Neuroscience Chapter on Synapses and Reflexes

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Questions and Answers

What was the name of the scientist who first described the synapse?

Charles Sherrington (correct)

Santiago Ramon y Cajal

Charles Darwin

Otto Loewi

What is the term used to describe the cumulative effect of repeated stimuli at a synapse?

Spatial summation

Temporal summation (correct)

Synaptic plasticity

Axonal transport

What is the name of the automatic muscular response to stimuli?

Neurotransmitter release

Reflex (correct)

Action potential

Synaptic transmission

Which of the following is NOT a property of synapses observed by Sherrington?

Synaptic transmission is faster than conduction along an axon. (A) Signup and view all the answers

What is the term used to describe the effect of multiple stimuli occurring simultaneously at different locations on a neuron?

Spatial summation (B) Signup and view all the answers

What happens as a result of spatial summation?

A nerve impulse is triggered when synaptic input from multiple locations has a cumulative effect. (B) Signup and view all the answers

What is the function of the reflex arc?

To provide a pathway for sensory information to reach the brain (C) Signup and view all the answers

What is the significance of inhibition in the nervous system?

Inhibition allows for the coordinated control of movement (D) Signup and view all the answers

Which of the following best describes the effect of an excitatory postsynaptic potential (EPSP) on the postsynaptic neuron's membrane potential?

The membrane potential becomes more positive. (A) Signup and view all the answers

What is the role of an interneuron in the reflex arc described in the text?

It integrates information from the sensory receptors and sends signals to both flexor and extensor muscles. (A) Signup and view all the answers

Why is the synapse considered the site of delayed transmission?

The synapse is where the action potential is converted into a chemical signal (A) Signup and view all the answers

Which ion movement is primarily responsible for the creation of an inhibitory postsynaptic potential (IPSP)?

Chloride ions (Cl-) moving into the cell (B), Potassium ions (K+) moving out of the cell (D) Signup and view all the answers

What is the main difference between temporal summation and spatial summation?

Temporal summation occurs over time, while spatial summation occurs across different locations on the neuron. (C) Signup and view all the answers

What is the effect of a neurotransmitter on a postsynaptic cell dependent on?

The type of receptor on the postsynaptic cell (D) Signup and view all the answers

What chemical process is responsible for the synthesis of neurotransmitters?

Dehydration synthesis (D) Signup and view all the answers

What process is responsible for the removal of neurotransmitters from the synaptic cleft?

All of the above (D) Signup and view all the answers

What is the term used for the process by which a presynaptic neuron releases neurotransmitters?

Exocytosis (B) Signup and view all the answers

What type of potential is a graded potential?

Local potential (D) Signup and view all the answers

What is the effect of an excitatory postsynaptic potential (EPSP) on the postsynaptic neuron?

Increases the likelihood of the postsynaptic neuron firing an action potential (A) Signup and view all the answers

What is the effect of an inhibitory postsynaptic potential (IPSP) on the postsynaptic neuron?

Inhibits the postsynaptic neuron from firing an action potential (D) Signup and view all the answers

Which of these is NOT a characteristic of ionotropic effects?

They are long-lasting effects. (B) Signup and view all the answers

What is the function of a G-protein in metabotropic effects?

It binds to the neurotransmitter and initiates the signaling cascade. (C) Signup and view all the answers

How do hallucinogenic drugs like LSD exert their effects?

They bind to and activate serotonin receptors, particularly the 5-HT2A subtype, at inappropriate times or for longer durations. (A) Signup and view all the answers

What is the mechanism by which psylocibin, the active compound in magic mushrooms, exerts its effects?

It converts into psylocin in the brain, which then binds to and activates serotonin receptors. (C) Signup and view all the answers

What is the primary mechanism by which neurotransmitters are removed from the synaptic cleft?

They are actively transported back into the presynaptic neuron, a process known as reuptake. (C) Signup and view all the answers

What is the role of transporters in neurotransmitter reuptake?

They facilitate the movement of neurotransmitters back into the presynaptic neuron, contributing to reuptake. (A) Signup and view all the answers

Which of the following is NOT a potential effect of the activation of second messengers in metabotropic signaling?

