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Nervous System > Sensory Systems > Flashcards

Sensory Systems Flashcards

1
Q

What are examples of sensory receptors?

A

Mechanoreceptors

Chemoreceptors

Thermoreceptors

Nociceptors

Proprioceptors

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2
Q

How does the nerve endings of different sensory receptors differ?

A

May have free nerve endings or complex structures

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3
Q

What are examples of sensory receptors that have free nerve endings?

A

Nociceptors

Cold receptors

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4
Q

What are examples of complex structures at the end of sensory receptors?

A

Pacininan corpuscle

Meissner’s corpuscle

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5
Q

What is the specific area that sensory receptors respond to stimulus over called?

A

Receptive field

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6
Q

How do sensory receptors tranduce their adequate stimulus?

A

Into depolarisation, the receptor (generator) potential

This evokes firing of action potentials for long distance transmission

Gives information on modality, intensity and location of the stimulus

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7
Q

What does the size of receptor potential encode?

A

Intensity of stimulus

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8
Q

What does the frequency of action potentials encode?

A

Intensity of stimulus

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9
Q

What does the receptive field encode?

A

Location of stimulus

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10
Q

What determines acuity?

A

Density of innervation and size of receptive fields

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11
Q

What are action potentials from sensory receptors transmitted to the CNS by?

A

Axons

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12
Q

What are the 3 types of primary afferent fibres that mediated cutaneous sensation?

A
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13
Q

What are Aß fibres also known as?

A

Large myelinated

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14
Q

What is the speed of Aß fibres?

A

30-70m/s

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15
Q

What kinds of sensory information is transmitted by Aß fibres?

A

Touch, pressure, vibration

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16
Q

What are Aσ fibres also known as?

A

Small myelinated fibres

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17
Q

What is the speed of Aσ fibres?

A

5-30m/s

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18
Q

What kind of information is transmitted by Aσ fibres?

A

Cold, “fast” pain, pressure

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19
Q

What are C fibres also known as?

A

Unmyelinated fibres

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20
Q

What is the speed of C fibres?

A

0.5-2m/s

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21
Q

What kind of information is transmitted by C fibres?

A

Warmth, “slow” pain

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22
Q

What are the 2 types of primary afferent fibres that mediate proprioception?

A

Aa and Aß (such as muscles spindles, golgi tendon organs etc)

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23
Q

What do proprioceptors give information about?

A

Position and movement

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24
Q

What do all primary afferent fibre types enter the spinal cord through?

A

Dorsal root ganglia (or cranial nerve ganglia for the head)

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25
Q

What fibres transmit information from mechanoreceptors?

A

Aa and Aß fibres

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26
Q

Explain the pathway of mechanoreceptor (Aa and Aß fibres)?

A

1) Project straight up through ipsilateral dorsal columns
2) Synapse in cuneate and gracile nuclei
3) The 2nd order fibres cross over midline in the brain stem and project to reticular formation, thalamus and cortex

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27
Q

Where do mechanoreceptor fibres cross the midline?

A

Brainstem

28
Q

What do mechanoreceptor fibres project up the spinal cord through?

A

Ipsilateral dorsal columns

29
Q

What fibres do thermoreceptors use?

A

Aσ and C fibres

30
Q

What fibres do nociceptive receptors use?

A

Aσ and C fibres

31
Q

Explain the pathway of thermoreceptive and nociceptive fibres?

A

1) Synapse in the dorsal horn
2) The 2nd order fibres cross over the midline in the spinal cord
3) Project up through the contralateral spinothalamic (anteriolateral) tract to reticular formation, thalamus and cortex

32
Q

What do mechanoreceptors detect?

A

Touch, pressure, stretching and motion

33
Q

What do nociceptive receptors detect?

A

Pain

34
Q

Where do thermoreceptive fibres cross the midline?

A

Spinal cord

35
Q

Where do nociceptive fibres cross the midline?

A

Spinal cord

36
Q

How are thermoreceptive fibres transmitted up the spinal cord?

A

Contralateral spinothalamic (anteriolateral) tract to reticular formation, thalamus, and cortex

37
Q

How are nociceptive fibres transmitted up the spinal cord?

A

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

38
Q

Different transmission for sensory information explains consequences of spinal cord injuries, what does damage to dorsal columns cause?

