Sensory Systems
What is the pathways for sensory systems?
- Physical stimulus interacts w/ receptors in the periphery.
- Signals are transduced and encoded into electrical signals from physical signal
- Electrical signals are relayed via synaptic transmission to higher order brain centers which eventually gives rise to consious perception. (actually smelling the scent)
Sensory Systems
What are the 4 qualities of sensory stimulus?
- Modality
- Location
- Intensity : firing rate
- Duration
Basics of Olfaction and the Olfactory Epithelium
What does the olfactory system do? What exactly are odorants?
Olfactory system process info about the identity, concentration, and quality of odorants which are small, volatile molecules.
Basics of Olfaction and the Olfactory Epithelium
What do we smell with?
Hint: Not the Nose
Olfactory Epithelium,
* Odorants interact with receptors or bind to receptors in the OE and are transduced and turned into electrical signals.
Humans have 12 million Odorant receptor neurons (ORNs)
Basics of Olfaction and the Olfactory Epithelium
What is the Cribiform plate?
A thin sheet of bone through which small clusters of axons penetrate to get to olfactory bulb.
Basics of Olfaction and the Olfactory Epithelium
What are the three main cell types and functions in the Olfactory Epithelium?
- Olfactory receptor cells (Odorant receptor neurons: ORNs)
- Supporting cells - Some may produce mucus
- Basal Cells (Stem Cells) - Source of New receptor cells
Basics of Olfaction and the Olfactory Epithelium
Describe the dendrites of the ORNs
ORNs have a single dendrite from which cilia protrude.
* Receptors are on cilia, not soma
Basics of Olfaction and the Olfactory Epithelium
What are the characteristis of the olfactory axons?
Thin, Unmyelinated
Basics of Olfaction and the Olfactory Epithelium
Which of the following statements about the OE is true?
a. Basal cells produce mucus and are affected by COVID.
b. Olfactory axons are large diameter and heavily myelinated
c. Receptors for odorant molecules are located on the cilia of Odorant receptor neurons (ORN)
d. Odorant receptor neurons have mutliple dendrites from which cilia protrude.
a. Basal cells produce mucus and are affected by COVID. Support cells are affected by COVID, not basal cells.
b. Olfactory axons are large diameter and heavily myelinated. Thin & unmyelinated
c.** Receptors for odorant molecules are located on the cilia of Odorant receptor neurons (ORN)** True!!!
d. Odorant receptor neurons have mutliple dendrites from which cilia protrude. Single dendrite
Olfactory Transduction
What are the steps of Olfactory Transduction?
In Your own words!
- Odorant receptor (GPCR) binds to Odorant NT.
* G- protein is called **Golf **(unique to olfactory system)
* Golf alpha and beta subunits dissociates upon odorant binding - Golf alpha stimulates adenyly cyclase (AC) which produces** Camp**
- Increased Camp opens a cAMP-gated cation channel
* leads to influx of Na+ and Ca2+ - Ca2+ then activated Cl- channel to open leading to the efflux of Cl-, therefore the cell starts to becoming more positive b/c negative ions are leaving the cell.
* This depolarizes the cell leading to action potential
* The signal then travels in the olfactory bulb.
Olfactory Transduction
What are ways Olfactory response might terminate?
- Diffuse Away or broken down by mucus (imagine being stuffy)
- Adaptation- Decreased response despite the continued presence of a stimulus. Ex. Being in a room and getting used to the scent.
Olfactory Transduction
A Mutation in Adenylyl cyclase in ORNs causes them to be constantly active. Which of the following is not true regarding signal transduction in these ORNs?
a. There is less Na+ and Ca2+ entering the ORN compared with a wildtype ORN.
b. Cl- efflux from the ORN will be increased compared with a wild-type ORN
c. The ORN will fire more APs compared with a wild-type ORN
d. There is more Na+ and Ca2+ entering the ORN compared with a wildtype ORN.
e. cAMP levels will be increased compared with a wild-type ORN.
**a. There is less Na+ and Ca2+ entering the ORN compared with a wildtype ORN. **
b. Cl- efflux from the ORN will be increased compared with a wild-type ORN
c. The ORN will fire more APs compared with a wild-type ORN
d. There is more Na+ and Ca2+ entering the ORN compared with a wildtype ORN.
e. cAMP levels will be increased compared with a wild-type ORN.
**More AC means that there would be more Na+, Ca2+ entering and more Cl- leaving the cell and more cAMP. **
Olfactory Transduction
Describe the receptor and ordorant relationship?
- Individual receptors are randomly scattered
- **Each odorant activates multiple receptors
- Each receptor responds to multiple odorants. **
- A single ORN expressing a single receptor can respond to multiple ordorants
Olfactory Transduction
What is population coding?
Population coding is a method to represent stimuli by using the joint activities of a number of neurons. In population coding, each neuron has a distribution of responses over some set of inputs, and the responses of many neurons may be combined to determine some value about the inputs.
Olfactory Transduction
You provide an antagonist that binds to only one type of olfactory receptor in the OE. Which of the following is the likely effect on the sense of smell?
a. Affects the sense of only one odorant
b. Complete anosmia
c. Affects the sense of several odorants
d. normal sense of smell
a. Affects the sense of only one odorant
b. Complete anosmia
c. Affects the sense of several odorants
d. normal sense of smell
Each receptor responds to many different ordors.
Central Olfactory Pathways
What are glomeruli and what do they represent?
Glomeruli are found on the surface of the olfactory bulb and are critical structures for transducing olfaction.
Each glomerulus recieves input from receptor cells expressing a specific receptor gene
Olfactory tracts are formed from glomerlus that lead to the olfactory cortex.
Central Olfactory Pathways
Why does the axons not go through the thalamus since it is known as the gateway to cortex?
Axons go striaght to the cortex from mitral cells because the outputs has a number of different targets. This is only unique to the olfactory system.
Central Olfactory Pathways
Describe the characteristics of a correct receptor neuron to glomeruli in the olfactory bulb.
Same color ORN is going to project to the same color glomerilus and at the level of individual cilia, the’re going to express the single receptor gene.
**Each ORN expresses one gene
and the colors need to go to the same glomeruli. **
Central Olfactory Pathways
What are the major pathways
- **Olfactory receptors–>Olfactory Bulb—>Piriform Cortext **or Olfactory Tubercule or Amygdala or Entorhinal cortex —> Orbitofrontal cortex or thalamus or hypothalamus or Hippocmpal formation.
Olfactory Maps & Anosmia
What are olfactory or sensory maps?
An ordered arrangement of neurons that correlates with features of the environment
Neurons in a particular place respond to a specific odor.
Olfactory Maps & Anosmia
What is anosmia?
Inability to smell.
Causes: Damage to olfactory nerve, tumore compressing olfactory nerve.
People with anosmia cannot smell: baby powder, chocolate, cinnamon, coffee, mothballs, peanut butter, and soap.
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Chapter 2: Neurons & Glia81
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Chapter 3: Resting Membrane Potential34
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Chapter 4: The Action Potential34
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Chapter 5: Synaptic Transmission44
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Chapter 6: Neurotransmitter Systems73
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Chapter 7: The Structure of the Nervous System79
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Chapter 8: Olfactory21
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Chapter 9: The Eye21
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Chapter 12: Somatic Sensory System37
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Guest Lecture: Infectious Diseases35
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Chapter 13: Spinal Control of Movement31
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Chapter 14: Brain Control of Movement31
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Chapter 15: Chemical Control of the Brain and Behavior64
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Chapter 22: Mental Health25
