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N - C > Sensory Systems > Flashcards

Sensory Systems Flashcards

1
Q

What is the range of sensory receptors?

A 
Mechanoreceptors
Chemoreceptors
Thermoreceptors
Nociceptors
Proprioceptors

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

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2
Q

How does the structure of sensory receptors differ?

A

May have free nerve endings:

  • Nociceptors,
  • Cold receptors

May have complex structure:

  • Pacininan Corpuscle
  • Meissner’s corpuscle
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3
Q

What is the receptive field?

A

The area that a sensory receptor will resond to a stimulus

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4
Q

What do Meissner’s corpuscle’s detect?

A

Light touch

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5
Q

What so Merkle’s corpuscles detect?

A

touch

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6
Q

What do Pacinian corpuscles detect?

A

Deep Pressure

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7
Q

What do Ruffini corpuscle’s detect?

A

Warmth

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8
Q

What do sensory receptors do when they detect a stimulus?

A

Transduce their adequate stimulus into a depolarisation called the generator potential.

The size of the generator potental encodes the intensity of stimulus.

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9
Q

What happens once a generator potential is evoked?

A

Receptor potential then evokes firing of action potentals for long distance transmission.

Then frequency of action potentials encodes intensity of stimulus.

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10
Q

What does the receptive field encode?

A

Receptive field encodes location of stimulus

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11
Q

What determines acuity?

A

Density of innervation and size of receptive fields

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12
Q

Cutaneous sensation is mediated by 3 types of primary afferent fibres.
What are they?

A

A-beta fibres
A-delta fibres
C fibres

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13
Q

What are A-beta fibres?

A

large myelinated
(30-70m/s)
Touch, pressure, vibration

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14
Q

What are A-delta fibres?

A

small myelinated
(5-30m/s)
cold, “fast” pain, pressure

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15
Q

What are C fibres?

A

Unmyelinated fibres
(0.5-2m/s)
Warmth, “slow” pain

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16
Q

What 2 types of primary afferent fibres mediate proprioception?

A

A-alpha and A-beta

e.g. spindle fibres, golgi tendon organs etc

17
Q

How is mechanoreceptive sensory information transmitted?

A

A-alpha and A-beta fibres

Project straight up through ipsilateral dorsal columns.
Synapse in cuneate and gracile nuclei.
The 2nd order fibres decussate in the brainstem and project to reticular formation, thalamus and cortex

18
Q

What is the reticular formation?

A

A diffuse network of nerve pathways in the brainstem connecting the spinal cord, cerebrum, and cerebellum, and mediating the overall level of consciousness.

19
Q

How is Thermoreceptive and Nociceptive information transmitted?

A

A-delta and C fibres

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

20
Q

Different pathways for transmission of sensory information explains consequences of spinal cord injuries.
What would damage to dorsal columns result in?

A

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

21
Q

Different pathways for transmission of sensory information explains consequences of spinal cord injuries.
What would damage to anterolateral quadrant result in?

A

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

22
Q

Where is the ultimate termination of sensory information?

A

Somatosensory cortex of the postcentral gyrus.

Endings are grouped according to the location of the receptors.

Extent of representation is related to the density of receptors in each location.
Produces the sensory homunculus.

23
Q

Will stimulation anywhere along a sensory pathway evoke the same sensation?

A

Yes

24
Q

What is adaptation?

A

Neural adaptation or sensory adaptation is a change over time in the responsiveness of the sensory system to a constant stimulus.
For example, if you rest a hand on a table, you immediately feel the table’s surface on your skin. Within a few seconds, however, you stop feeling the table’s surface.
The sensory neurons stimulated by the table’s surface respond immediately, but then respond less and less until they may not respond at all

25
Q

What is convergence?

A

Different sensory neurons synapse onto the same 2nd order neuron.

These may be the same sensory information from different locations (resulting in referred sensation) or different sensory inputs.

-Saves on neurones but reduces acuity

26
Q

What is lateral inhibition?

A

Activation of one sensory fibre causes synaptic inhibition of its neighbours.

Gives a better definition of boundaries and cleans up sensory information

27
Q

Does all sensory information reach the brain?

A

No

This gives changes in perception

28
Q

What is the difference between fast and slow pain?

A

Fast (initial) pain:

  • Sharp
  • Stabbing

Slow (delayed) pain:

  • Diffuse
  • Throbbing
29
Q

What can cause phantom limb pain?

A

Lesions at the end of axons can spontaneously fire

30
Q

What may activate signal transduction in Nociceptors?

A

Low pH, heat (via ASIC, TRPV1 etc)

Local chemical mediators:

  • Bradykinin
  • Histamine
  • Prostaglandins
31
Q

Describe the segmental control of pain

A

Activity in A-alpha/beta fibres of same area activates inhibitory interneurones.

Inhibitory interneurones release opoid peptides (endorphins) that inhibit transmitter release from A-delta/C fibres

This explains why rubbing a sore area makes it fell better

32
Q

Describe how descending controls can limit pain

A

Descending controls from Peri-aqueductal grey matter (PAG) through Nucleus raphe menus (NRM).

These act on the same inhibitory pathway as segmental control

Common in battlefield wounds (rush suppresses pain)

33
Q

How do prostaglandins and bradykinin cause pain?

A

Prostaglandins and bradykinin dont cause pain themselves.

Prostaglandins sensitise nociceptors to bradykinin

34
Q

How do NSAIDS work?

A

Inhibit cyclo-oxygenase which converts arachidonic acid to prostaglandins

35
Q

What are NSAIDs great for?

A

Analgesic, antipiretic and anti-inflammatory so work very well against pain associated with inflammation

36
Q

How do local anaesthetics work?

A

Block Na action potential and therefore all axonal transmission

37
Q

What is Trans-cutaneous Electric Nerve stimulation (TENS)?

A

Electrical stimulation to area that is painful.
Correct frequency selected for mechanocrepetor fibres so that nociceptor fibres are inhibited.

Sciency version of rubbing your sore leg better

38
Q

How do opiates work?

A

Reduce sensitivity of nociceptors.

Block transmitter release in dorsal horn (hense epidural administration)

Activate descending inhibitory pathways

N - C (35 decks)

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