The Somatosensory System

Front 1

"soma to sensory"
soma & sensory

Back 1

soma=body; sensory= sensation

Front 2

3 seperate but interacting systems of the somatosensory system

Back 2

exteroceptive system (senses external stimuli that are applied to the skin)
proprioceptive system (sesnes information about the position of the body from receptors in muscles, joints, and organs of balance

Front 3

3 stimuli that the exteroreceptive somatosensory system senses:

Back 3

1. mechanical stimuli= touch
2. thermal stimuli= temperature
3. nociceptive stimuli= pain

Front 4

What does the somatosensory system sense?

Back 4

external and internal sensory information from your body

Front 5

How does the hierarchal organization of somatosensory system work?

Back 5

Association cortex
Secondary Sensory cortex
Primary sensory cortex
Thalamus
Receptors

Front 6

Free nerve endings

Back 6

cutaneous receptors- receptors on the skin- that respond to temperature change and pain

Front 7

Pacinian corpuscles

Back 7

cutaneous receptors located underneath the skin (but before the fat) that respond to touch BUT ONLY TO RAPID VIBRATIONS

Front 8

Merkel's disks and Ruffini endings

Back 8

cutaneous receptors (receptors of the skin) that adapt slowly; gradual skin indentations and skin stretch

Front 9

What are all the cutaneous receptors?

Back 9

free nerve endings, Pacinian corpuscles, Merkel's disks, and Ruffini endings

Front 10

Organization of somatosensory processing: dorsal root

Back 10

where axons carrying sensory information from the cutaneous receptors gather to enter the spinal cord

Front 11

organization of somatosensory processing: dermatome

Back 11

the area of the body that sends sensory information into the dorsal roots

Front 12

*sensory neurons travel into the ------ and synapse on neurons in the ----- which will carry the information to the brain

Back 12

Sensory neurons travel into the DORSAL ROOT and synapse on neurons in the DORSAL HORN (DORSAL ROOT GANGLIA) which will carry the information to the brain

Front 13

2 major ascending sensory pathways: (& their responsibilities)

Back 13

1. dorsal-column medial lemniscus system: touch & proprioception
2. anterolateral system: pain & temperature

Front 14

what is the organization of the DORSAL-COLUMN MEDIAL LEMNISCUS SYSTEM

Back 14

7. SOMATOSENSORY ASSOCIATION CORTICES<--
6. SECONDARY SOMATOSENSORY CORTEX<--
5. PRIMARY SOMATOSENSORY CORTEX<--
4. VENTRAL POSTERIOR NUCLEI (THALAMUS)<-----
3. dorsal column nuclei (medulla) (CROSS OVER)
2. spinal cord
1. touch receptors

Front 15

what is the organization of the ANTEROLATERAL SYSTEM

Back 15

6. SOMATOSENSORY ASSOCIATION CORTICES
5. SECONDARY SOMATOSENSORY CORTEX
4. PRIMARY SOMATOSENSORY CORTEX
3. THALAMIC NUCLEI
2. spinal cord (cross over)
1. temperature and pain receptors

Front 16

How to the tracts of the anterolateral system differ?

Back 16

The 3 tracts of the anterolateral system differ:
-in whether or not they synapse (and where) prior to reaching the thalamus
-where in the thalamus they synapse

Front 17

What are the three tracts of the anterolateral system?

Back 17

1. spinothalamic (up the cord & into the thalamus- ventral posterior nucleus)
2. spinoreticular (synapse reticular activatig system; 3rd order neurons to the thalamus- parafascicular nurclei and intralaminar nuclei)
3. spinotectal (synapse in the tectum)

Front 18

somatosensory cortex- what is the organization?

Back 18

The organization of the somatosensory system is somatotopic (organized according to a map of the body's surfaces- the map being called the somatosensory homunculus)

Front 19

somatosensory homunculus

Back 19

map or the body's surface in the somatosensory cortex

Front 20

main characteristics of the somatosensory system

Back 20

-somatotopic (organized according to a map of the body's surfaces)
-map=somatosensory homunculus
-"strips" corresponding to each sensation we feel (e.g., touch vs. temperature)
-Association cortex- in the posterior parietal lobe

Front 21

where is the association cortex?

Back 21

in the posterior parietal lobe

Front 22

Reorganization

Back 22

-Reorganization is the major process through which function is restored in the CNS after damage
-Even in adults, our brains are capable of reorganizing themselves in response to experience or damage

Front 23

phantom limb

Back 23

Happens after reorganization, phantom limb is the sensation that a limb is still attached to the body after amputation

Front 24

phantom pain

Back 24

happens after reorganization, phantom pain is the sensation of pain in a limb that has been amputated

Front 25

Phantom pain elicited by?

Back 25

Phantom pain can be elicited by touching other parts of an amputee's body

Front 26

In amputees, what needs to be stimulated to produce pain in missing fingers?

Back 26

In amputees with phantom pain, stimulation of the lips produces pain in the missing fingers--> imaging shows that the lip cortical area on the contralateral side of the brain has moved into the finger cortical area

Front 27

Pain vs. Nociception

Back 27

The sensation of pain and the affect (emotion) of pain are anatomically and functionally seperated: the anterior cingulate cortex mediates the emotion of pain

Front 28

Which part of the brain mediates the emotion of pain?

Back 28

the anterior cingulate cortex mediates the emotion of pain

Front 29

Descending pain control; which systems can control pain?

Back 29

-Neurons in areas of the mesencephalon (specially, in the periaqueductal gray, PAG) can control pain

Front 30

Descending pain control: how do you reduce reduction of pain?

Back 30

-Electrical stimulation or the direct delivery of opiates to the neurons in the mesencephalon (especially, in the periaqueductal gray) can produce analgesia (pain reduction). The same opiate systems mediate the analgesic effect of stress.

Front 31

Which opiate systems mediate the analgesic effect of stress?

Back 31

The neurons in areas of the mesencephalon (specially, in the periaqueductal gray) have opiate systems that mediate the analegsic effect of stress

Front 32

How do endogenous opiates work?

Back 32

Endogenous opiates (endorphins) increase the activity of pariaqueductal gray neurons that stimulate serotonergic neurons in the raphe nuclei. The serotonin output stimulates inhibitory interneurons that enter the spinal cord

Front 33

What can spinal injuries do to one's sensitivity to pain?

Back 33

Spinal injuries can damage descending pain-control tracts and result in increased sensitivity to pain

Front 34

Pain control: gate theory

Back 34

-two types of nociceptive nerve fibers terminate in the dorsal spinal cord:
1. Ao: fast, relatively thick myelinated fibers
2. C: small, unmyelinated fibers
Other large-diameter A & B fibers do not transmit pain stimuli

Front 35

Pain control: gate theory (i, ii, iii)

Back 35

i. NO STIMULATION. The inhibitory interneuron (I) blocks the signal in the projection neuron (P). The "gate is closed" and therefore NO PAIN.
ii. NON-PAINFUL STIMULATION. Large nerve fibers are activated primarily. This activates the projection neuron (P), but also activates the inhibitory interneuron (I) which then blocks the signal in the projection neuron (P). The "gate is closed" and therefore NO PAIN.
iii. PAIN STIMULATION. Small nerve fibers become active. They activate the projection neurons (P) and block the inhibitory interneuron (I). Because activity of the inhibitory interneuron is blocked, it cannot block the output of the projection neuron. The "gate is open," therefore, PAIN!!!