Lecture 3

Question 1

Somatic system:
- Sense (6)
- Info (4)
- Subsystems (3)

Answer 1

Senses: smell, taste, touch, audition, vision, proprioception
Info: modality, location, intensity, temporal info
Subsystems:
- fine touch, vibration, pressure,
- propriception
- temp, pain, non-discriminative touch

Question 2

Transmission pathway (where are the fibers in the spinal cord?)

Answer 2

PATH (AKA):
↓Receptors (nerve endings)
↓afferent nerve fibers (axons)
↓afferent cell bodies (ganglia)
CNS circuits (CNS circuits)

*info via afferent axons in dorsal roots

Question 3

Trigeminal ganglia & dorsal root ganglia (DRG)

Answer 3

• TG near head
• DRG in body PSEUDONIPOLAR
  -> 1st synaptic terminal w/in spinal cord

Question 4

Pseudonipolar neurons + sensory pseudonipolar neurons

Answer 4

PUNs general: 2branches, NO DENDRITES

(see 3.4)

Sensory PUNs: cell body in DRG
> central → dorsal horn of spinal cord
> peripheral → through SC to periphery

Question 5

Sensory transduction steps

Answer 5

1) stimulus → depolarizing → POTENTIAL
2) APs generated in afferent fiber
3) APs travel on peripheral axon past cell body on central axon to spinal cord

Question 6

Afferent fibers terminals (2 types)

Answer 6

Types:
> encapsulated by receptor cells
> free terminals (for pain!)

Basic mechanisms:
> stimulus changes cation channel
> permeability → generates
> depolarizing current

Question 7

Piezo 1 & piezo 2

Answer 7

Mechanosensitive cation channels important in transduction

Question 8

Specialization of somatic sensory afferents (4 properties)

Answer 8

1) Axon diameter → speed of signal, larger = faster

2) Receptive field → spatial accuracy
2-point discrimination: min distance for distinct stimuli

3) Temporal dynamics → speed of response
> rapid: fire quickly, then stop (for △ in ongoing stimulation)
> slow adapting: continue to fire w/ sustained stimulation(for attributes)

4) Quality of stimuli → specific stimuli types

Question 9

TOUCH:
receptor (basic type)
haptics
stregnosis

Answer 9

Type: mechanoreceptors
Haptics: active touching & complex pattern
Stregnosis: capacity to identify an object via manipulation w/ your hand

Question 10

Merkel cells afferents

Answer 10

• Slow adapting
• 25% of hand receptors
• samples info epidermis
• HIGHEST spatial resolution
• sensitive to: points, edges, curvature (form & texture info)

Question 11

Meissner afferents

Answer 11

• Rapidly adapting
• 40% of hand receptors
• closer to skin surface Merkel
• less spatial resolution
• sensitive to: deformation, vibration, grip control (corpuscle deforms to trigger APs)

Question 12

Pacinian afferents

Answer 12

• Rapidly
• 10-15% of hand receptors
• deep in the dermis (lower threshold {displacements as small as 10 mm!})
• large receptive fold

Question 13

Ruffini afferents

Answer 13

• Slow adapting
• 20% of hand receptors
• In dermis, ligaments & tendons
• Sensitive to: cutaneous stretching, finger positon, hand conformation

Question 14

Proprioception basics (what, integration, proprioception)

Answer 14

• Info about mechanical frces in the body
• Integrates w/ vestibular system
• Important for complex movement
• proprioceptors: low threshold mechanoreceptors

Question 15

Proprioception speed vs touch

Answer 15

Larger diameter than touch
Wider & faster

(Bonus pain, free nerves, are smaller & slower)

Question 16

Muscle spindles (intra vs extrafusal fibers)

Answer 16

Extrafusal:
- outside fusiform capsule
- α MN
- produce force

Intrafusal:
- inside fusiform capsule
- γ MN
- muscle spindles here !!!
-> motor supply for stretch receptor

Question 17

Primary vs Secondary endings

Answer 17

Primary:
= Group 1a afferents
- Limb dynamics info
- (also senses length)
- Rapidly adapting
△ LENGTH & VELOCITY

Secondary:
- Group II afferents
- Static limb postion
- detect length
- sustained response (slow adapting)
STATIC INFO

Question 18

Golgi tendon organs

Answer 18

• Low threshold mechanoreceptors
• △ muscle tension detection
• Group 1b afferents
• Along collagen fibers in series w/ extrafusal fibers

Question 19

Central pathways: Tactile info

Answer 19

Via dorsal horn
Projection to lower medulla
AFFERENT

Question 20

Central pathways: proprioceptive info

Answer 20

Via dorsal horn
AFFERENT & EFFERENT
-> dorsal & ventral horn
ventral toward MN pools
Dorsal towards cuneate nucleus → cerebellum
SPINOCEREBELLAR TRACT: Clarke’s nucleus → cerebellum*

inferior cerebellar peduncle

Question 21

Central pathways: both

Answer 21

Gracile tract - lower body
Cuinate tract - upper body

Project to gracile & cuinate neucleus near medulla
1st order → 2nd → 3rd → cortex

Question 22

1st order neurons

Answer 22

*Periphery → spinal cord

SIDE - Ipsilateral
BODY - In dorsal root & trigeminal ganglia
PATH - Cuneatus & gracile tracts // trigeminal tract

Question 23

2nd order neurons

Answer 23

*Spinal cord → thalamus

SIDE - Ipsilateral
BODY - in gracile & cuneiform nuclei // trigeminal nucleus
PATH - Medial lemniscus // trigeminal lemniscus

Question 24

3rd order neurons

Answer 24

*Thalamus → cortex

SIDE - Contralateral
BODY - In ventral posterior complex, medial thalamic & medial prabrachial nucleus
PATH - Internal capsule

Question 25

Cortex (w/ pathways)

Answer 25

Cerebral cortex, primary somatosensory cortex, postcentral gyrus, PL // anterior cingulate cortex & insula

Question 26

sensory info in thalamus
(order neurons, converging pathways, somatotopic representation) What layer?

Answer 26

3rd order neurons
Ascending sms. pathways converge in VPT

Somatotopic:
from body; lateral thalamus via medial lemniscus
from head; medial thalamus via trigeminal lemniscus

Project to layer 4 (VPT neurons)

Question 27

Thalamus, S1, Broca’s areas

Answer 27

3b & 1: cutaneous stimulation
3a: proprioceptive stimulation
2: tactile & proprioceptive

• Rapid vs slow segregate within an area

Question 28

Thalamus VPC Pathway

Answer 28

(see 3.28)

Question 29

S1 Lesions

Answer 29

3b lesions: tactile issues
1&2 lesions: size. shape or texture issues