Study of the Senses: Introduction

Solo Sensory Sit: For this activity, you will find a spot and will sit or lie comfortably for 10 minutes, observing the world around you. Try closing your eyes, plugging your ears, and breathing out of your nose to change the sensory input your body receives.

Solo Sensory Sit Reflection: After your 10 minutes of observation are up, answer the questions below in reflecting on your experience.

1. What did you see?

2. What did you hear?

3. What did you feel?

4. What did you smell?

5. What did you taste?

6. Which of the sensory experiences you had left the strongest impression on you?

Burning Questions:

Write down a few questions that you have about the five senses in the space below.

Study of the Senses: Sight

The eye is a special sense organ for detecting light rays in the environment. The anatomy of the human eye allows light rays to enter the eye and strike photoreceptors, cells which generate nerve impulses that travel to the brain via the optic nerve.

Key structures of the eye:

1. ______--

2. ______--

3. ______--

4. ______--

5. ______--

6. ______--

7. ______--

8. ______--

Physiology of the Human Eye

When we look at an object, light rays pass through the cornea, and as they do, they bend and converge. Further bending occurs as they rays pass through the lens. The shape of the lens changes according to whether we are looking at an object nearby or far away. When looking at a nearby object, the lens rounds so that the light rays are bent a great deal in order to bring all rays to a focus on the retina. In this lab, you will be measuring the ability of your lens to bend (accommodate) in order to view a nearby object.

Where the optic nerve pierces the wall of the eyeball and, therefore, the retina, there are no rod cells and cone cells, and therefore vision is impossible. This is your blind spot. You will be finding your blind spot in this experiment.

Experimental Procedure:

When the eye accommodates in order to see objects at different distances, the shape of the lens changes. The lens shape is controlled by the ciliary muscles attached to it. When you are looking at a distant object, the lens is in a flattened state. When you are looking at a closer object, the lens becomes more rounded. The elasticity of the lens determines how well the eye can accommodate. Lens elasticity decreases with increasing age, a condition called presbyopia. Because of presbyopia, many older people need bifocals to see near objects.

Part 1 – Near Point

  1. Hold a pencil upright by the eraser and at arm’s length in front of one of your eyes.
  2. Close the opposite eye.
  3. Move the pencil from arm’s length toward your eye.
  4. Focus on the end of the pencil.
  5. Move the pencil toward you until the end is out of focus. Have your partner measure the distance in centimeters between the pencil and your eye. ______cm
  6. At what distance can your eye no longer accommodate for distance? ______cm
  7. If you wear glasses, repeat this experiment without your glasses, and note the accommodation distance of your eye without glasses. ______cm
  8. A younger lens can easily accommodate for closer distances. The nearest point at which the end of the pencil can be clearly seen is called the near point. The more elastic the lens, the younger the eye. How old is the eye you tested? ______.
  9. Try testing your other eye. What is the distance at which you lose focus of the pencil? ______cm

Is this the same distance as your other eye? Write a hypothesis to explain your results.

______

Near Point and Age Correlation

Age / 10 / 20 / 30 / 40 / 50 / 60
Near Point / 9 / 10 / 13 / 18 / 50 / 83

Part 2 – Blind Spot

The blind spot occurs where the optic nerves exit the retina. No vision is possible at the location because of the absence of rods and cones.

  1. Hold the figure seen below approximately 30 cm from your eyes. If you wear glasses, keep them on.
  2. Close your right eye.
  3. Stare only at the cross with your left eye. You should also be able to see the circle in the same field of vision. Slowly move the paper toward you until the circle disappears.
  4. Repeat the procedure as many times as needed to find the blind spot.
  5. Then slowly move the paper closer to your eyes until the circle reappears. Since only your left eye is open, you have found the blind spot of your left eye.
  6. Measure the distance from your eye to the paper when the circle first disappeared.
  7. Repeat for your right eye.

Blind Spot

Left eye ______cmRight eye ______cm

BLIND SPOT FIGURE

Study of the Senses: Hearing

Ears contain specialized receptors for detecting sound waves in the environment. They also often function as organs of balance. Sound is collected by the pinna (the visible part of the ear) and directed through the outer ear canal. The sound makes the eardrum vibrate, which in turn causes a series of three tiny bones (the hammer, the anvil, and the stirrup), collectively known as the ossicles, in the middle ear to vibrate. The vibration is transferred to the snail-shaped cochlea in the inner ear; the cochlea is lined with sensitive hairs which trigger the generation of nerve signals that are sent to the brain.

