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Neuro > Sensory Transduction physiology AND exteroception > Flashcards

Sensory Transduction physiology AND exteroception Flashcards

1
Q

Sensory nerves in the muscle spindle have what type of sensory receptor?

A
  • Stretch sensitive NSC channel

* Depolarizes on stretch, sending the signal

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2
Q

The receptor cells that function through hyperpolarizing receptor potentials have a resting membrane potential around where?

A
  • Btw. OmV and Ek (-70mV)
    • Ends up being btw -30 and -40mV
    • The general principle here is that there is pretty good resting cation conductance and the stimulus will result in closing of those channels
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3
Q

What kind of receptor cell is the rod photoreceptor?

A
  • Hyperpolarizing short receptor cell
    • Normally has cGMP-gated ion channels open that keep the membrane more depolarized (-30 or -40mV)
    • Light hitting transducin (protein that changes conformation when it is hight by phone) will activate a cGMP phosphodiesterase that will start closing channels
    • The more transducins hit, the more hyperpolarized, thus the concept of photobleaching
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4
Q

What is the molecular phenomenon that is the “eye seeing light”?

A
  • Photon hits 1-cis-retinal (in the context of the protein rhodopsin)
    • Energy flips it to 1-trans-retinal
    • Conformational change in rhodopsin into metarhodopsin
    • Metarhodopsin stimulates the GPCR transducin which turns on the cGMP phosphodiesterase
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5
Q

How is hyperpolarization of rod cells transmitted to the second neuron?

A
  • Normally a constant flow of NT
    • Hyperpolarized cell means less NT
    • The rod cell is short enough that hyperpolarization is transmitted from receptor end to synaptic end by electronic transmission
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6
Q

What five attributes of a stimulus is transmitted by sensory systems?

A
  • Modality
    • Intensity
    • Quality
    • Duration/frequency
    • location
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7
Q

What is the “modality” that is interpreted by sensory systems?

A
  • Different forms of energy are converted by the nervous system into different sensations or sensory modalities
    • Vision, hearing, smaell, taste, touch and thermoreception
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8
Q

What is “intensity” in interpretation by the sensory systems?

A

• Intensity or perceived amount of a sensation depends on the stimulus strength

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9
Q

What is the “quality” received by the sensory systems?

A

• Intensity or perceived amount of a sensation depends on the stimulus strength

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10
Q

A sensory system can interpret duration or frequency how?

A
  • Duration is the cell’s way of knowing how long the stimulus took place (like time of open receptors for stretch)
    • Frequency can also be reported if the cell conveys information about how often the stimulus was experienced
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11
Q

How is a sensory modality determined?

A
  • The molecular and physical structure of the sensory cell/organ
    • Sometimes the shape is obvious as to the function, but sometimes (cutaneous sensation) there is a mix of adequate stimuli that could activate a group of receptors
    • All about the receptor proteins and how the channels open and close
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12
Q

In general, information from the sensory systems that becomes conscious is relayed through where?

A
  • Thalamus
    • Thalamic nuclei
    • Keep in mind where the 2nd and 3rd order nuclei are for a given sensory system
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13
Q

The concept of “labeled lines”…

A
  • The nervous system organizes certain senses by the kind of information they are carrying
    • These separate chains are separate, labeled lines that are attributed to a certain sensory system
    • The stimulus modality is coded by which nerve cells are active
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14
Q

The LGN relays what information?

A

• LGN - lateral geniculate nucleus
• Thalamic nucleus
• Visual information to visual cortex in occipital lobe
The MGN relays what information?
• MGN - medial geniculate nucleus
• Auditory information to auditory cortex in temporal lobe

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15
Q

The olfactory system uses what thalamic nucleus as a relay?

A
  • Trick question, it doesn’t use the thalamus

* It’s all kinda structurally built into its own olfactory bulb that goes into the olfactory cortex

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16
Q

Sensory receptors work in an all-or-none fashion when it comes to the necessary stimulus. How is intensity encoded then?

