Body and behavior task 3
What is a neurotransmitter and what are the different types?
Neurotransmitter = a chemical messenger produced by nerve cells
(neurons) that transmits signals across a synapse to a target cell, such as
another neuron, muscle cell, or gland cell
Conduction of the Action Potential
Laws
The all-or-none law states that:
An action potential either happens completely or not at all.
o If the membrane reaches threshold, a full-size action potential
is produced.
o If threshold is not reached, no action potential occurs (and it
goes back to resting state).
Once triggered, an action potential travels down the axon without
getting weaker, even when the axon branches The size
(amplitude) and shape of the action potential are always identical,
regardless of stimulus strength.
Rate Law:
The rate law explains how neurons encode differences in stimulus
intensity.
Because all action potentials are the same size, neurons represent
stronger vs. weaker stimuli by firing at different frequencies:
Strong stimulus high firing rate (many action potentials per
second)
Weak stimulus low firing rate (fewer action potentials per second)
Dendrites Soma Axon Hillock Axon Nodes of Ranvier Axon
Terminals
(inputs) (AP starts) (AP travels)
(signal release)
- Axon hillock:
has the highest density of voltage-gated Na⁺ channels.
, It is the place where incoming signals are summed (EPSPs + IPSPs)
The axon transmits the signal by depolarizing the next membrane
segment:
Two forms:
- Unmyelinated Axons
Action potential moves continuously down membrane
Slower conduction (since every bit of the membrane must depolarize
in sequence).
Decremental conduction
- Myelinated Axons
Myelin insulates the membrane
Action potential occurs at nodes of Ranvier
This creates saltatory conduction (“jumping”)
Much faster and more energy-efficient
Decremental conduction
Decremental and Non-Decremental Conduction
- Decremental Conduction
Signal weakens as it travels along the membrane.
Happens in graded potentials (EPSPs/IPSPs) mainly in dendrites and
soma.
Signal fades because current leaks out (via leak channels) and
cytoplasm resists flow.
Example: EPSP gets smaller traveling from dendrite to axon hillock.
Graded potentials/postsynaptic potentials decrease with distance.
- Non-Decremental Conduction
Signal stays the same strength along the axon.
Happens in action potentials traveling down the axon.
Each axon segment regenerates the AP via voltage-gated Na⁺ and
K⁺ channels.
Like falling dominoes, one segment triggers the next, keeping signal
strong.
Example: AP travels from axon hillock to terminal without losing size.
Action potentials do not weaken over distance.
, Action potentials (APs) travel along axons differently from postsynaptic
potentials (EPSPs/IPSPs).
Decremental vs non-decremental: APs travel non-decremental PSPs
travel decremental
Slower transmission: APs travel more slowly than postsynaptic
potentials.
This difference arises because postsynaptic potentials are passive,
while axonal conduction is active—each segment of the axon
regenerates the AP through voltage-activated sodium channels.
o PSPs involves no channel opening — just charge diffusion
very fast.
o Aps involve ion channel activation and inactivation in every
small segment slower.
How do neurotransmitters and synapsis work? (look at the picture
in the course manual)
Structure of Synapses
Three main parts:
- Presynaptic membrane – the membrane of the terminal button of the
sending neuron.
Inside the presynaptic terminal are synaptic vesicles filled with
neurotransmitters When an action potential reaches the terminal,
these vesicles move toward special areas of the presynaptic
What is a neurotransmitter and what are the different types?
Neurotransmitter = a chemical messenger produced by nerve cells
(neurons) that transmits signals across a synapse to a target cell, such as
another neuron, muscle cell, or gland cell
Conduction of the Action Potential
Laws
The all-or-none law states that:
An action potential either happens completely or not at all.
o If the membrane reaches threshold, a full-size action potential
is produced.
o If threshold is not reached, no action potential occurs (and it
goes back to resting state).
Once triggered, an action potential travels down the axon without
getting weaker, even when the axon branches The size
(amplitude) and shape of the action potential are always identical,
regardless of stimulus strength.
Rate Law:
The rate law explains how neurons encode differences in stimulus
intensity.
Because all action potentials are the same size, neurons represent
stronger vs. weaker stimuli by firing at different frequencies:
Strong stimulus high firing rate (many action potentials per
second)
Weak stimulus low firing rate (fewer action potentials per second)
Dendrites Soma Axon Hillock Axon Nodes of Ranvier Axon
Terminals
(inputs) (AP starts) (AP travels)
(signal release)
- Axon hillock:
has the highest density of voltage-gated Na⁺ channels.
, It is the place where incoming signals are summed (EPSPs + IPSPs)
The axon transmits the signal by depolarizing the next membrane
segment:
Two forms:
- Unmyelinated Axons
Action potential moves continuously down membrane
Slower conduction (since every bit of the membrane must depolarize
in sequence).
Decremental conduction
- Myelinated Axons
Myelin insulates the membrane
Action potential occurs at nodes of Ranvier
This creates saltatory conduction (“jumping”)
Much faster and more energy-efficient
Decremental conduction
Decremental and Non-Decremental Conduction
- Decremental Conduction
Signal weakens as it travels along the membrane.
Happens in graded potentials (EPSPs/IPSPs) mainly in dendrites and
soma.
Signal fades because current leaks out (via leak channels) and
cytoplasm resists flow.
Example: EPSP gets smaller traveling from dendrite to axon hillock.
Graded potentials/postsynaptic potentials decrease with distance.
- Non-Decremental Conduction
Signal stays the same strength along the axon.
Happens in action potentials traveling down the axon.
Each axon segment regenerates the AP via voltage-gated Na⁺ and
K⁺ channels.
Like falling dominoes, one segment triggers the next, keeping signal
strong.
Example: AP travels from axon hillock to terminal without losing size.
Action potentials do not weaken over distance.
, Action potentials (APs) travel along axons differently from postsynaptic
potentials (EPSPs/IPSPs).
Decremental vs non-decremental: APs travel non-decremental PSPs
travel decremental
Slower transmission: APs travel more slowly than postsynaptic
potentials.
This difference arises because postsynaptic potentials are passive,
while axonal conduction is active—each segment of the axon
regenerates the AP through voltage-activated sodium channels.
o PSPs involves no channel opening — just charge diffusion
very fast.
o Aps involve ion channel activation and inactivation in every
small segment slower.
How do neurotransmitters and synapsis work? (look at the picture
in the course manual)
Structure of Synapses
Three main parts:
- Presynaptic membrane – the membrane of the terminal button of the
sending neuron.
Inside the presynaptic terminal are synaptic vesicles filled with
neurotransmitters When an action potential reaches the terminal,
these vesicles move toward special areas of the presynaptic