Direct stimulation of neurotransmitter release. (D) Signup and view all the answers

What is the primary difference between ionotropic and metabotropic effects?

Ionotropic effects involve the direct opening of ion channels, while metabotropic effects initiate a series of metabolic reactions. (B) Signup and view all the answers

Which of these is NOT a feature of a chemical synapse?

Transmission is rapid and direct, allowing for near-instantaneous communication. (C) Signup and view all the answers

How does the action of cannabinoids influence the transmission of signals at synapses?

They act as retrograde signals, binding to receptors on presynaptic neurons and inhibiting further transmitter release. (C) Signup and view all the answers

What is the primary function of gap junctions in electrical synapses?

To allow for the direct passage of electrical signals between neurons. (B) Signup and view all the answers

What is the main difference between the anterior and posterior pituitary glands?

The anterior pituitary is responsible for producing hormones, while the posterior pituitary only stores and releases hormones produced by the hypothalamus. (A) Signup and view all the answers

How do autoreceptors contribute to negative feedback in synaptic transmission?

They sense the amount of neurotransmitter released and inhibit its further synthesis and release. (D) Signup and view all the answers

Which of the following is a key difference between hormones and neurotransmitters?

Hormones are released into the bloodstream and travel to distant target cells, while neurotransmitters act locally at synapses. (A) Signup and view all the answers

Which of the following statements MOST ACCURATELY describes the relationship between the hypothalamus and the pituitary gland?

The hypothalamus regulates the pituitary gland by releasing hormones that control its hormone production, while the pituitary releases hormones that influence a wide range of bodily functions. (A) Signup and view all the answers

Study Notes

Synapses

Neurons communicate by releasing chemicals at junctions called synapses.
The term synapse was coined by Charles Scott Sherrington in 1906.
Sherrington's discovery was a major advance in scientific reasoning.
Reflexes are slower than electrical conduction along an axon.
Multiple weak stimuli occurring at slightly different times or places can produce a more powerful response than a single strong stimulus.
As one set of muscles becomes active, another set relaxes.
There is a delay in nerve transmission at synapses, which validates the idea of a synapse.

Chapter Objectives

Describe how Charles Sherrington used behavioral observations to infer major properties of synapses.
Explain how EPSPs and IPSPs produce temporal and spatial summation.
Discuss the importance of inhibition in the nervous system.
List and explain the sequence of events at a synapse starting from the synthesis of neurotransmitters, stimulating receptors, up to the disposition of transmitter molecules.
Distinguish between ionotropic and metabotropic receptors and explain how each of them work.
Discuss how certain drugs affect behavior by their effects on synapses.
List some hormones and their effects.

Concept of the Synapse

Synapses are junctions between neurons, where neurons communicate.

Temporal and Spatial Summation

Temporal summation: Repeated stimuli occurring in a short period of time can have a cumulative effect, leading to a nerve impulse even if single stimuli are too weak.
Spatial summation: Multiple stimuli from different locations can generate a nerve impulse collectively, while individual stimuli may not.

Excitatory Postsynaptic Potential (EPSP)

EPSP is a graded depolarization that decays over time and space.
The cumulative effect of EPSPs forms the basis for temporal and spatial summation.
EPSPs increase the likelihood of an action potential.

Inhibitory Synapses

Inhibitory postsynaptic potential (IPSP) is a temporary hyperpolarization of a membrane.
IPSPs occur when synaptic input opens the gates for positively charged potassium ions to exit the cell or negatively charged chloride ions to enter the cell.
IPSPs serve as an active brake to suppress excitation.

Recordings from a Postsynaptic Neuron During Synaptic Activation

Excitatory postsynaptic potentials (EPSPs) increase the frequency of action potentials above the spontaneous firing rate.
Inhibitory postsynaptic potentials (IPSPs) decrease action potential frequency below the spontaneous firing rate.

