Introduction to Physiology: Nerve Impulse and Synapse

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Questions and Answers

What defines the term 'adequate stimulus' in sensory physiology?

The maximum intensity of a stimulus.

The range of frequencies a stimulus can produce.

A specific type of receptor's sensitivity to a stimulus. (correct)

The overall perception of multiple stimuli combined.

In the process of stimulus transduction, what occurs immediately after the stimulus affects the receptor?

Receptor potential decreases to a resting state.

Voltage-dependent sodium channels close.

Ion channels in the receptor membrane open or close. (correct)

The action potentials are generated.

What effect does an increase in stimulus intensity have on receptor potentials?

Receptor potentials decrease as stimulus intensity increases.

Only receptors in the vicinity are activated.

More receptors become activated and firing frequency increases. (correct)

Receptor potentials become less graded as intensity rises.

What is a consequence of the receptor potential reaching the threshold for activation?

Action potentials are generated in the afferent neuron. Signup and view all the answers

How does stimulus intensity affect the activation of neighbouring units in sensory physiology?

Higher intensity activates both primary and neighbouring afferent units. Signup and view all the answers

Which statement correctly describes the role of sensory receptors?

They convert external stimuli into neuronal activity. Signup and view all the answers

What characterizes the response of all receptors within a sensory unit?

They respond exclusively to the same stimulus modality. Signup and view all the answers

Which receptor type is most sensitive to light stimuli?

Photoreceptors Signup and view all the answers

In the context of sensory systems, what is meant by 'receptive fields'?

They define the spatial area where a particular sensory receptor can detect stimuli. Signup and view all the answers

What role do mechanoreceptors play in the sensory system?

They are essential for interpreting stretch and pressure. Signup and view all the answers

What occurs in primary sensory neurons during stimulus presentation?

Some fire action potentials continuously as long as the stimulus is present. Signup and view all the answers

Which statement best describes adaptation in sensory receptors?

Adaptation results in decreased sensitivity to a stimulus of constant strength. Signup and view all the answers

What distinguishes rapidly adapting receptors from slowly adapting receptors?

Slowly adapting receptors signal ongoing stimulus presence, while rapidly adapting ones do not. Signup and view all the answers

How does the action potential frequency change in sensory receptors during adaptation?

It decreases with a constant stimulus strength over time. Signup and view all the answers

Which type of sensory receptor would be most responsive to changes in stimulus intensity?

Rapidly adapting receptors. Signup and view all the answers

What is the primary function of sensory receptors in relation to stimulus strength?

To exhibit decreased sensitivity to constant stimuli over time. Signup and view all the answers

What could be a result of failing adaptation in sensory receptors?

Heightened sensitivity to constant stimuli over time. Signup and view all the answers

Which of the following best characterizes action potentials in afferent neurons?

They fluctuate in response to the presence of various stimuli. Signup and view all the answers

In the context of sensory physiology, how is information about a stimulus's duration encoded?

By the frequency of action potentials over time. Signup and view all the answers

Which type of sensory receptor is likely to signal ongoing pressure from a stimulus?

Strictly slowly adapting receptors. Signup and view all the answers

Study Notes

Course Information

Course: MD137
Course Name: Introduction to Physiology
Lecturer: Dr. Leo Quinlan
Email: [email protected]
Dates: 2024-2025

Lecture 5: Nerve Impulse and the Synapse

Topic: Sensory system and nerve impulse
Subtopic: Synapse
Description: Collect data and pass it on
Learning Outcomes:
- Describe the basic role of neurons in sensory physiology
- Explain how physical stimuli are translated to nerve Action Potentials (APs)
- Stimuli classification
- Sensory adaptation
- Synapse function
- EPSP vs IPSP
General Properties of Sensory Systems:
- Stimulus (Internal/External)
- Energy source
- Receptors/Sense organs
- Transducer
- Afferent pathway
- CNS integration

Receptor Types

Various types of sensory receptors exist, including:
- Mechanoreceptors: Respond to stretch/pressure (skin, muscles, tendons)
- Thermoreceptors: Respond to temperature changes (skin)
- Photoreceptors: Respond to light (retina)
- Chemoreceptors: Respond to specific chemical stimuli (tongue, nose)
- Nociceptors: Respond to damaging stimuli (throughout the body)
All receptors in a sensory unit respond to the same stimulus modality
Receptive fields of sensory units responding to different modalities often overlap

Adequate Stimulus

Each stimulus has a specific type of receptor
- Taste buds - taste
- Rods and cones - light
The adequate stimulus of a receptor is the specific stimulus that it is most sensitive to

Stimulus Intensity - Encoding

Larger receptor potential --> Increased firing frequency in primary unit
More receptors activated --> Increased firing frequency in higher order neurons
Neighboring units activated

Generating a Sensation

Stimulus opens/closes ion channels in receptor membrane
Results in receptor potential (graded change in membrane potential)
If receptor potential reaches threshold, action potentials are generated
Action potentials propagate along afferent neurons and cause neurotransmitter release

Stimulus Duration

Some primary sensory neurons fire continuously as long as the stimulus is present
Adaptation is when sensory receptors decrease in sensitivity to a constant stimulus
Sensory receptors can be rapidly or slowly adapting:
- Rapidly adapting: signal change in stimulus intensity
- Slowly adapting: signal continuous presence of stimulus

AP Propagation (Unmyelinated)

Local current spread (electrotonic conduction) depolarizes nearby membrane parts, initiating the spike.
Propagation direction: site A à B à C à D.
Region of repolarization state, site C is refractory

AP Propagation (Myelinated)

Saltatory conduction, depolarization 'jumps' between nodes of Ranvier

Chemical Synapse

Action potential causes Ca²⁺ channels to open allowing Ca²⁺ to enter presynaptic terminal.
Synaptic vesicles fuse with membrane, releasing neurotransmitters
Neurotransmitter binds to receptors on postsynaptic cell, causing graded change in the postsynaptic membrane potential
Neurotransmitter breaks down, is taken up by presynaptic or diffuses away

Postsynaptic Potential (PSP)

EPSP: Excitatory postsynaptic potential – increases firing likelihood
IPSP: Inhibitory postsynaptic potential – decreases firing likelihood

Excitatory Transmission

Describes the process through which neurotransmitters increase firing of the nerve by causing sodium (Na⁺) channels to open

Inhibitory Transmission

Describes the process through which neurotransmitters decrease firing of the nerve by causing chloride (Cl⁻) channels to open

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Description

This quiz covers Lecture 5 of the MD137 course, focusing on the sensory system and the role of neurons in transmitting nerve impulses. You will explore synapse functions, action potentials, and the classification and adaptation of sensory stimuli.