1. SBI 4U: Metablic Processes
THE NERVOUS SYSTEM
Section 1.3

2. Try These! Brain teasers worksheet Stroop test
Reflex test with a yardstick
Short-term memory test at

3. Vertebrate Nervous Systems
Autonomic (involuntary) system
Brain
Central Nervous System
Motor pathways
Parasympathetic
Peripheral Nervous System
Sensory pathways
Somatic (voluntary) system
Spinal cord
Sympathetic

4. Vertebrate Nervous Systems

5. Our Communication System
SBI 4U: Metablic Processes
Our Communication System
Nervous system senses and responds to stimuli
Works in coordination with the endocrine system, among others, to maintain homeostasis
There are 100 billion nerve cells in the brain alone!
Section 1.3

6. Central Nervous System (CNS)
SBI 4U: Metablic Processes
Central Nervous System (CNS)
Composed of the brain, spinal cord, and nerves
Coordinating centre
Processes information sent by nerves
Section 1.3

7. Peripheral Nervous System (PNS)
SBI 4U: Metablic Processes
Peripheral Nervous System (PNS)
Network of nerves
Carry sensory messages to the CNS
Send info from the CNS to muscles, glands, and organs
Composed of somatic & autonomic systems
Section 1.3

8. Somatic vs. Autonomic 1. Somatic Nerves
Controls skeletal muscle, bones and skin
Relay info about the environment to the CNS and respond accordingly
2. Autonomic Nerves
Special motor nerves that control internal organs
Control involuntary processes like heartbeat and peristalsis

9. Autonomic System: 2 types
Divided into 2 systems that work in opposition to each other
1. Sympathetic  “fight or flight”
Initiates arousal and energy production
2. Parasympathetic  “rest & relax”
Calming
Returns systems back to homeostasis

10. Cells in the Nervous System
SBI 4U: Metablic Processes
Cells in the Nervous System
Nervous system is composed of 2 main types of cells:
1. Neurons  basic functional unit
Conduct nerve impulses
Specialized to respond to stimuli, conduct signals, and release chemicals that regulate body processes
2. Glial cells  from Greek word ‘glue’
Structural support of nerve cells
Nourishes neurons, removes their waste, defends against infection
Do not conduct electrical impulses like neurons
Section 1.3

11. SBI 4U: Metablic Processes
So What’s a Nerve Then?
A bundle of neurons
Nerves are tissue composed of clusters of neurons
(cells combine to form tissues, which combine to form organs, ...)
Section 1.3

12. Neuron Anatomy

13. SBI 4U: Metablic Processes
Anatomy of a Neuron
Dendrites  finger-like projections
Receive nerve impulses from other neurons or sensory receptors
Numerous and highly branched
Increases surface area available to receive information
Cell body  aka the soma
Contains nucleus and majority of cytoplasm
The cell’s metabolic reactions happen here
Processes input from dendrites
Section 1.3

14. SBI 4U: Metablic Processes
Anatomy of a Neuron
Axon  long, thin tube
Carries nerve impulses away from the cell body
Range in length from 1 mm to 1 m depending on its location in the body
axon diameter also affects speed
smaller diameter = faster impulse transmission
Terminal releases chemical signals into the space between it and the dendrites of neighbouring cells to communicate (with surrounding neurons, glands, or muscles)
Section 1.3

15. SBI 4U: Metablic Processes
Anatomy of a Neuron
Myelin Sheath  insulates the axon
Insulating layer made of fatty protein
Made by Schwann cells
Covers some neurons but not all
Called “myelinated” neurons
Speeds up nerve impulse transmission
Schwann cells  type of glial cell
Specialized cells that produce myelin
Section 1.3

16. SBI 4U: Metablic Processes
Anatomy of a Neuron
Nodes of Ranvier  gaps between myelin on an axon
regularly occurring
nerve impulses jump from one node to another
increases speed of the impulse
Section 1.3

17. SBI 4U: Metablic Processes
Anatomy of a Neuron
Neurilemma  thin membrane that surrounds the axon
Found on all nerve fibres in the PNS
Promotes regeneration of damaged axons
Not all nerve cells contain neurilemma
Ex: Grey matter in the CNS
do not regenerate after injury ( paralysis)
Section 1.3

18. Neuron Anatomy

19. myelinated, contains neurilemma
unmyelinated, does not contain neurilemma
The PNS has greater ability to regenerate than the CNS (ex: spinal cord injuries)
Scientists have found a growth inhibitor in the CNS, which prevents neurilemma & myelin production
Scientists are looking for ways around this with therapeutic cloning (stem cell research)
Possibility of nerve regeneration, reversal of paralysis, etc.

20. Types of Neurons

21. Sensory Neurons Aka afferent neurons
Carry impulses from sensory receptors to the CNS for processing
Ex of sensory receptors = photoreceptors in eyes (light), chemoreceptors in nose and skin (chemicals), thermoreceptors in skin, hypothalamus (heat/cold)
Ganglia  clusters of sensory neurons
Located outside of the CNS
Singular = ganglion

22. Motor Neurons Aka efferent neurons
Carry impulses from the CNS to effectors (muscles, organs, glands, etc.)
These are the neurons that actually produce a response
Ex: muscle contraction/ relaxation, secretion of hormones, etc.

23. Interneurons Link sensory & motor neurons within the body
Found mostly in the CNS
Integrate and interpret sensory information and connect neurons to outgoing motor neurons
Aka association neurons

25. The Reflex Arc
Look online or use p. 416 of your textbook to make your own note on a reflex arc
Record background info
Use an example to summarize a typical reflex arc
Draw a picture or find an image that illustrates a reflex arc

27. SBI 4U: Metablic Processes
The Reflex Arc
Neural circuit through the spinal cord that provides a framework for a reflex action
Simplest nerve pathway
Involuntary, unconscious
Section 1.3

28. Example: Accidentally touching a hot stove
SBI 4U: Metablic Processes
Example: Accidentally touching a hot stove
Heat is detected by thermoreceptors in skin
Sensory neuron carries the nerve impulse to the spinal cord
Interneuron in spinal cord passes the impulse to a motor neuron
Motor neuron carries impulse to muscles in arm/ hand
Muscles contract and hand pulls away
Section 1.3

29. SBI 4U: Metablic Processes
The Reflex Arc
Happens in less than a second
Information has not even travelled to the brain
When it does, the sensation of pain will become noticeable and you may scream!
If you had to wait to feel the pain first, the burn would be a lot worse
Section 1.3