MT1

Question 1

somatosensation (4)

- axons?

Answer 1

• touch (mechanical displacement of skin)
• kinesthesis (part of proprioception - position and movement of limbs in space)
• temperature (warm and cold)
• pain (sharp and dull)
• somatosensory receptors are neurons with peripheral (skin) and central axons (spinal cord)

Question 2

mechanoreceptors

• what kind of skin?
• fast-adapting vs slow-adapting
• small vs large receptive field

4 types
- size, adaptation rate, maximal feature sensitivity, perceptual function

Answer 2

• there are 4 types in glabrous skin (skin with no hair)
  fast adapting: stop firing after a bit, may respond again when stimulus gets turned off
  slow adapting: firing entire tie stimulus is present
  small receptive field: shallow location in skin (epidermis)
  large receptive field: deeper location in skin (dermis or subcutis)

1. merkel disc: SA 1 - epidermis (shallow)
   - slow adaptation rate, small receptive field
   - respond best to small slow sustained pressure at very low freq (<5Hz)
   - for coarse texture and pattern; fine spatial details
2. meissner corpuscle: FA 1 - epidermis (shallow)
   - fast adaptation rate, small receptive field
   - small fast temporal changes (5-50Hz); skin slip
   - low freq vibration, grasp stability
3. Ruffini ending: SA 2 - dermis
   - slow adaption rate, large receptive field
   - large slow sustained pressure (similar to Merkel but because they’re deeper they need more stimulation to be activated); lateral skin stretch (5-50Hz)
   - finger position
4. pacinian corpuscle: FA 2 - subcutis
   - fast adaptation rate, large receptive field
   - large fast temporal changes (like meissner but needs larger stimulus) (50-700Hz)
   - high freq vibration, fine texture

Question 3

thermoreceptors
- physiological zero

types of thermoreceptors:

1. warmth fibers
2. cold fibers

Answer 3

physiological zero: normal skin temperature (30-36 degrees C); no sensations of warmth or cold

thermoreceptors: sense CHANGES in temp
1. warmth fibers increase firing rate when there are increases in skin temperature above 36 deg
2. cold fibers increase firing rate when there are decreases in skin temp below 30 deg

Question 4

PNS
- what determines conduction speed? (2)

nerve fibers (4)

• diameter
• myelination
• conduction velocity
• receptor type
• inflammatory cells (4 types of chemical receptors)
• double pain

Answer 4

• these 4 different-sized nerve fibers carry somatosensory info to spinal cord (make up PNS) –> speed based on axon diameter and myelination

1. A-alpha
   - diameter: 13-20um (huge!)
   - myelination: LOTS
   - conduction velocity: 80-120m/s (very fast!)
   - receptor type: proprioceptor
2. A-Beta
   - diameter: 6-12um
   - myelination: some
   - conduction velocity: 35-75m/s
   - receptor type: mechanoreceptor (there are 5 types)
3. A-Delta
   - diameter: 1-5um
   - myelination: little bit
   - conduction velocity: 5-30m/s
   - receptor type: mechanonociceptors (physical stimuli - pain) or thermal nociceptors (temperature - hot/cold)
   eg. TRPM8 = thermal nociceptor
4. C fibers
   - diameter: 0.2-1.5 (tiny!)
   - myelination: none
   - conduction velocity: 0.5-2m/s (very slow)
   - receptor type: polymodal nociceptors (pain, temp, itch)

• inflammatory cells release prostaglandin, bradykinin or protons –> activate ion channels)
  eg. TRPV1 - capsaicin receptors

note: double pain - A-delta delivers sharp pain, followed by slower throbbing pain from C fibers (lack myelin)

Question 5

somatosensory receptor transduction

• where does it occur?
• what is channel sensitive to?
• what happens?

