lab 5

Bio 102 Lab 06, Nervous System and Sensory Reception

Copyright © 2020 by Mary Vander Maten, Jill Caporale, and Karla Henthorn

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Objectives

After completing this lab, you should be able to:

· Label and identify the parts of a typical neuron.

· Trace a reflex arc.

· Be able to identify the form and function of white and grey matter in the brain and spinal cord.

· Label designated parts of the eye.

· Label designated parts of the ear.

· Describe the results of sensory tests performed in the lab.

The basic conducting unit of the nervous system is the neuron. Neurons pick up information through dendrites and are capable of transmitting chemical information along the axon to other neurons, muscles, or glands through electrical conduction down the axon.

In this lab we will investigate three types of neuronal transmission:

1. Sensory neurons that transmit information from sense organ or receptors in eyes, ears, taste buds, olfactory organs, and sense receptors of the skin.

2. Interneurons that make up most of the neurons in the brain and spinal cord.

3. Motor neurons that transmit signals to muscles.

In addition to neurons, nervous tissue contains many supporting cells called glia. These glial cells have a number of different roles that support and protect the nervous system. One of the types of glial cells is the Schwann cell which wraps around the axons of motor neurons forming a protective layer, called the myelin sheath.

Exercise A: Motor Neuron

Identify and label these parts of the neuron on the previous page:

· axon • dendrite

· Schwann cell • nodes of Ranvier

· cell body • nucleus of neuron

· synaptic terminals

Exercise B: Simple Reflex

The patellar reflex, also known as the knee-jerk response, occurs when the patellar ligament, the ligament just under the knee cap, is stretched, resulting in an impulse that travels through the sensory neuron into the spinal cord and out to the motor neuron which triggers a contraction of the quadriceps muscle and causes an involuntary kick.

Sit and relax your leg. Test that your leg is completely relaxed by gently swinging the leg to see that it moves freely. Once your leg is completely relaxed, find the gap just below the patella (knee cap) by feel. Then gently hit the patellar ligament with a gentle chop of your hand.

Your leg should respond with a kick,

Did the kick happen automatically?

Do you think the message needed to be transmitted to the brain for a response?

Exercise C: Central Nervous System, White and Grey Matter

The white matter appears white because it is lined with a myelin sheath. The cells which have a myelin sheath have a higher fatty content, making the matter appear white, providing a sort of insulation, and facilitating a faster transmission of neurological impulses. The insulation is not for temperature protection, but rather to cover up the cell and allow for less space for ion channels to be exposed. This system allows for clusters of ion channels which results in ion signals being sent more rapidly.

Look at photographs of transverse section of the spinal cord. Identify the white and grey matter.

Is the white matter on the inside or outside?

Is the grey matter on the inside or outside?

Look at a photograph of a brain section. Identify the white and grey matter.

Photo: © Duke University

Is the white matter on the inside or outside?

Is the grey matter on the inside or outside? Exercise D: Sensory Reception, Touch Receptors

1. Touch Receptors

Examine the diagram of a skin cross-section below and locate the touch receptors:

1) Which layer contains touch receptors (called Pacinian corpuscles), the hypodermis, dermis, or epidermis?

2) Which layer contains touch receptors (called Meissner corpuscles), the hypodermis, dermis, or epidermis?

3) By evaluating the location of the Pacinian and Meissner corpuscles, which type of receptor detects pressure and vibration?

4) Which type of receptor detects light touch?

2. Touch Sensitivity

You will conduct what is referred to as a “two-point touch test” to determine sensitivity. This test is used by neurologists to determine how well a particular part of the skin is innervated and can detect different touch stimuli.

Set up the experiment as shown below.

Insert two pins in cardboard and gently touch the areas listed. Start so that you feel two pin points. Reduce the distance between the pins until you only feel one point. Record in the table below the smallest distance that two points were able to be perceived.

Fingertip: ____ mm

Back of hand: ___mm

What does the two-point discrimination test tell us about the sensitivity of the skin in that area?

How do you think this relates to the number, density, and type of touch receptors in that area?

Exercise E: Sensory Reception, Vision, Hearing, Taste, and Smell The purpose of the eye is to bring in light and focus those light rays onto the retina at the back of the eyeball. Receptors in the retina send messages to the brain via the optic nerve. Rods are receptors that are stimulated by low light and therefore allow you to see at night. There are also three different types of cones that are sensitive at different wavelengths, thus allowing you to see color. The area containing the greatest density of cones is the fovea, and is directly in line with the center of the pupil.

There are also photosensitive cells in the eye that do not aid in vision, but are rather thought to contribute to circadian rhythm—your sleep-wake cycle.

1. Eye Anatomy

Identify the parts of the eye listed below: Use the diagram from your text (Campbell: Biology in Focus, 2nd edition, page 808).

· cornea • iris • vitreous humor

· pupil • sclera • fovea centralis

· retina • optic nerve • aqueous humor

· lens • ciliary body • suspensory ligaments

· choroid • blind spot

2. Vision Tests

A. Near point

Hold a book in front of your face, and slowly bring it closer to your eyes. It will get blurry close to your eyes. Find the closest distance still in focus and have your partner measure the distance from your eyes to the book.

Near point distance in cm:

How does near point discrimination change as a person ages?

B. Blind spot

This test tests for the “blind” spot in each eye where the retina has no receptors due to the presence of the optic nerve.

X O

Close or cover your left eye. Stare at the X with your right eye with the screen very close to your face. Slowly move away from the screen and continue to stare at the X. When you notice the O disappear, you have found the blind spot in that eye.

