PSYC 367 Final Exam - UBC

Brain regions involved in processing olfactory info

Olfactory bulb -> olfactory tract (mitral & tufted cell axons) to O1 (piriform)
Other involved regions are; amygdala, entorhinal cortex, hypothalamus, orbitofrontal cortex, hippocampus

Which theory can explain specific anosmia?

In a test, people reported different smell perception of a specific odorant due to genetic differences in odorant receptor expression.
Only consistent with shape theory as vibrational patterns of said odorant are constant.

Which theory can explain stereoisomers?

Consistent with shape theory as molecules of different orientation would activate different receptors
NOT consistent with vibration theory as stereoisomers have similar vibrational frequencies

Olfactory Identification

attaching a verbal label to a smell
Ability peaks around age 20 and declines after 50; may be due to decline in verbal semantic processing

Are hedonic responses learned? - Evolutionary evidence

Innate odour responses are only adaptive and advantageous for specialist species (i.e., california ground squirl)
Disadvantageous for generalist species like rats and humans as we have learned taste aversion, where we avoid substances that have been paired with gastric illness, based on smell.

Evidence of chemosignals?

EEG evidence that body odour carries info about potential partners

Transduction of sourness

Tastants enter through H+ channel or as acid (then dissociated into H+ inside cell)

Evidence for labeled-line theory

Tastes can be "knocked out" in mice but they can still taste the other non-knocked out flavours, proving that some fibres are tuned to specific tastes

How does temperature affect absolute thresholds for taste?

sweet - most sensitive at high temperatures
sour - little effect of temperature
salty or bitter - most sensitive at low temperatures

how does self-adaptation affect absolute thresholds for taste?

detection thresholds for sodium chloride (3 concentrations) increase during continued stimulation of tongue with same tastant

Potential health complications of taster status

supertasters/medium tasters: higher risk of colon cancer
supertasters: lower risk of cardiovascular disease
nontasters: more likely to smoke/consume alcohol

Odorant

Odour-inducing chemical molecule that is small, volatile, hydrophobic, and fat-soluble.

Connections between sensory neurons and the olfactory bulb

Synapses occur in the glomeruli in olfactory bulb
Olfactory nerve synapses with mitral & tufted cells in the olfactory bulb
Axons of olf. sensory neurons form the olfactory nerve (cranial I)

Anosmia

Inability to smell

Mechanism of Anosmia and Covid-19

Not completely understood
- OSNs are not infected by the virus
Believed that instead, support (sustentacular) cells in the olf. epithelium are infected and their inflammatory response blocks odorant receptor expression in OSNs.

Treatment for Covid induced anosmia?

Most successful is olfactory training; active sniffing of same small number of odorants every day

Theories of olfactory neural coding

1. Amoore's lock and key theory
2. Shape theory
3. Vibration theory

Vibration theory

Posits that every odorant has a molecular vibrational frequency, odorants with the same frequency would smell the same.
These frequencies would activate odorant receptors through electron tunneling.

Why test vibration theory?

Odorant with same "shape" can smell different

Olfactory Detection - Factors affecting threshold

Sex, Age, Experience, Attention, Odorant

Olfactory Detection - Attention

Thresholds increase during demanding visual tasks

tip-of-the-nose phenomenon

Inability to name a familiar odor; we have fewer words for smell as opposed to other sensations

Cross-adaptation

Sensitivity for a particular odorant reduced after exposure to different but similar odorant; may occur between odorants that fit into the same receptor

Mechanisms for cognitive habituation? (3)

1. Continuous exposure may cause adaptation/recycling to take longer

2. Odorant molecules may be absorbed into bloodstream causing adaptation to continue

3. Cognitive-emotional factors - e.g. reduced habituation if odorant is believed to be harmful

Are hedonic responses learned? - Developmental evidence

Infants display different preferences from adults
Also some preference from in utero exposure

Pheromones

Chemicals secreted by animals through urine/sweat glands for communication; triggers physiological or behavioural response in another member of the same species.

2 types of pheromones

1. Releasers; trigger an immediate, specific behavioural response (i.e., swarming, attracting mates)
2. Primers; trigger slow physiological change, often hormonal (i.e., new queen production, accelerate puberty)

Neural structures involved in pheromone communication

Amygdala, hippocampus & thalamus

nerves innervating the tongue

Vagus nerve (cranial nerve X)
Glossopharyngeal nerve (cranial nerve IX)
Chorda tympani; a branch of the facial nerve (cranial nerve VII)

5 classes of taste stimuli

4 primaries; sweet, sour, salty, bitter
Umami may be a 5th primary quality

Transduction of sweetness

Tastants activate a pair of G protein-coupled receptors (heterodimer [TAS1R2 & TAS1R3, umami activate a similar heterodimer])

Different types of cells in taste buds and transudction (3)

type 1: housekeeping (also saltiness)
type 2: no synapses, but depolarize then release neurotransmitter (atp) that acts on adjacent receptor cells (sweet, bitter, umami)
Type 3: depolarize then release serotonin at synapse with taste nerve fibre (sour)

