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Physiology > Sensory Physiology 2 > Flashcards

Sensory Physiology 2 Flashcards

1
Q

Most somatosensory receptors are mechanoreceptors…

A

Meaning that they are sensitive to physical distortion such as stretching and send signals via mechanosensitive ion channels.

Picnian corpuscles are quite big, can be big enough to see with naked eye, are the best-studied mechanoreceptor

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2
Q

What is the receptive field?

A

The receptive field is the specific area in which neurons are activated by stimuli. Pacinian corpuscle receptive fields can span over an entire finger or half the palm of the hand

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3
Q

What are the touch receptors of the skin?

A
  • Pacinian corpuscle
  • Ruffini’s endings
  • Meissner’s corpuscle
  • Merkel’s Disc
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4
Q

Describe Pacinian corpuscle as a touch receptor in the skin

A
  • lies deep in dermis
  • responds to vibration
  • large receptive field
  • rapidly adapting
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5
Q

Describe Ruffini’s endings as a touch receptor of the skin

A
  • Slightly smaller than Pacinian corpuscles
  • Also in deep layers of dermis
  • Responds to skin stretch
  • Also large receptive fields
  • Slowly adapting
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6
Q

Describe Meissner’s Corpuscle as a touch receptor in the skin

A
  • Located on the ridges of glabrous skin (e,g. Ridges of fingerprints)
  • Responds to flutter, stroking
  • Small receptive field
  • Rapidly adapting
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7
Q

Describe Merkel’s disc as touch receptors in the skin

A
  • Located on superficial layers of the skin
  • Responds to steady pressure and texture
  • Small receptive field
  • Slowly adapting
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8
Q

Describe free nerve endings as touch receptors in the skin

A
  • Located around hair roots and under skin surface
  • Responds to various stimuli
  • Variable adaptation
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9
Q

How do touch signals get to the brain?

A

Primary Afferent axons of primary sensory neurons enter spinal cord in dorsal roots

-Cell bodies in DRG vary in diameter, function

Information travels to the medulla (the secondary sensory neuron)

Sensory information goes to cortex, via the thalamus( this is the tertiary sensory neuron)

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10
Q

What are the touch receptors in the skin?

A
  • Pacinian corpuscle
  • Ruffini corpuscle
  • Merkel receptors
  • Meissners corpuscle
  • free nerve endings
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11
Q

What is the function of Pacinian corpuscle ?

A

Senses vibration

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12
Q

What is the function of Merkel’s receptor?

A

Sense steady pressure and texture

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13
Q

What is the function of ruffini corpuscle?

A

Responds to skin stretch

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14
Q

What is the function of Meissner’s corpuscle?

A

Responds to flutter and stroking movements

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15
Q

Describe Pacinian corpuscle

A

Lies deep in dermis

  • Responds to vibration
  • large receptive field
  • rapidly adapting (large receptive field)
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16
Q

Describe Ruffini’s ending’s

A
  • Slightly smaller than Pacini’s
  • Also in deep layers of dermis
  • Responds to skin stretch
  • Also large receptive fields
  • Slowly adapting
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17
Q

Describe Meissner’s corpuscle

A

Located on the ridges of glabrous skin (e.g. ridges of fingerprints)

  • Responds to flutter, stroking
  • Small receptive field
  • Rapidly adapting
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18
Q

Describe Merkel’s disc

A
  • Located on superficial layers of skin
  • Responds to steady pressure and texture
  • Small receptive field
  • Slowly adapting
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19
Q

Describe free endings

A

Free nerve endings

  • located around hair roots and under skin surface
  • Responds to various stimuli
  • Variable adaptation
20
Q

How do touch signals get to the brain?

A
  • Primary afferent axons of primary sensory neurons
  • Enter spinal cord in dorsal roots
  • Cell bodies in DRG
  • Vary in diameter, function

Primary(first order neuron) in dorsal portion of spinal cord , this then synapses with the secondary sensory neuron in the medulla with then synapses in the thalamus. From here tertiary sensory neuron takes it to the parietal lobe

21
Q

Describe AB(alpha beta) nerve fibers

A

6-12 diameter um

35-75 m/s

Mechano-receptors of the skin

Heavy myelinated, this and diameter influence its speed

22
Q

Describe Alpha delta nerve fibers

A

1-5 um diameter

5-30 m/s

Sensory receptors: cold, fast pain , mechanical stimuli

23
Q

Describe C sensory nerve fibers

A
  1. 2- 1.5 diameter um
  2. 5-2 m/s

Sensory receptors: slow pain, cold, heat,

24
Q

Where in the brain does sensory information go?

A

Sensory information goes to primary somatosensiry cortex

  • Parietal lobe
  • Post central gurus
  • Brodkann areas 1, 2, 3a, 3b
  • 3b - primary somatosensory cortex
25
Q

What are cortical maps?

