Sensory System 3

Question 1

Stimulus energy conversion (steps) to get to CNS

Answer 1

Stimulus energy (stimulates transduction)
Receptor potential
Action potentials
Propagation of action potentials
Release of neurotransmitter
These are the broad steps to go from stimulus to transmission to CNS

Question 2

Is every stimulus we experience transmitted

Answer 2

No, if teh stimulus is not strong enough to result in a strong enough receptor potential, it wont cause an action potential, wont reach the nervous system and therefore wont be perceived

Question 3

How do some neurons adapt to a consistent stimulus

Answer 3

They can be non-adapting, so as long as the stimulus is there there will be action potentials firing at a rate proportional to the strength of the stimulus
They have slow adaptation, so initially the frequency of action potentials is proportional to the strength of stimulus but then it tapers off gradually, even if the stimulus is still present
They can have rapid adaptation, so initially the frequency is proportional to the strength of the stimulus, it stops entirely (stimulus still ongoing), same frequency picked up when stimulus dissipates (after it ends)
Note: most neurons are either slowly or rapidly adapting and not non-adapting

Question 4

What is non-adapting better for transmitting

Answer 4

Conveying stimulus intensity and slow changes

Question 5

What is slow adaption better for transmitting

Answer 5

They serve to transmit changes like some stimulus intensity and moderate stimulus changes

Question 6

What is fast adaptation better at conveying

Answer 6

Fast stimulus changes, on/off responses, tells you when something starts and when it ends

Question 7

What is the receptive field

Answer 7

The region in space that activates a sensory receptor or neuron

Question 8

If were talking abt the RF of one neuron, how could the frequency of APs be altered

Answer 8

If the receptor cell produces a signal in the “middle” of the afférent receptive field, it’ll produce a high frequency, but if its on the edge of its reach, the frequency will be lower
This is the graded response

Question 9

Overlapping receptive fields (why its important)

Answer 9

This allows for a stimulus to be detected by either one or multiple afférents and having an accurate representation in the sense that if it was just one neuron, a weak stimulus in the middle (best) zone would produce the same frequency of action potentials as a strong stimulus on the edges of the field, which wouldnt be good
The overlapping helps solve that

Question 10

Population response

Answer 10

When a stimulus stimulates multiple afférents into firing APs from the same stimulus
This info can be used by the stimulus to triangulate where exactly the stimulus has originated (like if its stronger in B and present in A we understand that the center/bulk of it was likely in B and A was collateral)

Question 11

Acuity

Answer 11

Acuity is teh ability to differentiate one stimulus from 2, so like they use the lip and back as examples

Question 12

Acuity and the RF

Answer 12

Related since if one neuron has a bigger receptive field, you will have a lower acuity, a lower ability to differentiate whether a stimulus is one or two cuz on your body it’ll be in the range one 1 field
In the example of lip and back, the lip is a region with high acuity and small RF and the back is a region with low acuity and high RF

Question 13

Bottom-up vs top-down perception

Answer 13

Bottom-up (automatic changes, out of our control) is when we take in the stimulus as is, recieve it and take it up to the CNS for processing
Top-down (this is in our control, what were sensitive to comes from our brain) is when the info flows from higher brain areas down to teh sensory portions, its more about know what to look for (like if 10 people call out name and someone calls your name, you’ll hear your name cuz you’re primed to hear it), on some level has to do with expectation and interpretation

Question 14

First vs second order sensory neuron

Answer 14

First order: recieves the stimulus either directly or from the specialized receptor cell
Second order: received the info from the first order and will take it up to brain, usually thalamus

Question 15

Lateral inhibition (the how)

Answer 15

So its when an excited sensory neuron inhibits its neighbours such that its stimulus is felt stronger, contrasting against its neighbours and telling teh brain specifically where it is (how it heightens acuity)
It does this by synapsing with (because its excited) inhibitory interneurons (neurons that “link” to other neurons) that will synapse at the lateral/neighbouring neurons to inhibit them

