Introduction to Physiology Lecture 5

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Questions and Answers

What is the primary characteristic of rapidly adapting receptors?

They are primarily located in muscle tissue.

They respond quickly to changes in stimulus but stop firing with continuous stimuli. (correct)

They continue to generate action potentials in response to constant stimuli.

They have a high threshold for activation.

How do slowly adapting receptors function over time when exposed to a constant stimulus?

They produce a consistent rate of action potentials for an extended period. (correct)

They sharply decrease their response after a short time period.

They only respond to the onset of the stimulus.

They increase their sensitivity to the ongoing stimulus.

What role do afferent neurons play in the context of sensory receptors?

They primarily respond to muscle tension changes.

They inhibit the activity of rapidly adapting receptors.

They convey signals from peripheral receptors to the central nervous system. (correct)

They generate receptor potentials in response to stimuli.

What happens to the receptor potential in rapidly adapting receptors during a prolonged stimulus?

It quickly returns to baseline after a short burst. Signup and view all the answers

In the context of sensory receptors, what is primarily measured by the action potentials generated by the receptors?

The intensity of the stimulus. Signup and view all the answers

What typically occurs in rapidly adapting receptors?

They signal changes in stimulus intensity. Signup and view all the answers

What happens to action potential frequency in slowly adapting receptors?

It remains consistent as long as the stimulus is present. Signup and view all the answers

How do sensory receptors adapt to a constant stimulus?

They demonstrate a decrease in sensitivity to the stimulus. Signup and view all the answers

What do primary sensory neurons that fire action potentials in response to stimuli do?

They release neurotransmitters only when a stimulus is present. Signup and view all the answers

In sensory physiology, what is the term used for a decreased action potential frequency as a result of constant stimulus strength?

Adaptation Signup and view all the answers

What is the primary function of sensory receptors in the body?

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

Which of the following receptor types is specifically sensitive to light?

Photoreceptors Signup and view all the answers

What does sensory adaptation refer to?

The decrease in sensitivity to a constant stimulus Signup and view all the answers

Which of the following statements about communicative pathways in sensory systems is true?

Afferent pathways carry sensory information to the CNS Signup and view all the answers

Which type of receptor is activated by stimuli that cause tissue damage?

Nociceptors Signup and view all the answers

What is an EPSP in the context of neuronal communication?

An excitatory postsynaptic potential that increases the likelihood of an action potential Signup and view all the answers

Which sensory receptor type would primarily respond to temperature changes?

Thermoreceptors Signup and view all the answers

Which receptors are distributed throughout the body and responsible for touch and pain sensations?

Nociceptors Signup and view all the answers

How are stimuli classified in the sensory systems?

By the type of receptor activated Signup and view all the answers

What occurs when a Post-Synaptic Potential (PSP) leads to increased firing in a neuron?

Excitatory postsynaptic potential (EPSP) Signup and view all the answers

Which ion is primarily involved in creating an excitatory postsynaptic potential (EPSP)?

Sodium (Na+) Signup and view all the answers

What happens to the membrane potential during an IPSP?

It becomes more negative Signup and view all the answers

What does the term 'electrotonic conduction' refer to?

The spread of local current that causes depolarization in neighboring membrane areas Signup and view all the answers

How does an excitatory neurotransmitter primarily affect the postsynaptic neuron?

By facilitating Na+ entry into the neuron Signup and view all the answers

Which of the following best describes the role of neurons in sensory physiology?

Neurons convert physical stimuli into action potentials Signup and view all the answers

What occurs when a PSP causes decreased firing in a neuron?

It is referred to as an inhibitory postsynaptic potential (IPSP) Signup and view all the answers

What determines whether a synapse is excitatory or inhibitory?

The type of neurotransmitter released Signup and view all the answers

What term describes the specific stimulus to which a receptor is sensitive?

Adequate stimulus Signup and view all the answers

What occurs when the receptor potential reaches the threshold for activation?

Action potentials are generated Signup and view all the answers

What is the result of a larger receptor potential?

Increased firing frequency in higher-order neurons Signup and view all the answers

What initiates the generation of a sensation in sensory receptors?

Opening or closing of ion channels Signup and view all the answers

Which characteristic describes the nature of receptor potentials?

They are graded changes in membrane potential. Signup and view all the answers

What is an effect of activating neighboring receptors?

Enhanced perception of the stimulus Signup and view all the answers

What mechanism primarily contributes to the coding of stimulus intensity?

Increasing the size of the receptor potential Signup and view all the answers

What happens when more receptors are activated by a stimulus?

Greater action potential frequency occurs Signup and view all the answers

Study Notes

Course Information

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

Sensory System and Nerve Impulse

Sensory system's role: Collects data and passes it on.
Learning Outcomes: Describe the basic role of neurons in sensory physiology, explain examples of how physical stimuli are translated to nerve APs, explain stimuli classification, describe sensory adaptation, define a synapse and how it functions, explain EPSP versus IPSP.

