Somatic & Special Senses

Types of Sensory Receptors

1. Chemoreceptor-Stimulated by changes in chemical concentrations

of substances

2. Pain receptor-stimulated by damage to tissue

Types of Receptors Cont’d

3. Thermoreceptor-stimulated by changes in temperature

4. Mechanoreceptor - Stimulated by changes in pressure or movement

5. Photoreceptor - Stimulated by light energy

Why are you not aware of every sensory input every minute?

• As you sit in this classroom, why are you not always 100% aware of the clock ticking or the air conditioner running?

– Sensory Adaptation- brains ability to prioritize sensory input it receives and ignore unimportant stimuli.

Sensations

• Definition: A feeling that occurs when the brain interprets sensory impulses.

• Projection: the brain causes a sensation to seem to come from the region of the body being stimulated.

Somatic Senses

• Somatic Senses are associated with receptors in the skin.

• Out of the 5 types of receptors, which ones do you think could be stimulated by the skin?– Mechanoreceptor – Thermoreceptor– Pain Receptor

Mechanoreceptors- Touch & Pressure Senses

1. Free nerve endings

2. Meissner’s corpuscles- found mostly in hairless parts of skin (ex: lips, fingertips, palms, soles). Respond to light touch.

3. Pacinian corpuscles- found in deeper parts of tissue (ex: tendons & ligaments). Respond to heavy pressure.

Temperature Senses

1. Warm receptors- Most receptive between 77°F to 113°F- Above 113°F stimulate pain receptors burning sensation

2. Cold receptors- Most sensitive between 50°F to 68°F- Below 50°F stimulate pain receptors freezing sensation

** Both receptors adapt quickly. This is why after a while your feeling of warmth or cold will begin to fade.

Pain Receptors

• Protect the body because damaged tissues stimulate them.

• Pain receptors adapt poorly

What is visceral pain?

• Pain that may feel as if it is coming from some part of the body other than the part being stimulated.

• Examples???– Heart: feel pain in left arm• Why does this happen?

– Because pain impulses of the heart travel over the same nerve pathways of the skin of the left arm. Brain (cerebrum) may misinterpret where the source of pain comes from.

Pain Nerve Fibers

• Acute pain fibers- thin, myelinated. Rapid impulses sent shooting pain

• Chronic pain fibers- thin, unmyelinated. Slower impulses sent dull, aching sensation

Regulation of Pain Impulses

• Thalamus- awareness of pain • Cerebral Cortex- determine pain intensity, pain

source, emotional & motor responses to pain.

• Enkephalins & endorphins are released in response to extreme pain & provide natural pain control.– How?

• Bind to neuron receptors/channels…slow down/stop nerve impulses from passing through

Sense of Smell

• Olfactory (smell) receptors are chemoreceptors– Chemicals dissolved in liquids stimulates it.

• In the nasal passage- lots of cilia (hairlike projections) come off of olfactory receptor cells

How it works

• Odorant molecules bind to the cilia in different patterns stimulates cell impulse sent to the brain.– Combinational olfactory code• Example: if there are 10 odor receptors, chocolate

might be receptor 6,7,10 while garlic is 1,3,5

Why do you have to smell deeply for faint scents?

• Olfactory organs & receptors are high in the nasal cavity above where usual inhaled air passes.

Comparing Humans to Animals

• 60% of genes that encode for human olfactory receptor proteins have mutated to be inactive.– Other animals (mice, monkeys, dogs, etc.) have a

higher % of genes encoded to be active– Why could this be?

• Humans do not rely on their sense of smell to find food as much as other animals.

• # of olfactory receptor cells…– Human: 12 million– Bloodhound: 4 billion

Taste

• How many taste buds do we have on the surface of our tongue?– 10,000

• On the roof & walls of throat?– 1,000

• Tiny elevations are called papillae

Taste Receptors

• Each taste bud has 50-150 receptor cells, each replaced every 3 days.

• Taste pore has taste hairs that protrude from the cells.

• Sensory nerves are next to the receptor cells and get stimulated by receptor cells.

Why is saliva important?

• Before a particular chemical can be tasted, it must be dissolved in the watery fluid surrounding the taste buds (saliva)

• Salivary glands secrete saliva.

Taste (Gustatory) Sensations

• Four primary sensations1. Sweet2. Sour3. Salty4. Bitter

**What is the difference between sour & bitter?-sour: lemon -bitter: caffeine

Tongue Mapping• The taste buds on the tongue are, of course, important for the flavor of

food. See if different parts of the tongue are most sensitive to different characteristics of food (i.e., salty, bitter, sour, sweet). Get examples of each of these tastes (for example, salty water, sugary water, vinegar for sour and coffee for bitter).

