Sense Organs

Mr. Hunter04-01-13

Kennedy High School

Anatomy and Physiology 04/04/2013

• Objective(s)• SWBAT• Compare and Contrast general and specialized sense organs• Describe the structure and functions of various parts of the

eye?

• Bell Ringer: What causes an optic disc (blind spot) to occur? Pg. 212 text.

Sense Organs• Besides the eyes, ears, nose and

taste buds, millions of other sense organs are located throughout the body in our skin, internal organs and muscles.

• Many receptors allow us to respond to internal and external stimuli. The receptors are located on the tips of dendrites of sensory neurons.

• Our ability to sense changes in our environment is a requirement for maintaining homeostasis.

Classification• General sense organs are microscopic

receptors widely distributed throughout the body in the skin, muscle, tendons joints and other internal organs.

• They are responsible for pain, temperature, touch and pressure.

• Special sense organs such as those responsible for smell, taste, vision, hearing and equilibrium are grouped into localized areas.

• Classification of individual receptor cells can be (1) encapsulated or unencapsulated and (2) types of stimuli that activate them.

• All sense organs must be able to detect changes in the environment.

General Sense Organs

• Various receptors are found and they do not all respond to the same type of stimulus.

• Mechanoreceptors – activated by mechanical stimuli that distort or change the position of the receptors.

• Ex. Lamellar (Pacini) corpuscle senses deep pressure.

• Free nerve endings associated with light touch:

a. Hair root plexus – basketlike nerve endings that encircle hair follicles.

b. Merkel disks – attached to nerve endings of the epidermis.

General Sense Organs

• Proprioceptors – near junction between tendons and muscles.

• They provide information about the position or movement of different parts of the body as well as the length and extent of contraction along with muscle tension. Ex. Golgi tendon organs.

Review 04/02/2013 Anatomy and Physiology

1. What two classes of stimuli does our sense organs allow us to respond to?

2. Where are sensory receptors located?3. Where are general sense organs located?4. What is a requirement for maintaining homeostasis?5. What types of sensory information are general sense organs

responsible for?6. What type of sensory information are specialized sense organs

responsible for?7. What are the two classifications of individual receptor cells?8. How are mechanoreceptors activated?9. Describe two free nerve endings associated with light touch.10. What are the functions of proprioceptors?

The Eye

• When you view a person’s eye, you are only able to see a small portion of the whole eye.

• Three layers of tissue form the eyeball.

• A. sclera• B. choroid• C. retina

• The outer portion of the sclera consists of tough fibrous connective tissue.

• The “white” of the eye is part of the front surface of the sclera.

• The other part of the front surface is called the cornea.

The Eye• The cornea lacks blood and lymph

vessels which contributes to its transparency.

• Inflammation of the cornea is called keratitis.

• The cornea, at first glance, does not appear to be transparent because it lies over the colored, muscular portion of the eye, the irs.

• The conjunctiva is a mucous membrane that lines the eyelid and covers the sclera in front. Inflammation of the conjunctiva is called conjunctivitis.

The Eye

• The middle layer of the eyeball is the choroid. It contains a dark pigment to prevent scattering of light rays.

• Two involuntary muscles make up the front part of the choroid.

• A. Iris• B. Ciliary muscle• The black center of the iris is called

the pupil. It is a hole in the doughnut-shaped muscular iris.

• When certain fibers of the iris contract , the pupils will dialate, allowing more light to enter.

• Other fibers contract, letting fewer light rays enter.

The Eye• The lens of the eye is directly behind

the pupil. It is held in place by a ligament attached to the ciliary muscle.

• When we look at distant objects, the ciliary muscle is relaxed, and the lens has only a slight curved shape.

• To focus on near objects, the ciliary muscle must contract.

• As it contracts, it pulls the choroid coat towards the lens, causing the lens to bulge and curve to bring the object into focus.

• Presbtopia is a condition where the lens lose some of their elasticity and cannot bulge to focus objects.

