somatic nervous system & special senses
DESCRIPTION
Somatic Nervous System & Special Senses. Chapter 12 . Special Senses. Part B. Sciences of Special Senses. Ophthalmology – is the science that deals with the eye and its disorders Otorhinolaryngology – deals with all the other senses. . Olfaction: Smell. Sense of smell - PowerPoint PPT PresentationTRANSCRIPT
Somatic Nervous System & Special Senses
Chapter 12
Special Senses
Part B
Sciences of Special Senses
• Ophthalmology – is the science that deals with the eye and its disorders
• Otorhinolaryngology – deals with all the other senses.
Olfaction: Smell
• Sense of smell • Requires 10 million to 100 million
receptors
Structures
• Olfactory epithelium • Located in the upper portion of the nasal
cavity • Consists of three types of cells
• Olfactory receptors • Supporting cells • Basal stem cells
Olfactory Receptors
• Are the stimulated by olfactory hairs, which project from knob-shaped tip of the olfactory receptor• Odorants (chemicals in the air) stimulate
the olfactory hairs • Short life span – only about 1 month
• See nose hairs are good
Supporting Cells
• Columnar epithelial cells of the mucous membrane lining of the nose
• Provide physical support, nutrients, and electrical insulation for the olfactory receptors
•
Basal Cells
• Cells that are responsible for producing new olfactory receptors
Olfactory glands
• Responsible for the production of mucus that moistens the surface the surface of the olfactory epithelium and serves as a solvent for inhaled odorants.
Stimulation of Olfactory Receptors
• Unique because adaptation to a chemical is very rapid• You may smell something bad but over
time if you remain in that environment you won’t smell it anymore.
Hyposmia
• Reduced ability to smell, affects over half of those over the age of 65 and 75% over 80.
• Caused by head injury, Alzheimer’s disease or Parkinson’s disease
• Also by certain drugs, such as antihistamines, or steriods
Gustation: Taste
• Five primary tastes• Sour• Sweet• Bitter• Salty• Umani
Umami
• Describe as a “savory” taste
Taste Buds• Taste buds – are the location of receptors for
taste• Taste buds are found on the papillae, which are
the bumps on the tough
• Number of tastes bud decrease with age• Location
• Mostly on the tongue • Some on the roof of mouth, throat and epiglottis
Tastants
• Chemicals that activate the gustatory receptors
Stimulation
• Tastants are dissolved in saliva which then allows them to enter the pores and come into contact with the gustatory hairs.
• Stimulation of hairs causes an electrical impulse to be sent to the brain
Vision
• More than half the sensory receptors in the human body are found in the eye
• The largest part of the cerebral cortex is devoted to vision
Careers Associated with vision
• Ophthalmologist – physician who specializes in the diagnosis and treatment of eye disorders with drugs, surgery and corrective lenses
• Optometrist – has a doctorate of optometry and is licensed to test the eyes and treat visual defects b y prescribing corrective lenses
• Optician – technician who fits, adjusts and dispenses corrective lenses using the prescription supplied by an ophthalmologist or optometrist
Accessory structures of the eye
• Accessory structures – are eyebrows, eyelashes, eyelids, muscles the move eyeballs and lacrimal (tear) apparatus
Eyelashes and Eyebrows
• Protect the eyeballs from foreign objects, perspiration, and direct rays from sun
Eyelids
• Upper and lower • Shade the eye during rest • Protect eyes from excessive light • Protect eyes from foreign objects • Spread lubricating secretions over the
eyeballs by blinking
Eye Muscles
• Six muscles control the movement of the eyeball • Right, left, up, down and diagonally
Lacrimal apparatus
• Group of glands, ducts, sacs that produce and drain lacrimal fluid as tears
• Lacrimal glands (one for each eye)• About the size and shape of an almond
and are responsible for secreting lacrimal through the lacrimal ducts to the eyeballs
• Tears can also pass through the nasolacrimal duct, which allows lacrimal to drain into your nasal cavity
Lacrimal
• Is a watery solution containing salts, some mucus, and a bacteria killing enzyme called lysozyme
Layers of the eyeball
• Adult eyeball measures about 2.5 cm across
• Three layers • Fibrous Tunic• Vascular Tunic• Retina
Fibrous Tunic
• Outer coat of the eyeball • Consists of
• Cornea – transparent fibrous coating that colors the iris (colored portion of your eye)
• Also helps focus light • Sclera – is the “white” of the eye, dense
connective cove • Gives the shape of the eye, makes it more rigid and
protects inside of eyeball • Conjunctiva – epithelial layer, covers the anterior
surface of eyeball and lines inner surface of eyelid
Corneal Transplant
• If your cornea is damaged it can be replaced with a donor cornea
Vascular Tunic• Middle Layer of the eye• Composed of:
• Choroid – thin membrane that lines most of the internal surfaces of the sclera
• Contains many blood vessels that nourish the retina• Ciliary body – consists of
• ciliary processes, which are folds on the inner surface of the ciliary body whose capillaries secrete a fluid called aqueous humor and the
• ciliary muscles, a smooth muscle that alters the shape of the lens for viewing objects up close or at a distance
• Lens – transparent structure that focuses light rays onto the retina
• Constructed of many layers of elastic protein fibers • Attached to ciliary muscles by zonular fibers
Iris and pupil
• Part of the vascular tunic • Iris
• Colored portion of the eye• Muscle that regulates the amount of light
let into the eye • Pupil
• Hole in the center of the eye through which light enters
Retina
• Portion that lines posterior of the eye about ¾ of the eyeball
• Consists of two layers • Neural layer • Pigmented layer
Neural Layer
• Consists of three distinct layers • Photoreceptor layer • Bipolar cell layer • Ganglion cell layer
Photoreceptor layer
• Two types of cells • Rods – allow us to see shades of gray in
dim light (6 million) • Cones – allow us to see color (120 million)
• Found in central fovea in the center of the macula lutea
Pigmented Layer
• A sheet of melanin is located between the choroid and the neural part of the retina• Melanin absorbs stray light, helping to
keep the image sharp and clear
Pathway
• Photoreceptor layer to • Bipolar cell layer to • Ganglion cell layer to• Optic nerve
Interior of Eyeball
• Two cavities divided by the lens • Anterior cavity • Vitreous cavity
Anterior cavity
• Contains aqueous humor that helps maintain the shape of the eye and supplies oxygen and nutrients to the lens and cornea.
Vitreous Chamber
• Contains the vitreous body, which helps maintain the shape of the eyeball and keeps the retina attached to the choroid• Vitreous body – develops in embryonic life
and is not replaced • Choroid – provides blood supply and
absorbs scattered light
Intraocular pressure
• Pressure in the eye • Maintains the shape of the eye • Keeps the retina pressed against choroid
• Normal pressure is 16mm of Hg