Answer 5

• not fully known
• occurs in peripheral axon
• channel sensitive to mechanical force, temperature or chemicals released by injured tissue open; Na+ and Ca+ enter
• neuron depolarizes (receptor potential = slow); action potential travels full length of axon to spinal cord (if threshold level is reached)

Question 6

dorsal column-medial lemniscal pathway

• cell body location
• axons combine
• layer 2
• DCML path for what?
• 4 synapses (what happens at and after the 2nd one? - 2 nuclei)

Answer 6

• cell bodies of A-beta, C and A-delta fibers are in the dorsal root ganglion (outside of spinal cord)
• many central axons combine into a single nerve trunk and synapse in the dorsal horn of spinal cord (bottom pair comes form feet)
• diff types of somatosensory nerve fibers project to diff layers of the dorsal horn, but layer 2 (substantia gelationosa) gets input from all 3 types of nerve fibers (A-delta, C, and A-beta)
• DCML path = for tactile perception and proprioception (mechanoreceptors) –> for all stimuli below your head (neck to toes)
  1. spinal cord (1st synapse for some)
  2. medulla (1st synapse for most)
• goes up dorsal column from spinal cord and synapses at gracile nucleus (lower body) or cuneate nucleus (upper body))
  3. thalamus (lemniscal pathway - info crosses from medulla to contralateral thalamus)
  4. parietal cortex (S1 - primary somatosensory cortex)

Question 7

reflex loop (3 steps)

Answer 7

1. noxious stimulus –> info travels to dorsal horn
2. interneuron connects sensory and motor neurons
3. motor neuron controls movement (withdraw finger)

Question 8

spinothalamic pathway

• what is it for? (2)
• 3 synapses

S1

• 4 brodmann’s areas
• where do neurons synapse in layer 4?
• which types of mechanoreceptors are in 3b?

Answer 8

• for pain and thermoreception (nociceptors/thermoreceptors)
• for head

1. brainstem (1st synapse) - principle sensory nucleus of trigeminal nerve (V)
2. thalamus (crossed to contralateral side - 2nd synapse) - ventral posteromedial nucleus
3. parietal cortex (3rd synapse) - S1

S1: includes 4 Brodmann’s areas

• 3a (most anterior), 3b, 1 and 2 (most posterior)
• neurons from the thalamus synapse in areas 3a (proprioception) or 3b (touch - mechanoreceptors) in layer 4
• hair follicles, meissner’s corpuscles, and Merkel cells synapse at 3b since they’re mechano (synapses in diff columns according to type)

Question 9

touch perception

• tactile sensitivity
• discrimination (higher sensitivity? webers fraction? moving stimulus?)

Answer 9

tactile sensitivity: detecting a touch - inverse of absolute threshold (small threshold = high sensitivity)
- highest sensitivity on the face, lowest on the foot

discrimination: JND inc with magnitude of standard stimulus
- JND for touch is smaller for areas of skin with higher sensitivity
- webers fraction = JND/standard (usually 0.02-0.3 for touch)
- moving your finger across = more activation than static touch

Question 10

homunculus

• what is it?
• example

acuity

• better acuity? (2)
• detection threshold vs 2 point threshold
• example

Answer 10

• each point on skin is represented by a corresponding area in the contralateral cortex but the map is distorted (cortical magnification)
  eg. thumb has equal size real estate to forearm even tho thumb is much smaller

acuity: minimum distance at which 2 stimuli are just perceptible as separate (2 point threshold)
- better acuity in skin regions with larger cortical representation, or with smaller receptive fields (they’re more densely packed, and if you want to feel 2 separate points they need to hit 2 separate receptive fields)
- detection threshold can be high when 2 point threshold is low
eg. detection is poor on feet, but if stimulus is strong enough you can have a low 2 point threshold

Question 11

Aristotle’s illusion

• failure
• success
• result

Answer 11

2 receptive fields close together on cortex may be stimulated at same time, but normal experience has taught us that one object can do this = failure of illusion because we perceive it as one object

2 receptive fields far apart on cortex being stimulated at the same time (normally only happens when 2 objects touch you)
eg. you cross ur fingers and touch with 1 pen = feels like 2 touches

therefore, learning component modifies how we experience touch

Question 12

somatosensory pathway - temperature and pain
A. skin below head (3)
B. head only (3)

Answer 12

skin below head:

1. substantia gelatinosa (1st synapse - in the dorsal horn)
2. thalamus (2nd synapse)
   - spinal cord neuron that synapses with A-delta and C fibers crosses to other side of spinal cord and travels up to thalamus (goes to ventral posterolateral nucleus)
   - same nucleus as DCML touch pathway
3. parietal cortex (3rd synapse - S1)

head only:

1. don’t go to spinal cord, go to medulla (1st synapse) –> go to spinal trigeminal nucleus (same side of body)
2. cross over to thalamus (2nd synapse - contralateral ventral posteromedial nucleus - same as spinothalamic touch pathway)
3. parietal cortex (3rd synapse - S1)

Question 13

limbic system

• inputs
• projections

descending pathway

• what is released?
• how? (3)

