Lecture Week 2 Flashcards
What is Taste?
- Sensations evoked by solutions in the mouth
- They contact receptors on the tongue and roof of mouth
- Food breaks down into molecules and evoke sensation by activating taste buds
- Taste buds transduce those molecules into electrical energy
- We then perceive taste
Flavour
- We can distinguish between taste and flavour
- Flavour is the combination of true taste and retronasal olfaction
True Taste
- Sweet
- Sour
- Salty
- Bitter
Retronasal Olfaction
- The sense of smell
- Research says majority of flavour comes from smell system
Gustatory System
- Detects taste molecules we put into our mouths
- Molecules dissolved in saliva
- They then make contact with tastebuds and taste receptors
Retronasal Olfactory Sensation
- The sensation of an odour that is perceived when chewing and swallowing
- Odourant is forced into the mouth, behind the palate and to the nose
- Reach the olfactory epithelium
- The combination of activation of taste buds on tongue, olfactory epithelium gives us the flavour of the stimulus
Mozell et al., 1960
Without smell our ability to identify foods by taste alone is poor
Taste Buds
A cluster of cells that convey neural signals to the brain by taste nerves
Taste Receptor Cells
A cell within a taste bud that contains sites that can interact with charged particles and chemical structures
Types of Papillae
- Circumvallate Papillae
- Foliate Papillae
- Fungiform Papillae
- Shaped like mushrooms
- distributed along the edge of tongue
- mostly found on tip of tongue
- taste buds buried in surface
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Circumvallate Papillae
- Structures shaped like circles and mounds
- Formed in a V shape on the back of tongue
- Surrounded by trenches
- Taste buds buried in sides of trenches
Foliate Papillae
- Folds of tissue that contain taste buds
- Located on rear and sides of tongue
- Lateral to circumvalate papillae
Bogus Tongue Map
- Taste buds are found randomly on all parts of the tongue
- Different taste receptors responsible for different tastes are randomly disperesed
- There is no map of the tongue that indicates places that focus on certain tastes
Neural Pathway for Taste Perception
- After leaving taste buds, taste information travels through Medulla and Thalamus
- Information the travels to the Insular Cortex
- Then projects to the orbitofrontals Cortex
Insular Cortex
- The insular cortex links sensory experience and emotional valence
- Receives sensory information from the environment.
- Also known as Gustatory Cortex
- Projects to the Orbitofrontal Cortex
Nucleus of the Solitary Tract
- a series of purely sensory nuclei (clusters of nerve cell bodies) forming a vertical column of grey matter embedded in the medulla oblongata.
Taste - Orbitofrontal Cortex
- Where we have our conscious experience of flavour
- Where taste pleasure and displeasure is processed
Basic Tastes
- to be a basic taste the recpetor must be specific to that taste and respond only to that taste
- There must be an evolutionary basis for that taste
- Salty
- Sour
- Sweet
- Bitter
Basic Taste - Salty
- Produced by positive charged Salt Ions
- Evolutionary necesity: forour bodies to work we need a certain amount of salt in our body
- We crave salt when we have a salt deficiency
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Basic Taste - Sweet
- Taste quality naturally found in glucos, sucrose and fructose
- Preference for natural sweeteners because they are used for producing energy in us
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Basic Taste - Sour
- Produced by hydrogen ions in acids
- generally a disliked taste in large quantities
- Evoutionary Benefit: Large quantities of acids can damage our internal organs
- found to be preffered in small quantities
Basic Taste - Bitter
- Generally considered unpleasant in large quantities
- produced by substances such as quinine or caffeine
- Evolutionary Beneft: A lot of poisons are bitter, so it is useful to identify bitter tastes as unpleasant
Basic Taste - Umami
- Considered a ‘delicious savoury’ taste
- Produced by MSG to give a pure umami sensation
- Tends to be undetectable on its own - it needs sodium to make it palatable
- Combined with certain odours and saltiness leads to pleasant taste sensation
- Evolutionary Benefit - May indicate the prescence of proteins
- May require L-glutamate receptors and Receptors for amino acids
Anosmia
- Inability to smell
- Usually found in older people
- Olfactory processing with complex link to depression (Croy et al., 2014
Aguesia
- Inability to taste
- Usually found in older people also
- Taste dysfunction can lead to poor diet choices and may be related to obesity and well being
Supertasters
- The ability to detect Propylthiouracil (PROP)
- Hayes et al., 2008 found that both genotype and number of fungiform papillae contribute to being a supertaster
- about 1/3 population can taste and respond badly to PROP
- about 1/3 population cannot detect PROP
How many senses do we have.
- Aristotle described 5 major senses
- Touch
- Sight
- Sound
- Taste
- Smell
- There is also the sense of Equilibrium that is run by the Vestibular System
- Falling
- Acceleration
- Tilt
- Balance
Vestibluar System
- Organs and neural pathways that sense head motion, head orientation and orientation in gravity
- Often overlooked but very old evolutionarily
- Vestibular organs around the size of a pea
- Connected to the Cochlear
- Is an autonomic system
Vestibular organs help us by providing a sense of
- Linear Motion
- Angular Motion
- Tilt
Vestibulo-Ocular Reflex (VOR)
- Activation of the motoneurons that innervate the extra-ocular muscles.