A
  • The time that these channels are open
    • Stretch receptor example - open for a small amount of time with weak force, but longer with strong force
    • The stimulus reaches a threshold and opens the channel, there is no channel-level partial opening.
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17
Q

Receptor cells would mess up intensity transduction if they had voltage gated cation channels to propagate their action potential. But how do long sensory receptor cells do it?

A
  • The long cells encode intensity by frequency of stimulation
    • The more action potentials close together, the more intense the stimulus
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18
Q

The numerical peripheral nerve scheme is used for what?

A

• Typically the numerical classificaiton is used for afferent axons from proprioceptors

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19
Q

The alphabetical peripheral nerve scheme is used for what?

A

• The alphabetical scheme is used for cutaneous sensory axons

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20
Q

A-alpha nerves are further classified how?

A
  • Ia and Ib
    • Ia - muscle spindle afferent
    • Ib - tendon, organ afferent
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21
Q

Nerve fibers in the category IV are how big and conduct how fast?

A
  • 0.2 - 1.5um

* 0.4-2m/sec

22
Q

Nerve fibers in the category III are how big and conduct how fast?

A
  • 1-5um

* 4-30m/sec

23
Q

Nerve fibers in the category II are how big and conduct how fast?

A
  • 5-10um

* 30-60m/sec

24
Q

Nerve fibers in the category I are how big and conduct how fast?

A
  • 10-20um

* 60-120m/sec

25
Q

C fibers are further classified how?

A
  • IV
    • Warm temperature
    • Burning pain
    • Itch
    • Crude touch
26
Q

A-delta fibers are further classified how?

A
  • III
    • Sharp pain
    • Cool temperature
    • Extreme hot temperature
27
Q

A-beta nerves are further classified how?

A
  • II
    • Mechanoreceptors of skin
    • Secondary muscle spindle afferents
28
Q

Somatosensory system has two major subdivisions….?

A 
• Dorsal coloumn/lemniscal system
		○ Discriminative touch
		○ Fine touch
		○ proprioception
	• Antero-lateral system
		○ Crude touch
		○ Pain
		○ temperature
29
Q

Rapidly adapting vs. slow adapting receptors

A
  • rapidly adapting will, with a constant touch stimulus, fire one action potential then quit
  • slow adapting will continue to fire action potentials as long as the touch stimulus is in place
  • these two are rather equally distributed in the glabrous portion of the hand
30
Q

Define receptive field

A

• Area of skin in which a mechanical stimulus elicits a response from a cell

31
Q

What are the two basic classes of somatosensory receptors (relating to size of receptive field)

A

• Small fields, sharp borders
○ 2-8mm diameter
• Large fields, poorly defined borders

32
Q

What do meissner’s corpuscles do?

A

• Correspond to the rapidly-adapting afferents with small receptive fields

33
Q

Ruffini endigns and pacinian corpuscles differ how?

A
  • Both large field
    • Ruffini - slowly adapting
    • Pacinian - rapidly adapting
34
Q

Pacinian corpuscles lie deep in subcutaneous tissues and dermis and therefore what’s their receptive field status?

A
  • Large field, poorly defined

* Rapidly adapting

35
Q

Merkel’s discs are what kind of receptor?

A

• Small field, slowly adapting

36
Q

The hair follicle stretch receptors work how?

A
  • They are myelinated untill they approach the hair follicle
    • They send out unmyelinated branches which wrap around the follicle or run up and down along it
    • Whenever the follicle is moved by the mechanical movement of the hair, the stretch receptors open
    • RAPIDLY ADAPTING
37
Q

A-beta fibers are what?

A
  • Large, myelinated axons
    • Mechanorecptors fall in this category
    • Touch, pressure, vibration, hair bending, proprioception
38
Q

What kind of fibers are muscle proprioceptors?

