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Systems: Neurology AB > Sensory Systems > Flashcards

Sensory Systems Flashcards

1
Q

What is each type of sensory information associated with?

A

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

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2
Q

Give examples of types of receptors.

A
  • Mechanoreceptors
  • Chemoreceptors
  • Thermoreceptors
  • Nociceptors
  • Proprioceptors
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3
Q

Give examples of receptors with free nerve endings.

A
  • Nocicpetors

- Cold receptors

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4
Q

Give examples of receptors with complex structures.

A
  • Pacininan corpuscle

- Meissner’s corpsucle

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5
Q

What is the receptive field?

A

Specific area that response to stimulus acts over

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6
Q

What do tactile (Meissner’s) corpuscle detect?

A

Light touch

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7
Q

What do tactile (Merkel’s) corpuscle detect?

A

Touch

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8
Q

What do free nerve endings detect?

A

Pain

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9
Q

What do lamellated (Pacinian) corpuscles detect?

A

Deep pressure

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10
Q

What do ruffini corpuscles detect?

A

Warmth

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11
Q

What do all sensory receptros transduce their adequate stimuli into?

A

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

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12
Q

What does the size of receptor potential encode?

A

Size of receptor potential encodes intensity of stimulus

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13
Q

What does the receptor potential evoke?

A

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

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14
Q

What does the frequency of the action potentials encode?

A

Intensity of stimulus

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15
Q

What does the receptive field encode?

A

Location of stimulus

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16
Q

What is duration of action potentials proportional to?

A

Stimulus duration

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17
Q

What does neurotransmitter release vary with?

A

The pattern of action potentials arriving at the axon terminal

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18
Q

What determines acuity?

A
  • Density of innervation

- Size of receptive field

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19
Q

What transmits action potentials to the CNS?

A

Action potentials are transmitted to CNS by axons

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20
Q

What is cutaneous sensation mediated by?

A

Cutaneous sensation is mediated by 3 types of primary afferent fibres

  • AB
  • Adelta
  • C
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21
Q

Describe AB fibres.

A

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

22
Q

Describe the A delta fibres.

A
  • Myelinated
  • 5-30m/s
  • Cold,
  • “Fast” pain,
  • Pressure
23
Q

Describe the C fibres

A
  • Unmyelinated fibres
  • 0.5-2m/s
  • Warmth
  • “Slow” pain
24
Q

What is proprioception mediated by?

A

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

25
Q

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

A

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

26
Q

What types of fibres are mechanorecetive?

A

Aα & Aβ fibres

27
Q

What types of fibres are thermoreceptive and nociceptive?

A

Aδ & C fibres

28
Q

Where do the mechanireceptive fibres project?

A

Project straight up through ipsilateral dorsal columns

29
Q

Where doe the mechanireceptive fibres synapse?

A

Synapse in cuneate & gracile nuclei

30
Q

Where do the 2nd order mechanoreceptive fibres decussate?

A

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

31
Q

Where do the thermoreceptive and nociceptive fibres synapse?

A

Synapse in the dorsal horn

32
Q

Where do the thermoreceptive and nocicipetive project?

A

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

33
Q

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

A

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

34
Q

What explain consequences of spinal cord injuries?

A

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

35
Q

What does damage to the dorsal columns result in?

A

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

36
Q

What does damage to the anterolateral quadrant result in?

A

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

37
Q

Where is the ultimate termination of sensory information?

A

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

38
Q

What are endings grouped according to?

A

Endings are grouped according to the location of the receptors

39
Q

What is extent of representation of endings related to?

A

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

40
Q

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

A
  • 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
41
Q

What are the 5 of processing in sensory pathways?

A
  • Adaptation
  • Convergence
  • Lateral inhibition
  • not all information reaches the brain
  • Perception
42
Q

What may underlie referred pain?

A

Convergence

43
Q

What is the advantages and disadvantage of convergence?

A

Saves on neurones but reduces acuity

44
Q

What is lateral inhibition?

A
  • Activation of one sensory input causes synaptic inhibition of its neighbours
  • Gives better definition of boundaries
  • Cleans up sensory information
45
Q

How does lateral inhibition occur?

A
  • Primary neuron response is proportional to stimulus strength
  • Pathway closest to the stimulus inhibits neighbours
  • Inhibition of lateral neurons enhances perception of stimulus
46
Q

Give examples of different types of pain.

A
  • Sharp, stabbing vs diffuse, throbbing pain
  • Fast (initial) pain vs slow (delayed) pain
  • Acute vs chronic pain
  • Visceral pain
  • Referred pain
  • Phantom limb pain
47
Q

What is signal transduction in nociceptors activated by?

A
  • Low pH, heat (via ASIC, TRPV1 etc)

- Local chemical mediators (eg bradykinin, histamine, prostaglandins)

48
Q

How can the ‘gate’ be closed to prevent pain?

A
  • 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”
49
Q

How do NSAIDs work?

A
  • 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
50
Q

How do local anaesthetics work?

A

Block Na+ action potential and therefore all axonal transmission

51
Q

How do opiates work?

A
  • Reduce sensitivity of nociceptors
  • Block transmitter release in dorsal horn (hence epidural administration)
  • Activate descending inhibitory pathways
52
Q

Give example of analgesia.

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

Systems: Neurology AB (51 decks)

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