Neural code for taste intensity

At higher concentrations, more neurons fire / fire faster

Neural code for taste quality theories (2)

Pattern-coding theory
Labeled-line theory

How does duration affect absolute thresholds for taste?

lower thresholds for longer durations of stimulation (for durations between 200 - 1500 ms)

How does location affect absolute thresholds for taste?

slight variation in absolute threshold for primary taste qualities for different tongue locations (but no areas explicitly for specific tastes)
suprathreshold concentrations can be tasted at any location except middle of tongue (no taste buds)

what makes someone a nontaster versus a taster for
PTC/PROP

No taste for nontasters with high thresholds, bitter for tasters with low thresholds.
nontasters have 2 recessive alleles; tasters have 1 or both dominant alleles (usually) for the gene (TAS2R38) that expresses a specific bitter G protein-coupled receptor

Taste hedonics

pleasure/displeasure evoked by primary taste qualities
- present at birth: evidence from newborn facial expressions for the different tastes smile for sweet, pucker for sour, spitting for bitter

flavour vs taste

Flavour; sensations arising when odorants in the mouth stimulate receptors for smell through the retronasal passage
Taste; refers to the 5 basic tastes

interactions between taste, flavour and/or touch sensations - mislocalization

flavour sensations are perceived to come from the mouth even though transduction occurs in olfactory epithelium

Olfactory Detection - Odorant

Easier to detect odorants with longer carbon chains

Kinesthesis

the system for sensing the position and movement of individual body parts (part of proprioception)

Proprioception

The cumulative sensory input to the central nervous system from all mechanoreceptors that sense body position and limb movement.

Mechanoreceptors

Sensory neuron that responds to mechanical stimulation

Glabrous skin

skin that does not contain hair; found on the palms and soles of the feet

4 Types of mechanoreceptors in glabrous skin

SA I (Merkel) - Closest to surface
FA I (Meissner)
SA II (Ruffini)
FA II (Pacinian)

SA I (Merkel)

Small adaptive field
Slow adaptation rate
MFS; < 5 Hz
Primary function; Coarse texture and pattern

FA I (Meissner)

Small Adaptive field
Fast adaptation rate
MFS; 5 to 50 Hz
Primary function; Low frequency vibration and grip

SA II (ruffini)

Large adaptive field
Slow adaptation rate
MFS; 5 to 50 Hz
Primary function; finger position

FA II (Pacinian)

Large adaptive field
Fast adaptation rate
MFS; 50 to 700 Hz
Primary function; high frequency vibration & fine texture

5th type of fast-adapting tactile mechanoreceptors in hairy skin?

Hair follicle receptor

Kinesthetic Mechanoreceptors

Muscle spindles (for muscle length) and golgi tendon organs (muscle tension & joint position)

Physiological zero

normal skin temperature (30-36 celsius)
No sensation of warmth or cold

The response of warmth and cold thermoreceptors with respect to physiological zero

Warmth fibres increase firing rate to increases in skin temp above 36 celsius
Cold fibres increase firing rate to decreases in skin temperature below 30 celsius

nociceptors (3 types)

Pain receptors stimulated by extreme temperature (thermo nociceptors), severe pressure or excessive stretching (mechano nociceptors), chemicals from injured tissue / spicy food (polymodal nociceptors

4 types of nerve fibres coming from skin

1. Proprioceptors (A-alpha)
2. Mechanoreceptors (A-beta)
3. Pain and Temp (A-delta)
4. Pain, temp, and itch (C)

Proprioceptor (A-alpha fibres)

13-20mm (micrometer) diameter
Very thick myelin
80-120 m/s conduction speed

Mechanoreceptor (A-beta)

6-12mm diameter
thick myelin
35-75 m/s conduction speed

Pain and Temperature (A-delta)

1-5mm diamter
thin myelin
5-30 m/s conduction speed

Pain, temperature and itch (C)

0.2 - 1.5 mm diameter
no myelin
0.5-2 m/s conduction speed

Double pain

Initial sharp pain followed by slower, throbbing pain.

types of chemical membrane receptors on C and A-delta fibres.

A-delta; cold fibres, thermal nociceptors or mechano receptors
C; warmth fibres or polymodal nociceptors

List the main stations where synapses occur, and the connecting pathways, in the dorsal-column-medial-lemniscal pathway and spinothalamic pathway

Dorsal-column-medial-lemniscal pathway; pressure and position
1st synapse for most neurons in the medulla (some synapse in spinal chord)
Then up the dorsal column
2nd synapse at the thalamus in the ventral posterolateral nucleus
3rd synapse in parietal cortex of S1
Spinothalamic pathway; temp & pain
1st synapse in substantia gelatinosa (layer 2) of dorsal horn in spinal cord.
Then through the medulla and up the lateral spinothalamic tract.
2nd synapse at the thalamus in the ventral posterior nucleus (VPL)
3rd synapse in parietal cortex of S1

Somatosensory cortex - 4 sub regions

Broadmann areas
3a, 3b, 1, and 2

Thalamic inputs in S1

Neurons from thalamus synapse in layer 4 of areas 3a (proprioception) and 3b (touch)

Somatotopic maps - Sensory homunculus

Demonstrates that the area of the cortex dedicated to the sensations of various body parts is proportional to how sensitive that part of the body is.

