Nervous system introduction for High School students.

1. Chapter 6: Coordination
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2. Physiology - Chapter 6 -
Coordination (pg 84)
• Main Learning Objectives:
• Understand how organisms are able to respond to
changes in their environment
• Understand that the central nervous system consists of
the brain and spinal cord and is linked to sense organs
by nerves
• Describe how the nervous system controls response
• Describe the structure and function of the eye as a
receptor and how it functions.
• Describe how a simple reflex arc works with the
example of your hand when it touches a hot object.
• Understand the role of neurotransmitters at a synapse.

3. Nervous System Organization
• Brain
• Spinal cord
• Nerves
– Cranial nerves
– Spinal nerves
• There are 31 pairs of spinal
nerves and 12 pairs of
cranial nerves.
•
Central Nervous System

4. Central Nervous System
• Brain
–Major parts:
Cerebrum
Cerebellum
Brain Stem
Hypothalamus
Made of 50-100
billion neurons

6. Spinal Cord
• Main communications link between the
brain and the rest of the body
• Certain kinds of info (reflexes) are
processed in spinal cord
• Reflex is a quick, automatic response to a
stimulus
– Sneezing and blinking
– Allows your body to respond to danger
immediately without thinking

7. Nervous System
• Messages carried by nervous system are
electrical signals called impulses
• Cells that transmit these impulses are called
neurons (basic units of nervous system)
– 3 types of neurons
1. Sensory
2. Motor
3. Interneurons

8. Neurons
• Sensory: Carry impulses from sense
organs (eyes, ears, etc) to the spinal cord
and brain
• Motor: carry impulses from the brain and
spinal cord to muscles and glands
• Interneurons: connect sensory and motor
neurons and carry impulses between them

9. Parts of a Neuron
• Cell Body
– Largest part; contains nucleus and most of cytoplasm
– Most metabolic activities occur here
• Dendrites
– Short, branched extensions
– Carry impulses from environment or other neuron toward cell body
– Neurons can have several dendrites
• Axon
– Long fiber which carries impulses away from cell body
– Ends in axon terminals, located a distance away from cell body
– Neurons only have one axon
• Myelin Sheath
– Insulating membrane surrounding axon
– it prevents short circuits with other axons
– speeds up the conduction of the impulses.

10. Neuron

11. Neuron

13. Nerve Impulse
• An impulse begins when a neuron is
stimulated by another neuron or the
environment

15. Stimulus and Response
Example : Sound of a doorbell.
Stimulus (sound of doorbell) ---> Receptor in the ear ----> Integrating center/CNS
(brain) ----> Effector (muscles in legs and hand) ----->
----→ Response (walk to the door and open the door)

16. Synapse
• Location where a
neuron can transfer
an impulse to another
cell
• Space between
neurons
• Neurotransmitters are
chemicals used by
neurons to transmit
an impulse across the
synapse

17. Synapse
• Location where a
neuron can transfer
an impulse to another
cell
• It’s the space
between neurons
• Neurotransmitters
are chemicals used
by neurons to
transmit an impulse
across the synapse

21. Look at figure 2, showing you the path of an impulse for a simple
involuntary reflex. The nerve impulse completes what is called a reflex
arc. A reflex arc is a nerve pathway that consists of a sensory neuron,
an interneuron, and a motor neuron. Notice the brain is NOT involved.
A reflex arc is a basic structure of the nervous system.

22. Reflex arc
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24. Transmission of a nerve signal
• Neuron has a similar system
– protein channels are set up in the neuron’s cell membrane
– once the first channel is opened, the rest open in succession
• all or nothing response
– a “wave” action travels along neuron
– The channels have to re-set so a neuron can react again
Neurons transmit electrical impulses.

25. Cells have voltage!
• Opposite charges on opposite sides of cell membrane
– membrane is polarized
• negative inside; positive outside
• charge gradient
• stored energy (like a battery)
+ + + + + + + +
+ + + + + + +
+ + + + + + + +
+ + + + + + +
– – – – – – – –
–
– – – – –
– – – – – – – –
–
– – – – –
Neurons pump sodium and potassium ions across their membranes to generate a
resting potential
1. Resting Potential

26. 1. Resting Potential
• Neurons are also highly polarized
(at about –70mV) due to:
» Differential membrane permeability to K+ and Na+
» The electrogenic nature of the Na+/K+ pump
» The presence of intracellular impermeable anions
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Neurons pump sodium and potassium ions across their membranes to generate a
resting potential

