The Senses The Olfactory and Optical/Visual Senses (Smell and Sight)

General Senses: Temperature Pain Touch Pressure Vibration Proprioception (body position) –The receptors for these senses are distributed throughout the body

Special Senses Olfaction Gustation (taste) Vision Equilibrium (balance) Hearing –These receptors are located within specific structures

Sensory Receptors Specialized cells that, when stimulated, sends a sensation to the CNS –Simple receptors are free nerve endings –Complex receptors are specialized to respond to only specific stimuli

Sensory Information Relayed by action potentials traveling through sensory fibers (collection of axons) Increase stimulus = Increase frequency of action potentials –Interpreted by the CNS depending on the area of the brain that is stimulated

A reduction in sensitivity in the presence of a constant stimulus –Due to changes in receptor sensitivity or inhibition along the sensory pathway Adaptation

Location: –Nasal cavity on either side of the nasal septum –Inferior to the cribiform plate of the ethoid bone Structure: –Olfactory epithelium Olfactory receptors (neurons sensitive to chemicals) Supporting cells Basal stem cells Olfaction

Secrete mucus to prevent a build-up of dangerous or overpowering stimuli Also keeps the area moist and free of debris Olfactory Glands

Highly modified neurons with elongated cilia (between million receptors in an area 5 sq. cm) Canines have 72 times greater surface area than humans in their olfactory organs = better smellers Receptors

Axons penetrate the cribiform plate Trigger the olfactory bulbs Travel along the olfactory tract Reach the olfactory cortex of the cerebrum Also affect the hypothalamus and parts of the limbic system Olfactory Pathway

How “smell” works

Olfactory stimuli is the only sensory information to reach the cerebral cortex without first synapsing in the thalamus. The connections to the limbic system and the hypothalamus help explain the emotional and behavioral responses triggered by smells. Fun Fact

Visual (the eye)

The Retina The neural tunic: contains several layers of cells, the outermost layer contains the photoreceptors –Photoreceptors: detect photons of light…humans only sensitive to the spectrum of visible light

Rods Do not discriminate color…only provide the CNS with info about the presence or absence of photons Very light sensitive and enable us to see in dim light (enhanced in most animals) Located around the sides of the retina (approx. 12 million)

Cones Color vision- provides info about the wavelength of photons Three types: red, blue, green- in different combinations provide the perception of different colors –Color blindness= one ore more classes of cones are absent or not functioning Located in the macula lutea with the highest concentration in fovea – when you look directly at an object this is where the image falls on the retina

Bipolar Cells Cells that synapse with the rods and cones (roughly 6 million)Cells that synapse with the rods and cones (roughly 6 million) Ganglion Cells Synapse with the bipolar cells and relay information to the brainSynapse with the bipolar cells and relay information to the brain

Horizontal and Amacrine Cells Regulate communication between photoreceptors and ganglion cells, adjust sensitivity of the retina by sending inhibitory or excitatory signals

Optic Disc The origin of the optic nerve, next to the fovea, also has blood vessels and lacks photoreceptors –The blind spot

Lens and Visual Accommodation Accommodation- focusing the image on the retina by changing the shape of the lens –Rounder = focuses the image of a nearby object –Flatter = focuses a distant object

Accommodation Problems Astigmatism: –irregularities in the shape of the lens or cornea

Myopia: –“near-sightedness”; the eye is too deep so images focus in front of the retina Corrected by a diverging lens

Hyperopia: –“Farsightedness”; The eye is too shallow so images focus past the retina Corrected with a converging lens

Masters of Illusion

Focus on the dot and move your head side to side or forward to back…

How many legs does the elephant have?

Stare at the black dot and watch the haze disappear…

Shapes that don’t exist The Kaniza Effect

What do you see?

The Impossible Trident

Straight or Crooked?

Count the Black Dots

Circles or Spirals?

Crooked or Straight?

Optical Illusions in Shapes

Floating Sphere?

Make ‘em stop spinning!!

Image Credits