Answer 13

projections from thalamus to limbic system (anterior cingulate, insula and amygdala) = processing of emotion
- limbic system projects to PFC = role in pain processing - modulate pain experience (eg. emotional experience of chronic pain) –> more than just stimulation of nociceptors/A-delta/C fibers

descending pathway: periaqueductal grey (receives input from PFC) –> sends inputs down –> synapses with C fiber in spinal cord in substantia gelatinosa

• modulates pain sensitivity with enkephalins/endorphins
  1. C fiber releases NT substance P
  2. substance P membrane receptors (NK-1) on spinal cord neuron - normally signal gets transmitted up to thalamus
  3. enkephalins/endorphins block release of substance P

Question 14

gate control theory

• nociceptive pain
• survival value
• what is gate control theory (how it works)
• example
• descending inputs

Answer 14

nociceptive pain: results from stimulation of free nerve endings in skin, muscles and joints
- survival value: avoid potentially harmful stimuli (reduce injury - learning) and immobilize yourself to promote healing

gate control theory = interaction btwn A-beta touch fibers and slow C and A-delta pain fibers stimulating mechanoreceptor (A-beta) blocks pain gate so that C or A-delta fibers cant synapse with transmission cells (spinal cord neurons) and send signal to brain along spinothalamic path

eg. rubbing sore spot makes it less sore
- descending inputs (central control) also close pain gate (endogenous opiates)

Question 15

relieving nociceptive pain

1. TENS (def + good for?)
2. anesthetics (def + local vs general)
3. analgesics (def + non-opiate (2) vs opiate)
4. acupuncture

Answer 15

1. Transcutaneous electrical nerve stimulation (TENS): electric current passed through skin near site of pain = activates A-beta = gate control theory = blocks gate + endogenous opiates released
   - good for back pain and childbirth
2. anesthetics: produce total loss of sensation by interrupting signals travelling to brain
   a) local anesthetics: block sodium channels, which neurons need to send APs
   b) general anesthetics: act on brain (unconsciousness)
3. analgesics: painkiller - loss of pain sensations only, not touch; don’t cause unconsciousness
   a) non-opiate: mild to moderate pain
   i. non-steroidal anti-inflammatory drugs (aspirin/ibuprofen/advil) - block prostaglandin production (binds to C fibers = blocks this level of nociception)
   ii. acetaminophen (tylenol) and COX-2 inhibitors (Celebrex) block prostaglandin production without gastrointestinal side effects like i.
   b) opiate analgesics: most potent
   i. morphine, cocaine, and heroin block nociceptor release of NT substance P and inhibit spinal cord neurons
4. acupuncture: insertion of long needles into specific places (may release endogenous opiates)

Question 16

persistent pain - inflammatory

• caused by (2)
• hyperalgesia
• allodynia

Answer 16

• nociceptors become increasingly sensitive with continuing stimulation
• caused by damage to tissues/tumours (damaged tissue produces more prostaglandin)
• hyperalgesia: nociceptors become overly reactive to noxious stimuli or generate signals in the absence of stimuli –> painful stimuli become more painful
• allodynia: nociceptors have lower thresholds for stimulation –> gentle touches become painful (eg. when ur sunburnt)

*usually goes away once tissue heals

Question 17

persistent pain - neuropathic

• nociceptors/harmful stimuli?
• symptoms
• caused by? (2)

sensitization

• peripheral sensitization
• central sensitization

Answer 17

• not related to stimulation of nociceptors/harmful stimuli
• burning, shooting pain, numbness, itching,
• caused by damage/dysfunction of PNS (sciatica = shooting pain down leg bc of pressure on sciatic nerve) or CNS (multiple sclerosis)
• sensitization (hyperalgesia or allodynia) exacerbated when pain not treated
• peripheral sensitization = change in nociceptors
• central sensitization = inc number of pain receptors, rewiring of connections or loss of inhibitory cells in spinal cord

Question 18

relieving persistent pain

• anticonvulsants
• capsaicin
• marijuana
• NMDA receptor blockers

Answer 18

anticonvulsants (gabapentin, pregabalin): inhibit specific type of calcium channel to prevent release of nociceptor NTs

capsaicin: stimulates nociceptors; may kill them or use up supply of NTs (can’t sent signal to brain anymore) - may cause pain initially but then relieves (C fibers have receptors of capsaicin)
marijuana: cannabinoids (THC, CBD) block NT release from nociceptors and reduce inflammation - shut down all symptoms (itching, pain, etc)

