Lecture 8 - Sensory Receptors

Sensory Reception

• Each sense is a "modality."
• General receptors are located throughout the body.
• Special receptors are in specific organs, the eye, inner ear, tongue, and nose.
• Transduction includes chemicals, pressure, and vibration.

Gustation (Taste)

• Gustation has five submodalities: sweet Salty, sour, bitter, and umami
• Papillae are present on the tongue, and taste buds are present inside the papillae
• Gustatory receptor cells are in the taste buds
• Salvia contains chemicals that are tasted
• Vallate papillae contain 1/2 of all tastebuds and have ~250 tastebuds each

Salty & Sour

• Salt crystals break into Na+ and Cl-.
• A high concentration of Na+ outside of receptor cells.
• Sodium diffuses into cells causing depolarization.

Sweet and Bitter

• Sweet receptors use G protein coupled receptors.
• A second messenger cascade depolarizes the cell.
• Calcium channels are activated, which releases neurotransmitters.
• Bitter receptors use G protein coupled receptors, cAMP and IP3 & DAG
• Bitter and Hyperpolarize or depolarize receptor cells.
• Taste buds are located near posterior tongue, which contain alkaloids.
• Bitter plant products (coffee, hops, etc.) can be toxic to some organisms and are antibacterial.

Umami

• L-glutamate, protein-rich foods, and MSG are commonly associated with umami flavor
• G proteins are the receptors

After Receptor Cell Depolarization

• Neurotransmitters are released to sensory neurons
• Graded and action potentials
• The Facial cranial nerve is at the anterior 2/3 of the tongue
• The Glossopharyngeal cranial nerve is at the posterior 1/3 of the tongue
• The Vagus nerve facilitates the gag reflex

Olfaction

• Olfaction uses chemical stimuli.
• The superior nasal cavity facilitates smelling
• Molecules dissolve in mucus.
• Binds to transport proteins.
• Transports to receptor dendrites using bipolar neurons
• The signals pass through the olfactory bulb to mitral cells
• Involves the olfactory tract
• Signals go to the cerebral cortex (inferior & middle temporal) then the limbic system
• Does not synapse in the thalamus before the cortex.
• Toxic chemicals can cause damage
• Neurons are replaced by basal cells.

Anosmia

• A person loses their sense of smell
• Trauma can lead to damaged olfactory nerves
• The frontal lobe and ethmoid bone are involved with smelling
• Anosmia can be temporary and caused by respiratory infections and allergies
• Can be caused by toxic chemicals
• Mild loss of taste
• Neurons repair less with age and in the elderly

Audition

• Sound waves cause action potentials
• Sound travels through the ear canal
• Sound passes through the tympanic membrane
• Sound travels through the malleus, incus, and stape to the vestibule and cochlea
• The inner ear is fluid-filled
• Vibrations pass through the scala vestibuli and scala tympani
• Fluid waves bend the basilar membrane.
• Location on the membrane is based on frequency
• Cilia with open ion channels bend towards the longest cilium
• Hair cells are depolarized and create an action potential in the Cochlear nerve
• The signal passes through the Thalamus to the Temporal lobe for Interpretation

Vision - Reception

• Hyperpolarization causes no release of neurotransmitters
• No NTs release causes the releases from inhibition
• Low light can hyperpolarize rods.
• More than one rod is needed to activate a bipolar cell.
• more than one bipolar cell to activate one ganglion cell.
• This effects on visual acuity of low light and peripheral vision?

Overview of sensory modalities including gustation, salty and sour receptors, and sweet and bitter receptors. Discusses taste submodalities, papillae, taste buds, and the role of saliva. Explains the mechanisms of depolarization and neurotransmitter release in taste reception.