Sensory: touch and proprioception

Question 1

Mechanically activated ion channels can be gated by forces from the membrane (stretching,
shrinking, bending) or from filaments tethered to extracellular or intracellular parts of the channels.
Give examples for each of these mechanisms.

Answer 1

Forces from filament: receptors involved in hearing (tip-link)
Forces from lipid: Piezo receptors

Question 2

What is proprioception? Which structures and channels are involved?

Answer 2

Sensing where your body parts are in space. Piezo receptors, muscle spindels, golgi tendon organs, joint receptors

Question 3

What structures are responsible for sensing touch?

Answer 3

Merkel’s disc, Meissner’s corpuscle (both located right beneath the epidermis, in the upper dermis) and hair follicle receptors (located around the hairs)

Question 4

What kind of sensing are the pacinian (or lamellated) corpuscle responsible for?

Answer 4

Vibration and pressure

Question 5

What kind of sensing are the Ruffini’s endings responsible for?

Answer 5

Stretch

Question 6

Are the merkel cell receptors and meisner corpuscle receptors low treshold or high treshold receptors?

Answer 6

Low treshold

Question 7

Describe the general route in the PNS for afferent noci-, mechano and proprioceptors

Answer 7

The primary afferent neuron go through the dorsal root ganglion (cell body) –> dorsal horn (Lissauer’s tract) innervating secondary afferent CNS neurons –> CNS neurons go through the spino-thalamic tract –> spine –> thalamus

Question 8

The proprioceptors also have an alternative root, describe this.

Answer 8

Afferent cells through dorsal horn, connected to efferent motorneurons by interneurons in the dorsal horn –> efferent motorneurons through ventral horn –> periphery. This allows for a quicker response

Question 9

What are the four types of mechanoceptors?

Answer 9

Pacinin corpuscles, Ruffini corpuscles, Meissner corpuscles and Merkel cell

Question 10

Describe the configuration of the pacini corpuscles.

Answer 10

Onion configuration, ion channels in the central part of the onion structure

Question 11

Describe receptive field.

Answer 11

How big of an area are sensing the stimuli

Question 12

Describe the receptive fields and adaption of the four kinds of mechanoceptors.

Answer 12

Ruffini: large and slow
Merkel: small and slow
Meissner: small and rapid
Pacinian: large and rapid

Question 13

How can mechanosensitive ion channels be gated?

Answer 13

• Membrane stretch
• Force on extracellular structures
• Deformations of cytoskeletal structures

Question 14

What are lanciform nerve endings sensing?

Answer 14

Detecting very small bends of hair (e.g., stroking)

Question 15

Describe the structure of piezo receptors.

Answer 15

Propella-like structure

Question 16

Where are propioceptors found?

Answer 16

Muscle spindles, golgi tendon organs and in joint receptors (extreme joint angle)

Question 17

Describe muscle spindles.

Answer 17

• stretch detectors (signal muscle length), and the normal function of stretch reflexes
• modified muscle cells
• group 1: afferents wrapped around the muscle fibers

Question 18

Describe the monosynaptic stretch reflex.

Answer 18

Muscle spindle detect stretch –> dorsal root ganglion –> dorsal root –> synapse in the ventral horn –> ventral root –> muscle

Question 19

Describe group 1 and 2 fibers dynamic and static responses.

Answer 19

Group 1: fire max during stretch, provides max input during rapid changes
Group 2: provide static signals at steady state

Question 20

Describe golgi-tendon organs.

Answer 20

• have a single (1b) sensory axon (polysynaptic)
• runs between collagen bundles
• stretch straightens collagen fibres and compress sensory nerve
• important for fine motor control

Question 21

Describe the negative feedback via 1b inhibitory interneurons in the golgi-tendon organ pathway.

Answer 21

• negative feedback via 1b inhibitory interneurons –> inhibits homonymous muscle + excite antagonist

Question 22

Describe the central projections of touch and proprioception from periphery.

Answer 22

Transmitted in the dorsal column-medial lemniscus pathway –> VPLN of thalamus –> primary somatosensory cortex

Question 23

Describe the central projections of touch and proprioception from the face.

Answer 23

Trigeminal ganglion –> principle nucleus of trigminal complex –> medial lemniscus –> VPMN of thalamus –> primary somatosensory cortex

Question 24

How are sensory input modulated in relay stations?

Answer 24

By lateral inhibition –> provides contrast

Question 25

Where in the somatosensory cortex are touch and proprioception perceived?

Answer 25

3a and -b

Question 26

Where are the signal send to from 3a and -b?

Answer 26

–> secondary somatosensory cortex –> amygdala and hippocampus

Question 27

How does the use of sense of touch impact the sensory system (plasticity of the sensory system)?

Answer 27

Changes the size of the receptive field, and the extent of the cortical representation

Question 28

What are the symptoms of lesions in area 5/7?

Answer 28

Sensory neglect