1. Module 1

1.31. Page 6

Lesson 5

Module 1—The Nervous System

Try This

 

TR 6. Choose one of the following activities.

 

Do questions 5 and 7 on page 418 of the textbook.

 

OR

 

Watch the segment called “Interpretation” in the video “The Eye: Vision and Perception: A Whole World to See,” which addresses how the brain is involved in interpretation of vision stimuli.

 

You may be required to enter a username and password to access the video. Contact your teacher for this information.

 

Module 1: Lesson 5 Assignment

 

As you worked through this lesson, you learned about the different structures of the eye and their functions in facilitating vision. You were also introduced to some disorders that are the result of one or more of these structures malfunctioning.

 

Retrieve the copy of the Module 1: Lesson 5 Assignment that you saved to your computer earlier in this lesson. Complete Part 2—Table of Vision Defects and Disorders. Recall that you have already studied some of these vision disorders. Make sure you add these to your table. Save your completed assignment in your course folder. You will receive instructions about when to submit your assignment to your teacher later in this lesson.

 

Self-Check

 

To ensure that you have mastered the concepts of this lesson, do this Self-Check that includes a numerical-response question and a closed written-response question. This is an excellent opportunity to practise for the types of questions that will be presented on the Diploma Exam.

 

Use the following information to answer question SC 2.

 

Visual Interpretation

 

The brain integrates visual information from both eyes. Some of the steps in the visual pathway are shown below. Note that these steps are NOT in the correct order and that NOT all steps are part of the visual pathway.

  1. Rods and/or cones change light energy into a nerve impulse.
  2. The nerve impulse travels to the temporal area of the brain for sorting.
  3. The nerve impulse travels to the occipital lobe of the cerebral cortex for interpretation.
  4. Ganglion cells are stimulated.
  5. The nerve impulse leaves eye via the auditory nerve.
  6. Light energy enters the eye and strikes the retina.

 

SC 2. In the four spaces below, record the assigned numbers of the four steps that are part of the visual pathway. Record the steps in the correct order in which they occur during the visual pathway.

____  ____  ____  ____

 

SC 3. There are two main types of light-sensitive cells (called X and Y in this question) in the healthy human retina, but they are not evenly distributed. An investigation of the distribution of sensory cell types X and Y across an area of the retina (shown as PQ on the diagram below) was developed.



A diagram shows a large circle. A horizontal line bisects the circle. The left side of the line is labelled “P,” and the right side is labelled “Q.” Two smaller circles appear inside the larger circle. Both of these circles are bisected by the line. The circle on the left is labelled “R,” the circle on the right is labelled “S.”

The relative numbers of cell types X and Y were more or less constant, except in positions R and S. Using relative numbers, the following graph indicates the relative frequency of sensory cell type X along the axis PQ.

A graph is shown. The horizontal axis is titled “Site in Retina,” the vertical axis is titled “Relative Number of Cell Type X.” Along the horizontal axis, positions in the diagram above are indicated. At each position, the height corresponding to the relative number of cells will be given: position P height of line is one-quarter of the way up the vertical axis; position R line is along the horizontal axis; immediately after position R, height of line is one-quarter of the way up the vertical axis; position S height of line is three-quarters of the way up the vertical axis; position Q height of line is one-quarter of the way up the vertical axis.

    1. Identify cell type X.
    2. Identify cell type Y.
    3. What structure is represented by region R?
    4. What structure is represented by region S?

  2. Copy the graph above and clearly superimpose a curve to indicate the relative frequency of cell type Y along the axis PQ.

SC 4. The diagram below represents the different states of the iris in bright and in dim light.

Two diagrams showing the iris in bright and dim light. The diagram on the left shows a constricted pupil, producing a small central dark area in the centre of the eye. The diagram on the right shows a dilated pupil, producing a large central black area in the centre of the eye. The central black area is labeled “M,” the surrounding blue area is labeled “N.”

 

  1. What structures are represented by M and N?
  2. Briefly explain what causes the iris of eye B to have a different appearance than that of
    eye A.
Check your work.
Self-Check Answers

 

SC 2. 6, 1, 4, 3

SC 3. a. i. Cell Type X represents the cones.

    ii. Cell Type Y represents the rods.

    iii. Region R represents the blind spot.

    iv. Region S represents the fovea centralis.

b. Cell Type Y would be constant with a sharp dip in region R and S.

SC 4. i. M and N represent the circular muscle of the iris or, more specifically, M represents the circular muscle and N represents the radial muscle.

ii. In bright light, represented by A, the parasympathetic nervous system (a division of the autonomic nervous system) stimulates the contraction of the circular muscle (M) of the iris, and allows the relaxation of radial muscle (N). This reduces the pupil diameter and allows less light to enter the eyeball and strike the retina.

In dim light, represented by B, the sympathetic nervous system (a division of the autonomic nervous system) stimulates the contraction of the radial muscle (N) of the iris and allows the relaxation of circular muscle (M). This increases the pupil diameter, which allows more light to enter the eyeball and strike the retina.