Neurology 3: Tactile And Proprioception

Question 0

Look at the fundamental attributes on slide 7 of the receptors

Answer 0

H

Question 1

What are the 2 major ascending pathways of Somatic sensation?
Their pathway and main function

Answer 1

Dorsal-column medial lemniscus pathway (touch, vibration, 2-point discrimination, proprioceotion
Dorsal root axon➡ dorsal column➡ dorsal column nuclei ➡ medial lemniscus ➡ cerebral cortex
and Spinothalmic pathway (pain, temperature, some touch):
Dorsal root axon➡ lateral Spinothalmic tract➡ thalamus ➡cortex

Question 2

Check out the major classes of somatic sensory receptors on slide 6

Answer 2

1) Free nerve endings –> all skin–> pain temp and crude touch
2) Meissners Corpuscles–> Skin, touch, pressure
3) Pacinian Corpuscles–> Subcutaneous tisssues, interosseus membranes + viscera –> deep pressure and vibration
4) Merkel discs- all skin and hair follicles- touch + pressure
5) Ruffini Corpuscles- skin- stretching

Question 3

In the skin acuity depends on what 3 factors?

Answer 3

• size and number of receptive fields
• degree of overlap between receptive fields
• lateral inhibition.

Localizations is enhanced by having smaller receptive fields and greater overlap of receptive fields

Question 4

Tell me about location: lateral inhibition when it comes to perception of stimulus

Answer 4

Primary neuron response is proportionally to stimulus strength➡ pathway closest to the stimulus inhibits neighbours➡ inhibition of lateral neurons enhances perception of stimulus

Question 5

Tell me about the Intensity: Frequency

What is the stimulus strength proportional to?

Answer 5

-amplitude of generator potential (graded potential)
-rate at which action potentials generated in afferent neuron
Slide 10

Question 6

Intensity: recruitment

Side 11

Answer 6

Strong stimulus activates (recruits) greater number of receptors
Recruitment may be within single sensory unit, or by stimulation of additional units

Question 7

Stimulus duration: Tonic receptors

Answer 7

-most receptors adapt to stimulus
-tonic receptors adapt slowly
With a constant stimulus intensity, there is a decrease in:
-magnitude of receptor potential
-AP rate in afferents neuron
Suited to signalling prolonged stimuli

Examples are:

• GTOs
• type 2 muscle spindles
• stretch receptors in skin

Question 8

Stimulus duration: Phasic Receptors

Answer 8

-Phasic receptors adapt rapidly
-suited t detecting dynamic qualities of mechanical stimuli
Examples are:
-pacinian corpuscles (detect high frequency vibrations)
-type Ia muscle spindle endings

Question 9

Check out the summary of skin mechanoreceptors on slide 15

Answer 9

H

Question 10

Superficial cutaneous mechanoreceptors: Merkels discs
Located in? 
Aligned with? 
Were? 
Job?

Answer 10

• Superficially located in epidermis
• aligned with papillae beneath dermal ridges
• in fingertips, lips, external genitalia
• 25% of mechanoreceptors of hand
• form and texture perception
• role on discrimination of shapes, edges and rough textures

Question 11

Superficial cutaneous mechanoreceptors; meissners corpuscles
Location?
Job?

Answer 11

Most common receptors of hairless skin

• located superficially between dermal papillae
• fingers, palms, soles
• 40% of sensory innervation of hand
• motion detection; grip control skin depression
• detects movement across skin

Question 12

Deep cutaneous mechanoreceptors: pacinian corpuscles

Answer 12

• large encapsulated endings (onion like structure)
• located in subcutaneous tissue
• 10-15% of cutaneous receptors of hands
• laps on inter osseous membrane and intestinal mesentery
• more rapidly adapting than meissners corpuscles, with lower response threshold
• perception of distant events through transmitted vibrations
• detects vibrations

Question 13

Deep cutaneous mechanoreceptors:

Ruffini’s corpuscles:

Answer 13

• spindle shaped receptor located in dermis
• 20% of receptors in hands
• also in ligaments and tendons
• long axis aligned parallel to skin stretch lines
• tangential force; hand shape; motion direction (eg finger position)
• detection of skin stretch; proprioception

Question 14

Tell me about the sensory (ascending) pathways.

