Sensory Systems

Question 1

What is each type of sensory information associated with?

Answer 1

Each type of sensory information is associated with a specific receptor type responding to a specific sensory modality

Question 2

Give examples of types of receptors.

Answer 2

• Mechanoreceptors
• Chemoreceptors
• Thermoreceptors
• Nociceptors
• Proprioceptors

Question 3

Give examples of receptors with free nerve endings.

Answer 3

• Nocicpetors

- Cold receptors

Question 4

Give examples of receptors with complex structures.

Answer 4

• Pacininan corpuscle

- Meissner’s corpsucle

Question 5

What is the receptive field?

Answer 5

Specific area that response to stimulus acts over

Question 6

What do tactile (Meissner’s) corpuscle detect?

Answer 6

Light touch

Question 7

What do tactile (Merkel’s) corpuscle detect?

Answer 7

Touch

Question 8

What do free nerve endings detect?

Answer 8

Pain

Question 9

What do lamellated (Pacinian) corpuscles detect?

Answer 9

Deep pressure

Question 10

What do ruffini corpuscles detect?

Answer 10

Warmth

Question 11

What do all sensory receptros transduce their adequate stimuli into?

Answer 11

All sensory receptors transduce their adequate stimulus into a depolarisation, the receptor (generator) potential

Question 12

What does the size of receptor potential encode?

Answer 12

Size of receptor potential encodes intensity of stimulus

Question 13

What does the receptor potential evoke?

Answer 13

Receptor potential then evokes firing of action potentials for long distance transmission

Question 14

What does the frequency of the action potentials encode?

Answer 14

Intensity of stimulus

Question 15

What does the receptive field encode?

Answer 15

Location of stimulus

Question 16

What is duration of action potentials proportional to?

Answer 16

Stimulus duration

Question 17

What does neurotransmitter release vary with?

Answer 17

The pattern of action potentials arriving at the axon terminal

Question 18

What determines acuity?

Answer 18

• Density of innervation

- Size of receptive field

Question 19

What transmits action potentials to the CNS?

Answer 19

Action potentials are transmitted to CNS by axons

Question 20

What is cutaneous sensation mediated by?

Answer 20

Cutaneous sensation is mediated by 3 types of primary afferent fibres

• AB
• Adelta
• C

Question 21

Describe AB fibres.

Answer 21

-Large myelinated
-30-70m/s
Touch
-Pressure
-Vibration

Question 22

Describe the A delta fibres.

Answer 22

• Myelinated
• 5-30m/s
• Cold,
• “Fast” pain,
• Pressure

Question 23

Describe the C fibres

Answer 23

• Unmyelinated fibres
• 0.5-2m/s
• Warmth
• “Slow” pain

Question 24

What is proprioception mediated by?

Answer 24

Proprioception is mediated by 2 types of primary afferent fibres
-Aα & Aβ eg muscle spindles, golgi tendon organs etc

Question 25

What do the primary afferent fibres enter the spinal cord via?

Answer 25

All enter spinal cord via the dorsal root ganglia (or cranial nerve ganglia for head)

Question 26

What types of fibres are mechanorecetive?

Answer 26

Aα & Aβ fibres

Question 27

What types of fibres are thermoreceptive and nociceptive?

Answer 27

Aδ & C fibres

Question 28

Where do the mechanireceptive fibres project?

Answer 28

Project straight up through ipsilateral dorsal columns

Question 29

Where doe the mechanireceptive fibres synapse?

Answer 29

Synapse in cuneate & gracile nuclei

Question 30

Where do the 2nd order mechanoreceptive fibres decussate?

Answer 30

The 2nd order fibres cross over midline (decussate) in the brain stem & project to reticular formation, thalamus and cortex

Question 31

Where do the thermoreceptive and nociceptive fibres synapse?

Answer 31

Synapse in the dorsal horn

Question 32

Where do the thermoreceptive and nocicipetive project?

