The Senses

Sensory Receptors

• When receptors are triggered, they open up Na+ and K+ channels to trigger an action potential

The Sense of Smell

• Odorant molecules enter the nasal cavity and bind to specific chemoreceptors called olfactory sensory cells

• The binding of these molecules trigger ion channels to open, allowing ions to flow, thus creating the depolarization of the membrane

Animation

The Sense of Smell

The Sense of Smell

The Sense of Taste

• Chemicals found in foods bind with specific chemoreceptors (taste buds) on the tongue

Animation

The Sense of Sound

• The auditory system for mammals involves several specialized structures found in the ear– pinna collect and funnels sound waves to the auditory

canal– tympanic membrane (eardrum), vibrates in response

to sound waves. – movements of the tympanic membrane are amplified

through a chain of ossicles that conduct the vibrations to the oval window.

– Movements of the oval window create pressure waves in the fluid-filled cochlea.

animation of the ear

The Ear

• The basilar membrane running down the center of the cochlea is distorted by sound waves at specific locations that depend on the frequency of the sound. Animation

• These distortions cause the bending of hair cells in the organ of Corti, which rests on the basilar membrane.

• Receptor potentials in hair cells cause them to release neurotransmitter, which creates action potentials in the auditory nerve

Animation basilar membrane

Good overview animation

Balance and equilibrium

Your sense of balance relies on the movement of fluid In the sacule and utricle and semicircular canals

• Movement of the head in one plane (static) is monitored by the sacule and the utricle – nerve impulses triggered by movement of otoliths against

hair receptor due to gravity

Balance animation

Balance and equilibrium

• Rotation of the head is monitored by movement of fluid in the 3 semicircular cells and their ampulla

• Movement of fluid causes cillia on the hair cells in the ampulla– Motion sickness is

caused by rapid continuous movement of these fluids

Rotation animation

The Sense of Sight

• The Eye

Photoreceptors (eye)

• The image-forming eyes of vertebrates focus detailed images of the visual field onto dense arrays of photoreceptors that transduce the visual image into neuronal signals.

Eye structure

Focusing

Photoreceptors (eye)

• Vertebrates have two types of photoreceptors, rod cells and cone cells. In humans, the fovea contains almost exclusively cone cells, which are responsible for color vision but are not very sensitive in dim light.

• Color vision is based on the fact that different cone cells contain different isomers of opsin, which give them different spectral absorption properties.

Photoreceptors (eye)

• Photosensitivity depends on the absorption of photons of light by rhodopsin, a photoreceptor molecule that consists of a protein called opsin and a light-absorbing prosthetic group called retinal.

• Absorption of light by retinal is the first step in a cascade of intracellular events leading to a change in the membrane potential of the photoreceptor cell.

Overview animation

Photoreceptors (eye)

• The innermost layer of the retina consists of the ganglion cells, which send their axons in the optic nerve to the occipital lobe of the brain.

• Between the photoreceptors and the ganglion cells are neurons that process information from the photoreceptors.

Photoreceptors (eye)

• When excited by light the photoreceptor cells hyperpolarize and release less neurotransmitter onto the neurons with which they form synapses. They do not fire action potentials.

Excellent overview animation

Homeo & NS Unit Exam

• 39 M.C.

• 4 N.R.

• 1 S.A. (12) marks

• Lots of Structure and function

• Apply knowledge to new situations/conditions