Lecture 8 - Sensory System Flashcards
Sensory Systems
- Olfaction
- Taste
- Touch
- Hearing
- Vision
Chemical Stimuli
(chemoreceptors) Olfaction Taste
Mechanical Stimuli
(mechanoreceptors)
touch hearing
Electromagnetic Stimuli/light waves
(photoreceptors)
vision
Sensory Receptor Cells - Initial stimuli Conversion
- convert physical and chemical stimuli into neural signals
- stimulus causes change in neurotransmitter release
1. sensory receptor detects stimuli and directly or indirectly opens/closes ion channels
2. change in membrane potential –> neurotransmitter release - some sensory cells do not use action potentials
- graded depolarization causes neurotransmitter release
- released neurotransmitter can cause AP in subsequent neurons downstrea,
What is a sensation and how is it interpreted? How are different ones interpreted?
- the sensations we perceive
- specific sensation = which combinations of neurons are firing action potentials (smell vs round, rose vs vanilla)
- intensity of stimulus = frequency of action potentials (how many APs fire, not which ones)
Olfactory Receptor Neurons
Location: epithelium on top pf nasal cavity
- receptors on cilia of cells extending into nasal cavity
- chemoreceptors
- odorant
- axons extend up to olfactory bulb in brain
*travel farther, DO need action potential
* humans have 20 million olfactory receptors in our nose * dogs have 1 billion
Olfaction
How? Process?
- odorant - molecules that activate an olfactory receptor
- olfactory receptors - sensitive for particular types of odorant molecules
- one cell receives the stimulus and carries signal all the way to the brain
Process:
- Odorant binds to receptor
- activation of receptor causes increased levels of cAMP - second messenger (odorant stays outside)
- cAMP opens Na+ channels
- Na+ influx –> depolarization –> action potential
Distinctness of olfactory receptors
~ 350 different types in humans (mice have 1,000)
- each receptor recognizes a unique aspect of smell
- each type of receptor is found in a limited number of receptor neurons
- each receptor neuron expresses just one type of receptor
*not a 1:1 relationship of smell:receptor
How a “smell” originates
- the combined activity of multiple distinct receptors
- more than one “odor” can activate a receptor
- one odor can activate more than one receptor
- almost infinite combinations
- population coding
- a particular smell = unique combo of receptors activated
Taste Receptor Cells
PAPILLAE - large bumps
–> each papillae has several hundred TASTE BUDS
–> each taste bud has 50-150 TASTE RECEPTOR CELLS
5 Basic Tastes
Bitter
Sour
Salty
Sweet
Umami
5 Types of taste receptor cells
Each cell recognizes one of the 5 tastes: salty, sweet, sour, bitter, umami
Process of Taste Reception
- cause depolarization of cell (NO action potential) (different mechanism of depolarization for each cell)
- depolarization leads to the Ca++ channels to open
- triggers neurotransmitter release onto sensory neurons
- sensory neurons convey the information to the brain via action potential
Transduction for Salty Taste
NaCl/Na+
type of Na+ pump that is always open
- increase in sodium concentration from food
- ions flow across this channel into receptor cell
- depolarization
- ca++ influx
- neurotransmitter release
- other cell carries signal to brain
Transmission for sour taste
H+ - sourness = acidity
- H+ flows in through Na+ channel (and H+ blocks K+ channel)
- depolarization
- Ca++ influx
- neurotransmitter release
- Other cell carries signal to brain
Transduction for bitter, sweet and umami
- molecule binds to outside
- activates second messengers on inside - not ion channels themselves
- second messengers open unique type of Na+ channel
- Na+ flows in = depolarization
- ca++ influx
- neurotransmitter release
- other cell carries signal to brain
Similarities and differences between bitter, sweet and umami receptors
- different types of receptors, same cellular effect
- same intracellular pathway
- expressed on different taste cells, each connected to different target
- for all sensory systems, end product of difference types of stimuli is always the same (neurotransmitter release)
- matter of WHICH cells are activated
Population Coding (for taste)
- gives us infinite flavors from 5 types of taste receptors
- particular combination of different receptors activated (and level of activation) once again gives us large array of possible flavors
- olfaction also influences our taste
Miraculin
- binds to sweet receptors (but does not activate them)
- in the presence of acid changes conformation
- activates the receptors
- sour food tastes sweet
Taste Transduction Summary
Salty: Na+ flows directly into Na+ channels
Sour: protons flow in through the Na+ channel and close K+ channel
Bitter, sweet and umami: receptors that are not ion channels increase levels of second messengers. these open Na+ channels
* for all: depolarization opens voltage gated Ca++ channels and causes neurotransmitter release
Touch
- mechanoreceptors
- physical distortion of plasma membrane causes ion channels to open
- generates depolarization and action potential
- diverse - generates varied sensations
- receptors distributed throughout the body -
respond to different kinds of stimuli (touch, temperature, pain, body position)
Types of touch receptors
- human skin packed with many different types of mechanoreceptors that generate varied sensations
- provide different aspects of sensory information
- sensitivity
- rapid vs slowly adapting (change)
- pressure and vibration
Spatial resolution of touch
Why more sensitive in some places?
- ability to discriminate detailed features of a stimulus varies greatly across different points in the body
- two point discrimination test
- reasons for better resolution
1. higher density of mechanoreceptors
2. enriched mechanoreceptors w/small receptive field
3. more brain tissue devoted to the sensory info of each mm of skin