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Neuroscience > Somatosensory > Flashcards

Somatosensory Flashcards

1
Q

Define sensation

A
  • used to investigate about the outside & inside, avoid/minimize injuries, & required to move accurately
  • sensory input can be used unconsciously, ex. by cerebellum
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2
Q

Define the different sensations

A
  • Somato-sensation: info from skin & musculoskeletal system
  • Visual sensation: from the eyes
  • Audition: from the ears
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3
Q

Define perception

A
  • when sensory input reaches conscious levels
  • perception needs input to reach cortex & be processed further
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4
Q

What do mechanoreceptors respond to

A
  • touch
  • pressure
  • stretch
  • vibration
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5
Q

What do thermoreceptors and chemoreceptors respond to

A
  • Thermoreceptors: respond to heating/cooling
  • Chemoreceptors: respond to chemicals
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6
Q

Different kinds of somatosensory receptors

A
  • mechanoreceptors
  • thermoreceptors
  • chemoreceptors
  • nociceptors: sub set of each
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7
Q

Describe nociceptors

A
  • respond to stimuli that are damaging/threaten to damage tissue
  • perceived as pain
  • high threshold receptors
  • also elicit spinal reflexes
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8
Q

Describe sensory reception from the skin/cutaneous

A

-Touch: fine/discriminative (superficial pressure & vibration) & non-discriminative (deep pressure & deep touch)
- temperature
- nociception: fast & discriminative or slow & non-specific

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9
Q

Describe sensory reception from the musculoskeletal system

A
  • proprioception: joint position, information regarding tension on muscles/tendons, & deep vibration
  • nociception
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10
Q

Describe light touch sensation

A
  • via Aβ afferents
  • vibration
  • skin stretch
  • skin pressure (light)
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11
Q

Describe coarse touch

A
  • by free nerve endings via Aδ & C afferents
  • pleasant touch (like a hug)
  • firm/deep pressure
  • tickle/itch
  • nociception (pinch)
  • thinner or non-myelinated axons transmit course touch
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12
Q

Describe Tonic receptors

A
  • pressure receptors: therapeutic touch
  • stretch receptors in muscle
  • slowly adapting receptors that respond for the duration of a stimulus
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13
Q

Describe phasic receptors

A
  • tendon stretch receptors
  • pressure receptors
  • thermoreceptors
  • rapidly adapt to a constant stimulus & turn off, they fire once more when the stimulus turns off
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14
Q

What is a receptive field of receptors

A
  • area of skin innervated by single afferent neuron
  • smaller distally & larger proximally
  • also greater density of receptors distally, fingers vs back
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15
Q

Describe a muscle spindle

A
  • sensory receptor organ inside muscle–stretch detectors– contribute to muscle tone
  • spindle-like structure located inside muscle belly
  • contains special muscle fibers, sensory nerve endings & motor nerve endings
  • responds to changes in muscle length (static) & rate of length change (dynamic)
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16
Q

In order to convey dual info about muscle length change & rate of length change, muscle spindles has

A
  • 2 types of intrafusal muscle fibers
  • 2 types of sensory afferents (carry sensory information toward the CNS)
  • 2 types of motor efferents (carry motor info away from the CNS)
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17
Q

Describe the 2 types of intrafusal muscle fibers

A
  • are contractile only at the ends of a muscle spindle
  • more elastic in the middle & less elastic on the ends
  • Nuclear bag fibers: more elastic & stretch quickly
  • Nuclear chain fibers: less elastic & stretch slowly
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18
Q

Sensory afferents of muscle spindle

A
  • sensory nerves attach to the central region
  • type Ia (primary): wrap around center of both fibers (more elastic region), responds better to quickly changing muscle length using phasic discharge pattern–velocity dependent discharge (dynamic sensitivity) continues to detect change
  • type II (secondary): wrap around adjacent regions of both fibers (less elastic region), responds better to slowly changing muscle length using tonic discharge pattern– not dependent on velocity of change in muscle length (static sensitivity)
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19
Q

Motor efferents to muscle spindle

A
  • Gamma motor neurons: terminate at the polar contractile regions of the fibers
  • Gamma dynamic: activate bag fibers
  • Gamma static: activate both bag & chain fibers
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20
Q

What is the purpose of motor innervation to muscle spindles

A
  • whenever there is voluntary muscle contraction, there is co-activation of both extrafusal & intrafusal fibers
  • motor connections to the intrafusal fibers keep them tight to be able to remain active in shortened muscle positions
  • so with co-activation intrafusal fibers can keep monitoring changes in length during dynamic muscle activity & protect it from injury
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21
Q

Describe Golgi tendon organs (GTOs)

