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9.5: Sensory Information (Vision)Pages 438 - 444
Recap
•Anatomy of the nerve cell•Electrochemical Impulse•Synaptic Transmission•CNS (Brain and Spinal Cord structure and
function)•Autonomic Nervous System
▫Sympathetic and Parasympathetic Nervous Systems
•Natural/Artificial Pain Killers
Sense and Perception
• All sensory responses convert one source of energy into another
• Taste and Smell: chemical stimuli are converted to nerve action potentials
• Touch: mechanical stimuli are converted to nerve action potentials
Sense and Perception
• Vision: light stimuli are converted to nerve action potentials
• Balance: mechanical energy and gravitational energy converted to nerve action potentials
•Sensory receptors: modified ends of sensory neurons that are activated by specific stimuli
•Much of the environment remains undetected
•What we detect is what is relevant to our survival
•For example: ▫Electromagnetic Spectrum▫Sound Frequency
Sensory Adaptation
•Occurs once the receptor becomes accustomed to the stimulus
•The neuron ceases to fire even though stimulus is still present
•This adaptation indicates that the new environmental condition is not dangerous
Example of Sensory Adaptations Clothes• Touch receptors in the skin
are usually stimulated when you put on or take off clothes
• Sensory information is not continually sent while your clothes are on
Hot-tubbing• Hot at first• Tolerated if
thermoreceptors in your skin are given time to adjust to the stimulus
The Structure of the Eye
•Made of three separate layers – the sclera, the choroid, and the retina
•Sclera is the outermost layer – protective, and maintains eye shape
•The front of the sclera is clear and bulges forward, forming the cornea – the “eye window” that bends light toward the pupil
The Structure of the Eye
Cornea (outer layer)•Requires oxygen and nutrients, but cannot
get these from blood since capillaries would prevent it from being transparent
•Receives O2 in a dissolved form from tears
•Receives nutrients the aqueous humor, a transparent fluid
Bending Light
•http://www.kscience.co.uk/animations/eye.swf
The Structure of the Eye (middle layer)
Choroid Layer•Pigmented granules prevent light from
scattering
Iris•Regulates amount of light entering the eye
Pupil•The opening in the iris that allows light
into the eye
The Structure of the Eye (middle layer)
Vitreous Humour•Maintains the shape of the eyeball and
permits light transmission to the retina
Lens•Forces image on retina
The Retinal Layer (innermost layer)
• The retinal layer is made of three layers of cells:
1.Light-sensitive cells▫ Rod cells▫ Cone cells
2.Bipolar cells3.Cells from the
optic nerve
Rods vs. Cones
Rods•Photoreceptors that operate in dim light
to detect black and white
Cones•Photoreceptors that operate in bright
light to identify colour
Protanomaly or “Red Weakness”
Blind Spot
•No rods or cones in the area in which the optic nerve comes in contact with the retina
•Because of the absence of photoreceptive cells, this area is called your blind spot
Figure 3. page. 440 shows how the nerve carries the impulse to the central nervous system (occipital lobe)
Pathway: From Retina to Brain
•Once excited, the nerve message is passed from rods and cones to bipolar cells
•Biopolar cells relay message to the optic nerve
•Optic nerve carries message to CNS
How Vision Works
•Video