Somatosensory Pathways

Question 1

What is meant by negative symptoms?

Answer 1

Loss of sensation

Question 2

What is meant by positive symptoms?

Answer 2

Abnormal sensory phenomenon

Question 3

Define analgesia.

Answer 3

Loss of pain

Question 4

Define anesthesia.

Answer 4

Loss of touch

Question 5

Define paresthesia.

Answer 5

Temporary mild pain (pins and needles, tingling, burning, prickling)

Question 6

Define neuropathic pain/central pain syndrome.

Answer 6

Chronic intense pain (shooting, stabbing or electric shock like jolts”

Question 7

What four areas contribute to encoding of elementary sensory attributes?

Answer 7

Modality
Intensity
Timing
Location

Question 8

What is modality?

Answer 8

subsystem for processing different kinds of stimuli or the nature of sensory loss

Question 9

What does the dorsal column-medial lemniscus system transmit?

Answer 9

Sensory: vibration, joint position, fine touch

Question 10

What is the site of decussation of the DCMLS?

Answer 10

Internal arcuate fibers (lower medulla)

Question 11

What does the spinothalamic tract transmit?

Answer 11

Sensory: pain, temperature, crude touch

Question 12

Where does the spinthalamic tract decussate?

Answer 12

Anterior commissure (spinal cord)

Question 13

Why do we have parallel pathways in the spinal cord?

Answer 13

1. Redundancy/reliability

2. Increase speed to the cortex (multiple train line analogy)

Question 14

What do DCMLS and STT have in common?

Answer 14

1. receptors throughout body
2. use sensory DRG as 1 neuron
3. 3 neurons w/ 2 relay points
4. cross over to contralateral side

Question 15

How are DCMLS and STT different?

Answer 15

1 Types of receptors

2 Morphology of DRG

Question 16

What is intensity?

Answer 16

Strength of stimulus

Question 17

What is sensory threshold?

Answer 17

Lowest stimulus strength a subject can detect

Question 18

How is sensory threshold determined?

Answer 18

Determined by lowest sensitivity of receptors

Question 19

How does a slowly adapting receptor work?

Answer 19

Tonic: detect static qualities of stimulus

Question 20

How does a rapidly adapting receptor work?

Answer 20

Phasic: detects dynamic qualities of stimulus

Question 21

How does the two point discrimination test work?

Answer 21

Minimal interstimulus distance required to perceive two simultaneously applied stimuli as distinct

Question 22

What 3 factors affect resolution of sensory attributes?

Answer 22

1 receptor diversity
2 receptive field
3 inhibitory mechanisms

Question 23

What is the receptive field and how does it determine resolution?

Answer 23

The region in sensory space within a which a specific stimulus elicits the greatest action potential response

Question 24

What is a dermatome?

Answer 24

Area of skin innervated by a single dorsal root

Question 25

What causes an overlaps of dermatomes?

Answer 25

1. Axons makes up a dorsal root originate from several different peripheral nerves 2. Individual peripheral nerves contribute axons to adjacent dorsal roots

Question 26

What is the order of cutaneous mechanoreceptors from surface of the skin inward?

Answer 26

Meissner Merkel cell Ruffini corpuscle Pacinian corpuscle

Question 27

What is the function of Meissner corpuscle?

Answer 27

Detects surface, motion

Question 28

What is the function of a Merkel cell?

Answer 28

Detect edges, indentation

Question 29

What is the function of a a Ruffini corpuscle? How is it aligned?

Answer 29

detects skin stretch | With stretch lines

Question 30

What is the function of a Pacinian corpuscle?

Answer 30

vibration sense

Question 31

What is the morphology of a Pacinian corpuscle?

Answer 31

Deep and with onion like layers

Question 32

What is the pathway of the DCMLS?

Answer 32

Lumbar (lower body) -- gracile tract Cervical (upper body) -- cuneate tract Caudal medulla: relay point 1: dorsal column nuclei Decussate to internal arcuate fibers Rostral medulla, mid pons, midbrain Ventral posterior lateral nucleus of thalamus: relay point 2 To primary somatic sensory cortex / postcentral gyrus

Question 33

What is the pathway of the trigeminal mechanosensory system?

Answer 33

Trigeminal ganglion Principal nucleus of trigeminal complex (mid-pons): Relay point 1 Decussate across medial lemniscus Ascends through midbrain Ventral posterior medial nucleus of thalamus: relay point 2 Terminates: primary somatic sensory cortex

Question 34

What does the trigeminal mechanosensory system relay?