Answer 32

Project up through the contralateral spinothalamic (anterolateral) tract to reticular formation, thalamus and cortex

Question 33

Where do the 2nd order thermoreceptive and nociceptive fibres decussate?

Answer 33

The 2nd order fibres cross over the midline in the spinal cord

Question 34

What explain consequences of spinal cord injuries?

Answer 34

Different pathways for transmission of sensory information explains consequences of spinal cord injuries

Question 35

What does damage to the dorsal columns result in?

Answer 35

Causes loss of touch, vibration, proprioception below lesion on ipsilateral side

Question 36

What does damage to the anterolateral quadrant result in?

Answer 36

Causes loss of nociceptive & temperature sensation below lesion on contralateral side

Question 37

Where is the ultimate termination of sensory information?

Answer 37

Ultimate termination is in the somatosensory cortex (S1) of the postcentral gyrus

Question 38

What are endings grouped according to?

Answer 38

Endings are grouped according to the location of the receptors

Question 39

What is extent of representation of endings related to?

Answer 39

Extent of representation is related to the density of receptors in each location

Question 40

What is the order of the sensory homunculus from median to lateral?

Answer 40

- Genitalia - Toes - Foot - Leg - Hip - Trunk - Neck - Head - Shoulder - Arm - Elbow - Forearm - Wrist hand - Pinky - Ring - Middle - Index - Thumb - Eye - Nose - Face - Lips - Gum and jaw - Tongue - Pharynx - Intraabdominal

Question 41

What are the 5 of processing in sensory pathways?

Answer 41

- Adaptation - Convergence - Lateral inhibition - not all information reaches the brain - Perception

Question 42

What may underlie referred pain?

Answer 42

Convergence

Question 43

What is the advantages and disadvantage of convergence?

Answer 43

Saves on neurones but reduces acuity

Question 44

What is lateral inhibition?

Answer 44

- Activation of one sensory input causes synaptic inhibition of its neighbours - Gives better definition of boundaries - Cleans up sensory information

Question 45

How does lateral inhibition occur?

Answer 45

- Primary neuron response is proportional to stimulus strength - Pathway closest to the stimulus inhibits neighbours - Inhibition of lateral neurons enhances perception of stimulus

Question 46

Give examples of different types of pain.

Answer 46

- Sharp, stabbing vs diffuse, throbbing pain - Fast (initial) pain vs slow (delayed) pain - Acute vs chronic pain - Visceral pain - Referred pain - Phantom limb pain

Question 47

What is signal transduction in nociceptors activated by?

Answer 47

- Low pH, heat (via ASIC, TRPV1 etc) | - Local chemical mediators (eg bradykinin, histamine, prostaglandins)

Question 48

How can the 'gate' be closed to prevent pain?

Answer 48

- Segmental controlseg gate control theory of pain: activity in Aα/β fibres activates inhibitory interneurones - Descending controls: The same inhibitory interneurones are also activate by descending pathways from PAG and NRM, hence also “closing the gate” - Inhibitory interneurones release opioid peptides (endorphins) that inhibit transmitter release from Aδ/C fibres, hence “closing the gate”

Question 49

How do NSAIDs work?

Answer 49

- Prostaglandins sensitise nociceptors to bradykinin - NSAIDs are analgesic (and antipiretic & anti-inflammatory) because they inhibit cyclo-oxygenase which converts arachidonic acid to prostaglandins - So NSAIDs work well against pain associated with inflammation

Question 50

How do local anaesthetics work?

Answer 50

Block Na+ action potential and therefore all axonal transmission

Question 51

How do opiates work?

Answer 51

- Reduce sensitivity of nociceptors - Block transmitter release in dorsal horn (hence epidural administration) - Activate descending inhibitory pathways

Question 52

Give example of analgesia.

Answer 52

- NSAIDs - Local anaesthetics - Trans cutaneous electric nerve stimulation (TENS) - Opiates (e.g. morphine)