• PROCEDURE: Dip the toothpicks into the solutions and lightly touch the tongue. Repeat the tests on different portions of the tongue. It may help to drink a bit of water in between tests. Also be careful in testing the back part of the tongue...some people may gag! Are parts of the tongue more sensitive to specific flavors or are all parts of the tongue equally sensitive to the flavors? If so, indicate on a drawing of the tongue the areas that are most sensitive to the different tastes. Compare tongue drawings with tongue drawings from other people.

Where are each of these sensations predominate on the tongue?

What is that flavor??

• Flavors result from a combination of primary sensations.

• Also involves smelling & feeling the texture & temperature of foods.

• Some foods may also stimulate pain receptors to give a burning sensation

Relationship Between Smell & Taste

• Both chemoreceptors• Function closely together & aid in food

selection• Both smell & taste adapt rapidly– This is why you do not lose the taste of something

as you eat it b/c it stimulates different receptors on your tongue

Sense of Sight

Eye Structure

A. Visual Accessory Organs– Assist the eye in providing vision

• Eyelids & Lacrimal apparatus– Protect the eye

• Extrinsic muscles– Move the eye

The Eyelid

• Has 4 layers– Skin

• Thinnest skin of the body– Muscle

• Open & close eye– Connective Tissue– Conjunctiva

• Mucous membrane that lines the inner surface of the eyelids and folds back to cover the anterior surface of the eyeball, except for the cornea.

Lacrimal Apparatus

• Lacrimal Gland: Secretes tears• Series of ducts: carry tears to nasal cavity

Tears are secreted continuously to lubricate the surface of the eye and lining of the lid.– Tears drain into nasal cavity

Tears also contain an enzyme, Lysozyme, which reduced the risk of eye infection.

Extrinsic Muscles

• 6 types which rotate the eye in various directions.1. Lateral rectus2. Medial rectus3. Inferior rectus4. Superior rectus5. Inferior oblique6. Superior oblique

Eye Structure

• Hollow, spherical shape• 2.5 cm in diameter• Has 3 distinct layers & spaces between– Outer (fibrous) layer– Middle (vascular) layer– Inner (nervous) layer

Eye Structure

• B. Outer Layer– Cornea: tissue that is the window of the eye &

helps focus entering light rays• It is clear because it contains few cells & no blood

vessels– Sclera: white portion of the eye which protects the

eye– Optic Nerve

Eye Structure

C. Middle Layer Choroid coat: joined to the sclera,

honeycombed with blood vessels to nourish surrounding tissue. – contains many pigment-producing melanoncytes.• What do you think these pigments are called?

– Melanin: these pigments absorb extra light & help keep inside the eye dark

Eye Structure

C. Middle Layer• Ciliary Body: thickest part of middle layer

which forms a internal ring around the front of the eye.

• Lens: located directly behind pupil & held in place by suspensory ligaments.– Ciliary muscles & suspensory ligaments attached

to the lens allow accommodation occur.

What is accommodation?

• The ability of the lens to adjust shape to facilitate focusing– When lens flatter (more concave) your eye is

focusing on distant objects– When the lens is more convex your eye is focusing

on closer objects.

Eye Structure

C. Middle Layer• Iris: colored portion of the eye which lies

behind cornea & lens. It divides the space in the eye into anterior chamber & posterior chamber.

• Aqueous humor: secretes watery liquid into posterior chamber.

Eye Structure

C. Middle Layer• Pupil: a circular opening in the center of the

iris– Smooth muscles of the iris determine the size of

the pupil• Circular set: contracts with bright light (pupil gets

smaller less light enter)• Radial set: contracts with low light (pupil gets bigger

more light enters)

Light Experiment

• Look at your partners’ pupil as I turn on the lights. What happens to them? Why?

Eye Structure

D. Inner Layer• Retina: tissue on the back

of the eyeball which contains visual receptor cells (photoreceptors)

• Fovea Centralis: region in the retina that produces the sharpest vision.

Eye Structure

D. Inner Layer• Optic Disc: nerve fibers from the retina leave

the eye and join the optic nerve. It contains a central vein & artery. – There are NO receptor cells here.– Known as the blind spot• Can you find your optic disc?

Eye Structure

D. Inner Layer• Vitreous humor: jellylike fluid that fills the

posterior chamber. It supports internal parts of eye & help maintain its shape.

Label This Diagram

Light Refraction

• Light waves enter the eye an image of the object is focused on the retina.

• Refraction is the bending of these light waves as focusing occurs.

• The resulting image formed on the retina is upside down & reversed from left to right.– The visual cortex interprets the proper position.

Visual Receptors

• Located in a deep portion of the retina• Stimulated only when light reaches them

• Two Types:– Rods– Cones

Rods

• One type• Provide black & white vision• 100x more sensitive to dim light without color.• Provide more general outlines of objects than sharp

images.– This is because the nerve fibers from many different rods

converge and travel to the brain on the same nerve fiber.– Because of this the brain cannot tell where exactly

stimulus is.

