SensesInput into the Nervous System

Senses

Input

• Sensory input begins with sensors that react to stimuli in the form of energy that is transmitted into an action potential and sent to the CNS.

Five Senses

– Touch…Pain/Pressure/Temperature – Vision – Taste– Smell– Hearing & Balance

Somatic Senses

• Pain

• Temperature

• Pressure

Sensory Receptors• Sensory receptors are classified according to the

type of energy they can detect and respond to.– Mechanoreceptors: hearing and balance, stretching.

– Photoreceptors: light.

– Chemoreceptors: smell and taste mainly, as well as internal sensors in the digestive and circulatory systems.

– Thermoreceptors: changes in temperature.

– Electroreceptors: detect electrical currents in the surrounding environment.

Ear

1. Antihelix –

2. Helix -

3. Lobule –

4. Crest of Helix

5. External Auditory Meatus

6. Eardrum - (tympanic membrane)

Continued………

Ear 7. Auditory Ossicles - (malleus), anvil (incus) and stirrup (stapes)

8. Oval Window

9. Cochlea

10.Semicircular Canals

11.Eighth Nerve

12.Eustachian Tube

Ear

Hearing• Hearing involves the actions of the external ear,

eardrum, ossicles, and cochlea. • In hearing, sound waves in air are converted into

vibrations of a liquid then into movement of hair cells in the cochlea.

• This is converted into action potentials in a sensory dendrite connected to the auditory nerve.

• Very loud sounds can cause violent vibrations in the membrane under hair cells, causing a shearing or permanent distortion to the cells, resulting in permanent hearing loss.

Balance, Orientation and Gravity

• Orientation and gravity are detected at the semicircular canals.

• Hair cells along three planes respond to shifts of liquid within the cochlea, providing a three-dimensional sense of equilibrium.

• Calcium carbonate crystals can shift in response to gravity, providing sensory information about gravity and acceleration.

Eye

Photoreceptor Cells

• Retina– Two types of

photoreceptors are located in this area

• Rods-light intensity

more common near the edge of the eye

• Cones-color detection found in the fovea centralis center of the eye

Cones

• Humans have three types of cones, each sensitive to a different color of light:– red– blue – Green

Opsins are chemicals that bind with cone cells to make them sensitive to a particular wave length of light (color)

Vision

• Light reaching a photoreceptor causes the breakdown of the chemical rhodopsin, which in turn causes a membrane potential that is transmitted to an action potential. The action potential transfers to synapsed neurons that connect to the optic nerve. The optic nerve connects to the occipital lobe of the brain.

Electromagnetic Spectrum

Normal Vision

• 20/20 vision is normal visual acuity (the clarity or sharpness of vision) measured at a distance of 20 feet.

• 20/20 vision, you can see clearly at 20 feet what should normally be seen at that distance.

• 20/100 vision, it means that you must be as close as 20 feet to see what a person with normal vision can see at 100 feet.

Common Refractive Errors

• Hyperopia can see well at a distance(farsightedness)

• Presbyopia (loss of focusing ability• Myopia can see items that are close, but

cannot see those far away(nearsightedness).

• Astigmatism (distorted vision)- irregular cornea

• Amblyopia, a serious vision condition commonly known as lazy eye.

Hyperopia

• The eye is shorter than normal close objects are difficult to focus on.

Presbyopia

• The lens becomes rigid and doesn’t change shape as easily as it once did- this makes focusing difficult.

Myopia

The eye is longer than normal- close objects look clear

Astigmatism

• Distorted Cornea

Eye Conditions

• Conjunctivitis (Pink Eye). This term describes a group of diseases that cause swelling, itching, burning, and redness of the conjunctiva

• Fuchs' dystrophy -endothelial cells gradually deteriorate without any apparent reason. The endothelium becomes less efficient at pumping water out of the stroma. This causes the cornea to swell and distort vision.

Eye Conditions

Glaucoma-internal pressure in your eyes increases enough to damage the nerve fibers in your optic nerve and cause vision loss

Cataract-clouding of all or part of the normally clear lens

Macular Degeneration-changes to the macula, a portion of the retina that is responsible for clear, sharp vision

Eye Conditions

Keratoconus-cornea (the front part of the eye) becomes thin and irregular (cone) shaped. This abnormal shape prevents the light entering the eye from being focused correctly on the retina and causes distortion of vision.

• Retinitis pigmentosa-damage the light-sensitive rods and cones

• Simulates eye disorders:http://www.nei.nih.gov/photo/sims/sims.htm