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Neuroanatomy > Somatosensory Systems > Flashcards

Somatosensory Systems Flashcards

1
Q

Function of Somatosensory systems

A

Transmits and processes sensory input/information

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2
Q

Overview of functions

A

-Cutaneous sensation of touch (discriminating and non-discriminating) from physical contact
-Position sense (proprioception) and movement sense (kinethesis) of the body
-Temperature from objects and the external environment
-Pain (nociception); also many other sensations including: itch, tickle, specific chemical

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3
Q

Receptors & their associated afferent nerves

A

Cell bodies often in dorsal root ganglion (DRG)

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4
Q

Spinal cord

A

-Dorsal horn (gray matter)
-Tracts (dorsal columns, spinothalamic tract, spinocerebellar tract, etc.)

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5
Q

Brainstem

A

Decussation and tracts

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6
Q

Cerebellum

A

Proprioceptive feedback

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7
Q

Diencephalon

A

-Thalamus (VPL,VPM, VMpo): primary target of most somatosensory information
-Hypothalamus

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8
Q

Cerebral cortex

A

Primary & secondary somatosensory areas; insula, cingulate cortex)

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9
Q

Dorsal column/ Medial lemniscus Pathway

Touch (discriminatory), vibration, conscious proprioception from the body

A

Receptors (via DRG)→dorsal columns→synapse in dorsal column nuclei (brainstem) →fibers decussate & pass through medial lemniscus→VPL (thalamus) →somatosensory cortex

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10
Q

Where do the receptors enter ?

A

Enter spinal cord near dorsal horn (Lissauer’s tract)

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11
Q

Axons have somatotopic arrangement

A
  • information from the highest spinal level is furthest lateral
  • information from the lowest spinal levels in most medial
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12
Q

Fasciculus gracilis in dorsal columns

A
  • from LE (below T6)
  • more medial
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13
Q

Fasciculus cuneatus in dorsal columns

A
  • from UE (rostral to T6)
  • more lateral
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14
Q

Primary somatosensory cortex (S1)

A

In postcentral gyrus of parietal lobe
▪ primarily function in localization and discriminatory touch
➢ also conscious propriocetion
▪ somatopically organized
➢ medial to lateral: LE, UE, face
➢ sensory homunculus

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15
Q

Secondary somatosensory cortex (S2)

A

Primarily functions in texture & roughness

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16
Q

What can result from internal capsule damage?

A

MS, lacunar stroke, or others

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17
Q

Tabes dorsalis

A

Damage to dorsal column in late stage neurosyphilis

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18
Q

Friedrich ataxia

A

➢ degeneration of DRG neurons (and their axons)
➢ damages more than dorsal columns [also corticospinal tract (motor), dorsal spinocerebellar tract (proprioception)]

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19
Q

Is touch destroyed with a loss of complex discrimination?

A

No, but it is impaired.
You know something is happening (can probably localize stimuli)

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20
Q

Asterognosis

A

➢ unable to recognize patterns drawn on the skin
➢ unable to recognize object place on skin
➢ unable to recognize objects by manipulation

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21
Q

Sensory ataxia

A

loss (usually total) of conscious proprioception and kinesthesia
results in:
-steppage gait: high stepping & slapping feet due to loss of proprioception
-Romberg’s sign: sway and fall with eyes closed

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22
Q

Trigeminal nerve (CN V) Pathway

Touch (discriminatory), vibration, conscious proprioception from the face

A

Receptors (via DRG)→brainstem at mid-pons→synapse in main sensory bucleus of trigeminal nerve →fibers decussate & join medial lemniscus→VPM (thalamus) →somatosensory cortex

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23
Q

Dorsal trigeminal tract

A

An uncrossed pathway that carries some information
from the inside of the mouth; this info ends up on the same side of the brain as gustatory (taste)
info (gustatory info is also uncrossed)

24
Q

Pain vs Nociception

A

-Pain: “An unpleasant sensory and emotional experience associated with actual or potential
tissue damage, or described in terms of such damage” (International Association for the
Study of Pain) {emphasis mine}

-Nociception: “Encoding and processing of harmful (or potentially harmful) stimuli”
▪ in other words – pain is an emotion, while the term nociception is separate from the
emotional aspects of tissue damage (affect)

25
Q

Two primary spinothalamic pathways: Lateral STT & Anterior STT

A

-Separate pathways as they pass through the spinal white matter
▪ lateral STT is larger & contains more afferents
➢ classic pain & temperature pathway
▪ anterior STT carries crude touch & deep pressure
-Merge at the brainstem as they adjoin the medial lemniscus

26
Q

Nociceptors

A

-Small diameter fibers with moderate (Aδ) or no (C) myelin
▪ Aδ fibers - ‘fast pain’ (pricking, stabbing, bright)
▪ C fibers – ‘slow pain’ (aching, throbbing, etc)
-Specific receptors respond to mechanical (including blood vessel distention, affective touch, itch, tickle), specific chemicals (capscacian, acids, CO2, etc), temperature (specific ranges); and combinations of these (polymodal)
▪ some hypothesized as ergoreceptors (sense energy utilization)

27
Q

Pain & Temperature (Homeostatic) Sensation from the BODY

A

Nociceptors–>SC through Lissauer’s tract–>synapse Lamina I (superficial dorsal horn)–>Decussate immediately (origin) + travel in CL Lateral Spinothalamic tract–>Synapse in posterior part of Ventral medial nucleus of the thalamus (VMpo)—>Posterior insula