General Properties of Sensory Systems

Stimulus: Internal or external source of energy
Energy Source: Internal or External
Receptors: Sense organs that transduce energy and convert it to something the nervous system can use.
Transducer: Converts energy of stimulus into a signal.
Afferent Pathway: Pathway for sensory signals that travel to the CNS.
CNS Integration: Where sensory input is processed.

Receptor Types

Receptors: Specialized cells that detect stimuli.
Examples of receptor types: Sclera, Ciliary body, Suspensory ligament, Cornea, Iris, Pupil, Aqueous humour, Lens, Vitreous humour, Choroid, Retina, Fovea (centre of visual field), Optic nerve, Nasal cavity, Olfactory bulb, Bone, Epithelial cell, Chemoreceptor cell, Cilia, Mucus.
Image diagrams show specific locations of these receptors types.

Somatic Senses

Function: Enables body to feel sensations such as ache, chill, touch and pain.
Receptors: Broadly distributed.
Receptor Types: Merkel's disk, Epidermal-dermal border, Free nerve endings, Meissner's corpuscles, Hair follicle receptor, Pacinian corpuscles, Ruffini's endings.
Stimulus Response: Responds to a wide variety of stimuli.

Somatosensory Pathway

Function: Convey the type and location of sensory stimuli.
Type determination: Based on the type of receptor activated.
Location determination: Brain has a map of each receptor location.

Somatic Senses - Internal Stimuli

Sensory System includes Touch, Temperature, Pain, Itch, Proprioception, and Pathway.
Sensory signals cross to the cerebral cortex
Sensory cortex space allocated is proportional to its sensitivity.

Stimulus Type

Each receptor is sensitive to one specific stimulus type or modality.
Types and examples of receptors: Mechanoreceptors (stretch and pressure), Thermoreceptors (cold and warmth), Photoreceptors (light), Chemoreceptors (chemicals), Nociceptors (tissue damage).
Receptor Location: Skin, muscle and tendons, blood vessels (Mechanoreceptors). Skin (Thermoreceptors). Retina (Photoreceptors). Tongue and nose (Chemoreceptors). Throughout the body (Nociceptors).
Receptive Fields: Receptive fields of sensory units overlap.

Adequate Stimulus

Specific type of stimulus which a receptor responds to (I.e: Taste buds-taste; Rods and cones-light).

Stimulus Intensity - Encoding

Larger receptor potential leads to increased firing frequency in the primary unit.
More receptors and neighbouring unit activation leads to increased firing frequency in higher order neurons.

Generating a Sensation

Stimuli cause opening or closing of ion channels.
Current flows causing a graded receptor potential change in membrane potential.
Threshold reaching results in action potential generation.
Action potentials propagate and neurotransmitter release occurs.

Stimulus Duration

Some primary sensory neurons continuously fire action potentials while stimulus is present.
Others do not.
Sensory adaptation: Receptors decrease sensitivity to consistent stimuli.
Sensory receptors can be rapidly or slowly adapting.
Rapidly adapting receptors respond to changes in stimulus intensity.
Slowly adapting receptors respond to the continued presence of a stimulus.

Adaptation

Diagrams of rapidly and slowly adapting receptors.
Receptor responses to stimulus on and off are shown.

AP Propagation

Action Potential Propagation: Propagates along the afferent neuron.
Explains the steps involved in propagation.
Depolarization and re-polarization of nearby parts of the membrane are shown.
Unmyelinated and myelinated nerve fiber are shown. The myelinated uses saltatory conduction whereas the unmyelinated uses continuous conduction.

Chemical Synapse

Action potential triggers voltage-gated ion channels opening.
Calcium (Ca2+) influx release neurotransmitters from synaptic vesicles into the synaptic cleft.
Neurotransmitter binds to receptors on postsynaptic cell, causing a response.

Post-Synaptic Potential (PSP)

EPSP (excitatory postsynaptic potential): Increases firing rate.
IPSP (inhibitory postsynaptic potential): Decreases firing rate.

Excitatory Transmission

Process of excitation.
Diagram illustrating the flow of ions (Na+, Ca2+) through channels.

Inhibitory Transmission

Process of inhibition.
Diagram illustrating the flow of ions (Cl-, Ca2+) through channels.

Learning Outcomes (Page 33)

Learning outcomes for the lecture are repeated.

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Description

This quiz explores the nervous system's role in sensory physiology, focusing on nerve impulses and synaptic functions. It requires an understanding of how physical stimuli are transformed into action potentials, the classification of stimuli, and mechanisms like EPSP and IPSP. Prepare to demonstrate your knowledge of neuron functions and sensory adaptation.