Biology - Lecture 10 (The Chemical Senses)
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- Created on: 11-04-16 22:05
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- Lecture 11 - The Chemical Senses
- Senses
- Sense organs: structures specialised for detecting particular types of stimuli
- Sensory receptor neuron: converts stimulus into electrical signal
- Receptor neurons have cilia at one end; they receive info through receptors. They output their processing at synapses
- Sensory transduction: conversion of stimulus energy into electrical signal
- Sensory stimulus induces ion channels to open, depolarising the cell membrane
- Sensory (afferent) pathways to the cortex
- Information travels from the sense organ to the brainstem, tectum, thalamus, cortex
- Information from the left side crosses to the right side of the brainstem and vice-versa
- Information travels from the sense organ to the brainstem, tectum, thalamus, cortex
- A nerve is a bundle of axons. Afferent (or sensory) nerves carry information from sensory receptors towards the brain
- The principle that sensory info remains segregated along entire pathways is often described as labelled lines
- Gustation
- Five types of taste:
- Sour, bitter, salty, sweet / umami
- Five nutritional categories:
- Sour: acid (not good for digestion). Bitter: poisonous. Salty: NaCl (ions needed for cell function). Sweet/umami: sugar/protein (needed for energy/growth)
- The tongue is the taste organ. Taste buds found on papillae.
- Saliva carries tastiest through taste pore into taste bud. Each taste bud contains 50-150 taste receptor cells
- Sensory receptors are on the apical end of the cell. Action potentials and neurotransmitter release occurs in the basal end of the cell
- Membrane depolarisation or second messengers in cytoplasm travel from apical to basal end
- Two tastes triggered by influx of positive tasting ions through channels. The channels remain open.
- Depolarisation occurs when positive ions from the saliva enter through channels reside the receptor cell
- Sweet and umami receptors use combinations of two G-protein coupled receptors.
- Bitter tastes are triggered by a family of G-protein coupled receptors. There are 25-30 different types of T2R bitter receptor
- A taste cell may express more than one type of bitter receptor. But a bitter receptor will never be on the same cell as a salt/sour/sweet/umami receptor
- Bitter receptors at back of tongue can trigger reflexes to prevent food from being swallowed
- A taste cell may express more than one type of bitter receptor. But a bitter receptor will never be on the same cell as a salt/sour/sweet/umami receptor
- Five types of taste:
- Taste
- Taste receptor cells are synapse (using serotonin as transmitter) with primary afferent neurons
- These are organised in three cranial nerves that terminate in the brainstem
- Gagging and regurgitation reflex determined by processing in brainstem. Afferent pathways continue through the thalamus to the cortex
- Hypothalamus activates secretion of digestive fluids. Amygdala processes contextual info for future use
- Taste receptors roles is to monitor nutritional state. Can also aid in long-term learning by providing reward signals
- Senses
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