Touch, Taste, Smell

Cutaneous Senses

Provide information about the outside of the body.

Organic Senses

Provide information about the inside of the body.

Kinesthetic System

Provides information about the posture of the body and whether it is moving.

Meissner’s Corpuscles

Only found in glaberous skin and detect very light tough and localized edge contours (braille).

Thermal Receptors

Temperature-gated ion channels that are activated by cold, heat, or ligands. Capsaicin activates heat receptors and menthol activates cold receptors.

TRPV1

A modified thermal receptor found in birds so that they can’t perceive the heat of spicy peppers.

Nocireceptors

Pain-sensing neurons that respond to pressure or heat. Some have sensors for extracellular ATP which indicates that neighboring cells have ruptured.

Dorsal Column of the Somatosensory Cortex

Carries highly localized touch information that we can use to identify what is touching us and where. First synapses in the medulla then second in the thalamus.

Spinothalamic Tract

Carries poorly localized touch information that we can use to identify how we feel about the touch. First synapses in the spinal cord then in the thalamus.

Tactile Agonsia

Trouble identifying objects by touch alone caused by damage to the parietal lobe. People misidentify objects they can touch but not look at. Can draw an object that they are touching without looking.

Taste Cells

There are 20-150 located in each taste bud and they continuously regenerate. Do not have axons or action potentials and the molecules we taste are the ligands for these receptors.

Sweetness

Detected by a single metabotropic receptor that is activated by sugar. Some bird species and cats lost the gene that encodes the sweetness receptor.

Umami

Detected by a single metabotropic receptor that is activated by glutamate. Highly sensitive to protein-rich foods.

Bitterness

Detected by 25 different metabotropic receptors.

Saltiness

Detected by a single ion channel that is highly permeable to sodium ions.

Sourness

Detected by a single ion channel thatt is highly permeable to hydrogen ions and these taste cells are also responsible for the sensation of carbonation.

Fat

Several metabotropic receptors and fatty acid transporters are thought to contribute to the taste of fat.

What happened when a bitter receptor gene was placed in the part of the genome where the sweet receptor gene normally is?

Animals could no longer taste sugar but enjoyed the taste of the bitter molecule.

What receptors transduce odorants?

Metabotropic g proten-coupled receptors and humans express 400 different types of odorant receptors.

Olfactory Epithelium

Located in the nasal cavity as is where our sense of smell starts.

Glomeruli

Olfactory cells synapse here and processes information from one type of olfactory receptor.

How is olfaction different from the processing of other senses?

It is not relayed through the thalamus and goes directly to the primary olfactory cortex in the temporal lobe.

Pheremones

Molecules released by one animal to signal something to another member of the same species. Behavioral responses to pheremones are innate.

Where are pheremones detected?

The vomeronasal organ.

How do animals pick up pheromones?

Some are picked up in the air but most have to be sniffed upon close contact.

What happens when the vomeronasal organ of a male mouse is damaged?

It will try to mate indiscriminately with male and female mice.

Lee-Boot Effect

Estrous cycling slows or ceases when female mice are housed without males.

Whitten Effect

Exposure to male urine can synchronize estrus among groupes females.

Vanderbergh Effect

Female mice exposed to males usually have an earlier puberty.

Bruce Effect

Exposure to the urine of an unfamiliar male can trigger the termination of a pregnancy.