Synapses
1. Electrical Synapses
2. Chemical Synapses
a. ionotropic (chemically gated)
b. metabotropic (G-protein mediated)
Synapse: junction between the
axon terminus of one neuron
and another neuron or effector
(muscle or gland).
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.
Chemical Synapse: ionotropic
Requires neurotransmitter for
transmission
Requires chemically gated channels
on
post-synaptic membrane
May involve degradative enzymes
May involve reuptake transporters on
pre-synaptic membrane
Chemical Synapse: ionotropic
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.
• 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 Effects
A. monoamine oxidase inhibitors (MAOI)
B. Prozac (selective serotonin reuptake inhibitors)
C. Cocaine ( dopamine reuptake inhibitor)
Post-Synaptic Effects
of Ionotropic Synapses
• Excitatory Post-Synaptic Potentials
• Inhibitory Post-Synaptic Potentials
Chemical Synapse: metabotropic
Requires neurotransmitter for
transmission
Requires 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
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
Neurons
Neuroglia (supporting cells)
- Detect physical and chemical changes in
their environment
- Provide physical support to neurons
-Transmit electric impulses (action potentials)
from one end to the other (one cell may be
more than 3 feet long)
- May be involved in processes such as
memory.
- Communicates with other neurons, muscles
and glands using chemicals called
neurotransmitters.
- Provide electrical insulation to neurons
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
Pyramidal cells (neurons) of the cerebral cortex (Golgi stain)
Cells of the
Central Nervous
System
Microglia - immune-like
cells
Oligodendrocyte
produce myelin sheath
Ependymal cells
- line ventricles and
help produce
cerebrospinal fluid
Astrocyte - blood brain
barrier