Wilder penfield

Created the somatotopic map (sensory homunculus)

Somatosensory Sensitivity (measure & highest sensitivity)

Sensitivity measured as the inverse of absolute threshold (small threshold = high sensitivity)
Highest sensitivity on face, lowest on foot

Somatosensory discrimination (measure)

Weber's law

Somatosensory acuity (measure and higher sensitivity)

Minimum distance at which two stimuli are just perceptible as 2 seperate (2-point threshold)
Measured by seeing when and where 2 touches are perceptible.
More likely to be detected in areas with larger cortical representation.

the relationship between the sensory homunculus, receptive field size and 2-point thresholds.

areas with smaller receptive fields and larger representation on the sensory homunculus (e.g., hands and face) can detect finer spatial details and have lower 2-point thresholds.

Aristotle's illusion

A touch to fingers crossed or uncrossed can either feel 1 or 2 touches due to differences in cortical representation and location of the areas touched.

Limbic system structures responsible for processing emotion

Anterior cingulate, insula, amygdala

Prefrontal cortex

responsible for modulating pain perception and chronic pain emotional response

modulation of pain

Modulation of pain sensitivity by enkephalins & endorphins (endogenous opiates) released by descending inputs from brain. These opiates block the release of neurotransmitters involved in pain

Neurotransmitters involved in pain

Substance P released by C fibres, picked up by NK-1 receptors on spinal cord. Also glutamate

Gate control theory

Theory that spinal cord contains transmission cells that carry pain signal to the brain to the brain but that there exists fast mechanoreceptor signals that close the pain gate and slow nociceptor signals that open the pain gate.

Transcutaneous Electrical Nerve stimulation (TENS)

Device that delivers electric current through skin near site pain

How does transcutaenous electrical nerve stimulation support gate control theory?

The electric current activates A-beta fibres to close the pain gate and stimulates the release of endogenous opiates.

How do anesthetics work to relieve pain

Produces a total loss of sensation by interrupting signals travelling to brain.
Local anesthetics act at site of injection and block sodium channels
General anesthetics act on brain itself and cause unconsciousness

How do analgesics work to relieve pain?

Non-opiate analgesics like aspirin & ibuprofen block prostaglandin
Opiate analgesics like morphine, codeine & heroin block nociceptor release of neurotransmitter and inhibit spinal cord neurons

How does acupuncture work to relieve pain

Believed to cause a release in endogenous opiates.

Nociceptive pain

pain as a result of stimulation of free nerve endings in skin, muscles & joints.

Inflammatory pain

signal that some type of tissue damage has occurred

Neuropathic pain

pain from damage to neurons of either the peripheral (eg sciatica) or central nervous system (eg MS)

Allodynia

pain due to stimulus that should not be painful, the nociceptors have lower threshold for stimulation

Hyperalgesia

Painful stimuli become more painful, exaggerated sensitivity.

peripheral sensitization

Change in nociceptors

Central sensitization

Increased # of pain receptors, rewiring of connections or loss of inhibitory cells in spinal cord

In terms of sensitization, what happens when pain is not treated?

Hyperalgesia and/or allodynia are exacerbated.

How do anticonvulsants work to relieve pain?

they inhibit a specific type of calcium channel to prevent release of nociceptor neurotransmitter

How does capsaicin work to relieve pain?

Stimulates nociceptors; killing them or using up their supply of neurotransmitter.

How do cannabinoids work to relieve pain?

Block neurotransmitter release from nociceptors and reduce inflammation.

How do NMDA-receptor blockers work to relieve pain?

Prevents glutamate from binding with NMDA receptors on spinal cord neurons

Phantom limb pain (Ramachandran)

Described phantom limb pain through cortical organization of somatosensation. Said phantom limb pain arises due to cortical reorganization, sensory confusion, and a mismatch between the brain's body map and actual physical sensations, which the brain interprets as pain.

Mirror box treatment for phantom limb pain

Placing an injured limb in a box and the uninjured limb in front of a mirror. Move both limbs symmetrically while looking in mirror. This makes it feel like the amputated limb is moving; relieving pain

Electrical stimulation implant treatment for phantom limb pain

Electrical stimulation in spinal cord dorsal column to close pain gate

Visible light wavelength

400-700 nanometers

Properties of light

wavelength, intensity, absorption, diffraction, reflection, transmission, and refraction

Light - Wavelength

the distance between peaks in light waves