Cones

• 3 types• Colored vision• Provide sharp images because each cone has its

own sensory nerve fiber which travels to the brain. – The brain can pinpoint where exactly a stimulus is

coming from.• Fovea centralis (area of sharpest vision) contains

ONLY cones.

Visual Pigments

• Both rods & cones contain light-sensitive pigments that decompose when they absorb light.

• Rhodopsin: light-sensitive pigment in rods.– When light hits it breaks down into opsin– An enzyme will be activated changing the

permeability of cell membrane nerve impulse– Opsin will revert back into rhodopsin

Visual Pigments• Light-sensitive pigments in cones are retinal

and protein.– Each pigment is sensitive to one of these colors• Red• Green• Blue

– The color a person perceives depends on which set of cones or combination of sets the light in the given image stimulates.• For example: if sense all cones white; no cones black• Color blindness results from lack of different types of

cone pigments.

Visual Nerve Pathways

• Retina Optic Nerve Visual Cortex

• Optic Chiasma– Nasal (medial) half of eye crosses over to other

part of the brain.

Optical Illusions

Prepare to be amazed…

Longer or Shorter?

Which has a larger center?

Look at the white dots…how many grey dots do you see?

Are those lines bent?

Look at dot for 20 sec. What happens?

How many colors does this flag have?

Do the grey lines slope up and down?

Eye Videoclips

• http://www.youtube.com/watch?v=nspVjwAnGb4&feature=related (how eye works)

• http://www.youtube.com/watch?v=yw1ByhaSvHo&feature=related (how night vision works)

The Ear

Outer (External) Ear

1. Auricle (pinna)2. Auditory Canal (External Acoustic Meatus)3. Eardrum (tympanic membrane)

Functions of External Ear

1. Aurical: structurally designed to collect sound waves and direct them inward, into the ear canal.

2. Auditory canal: The combination of hair and wax prevents entry of dust and foreign particles into the ear.

3. Ear Drum: Cone shaped thin layer of skin with mucous membrane inside. It is the surface that vibrates when sound waves strike it and changes pressure.

• Label on the diagram each of the outer ear parts

Middle Ear

• Contains 3 small bones called auditory ossicles1. Malleus2. Incus3. Stapes

• These bones bridge the eardrum to the inner ear, transmitting vibrations between the parts.**think of it like the wave: when the eardrum vibrates,

the malleus then vibrates, then incus, then stapes **

• Label on the diagram each auditory ossicle

Auditory Tube

• Also known as eustachian tube• Connects middle ear to throat• Helps maintain equal air pressure on both

sides of the eardrum

Can’t Pop Your Ears?

• When you are changing altitude, the pressure changes outside your ear drum.

• For example: high to low altitude causes increased pressure outside the eardrum. This will cause the eardrum to push inward & impair hearing.– The auditory tube will eventually come into play &

equalize the pressure on both sides aka popping your ears.

Inner Ear

• Osseous labyrinth• Membranous labyrinth- inside the osseous

labyrinth

• The labyrinths have many parts:1. 3 semicircular canals- provide a sense of equilibrium2. Cochlea- functions in hearing3. Organ of Corti- (in cochlea) contains hearing

receptors

Ear fluids

• Between osseous labyrinth & membranous labyrinth = perilymph

• Inside the membranous labyrinth = endolymph

Oval Window

• Stapes (bone in middle ear) is attached to this part of the inner ear. Vibrations in stapes will move fluid within inner ear stimulate hearing receptors

Steps in the generation of sensory impulses from the ear

1. The aurical collects the sound waves and transmits them through the auditory canal to the ear drum.

2. The ear drum vibrates with the sound waves frequency, converts sound waves into mechanical vibrations.

3. Its vibrations are imparted to the ear ossicles (malleus, incus and stapes).

4. The stapes relays the sound waves to the oval window membrane which causes vibrations of the perilymph in the semicircular canals.

5. Sensory (hair) cells in the organ of corti are stimulated by the vibrations travelling in the fluids and send nerve impulses via the auditory nerve to the temporal area of the cerebral cortex.

6. The neurons of the temporal cortex are stimulated and the interpretation of the impulses by the brain results in hearing.

Steps in the generation of sensory impulses from the ear

Hearing Loss Example

• http://www.youtube.com/watch?v=1EJ4g3J6cJM&feature=related

News: Health Loss in Teens

• http://www.youtube.com/watch?v=J33mELqo42A

• Swimmer’s Ear• Deafness or Hearing Impairment• Broadly speaking, there are two types of hearing impairment -

nerve loss (sensorineural) and conduction loss.• 1. Sensorineural hearing loss: Damage to cochlea or auditory

nerve prevents the sound waves from being converted into electrical signals and relayed to the brain.

• 2. Conduction hearing loss: Sound waves are blocked in either the outer or mid{dle} ear and hence cannot be transmitted to the inner ear.

• A ruptured eardrum, excessive bone growth of the ossicles, or blockage in the ear canal could be the cause of this impairment.