Lecture 16: Smell lecture 2 Flashcards
Describe the olfactory bulb projections;
ORNS (Olfactory nerve 1) Olfactory bulb (Lateral Olfactory tract) Olfactory bulb targets; - Pyriform cortex - Olfactory tubercle - Amygdala - Entorhinal cortex
Describe the projections from the olfactory primary targets
- Pyriform cortex
- Olfactory tubercle
- Amygdala
- Entorhinal cortex
All innervate the
- Hypothalamus
- Thalamus
- Orbitofrontal cortex
The entorhinal cortex especially innervates the Hippocampus
The Pyriform cortex especially innervates the
orbitofrontal cortex.
Whats the importance of the entorhinal cortex?
Provides major sensory input into the hippocampus, also receives direct sensory input from olfactory regions
Whats the importance of the limbic system?
A group of neural structures which includes;
- Pyriform cortex
- Olfactory tubercle
- Amygdala
- Entorhinal cortex
Involved in many aspects of memory and emotions
How is the olfactory sense unique among the system?
B/c of its direct and intimate contact with the limbic system
explains why smell has strong emotional associations
What does a functional MRI shown in terms of brain activity to smell?
Different parts of the brain detect pleasant (orbitofrontal cortex) and unpleasant odours (Cingulate cortex)
What are the theories of olfactory perception?
Vibrational Theory
Shape-pattern theory
What is the vibrational theory;
Every perceived molecule has a vibrational frequency, molecules that have the same vibrational Hz will smell the same.
old theory
What is the shape pattern theory;
(dominant biochem theory)
Different scents activate different arrays of ORNs in the olfactory epithelium
A combination of receptor activation is responsible for a given smell
Various arrays produce specific firing patterns of neurons in olfactory bulb which determine the scent we perceive.
Describe the shape pattern theory in terms of receptors;
A odorant can bind the receptor binding site and produce a response, but the intensity of the response will depends on the ‘pattern” matching of receptor-odorant
i.e needs same shape and colour (receptor and odourant), not just shape.
correct shape-pattern = best response
Give rise to odotopic mapping
Describe odotopic mapping using shape-pattern theory
In the olfactory bulb there is shape mapping (same) in the longitudinal plane and pattern mapping (same) in the transverse.
Why is the shape pattern theory good?
Explains why we can detect many odours with only 400 genes.
We can detect a pattern of activity across receptors.
How does intensity influence receptor activation?
Intensity of odorant changes which receptors will be activated
Weak concentrations of odourants will not smell the same as strong concentrations
Therefore specific time order of ORN activation is important
Whats a complication of odour detection?
We rarely smell pure odours, usually mixtures
How do process the components in odorants mixture?
Olfaction is primarily a synthetic sense; but some analytic properties can develop
synthesis; i.e red + green makes yellow light, but in yellow light we cannot detect red or green
Analysis: High and low notes can be played together but we can detect individual notes