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

2. INTRODUCTION TO THE NERVOUS SYSTEM
SBI 4U: Metablic Processes
INTRODUCTION TO THE NERVOUS SYSTEM
Communication system
100 Billion nerve cells in the brain alone
2 main divisions to a vertebrate nervous system:
Section 1.3

3. SBI 4U: Metablic Processes
TWO MAIN DIVISIONS
Central Nervous System (CNS)
nerves, brain, spinal cord
coordinating centre
Section 1.3

4. SBI 4U: Metablic Processes
Peripheral Nervous System (PNS)
nerves that carry info between the CNS and the organs
Somatic Nerves
skeletal muscle, bones and skin
sensory and motor somatic nerves
Autonomic Nerves
special motor nerves that control the internal organs
sympathetic nervous system and parasympathetic nervous system
Section 1.3

5. SBI 4U: Metablic Processes
NERVE CELLS
Two cells types: neurons and glial cells
Glial cells (neuroglial cells): structural support and metabolism of nerve cells (do not conduct)
Neurons: nerve cells that conduct nerve impulses (functional unit). A nerve is a bundle of many neurons.
Section 1.3

6. SBI 4U: Metablic Processes
Types of Neurons
Sensory Neurons: (afferent neurons) carry impulses from sensory receptors to the CNS
Sensory receptors ex. photoreceptors in eyes (light), chemoreceptors in nose and skin (chemicals), thermoreceptors in skin, hypothalamus (heat/cold).
Ganglia (singular – ganglion): clusters of sensory nerve cell bodies located outside of the CNS.
Section 1.3

7. SBI 4U: Metablic Processes
Motor Neurons: (efferent neurons) carry impulses from the CNS to effectors (muscles, organs, glands...i.e. Things that produce a response)
Interneurons: link neurons within the body (found mostly in the CNS).
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8. SBI 4U: Metablic Processes
NERVE CELL ANATOMY
Cell body: nucleus and majority of cytoplasm.
Dendrites: projections of cytoplasm that carry impulses TOWARD the cell body
Axon: extension of cytoplasm that carries nerve impulses AWAY from the cell body.
Section 1.3

9. SBI 4U: Metablic Processes
Myelin Sheath: insulated covering (fatty protein) over the axon of some nerves, “myelinated”
prevents loss of charge
Schwann cells: type of glial cell that produces myelin sheath
nodes of Ranvier: regularly occurring gaps between sections of the myelin sheath
Section 1.3

10. SBI 4U: Metablic Processes
nerve impulses jump from one node to another – increases speed of the impulse
nonmyelinated nerves carry impulses at a slower rate
axon diameter also effects speed – narrower = faster.
Neurilemma: PNS axons have a thin membrane surrounding the axon. Promotes regeneration of damaged axons.
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11. SBI 4U: Metablic Processes
Cells without myelin sheath or neurilemma do not regenerate, damage is permanent. (“grey matter” in brain and spinal cord; white matter has myelin sheath).
PNS has greater ability to regenerate than the CNS (spinal cord injuries). Presence of a growth inhibitor in the CNS. Scientists are looking for ways around this (stem cells)
Section 1.3

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

13. Ex. Accidentally touching a hot stove (see handout)
SBI 4U: Metablic Processes
Ex. Accidentally touching a hot stove (see handout)
Heat detected by temperature receptors in skin
nerve impulse carried by a sensory neuron to the spinal cord
interneuron in spinal cord passes the impulse to a motor neuron
motor neuron carries impulse to muscles arm/hand
causes the muscles to contract and pull hand away
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14. SBI 4U: Metablic Processes
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.
HOMEWORK: Handout Questions #1-9
Section 1.3