- The function of these reflexes is to maintain the orientation of the eyes in space during head movements
- Assists the visual image remains stable on the retina.
Sense of Equilibrium
- Composed of multiple reflexes and perceptual Modalities
- Visual Stability
- Balance
- Autonomic Nervous System
- regulates oBlood Pressure when we stand
- Spatial Orientation
- Begins in Vestibular Organs in inner ear
Sense of Proprioception
- Sense of where your body is in space
Spatial Orientation
- Sense of where your head in relation to gravity
- consists of three interacting modalities
- Linear Motion
- Angular Motion
- Tilt
Sense of Linear Motion
- Going forward and back and side to side
Sense of Angular Motion
- Rotation of the head
Sense of Tilt
- Leaning left and right, forward and back
Three Directions for Sense of Rotation:
Roll
Rotation around the x-axis
Three Directions for Sense of Rotation:
Pitch
Rotation around the y-axis
Three Directions for Sense of Rotation:
Yaw
Rotation around the z-axis
Stereocilia
- Hair cells that transduce mechanical stimulus in inner ear and send neural activity to the brain
- Depending on the directions of movement it will move towards the largest hair in the cell or away from it
- It will then depolarise increasing action potential or hyperpolarise decreasing action potential
The Five Vestibular Organs
- Semicicular Canals
- Respond to pitch yaw and roll
- Otolith Organs
- Utricule
- Saccule
Semicircular Canals
- Three tubes in vestibular system that sense angulare acceleration
- Sense of angular motion “head spinning” in pitch, yaw and roll
- Each canal is sensitive to each type of rotation
The Vestibular Push-Pull Relationship
- We have two sets of Vestibular Organs one in each ear
- Movement in one direction will polarise stereocilia in one ear and hyperpolarise them in another
- this type of pattern of hyperpolarisation and depolarisation that gives us sensation of movement
What is endolymph?
the fluid contained in the membranous labyrinth of the inner ear
Neural Activity in Semicircular Canals
- Neural activity in these canals are senstive to change in rotation velocity
- constant rotation leads to decreased responding from the stereocilia after a few seconds
- We sense the acceleration in the movement of a car but then do not sense that we are moving unless there is a sudden brake or change in the level of accelaration
Otolith Organs
- Sense linear velocity
- where the endolymph from the canals end up
- contain stereocilia
- Utricle has 30,000 hair cells
- Saccule has 16,000 hair cells
- Semicircular
Utricula Macula
- Responsible for detecting movement along horizontal plane; forward and back, left and right
- eg: walking, running, driving
Saccular Macula
- Responsible for detecting vertical movement
- sky diving, falling, landing in a plane
Otolith Organs - Anatomy (8)
- Striola
- Otoconia
- Otolithic Membrane
- Gelatinous layer
- Reticular Membrane
- Supporting Cells
- Hair cells
- Afferent Neurons
Otoconia
- calcium carbonate crystals that sit on top of the otolithic membrane
- they shift around and this movements shifts the hair cells
- they then either polarise or depolarise whcihc tells us the change in movement
- watch Video in Week 2 Lecture 1:10:00 mins
Striolia
- a narrow curved zone that divide each macula in two areas:
- Saccule
- Utricle
- It is observable in all mammalians.
Otolithic Membrane
- a fibrous structure located in the vestibular system of the inner ear
- Plays a critical role in the brain’s interpretation of equilibrium.
- Serves to determine if the body or the head is tilted
- Also serves to perceive the linear acceleration of the body.
Gelatinous Layer
- Overlying the hair cells and their hair bundles is a gelatinous layer
- Above that layer is the otolithic membrane
Reticular Membrane
- In the ear
- A stiff membrane that forms a division between endolymph and perilymph
- Some of the hair cells of the stereocilia make contact with the reticular membrane.
Hair Cells
The sensory cells within the inner ear that transduce mechanical displacement into neural impulses.
Afferent Neurons
- Also known as sensory neurons or afferent nerve fibers
- Pathways that carry sensory information from the body to the central nervous system
- From the sense organs to the brain and spinal cord
3 Experimentational techniques used to examine spatial orientation
- Threshold Estimation
- Magnitude estimation
- Cross Modality Matching
Threshold Estimation
- What is the minimum motion needed to correctly perceive motion?
Magnitude Estimation
- Participants report how much or how many degrees they have tilted rotated or translated in linear motion
Cross Modality Matching
- Participants are tilted and then orient a line with the direction of gravity.