Question 16

How does lateral inhibition change teh population profile

Answer 16

Population refers to all teh neurons capable of detecting this stimulus and lateral inhibition changes their profile by inhibiting their activity, therefore stopping them from firing and reducing the peak they would’ve had
Helps the CNS narrow down where its coming from

Question 17

Presynaptic inhibition

Answer 17

Top-down change run by CNS where it send inhibitory neurons to synapse on first and second orde neurons to grade how much of that signal we get
So that inhibitory neuron releases GABA so that the first order neuron transmits a weaker signal to teh second order neuron and so the 2nd order neuron is less likely to fire its AP to teh CNA, decreasing teh frequency of APs and therefore the stimulus
Note: an example of this is if you get hurt while being attacked, your mind will inhibit the pain receptors for the moment because there are more important things going on, same idea

Question 18

Mechanoreceptors

Answer 18

Detect touch, they are receptors that sense changes in pressure, found in the nerve terminal
Interacts with other specialized end organs

Question 19

Types of mechanoreceptors well see in the skin (no details)

Answer 19

Meissner’s corpuscle
Merkel Disk
Pacinian corpuscle
Ruffini endings

Question 20

Meissner’s corpuscle

Answer 20

Fluid filled structure enclosing the nerve terminal
It’s rapidly adapting
Detect light strokes and fluttering
Located near surface of skin so very sensitive
Note: teh capsule it has adjusts to teh changes in pressure it may experience but then redistributes so it chills out, which is why its rapidly adapting and why its good to light strokes or temporary changes like that and not constant/steady pressure cuz the capsule wouldn’t really let it register that

Question 21

Merkel disk

Answer 21

Also near skin surface
Slowly adapting
Epithelial cells that surround the nerve terminal
Sensitive to light pressure and texture, understand shape of an object

Question 22

Pacinian corpuscle

Answer 22

Has like layers of capsule of CT surrounded nerve terminal, found deeper in teh skin that Meissner’s corpuscle
Rapidly adapting
Detects strong vibrations

Question 23

Ruffini endings

Answer 23

Also deep in the skin
The nerve endings are wrapped around a spindle liek structure
Detect stretch and bending of the skin
Slowly adapting
Note: the spindle structures deform when you grab onto something, not temporary as with teh capsule

Question 24

What is proprioception

Answer 24

Your body’s ability to sense its own position, movement and muscle tension, like bodily self-awareness
Muscle spindles provide that

Question 25

How are mechanoreceptors activated (ie transduction)

Answer 25

In teh context of teh somatosensory system they respond to deformation in teh skin So if theres an external pressure, say someone poking you, the cell membrane of teh nerve terminal is pushed in (like its membrane is pushed in) On this cell membrane we have the ion channels that are linked to cytoskeletal strands. The mechanical deformation causes tension in these strands which pulls the ion channels open, allowing teh inflow of ions and therefore transduction Note: the nerve terminals are surrounded by end organs

Question 26

Thermoreceptors

Answer 26

Sensory neurons that detect changes in temperature via free nerve endings (basically axon terminal extension-type which act like dendrites), also found in the skin, 2 kinds Cold afférents: neurons with free nerve endings that detect temperatures from 0-35 cel. Warm afferents: neurons with free nerve endings that detect temperatures from 35-50 cel. Ion channels open or close based on temperature, has to do based on their structure and how their membranes react to temperatures

Question 27

Extreme temperatures

Answer 27

Extreme in the sense that too long an exposure will cause damage to tissue Activates pain receptors as a warning sign Anything outside of the range given so below 0 and above 50

Question 28

What can activate cold afferents

Answer 28

Menthol

Question 29

What can activate warm afferents

Answer 29

Capsaicin and ethanol

Question 30

Nociceptors

Answer 30

Pain receptors, free nerve endings, ion channels that open in response to intense mechanical deformation or temp or chemicals Basically a signal that tells the CNS that wtv the stimulus is will/is causing tissue damage