Answer 34

Touch and vibration information from face to cortex

Question 35

Why does the spincerebellar tract have large diameter sensory neurons?

Answer 35

1 receptor goes to multiple endpoints

Question 36

What is the spinocerebellar tract's function?

Answer 36

Proprioception for the cerebellum

Question 37

How do lesions of the spinocerebellar tracts present?

Answer 37

Ipsilateral loss of muscle coordination | BUT: unlikely to be damaged in isolation.

Question 38

What are two ways that the dorsal columns or spinocerebellar tract can be damaged?

Answer 38

1. Tabes Dorsalis (tertiary syphilis) | 2. Subacute combined degeneration caused by B12/vit E deficiency

Question 39

What is the Romberg test?

Answer 39

tests stability and vision, particularly balance

Question 40

What is the somatotopic organization of DCMLS in the spinal cord?

Answer 40

(medial) leg --> arm --> neck --> occiput (lateral)

Question 41

What is the somatotopic organization of DCMLS in the medulla?

Answer 41

Upper limb: posterior | Lower limb: anterior

Question 42

What is the somatotopic organization of DCMLS in the midbrain?

Answer 42

Upper limb: medial | Lower limb: lateral

Question 43

How do the somatosensory and motor humunculus' relate to each other?

Answer 43

They parallel each other

Question 44

Which receptors are located in the epidermis?

Answer 44

Free nerve endings Meissner corpuscle Merkel cell

Question 45

Which receptors are located in the dermis?

Answer 45

Ruffini corpuscle

Question 46

Which receptors are located in the dermis/subQ layer?

Answer 46

Pacinian corpuscle

Question 47

How many types of receptors can a thermoreceptive neuron have?

Answer 47

Only ONE!

Question 48

When do cold and warm receptors fire?

Answer 48

During changes of temperature and someone tonically at baseline

Question 49

What is the pathway of the spinothalamic system for discriminative aspects of pain and temperature in the body?

Answer 49

Lower body: Lissauer's tract --> lumbar spinal cord Upper body --> cervical spinal cord Relay point 1 in dorsal horn Decussates at segmental levels: takes 2 levels to traverse! Anterolateral system: medulla (with anterolateral tract), pons, midbrain (with spinothalamic tract) Relay point 2 at ventral posterior lateral nucleus of thalamus Endpoint: Primary somatic sensory cortex

Question 50

What is the pathway for discriminative aspects of pain and temperature in the face?

Answer 50

1. Mid pons: trigeminal ganglion enters 2. Spinal trigeminal tract descends to caudal medulla and middle medulla 3. Relay point 1: caudal medulla and middle medulla and DECUSSATES here 4. Rises through middle medulla, mid-pons and midbrain 5. Relay point 2: ventral posterior medial nucleus of the thalamus 6. Terminates at Cerebrum

Question 51

What is the somatotopic orientation of the anterloateral system of the spinothalamic tract?

Answer 51

Ventral side | Neck: lateral ---> leg medial

Question 52

What is the blood supply trend to the DCMLS and STT?

Answer 52

Caudal: anterior/posterior spinal artery Cranial: PICA, AICA, vertebral

Question 53

What is Brown-Sequard syndrome?

Answer 53

Hemisection on the left side of the spinal cord at C5 | Results in pain/temp from R side of body, touch/proprioception/vibration from L side of body

Question 54

Why does an individual experience a phantom limb? What is the result?

Answer 54

Reorganization of somatosensory cortex occurs in amputees so that neurons that used to be innervated by limb now respond to stimulation of other body parts

Question 55

What has shown to be the best treatment for phantom limb pain?

Answer 55

Mirror therapy

Question 56

What causes subacute combined degeneration?

Answer 56

Caused by B12/vit E deficiency:

Question 57

What are the symptoms of subacute combined degeneration?

Answer 57

demyelination causes: ataxic gait paresthesia impaired position and vibration sense

Question 58

What causes Tabes Dorsalis?

Answer 58

tertiary syphilis infection: degeneration causes impaired sensation, proprioception and progressive sensory ataxia

Question 59

What are the symptoms of Tabes Dorsalis?

Answer 59

impaired sensation. proprioception, progressive sensory ataxia