The Nervous System:

1
The Nervous System

• Command Control Centers

2
Nervous systems

• Effector cells muscle or gland cells
• Nerves bundles of neurons wrapped in connective
  tissue
• Central nervous system (CNS) brain and spinal
  cord
• Peripheral nervous system (PNS) sensory and
  motor neurons

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Structural Unit of Nervous System

• Neuron structural/functional unit (the actual
  Nerve Cell)
• Cell body nucleus and organelles
• Axon Hillock where impulses generate
• Dendrites impulses from tips to neuron
• Axons impulses toward tips (away!!)
• Myelin sheath supporting, insulating layer
• Schwann cellsPNS support cells
• Astrocytes Oligodendrocytes CNS support
• Synaptic terminals neurotransmitter releasers

Animation
4
Simple Nerve Circuit

• Sensory neuron convey information to spinal cord
• Interneurons information integration
• Motor neurons convey signals to effector cell
  (muscle or gland)
• Reflex simple response sensory to motor
  neurons
• Ganglion (ganglia) cluster of nerve cell bodies
  in the PNS
• Supporting glial cells nonconducting cell that
  provides support, insulation, and protection

5
Neural signalingFirst, in the resting state,
there is.

• Membrane potential (voltage differences across
  the plasma membrane)
• Intracellular/extracellular ionic concentration
  difference
• K diffuses out (Na in) large anions cant
  follow.selective permeability of the plasma
  membrane
• and of course the Sodium/Potassium pumps never
  sleep!
• Net negative charge of about -70mV

6
Neural Signaling, continued.

• Excitable cells cells that can change membrane
  potentials (neurons, muscle)
• Gated ion channels (open/close response to
  stimuli) Examples of stimuli
• Photoreceptors vibrations in air (sound
  receptors)
• Chemical (neurotransmitters)
• Voltage (membrane potential changes)
• Graded Potentials (depend on strength of
  stimulus)
• 1- Hyperpolarization (outflow of K) increase in
  electrical gradient cell becomes more negative
• 2- Depolarization (inflow of Na) reduction in
  electrical gradient cell becomes less negative.

7
Neural signaling, continued still

• 1-Resting stateboth channels closed
• 2-Threshold a stimulus opens some Na channels
• 3-Depolarization action potential generated
• Na channels open cell becomes positive (K
  channels closed)
• 4-Repolarization Na channels close, K
  channels open K leaves cell becomes
  negative
• 5-Undershoot both gates close, but K channel
  is slow resting state restored
• 6-Refractory period insensitive to
  de-polarization due to closing of Na gates
• (region is hyperpolarized)
• Animation

8
Neural signaling, finale

• Travel of the action potential is
  self-propagating
• Regeneration of new action potentials only
  after refractory period
• Forward direction only
• Action potential speed
• 1-Axon diameter (larger faster 100m/sec)
• 2-Nodes of Ranvier (concentration of ion
  channels) saltatory conduction

9
Synaptic communication

• Presynaptic cell transmitting cell
• Postsynaptic cell receiving cell
• Synaptic cleft separation gap
• Synaptic vesicles neurotransmitter releasers
• Ca influx caused by action potential causes
  vesicles to fuse with presynaptic membrane and
  release.
• Neurotransmitters!!
• So lets talk neurotransmitters

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Neurotransmitters 2 main types
Those that relay an
EPSP-
Excitatory Post Synaptic Potential
Occur when terminal releases a neurotransmitter
that opens Na channels.
And then there are those that relay an
IPSP-
Inhibitory Post Synaptic Potential
Occur when terminal releases a neurotransmitter
that opens either K channels or Cl- channels.
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Neurotransmitters, some examples

• Acetylcholine (most common)
• Might be either EPSP or IPSP.
• Important for skeletal muscle contraction.
• Biogenic amines (derived from amino
  acids) norepinephrine excitatory dopamine
  - generally excitatory.
• Too little Parkinsons Too much
  schizophrenia
• Cocaine prevents the reuptake/breakdown in cleft.
• Serotonin- Usually inhibitory important for
  sleep/relaxation

12
Neurotransmitters, more examples

• Single Amino acids

• G.A.B.A.- Gamma AminoButeric Acid inhibitory
  at neuromuscular junction.

• Aspartate- Excitatory (found in high
  concentrations in artificial sweeteners)

• Tryptophan- Inhibitory (Happy Thanksgiving!!)

• Glutamate- Excitatory (like acetylcholine
  important at neuromuscular junction)
• (Blocked by alcohol)

• Neuropeptides (short chains of amino acids)

Endorphins- generally inhibitory (see why theyre
called natural painkillers?)
Substance P- Excitatory
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Vertebrate PNS

• Sensory division (Afferent)
• Somatic system-
• Information from voluntary/conscious parts.
• Visceral system-
• senses information from involuntary parts.
• Motor division (Efferent)
• somatic system carries signals to
  skeletal muscle (mostly voluntary, but some are
  reflex)
• autonomic system vparasympathetic
  conserve energy (digestion, decrease
  heart/breathing rates) vsympathetic
  increase energy consumption

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Vertebrate CNS

• Basically,
• its Brain Spinal Cord
• Axons are in well defined bundles
• White Matter- heavily myelinated
• Gray Matter- not as myelinated
• In brain, white is in, gray is out
• Reversed in Spinal Cord

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The Vertebrate Brain

• Forebrain
• cerebrummemory, learning, emotion
• cerebral cortexsensory and motor nerve cell
  bodies
• corpus callosumconnects left right
  hemispheres
• thalamus- sorts info emotion hypothalamus-
  hormones, thermostat
• Midbrain
• inferior (auditory) and superior (visual)
  colliculi
• Hindbrain cerebellumcoordination of
  movement balance
• medullaoblongata/pons
• homeostatic functions

Mike the Headless Chicken!