Chemical Events at the Synapse

Neurons synthesize chemicals called neurotransmitters.
Action potentials travel down the axon and trigger the release of neurotransmitters.
Released neurotransmitters cross the synapse, attach to receptors, and alter the activity of the postsynaptic neuron.
Neurotransmitters detach from receptors and are either reabsorbed by the presynaptic neuron for recycling or diffuse away.
Some postsynaptic neurons send messages back to the presynaptic neuron to slow its release of neurotransmitters.

Synthesis of Transmitters

Neurotransmitters are synthesized from substances in the diet.
Acetylcholine is synthesized from choline found in milk, eggs, and nuts.
Tryptophan is a precursor for serotonin.
Catecholamines (epinephrine, norepinephrine, and dopamine) contain a catechol group and an amine group.

Effects on the Postsynaptic Cell

The effect of a neurotransmitter is determined by its receptor.
Ionotropic effects occur when a neurotransmitter attaches to receptors and immediately opens ion channels.
- Ionotropic effects happen very quickly and are short-lived.
- Ionotropic effects rely on glutamate or GABA.
Metabotropic effects occur when neurotransmitters attach to receptors and initiate a sequence of slower metabolic reactions.

G-Proteins

G-protein activation is coupled to GTP (an energy-storing molecule).
G protein activation increases a second messenger concentration.
Second messenger communications occur within the cell.
G proteins can open or close ion channels, alter protein production, or activate chromosomes.

Variation in Receptors

Many neurotransmitters bind to more than one receptor type.
Different receptors can have specific effects on behavior depending on the part of the brain and individual.

Drugs That Bind to Receptors

Hallucinogenic drugs distort perception by mimicking serotonin and stimulating serotonin type 2A receptors.

Magic Mushrooms

Psylocibin converts into Psylocin and activates their function.
Psylocin impacts the brain's default mode network, changing brain activity during "resting" states.

Inactivation and Reuptake of Neurotransmitters

Released neurotransmitters in the synapse are either inactivated or reabsorbed by the presynaptic neuron.
Transporters are special membrane proteins that facilitate reuptake.

Negative Feedback from the Postsynaptic Cell

Autoreceptors detect the amount of released neurotransmitter and inhibit further neurotransmitter synthesis and release.
Postsynaptic neurons respond to stimulation by releasing chemicals that travel back to the presynaptic terminal, inhibiting further release.

Effects of Drugs on Dopamine Transmission

Active chemicals in marijuana (cannabinoids) bind to receptors on presynaptic neurons.
This changes the signaling to the postsynaptic neuron, affecting both excitatory and inhibitory messages from various neurons.
Cocaine and other drugs influence dopamine by affecting its reuptake or other mechanisms.

Cannabinoids

Cannabinoids bind to anandamide or 2-AG receptors on presynaptic neurons, a process called retrograde signaling.
When cannabinoids attach to these receptors, the presynaptic cell stops sending signals.
Cannabinoids reduce both excitatory and inhibitory messages in the brain.

Electrical Synapses

Electrical synapses operate more quickly than chemical transmissions.
Gap junctions provide direct contact between the membranes of two neurons, allowing depolarization to pass directly.

Endocrine System

Hormones are chemicals secreted by glands or cells that travel via the bloodstream to affect activity in other organs.
Hormones are produced by endocrine glands.
Hormones affect long-lasting changes in multiple body parts.

The Pituitary Gland

The pituitary gland is attached to the hypothalamus, composed of anterior and posterior lobes.
The hypothalamus controls the anterior pituitary through releasing and inhibiting hormones.
The hypothalamus produces oxytocin and vasopressin, which the posterior pituitary releases in response to neural signals.

Negative Feedback in the Control of Thyroid Hormones

Thyrotropin-releasing hormone (TRH) from the hypothalamus stimulates the anterior pituitary to release thyroid-stimulating hormone (TSH).
TSH stimulates the thyroid gland to produce thyroid hormones (T3 and T4).
Thyroid hormones exert negative feedback on the hypothalamus and anterior pituitary to regulate their own release.

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Description

Test your knowledge on the properties of synapses, reflex arcs, and related neural mechanisms. This quiz covers key concepts such as synaptic transmission, spatial summation, and the roles of excitatory and inhibitory postsynaptic potentials. Perfect for students studying neurobiology or related fields.