A

Loss of touch, vibration, proprioception below lesion on ipsilateral side

39
Q

Different transmission for sensory information explains consequences of spinal cord injuries, what does damage to anteriolateral quadrant cause?

A

Loss of nociceptive and temperature sensation below lesion on contralateral side

40
Q

Where is the ultimate terminate of all sensory receptor fibres?

A

Somatosensory cortex (S1) of the postcentral gyrus

41
Q

What is S1?

A

Somatosenosry cortex

42
Q

What are the endings of sensory fibres grouped according to?

A

Location of the receptors, forming sensory homunculus

43
Q

What are the steps of processing in sensory pathways?

A

Adaptation

Convergence

Lateral inhibition

44
Q

What is the adaptation step of processing in sensory pathways?

A

Decline in the electrical response of a receptor neuron over time in spite of the continued presence of an appropriated stimulus of constant strength

Is apparent as a gradual decrease in frequency of spikes generated within the receptor neuron

45
Q

What are the 2 kinds of adapting that sensory receptors can display?

A

Rapidly adapting

Slowly adapting

46
Q

What are consequences of convergence occuring when processing sensory information?

A

Saves on neurons

But reduced acuity

May underlie referred pain

47
Q

What is the lateral inhibition step of processing in sensory pathways?

A

Activation of one sensory input causes synaptic inhibition of its neighbours

48
Q

What are consequences of lateral inhibition in sensory receptors?

A

Gives better definition of boundaries

Cleans up sensory information

49
Q

What is perception?

A

The ability to see, hear or become aware of something through the sense, or the way something is interpreted

50
Q

What are examples of the different kinds of pain?

A

Sharp, stabbing vs diffuse, throbbing

Fast (initial pain) vs slow (delayed) pain

Acute vs chronic pain

Visceral pain

Referred pain

Phantom limb pain

51
Q

What is signal transduction?

A

Transmission of molecular signals from a cell’s exterior to its interior

52
Q

What is signal transduction in nociceptors activated by?

A

Low pH, heat (via ASIC, TRPV1 etc)

Local chemical mediators (such as bradykinin, histamine, prostaglandins)

53
Q

What are examples of local chemical mediators that activates signal transduction in nociceptors?

A

Bradykinin, histamine, prostaglandins

54
Q

Explain the processing of nociceptive pathways?

A

1) Segmental controls (such as gate theory control of pain where activity in Aa/ß fibres activates inhibitory interneurons)
2) Inhibitory interneurons release opiod peptides (endorphins) that inhibit transmitter release from Aσ/C fibres, “closing the gate”
3) Descending controls, the same inhibitory interneurons are also activated by descending pathways from PAG and NRM, hence also “closing the gate”
4) Transmitted to thalamus

55
Q

What does PAG stand for?

A

Peri-aqueductal grey matter

56
Q

What does NRM stand for?

A

Nucleus raphe magnus

57
Q

What is the medical term for the inability to feel pain?

A

Analgesia

58
Q

What is the “gate control theory of pain”?

A

Non-painful stimulus input closes the nerve “gates” to painful input, which prevents pain sensation form travelling to the central nervous system

59
Q

What can analgesia be achieved with?

A

Non-steroidal anti-inflammatory drugs (NSAIDs)

Local anaesthetics

Transcutaneous electrical nerve stimulation (TENS)

Opiates

60
Q

What does NSAIDs stand for?

A

Non-steroidal anti-inflammatory drugs

61
Q

How do NSAIDs achieve analgesia?

A

1) Prostaglandins sensitive nociceptors to bradykinin
2) NSAIDs inhibit cyclo-oxygenase which converts arachidonic acid to prostaglandins
3) So NSAIDs work well against pain associated with inflammation

62
Q

How do local anaesthetics achieve analgesia?

A

Block Na+ action potential and therefore all axonal transmission

63
Q

What does TENS stand for?

A

Transcutaneous electrical nerve stimulation

64
Q

What is an example of an opiate?

A

Morphine

65
Q

How do opiates achieve analgesia?

A

Reduce sensitivty of nociceptors

Block transmitter release in dorsal horn (hence epidural administration)

Activate descending inhibitory pathways

Nervous System (48 decks)

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