NMDA-receptor blockers (eg. methadone): prevent glutamate from binding with NMDA receptors on spinal cord neurons
(NK-1 receptors are for substance P)

Question 19

phantom limb

• sensations
• local anesthetics
• what type of pain is phantom limb pain?
• what happens during central sensitization
• example
• glitch?
• treatment

Answer 19

• sensations perceived to come from an amputated limb
• local anesthetics block nociceptors and prevent central sensitization, but general anesthesia does not block everything (nociceptors still active and can feel phantom limb pain - neuropathic)
• nociceptors still activate = central sensitization can occur (rewiring connections)
  eg. hand representation in homunculus usually flanked by face and upper arm –> stroking face/upper arm feels like stroking hand even tho its not there because those regions took over the hand region in the cortex
• if a glitch occurs in the remapping, touching face/upper arm can cause pain that seems to come from amputated hand

treatment: place injured hand or foot in box, place uninjured limb in front of mirror, move both limbs symmetrically while looking in mirror = feels like amputated hand is moving = relieves pain

Question 20

discriminative touch vs pleasant touch (mediated by?)

path differences (what is activated? what does it do?)

• orbitofrontal cortex
• intensity vs rating

Answer 20

discriminative touch: traditional; tactile, thermal, pain, and itch

pleasant touch: emotional properties of nonpainful bodily touch mediated by C fibers known as C tactile (CT) afferents that are not related to pain or itch
- responds to mechanical stimulation in the form of slow-moving, lightly applied forces (like petting!) - hairy skin only

Path differences: in discrim touch, S1 is activated by physical aspects of stimulus (eg. pressure produced or temperature changes), but the CT system is associated with the insula –> plays a role in regulating body and linking sensory and emotional systems

• the orbitofrontal cortex (in the frontal lobe) is also activated by pleasant touch
• intensity of stimulus is recorded in S1 and S2 (discrim) as well as the insula (pleasant)
• pleasantness RATINGS were related to brain activity in the anterior cingulate cortex

Question 21

what vs where pathways

• location
• dorsal vs ventral
• example for what deficit (2)

Answer 21

• brain activation happens in diff places depending on whether you are identifying or locating an object
• relatively more dorsal activation for locating objects and more ventral activation for recognizing objects
• someone couldnt recognize objects by touch (what), but she showed no deficit in her spatial ability (where)
• someone could locate and manipulate objects by touch without recognizing them

Question 22

vibration frequencies

• SA I
• FA I
• FA II

Answer 22

• SA I (Merkel) units would seem to mediate our absolute vibratory thresholds for frequencies below about 5 Hz
• FA I (Meissner) fibers, for frequencies from about 5 to 50 Hz
• FA II (Pacinian) units, for frequencies above about 50 Hz

Question 23

tactile sensitivity differences

• age
• genes
• ASD

Answer 23

• adults lost about 1% per year in their acuity levels between their teens and their 80s
• tactile spatial acuity and vibratory sensitivity are more correlated in identical than in non-identical twins
• individuals diagnosed with autism spectrum disorder display heightened sensitivity to a broad range of touch stimulation: thermal and vibratory, and in glabrous and hairy skin

Question 24

light

• wavelength
• intensity
• particle property
• transmission
  a) once emitted (2)
  b) interface btwn 2 media (3)
• how is colour determined? (solid vs transleucent)

Answer 24

wavelength: distance between the peaks of an energy wave (can see from 400-700nm)
intensity: wave property - height of peaks of an energy wave (amplitude)
- particle property: number of quanta (photons) emitted by a light source or reflected off a surface –> determines brightness perceived

transmission:

a) once emitted
- absorbed: taken up and not transmitted at all
- diffracted (scattered) = dispersed in an irregular fashion (usually happens in atmosphere)
b) interface between 2 media
- transmitted: conveyed from one place to another, usually with refraction (change in direction/bending –> short bends most, long bends least)
- absorbed: medium heats up
- reflected: redirected back towards its origin

*note: colour of solid objects depend on wavelengths reflected off object to eye; colour of transleucent objects depends on wavelengths transmitted through object to eye

Question 25

anatomy of eye

• pupil
• sclera
• iris
• cornea
• ciliary muscle
• aqueous humor
• vitreous humor
• choroid
• retina
• macula
• fovea
• optic disk
• optic nerve

