract

Answer 9

both use 3 neuron system; ascend; decussate; synapse in the VPL of the thalamus

Question 10

Medial Lemniscus System

Answer 10

also called “Posterior Column System”

carries sensations for two point sensation ie fine touch, pressure, vibration

primary fibers ascend entire length of spinal cord and synapse in the secondary neurons in the medulla

fasciculus gracilis
fasciculus cuneatus

secondary fibers decussate, ascend, synapse in VPL of thalamus

tertiary ascend through internal capsule to primary motor cortex

Question 11

fasciculus gracilis

Answer 11

fibers of the FG synapse in nucleus gracilis

convey sensations from below midthoracic level

Question 12

fasciculus cuneatus

Answer 12

fibers of the FC synapse in the nucleus cuneatus

conveys sensations from above midthoracic level

also conveys proprioceptic sensation from arms to cerebellum