Sensory Physiology

Question 1

What are the 4 major groups of receptors?

Answer 1

Chemoreceptors
Mechanoreceptors
Thermoreceptors
Photoreceptors

Question 2

What is another name for primary and secondary sensory neurons?

Answer 2

1st and 2nd order neurons

Question 3

What are the 4 properties of a stimulus?

Answer 3

1. Modality
2. Location
3. Intensity
4. Duration

Question 4

What are the classes of somatosensory nerve fibres?

Answer 4

AB- large, myelinated
Ad- small, myelinated
C- small, unmyelinated

Question 5

What is AB fibres associated with?

Answer 5

Mechanical stimuli

Question 6

Whay is Ad fibres associated with?

Answer 6

Cold
Fast pain
Mechanical stimuli

Question 7

What are C fibres associated with?

Answer 7

Heat
Cold
Slow pain
Mechanical stimuli

Question 8

What are the mechanoreceptive fibres and how do they transmit sensory information?

Answer 8

Aa and AB
Project straight up through ipsilateral dorsal column
Synapse in cuneate and gracile nuclei
2nd order fibres decussate in brainstem and project to reticular formation, thalamus an dcortex

Question 9

What are the thermoreceptive and nociceptive fibres and how do they transmit sensory information?

Answer 9

Ad and C
Synapse in dorsal horn
2nd order fibres cross over midline in spinal cord
Project up through lateral spinothalamic tract to reticular formation, thalamus and cortex

Question 10

What is the gate control theory of pain modulation?

Answer 10

AB fibres activate inhibitory interneurons
Descending pathways also activate inhibitory interneurons
Inhibitory interneurones release endorphins that inhibit transmitter release from Ad and C fibres

Question 11

What is hyperalgesia?

Answer 11

Increased perception of pain

Question 12

What are the type of peripheral sensitization?

Answer 12

Hyperalgesia- exaggerated response to stimuli
Allodynia- decreased threshold for nociceptor response

Question 13

What are the types of central sensitization?

Answer 13

1. Wind up- winding up response of activated synapses
2. Classical- opening up of silent synapses
3. Long term potentiation- involves activated synapses primarily for very intense stimuli

Question 14

What are the 3 types of pain?

Answer 14

1. Nociceptive
2. Neuropathic
3. Nociplastic

Question 15

What is nociceptive pain?

Answer 15

Nociceptors respond to noxious stimuli
Localised at site of injury
Resolves when damaged tissue heals

Question 16

What is neuropathic pain?

Answer 16

Pain caused by lesion/disease of somatosensory nervous system
Pain in neurological territory of affected structure
Chronic

Question 17

What is nociplastic pain?

Answer 17

Arises from altered nociception with no clear evidence of tissue/somatosensory damage
Stimulus independent
No injury, inflammation of neuronal damage
Serves no protective or adaptive function

Question 18

Where is the vestibular system?

Answer 18

Inner ear

Question 19

What is the vestibular system composed of?

Answer 19

Membranous labyrinths: A series of fluid filled labyrinths embedded in temporal bone
- Otolith organs
- Semi-circular canals

Question 20

What are the 2 otolith organs?

Answer 20

Utricle
Saccule

Question 21

What fills the vestibular apparatus?

Answer 21

Endolymph secreted by epithelial cells

Question 22

What do the semi-circular canals monitor?

Answer 22

Rotational acceleration
Posterior canal- tilt of head left or right
Horizontal canal- rotation of head left or right (‘no’)
Superior canal- rotation of head front and back (‘yes’)

Question 23

What is at the base of each canal?

Answer 23

Ampulla- enlarged chamber containing a crista

Question 24

What is a crista?

Answer 24

Sensory structure that consists of hair cells and a gelatinous mass, the cupula
Hair cell cilia are embedded in the cupula

Question 25

How is rotation sensed in the semi-circular canals?

Answer 25

1. If the skull is rotated the endolymph at first does not move because of its inertia.
2. However the ampullae moves instantly because it is embedded in the skull.
3. Inertia of endolymph produces drag which bends cupula and embedded cilia in the opposite direction to movement
4. If rotation continues, the endolymph catches up and rotates at the same speed, removing the shearing forces, but this takes several seconds
5. Sudden stop will cause endolymph to continue to move due to momentum creating a sense of movement and dizziness

Question 26

What are the 2 types of hair cilia?

Answer 26

Kinocilium- single, very large
Stereocilia- smaller

Question 27

What do the otolith organs sense?

Answer 27

Linear acceleration and head position

Question 28

What is the sensory structure of the otolith organs?

Answer 28

Maculae
Consists of hair cells which protrude into a gelatinous mass called the otolith membrane
Embedded in the otolith membrane are calcium carbonate and protein particles called otoliths

Question 29

How do otolith organs sense linear acceleration and head position?

Answer 29

If gravity or acceleration causes the otoliths to slide forwards or back, the otolith membrane slides with them, bending the hair cell cilia and setting off a signal

Question 30

What do the maculae of the utricle sense?

Answer 30

Horizontal orientation
Forward acceleration or deceleration,
Head tilt

Question 31

What do the maculae of the saccule sense?

Answer 31

Vertical orientation when head is erect
Sensitive to vertical forces

Question 32

What are the vestibular system reflexes?

Answer 32

1. Tonic labyrinthine reflexes- keep axis of head in a constant relationship with the rest of the body
2. Dynamic righting reflexes - rapid postural adjustments to stop you falling when you trip
3. Vestibulo-ocular reflexes- strong association is evident between vestibular apparatus, visual apparatus and postural control

Question 33

What are the clinical associations with the vestibular system?

Answer 33

Motion sickness: nausea, vomiting, low BP, dizziness, sweating, pallor
Labyringitis: ANS symptoms, vertigo
Meniere’s disease: vertigo, nausea, nystagmus, tinnitus