Answer 25

• pupil: hole for light entry
• sclera: protective white outer surface; covers nearly entire eyeball
• iris: outer pigmented layer; inner layer of blood vessels (less pigment = more blood vessels visible)
• cornea: very sensitive to touch; clear outer covering –> most rays are transmitted/refracted through it
• ciliary muscle: controls shape of lens
• aqueous humor: fluid in anterior chamber; continually replenished –> supplies nutrients and removes waste; maintains shape of eyeball
• vitreous humor: fluid in posterior chamber; not replenished, floaters may form (dead cells build up); maintains shape of eyeball
• choroid: blood vessels; nourishes retina; absorbs light so it won’t scatter
• retina: detects light and initiates neural messages (inner layer = transmission/transduction into APs)
• macula: yellow pigmented spot
• fovea: best vision –> in the center of macula
• optic disk: axons leave eye; form optic nerve (cranial nerve II)
• optic nerve: axons of retinal neurons

Question 26

optical apparatus vs neural apparatus
A. optical:
- parts
- function
- sharpness
- pupil size

B. neural:

• parts
• function

Answer 26

optical: cornea, lens, pupil (iris sort of, bc it controls size of pupil, but doesnt contribute to transmission specifically)
- light emitted, transmitted, or reflected to the eye is transmitted through cornea, aq humor, lens and vitreous humor –> focuses image on retina
- sharpness of image depends on ability of cornea (mostly) and other parts to refract light
- pupil size ranges from 2-8mm and changes with light level and emotional responses

neural: retina - photoreceptors absorb light and –> turns it into neural energy

Question 27

accommodation

• process
• fatter vs flatter
• camera example

Answer 27

• the process by which the eye changes its focus by changing the shape of the lens
• fatter lens = inc optical power of eye = brings near objects into focus (accommodation)
• flatter lens = dec optical power (regular)
• in a camera, lens is moved closer or farther from film/sensors to change focus

Question 28

pupil reflexes

• direct light reflex
• consensual light reflex
• right oculomotor nerve damage
• right eye blind

Q: try doing the opposites!

Answer 28

direct light reflex: shining a light into one eye causes pupil of that eye to contract

consensual light reflex: shining a light into one eye causes pupil of other eye to contract

right oculomotor nerve (cranial nerve III) damage: no direct or consensual reflex is right eye, normal reflexes in left eye
- left eye will still contract with stimulus in right eye, but right eye won’t = problem with the nerve controlling the pupil, not the pathway connecting to left eye (since consensual left is still happening)

right eye blind: consensual but no direct reflex in right eye, direct but no consensual in left eye

• when light shines into the right eye, right eye will not contract (no right direct) and neither will left eye (no left consensual)
• if we shine light into left eye (left direct), left eye will contract and so will right eye (right consensual)
• right eye is not sensitive to light

Question 29

depth of field

Answer 29

depth of field: range of distances over which objects are in focus
- camera f-stop: diameter of the aperture on camera

large pupil: like a large aperture = small f-stop (4) = small depth of field
- range of distances that things are focuses for is small

small pupil: like a small aperture = large f-stop (32) = large depth of field (more things in focus)

Question 30

refractive errors
- emmetropia

1. myopia
   - cause (2)
   - near or farsighted?
   - problem
   - solution
2. hyperopia
   - cause (2)
   - near or farsighted?
   - problem
   - solution
3. astigmatism
   - cause (2)
   - solution

Answer 30

emmetropia: normal - eyeball is right length of optical elements
- focal length 16.8mm; optical power 59.52 D

myopia: eyeball is too long or optics too strong (too thick lens) = distant objects focused in front of retina = blurry
- near-sighted (things close are in focus)
- can’t relax lens enough to bring distant objects into focus
- solution: negative, concave lens brings distant objects into focus (removes optical power from eye)

hyperopia: eyeball too short or optics too weak (lens too thin) = near images focused behind retina = blurry
- far-sighted (things further away are in focus)
- don’t have enough accommodative power to bring closer objects into focus (constant accom is too big of a strain)
- solution: positive, convex lens brings both near and distant objects into focus

astigmatism: visual distortion produced by nonspherical cornea –> everything looks stretched out
- cause unknown; genetic and env factors
- solution: glasses with cylindrical lenses (2 focal points) –> since astigmatism cannot focus on 2 orientations at the same time, 2 focal points will fix orientation when brought to retina