MD137 Introduction to Physiology Lecture 5

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Questions and Answers

What is the primary function of adaption in sensory receptors?

To increase action potential frequency with constant stimulation

To decrease sensitivity to a constant stimulus (correct)

To completely stop firing action potentials

To enhance sensitivity to all stimuli

Which type of sensory receptors signal the changes in stimulus intensity rapidly?

Constantly firing receptors

Non-adapting receptors

Slowly adapting receptors

Rapidly adapting receptors (correct)

What happens to the action potential frequency in sensory receptors when a constant strength stimulus is present?

It remains unchanged

It increases continuously

It fluctuates randomly

It decreases over time (correct)

How do slowly adapting receptors respond to stimulation over time?

They signal the presence of the stimulus continually Signup and view all the answers

What is indicated by the adaptation of sensory receptors to a constant stimulus?

Decreased sensitivity to changes in the stimulus Signup and view all the answers

What describes the primary function of rapidly adapting receptors?

They respond quickly to changes in stimulus intensity. Signup and view all the answers

Which statement accurately describes slowly adapting receptors?

They provide a continuous signal even when a stimulus is constant. Signup and view all the answers

How do afferent neurons contribute to the function of receptors?

They transmit information about stimulus duration and intensity to the central nervous system. Signup and view all the answers

What would be an expected response from a rapidly adapting receptor upon stimulus removal?

Continued action potentials for a brief period. Signup and view all the answers

Which characteristic distinguishes slowly adapting receptors from rapidly adapting ones?

The ability to detect prolonged stimuli. Signup and view all the answers

What is the role of excitatory postsynaptic potentials (EPSPs) in neuron signaling?

They increase the likelihood of action potential generation. Signup and view all the answers

Which ion primarily contributes to the generation of inhibitory postsynaptic potentials (IPSPs)?

Chloride (Cl-) Signup and view all the answers

What initiates the action potential in regions adjacent to a site of depolarization?

Local current spread Signup and view all the answers

What is the primary difference between excitatory and inhibitory neurotransmission?

Excitatory neurotransmission increases membrane potential while inhibitory reduces it. Signup and view all the answers

What effect does a decrease in the postsynaptic potential (PSP) usually have?

It causes hyperpolarization. Signup and view all the answers

What is the significance of chemical synapses in neuron communication?

They allow for complex integration of signals. Signup and view all the answers

Which of the following accurately describes depolarization?

It occurs when Na+ ions enter the neuron. Signup and view all the answers

What primarily determines whether a neuron fires an action potential?

The balance between EPSPs and IPSPs. Signup and view all the answers

What is the term used to describe the specific type of stimulus to which a particular receptor is sensitive?

Adequate stimulus Signup and view all the answers

How does an increase in stimulus intensity affect receptor activation?

It activates neighboring receptor units. Signup and view all the answers

Which process describes the opening or closing of ion channels in a specialized receptor membrane?

Stimulus transduction Signup and view all the answers

What occurs when the receptor potential reaches a certain threshold?

Action potentials are generated. Signup and view all the answers

What is the primary factor that leads to an increased firing frequency in sensory neurons as stimulus intensity increases?

Greater current flow through ion channels. Signup and view all the answers

The spread of receptor potential within an afferent neuron occurs until it reaches which region?

Region with high density of voltage-dependent sodium channels. Signup and view all the answers

Which of the following factors does NOT relate to changes in stimulus intensity?

The concentration of neurotransmitters. Signup and view all the answers

In the context of sensory physiology, what does a receptor potential represent?

A graded change in membrane potential. Signup and view all the answers

What is the primary function of sensory receptors?

To convert stimuli into neuronal activity Signup and view all the answers

Which of the following statements about sensory adaptation is correct?

Sensory adaptation occurs when receptors become less responsive over time. Signup and view all the answers

Which receptor type is primarily responsible for detecting light?

Photoreceptors Signup and view all the answers

How do the somatic senses contribute to the perception of stimuli?

By enabling the body to feel pain and touch Signup and view all the answers

Which statement about the somatosensory pathway is accurate?

