BIOL 1020 HUMAN SENSORY SYSTEMS OBJECTIVES

16 Jun BIOL 1020 HUMAN SENSORY SYSTEMS OBJECTIVES

Question
Human Sensory Systems

Objectives
· Describe how sensory receptors communicate to the central nervous system.

· Describe receptors that detect temperature, pain, touch and pressure, muscle length and tension, and blood pressure.

· Describe the nature of vision in terms of its stimulus on the function of rod and cone cells.

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Introduction

The function of the brain is to convey messages to different parts of the body. Messages are conveyed from a nerve cell to another nerve cell, muscle cell, or a gland. The messages are in the form of electrical signals called neurotransmitters. Neurotransmitters are chemicals that are released from a nerve cell that relay a message. Examples of neurotransmitters are acetylcholine, norepinephrine, dopamine, and serotonin.Acetylcholine stimulates voluntary movement of the muscles andnorepinephrinestimulates wakefulness or arousal.Dopaminestimulates voluntary movement and

emotional arousal andserotoninmemory, emotions, wakefulness, sleep as well as temperature regulation.

Nerve cells, neurons, are found in the brain and the spinal cord. They consist of thecell body(soma) which contains thenucleus. Nerve cells also have extensions that branch out from the cell body called thedendrites. The dendrites are the portion of a nerve cell that receives a message. Theaxonis a long structure that extends out from the cell body, in the opposite direction of the dendrites. It is covered with amyelin sheath. The sheath is an insulator that enables a message to travel down an axon, away from the cell body, very quickly.Schwann cellsare cells that form the myelin sheath. Also, there are gaps between the myelin sheath that are not insulated. The gaps are calledNodes of Ranvier. A message traveling down an axon will eventually reach the end of a nerve cell, which is called an axon terminal. Theaxon terminalreleases neurotransmitters into a gap that occurs before the receiving cell. The space between the presynaptic cell (signaling cell) and thepostsynaptic cell (receiving cell) is called asynaptic cleft.

When a message is conveyed, an action potential can occur. The resting potential of a nerve cell is approximately -70 mV (millivolts). When a neurotransmitter triggers an action potential,sodium voltage gated channels open and allow sodium (positively charged) to diffuse into the cell. The diffusion of sodium causes the inside of the cell to obtain a positive charge. When the inside of the cell reaches +30 mV, the sodium voltage gated channels close preventing any additional sodium to diffuse into the cell. Next, thepotassiumvoltage gated channelsopen and enable potassium to diffuse out of the cell.

This allows the inside of the cell to return to its original negative charge.

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Laboratory Activities
Exercise 1: Understanding the Human Brain
You have been entrusted with the care and feeding of the most extraordinary and complex creation in the universe. Home to your mind and personality, your brain houses your cherished memories and future hopes. It orchestrates the symphony of consciousness that gives you purpose and passion, motion and emotion.

Go to, http://www.alz.org/alzheimers_disease_4719.asp, which is sponsored by the Alzheimer’s Association and take a tour of the brain. Click on “Start Tour”.

Questions: Understanding the Brain

1. What is the texture of the brain?

2. Name the general function of each main brain part:

Cerebrum –

Cerebellum –

Brain Stem –

3. Supply Lines: What percent of energy and oxygen carried throughout your body will the brain use when you are thinking hard?

4. The Cortex: “Thinking Wrinkles”: Explain the concept of cortex mapping.

5. Left Brain/Right Brain: Where is the language area of the brain?

6. The Neuron Forest: How does Alzheimer’s affect neurons?

7. Cell Signaling:What is the function of a neurotransmitter?

8. Signal Coding: What lobe of the brain lights up on a PET scan when you:

Read words?

Hear words?

Think about words?

Exercise 2: Neuroanatomy & Function Activities
I. Cerebellum: function = balance and coordination

Knee Flexion
a. Stand straight; support yourself by holding onto a table with one hand

b. Slowly bend knee as far as possible, so foot lifts up behind you; hold this position

c. Now, use one fingertip to hold onto the table

d. Next, no hands

e. Finally, with your eyes closed if you are steady

Hip Extension
a. Stand 12-18 inches from table

b. Bend at hips; hold onto table

c. Slowly lift one leg backwards (like an ice skater); hold this position

d. Now hold onto the table with one fingertip, then no hands, and finally with your eyes closed.

Questions:

Why do you think closing your eyes makes these two activities more difficult?
II. Parietal Lobe (part of the cerebral cortex): function = sensory processes (touch); attention and language

Cutaneous (Skin) Sensations
Work with a partner for this exercise. Have your partner sit comfortably with his/her eyes closed and both forearms resting on a table.
One arm should have the hand up, the other with hand facing down. Hair or clothing from the back of the neck should be pinned back so the surface of the neck is exposed.
Do not allow your partner to open his/her eyes at any time during this part of the lab!
Use a protractor or two straight pins or anything else to simulate a caliper with two points that can be separated from each other. Use the caliper to perform the test described in step “e” on the body areas listed in Table 1 below. You should perform the tests in a random order.
To perform the test: starting with the two points together in the specified location of the body, ask if your partner can feel two points or one. Move the points away from each other in slight increments, until your partner is able to detect two separate points. Measure the distance between the points (in millimeters), when your partner indicates he/she can feel two stimuli instead of one. Record this information in the table below.
Table 1. Two-point discrimination on various body parts.

Location

Two-Point Distance (mm)

Mid- Forearm

Tip of Pointer Finger

Tip of Little Finger

Palm of Hand

Back of Hand

Back of Neck

Cheek

Forehead

Questions:

1. Which areas of the skin are most sensitive to the two-point discrimination test?

2. Which areas of the skin are least sensitive to the test?

What causes this difference in sensation?
Why is greater sensitivity in some areas important to an organism?
III. Occipital lobe: function = vision

Two eyes are better than one, especially when it comes to depth perception. Depth perception is the ability to judge objects that are nearer or farther than others. To demonstrate the difference of using one eye versus two to judge depth complete the following:

Depth Perception
a. Hold the ends of a pencil/pen in each hand, hold them vertically or horizontally facing each other at arm’s length from your body.

b. Now, close one eye and try to touch the ends of the pencils together

c. Now try with two eyes: it should be much easier

d. It is easier with two eyes because each eye looks at the image from a different angle.

Why do you need two eyes?
a. With your arms fully extended, hold a plastic drinking straw in one hand and a pipe cleaner in the other.

b. With both eyes open, try to insert the pipe cleaner into the straw.

c. Now close your right eye. Try to insert the pipe cleaner into the straw. Repeat step “c”, but this time close your left eye instead.

Questions:

How does closing one eye affect the ability to judge distances?
Exercise 3: Testing the Optic Nerve
The function of the optic nerve is to carry sight messages from the retina of the eye to the brain.

Questions:

To which specific lobe(s) does the optic nerve send information?
How do the rod and cone cells differentially contribute to an organism’s ability to perceive a visual stimulus?