Week 2 Sensory Receptors, Sensory Pathways, Lesions Flashcards Preview

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Flashcards in Week 2 Sensory Receptors, Sensory Pathways, Lesions Deck (29)
1

Define stimulus transduction.

The process by which a sensory receptor converts the sensory stimulus into an electrical signal that is carried by sensory axons

2

What is a graded potential (aka generator potential or receptor potential)?

-changes in ion fluxes across the membrane in varying degrees (not all or none)
-an increase in magnitude of a receptor potential (stimulus energy) causes an increase in frequency of action potentials

3

Define adaptation or desensitization.

-decrease in frequency of action potentials in a sensory neuron despite maintenance of the stimulus at constant strength

4

What is the difference between rapidly adapting (phasic) receptors and slowly adapting (tonic) receptors?

-rapidly adapting: response quickly to onset of stimulus then decreases over time or may stop responding. important for indicating change in stimulus. E.g. putting on a sock, then forgetting it is on your feet
-slowly adapting: responses that maintain response to stimulus over time, e.g. receptors in joints/muscles that convey positional info, receptors that measure oxygen tension in blood

5

What are the 4 attributes coded for by a sensory stimulus?

1. modality (what it is)
-touch, temperature, pain receptors
2. location (where it is)
-related to size of receptive fields of neurons
3. intensity
-conveyed via freq of action potentials
4. duration

6

How do receptive fields of neurons convey the degree of acuity of a particular sense?

-overlapping receptive fields give more precise location (e.g. if recorded by 3 neurons, stimulus is at the intersection of those receptive fields)
-size of receptive field: small on fingertips and large on back (less able to distinguish between two points close together) [2 point discrimination]
-lateral inhibition: ability of excited neuron to reduce activity of it neighbors and sharpen spatial profile of excitation

7

Where is neuron 1 and its axons for the DC/ML pathway?

Neuron 1 is in DRG
Its axons for C1-T5 are in Fasciculus cuneatus in spinal cord
Its axons for T6-S5 are in Fasciculus gracilis in the spinal cord

8

Where is neuron 2 and its axons for the DC/ML pathway? Where is neuron 3?

Neuron 2 is the Nucleus cuneatus and Nucleus gracilis in the lower medulla. Its axons take the ML pathway after decussation. Neuron 3 is VPL in the thalamus.

9

Where is neuron 1 and its axons for the STT pathway?

Neuron 1 is DRG
Its axons doesn't have a name

10

Where is neuron 2 and its axons for the STT pathway? Where is neuron 3?

Neuron 2 is nucleus proprius in the dorsal horn where the axons of neuron 1 enter the spinal cord.
Axons of neuron decussate 1-2 segments above nucleus proprius through white commissure and follow STT tract to Neuron 3-VPL in thalamus

11

Where is neuron 1 and its axons for the TL (trigeminal lemniscus) pathway?

Neuron 1: trigeminal ganglion
Its axons aren't named

12

Where is neuron 2 and its axons for the TL pathway? Where is neuron 3?

Neuron 2: Chief/main sensory nucleus of V in mid pons
The axons decussate in the mid pons and follow the TL pathway
Neuron 3: VPM in thalamus

13

Where is neuron 1 and its axons for the TTT (Trigeminal thalamic tract) pathway?

Neuron 1: trigeminal ganglion
The axons follow spinal tract of V in mid pons-descending to lower medulla

14

Where is neuron 2 and its axons for the TTT pathway? Where is neuron 3?

Neuron 2: Spinal nucleus of V
Axons follow TTT pathway, decussating in lower medulla and ascending to Neuron 3
Neuron 3: VPM in thalamus

15

What is the sensory pathway for taste?

Neuron 1: sensory ganglion of VII, IX, and X
Neuron 1 axons: solitary tract
Neuron 2: nucleus solitarius
Neuron 2 axons central tegmental tract
Neuron 3: insula, SS1 for tongue

16

List the four sensory pathways for the head/neck and body and what sensory information they carry.

