Three canals connected to the utricle detect movement

Three canals connected to the utricle detect movement and turning of the
head in any direction because hair cells are organized in all directions and
go into a cap called the cupula
- When you spin quite a bit, the cupula becomes stationary as the body
reaches equilibrium and stimulates the sense of dizziness
Hearing and Equilibrium in Other Vertebrates
- Fish do not have an ear that connects to the outside; instead vibrations
travel along skeletal structures to their inner ear
- Fish and aquatic amphibians have a lateral line system that goes along
both sides of their body that detect the water movement against their body
as they swim
Concept 50.3 – Visual receptors in diverse animals
depend on light-absorbing pigments
- Although animals differ in how they sense light, there are similarities that
indicate evolutionary origin
Evolution of Visual Perception
- All light detectors contain photoreceptors , cells that contain light-
absorbing pigment molecules
Light-Detecting Organs

- The simplest light-detecting organ consists of a pair of ocelli surrounded
by darkly pigmented cells that block light so that light can be read only by
the photoreceptors in the ocelli
Compound Eyes
- Insects and crustaceans and some worms have compound eyes
- These consist of several thousand light detectors called ommatidia that
have their own light-focusing lenses and each detect light from a tiny field
- They are especially effective at detecting movement and can see different
colors beyond the visual light range of humans
Single-Lens Eyes
- Single-lens eyes are found in jellies, some worms, spiders, and molluscs
and work somewhat like a camera in that they have a small opening, the
pupil , through which light enters and an iris that contracts and expands to
function like aperture
- All vertebrates have single-lens eyes
The Vertebrate Visual System
- Vision begins when photons of light enter the eye through the pupil and
strike the rods and cones, where the energy is captured in the
reconfiguration of a chemical bond in the retinal
- Images are perceived in the brain, not the eye
Sensory Transduction in the Eye
- Chemical bonding sets off a chain reaction in the retinal that converts cis-
retinal to trans-retinal
- Once light has been converted, enzymes in the retinal change it back to
cis-retinal, but this takes time and can blind you if changes in light occur
drastically and suddenly
Processing of Visual Information in the Retinal
- Processing of visual information begins in the retinal, where cells
depolarize or polarize in response to light
- Sometimes information goes directly from the photoreceptors to bipolar
cells to ganglion cells, or it may go through several sets of rods and
cones, which enhances contrast in what is called lateral inhibition
- The rods and cones that feed information to one ganglion cell are called a
receptive field
o A smaller receptive field results in a sharper image
Processing of Visual Information in the Brain
- The axons of ganglion cells form optic nerves that transmit information to