The Eye

• When over exposure to UV radiation occurs, the lens of the eye can be hard and lose its transparency. The result is a milky film that permanently covers the lens.

• This condition is known as cataracts.• It can occur in one or both eyes. • It tends to be progressive and could

eventually lead to blindness.• The retina is the innermost layer of

the eye. It contains photoreceptor cells called rods and cones.

• Dim light can stimulate the rods and bright light can stimulate the cones.

• There are three kinds of cones sensitive to red, blue or green light

The Eye

• Yellowish area near the center of the retina is called the macula lutea.

• It surrounds a small depression called the fovea centralis. This location contains the greatest concentration of cones of any area of the retina.

• Fluids fill the hollow inside of the eyeball. They maintain the normal shape of the eyeball and help to refract light rays – they bend light rays and help them to focus on the retina.

• Aqueous humor is the fluid in the anterior chamber.

• This fluid is drained and replaced constantly. If there is a build up of this fluid pressure, glaucoma can occur.

• Vitreous humor is the jelly-like fluid located in the posterior chamber behind the lens.

The Eye

• Light enters the pupil and is refracted so that it is focused on the retina.

• The rods and cones respond to a light stimulus by producing a nerve impulse.

• Nerve signals leave the eye via the optic nerve located on the posterior surface of the eyeball. No rods or cones are located in this area where the optic nerve exits. This is the blind spot known as the optic disc.

• The optic nerve exits and enters the occipital lobe in the visual cortex.

The Ear

• In addition to the function of hearing, the ear also helps to maintain equilibrium and balance.

• Physical forces that involve sound vibrations and fluid movements are responsible for initiating nerve impulses eventually perceived as sound as balance.

• The ear is divided into anatomical areas.

• External Ear• Middle Ear• Inner Ear (internal ear)

The Ear

• The external ear has two parts:

• Auricle (pinna)• External auditory canal

• The auricle is the appendage on the side of the head surrounding the external auditory canal.

• The canal is a curved tube, approximately 1 inch in length. It extends into the temporal bone and ends at the tympanic membrane (eardrum) – partition between external and middle ear.

The Ear

• The outer third of the skin of the auditory canal contains numerous short hairs and ceruminous glands.

• These glands produce a waxy substance called cerumen that may collect in the canal and impair hearing by absorbing or blocking the passage of sound waves.

• Normally sound waves travel through the external auditory canal and strike the tympanic membrane causing it to vibrate.

The Ear

• The middle ear is a tiny, thin epithelium lined cavity hollowed out of the temporal bone.

• It contains three very small bones called ossicles.

• Malleus• Incus• Stapes• The oval window separates • the middle ear from the inner ear.• Movement of the stapes against the oval

window causes movement of fluid in the inner ear.

• Sound waves cause the eardrum to vibrate, the movement is transmitted and amplified by the ossicles.

The Ear

• The eustachian (auditory) tube connects the throat with the middle ear.

• The epithelial lining of the auditory tubes of the middle ear and the throat is made of one continuous membrane.

• A sore throat can spread to produce a middle ear infection – ottis media.

• The activation of specialized mechanoreceptors in the inner ear generates nervous impulses that result in hearing and equilibrium.

Review 04/02/2013 Anatomy and Physiology

1. Name the three layers of tissue that form the eyeball.2. What two structures are located on the front part of the sclera?3. What two physiological factors contribute to the cornea being

transparent?4. What is inflammation of the cornea called?5. Where is the conjunctiva located and what does it cover?6. What is inflammation of the conjunctiva called?7. What is the middle layer of the eyeball called? What does it contain to

prevent the scattering of light rays?8. Name the two involuntary muscles that make of the front part of the

choroid. 9. What is the name of the center of the iris?10. What causes the pupil to dilate and constrict?11. Where is the lens located and what holds it in place?12. What happens to the lens when we look at near and far objects?