1. How Nerve Signals Maintain Homeostasis
Chapter 9

2. The Nervous System Intro
Every single stimulus (light, touch, feeling of muscles moving, pressure, blinking, etc.) involves your nervous system.
Coordinated motions (which do not seems to be coordinated) are controlled mostly by the nervous system.
nervous system + endocrine system control the actions of the body.

3. The Nervous System Elaborate communication system
Contains 100 billion nerve cells in the brain alone.
Humans: memory, learning, language, etc.

4. Vertebrate Nervous System
2 main divisions:
Central nervous system (CNS)
Brain + spinal cord  coordinating centre
Incoming and outgoing info.
Peripheral nervous system (PNS)
Info between organs of body and CNS.
Two peripheral divisions:
Somatic
Skeletal muscles, bones, and skin
Sensory somatic PNS: relay info about environment to CNS.
Motor somatic PNS: initiate appropriate responds.
Autonomic
Motor nerves which control internal organs of body.
Sympathetic
Parasympathetic

5. Organization of the Nervous System

6. Nerve Cells Glial cells Neurons
Nonconducting cells  structural support and metabolism of nerve cells.
Neurons
Functional units of nervous system (conduct electricity)
Sensory neurons
“afferent neurons”
Sense and relay info (stimuli) from environment to CNS
(ex// photoreceptors, chemoreceptors, thermoreceptors, etc.)
Ganglia: clusters of sensory receptors.
Interneurons
Integrate and interpret sensory and motor neurons (found mostly in the CNS)
Motor neurons
“efferent neurons”
Relay info to effectors: muscles, organs, and glands (can produce a response)

7. Anatomy of a Nerve Cell (Neuron)
All neurons contain:
Dendrites
Receive info from other nerve cells
Conduct info towards the neuron’s cell body
Soma: neuronal cell body (containing nucleus)
Axon
Extension of cytoplasm
Carries nerve impulse towards other neurons or effectors.
Creates an “attachment” to other neurons.
Super super thin (100 could fit inside single human hair!)

8. Myelin Sheath Insulation
Myelin sheaths are formed by special glial cells called Schwann cells
Myelin sheaths prevents the loss of ions from axon.
(important when you understand how these cells work!)
Made of ‘fatty protein’

9. Nodes of Ranvier Between sections of myelin sheath
Nerve impulses jump from one node to another  speed up movement of nerve impulses.
Nerve impulses move much faster along myelinated nerve fibres than nonmyelinated ones.
(Nerve impulses move much faster along smaller diameter axons)

10. Neurilemmas
Thin membrane which surrounds the axon in peripheral nervous system
Promotes regeneration of damaged axons
Severed neurons can be rejoined.
(feeling gradually returns to your finger following a paper cut)

11. White and Grey Matter White matter Grey matter
Nerve cells within the brain that contain myelinated fibres and neurilemma
Myelinated axons white in appearance
Grey matter
Nerve cells within the brain and spinal cord referred to as grey matter: lack myelin sheath and neurilemma  do not regenerate after injury
Damage to grey matter is usually permanent.

14. Categories of Neurons
Sensory Neurons: AFFERENT neurons: relay info from environment  CNS
Located in clusters called ganglia
Photoreceptors (eyes)
Chemoreceptors (tongue and nose)
Thermoreceptors (skin and hypothalamus)
Interneurons
Interpret sensory info and send info to outgoing motor neurons (mostly in CNS)
Motor neurons: EFFERENT neurons: relay info from interneurons  effectors (produce a response)
Muscles
organs,
glands

16. Organization of Nerves
Most nerves are part of many neurons/axons held together in a ‘bundle.’

17. Neural Circuits Reflex Example: touching a hot stove
Involuntary and often unconscious
Example: touching a hot stove
How long does it take you to remove your hand?
Nerve impulse is carried to the spinal chord  motor neuron (skipping brain)  sensation felt after removing hand.

18. Reflex arc Simplest nerve pathway. Occurs without brain coordination
Five essential components:
Receptor
Sensory neuron
Interneuron (spinal chord)
Motor neuron
Effector

21. Seatwork/Homework Page 417 1) # 1-6, 8.
2) Draw/ Label a general neuron: dendrite(s), soma, nucleus, axon, myelin sheath, axon terminals, direction of impulse.
3) Read page 415 article. Make brief notes.