Repeat with the left eye (close or cover your right eye).

Why are there no receptors in the blind spot of the retina?

C. Afterimage

When an image remains on the retina after the object is removed, that image is called an afterimage. If you saw a flash of bright light and then close your eyes and the image still remains it is probably because the photochemical response has continued even though the light no longer shines. This is a positive afterimage.

If you stare at an image and fatigue the cones and rods in an area of the retina, you may also see an image beyond the source of the stimuli. This is referred to as a negative afterimage.

To create a negative afterimage, rest your elbows on the table about two feet apart and hold your head steady using your hands cradled around the side of your face.

Stare at the image for one minute without moving your head or eyes. Then shift your gaze to the plain white area next to the image.

www.wikipedia.org

Scroll down on this Wikipedia page and watch the video to observe an illusion sometimes called a “motion aftereffect:” https://en.wikipedia.org/wiki/Afterimage

A similar video, with a twist, is found:

https://www.youtube.com/watch?v=LFqnyeufcjs

D. Astigmatism, Color Vision, and Visual Acuity

Test your vision with interactive eye tests for visual acuity, astigmatism, and color vision at: https://www.essilor.com/en/vision-tests/test-your-vision/ .

Astigmatism:

Do you already know you have astigmatism?

According to this test, do you have astigmatism? If so, in which eye(s)?

Color Vision:

Sometimes an individual is born with a defect of certain cones (photoreceptors for color vision). This may result in difficulty differentiating colors, particularly red and green.

Do you already know you are colorblind?

According to this test, are you colorblindness?

The test shows 6 colored pictures. How many did you identify correctly?

Visual Acuity:

According to this test, does your left or right eye have greater acuity or do both eyes have equal visual acuity?

According to the test, what was your rating of visual acuity? , , or

Eye Chart

Repeat the test of visual acuity using an eye chart. Follow the instructions for downloading, printing, and using the eye chart at https://visionsource.com/patients/free-eye-chart-download/

Stand 10 feet from the chart. Cover one eye to determine how far down the chart you can read. Repeat with the other eye.

What is your left eye acuity?

Right eye acuity?

What is your vision with both eyes open?

3. Ear Anatomy

The outer ear gathers sound waves and directs them into the ear canal. The tympanic membrane (ear drum) vibrates, causing small ear bones to vibrate and transmit the sound to the cochlea. These vibrations travel through the fluid-filled cochlea, where receptors take the messages to the brain via the auditory nerve.

Identify the parts of the ear listed below. Use the diagram from your text (Campbell: Biology in Focus, 2nd edition, page 807).

· stapes • external auditory canal • semicircular canals

· cochlea • incus • pinna (external ear)

· malleus • tympanic membrane • inner ear

· middle ear • auditory tube (Eustachian) • auditory nerve

4. Taste

A. Map the area(s) of your tongue that can taste saltiness and sweetness.

Sweetness: Mix 1 teaspoon of sugar in ¼ cup of water. Use a cotton swab dipped in the sugar water and then touched to a paper towel (to remove excess liquid). Touch the swab lightly to the left or right side of your tongue of your tongue. Do you taste the sweet flavor? Wait a minute and then repeat for the other areas of your tongue (back, center, tip), waiting a minute in between the tests of each tongue region. Mark the diagram to show which areas allow taste reception of sweetness.

Saltiness: Mix 1 teaspoon of salt in ¼ cup water (some of the salt may not dissolve). Use a clean cotton swab to repeat the process of testing the different areas of your tongue. Mark the diagram to show which areas allow taste reception of saltiness.

B. Test the interaction of the senses of taste and smell.

Use 4 or 5 different flavors of fruit-flavored candy to test the interaction of taste and smell reception. Starburst jellybeans are ideal because they are small, soft, and the fruit flavors taste reasonably different. Other types of candies can also be used.

1) Choose 1 jellybean of each color/ flavor and put the jellybeans in a small dish. Record the jellybean colors in the table below. Do not look at the jellybeans during the taste test!

2) Hold your nose closed with your fingers.

3) Without looking at the jellybeans, pick up one jellybean and put it in your mouth. Chew it a little and record the flavor on scratch paper.

4) Stop holding your nose closed and chew the jellybean a little more. Record the flavor on scratch paper again.

5) If you are alone, you may need to look in the mirror to see which jellybean color you have before you swallow it. Record all information for that jellybean color in the table below.

Fruit Candy Color	Flavor with Nose Closed	Flavor with Nose Open	Easier to Guess Flavor with Nose Open? Y/N
1)
2)
3)
4)
5)

Review Questions

1. How do Schwann cells speed nerve impulses?

2. Which part of the neuron conveys impulses away from that neuron?

3. Why do nerve tracts appear white?

4. What kind of touch do Pacinian corpuscles detect?

5. How does touch sensitivity correlate to number of touch receptors?

6. What is astigmatism and how can it be corrected?

7. Describe the location of the blind spot and explain why that portion of an image hitting this area of the eye does not convey information to the brain.

8. What causes negative afterimages and what is unique about colors in a negative afterimage?

9. Sound waves hit the ear and sound vibrations cause other structures to vibrate. Number these structures in order of movement/stimulation:

___ malleus (hammer) ___ cochlear fluid ___ incus (anvil)

___ tympanic membrane ___ stapes (stirrup) ___ receptor cell

11. If a person has a car accident that injures their face, the sense of smell may be lost. How does this affect taste?

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Bio 102 Lab 06, Nervous System and Sensory Reception