Sensory and Motor Mechanisms

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Surrounding water

Lateral line

Lateral line canal

Epidermis

Hair cell

Cupula

Axon

Sensory hairs

Scale

Lateral nerve

Opening of lateral line canal

Segmental muscles

Fish body wall

Supporting cell

Slide 33

The senses of taste and smell rely on similar sets of sensory receptors

In terrestrial animals:

Gustation (taste) is dependent on the detection of chemicals called tastants

Olfaction (smell) is dependent on the detection of odorant molecules

In aquatic animals there is no distinction between taste and smell.

Taste receptors of insects are in sensory hairs called sensilla, located on feet and in mouth parts.

Slide 34

Taste in Mammals

In humans, receptor cells for taste are modified epithelial cells organized into taste buds.

There are five taste perceptions: sweet, sour, salty, bitter, and umami (elicited by glutamate).

Each type of taste can be detected in any region of the tongue.

When a taste receptor is stimulated, the signal is transduced to a sensory neuron. Each taste cell has only one type of receptor.

Slide 35

Smell in Humans

Olfactory receptor cells are neurons that line the upper portion of the nasal cavity.

Binding of odorant molecules to receptors triggers a signal transduction pathway, sending action potentials to the brain.

Slide 36

Smell in humans

Olfactory bulb

Odorants

Bone

Epithelial cell

Plasma membrane

Odorant receptors

Odorants

Nasal cavity

Brain

Chemo- receptor

Cilia

Mucus

Action potentials

Slide 37

Similar mechanisms underlie vision throughout the animal kingdom

Many types of light detectors have evolved in the animal kingdom.

Most invertebrates have a light-detecting organ.

One of the simplest is the eye cup of planarians, which provides information about light intensity and direction but does not form images.

Slide 38

Eye cup of planarians provides information about light intensity and direction but does not form images.

Nerve to brain

Ocellus

Screening pigment

Light

Ocellus

Visual pigment

Photoreceptor

Slide 39

Two major types of image-forming eyes have evolved in invertebrates: the compound eye and the single-lens eye.

Compound eyes are found in insects and crustaceans and consist of up to several thousand light detectors called ommatidia.