Sensory Organs Sensory System
Sensory system allows us to experience the world.
Sound of a dog barking
Sudden change in blood pressure
Five Types of Sensory Receptors
Receptor: Specialized area of a sensory neuron that detects a specific stimulus
Pain receptors (nociceptors)
Four Components of Sensation
Two Characteristics of Sensation: Projection and Adaptation
Projection: Brain refers sensation back to its source
Phantom limb pain
with continuous stimulation
, sensory receptors become less responsive.
Receptors vary in their ability to adapt.
Smell and temperature receptors adapt well.
Pain receptors do not adapt at all.
Five General Senses
Pain, Touch, Pressure, Temperature, Proprioception
Pain Receptors or Nociceptors
Consist of free nerve endings stimulated by tissue injury, chemicals, tissue hypoxia
Widely distributed throughout the skin, viscera, other internal tissues
Sites of Referred Pain
Compare heart’s location with possible sites of pain during a heart attack.
Gallbladder attack may present with shoulder pain.
Touch and Pressure Receptors
Touch (tactile) receptors
Found mostly in skin
Located in the skin, subcutaneous tissue, and deep tissue
Receptors for cold and heat
Located in free nerve endings and other specialized sensory cells in the skin
Temperature extremes experienced as pain
Proprioception: Sense of orientation or position in space
Located in muscles, tendons, joints, and inner ear
Sensory information parietal lobe, cerebellum
Five Special Senses
Smell, Taste, Sight, Hearing, Balance
Gustatory Sense: Taste
Taste receptors are chemoreceptors.
Nerve impulses move along three cranial nerves to parietal and temporal lobes.
Olfactory Sense: Smell
Chemoreceptors in nasal tissue
Nerve impulses travel on Olfactory cranial (CN I) nerve to temporal lobe for interpretation
Vision: Sense of Sight
Primary visual structures are the eye and visual pathway.
Visual Accessory Structures
Eye: Organ of Vision
Eyeball: Three Layers
Tough outer layer in posterior eyeball
Forward extension becomes cornea
Extrinsic eye muscles attach here
Middle layer in the posterior eyeball
Forward extension becomes ciliary body and iris
vascular to nourish retina
Inner layer in posterior eyeball
Site of photoreceptors
Exit of CN II
Located on periphery
Responsible for black and white or night vision
Located on central part of posterior eye
Concentrated in fovea centralis in center of macula lutea
Responsible for color vision
Cavities of Eyeball
lens and retina
Contains vitreous humor
Between lens and cornea
Contains aqueous humor
Formation and Drainage of Aqueous Humor
Formed by ciliary body
Circulates through pupil behind cornea
Drains through canals of Schlemm
Muscles of the Eye
Extrinsic muscles: Move eyeball in its bony orbit
Intrinsic muscles: Move structures within eyeball
Extrinsic Muscles of the Eye
Four rectus muscles
from CN III
Three Intrinsic Eye Muscles
Ciliary muscles pull on suspensory ligaments.
Suspensory ligaments pull on lens.
Lens changes shape.
Bending light rays to focus on retina
Lens, primary refracting structure
Focal point on retina
Errors of Refraction
Myopia, focal point in front of retina
Hyperopia, focal point behind retina
Astigmatism, result of irregularly curved cornea
Photoreceptors generate nerve impulse
Nerve impulse travels along CN II to occipital lobe
Occipital lobe “sees” Rover
Lateral fibers of CN II ascend to same side of brain.
Medial fibers of CN II cross to opposite sides, forming the optic chiasm.
The brain sees one image.
How Seeing Occurs
Pathway of light
Cornea aqueous humor pupil lens vitreous humor rods and cones
Pathway of nerve impulses
Rods and cones CN II occipital lobe
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Human head and neck