It maps the location of each receptor involved in sensation. Signup and view all the answers

What distinguishes mechanoreceptors from other receptor types?

They respond to stretch and pressure. Signup and view all the answers

What characterizes the response of receptors within a sensory unit?

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

Which of the following is true regarding nociceptors?

They detect stimuli causing tissue damage. Signup and view all the answers

What is the role of transducers in sensory physiology?

To convert one form of energy into another. Signup and view all the answers

Study Notes

Course Information

Course: MD137
Course Title: Introduction to Physiology
Year: 2024-2025
Lecturer: Dr. Leo Quinlan
Lecturer Email: [email protected]
Lecture 5: Nerve impulse and the synapse

Lecture 5: Nerve Impulse and the Synapse

Topic: Sensory system and nerve impulse at the synapse
Subtopic: Sensory systems 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, with examples
- Classify stimuli
- Explain sensory adaptation
- Explain synapses and how they work
- Compare and contrast EPSPs and IPSPs

General Properties of Sensory Systems

Stimulus: Internal or external
Energy source
Sense organs
Transducer: Converts energy into nerve signals
Afferent pathway: carries signals to the central nervous system (CNS)
CNS integration: where signals are processed

Receptor Types

Location: Diagrams show locations of various receptor types, including within the eye, nose, skin, and throughout the body
Types: mechanoreceptors, thermoreceptors, photoreceptors, chemoreceptors, and nociceptors are detailed in a table alongside their stimuli modality and the location

Adequate Stimulus

Each stimulus has a specific receptor (e.g. taste buds for taste, rods and cones for light)
The stimulus the receptor is sensitive to is termed the adequate stimulus

Stimulus Intensity - Encoding

Intensity: Larger receptor potential, activation of more receptors, and activation of neighbouring units leads to increased firing frequency.
Diagram: Shows how different pressure levels correlate with firing frequency in neurons.

Generating a Sensation

Steps:
- Stimulus causes ion channels to open/close
- Current flow creates a receptor potential (graded change in membrane potential)
- If receptor potential reaches threshold, action potentials are generated and propagate along afferent neurons.
- Neurotransmitter release

Stimulus Duration

Adaptation:
- Some sensory neurons fire action potentials as long as stimulus is present.
- Others decrease firing frequency (adapt) if stimulus is constant.
- Sensory receptors can rapidly or slowly adapt to stimuli, signaled by changes in stimulus intensity or continuous presence.
Diagrams: Show graphs for rapidly and slowly adapting receptors.

Adaptation

Rapidly adapting receptor: Diagram shows rapid firing at onset of stimulus and reduced response during continued stimulus.
Slowly adapting receptor: Diagram shows continuous firing throughout stimulus duration.

AP Propagation

The propagation of action potentials is detailed, with focus on unmyelinated axons (continuous conduction) and myelinated axons (saltatory conduction) showing differences in conduction.
Diagrams: Show various aspects of action potential propagation.

Chemical Synapse

Diagram: Shows the sequence of events at the synapse, including: neurotransmitter release, docking protein, and postsynaptic receptor activation.
Summary of steps:
- Action potential reaches axon terminal.
- Ca2+ channels open, Ca2+ enters.
- Vesicles fuse with membrane.
- Neurotransmitter released into synapse.
- Neurotransmitter binds to receptors on postsynaptic neuron.
- Postsynaptic potential (PSP) is generated.

Excitatory/Inhibitory Transmission

Excitatory (EPSP): Neurotransmitter binding leads to a depolarizing postsynaptic potential which increases the likelihood of an action potential.
Inhibitory (IPSP): Neurotransmitter binding leads to a hyperpolarizing postsynaptic potential which decreases the likelihood of an action potential

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Description

This quiz covers Lecture 5 of MD137, focusing on nerve impulses and synaptic function in the sensory system. Participants will explore the role of neurons, sensory adaptation, synapse mechanisms, and the classification of stimuli. Test your knowledge on how sensory stimuli are transformed into nerve signals.