Somatosensory system

Question 1

What is the most important sense for humans?

Answer 1

Vision.

Question 2

True or false: not all nerve endings require receptors to convert afferent signal to electrical impulses.

Answer 2

True

Question 3

What are 4 types of information conveyed by the somatosensory system?

Answer 3

• Modality
• Location
• Intensity
• Time course

Question 4

For afferent information, name from where start and end the three neuron orders (first-order, second-order, …).

Answer 4

• First-order neurons reach to spinal cord
• Second-order neurons reach to thalamus (relay)
• Third-order neurons reach to proper area of the brain for perception

Question 5

What are the three sub-systems of somatosensory system?

Answer 5

• Fine touch, vibration and pressure (cutaneous mechanoreceptors)
• Proprioception
• Temperature, pain

Question 6

Where are located the cell bodies of afferent fibers in the body (spinal cord)? In the head (brainstem)?

Answer 6

Spinal cord -> dorsal root ganglion

Brain -> trigeminal ganglion

Question 7

What kind of neuron is found in dorsal root ganglia? Why does it have a faster information transmission than bipolar neurons?

Answer 7

Pseudounipolar neurons. They have a fast transmission because information does not need to be pass by the soma.

Question 8

True or false: afferent fiber terminals that are encapsulated have an higher excitation threshold than free terminals?

Answer 8

False: lower excitation threshold.

Question 9

What is the required stimulus for activation of mechanosensitive channels? Name on mechanosensitive channel.

Answer 9

Stimulus: physical deformation. Piezo1 and Piezo2 are mechanosensitive channels.

Question 10

What is the fastest sensory perception? Why?

Answer 10

Proprioception. It is vital.

Question 11

What are the receptors of proprioception?

Answer 11

Muscle spindles
Golgi tendons
Joint receptors

Question 12

What factors determine the receptive field?

Answer 12

• Branching of sensory afferents in the skin (arborization level).
• Density of afferent innervation.

Question 13

Sensory receptors closer to skin surface tend to have a smaller or bigger receptive field?

Answer 13

Smaller.

Question 14

There are two general types of sensory afferents that respond differently to temporal dynamics upon stimulation. What are they?

Answer 14

Rapidly adapting afferents (fire upon initiation of stimulation) and slowly adapting afferents (fire upon sustained stimulation).

Question 15

Arrange the mechanoreceptors of touch in order of depth (from close to skin surface to away): Ruffini corpuscles, Merkel cells, Pacinian corpuscles and Meissner corpuscles.

Answer 15

Meissner > Merkel >Ruffini >Pacinian

Question 16

Link the stimuli to the touch mechanoreceptor.

Mechanoreceptors:

• Ruffini corpuscles
• Merkel cells
• Pacinian corpuscles
• Meissner corpuscles

Stimuli:

• Edges and curvature
• Skin motion
• Skin stretch
• Vibration

Answer 16

Ruffini corpuscles - Skin stretch
Merkel cells - Edges and curvature
Pacinian corpuscles - Vibration
Meissner corpuscles - Skin motion

Question 17

Information in spinal cord is organized ipsilaterally or contralaterally?

Answer 17

Ipsilaterally.

Question 18

What are the two type of mechanoreceptors specialized for proprioception?

Answer 18

Muscle spindles and golgi tendon organs.

Question 19

Give two differences between muscle spindles and golgi tendon organs.

Answer 19

Muscle spindles:

• Parallel to extrafusal muscle fibers
• Provides sensory information about position

Golgi tendon organs:

• In serial position compared to extrafusal muscle fibers
• Provides sensory information about force

Question 20

Name two differences about the afferent circulation to the cerebellum of information between lower body parts and upper body parts.

Answer 20

Information from lower body parts ascend in the dorsal spinocerebellar tract.
Information from upper body parts ascend in the dorsal column.

Information from lower body parts synapse to Clarke’s nucleus.
Information from upper body parts synapse to cuneate nucleus.

Question 21

Where is limb proprioceptive information conveyed? Neck and head proprioceptive information?

Answer 21

Limb: primary somatosensory cortex.
Head: anterior cingulate and insula, and second somatosensory complex.

Question 22

True or false: information from different somatosensory receptor types become mixed in their passage to thalamus before reaching the cortex.

Answer 22

False: information remains segregated.

Question 23

What are the four Bordmann’s areas of the primary somatosensory cortex (S1)? What are they responsible for?

Answer 23

3a -> proprioceptive stimulation
3b and 1 -> cutaneous stiumlation
2 -> integration of tactile and proprioceptive information

Question 24

Exlain the dynamics of the functional hierarchy of S1.

Answer 24

REFER TO DIAGRAM.

Question 25

Describe the ascending somatosensory pathways for upper body and lower body limbs to the cerebrum. Describe also the ascending somatosensory pathway for head and neck proprioceptive information.

Answer 25

Lower body parts’ proprioceptive information pathway: dorsal root ganglion -> spinal dorsal column through Gracile tract ->Gracile nuclei ->medial lemniscus ->ventral posterior lateral nucleus of the thalamus -> internal capsule -> S1

Upper body parts’ proprioceptive information pathway: dorsal root ganglion ->spinal dorsal column through Cuneate tract ->Cuneiform nucleus -> medial lemniscus -> ventral posterior lateral nucleus of the thalamus -> internal capsule -> S1

Head and neck’s proprioceptive information pathway: trigeminal ganglion ->trigeminal tract -> trigeminal nucleus -> trigeminal lemniscus ->ventral posterior medial nucleus of the thalamus ->anterior cingulate and insula, S2

Question 26

What is the central pathway conveying ascending tactile information?

Answer 26

Main ascending axons extend ipsilaterally through dorsal columns → synapse in lower medulla to dorsal column nuclei.

Question 27

Where is situated the primary somatosensory cortex (S1)?

Answer 27

Postcentral gyrus of parietal lobe.