A

Specific areas responsible for processing specific functions

These are dynamic and can adjust depending on amount of sensory experience

26
Q

What is the phantom limb?

A

Sensation from a limb that has been removed

27
Q

What are no I empties?

A

Receptors of pain, they don’t exist in the brain(but there are in meninges)

28
Q

How are nociceltors activated ?

A

Activated by stimuli that have potential to cause tissue damage

These stimuli activate membrane ion channels (TRP-channels; transient membrane potential : page 340)

As well as mechanically gated channels, nociceptor chanhels can respond to substances released by damaged cells at injury sites -e.g. ATP, K+ bradykinin

29
Q

What are nociceptors?

A
  • Polymodal nociceptors
  • mechanical nociceptors
  • thermal nociceptors, e.g. vanilloid R
  • Chemical nociceptors
30
Q

Which nerves are responsible for itch, slow and fast pain?

A

Itch- C fibers

Slow pain- C fibers(unmyelinated)

Fast pain- A delta fibers

31
Q

How do pain signals get to the brain?

A

Uses Anterolateral system or spinothalamic tract

Primary sensory neuron enters dorsal aspect of spinal cord. However, synapses with the secondary sensory neuron and ascends up the spinal cord and medulla until it synapses in the thalamus where the tertiary sensory neuron which leads to the somatosensory cortex

32
Q

Explain the gate theory of pain

A

Second order neuron is inhibited by inhibitory neuron

In the absence of input from C fibers, tonically active inhibitory interneuron suppresses pain pathway.

Pain can be modulated by simultaneous somatosensory input

Touch or non painful stimulus stimulates inhibitory interneuron

Painful stimulus is decreased

33
Q

What are the types of physiological pain?

A
  • Cutaneous
  • Somatic (deep)
  • Visceral-referred pain (perceived at a location at sight other than actual location of the pain)
  • Phantom limb
  • Neuropathic
34
Q

How can anti-inflammatory agents be used to control pain?

A
  • Prostaglandins = inflammatory mediators
  • PG’s use the cyclooxygenase (COX) pathway; COX-1, COX-2
  • NSAIDs: Non-steroidal Anti-inflammatory Drugs
    • Broad spectrum: e.g., aspirin, ibuprofen
    • COX-2 selective: e.g. celecoxib (Celebrex)
35
Q

How are opioids involved in the Pharmological control of pain?

A
  • Endogenous opioid peptides: endorphins, enkephalins

- Opiates: heroine, cocaine, morphine

36
Q

What are the basic tastes?

A
  • saltiness
  • sweetness
  • sourness
  • bitterness
  • Umami(MSG)=mono sodium glutamate
37
Q

What are taste buds?

A

Taste cells (50- 150)

  • basal cells
  • support cells

They extend through the epithelium

Made up of taste pore at apical side

Sensory cells synapse with cranial nerves which carry the taste to the cortex

38
Q

What are taste cells?

A
  • Non-neural epithelial cells
  • taste pore
  • synapses with primary sensory neuron
  • Constant cycle of growth, death and regeneration
39
Q

Explain testing and taste transduction

A
  • Receptor cell activation by chemical
  • Depolarizing receptor potential (transduction)
  • Opening of VGCC’s
  • influx of Ca2+
  • Release of neurotransmitter
  • Trigger AP’s I post-synaptic cell- the primary sensory neuron
40
Q

How does tastant initiate taste transduction in the cell?

A

Tastants may:
-Directly pass through ion channels (salt and sour)

  • Bind to and block ion channels (sour)
  • Bind to G-protein-coupled receptors that lead to ion channel opening (bitter, sweet, umami; G-protein e.g. gustducin)
41
Q

How does taste get to the cortex?

A

Primary sensory neuron which leads to brain stem which synapses at brain stem (cranial nerves 9 and 10 then lead to the thalamus. From there, it will move to the gustatory cortex (deep to the Sylvia fissure )

42
Q

What is population coding /cross fiber theory?

A

A given taste is believed to be determined by the pattern of activity in a population of broadly-tuned sensory neurons

43
Q

Where is the olfactory epithelium?

A

The olfactory epithelium lies high within the nasal cavity, and its olfactory cells project to the olfactory bulb then olfactory tract(cranial nerve 1) then olfactory cortex

Smell doesn’t go to thalamus

44
Q

Explain olfactory transduction

A
  • Binding of odorant molecule
  • G-protein activation - Gflux
  • Na+ and Ca2+ influx
  • Ca2+ activated Cl- channels open
  • Current flow and membrane depolarization (receptor potential)
45
Q

What is synesthesia?

A

For the synaesthete the senses are mixed and one stimulus elicits a double perceptual experience. This relatively rare phenomenon provides us with an insight into the relationship between various sensory modalities

Physiology (36 decks)

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