Unit 3 Project
Unit Question: How does the action of the cell membrane affect the actions of the
transmission across a synapse between Neurons?
Our way of Exploring the Unit Question: Transmission across a Synapse between
Neurons.
Definitions:
Action potential- is a series of electrical responses that occur in the cell.
Depolarization- is a sudden change within a cell during which the cell undergoes
dramatic electrical change.
Introduction
i.
ii.
Synapse:
a) Synapse is a structure that permits a neuron to pass an electrical or
chemical signal to another cell
b) Places where neurons pass signals to other neurons muscle cells, or
gland cells.
c) Chemical Signal: nerve-to-nerve signaling
nerve-to-muscle signaling
nerve-to-signal
Types of Synapse:
a)
Excitatory ion channel synapse-have neuroreceptors that are
sodium channels, which open up allowing positive ions to flow
in and cause a local depolarization. Resulting in an action
potential.
Typical neurotransmitters- Acetylcholine, glutamate or aspartate
b) Inhibitory ion
channel synapses-have
neuroreceptors that are
chloride channels, which open
up allowing negative ions to
flow in causing
hyperpolarization making
action potential less
likely.
Typical
neurotransmitters - Glycine
or GABA
c)
Non-channel synapses-have neuroreceptors that are
membrane bounded enzymes (No channels). When activated
they, catalyze the ‘messenger chemical’ inside the cell, which
affect many aspects of the cell’s metabolism.
These synapses are involved in slow and long-lasting responses
like learning and memory.
d)
e)
iii.
Typical neurotransmitters - Adrenaline, endorphin,
angiotensin, dopamine and acetylcholine
Neuromuscular junctions- synapses formed between motor
neurons and muscle cells. They always use the neurotransmitter
acetylcholine and are always excitatory. These neurons form
special synapses with the excretory cells.
Electrical synapses-in these synapses the membranes of the
two cells actually touch, and they share proteins allowing the
action potential to pass directly from one membrane to the next.
Although there are very quick they are only and rarely found in
the heart and eye.
During Synapse:
a) Axon branches split into many fine endings. There tipped by a
swelling called axon terminal.
b) These terminals are close to each other, this place is called a synapse.
c) The two neurons are separated by a tiny gap called the synaptic cleft.
iv.
At Synapse:
a) The membrane of the first neuron is called the presynaptic membrane.
b) Membranes of other neurons are called the postsynaptic membrane.
c) Molecules called neurotransmitters are involved in the communication
between the synapse.
d) Neurotransmitters are stored in synaptic vesicles in the axon terminals.
v.
When does it occur?
The transmission across a synapse occurs when a neurotransmitter is
released at the presynaptic membrane, diffuses across a synaptic cleft and
binds to a receptor in the presynaptic membrane.
The Step-by-step Process
 Axons of a sending neuron connect with the dendrites of a receiving neuron
 This connection triggers the release of calcium ions which allow for the
transmission of chemical messengers called neurotransmitters
 The neurotransmitter molecules cross the synapse and bind to receptor sites on
the receiving neuron
 Fits as precisely as a key fits a lock
 Afterwards, a process called reuptake, the sending neurons reabsorb the excess
neurotransmitters
Key Terms:
Neurotransmitters: Chemical messengers that carry out functions in order for your body
to survive
Synapse: The gap between a sending neuron and a receiving neuron where
neurotransmitters are transmitted
Reuptake: The reabsorption of excess neurotransmitters
How is the membrane important to this process?
During the process of transmission across a synapse between neurons, membranes
are highly involved.
e.g)
The synaptic cleft connects the presynaptic and postsynaptic
membranes so that neuron transmitters can travel from neuron to
neuron.
The importance of the presynaptic membrane is to initially send
the neuron transmitters that are infused into the presynaptic
membrane by synaptic vesicles into the synaptic cleft (the
“sender”).
It then travels down and will get received and bonded into the
receptors.