Sensory Receptors; specialized cells that monitor internal and external conditions.

Receptors CNS for interpretation

Adaptation is a decreased sensitivity to the presence of a constant stimulus.

I.e. not feeling your watch; jumping into cold lake (Work of RAS)

Your Senses can be divided into two categories

General Senses – receptors for temperature, pain, touch, pressure, vibration and body positionScattered throughout the body

Special Senses – smell, taste, vision, balance and hearingConcentrated with specific structures, called

sense organs

General Senses• Part of PNS

• Pain Receptors– Common in the superficial portions of the skin,

joint capsules, along periosteum of bones,– Fast pain: carried by myelinated fibers– Slow pain: carried by unmyelinated fibers– Referred Pain: perception coming from other

parts of body; parts of body are connected to by same spinal nerves. I.e. cardiac pain – originates in chest and left arm.

Temperature (thermoreceptors)

• Nerve endings scattered beneath skin surface

• Located in skeletal muscles, liver and hypothalamus as well. Why?

• Receptors RAS system (Working right now in this room!!!)

Touch, Pressure and Position(Mechanoreceptors)

• Respond to stretching, compression, twisting or other distortions of the cell membrane.

3 classes of Mechanoreceptors

• Tactile (touch)

• Baroreceptors (pressure)

• Proprioceptors (position)

Baroreceptors: monitor changes in pressure

• Surround the walls of hollow organs. I.e. blood vessels, lungs, stomach, bladder

• Monitors BP – plays a role in regulating cardiac function and blood flow to tissues

Examples of pressure receptors

Proprioceptors

• Monitors the position of joints,

• tension in tendons and ligaments

• State of muscle contraction

• Lab Activity

Smell and Taste

Chemoreceptors respond to chemical in a water solution.

Olfactory organs – provide a sense of smell•Consists of olfactory epithelium, receptors, supporting cells and basal (stem) cells•Olfactory glands produce a mucus that covers epithelium

•Keeps area moist and free of dust/debris•Solvent that captures and dissolves air borne molecules•Constantly replaced; flushes away old odors

Olfactory Receptors: modified neurons

• An odor causes olfactory receptors to open Na+ channels and change membrane permeability.

• Research in the 1990’s suggests we have 1000 smell genes– Genes only active in nose– Each gene codes for an odor binding protein;

these receptor proteins only allow certain odors to bind to it.

Olfactory Bulb: Cranial Nerve I• Axons leaving bulb travel to the olfactory

cortex of cerebrum, hypothalamus and part of limbic system.

• Elicits emotional responses to odors– Smells associated with danger (smoke, skunk)– Pleasant smells cause increased secretion of

saliva and gastric juice– Unpleasant smells trigger protective reflexes

(sneezing/coughing)Lab Activity

• Tongue contains 3 types of cells: receptor, support and basal cells

• Taste buds are the gustatory receptors distributed over tongue.– Basal cells replace receptors q 7-10 days

• Taste hairs extend from receptor cells and are bathed in saliva

• Dissolved chemicals touch taste hair, causing Na+ channels to open → A.P.

Four Primary Tastes

Sweet – tip of tongue

Salt – lateral tip

Sour – sides of tongue

Bitter – back of tongue

• Taste Receptors respond more to unpleasant stimuli

• Taste buds are monitored by cranial nerve 7 (facial), 9 (glossopharyngeal), 10 (vagus).

• Taste is 80 % smell. • Think of how food

tastes when you have a cold.

• Try This!

• Eyes are hollow organs divided into two cavities.

• Aqueous humor – liquid inside eyeball gives the eye shape

• Wall of the eye contains 3 layers– Fibrous tunic – outer layer– Vascular tunic – middle layer– Neural tunic – inner layer

• Contains– Sclera – white of

eye• 6 eye muscles

attach

• Posterior surface contains blood vessels and nerves

– Cornea – transparent light passes thru.