27. Measuring cell voltage
(measures the difference in concentration of charges)
unstimulated neuron = resting potential of -70mV
1. Resting Potential
Neurons pump sodium and potassium ions across their membranes to generate a
resting potential. mV = millivolt

28. • 2. Stimulus Depolarization
• Resting potential goes from -70mV to 0
mV
• Na+ ions rush into cell & K +
rush out
Chain reaction along axon to create an
impulse
NERVE IMPULSES

29. • Action potential = nerve impulse
–Travels along surface of axon
–Nodes of Ranvier increase rate by
saltatory conduction
–Impulse jumps across nodes
NERVE IMPULSES

30. • 3. Repolarization
–Occurs within 0.001 sec
(1 millisecond)
– Resting membrane potential
(polarization) restored by sodium-
potassium pump.
NERVE IMPULSES

31. • Click on the link below and then use the
Action Potential animation.
• http://outreach.mcb.harvard.edu/animation
s.htm
Action Potential tutorial

32. Sight
The light first enter the eye through:
• a transparent, yet durable layer of cells called
the cornea (transparent outer most layer of the
eye). The cornea helps us focus the light
through an opening called the pupil.
• The size of the pupil (The round opening in the
center of the iris) is regulated by the muscles in
the iris (the colored part of your eye).
• Behind the iris we have the lens (A clear disk
that focuses the light. It inverts the image and
projects it onto the retina).
• The image travels through the vitreous humor,
a gelatin-like liquid between the lens and retina.
Coordination
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• The retina is a layer at the back of the
eyeball that contains cells sensitive to
light. It contains numerous receptor cells
called rods and cones.
• Rods are light-sensitive cells and get
excited with low levels of light.
• Cones function in bright light and provide
information about color to the brain. The
rods and cones provide information to the
optic nerve which brings the information
to the occipital lobe in the brain (CNS).
This forms an image in our brain.
• Cones are concentrated at the center of
the retina, in an area called the fovea.
Cones give a shaper image than rods,
which is why we can only see objects
clearly if we look directly at them, so the
image falls on the fovea.

33. How is an image formed in the eye?
• An image is formed on the retina when light is bent or refracted.
• Refraction takes place when light passes from one medium to another of a different density.
• This happens in the air/cornea and then again at the lens.

34. What is the role of the iris?
• The iris controls the amount of light that enters by changing the size of the pupil.
• The iris has circular muscles that form a ring shape and radial muscles that are
like lines (like the spokes of wheels).
• In bright light the pupil in constricted (smaller). Light that is too bright can damage
the rods and cones.
• In dim light, the pupil is dilated (widened).Not enough light makes it difficult for the
brain to create an image.

35. What is the role of the iris?

36. What is the blind spot?
Our eyes have an area called a "blind spot" on the retina. In this
area an image cannot be formed and there are no rods and
cones here. Why? Because this is where the optic nerve leaves
the eye and connects to the brain. Each eye has a blind spot, but
our brain is still able to create a complete image by using
information from both eyes to create a full image.

37. What is the role of the iris?

38. What is the role of the lens?
Our eye adjusts in order to allow us to see. These adjustments are called
accommodations. The shape of the lens can be changed, A lens that is fatter in
the middle (convex) can refract light rays MORE than a thinner (less convex)
lens.
The lens in the eye can change shape because it is made of cells containing an
elastic crystalline protein. The lens is held in place with fibers called suspensory
ligaments. They are attached to the ciliary muscle (spokes of a wheel). The eyes
are filled with watery fluid (vitreous fluid) which pushes outward on the eye and
creates slight positive pressure.

39. What is the role of the lens?
When we look at an object far away (distant object - far sight) the lens does not
need to refract much light so it is not very convex. The ciliary muscles relax and
our eye is at rest - allowing us to focus on long distances.
When we focus on an object nearby (near sight) like reading a book, the light rays
are spreading out (diverging) and the lens has to be more convex to refract the
rays and focus the light on the retina. The ciliary muscles have to contract, and
the lens becomes a more convex shape.
The dilation and constriction of the pupil is an example of a reflex action. The
convex shape of the lens to adjust to near sight or far sight is an example of a
reflex action. The iris-puil reflex also protects the eye against damage by bright
light.

40. The path of light as it travels through the eye.
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