Body
1. DC/ML: fine touch, proprioception, vibration, and 2 point discrimination
2. STT: temperature and pain
Head/neck
1. TL: fine touch, proprioception, vibration, and 2 point discrimination
2. TTT: temperature and pain

17

What type of injury does a decreased deep tendon reflex indicate? What type of injury does a increased deep tendon reflex indicate?

decreased reflex: Peripheral injury
increased reflex: CNS injury

18

Identify the connections that mediate the corneal blink reflex.

-afferent limb: opthalmic nerve (V) innervates cornea and conveys sensation of touch
-sensory nuclei are parts of spinal trigeminal nucleus and chief sensory nucleus that projects laterally to the facial motor nuclei (VII)
-efferent limb: cranial nerve VII to orbicularis oculi muscles that contract to close eye

19

What are the features of isolated peripheral nerve lesion (mononeuropathy)?

-Sensory: numbness and loss of light touch, pinprick, and vibration sense in a targeted dermatome or area of an individual limb or trunk dermatome
-motor: weakness or loss of limb or digit movements, possible atrophy of muscle. decreased deep tendon reflex
-common causes: contusion, crush, or laceration of a ventral rams of a peripheral nerve

20

What are the features of distal symmetrical polyneuropathy? [degeneration of distal axons]

-Sensory: bilateral sensory loss-Glove and/or stocking distribution in all modalities. vibration may be earliest sensor modality effected
-motor: muscle wekaness, areflexia, flaccid paralysis
-Common causes: metabolic diseases (diabetes), deficiency syndromes, acute inflammatory disease causing demyelination, chemical toxins (cancer drugs)

21

What are the features of radiculopathy?

-lesion at spinal nerve at intervertebral foramen
-numbness and pain along course of nerve or dermatome
-causes: compression of nerve root/area of spinal nerve, disc herniation

22

What are the features of transverse cord lesion?

-Sensory: bilateral loss of all sensory modalities at and below the lesion
-motor: upper motor neuron syndrome bilateral
-common causes: trauma, tumors, multiple sclerosis

23

What are the features of a hemicord lesion: brown-sequard syndrome?

-Sensory: loss of vibration and proprioception ipsilateral to lesion (DC/ML pathway). Loss of pain and temperature contralateral but slightly below lesion (STT pathway)
-motor: upper motor neuron syndrome ipsilateral to lesion
-common causes: penetrating injury, lateral compression from tumor

24

What are the features of a central cord syndrome (springomyelia-small lesion)?

-Sensory: segmental loss of pain and temperature bilaterally at the level of lesion. Lose crossing fibers in 1-2 segments (STT)
-motor: only occur with larger lesion that effects the anterior horns of spinal cord
-common causes: central cavitation can be congenital or acquired due to trauma, tumor, etc.

25

What are the features of a posterior cord syndrome?

-sensory: loss of vibration and position sense below the level of the lesion (DC/ML). Pain and temp normal (STT unaffected)
-motor: only occur with larger lesion that affects corticospinal tract
-common causes: compression from posterior located tumor, vitamin B12 deficiency, tabes dorsal is (tertiary syphilis), multiple sclerosis

26

What are the features of anterior cord syndrome?

-sensory: loss of pain and temperature below the level of lesion (STT). vibration and position sense normal.
-motor: upper motor syndrome due to damage to anterior horns of spinal cord and corticospinal tract
-common causes: trauma, MS, ant spinal artery infarct

27

What are the features of a medial medullary lesion in the brain stem?

-sensory: contralateral loss or decrease in vibration and position sense (ML)
-motor: contralateral loss or weakness in arm and leg (pyramid). ipsilateral tongue weakness (CN 12)
-common causes: infarct of paramedic branches of ant spinal or vertebral artery

28

What are the features of a lateral medullary lesion (wallenberg's syndrome)?

-ipsilateral loss of pain and temperature to face (TTT)
-contralateral loss of pain and temp to body (STT)
-unilateral horner's syndrome-ipsilateral eye
-hoarseness, difficulty swallowing, loss of gag reflex

29

What are the features of a primary sensory cortex or thalamic lesion?

-contralateral sensory deficits of all sensory modalities to parts of the body or face dependent on the size of the injury (think of the person lying over the lobe of the brain)
-lesions of parietal lobe: contralteral deficits in higher order sensory processing
-lesions of parietal lobe on the left: contralteral hemineglect

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