A
  • encapsulated sensory nerve endings among collagen strands of tendons near musculotendinous junction
  • sensitive to very slight changes in tension in tendon
  • respond to tension changes during both active contraction or passive stretch
  • contributes to autogenic inhibition
  • information transmitted by Ib afferent fibers
22
Q

Describe joint receptors for joint position sense

A
  • respond to mechanical deformation of joint capsule/ligaments
  • various types conveyed by all types of fibers (Ib, II, III, IV)
  • Ruffini’s endings respond to extremes of passive joint ROM
  • Paciniform corpuscles respond when joint is moving, silent when joint position is static
23
Q

Describe the central somatosensory system

A
  • transmission & processing of peripheral sensory information via the central pathways called tracts/columns/lemniscus
  • sensory info reaches thalamus/brain & is further processed to generate conscious interpretation in response to which the motor system acts in a purposeful manner
  • some sensory info can be processed unconsciously at spinal levels or cerebellum
24
Q

Describe Sherrington’s experiments

A
  • cut all dorsal nerve roots entering spinal cord from one arm of monkey & after recovery from surgery, monkey avoided using that limb
25
Q

Describe Rothwell’s studies

A
  • functional problems in person with severe peripheral sensory loss
  • motor function (strength, speed of movements) was normal, still could not perform functional activities like writing, holding a cup, or buttoning up a shirt
26
Q

Describe somatosensory 1st order neurons (FONs)

A
  • cell bodies in dorsal root ganglions
  • distal axon
  • proximal axon
  • axons for light touch, proprioception, & vibration stay on the same side & travel up to the medulla then synapse
  • axons for pain & temperature synapse right after entering spinal cord
27
Q

Describe central somatosensory pathways

A
  • consist of high vs low fidelity pathways to determine precision of location, intensity, & timing
  • High fidelity pathways: consist of thick & heavily myelinated axons, create somatotopically arranged point to point connections from specific sensory regions to specific regions in brain’s somatosensory cortex (somatosensory homunculus)
28
Q

High fidelity information versus low fidelity information

A
  • High fidelity: light touch, proprioception, sharp discriminative pain/temperature
  • Low fidelity: aching pain, itch
29
Q

3 types of somatosensory pathways

A
  • Conscious relay pathways: light touch, proprioception, discriminative pain/temperature (high fidelity)
  • Conscious divergent pathways: info covered to many locations, conscious & emotional levels, aching pain/chronic pain (low fidelity)
  • Non-conscious pathways: proprioceptive info to cerebellum for postural control
30
Q

Describe the different conscious relay pathways

A
  • Dorsal column/medial lemniscus: conveys light touch, vibration, & conscious proprioception to the primary somatosensory area of cerebral cortex
  • Spinothalamic: conveys discriminative nociception & temperature to the primary somatosensory area of cerebral cortex
31
Q

Describe the different conscious divergent pathways

A
  • Spinomesencephalic: conveys slow nociception to the midbrain
  • Spinoreticular: conveys slow nociception to the reticular formation
  • Spino-emotional: conveys slow nociception to the amygdala, basal ganglia, & many areas of cerebral cortex
32
Q

Describe non-conscious relay pathways

A
  • Spinocerebellar: conveys movement related information to the cerebellum
33
Q

Describe the steps in the dorsal column/medial lemniscus pathway

A
  • information enters at dorsal root ganglion
  • synapse on FON
  • lower limbs use fasciculus gracilis while upper limbs use fasciculus cuneatus
  • lower limb synapse on SON at nucleus gracilis while upper limb synapse on SON at nucleus cuneatus
  • cross midline in the lower medulla at the decussation
  • travel up the medial lemniscus tract
  • synapse on TON in the VPL nucleus of thalamus
  • information is then taken to the primary somatosensory cortex
34
Q

Describe the primary somatosensory area (S1)

A
  • somatotopic arrangement of sensory information (touch, proprioception, nociception, & temperature)
35
Q

Describe the secondary somatosensory area

A
  • processes combined sensations: stereognosis (ability to tell what an object is w/o seeing it), barognosis (ability to tell how much an object weighs w/o weighing it), graphesthesia, 2 point discrimination
  • further processing of S1 information to send to association/cognitive areas to provide perception to incoming sensory information
36
Q

Describe the anterolateral columns

A
  • convey nociception/pain, temperature, & crude touch information to the brain
  • Spinothalamic pathway: fast, discriminative pain, temperature, & crude touch, somatotopic arrangement in S1, 3 neuron pathway
  • Divergent pathways: slow, non-specific nociception, 2 or 3 neuron pathways
37
Q