A

• A-alpha

39
Q

What tract do mechanoreceptors follow?

A
  • A-beta and A-alpha fibers
    • Cell body of receptor cell lin DRG ipsilateral side
    • Send off local interneuron for spinal reflex
    • Ascend in dorsal column either fasciculus cuneatus or fasciculus gracilis to the thalamus
    • Synapse on nucleus gracilis or cuneatus
    • This is the lemniscal system
40
Q

What tract do mechanoreceptors follow?

A
  • A-beta and A-alpha fibers
    • Cell body of receptor cell lin DRG ipsilateral side
    • Send off local interneuron for spinal reflex
    • Ascend in dorsal column either fasciculus cuneatus or fasciculus gracilis up the spinal cord
    • Synapse on nucleus gracilis or cuneatus (medulla)
    • This is the lemniscal system
41
Q

What is the ventrobasal complex?

A
  • Made of the VPM and VPL
    • All 2nd order neurons from the dorsal column/lemniscal pathway or the trigeminal nuclei
    • VPM - head sensation
    • VPL - trunk and limbs sensation
42
Q

What’s the medial lemniscus?

• A structure formed from the crossing fibers of the 2nd order neurons in the dorsal column/lemniscal system

A
  • These second-order fibers are joined in the midbrain by 2nd order fibers crossing from the trigeminal nuclei
    • Medial lemniscus fibers ascent to synaps in the ventro-basal complex of thalamus
    • Trunk and limbs are represented by cells in the ventral-posterior-lateral nucleus (VPL)
    • Head is represented in the ventral-posterio-medial (VPM) nucleus
    • The VPM and VPL form the ventrobasal complex
43
Q

Where do cells in the ventrobasal complex project?

A
  • Areas 3,1, 2
    • Posterior bank of the central sulcus
    • (primary somatosensory area)
    • From here cells go to SII or secondary somatosensory area in primary motor cortex and nearby association somatosensory cortical areas in parietal cortex
44
Q

What is a column in the cortex?

A
  • Vertical stacks of related cells
    • Essentially they all have the same receptive fields and the same modality
    • Information in the cortex is organized in vertical stacks or columns
45
Q

Somatosensory information is organized in vertical columns. But what’s with the cortical organization into layers of cells?

A
  • Different layers relay information from and two different places
    • Layer IV recieves input from thalamus
    • Layer VI projects back to thalamus
    • Layer II and III project to other areas of somatosensory cortex
46
Q

The layered interconnections in the cortex tell us what about the columns?

A

• Cortical columns serve as computational modules that transform information received from the thalamus and redistribute it to other regions of the brain

47
Q

The trigeminal ganglion can be thought of as what?

A

• The dorsal root ganglion for the head, with motor fibers running through it

48
Q

The principal nucleus is the trigeminal ganglion version of what?

A
  • Main sensory nucleus = principal nucleus of trigeminal ganglion
    • Analogue of the dorsal column nuclei
    • Afferents in fine touch, vibration and proprioception synapse here (from head and face)
49
Q

After the principal nucleus, where do 2nd order neuron’s axons go?

A
  • Second order neurons in the main sensory nucleus send axons across the midline to join the medial lemniscus
    • Some fraction of the cells in the principal nucleus project ipsilaterally
50
Q

What makes up the mesencephalic nucleus?

A
  • Proprioceptive afferents like lmuscle stretch receptors that run in the trigeminal nerve
    • Involved in muscles of mastication and some mechanorecpeotors in the mouth
    • They make monosynaptic connections with motor neurons to the muscles of mastication in the motor trigeminal nucleus
    • Analogous to stretch receptors and reflex in spinal cord
51
Q

The medial lemniscus has fibers from the head, trunk and limbs. How do you know which ones came from the head and the principal ganglion?

A
  • The neurons that go to the VPM are the neurons that come from the head
    • VPM 3rd order neurons relay to the cortex

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