Sensory Systems

Question 1

What is each type of sensory info associated with?

Answer 1

Specific receptor type responding t specific sensory modality
Ex. mechanoreceptor, chemoreceptor, thermoreceptor, nociceptors and proprioceptors

Question 2

What is a receptive field?

Answer 2

Specific area which responds to the stimulus
Sensory receptors can have free nerve endings or complex structure

Question 3

What are some range of sensory receptors in skin?

Answer 3

Meissener’s corpuscle - light touch
Merkle’s corpuscle - touch
Free nerve endings - pain
Lamellated corpuscle - deep pressure
Ruffini corspuscle - warmth

Question 4

What is the difference between sensory vs pharmacological receptors?

Answer 4

Sensory - have terminal in periphery responding to specific modality and sends to CNS
Pharmacological - protein in cell membrane and ligands binding

Question 5

What is the generator potential?

Answer 5

Receptor potential - depolarisation which is transduced by adequate stimulus
Size of potential depends on intensity of stimulus

Question 6

What does the generator potential evoke?

Answer 6

Firing of APs for long distance transmission - frequency of APs encodes intensity of stimulus
Receptive field encodes the location
Info on modality, intensity and location

Question 7

Where is receptor potential integrated?

Answer 7

At trigger zne

Question 8

What determines acuity?

Answer 8

Density of innervation and size of receptive fields

Question 9

What are the 3 primary afferent fibres which mediate cutaneous sensation?

Answer 9

Alpha-beta - large and myelinated
Alpha-delta - small and myelinated
C - unmyelinated

Question 10

What do Alpha-beta fibres sense?

Answer 10

Touch, pressure and vibration

Question 11

What do alpha-delta fibres sense?

Answer 11

Cold, Fast pain and pressure

Question 12

What do C fibres sense?

Answer 12

Warmth, and slow pain

Question 13

What 2 primary afferent fibres are proprioception mediated by?

Answer 13

Alpha-alpha and alpha-beta

Question 14

Describe the transmission of sensory info for mechanoreceptors

Answer 14

Alpha-alpha and alpha-beta
Project up through ipsilateral dorsal columns and synapse in cuneate and gracile nuclei
2nd order fibres decussate in brainstem and project to reticular formation, thalamus and cortex

Question 15

Describe the transmission of sensory info for thermoreceptors and nociceptor fibres

Answer 15

Alpha-delta and C fibres
Synapse in dorsal horn, 2nd order fibres decussate in spinal cord, and project up through the lateral spinothalamic tract to reticular formation, thalamus and cortex

Question 16

Describe Brown-Sequard syndrome

Answer 16

On contralateral side - loss of pain and temperature
On ipsilateral side - loss of vibration, motor function, deep touch and proprioception

Question 17

Where is the ultimate termination of sensory info?

Answer 17

Somatosensory cortex (S1) of postcentral gyrus in parietal lobe
Endings are grouped according to location of receptors and extent of density of receptors - produces sensory homunculus

Question 18

Describe adaption

Answer 18

Happens at level of sensory terminals
There is rapidly and slowly adapting
Slow fire APs till end of stimulus as rapidly are at start and end of stimulus

Question 19

What controls processing sensory information?

Answer 19

Adaption, convergence and lateral inhibition

Question 20

Describe convergence

Answer 20

Synapse onto same second order neuron
Saves on neurons, reduces acuity and may underlie referred pain

Question 21

Describe lateral inhibition

Answer 21

Activation of one sensory input causes synaptic inhibition of neighbours
Gives better definition of boundaries and cleans up sensory info

Question 22

What are the types of pain?

Answer 22

Sharp, stabbing, diffuse, throbbing, acute vs chronic, fast vs slow, visceral, referred or phantom limb pain

Question 23

What is signal transduction in nociceptors activated by?

Answer 23

Low pH and heat via ASIC, TRPVI…
Local chemical mediators - bradykinin binds to G protein, histamine and prostaglandins (sensitise bradykinin)

Question 24

What is a type of analgesia?

Answer 24

NSAIDs - aspirin and ibuprofen

Question 25

How does NSAIDs work?

Answer 25

Prostaglandins sensitise nociceptors to bradykinin
They inhibit cyclo-oxygenase which converts arachidonic acid to prostaglandins
Works well against pain associated with inflammation

Question 26

How do local anaesthetics work?

Answer 26

Block Na action potential and therefor all axonal transmission

Question 27

What are some other analgesia?

Answer 27

Local anaesthetics, trans cutaneous electric nerve stimulation and opiates

Question 28

How do opiates work?

Answer 28

Reduce sensitivity of nociceptors
Block transmitter release in dorsal horn
Activate descending inhibitory pathways

Question 29

Describe the closing the gate pathway

Answer 29

Segmental controls - activity in alpha-alpha/beta fibres activate inhibitory interneurons
Inhibitory interneurons release opioid peptides that inhibit release of alpha-delta fibres hence closing the gate - blocks Na channels so less transmitter released

Question 30

Describe the descending controls in closing the gate

Answer 30

Same inhibitory interneurons are also activated by descending pathways from Periaqueductal grey matter (PAG) and Nucleus raphe magnus (NRM) hence closing the gate