Physiology of Refractory Periods

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Questions and Answers

What is the primary function of synapses?

To inhibit impulse transmission

To transmit impulses from one neuron to another (correct)

To connect sensory neurons to motor neurons

To store neurotransmitters

Which type of synapse transmits impulses to the postsynaptic neuron?

Connector synapses

Excitatory synapses (correct)

Receptor synapses

Inhibitory synapses

What triggers the release of neurotransmitters during synaptic transmission?

The action potential reaching the postsynaptic membrane

The influx of sodium ions into the presynaptic neuron

The opening of voltage-gated calcium channels (correct)

The binding of neurotransmitters to receptors

What is an Excitatory Postsynaptic Potential (EPSP)?

A non-propagated electrical potential resulting from neurotransmitter binding Signup and view all the answers

What action does the neurotransmitter-receptor complex cause in the postsynaptic membrane?

Opening of ligand-gated sodium channels Signup and view all the answers

What role do calcium ions play during synaptic transmission?

They trigger the exocytosis of neurotransmitters Signup and view all the answers

How are synapses classified based on their functions?

As either excitatory or inhibitory Signup and view all the answers

What is the effect of inhibitory synapses on impulse transmission?

They inhibit the transmission of impulses Signup and view all the answers

Which type of synapse involves the axon of one neuron terminating on the dendrite of another neuron?

Axodendritic synapse Signup and view all the answers

What is the primary function of synaptic vesicles found in the presynaptic neuron?

They contain the chemical transmitter. Signup and view all the answers

What occurs during the absolute refractory period of a nerve?

The nerve is completely unexcitable to stimulation. Signup and view all the answers

During the relative refractory period, what is required for excitation of a nerve?

A stronger stimulus than normal is required. Signup and view all the answers

How can impulse transmission at a synapse be affected?

By physiological, pathological or pharmacological influences Signup and view all the answers

Which statement about antidromic impulse transmission is accurate?

It dies off at the first set of synapses it encounters. Signup and view all the answers

Which factor is known to increase nerve excitability?

Alkalinity of pH Signup and view all the answers

How do synapses function in the nervous system?

They serve as one-way valves ensuring impulses flow forward. Signup and view all the answers

Which of the following classifications of synapses is based on structure?

Axoaxonic synapses Signup and view all the answers

What effect does mechanical pressure on a nerve typically have?

It reduces nerve excitability. Signup and view all the answers

What characterizes an axosomatic synapse?

The terminal axon connects to the soma of another neuron. Signup and view all the answers

What is the effect of physiological influences on synaptic transmission?

They can enhance or block impulse transmission. Signup and view all the answers

Which electrolyte imbalance is associated with decreased nerve excitability?

High potassium ion levels Signup and view all the answers

Which option is NOT an anatomical classification of synapse?

Chemical synapse Signup and view all the answers

What corresponds to the descending limb of the action potential during the refractory periods?

Both refractory periods together. Signup and view all the answers

What is a consequence of ischemia on nerve function?

Decreased excitability of nerves. Signup and view all the answers

Study Notes

Refractory Period

The absolute refractory period is a phase where a nerve is completely non-responsive, unable to be excited by stimuli of any strength.
This period corresponds to the ascending and the overshoot parts of the action potential, continuing until the resting potential is approximately one-third complete.
The relative refractory period allows for partial recovery of nerve excitability, requiring a stronger-than-normal stimulus for activation.
This period aligns with the remaining portion of the descending limb of the action potential until the onset of another depolarization.

Factors Affecting Nerve Excitability

Temperature: Cooling decreases excitability, while warming enhances it.
Pressure: Mechanical pressure can diminish nerve excitability.
Blood Supply: Ischemia leads to decreased nerve excitability.
Oxygen Supply: Lack of oxygen reduces nerve excitability.
pH Level: Alkaline conditions increase excitability, while acidic conditions decrease it.
Electrolytes: Low calcium and hydrogen ion concentrations enhance excitability, whereas high potassium levels can decrease it.

Synapse

A synapse is a junction facilitating communication between two neurons, enabling physiological continuity rather than a physical connection.
Synapses serve as unidirectional valves, only allowing impulse flow from pre-synaptic to post-synaptic neurons, thereby ensuring orthodromic impulse direction.
Divergence: Process where one presynaptic neuron connects to multiple postsynaptic neurons.

Functions of Synapse

The primary role of synapses is to transmit action potentials between neurons.
Synapses can be classified into:
- Excitatory Synapses: Facilitate impulse transmission.
- Inhibitory Synapses: Hinder the transmission of impulses.

Excitatory Postsynaptic Potential (EPSP)

EPSP is a non-propagated electrical signal occurring during synaptic transmission.
When an action potential reaches the presynaptic terminal, calcium channels open, allowing calcium ions to enter and triggering neurotransmitter release (e.g., acetylcholine).
Acetylcholine crosses the synaptic cleft, binds to receptor proteins on the postsynaptic membrane, forming a neurotransmitter-receptor complex that generates an EPSP.
The neurotransmitter-receptor complex prompts the opening of ligand-gated sodium channels.

Antidromic Impulse Transmission

Impulses traveling in the wrong direction (antidromic) cannot propagate beyond the initial synapses they encounter.

Neurotransmitter Dynamics

Synapses serve as regulatory sites in nervous pathways where impulse transmission can be modulated—enhanced, inhibited, or blocked—due to various physiological, pathological, or pharmacological factors.

Neuron Types in Synapses

Presynaptic Neuron: The neuron transmitting impulses to the synapse.
Postsynaptic Neuron: The neuron receiving impulses from the synapse.
Synaptic knobs in presynaptic neurons contain vesicles filled with chemical transmitters.

Synapse Classification

Anatomical Classification:
- Axoaxonic: Axon of one neuron connects to the axon of another.
- Axodendritic: Axon of one neuron connects to the dendrite of another.
- Axosomatic: Axon of one neuron connects directly to the cell body of another.
Physiological/Functional Classification:
- Chemical Synapses: Utilize neurotransmitters for signal transmission.
- Electrical Synapses: Allow direct ionic current flow between neurons.
- Conjoint Synapses: Function through combined mechanisms.

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Description

Explore the intricacies of the absolute and relative refractory periods in nerve excitability. This quiz delves into the physiological mechanisms and factors influencing nerve responsiveness, such as temperature, pressure, and blood supply. Test your understanding of these critical concepts in neurophysiology.