Synapse & Neuroanatomy

Charles Sherrinton (1906)

Term “synapse” introduced by???

behavioral observations (reflexes in dogs)

Charles Sherrinton (1906) inferred the existence and properties o synapses through??

Reflexes are slower, temporal summation, spatial summation, and inhibitory processes.

What are the key findings of Charles Sherrington on his behavioral observation through flexes?

Temporal summation

Repeated stimuli within a brief time can combine to produce a stronger response.

Spatial summation

Separated stimuli from multiple can combine their effects.

Inhibitory process

Some synapse activity decreases the chance of an action potential.

Chemical synapse

neurons stimulate nearby cells by sending neurotransmitters across the synaptic gap.

Electrical synapse

neurons directly stimulate nearby cells by sending ions across the gap through channels that actually touch.

EPSP (Excitatory Postsynaptic Potential)

A graded depolarization that increases the chance of an action potential.

IPSP (Inhibitory Postsynaptic Potential)

A graded hyperpolarization that decreases the chance o an action potential.

Summation

Both temporal and spatial summation explain how weak inputs can collectively trier a response.

Otto Loewi (1920s)

Who demonstrated chemical transmission by stimulation a frog’s vague nerve and transferrin fluid to another heart?

Small neurotransmitters are synthesized in the axon terminals, while neuropeptides are synthesized in the soma.

Where are small neurotransmitters and neuropeptides synthesized and stored?

An action potential depolarizes the presynaptic terminal, causing calcium ions to enter, which leads to vesicle fusion with the membrane and exocytosis.

What triggers the release of neurotransmitters from the presynaptic terminal?

They cross the synaptic cleft and bind to receptors on the postsynaptic membrane.

What happens after neurotransmitters are released into the synaptic cleft?

Ionotropic effects are fast and direct, involving ligand-gated ion channels. Metabotropic effects are slower, longer-lasting, and involve second messenger systems.

What is the difference between ionotropic and metabotropic effects?

• Enzymatic breakdown (e.g., acetylcholine).

• Reuptake into the presynaptic neuron (e.g., serotonin, dopamine).

• Diffusion away from the synaptic cleft.

Three ways neurotransmitters are inactivated or removed from the synaptic cleft.

Autoreceptors provide negative feedback by monitoring and regulating neurotransmitter release.

What is the role of autoreceptors on the presynaptic neuron?

Neurotransmitters are chemicals that affect another neuron by transmitting signals across a synapse.

What are neurotransmitters?

Amino acids, monoamines, and acetylcholine

What are the three main categories of conventional small-molecule neurotransmitters?

Amino acids are the molecular building blocks of proteins and function as small-molecule neurotransmitters.

What are amino acids in the context of neurotransmitters?

• Dopamine → pleasure, satisfaction, and motivation.

• Epinephrine (adrenaline) → fight or flight response.

• Norepinephrine → arousal, attention, cognitive function, and stress reactions.

• Serotonin → mood, happiness, sleep, and digestion.

Name the four monoamine neurotransmitters and their main functions.

Acetylcholine is important for brain and muscle functions and is a modified amino acid.

What is the role of acetylcholine?

They act in ways that are different from typical neurotransmitter

How do unconventional neurotransmitters differ from conventional ones?

Nitric oxide (NO) and carbon monoxide (CO) are soluble-gas neurotransmitters; they pass easily through cell membranes because they are lipid-soluble.

Give examples of soluble-gas neurotransmitters and explain why they easily pass through membranes.

Neuropeptides are large-molecule neurotransmitters made of chains of amino acids. They modulate the postsynaptic response to a neurotransmitter. Examples include endorphins, substance P, and neuropeptide Y.

What are neuropeptides, and what is their function?

Endocrine glands

Produces/release hormones; they influence growth, metabolism, and behavior.

Neurotransmitter

act at a specific synapses —→ rapid effects.

Hormones

act via bloodstream —→ slower, widespread effect.

Neuropeptide (e.g., endorphins)

Act like neurotransmitters but are released more diffusely and have longer-lasting effects.

Antidepressants

block serotonin reuptake

Antipsychotics

block dopamine receptors

Nicotine

stimulates acetylcholine receptors