Olfactory system

Question 1

The Olfactory System - General

Answer 1

Very primitive sense, essential for survival across terrestrial species Innate, sharp from birth (babies’ orientation)
Functions:
Pleasure (nice food or drink) Recognize safe foods
Avoid hazards (gas, fire)
Perceive hormones (social response)

Question 2

The Olfactory System - Odorants

Answer 2

Types of odors:
- Pungent (acre)
- Earthy (tierra)
- Musky (almizcle)
- Pippermint (menta) - Ether (alcohol)
- Floral (floral)
- Camphor (madera) - Putrid (putrefacto)

Question 3

Physiological responses to smell:

Answer 3

SALIVATION – GASTRIC MOTILITY
GAGGING – VOMIT
REPRODUCTIVE – ENDOCRINE FUNCTIONS

Question 4

The Nose
Simple anatomy

Answer 4

• Enter through the nose (breathe or sniff, passive flow) or mouth
• Hair to trap particles • Neuroepithelium
Sinusitis or infection → more mucus and less air movement = harder for volatile molecules to settle in→reduced smelling

Question 5

The Nostrils and odorants

Answer 5

The 2 nostrils have slightly different sizes (varies in cycles of hours)
High absorption odorants = larger neuronal response in larger nostril
Low absorption odorants = larger neuronal response in smaller nostril

Question 6

Odor Receptors (OR):

Answer 6

Odor binds into rc cilia → Prot G → Calcium and Sodium ion gates→depolarization

Question 7

OR properties:

Answer 7

1) Specificity
We have an OR for every odorant
-40M different OR
-Detect around 10K different smells
2) Rapid adaptation
• Thresholdvarydependingonthestimuli • Rapid adaptation in most cases

Question 8

Olfactory maps

Answer 8

Smell of particular chemical is converted into a certain neuronal map in the olfactory bulb (minty and fruity produce diff patterns)

Question 9

Temporal coding

Answer 9

temporal coding (timing of spikes) might code for the quality of odors
- change the spiking rate of neurons but not timing (odor 2)
- change spiking rate and timing (odor 3)

Question 10

Pyriform cortex = Primary Olfactory Cortex

Answer 10

Detection of smell appearance + sniffing rate

Question 11

Orbitofrontal Cortex = Secondary Olfactory
Cortex

Answer 11

Identifying the odor itself

Question 12

Amygdala + Hypothalamus

Answer 12

Emotional and motivational aspects of smell

Question 13

Hippocampus

Answer 13

Odor memory

Question 14

Uniqueness of the olfactory system transmission!

Answer 14

Receptors directly to the brain through the ethmoid bone.
Most of the axons of the olfactory nerve project to ipsilateral cortex.
Arrives at the primary olfactory cortex without previous relay at the thalamus

Question 15

Alterations

Answer 15

Anosmia = total loss of smell
Hyposmia = reduced
Parosmia = distorted smell
Phantosmia = smelling things that aren’t there

Question 16

Anosmia

Answer 16

Fisiopathology
Nasal obstruction
Destruction of the neuroepithelium Degeneration of olfactory nerve or bulb

Main causes
Brain Trauma
Viral infection
Alzheimer’s diseaseObstructuion: Common cold, flu, allergies, nasal polyps, tumor

Treatment = treat the underlying cause + smell training

Question 17

Electronic nose (applications)

Answer 17

Applications:
Comparison with a reference product
Detection of contamination, spoilage, adulteration Detection method (drugs, bombs, etc.)

Question 18

The Gustatory System - Tastants

Answer 18

5 basic tastes: Salty
Sour
Bitter
Sweet
Umami*

For us to taste some food component, it must be dissolved in saliva

Question 19

The Gustatory System – Mouth and tongue

Answer 19

Lingual papillae: small structures on the upper surface of the tongue that give it its characteristic rough texture.

Four types of papillae
All except the filiform = associated with taste buds.

Multiple functions
• Gustation
• Nociception (for detecting irritating
substances)
• Saliva secretion

Question 20

Papillae

Answer 20

Papillae are located in the tongue, soft palate, pharynx, and upper part of the esophagus.

Question 21

Taste cells (transduction)

Answer 21

Transduction:
Tastants → receptors in taste cells → cascade of chemical messengers → depolarization. Each basic taste has a different form of chemical signal transduction.

Question 22

Taste cells (general)

Answer 22

Taste cells are specialized epithelial cells, not nervous tissue:
• Basal cells are stem cells that replace gustatory cells every week or so (burnt tongue)

One can estimate:
• That 10% of cells are lost each day via natural attrition
• ∼20-30% of the cells are new and undergoing differentiation
• The remaining 60-70% are functional taste cells.

