6.1 Touch & Proprioception

Question 1

What is the kind of receptor used for touch (light touch, pressure, vibration) ?

Answer 1

mechanoreceptor

Question 2

What kind of receptor is used for proprioception (joint position, muscle length, muscle tension)?

Answer 2

mechanoreceptor

Question 3

What kind of receptor is used for temperature?

Answer 3

thermoreceptor

Question 4

What kind of receptor is used for pain?

Answer 4

nociceptor

Question 5

What are the characteristics of a slow adapting receptor?

Answer 5

Starts firing immediately at onset of stimulus → continuous firing as long as stimulus remains (frequency may decrease but still continuous)

Question 6

What are the characteristics of a fast adapting receptor?

Answer 6

Does not fire continuously throughout (may only fire at the onset or the end of the stimulus or both at the beginning and the end)

Question 7

What are the characteristics of a plexus?

Answer 7

Simple structures (plexus of axons with free nerve endings)

Question 8

What are the characteristics of a peritrichial ending?

Answer 8

Nerve terminal wound around hair shaft → movement of hair causes appreciable amount of leverage → increases receptor sensitivity

Question 9

Pacinian corpuscle: Nerve terminal surrounded by ______________ → allows good response to vibration (on top of pressure)

Answer 9

concentric circles of epithelial cells

Question 10

Primary sensory neurones have cell bodies in the PNS in the __________ (along spinal cord if from the body) or _____________ (along brainstem if from the head):
• All the sensory neurones transmitting touch and proprioception are ____________ → with variable receptive fields but same coding of stimulus intensity
• Stimulus intensity is coded by the firing frequency in all the neurones → higher stimulus intensity is coded as higher firing frequency

Answer 10

dorsal root ganglion;

trigeminal ganglion;

fast-conducting;

Question 11

What types of structures have Ia kind of fibres?

Answer 11

Muscle spindle primary afferent

Question 12

What types of structures have Ib kind of fibres?

Answer 12

Golgi tendon organs

Question 13

What types of structures have ‘a’ kind of fibres?

Answer 13

Efferents to extrafusal muscle

Question 14

What types of structures have II/ Aβ kind of fibres?

Answer 14

other encapsulated endings and endings with accessory structures: Meisners corpulscles, Merkle endings, muscle spindle secondary endings

Question 15

What types of structures have γ kind of fibres?

Answer 15

efferents to intrafusal muscles

Question 16

What types of structures have III Aδ kind of fibres?

Answer 16

some nociceptors (sharp pain), cold receptors, most hair receptors

Question 17

What types of structures have B kind of fibres?

Answer 17

preganglionic autonomic efferents

Question 18

What types of structures have C kind of fibres?

Answer 18

most nociceptors (dull, aching pain), warm receptors, postganglionic autonomic efferents

Question 19

Face, fingertips

• size: _______
• density: ___________
• localisation: ______________

Answer 19

small;

high;

higher resolution

Question 20

[dorsal column/ medial leminiscus pathway: primary neurones]

• lumbar & sacral: Impulses from axon of primary sensory neurone (cell body in dorsal root ganglion) → dorsal horn → immediately enters dorsal columns (area of white matter) → move towards _____________ → form ________________
• cervical & thoracic: Impulses from axon of primary sensory neurone (cell body in dorsal root ganglion) → dorsal horn → enters dorsal columns (stay __________ placed) → form ______________
• face: Impulses from axon of trigeminal nerve (cell body in trigeminal ganglion) → _________ → _____________ (synapse with secondary neurone)

Answer 20

midline (more medially);

gracile fasciculus;

laterally;

cuneate fasciculus;

pons (mid-pons)

trigeminal nucleus

Question 21

[dorsal column/ medial leminiscus pathway: secondary neurones]

• Medulla: Gracile fasciculus and cuneate fasciculus pass up to the level of the medulla → synapse with secondary sensory neurones (gracile and cuneate nuclei) → decussates → turn upwards to form ________ → ___________
• Pons: Secondary neurones (from face) decussate → axons join onto the ____________ end of the medial lemniscus → pass upwards to ____________

Answer 21

medial lemniscus;

thalamus;

medial;

thalamus

Question 22

[dorsal column/ medial leminiscus pathway: tertiary neurones]

• Brain (from body): Secondary neurones synapse in the thalamic _________________ nucleus (relays somatosensory information from the body) → __________ (white matter) → appropriate part of cortex depending on part of body (according to homunculus)
• Brain (from face): Secondary neurones synapse in the thalamic ____________ nucleus (relays somatosensory information from the face) → somatosensory cortex (more lateral area for the face)

Answer 22

ventroposterolateral (VPL) ;

internal capsule;

ventroposteromedial (VPM)

Question 23

Where does the sensory information from the body in the dorsal column decussate at?

Answer 23

decussates in the medulla

Question 24

Where does the sensory information from the face in the dorsal column decussate at?

Answer 24

decussates in the pons

Question 25

how is the information in the dorsal columns organised (from median to lateral)?

Answer 25

axons from sacral, lumbar, thoracic, cervical

Question 26

how is the information in the medial lemniscus organised (from median to lateral)?

Answer 26

face, upper limb, lower limb

Question 27

Intensity of information carried varies depending on the stimulus intensity (firing frequency of various axons):
• As axons synapse with the relay nuclei (gracile and cuneate nuclei), axons with _______________ tend to inhibit axons around them via collateral inhibitory synapses
• Intensifies the process of distinction between the intensity of various inputs → improves resolution of localisation

Answer 27

highest firing frequency

Question 28

What is the function of the Primary Somatosensory cortex (S1)?

Answer 28

Receives information from dorsal column/medial lemniscus pathway:
• Cells respond according to stimulus properties (e.g. type – touch/vibration, intensity, abstract properties – shape/movement)
• Projects to S2 and posterior parietal cortex

Question 29

What is the function of the secondary somatosensory cortex (S2)?

Answer 29

Amalgamation of information coming into both hemispheres (strong connections in corpus callosum in S2 areas between hemispheres)

Question 30

What is the function of the Posterior parietal cortex?

Answer 30

Construction of internal map of body and the body within its extrapersonal space (receives input from S1 area and other modalities like visual inputs)