Question 31

What does it mean for pain receptors to be highly modulated

Answer 31

Means that they arent fixed or automatic, they’re subject to regulation. They can be enhanced, inhibited or entirely ignored Enhancement: bottom-up adaptation Suppression: top-down adaptation

Question 32

What/where are visceral pain receptors

Answer 32

Pain receptors for the inside, respond to inflammation in internal organs Basically nociceptors of the internal organs

Question 33

Enhancement of nociceptors (steps leading up to it and it)

Answer 33

Their effect can be enhanced by many mediators 1: you prick yourself with a knife, nociceptors go off, 2: action potentials are fired to reach the CNS to alert it, 3: substance P (neurotransmitter) is released in the spinal cord (as the signal is on its way up to brain), 4: awareness of pain, 5: take care of it Note: none of that is enhancement, that’s just standard practice Enhancement: the morning after when you touch stuff, it hurts, you’re extra sensitive, thats the enhancement effect

Question 34

What does substance P do

Answer 34

Activates second order neurons that will continue conveying a pain stimulus up to the brain

Question 35

What are the factors that result in enhancement of nociceptors

Answer 35

Histamine from mast cells Bradykinin, 5-HT, prostaglandins and K+ from ruptured tissue/cells Dilation of blood vessels, contributes to swelling Caused by the nociceptors releasing substance P onto these cells (except the bradykinin one, thats from damaged cells)

Question 36

What is hyperalgesia

Answer 36

An increased sensitivity to pain in a region likely recently exposed to damage Bottom up because its a change at the reception site that changes how that stimulus is integrated (in this case its enhanced)

Question 37

When does hyperalgesia occur with regards to the injury

Answer 37

Occurs after time has passed like next day, not while the damage is being done or even immediately after

Question 38

Path from stimulus to CNS of a touch or proprioception stimulus

Answer 38

Say you touch a feather. Very light and fluttery so likely the Meissner corpuscles (mechanoreceptor) that are being activated and sending APs down the afférent path to communicate this change (communicates to first order neuron), this info goes to the spinal nerve through the dorsal root ganglion and then starts ascending the dorsal column (white matter). We get all the way up to the brainstem and when they reach the medulla they synapse and cross the midline (contralateral). Info now in the second-order neuron. We go up a little further to the thalamus and synapse again, that final neuron (third order neuron) going to the somatosensory cortex

Question 39

Pathway from stimulus to CNS of temperature and pain stimulus

Answer 39

Stimulus activates nocireceptors or thermoreceptors that start firing APs to the first-order neuron (its teh nociceptor itself), the info travels to the spinal nerve, also passed through teh dorsal root ganglion, they enter the dorsal horn where they synapse with the second-order neurons. The axon of this second order neuron crosses the midline to the opposite side and ascend by the anterolateral column to the brain. Note: this is white matter. Goes all the way up to the thalamus where it synapses with the third order neuron that goes to the somatosensory cortex

Question 40

Dorsal column vs anterolateral column

Answer 40

Dorsal column carries ipsilateral touch and proprioception and anterolateral column carries contralateral temperature and pain

Question 41

Where is the somatosensory cortex located

Answer 41

Just posterior to the central sulcus, in the parietal lobe

Question 42

What is the somatotopic map

Answer 42

Like a map of your somatosensory cortex that shows what region of the cortex recieves info regarding a certain body part Refer to slide 49 Regions with higher acuity are larger like that of the face and hands/arms, where there are small receptive fields

Question 43

How does referred pain happen

Answer 43

Happens when a visceral afferent synapses in the same place as a somatic afférent in the spinal cord, making our brain believe that its a physical topical pain when its actually internal Basically they share the same second order neuron in the spinal cord Classic example is teh heart, when theres pain in the cardiac muscle this synapses at the same interneurons as pain in the left arm