Nervous System

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Nervous System
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Divisions

• Central Nervous System
• Brain Spinal Chord
• Peripheral Nervous System
• Autonomic-involuntary
• Sympathetic Parasympathetic
• Somatic-voluntary
• Skeletal muscles, skin, senses

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Nervous Tissue

• Glial Cells
• 90 of CNS
• Structural framework
• Fatty Myelin sheath
• Phagocytosis
• Cerebrospinal fluid circulation

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Neurons I

• Cell Body
• Nucleus
• Cytoplasm
• Other common organelles
• NO mitotic spindles!
• (what problems does this cause?)
• Dendrites
• Highly branched
• Receive impulses

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Neurons II

• Axon
• Always only 1
• Conducts impulse AWAY from cell body
• Can extend as much as 1 meter
• Encased by Schwann cells ? Myelin sheath
• (In CNS, Oligodendrocytes may provide sheath)
• Nodes of Ranvier
• Sensory Neurons
• Motor Neurons

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Action Potential Resting I
At its most basic, an action potential is a very
rapid swing in the polarity of the membrane
potential from negative to positive and back, the
entire cycle lasting a few milliseconds
(http//en.wikipedia.org/wiki/Action_potential )

• Resting Potential (-70mV)
• Result of unequal distribution of ions
• Ion channels
• Na K (mostly)
• 10X more Na outside than inside
• Na/K Pump

Animation?
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Action Potential!!!!!!!!!!

• Stimulus causes Na channels to open
• Flow into cell causes depolarization
• Adjacent region subsequently depolarized
• Voltage climbs to 30 or more
• Repolarization
• Diffusion of K out K channels
• closing of Na channels
• All this, 1/1000 sec!

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Action Potential Resting II

• Concentration Gradient
• 3 Na vs. 2 K
• Plasma Membrane more permeable to K
• Leak out

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Action Potential II
animation
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(No Transcript)
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All or none!

• Threshold Stimulus -55 mV
• Subthreshold those stimuli that are weaker than
  threshold (No AP)
• Summation

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Action Potential III

• How does the myelin sheath improve conductance
  speed?

• Answer Blocks the continuous flow of ions
  through the membrane
• Saltatory Conduction impulse jumps! between
  Nodes of Ranvier

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Synaptic Gap

• Junction between neurons
• from presynaptic neuron to postsynaptic neuron
• Synaptic vesicles at bulb (end of axon) contain
  neurotransmitters

Synapse Movie
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Chemical Influences

• How might stimulants work? (Amphetamines,
  caffeine, nicotine)
• Increase synaptic transmission ? increased
  energy/mood, decreased appetite.
• Increased irritability and anxiety
• How might depressants work? (Alcohol,
  anti-anxiety drugs, heroin)
• Inhibition of impulses (blocking receptors of NT
• Can result in depression

Animations
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The Peripheral Nervous System

• Divided into 2 parts
• Sensory Transmits signals from sense organs to
  the Central Nervous System (CNS)
• Motor Transmits signals from the CNS to the
  muscles and glands
• Somatic Nervous System conscious control
• Autonomic Nervous System automatic, or
  involuntary control

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Somatic Nervous System

• When you walk, sit down, move your finger, kiss
• Every time you want to move, your brain tells
  your muscles (what type?) through the motor
  neurons to do so.

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Autonomic Nervous System

• Control functions we cant willingly control
• Like heart contractions and smooth muscles of
  digestion.
• Also further divided into 2 parts
• Sympathetic (on switch or gas pedal)
• Increases heart rate
• Parasympathetic (off switch or brakes)
• Decreases heart rate

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Spinal Reflexes

• Does not reach higher brain levels!
• No thought involved
• Receptor Stimulated
• Sensory AP
• Association neurons in spinal column
• (Multiple) Motor signal
• Effectors (muscles)

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Reflex test

• Try the knee-jerk reflex yourself.
• Do you have any voluntary control?
• Can you find any other places on your body that
  have a similar reflex?
• What do the knee-jerk and other reflex spots have
  in common?

Positive Feedback loops
Negative Feedback loops