Read the definitions below and label the ear anatomy diagram.

anvil - (also called the incus) a tiny bone that passes vibrations from the hammer to the stirrup.
cochlea - a spiral-shaped, fluid-filled inner ear structure; it is lined with cilia (tiny hairs) that move when vibrated and cause a nerve impulse to form.
eardrum - (also called the tympanic membrane) a thin membrane that vibrates when sound waves reach it.
Eustachian tube - a tube that connects the middle ear to the back of the nose; it equalizes the pressure between the middle ear and the air outside. When you "pop" your ears as you change altitude (going up a mountain or in an airplane), you are equalizing the air pressure in your middle ear.
hammer - (also called the malleus) a tiny bone that passes vibrations from the eardrum to the anvil. / nerves - these carry electro-chemical signals from the inner ear (the cochlea) to the brain.
outer ear canal - the tube through which sound travels to the eardrum.
pinna - (also called the auricle) the visible part of the outer ear. It collects sound and directs it into the outer ear canal
semicircular canals - three loops of fluid-filled tubes that are attached to the cochlea in the inner ear. They help us maintain our sense of balance.
stirrup - (also called the stapes) a tiny, U-shaped bone that passes vibrations from the stirrup to the cochlea. This is the smallest bone in the human body (it is 0.25 to 0.33 cm long).

Physiology of the Human Ear

The process of hearing begins when sound waves enter the auditory canal. The sound waves are detected by the tympanum and amplified by the ossicles. The last ossicle, the stirrup, strikes the oval window of the cochlea. As a result of the movement of the fluid within the cochlea, the hair cellsare stimulated. The hair cells are sensory receptors that cause nerve impulses to be conducted to the cochlear nerve to the brain.

Humans locate the direction of sound according to how fast it is detected by either or both ears. A difference in the hearing ability of the two ears can lead to a mistaken judgment about the direction of sound. Both you and a laboratory partner should perform this experimental procedure on each other. Enter the data for your ears – not your partner’s.

Experimental Procedure:

  1. Ask your partner to be seated, with eyes closed.
  2. Strike a tuning fork or rap two spoons together at each of five locations listed in number 4 in a random order.
  3. Ask your partner to give the exact location of the sound in relation to his or her head.
  4. Record your partner’s perceptions when the sound is:
  1. directly below and behind the head
  1. directly behind the head
  1. directly in front of the face
  1. directly above the head
  1. to the side of the head
  1. Is there an apparent difference in hearing between your two ears?

Study of the Senses: Touch

While you other four senses (sight, hearing, smell, and taste) are located in specific parts of your body, your sense of touch is found all over. This is because your sense of touch originates in the bottom layer of your skin called the dermis.

The dermis is filled with many tiny nerve endings which give you information about the things with which your body comes in contact. They do this by carrying the information to the spinal cord, which sends messages to the brain where the feeling is registered.

The nerve endings in your skin can tell you if something is hot or cold. They can also feel if something is hurting you. Your body has about twenty different types of nerve endings that all send messages to your brain. However, the most common receptors are heat, cold, pain, and pressure or touch receptors. Pain receptors are probably the most important for your safety because they can protect you by warning your brain that your body is hurt!

Some areas of the body are more sensitive than others because they have more nerve endings. Have you ever bitten your tongue and wondered why it hurt so much? It is because the sides of your tongue have a lot of nerve endings that are very sensitive to pain. However, your tongue is not as good at sensing hot or cold. That is why it is easy to burn your mouth when you eat something really hot. Your fingertips are also very sensitive. For example, people who are blind use their fingertips to read Braille by feeling the patterns of raised dots on their paper.

Our skin has receptors that detect whenever something touches us. These “touch receptors” feed into the central nervous system in such a way that it creates a map. Our central nervous system preserves that “map” even to the level of the brain. What adds an interesting twist is that there are more touch receptors in certain areas of our bodies compared to other areas. This means that there is more cerebral cortex used to process the feeling of touch in some areas of our body compared to other areas. The “Homunculus” (see below) is a body map based on the amount of cerebral cortex used to process “touch receptors.”

Human Skin

Read the definitions and label the skin anatomy diagram below.

