A&P2 Wk1 LECTURE Nuerotransmitters (NT)

What are neurotransmitters?

Chemical messengers that allow neurons to communicate with other neurons, muscles, or glands.

Where are neurotransmitters released?

From the axon terminal of the presynaptic neuron.

Where do neurotransmitters bind?

To receptors on the postsynaptic cell.

What are the two functional classifications of neurotransmitters?

Excitatory and inhibitory.

What do excitatory neurotransmitters do?

Cause depolarization and increase the likelihood of an action potential.

What do inhibitory neurotransmitters do?

Cause hyperpolarization and decrease the likelihood of an action potential.

What is an EPSP?

Excitatory postsynaptic potential; a local depolarization that moves the membrane closer to threshold.

What is an IPSP?

Inhibitory postsynaptic potential; a local hyperpolarization that moves the membrane farther from threshold.

What happens during depolarization?

The membrane becomes less negative.

What happens during hyperpolarization?

The membrane becomes more negative than resting membrane potential.

What is the threshold for an action potential?

-55 mV.

What is the resting membrane potential?

 -70 mV.

Which ion entering the cell usually causes depolarization?

Na⁺ (sodium).

Which ion leaving the cell usually causes hyperpolarization?

K⁺ (potassium).

What type of channels do direct neurotransmitters open?

Chemically (ligand)-gated ion channels.

Why are direct neurotransmitters fast?

They directly open ion channels.

Where is acetylcholine (ACh) a direct neurotransmitter?

At the neuromuscular junction (skeletal muscle).

What happens when ACh binds at the neuromuscular junction?

Na⁺ channels open, sodium enters the cell, causing depolarization.

What kind of membrane potential does ACh produce at skeletal muscle?

A local depolarization (EPSP).

Is ACh excitatory or inhibitory at skeletal muscle?

Excitatory.

What type of receptors do indirect neurotransmitters bind to?

G protein-coupled receptors (GPCRs).

Do G protein-coupled receptors contain ion channels?

No.

What happens after a neurotransmitter binds a GPCR?

The G protein becomes activated.

What second messengers are commonly produced?

cAMP and cGMP.

What are second messengers?

Molecules that carry signals inside the cell.

Why are indirect neurotransmitters slower?

They activate G proteins and second messenger pathways before producing an effect.

Where is ACh an indirect neurotransmitter?

Cardiac muscle and smooth muscle.

Is ACh excitatory or inhibitory in cardiac muscle?

Inhibitory.

What ion channel opens when ACh acts on cardiac muscle?

K⁺ channels.

What happens when K⁺ leaves the cardiac muscle cell?

The membrane hyperpolarizes.

What effect does hyperpolarization have?

Decreases the likelihood of an action potential.

Where is norepinephrine (NE) an indirect neurotransmitter?

Cardiac muscle.

Is norepinephrine excitatory or inhibitory at the heart?

Excitatory.

Can one neurotransmitter be both excitatory and inhibitory?

Yes, depending on the receptor it binds to.

What determines whether a neurotransmitter is excitatory or inhibitory?

The receptor, not the neurotransmitter itself.

What is an agonist?

A drug that binds to a receptor and activates it like the normal neurotransmitter.

What does an agonist do to a receptor?

Activates the receptor.

How does alcohol act as a GABA agonist?

It enhances GABA’s inhibitory effects, making neurons less likely to fire.

What is an antagonist?

A drug that binds to a receptor but blocks the neurotransmitter from binding.

What does an antagonist do?

Blocks receptor activation.

How does caffeine work?

It is an adenosine antagonist.

How does caffeine make you feel awake?

It blocks adenosine receptors, preventing adenosine from causing drowsiness.

What are the three ways neurotransmitters are removed from the synapse?

Enzymatic breakdown, diffusion away, and reuptake.

What enzyme breaks down acetylcholine?

Acetylcholinesterase (AChE).

What is reuptake?

The presynaptic neuron reabsorbs the neurotransmitter.

What is diffusion?

The neurotransmitter drifts away from the synaptic cleft.

Where is dopamine primarily found?

Brain.

Function of dopamine?

Reward, motivation, movement.

Is dopamine generally excitatory or inhibitory?

Usually excitatory.

Where is serotonin found?

Brain.

Function of serotonin?

Mood, sleep, appetite.

Is serotonin generally excitatory or inhibitory?

Usually inhibitory.

Where is norepinephrine released?

Sympathetic nervous system and heart.

Function of norepinephrine?

Increases heart rate and alertness.

Where is GABA found?

Brain. GB

Function of GABA?

Reduces neuronal activity.

Is GABA excitatory or inhibitory?

Where is glycine found?

Spinal cord.

Function of glycine?

Inhibits motor neurons.

Is glycine excitatory or inhibitory?

Inhibitory. gl

Where is glutamate found?

Brain. gl

Function of glutamate?

Learning and memory.

Is glutamate excitatory or inhibitory?

Excitatory.

Where is Substance P found?

Pain pathways.

Function of Substance P?

Pain transmission.

Is Substance P excitatory or inhibitory?

Excitatory.

Where are endorphins released?

Brain and pituitary.

Function of endorphins?

Pain relief.

Are endorphins excitatory or inhibitory?

Inhibitory.

Where is adenosine found?

Brain.

Function of adenosine?

Promotes sleep and decreases neuronal firing.

Is adenosine excitatory or inhibitory?

Inhibitory.

Where are endocannabinoids found?

Brain. E

Function of endocannabinoids?

Decrease neurotransmitter release, affect appetite and memory.

Are endocannabinoids excitatory or inhibitory?

Inhibitory.

Where is oxytocin released?

Hypothalamus and posterior pituitary.

Function of oxytocin?

Uterine contractions, milk letdown, bonding.

Is oxytocin excitatory or inhibitory?

Excitatory. O

What are the two functional classifications of neurotransmitters besides excitatory/inhibitory?

Direct and indirect.

What is the main difference between direct and indirect neurotransmitters?

Direct neurotransmitters open ion channels immediately; indirect neurotransmitters activate G proteins and second messengers first.

What ultimately determines a neurotransmitter’s effect?

The receptor on the target cell.