BBB - lecture 6 - Smell

what is chemoreception?

it is the oldest sensory system, detects presence of specific chemicals → this includes both taste and olfaction (smell) working together to analyse stimuli

properties of olfaction (our sense of smell)?

hardest sense to describe, seems to be about familiarity recognition → chemosignals similar to other senses in those chemicals are translated into nerve impulses

What are olfactory receptors?

receptors related to smell - large, diverse set coded in 350 genes, allowing differentiation of 10,000+ smells → receptors very hard-worked, must be replaced every 60 days → sensitivity of olfactory receptors differs between substances

What 2 segments does the nasal cavity consist of?

respiratory segment, olfactory segment

location and structure of the olfactory segment?

along roof of the nasal cavity, lined with the olfactory epithelium (olfactory mucous membrane - tiny hairs), contains receptors for the sense of smell

Function of the olfactory segment (olfactory epithelium)

the epithelium is a receptor surface where different molecules bind to different receptors → area 2-4cm, dogs/cats have 10x more receptor area, each receptor has short thick dendrite ending in 10-20 cilia that projects into a mucous layer (olfactory mucosa) → chemicals in air dissolve in mucosa to interact with cilia, bipolar cells, size/number varies across species

what is the pathway to brain (olfaction)?

olfactory receptors → olfactory bulbs → range of forebrain areas

How do the olfactory receptors project to the olfactory bulb?

olfactory nerves from the brain are non-myelinated and consists of bundles of slim fibres held together by thin strips of connective tissue, forming the olfactory cranial nerve → receptors form synapses with dendrites of mitral cells at glomeruli → these mitral cells send axons from the bulb to forebrain areas

what kind of forebrain areas do the mitral cells send axons to from the olfactory bulb?

primary olfactory cortex (including pyriform cortex), amygdala, hypothalamus, thalamus, orbitofrontal cortex (secondary olfactory cortex), entorhinal cortex, hippocampus

What are the 3 types of abnormalities regarding olfaction?

anosmia, hyposmia, dysosmia

What is anosmia?

absence of smell - can be anosmic for certain odours, can be temporary or permanent

What is hyposmia?

diminished olfactory sensitivity - this could be a very early sign of Parkinson’s disease

What is dysosmia?

distorted sense of smell - misinterpreted smells or hallucination of smells

more than ___% of humans over the age of 80 have an impaired ability to identify smells

75%

What is another term for the sense of taste?

gustation - allows perception of taste through chemical stimuli

What is the name of the muscular organ which is the primary organ of gustation?

the tongue