blood vessels - tubes that carry blood as it circulates. Arteries bring oxygenated blood from the heart and lungs; veins return oxygen-depleted blood back to the heart and lungs.
dermis - (also called the cutis) the layer of the skin just beneath the epidermis.
epidermis - the outer layer of the skin.
hair follicle - a tube-shaped sheath that surrounds the part of the hair that is under the skin. It is located in the epidermis and the dermis. The hair is nourished by the follicle at its base (this is also where the hair grows).
hair shaft - The part of the hair that is above the skin.
hair erector muscle - a muscle is connected to each hair follicle and the skin - it contracts (in response to cold, fear, etc.), resulting in an erect hair and a "goose bump." / melanocyte - a cell in the epidermis that produces melanin (a dark-colored pigment that protects the skin from sunlight).
Pacinian corpuscle - nerve receptors that respond to pressure and vibration; they are oval capsules of sensory nerve fibers located in the subcutaneous fatty tissue
sebaceous gland - a small, sack-shaped gland that releases oily (fatty) liquids onto the hair follicle (the oil lubricated and softens the skin). These glands are located in the dermis, usually next to hair follicles.
sweat gland - (also called sudoriferous gland) a tube-shaped gland that produces perspiration (sweat). The gland is located in the epidermis; it releases sweat onto the skin.
subcutaneous tissue - fatty tissue located under the dermis.

Physiology of Touch

The dermis of the skin contains touch receptors whose concentration differs in various parts of the body.

Experimental Procedure:

  1. One partner should be seated, with eyes closed, acting as the test subject.
  2. The other partner will test the ability of the test subject to discriminate between the two points of a hairpin or a pair of scissors at the four locations in number 5.
  3. Hold the points of the hairpin or scissors on the given skin area, with both of the points simultaneously and gently touching the subject.
  4. Ask the subject whether the experience involves one or two touch sensations.
  5. Measure and record the shortest distance between the hairpin or scissor points that the test subject was able to discriminate two points in the following areas:
  1. Forearm ______mm
  1. Back of the neck ______mm
  1. Index finger ______mm
  1. Back of the hand ______mm
  1. Which of these areas apparently contains the greatest density of touch receptors?
  1. Why is this useful?

Sense of Heat and Cold

Experimental Procedure:

  1. Obtain three beakers, and fill one with ice water, one with tap water at room temp and one with warm water.
  2. Immerse your left hand in the ice water beaker and your right hand in the warm water beaker for 30 seconds.
  3. Then place both hands in the beaker with room-temperature tap water.
  4. Record the sensation in the right and left hands.
  1. Right hand
  1. Left hand

Study of the Senses: Taste

Our sensory system for taste, or our taste perception, is remarkably sensitive. Not only can we detect compounds at extremely low concentrations, but we can also discriminate between molecular compounds that are closely related. For example, for some molecules we can distinguish between different stereoisomers, which are molecules that are made of exactly the same components but are mirror images of one another. The artificial sweetener aspartame is an example of this. It tastes sweet to us, but its stereoisomer does not.

This amazing sensitivity is made possible by our taste buds. Taste buds are located on small bumps on the tongue called papillae. Each taste bud is made up of 50 to 150 taste receptor cells. On the surface of these cells are receptors that bind to small molecules related to flavor. The receptors then relay the taste sensation information to the brain. This entire process allows us to discern the five basic tastes.

5 basic tastes:

1. ______2. ______3. ______4. ______5. ______

Study of the Senses: Smell

Although the human sense of smell is feeble compared to that of many animals, it is still very acute. We can recognize thousands of different smells, and we are able to detect odors even in infinitesimal quantities. Our smelling function is carried out by two small odor-detecting patches – made up of about five or six million yellowish cells – high up in the nasal passages.

For comparison, a rabbit has 100 million of these olfactory receptors, and a dog 220 million. Humans are nonetheless capable of detecting certain substances in dilutions of less than one part in several billion parts of air. We may not be able to match the olfactory feats of bloodhounds, but we can, for example, ‘track’ a trail of invisible human footprints across clean blotting paper.

The human nose is in fact the main organ of taste as well as smell. The so-called taste-buds on our tongues can only distinguish four qualities – sweet, sour, bitter and salt -all other ‘tastes’ are detected by the olfactory receptors high up in our nasal passages.

Key structures of the olfactory system:

1. ______--

2. ______--

3. ______--

The Anatomy of a Frog

Pre-Lab Discussion:

Frogs belong to the phylum Chordata and class Amphibia. Amphibians have adaptations for living in terrestrial as well as aquatic environments. Frogs are among the most commonly studied organisms in biology. Although many differences exist between humans and frogs, the basic body plans are similar. Humans and frogs both belong to the phylum Chordata because a notochord forms along the dorsal midline of the embryos of both frogs and humans. Frogs and humans are also classified in the subphylum Vertebrata because the adult organism has a backbone. Although humans belong to the class Mammalia and frogs belong to the class Amphibia, their bodies show many similarities of structure and organization. By studying the anatomy of the frog, you will be better able to understand your own body.

You will examine the external features of a frog and identify parts of its external anatomy. In addition, you will dissect a preserved frog to observe its internal anatomy.

Problem:

What environment would you find frogs living in? What features do frogs have that help them survive in this environment?