Pathway to we’re? Their functions?

Answer 14

1. Pathways to cerebral cortex➡ tracts carry tactile info from skin mechanoreceptors and proprioceotion e info from muscles, tendons and joint mechanoreceptors
2. Pathway to cerebellum
   - tracts carry proprioceptive info from mechanoreceptors in muscles, tendons, joint with some contribution from skin receptors
3. Nociception/ temp perception p:
   - tracts carry info from mechanoreceptors, thermoreceptors and nociceptors to cerebral cortex

Question 15

Pathways to cerebral cortex are assosiated with?
Name the pathways?
Were do they all pass through?

Answer 15

Assosiated with conscious somatosensory perception (touch) and conscious proprioceotion

Dorsal column- medial lemniscus pathway
-fasciculations gracilis (=slender) contains ascending fibres from pelvic limbs and trunk to T6
-fasiculus cuneatus (=wedge shaped) contains fibres from thoracic limbs and trunk cranial to T6
Trigeminal pathway carries information from face
All the above pathways go through the thalamus

Question 16

Discuss the Trigeminal pathway

Answer 16

Carries mechanosensory info from face, via neurons in Trigeminal ganglion

• signs of damage to this pathway would include loss of tactile sense (vibration, deep touch, 2-point discrimination)
• depends on site of damage, deficits contra- or ipsilateral

Question 17

Ventral posterior lateral (VPL) receives projections from we’re?

Answer 17

• medial lemniscus

- Trigeminal projections

Question 18

What neurons are in charge of general proprioception?

What is their course?

Answer 18

Afferent neuron has dentritic zone in muscle spindle, Golgi tendon organs or joint
Afferents neurons travel in peripheral nerves to the spinal nerves
Cell bodies of afferents neurons are in dorsal root ganglia of spinal nerves
Info is transmitted along 2 basic pathways:
1. Dorsal column-medial lemniscus pathway for transmission of inf to sensory cerebral cortex (consciously percieved(
2. Pathway for segmental (spinal) reflex activity, and transmission of information to cerebellum (not consciously percieved)

Question 38

Pathways for spinal reflex activity and to cerebellum

Answer 38

• Anterior and posterior sincerebellar tracts carry proprioceotive information from trunk and lower limbs to cerebellum
• DSCT (dorsal) and VSCT go cranial lu through entire spinal cord, carrying info from muscle spindles, Golgi tendon organs and joint receptors
• both influence cerebellum ipsilaterally (same side) -(VSCT - crosses in spinal cord but then crosses back in cerebellum)
• cuneocerebellar tract carries proprioceptive info from upper limbs to ipsilateral cerebellum
• the obove tracts provide the cerebellum with spatial info about trunk and limbs, both during movement and a fixed posture.

Question 39

What are the clinical signs of damage to the proprioceptive pathways

Answer 39

• Ataxia (in coordination)
• lack of sense of motion or of spatial position of the body and limbs
• positive Romberg sign-eyes closed and sways/falls. Tests (unless sway with eyes open)
• patients have a base-wide stance
• on moving have abnormal limb movement
• damage to spinocerebellar tracts may result in reduced proprioceptive input to cerebellum and may assosiate with hypermetria (overshooting intended position)

Question 40

What are the clinical sign of damage to dorsal columns

Answer 40

• signs ipsilateral in dermatomes at and below level of lesion
• include loss of tactile (vibration, deep touch, 2-point discrimination) and kinaesthetic (position and movement) sense
• Cervical lesion- patient can’t identify object placed in hand ipsilateral to lesion
• Lumbar lesion- analogous deficits restricted to ipsilateral Lower limb
• Movements poorly coordinated due to loss of conscious Proprioception