28
Q

Pain & Temperature (Homeostatic) Sensation from the FACE

A

Nociceptors–> CNS through pons via trigeminal nerve (CN V)–> synapse in Ipsilat. spinal nucleus of trigeminal nerve–>Decussate immediately joining CL STT–>synapse in VMpo–>middle insular cortex

29
Q

Spinoretucular

A

to reticular formation in brainstem

arousal/alertness caused by pain stimuli

30
Q

Spinomesencephalic

A

to PAG (periaqueductal gray….and eventually amygdala)

descending pain modulation
ANS response to painful stimuli

31
Q

Spinohypothalamic

A

to hypothalamus
ANS response to painful stimuli

32
Q

Spinotectal

A

to superior colliculus
orienting/turning of eyes toward painful stimulus

33
Q

Allodynia

A

Previously innocuous stimuli now painful (sensitization)
dysesthesis = unpleasant, abnormal sensation

34
Q

Hyperglesia

A

Increased pain (to previous mild painful stimuli)

35
Q

Analgesia

A

Loss/reduction of pain sensation

36
Q

Anesthesia

A

Loss of sensation

37
Q

Hypesthesia

A

Partial loss of touch sensation

38
Q

Hyperesthesia

A

Increased touch sensitivity

39
Q

Centralmodulation

A

Suppression of pain by descending signals (from PAG and rostral medulla)

40
Q

Opiates

A

Increase activity of (particularly) PAG & rostral medulla and dorsal horn

41
Q

Endogenous opiates

A

enkephalins, endorphins, dynorphin
▪ made in response to exercise and stress

42
Q

Exogenous opiates

A

morphine, heroin, etc
▪ issues with habituation and addiction

43
Q

Damage to lateral STT system

Trigeminal neuralgia (tic doulourex)

A

-facial pain syndrome (may be severe)
-thought to be caused by vascular compression leading to demyelination
-affects V2 & V3
-almost always unilateral

44
Q

Damage to lateral STT system

Anterior cord lesion

A

-e.g., from damage to anterior spinal artery
-spares dorsal horns & Lisseur’s tracts, but…
-destroys STT (lateral & anterior)
a loss of all pain & temperature caudal to injury
-also destroys many other tracts & ventral horn neurons – so will discuss later

45
Q

Damage to lateral STT system

Brown-Sequard syndrome

A

-cord hemisection
-destroys STT (lateral & anterior) on one side
loss of all pain & temp on contralateral side, caudal to injury
-also destroys many other tracts as well as the neurons in the spinal gray matter

46
Q

3 primary pathways for Proprioception/Kinesthetic Sensory Pathways (unconscious)

A

Posterior Spinocerebellar Tract (from LE)
Anterior Spinocerebellar Tract (from LE)
Cuneocerebellar Tract (from UE)

47
Q

Post SCT

A

Origin: Clarke’s nucleus (T1-L2/3)
Body Region: LE
Major inputs: Mechanoreceptors in muscles, joints, & skin
Midline crossing: None
Peduncle used to enter cerebellum: Inferior
End Target: Vermis

48
Q

Ant SCT

A

Origin: Spinal border cells (T12-L5)
Body Region: LE
Major inputs: Mechanoreceptors, movement related interneurons
Midline crossing: Two: one in cord, again in cerebellum
Peduncle used to enter cerebellum: Superior
End target: ?

49
Q

Cuneocerebellar

A

Origin: Lateral cuneate nucleus (medulla)
Body Region: UE
Major inputs: Mechanoreceptors in muscles, joints, & skin
Midline crossing: None
Peduncle used to enter cerebellum: Inferior
End Target: vermis

50
Q

Muscle spindles

A

Long, thin stretch receptors inside skeletal muscle
▪ sensitive to length and rate of muscle stretch
▪ collection/bundle of intrafusal muscle fibers
▪ as opposed to extrafusal
▪ which are the larger & much more common fibers that generate force/torque to move & control limbs

51
Q

Muscle spindles are composed of 2 types of intrafusal fibers

A

Both types have a central, non-contractile region where most receptors are found
▪ nuclear chain fibers
➢ thinner
▪ nuclear bag fibers
➢ have swelling at center

52
Q

Primary endings (annulospiral)

A

Wrap around central region
➢ sense onset of stretch; rate of stretch
➢ have lower tonic discharge
▪ rapidly adapting
➢ are Type Ia fibers
▪ larger, faster

53
Q

Secondary endings (flowerspray)

A

Found at either side of central regions
➢ less sensitive to changes in stretch, stronger response to continuing stretch = length
▪ slowly adapting, tonic
➢ are Type II fibers
▪ smaller, slightly slower conduction speed

54
Q

Motor stimulation to muscle spindles, what needs to happen?

A

If spindles do not contract with the extrafusal fibers, the spindles will be unable to sense stretch in a contracted muscle

55
Q

Spindles have their own motor neurons in spinal cord, what are they?

A

gamma motor neurons
* (actually two types: one for chain/another for bag; but who cares?)
* note that alpha motor neurons control extrafusal fibers
▪ match intrafusal & extrafusal contraction

56
Q

Golgi tendon organs (GTOs)

A

sense muscle tension/torque
▪ very sensitive
▪ can respond to contraction of just a few muscle fibers
similar to Ruffini endings
found at junction of muscle and tendon

57
Q

Joint receptors

A

Pacinian, Ruffini, & Golgi tendon organs
Sense joint position and movement
Usually tonic

Neuroanatomy (18 decks)

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