Describe the steps in the Spinothalamic pathway from the body

A
  • information enters dorsal root ganglion and synapse on FON
  • information enters the dorsal horn of spinal cord at synapse on SON
  • information then crosses over at the spinal cord level it entered on
  • information travels up the spinothalamic tract
  • enters the VPL nucleus of the thalamus and synapse on TON
  • information is then passed through the thalamocortical radiations
38
Q

Describe the steps in the Spinothalamic pathway from the face

A
  • synapse on FON in trigeminal ganglion
  • synapse on SON in the spinal nucleus of trigeminal nerve
  • synapse on TON in the VPM nucleus of thalamus
  • information is then passed through the thalamocortical radiations
39
Q

Similarities between the dorsal column/medial lemniscus and the spinothalamic pathways

A
  • both are 3 neuron pathways
  • both end SON in VPL nucleus of thalamus
  • both project sensory info somatotopically in S1
40
Q

Differences between the dorsal column/medial lemniscus and the spinothalamic pathways

A
  • DC/ML: conveys light touch, proprioception, & vibration; ascending axons are FONs; ascend ipsilaterally in spinal cord; cross midline in medulla
  • Spinothalamic: conveys discriminative pain & temperature; ascending axons are SON; ascend contralaterally in spinal cord; crosses midline at spinal cord level
41
Q

What gives rise to dermatomes

A
  • the somatotopic arrangement of the DC/ML and spinothalamic pathways at all spinal levels
42
Q

Define dermatomal innervation pattern

A
  • area of skin innervated by single spinal nerve root
43
Q

Define peripheral innervation pattern

A
  • area of skin innervated by an individual peripheral nerve
44
Q

Key landmarks for dermatomes

A
  • C2: posterior half of skull
  • C3: medial end of clavicle
  • C4: medial acromion below clavicle
  • C5: lateral elbow
  • C6: 1st digit/thumb
  • C7: 3rd digit/middle finger
  • C8: 5th digit/pinky
  • T1: medial elbow
  • T2: anterior axilla
  • T4: nipple line
  • T6 or T7: xiphoid process
  • T10: umbilicus
  • T12: anterior iliac crest/pubic symphysis
  • L1: inguinal region/upper medial thigh
  • L2: medial thigh mid-distance
  • L3: medial knee
  • L4: medial malleolus
  • L5: base of great toe
  • S1: lateral heel/lateral malleolus
  • S2: posterior knee
  • S3: ischial tuberosity
45
Q

Describe the divergent pathways in the anterolateral column (medial nociception system)

A
  • slow, less localized, non-specific pain
  • more involved with chronic pain
  • information reaches many areas in brainstem & cortex
  • information is carried by spinomesencephalic, spinoreticular, & spino-emotional tracts
  • elicits emotional, motivational, reflexive, arousal responses of pain
46
Q

Steps in divergent slow nociception pathways

A
  • 1st order neuron: C fibers, synapse with interneurons in dorsal horn, interneurons release substance P, & can get sensitized by repeated stimulation during chronic injury
  • 2nd order ascending neurons: spinoreticular-to reticular formation for arousal changes due to pain, spinomesencephalic-to superior colliculus via PAG turning head/eye towards painful stimuli, & spino-emotional-to midline/intralaminar nuclei in thalamus
  • 3rd order neurons only for spino-emotional: to wide areas in cortex anterior cingulate, insula, amygdala, dorsal prefrontal cortex, affect emotions, behavior, personality
47
Q

For peripheral nerve injury, sensory loss proceeds in the following order of descending diameter

A
  • conscious proprioception/light touch
  • cold
  • fast nociception (sharp pain)
  • heat
  • slow nociception (aching pain, tingling, prickling sensations)
  • during recovery sensation returns in the reverse order
48
Q

What does the removal of the anterior cingulate cortex used to treat

A
  • can treat chronic pain
  • person can still localize & qualify pain but it interferes less with thinking, behavior, & social activities
49
Q

What is sensory nerve conduction velocity (NVC) studies

A
  • to test the integrity of peripheral nerves following injuries
50
Q

Define conduction velocity

A
  • distance between electrodes/time between stimulus & first depolarization at recording electrode
51
Q

How to determine whether NCS (nerve conduction velocity studies) result is normal

A
  • 3 values are compared with contralateral side or normative data
  • latency
  • amplitude of the evoked potential
  • conduction velocity
52
Q

Describe referred pain

A
  • pain perceived as coming from a site distinct from actual site of origin
  • ossuary when branches of nociceptive fibers from internal organs (GVA) & branches of nociceptive fibers from skin (GSA) converge on same 2nd order neuron in dorsal horn or thalamus, & those pathways become sensitized

Neuroscience (10 decks)

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