Synapses

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Synapses

1. Electrical Synapses
2. Chemical Synapsesa. ionotropic (chemically
   gated)b. metabotropic (G-protein mediated)

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Synapse junction between the axon terminus of
one neuron and another neuron or effector (muscle
or gland).
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Electrical Synapse (rare)
In an electrical synapse, current passes directly
from one cell to the next. Very rapid (a few
milliseconds) Examples include neurons that
control the snap of a crayfish tail and the
flip of a caudal fin of a fish.
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Chemical Synapse ionotropic
Requires neurotransmitter for transmission Require
s chemically gated channels onpost-synaptic
membrane May involve degradative enzymes May
involve reuptake transporters on pre-synaptic
membrane
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Chemical Synapse ionotropic
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Examples of Neurotransmitters

• Acetyl choline found at all nerve-muscle
  synapses (neuromuscular junctions)
• Norepinephrine important neurotransmitter found
  throughout the central nervous system and
  peripheral nervous system.
• Serotonin found primarily in the brain
  effects mood.
• Dopamaine found primarily in the brain
  controls motor pathways and effects mood.

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• What is the function of degradative enzymes at
  the synapse?
• What is the function of reuptake transporters at
  the presynaptic membrane?
• Therapeutic and Recreational Drug EffectsA.
  monoamine oxidase inhibitors (MAOI)B. Prozac
  (selective serotonin reuptake inhibitors)C.
  Cocaine ( dopamine reuptake inhibitor)

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Post-Synaptic Effects of Ionotropic Synapses

• Excitatory Post-Synaptic Potentials
• Inhibitory Post-Synaptic Potentials

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Summation at the Hillock
Excitatory opens Na channels and causes graded
depolarization. Inhibitory opens K channels
and causes graded hyperpolarization.
Excitatory

Inhibitory
-
Summation of excitatory and inhibitory
post-synaptic potentials - may lead to
threshold and initiate an action potential.
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Chemical Synapse metabotropic
Requires neurotransmitter for transmission Requir
es G-protein coupled receptor on post-synaptic
membrane G-protein activates an enzyme on the
cytoplasmic side of the membrane May involve
degradative enzymes May involve reuptake
transporters on pre-synaptic membrane Examples
transmission of smell, control of cardiac muscle
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Cells of The Nervous System
Two neurons releasing neurotransmitters that act
on a third neuron. The first two neurons could
be in the Central Nervous System, and the third
might be a motor neuron leading out to a muscle
or gland.
Schwann Cells form a myelin sheath Around the
axon of motor neurons

• Neuroglia (supporting cells)
• Provide physical support to neurons
• Provide electrical insulation to neurons
• - May be involved in processes such as memory.

• Neurons
• Detect physical and chemical changes in their
  environment
• Transmit electric impulses (action potentials)
  from one end to the other (one cell may be more
  than 3 feet long)
• - Communicates with other neurons, muscles and
  glands using chemicals called neurotransmitters.

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Motor neurons have their cell bodies in the
spinal cord, but their axons extend outward into
the body to stimulate muscles or glands.
Spinal cord smear
Dendrites
Microglia
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Pyramidal cells (neurons) of the cerebral cortex
(Golgi stain)
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Cells of the Central Nervous System
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Microglia - immune-like cells
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Oligodendrocyte produce myelin sheath
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Ependymal cells - line ventricles and help
produce cerebrospinal fluid
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Astrocyte - blood brain barrier
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Cerebrum
Cerebellum
Brain Stem
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Central Sulcus
Sulcus
Gyrus
Transverse Fissure
Lateral Fissure
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Lobes of the Cerebrum
Parietal Lobe
Frontal Lobe
Occipital Lobe
Temporal Lobe
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Cerebrum
Corpus Callosum
Thalamus
Hypothalamus
Pons
Midbrain
Medulla
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Cerebrum
Corpus Callosum
Thalamus
Basal Ganglia
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Limbic System amygdala, hippocampus,
hypothalamus and cingulate gyrus The four Fs