Olfactory system Flashcards
The Olfactory System - General
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)
The Olfactory System - Odorants
Types of odors:
- Pungent (acre)
- Earthy (tierra)
- Musky (almizcle)
- Pippermint (menta) - Ether (alcohol)
- Floral (floral)
- Camphor (madera) - Putrid (putrefacto)
Physiological responses to smell:
SALIVATION – GASTRIC MOTILITY
GAGGING – VOMIT
REPRODUCTIVE – ENDOCRINE FUNCTIONS
The Nose
Simple anatomy
• 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
The Nostrils and odorants
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
Odor Receptors (OR):
Odor binds into rc cilia → Prot G → Calcium and Sodium ion gates→depolarization
OR properties:
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
Olfactory maps
Smell of particular chemical is converted into a certain neuronal map in the olfactory bulb (minty and fruity produce diff patterns)
Temporal coding
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)
Pyriform cortex = Primary Olfactory Cortex
Detection of smell appearance + sniffing rate
Orbitofrontal Cortex = Secondary Olfactory
Cortex
Identifying the odor itself
Amygdala + Hypothalamus
Emotional and motivational aspects of smell
Hippocampus
Odor memory
Uniqueness of the olfactory system transmission!
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
Alterations
Anosmia = total loss of smell
Hyposmia = reduced
Parosmia = distorted smell
Phantosmia = smelling things that aren’t there
Anosmia
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
Electronic nose (applications)
Applications:
Comparison with a reference product
Detection of contamination, spoilage, adulteration Detection method (drugs, bombs, etc.)
The Gustatory System - Tastants
5 basic tastes: Salty
Sour
Bitter
Sweet
Umami*
For us to taste some food component, it must be dissolved in saliva
The Gustatory System – Mouth and tongue
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
Papillae
Papillae are located in the tongue, soft palate, pharynx, and upper part of the esophagus.
Taste cells (transduction)
Transduction:
Tastants → receptors in taste cells → cascade of chemical messengers → depolarization. Each basic taste has a different form of chemical signal transduction.
Taste cells (general)
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.
Complexity of taste
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.
Anomalies in taste perception
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!
The Somatosensory System - General
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.
Touch (general)
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).
Mechanoreceptors – Properties
- Adaptation speed
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
TOUCH
Mechanoreceptors – Properties
- Mechanical sensitivity
Amount of pressure needed for detection to be done
TOUCH
Mechanoreceptors – Properties
- Size of receptive field
• Receptive field = Extent of skin surface innervated by a single neuron.
• More small receptor fields = better tactile discrimination than fewer large receptor fields.
Mechanoreceptors – 4 main types
a) Merkel’s disk
• Slowly adapting
• Small receptive fields
• Especially dense in the finger
• Processing of shape and texture (epicritic)
Mechanoreceptors – 4 main types
b) Meissner’s corpuscles!
• 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).
Mechanoreceptors – 4 main types
c) Pacinian corpuscles
• Rapidly adapting
• Very large receptive fields
• Vibration in contact with the hand
• Use of tools
Mechanoreceptors – 4 main types
d) Ruffini’s ending
• Slowly adapting
• Large receptive fields
• Poorly understood physiology (skin
stretching like finger movement, motion direction).
TOUCH (nerves)
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.
TOUCH (somatosensory cortex)
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
PAIN AND NOCEICEPTION
Vital lo life: life without pain is dangerous!
Drives motivated behavior and has a learning component.
Nociception vs Pain
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
Nociception vs Pain
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
Types of pain
Based on pathophysiology
- nociceptive
neuropathic
Based on the duration
- acute
chronic
Based on anatomic location
From the spine, 2 ways for the information:
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