Rotation Perception
- Tested in the dark
- Generally people can tell if they spin in clockwise or anti clockwise direction
- They soon feel like they are slowing down even though the rotation is constant
- After a short time they no longer feel like they are rotating at all
- Upon stopping they feel like they are spinning in the opposite direction
Vestibular response
- Only respond to changes for 20-30 seconds
- After this it normalises again until there is another change
- If endolymph is not changing then the current position is perceived as normal
Translation Perception
- People can reproduce the velocity and direction of a linear trajectory even if they have been translated in the dark
Tilt Perception
- People can reproduce the angle of movement if they have been tilted in the dark
Sensory Integration
- The ability to combine several senses together to more accurately perceive our environment.
- Visual and Vestibular senses combine strongly to give sense of where we are oriented
Vection
- The illusion that we are moving when we are in fact still
eg: non moving escalators, train moving next to your own train
Visual-Vestibular Integration
Visual and Vestibular senses combine strongly to give sense of where we are oriented
What happens when the vestibular system fails
- Spatial disorientation
- Imbalance
- Distorted vision unless head is perfectly still
- Motion sickness
- Cognitive problems
Meniere’s Syndrome
- Sever sudden dizziness, imbalance, spatial disorientation
- Can cause sudden falling
- Unpredictable and terrifying
Vestibular Function - Gurvich et al., 2013
Common neural pathways for vestibular function and many psychiatric disorders
Vestibular Function – Staab 2016
30-50% of patients with vestibular disorders have a co-existing psychiatric disorder such as anxiety, depression, PTSD, OCD
Vestibular Function – Smith et al., 2016
- Vestibular system influences higher order cognitive processing including working memory, spatial memory, attention and executive function
Vestibular Function – Smith & Darlington, 2013
- Personality can be affected by vestibular disturbances
- Patients with vestibular dysfunction report depersonalisation & derealisation
- This indicates vestibular system makes a key contribution to the sense of self.
Why do we need a sense of touch
- Detect damage
- Detect disease and maintain homeostasis
- Sense temperature changes
- Determine body position and where our muscles are moving
- Feeling deformities
- Sustained pressure on our skin
- Detect low and high frequency changes
Touch Receptor Physiology
- Touch receptors found in the Dermis and Epidermis
- Grouped by:
- Type of stimulation receptor responds to
- Mechanorecepters
- Olfactory sensory neurons
- Size of receptive field
- Rate of adaptation
- Type of stimulation receptor responds to
Receptor Fields
- Each receptor cell will synapse to a single neuron
- Each Neuron receives messages from multiple receptors
- Neurons don’t differentiate which receptor it receives information from
- Activation is activation from a many receptors which then synapse to one neuron
Rate of Adaption – Fast Adapting
- Responds when pressure is first applied
- Responds again when pressure is taken off
Rate of Adaptation – Slow Adapting
Fires continuously when pressure is applied to the skin
Tactile Sensations
- All mechanical displacement
- Picking things up or touching things
- Tactile Mechanoreceptors
Kinesthetic Mechanoreceptors
- Located in ligaments, muscles and bones
- Tell us position of our body and limbs in space
Thermoreceptors
- Sense changes in temperature
- Both Heat and Cold receptors
- Regulate body temperature to assist in Homeostasis
Nociceptors
- Pain Receptors
- Synapse whenever they detect damage to the body tissue.
Eg: when pin is pressed to skin mechanoreceptors fire but if pressure continues to pierce skin nociceptors begin to respond
Kinesthesia
Perception of the movement of our limbs in space
Proprioception
Perception of the position of our limbs in space
Somatosensation
- Sensory signals from the skin muscles tendons, joints and internal receptors
- All sensory receptors and perception combine together to create a sense of Somatosensation
- Different types of receptors can send messages via the same kinds of channels
Mechanoreceptors – Meissner Corpuscle
- In the Epidermis
- Generally found in hairless skin
- Fast Adapting type 1
Meissner Corpuscle
Hand Grip Control
Mechanoreceptors - Merkel Cells
- In the Epidermis
- Generally found in hairless skin
- Slowly adapting type 1
Merkel Cells
- Fires to continous pressure
- Fine details
Mechanoreceptors - Ruffini Endings
- Located in the Dermis
- Generally found in hairless skin
- Slowly Adapting Type II
Ruffini Endings
- Fires to continuous pressure
- Responsible for stretching muscles
- Large Receptive fields
Mechanoreceptor - Pacinian Corpuscle
- Located in the Dermis
- Generally found in hairless skin
- Fast Adapting Type II
Pacinian Corpuscle
- Large Receptive Fields
- Fires to On and Off
- Responsible for perceiving vibration and finetwxture by moving fingers
Kinesthetic Receptors
Mechanoreceptors in muscles, tendons and joints
Muscle Spindles
- Mostly perceive angles and tension of limbs
- lenght of the change of the spindle that tells our brain that the muscle is moving in a certain way
Range of response for Thermoreceptors
- Respond when we make contact with objects warmer than 36o
- Respond to objects colder than 30o
- This helps to keep the body in homeostasis
- respond to Heat, Cold, pressure and chemicals