• Functions– Mechanical support

and some protection

– Attachment site for 6 extrinsic eye muscles

– Assists in focusing

Contains • Iris – contains blood vessels, pigment cells, smooth muscle

– Controls the size of pupil (center of iris) in response to light

• Ciliary body – forms aqueous humor– Glaucoma – increased pressure in eye due to imbalance of A.

humor

• Choroid – delivers oxygen and nutrients to retinaFunctions• Provide route for blood and lymph tissue• Regulate amount of light entering eye• Circulate aqueous humor within eye• Control shape of lens

Contains• Photoreceptors –

respond to light– Rods – light sensitive

– Cones – color vision• 3 types of cones

Red/Green/Blue

• provides perception of color

• Give more clarity than rods

• Fovea – largest concentration of cones; sharpest vision

• Volunteers??? Anyone, Anyone!!

What number do you see?

Red/Green Colorblind?

Optic disc – where the axons from neurons converge, forms optic nerve

No photoreceptors are found here.

LensPrimary function is to focus image on the retinal receptors in the back of eye.Focusing requires two steps•Light is bent when it passes between mediums of varying densities (Physical Science taught us that)•Greatest refraction occurs when light passes thru cornea.•Focal point – when light bends to form a point•Focal Distance – distance between center of lens and focal point.

Close Images – longer focal distance; lens is rounded because ciliary muscles contract.

The closer the source, the longer the focal distance

Distant Objects –Shorter focal distance and flattened lens.

• The lens constantly changes shape to keep the focal distance constant. – Image stays focused on retina.

• I.e. looking at the board and then your paper.

• 20/20 vision means a person can see details at a distance of 20 feet as clearly as the “normal population” would.

Normal Vision; what is happening in the eye.

• Near sighted (myopia) 20/30 vision• Images forms in front of retina• Vision at close range will be normal, because lens

can adjust and round up to focus.

Corrected by wearing a diverging lens!

Far Sighted (Hyperopia)

Eyeball is too shallow

Person can see distant objects; not near objects

Corrected by wearing converging lens!

Lasik Surgery

• The cornea is cut and reshaped by using a laser.

• The purpose is to even out the shape of the cornea so glasses/contacts are not longer needed.

                                    

Corrected Vision with Lasik.

• Once the flap is laid back, the cornea is flatter.

• Used for treating myopia (near sighted).                               

Astigmatism occurs when the cornea is more oval than spherical. The result is an unequal bending of the light

which results in multiple focal points.

                                                  

Test for Astigmatism

To test your vision, stand about 20 feet from the chart. Test one eye at a time. If you see lines grey and other black you have an astigmatism.

3 Sections of EAR

• Organs– Pinna (auricle)– External Auditory Canal– Functions to collect, direct sound waves to ear drum.

Tympanum – ear drum; Auditory Tube (Eustachian tube)

Auditory Ossicles –

1. Malleus (hammer) 2. Incus (anvil) 3. Stapes (stirrup)

• Vestibule – provides sensations of gravity and acceleration

• Semicircular Canals – detect movement of head

• Cochlea – provide sense of hearing

• Hair Cells – receptors of inner ear for sound

How do we hear?

• Sound waves cause the tympanic membrane to vibrate which moves the ossicles. Sound energy are converted to mechanical energy.

• Ossicles transmit the in/out vibrations from tympanic membrane to ear’s inner fluid-filled chamber.

How Do you Hear?

• Sounds set up vibrations in air that beat against the tympanic membrane.

• Vibrations push the ossicles that press fluid in the inner ear against membranes.

• Fluid causes forces that pull on tiny hair cells and stimulate neurons.

• Neurons send impulses to the brain, which interprets them.

Tiny Hair cells are in the cochlea in an area called the Organ of Corti.

Larger view of Organ of Corti.

Maintaining Equilibrium: How does it work?

When the head is upright, otoliths pushes the sensory hairs downward rather than side to side.

By tilting the head, the otoliths move causing the sensory hairs to be distorted. This is sent to the CNS for interpretation.

• Ear responds to various head movements.• Static Equilibrium is controlled by the vestibule.Respond to straight-line changes in speed and direction, but not rotation.

•Dynamic Equilibrium is controlled by the semicircular canals.

•Respond to changes in head position; rotating the head to say no.