Question 23

Complexity of taste

Answer 23

We only have 5 types of taste cells but a wide array of flavors Proportion of activation (+ or – sweet, + or – sour…).
Chemical systems intimately related - Integration of information
• Usually, when eating, taste and smell combined. Flavors are 80% smell.
• When we eat, odorants go up to the olfactory epithelium.
• When we have a cold, we only taste (from complexity to 5 flavors).
• Smell adds complexity to flavors→IFG regions respond selectively to O +T combinations
• Sugar is sweeter when paired to strawberry smell than peanut butter or no odor.

Question 24

Anomalies in taste perception

Answer 24

Hypogeusia: Reduced gustatory perception Dysgeusia: Persistent bad taste (metallic, sour, etc). Ageusia: Complete loss of gustatory perception
Different possible causes: drug or medicine, trauma, tumor… Usually associated with olfactory alterations
!Normally rc are functional, the problem is in transmission or higher order processing!

Question 25

The Somatosensory System - General

Answer 25

Perception of all mechanical stimuli that affect the body:
• Touch, temperature, pressure, pain, body position.

Single receptors encode multiple features like stimulus intensity, duration, position and/or direction.

Question 26

Touch (general)

Answer 26

Most of the somatosensation by the skin = largest sensory organ.
Variety of rc within dermis and epidermis, and all associated to non-neural tissues (except free nerve endings).

Question 27

Mechanoreceptors – Properties
- Adaptation speed

Answer 27

Rapidly adapting
Activated when a stimulus is encountered but fall silent if stimulus remain present
Important for detecting movement
• Slowly adapting
Keep responding to continuous stimulus Important for detecting size and shape of objects

Question 28

TOUCH
Mechanoreceptors – Properties
- Mechanical sensitivity

Answer 28

Amount of pressure needed for detection to be done

Question 29

TOUCH
Mechanoreceptors – Properties
- Size of receptive field

Answer 29

• Receptive field = Extent of skin surface innervated by a single neuron.
• More small receptor fields = better tactile discrimination than fewer large receptor fields.

Question 30

Mechanoreceptors – 4 main types
a) Merkel’s disk

Answer 30

• Slowly adapting
• Small receptive fields
• Especially dense in the finger
• Processing of shape and texture (epicritic)

Question 31

Mechanoreceptors – 4 main types
b) Meissner’s corpuscles!

Answer 31

• Rapid adapting
• Small receptive fields (but lower spatial
resolution than merkel’s)
• Transmission of information about movement
between skin and other surfaces (sense of texture and grip maintaining).

Question 32

Mechanoreceptors – 4 main types
c) Pacinian corpuscles

Answer 32

• Rapidly adapting
• Very large receptive fields
• Vibration in contact with the hand
• Use of tools

Question 33

Mechanoreceptors – 4 main types
d) Ruffini’s ending

Answer 33

• Slowly adapting
• Large receptive fields
• Poorly understood physiology (skin
stretching like finger movement, motion direction).

Question 34

TOUCH (nerves)

Answer 34

Extensive network of peripheral nerves innervating the skin = Afferent axons (Not Efferent) Varying diameters that correlate with AP speed conduction and depends on type of information.

Afferent axons take sensory information and enter the spinal cord through dorsal routes. Innervation of the skin relates to the segmental organization of the spine (cervical, thoracic, etc).
Organization reflects quadrupedal ancestry.

Question 35

TOUCH (somatosensory cortex)

Answer 35

Complete but distorted map of the body - More sensitive areas are inflated

Dual stream models of haptic processing (Reed, 2005):
Ventral stream: object identity
Dorsal stream: spatial location

Question 36

PAIN AND NOCEICEPTION

Answer 36

Vital lo life: life without pain is dangerous!
Drives motivated behavior and has a learning component.

Question 37

Nociception vs Pain

Answer 37

Nociception = neural encoding of tissue damage = sensation of pain (stepping on a lego). Pain = subjective experience of actual or impeding harm = perception of pain (love).

One can have pain without nociception or the other way around.
We all have the same pain threshold (AP triggered in nociception) but different tolerance (pain) → Pain scale

Question 38

Nociception vs Pain

Answer 38

Nociception = neural encoding of tissue damage = sensation of pain (stepping on a lego). Pain = subjective experience of actual or impeding harm = perception of pain (love).

One can have pain without nociception or the other way around.
We all have the same pain threshold (AP triggered in nociception) but different tolerance (pain) → Pain scale

Question 39

Types of pain

Answer 39

Based on pathophysiology
- nociceptive
neuropathic

Based on the duration
- acute
chronic

Based on anatomic location

Question 40

From the spine, 2 ways for the information:

Answer 40

A) Reflex arc
B) Higher processing:

Spinothalamic tract (most fibers)
• Thalamus (integration and splits message)
• Somatosensory (identifies and localizes)
• Limbic system (emotional suffering)
• Frontal cortex (assign meaning to it all).

Spinomesencephalic tract→Pain modulation:
Same path with a synapse in periaqueductal gray → activate pain suppression system