Chapter 9

• 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.

• Elaborate communication system
– Contains 100 billion nerve cells in the brain alone.
– Humans: memory, learning, language, etc.

• 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

• Glial cells
– 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)

• 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!)

• 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’

• 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)

• 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)

• White 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.

• 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

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

• Reflex
– 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.

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

• 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.