10 Questions
What is the term for the phenomenon where a receptor adapts to a sustained stimulus by decreasing its response?
Adaptation
Which type of receptors are always active and provide continuous information about stimulus?
Tonic receptors
In which receptor type does a decrease in stimulus intensity lead to a decrease in action potential frequency?
Phasic receptors
What is the term for the region of skin monitored by a sensory neuron, with greater receptor density leading to greater acuity?
Receptive field
Which phenomenon involves the most intensely activated pathway inhibiting less excited pathways at the peripheries, leading to localization and contrast sharpening?
Lateral inhibition
Which of the following statements about receptor potentials is correct?
Receptor potentials are generated by sensory transduction, which alters the receptor's permeability.
Which component of the reflex arc is responsible for integrating and processing information received from sensory receptors?
Integrating center (CNS)
Which of the following is NOT a step in a simple reflex arc?
Repolarization of the receptor potential
What is the primary function of the afferent division in a reflex arc?
To detect and respond to stimuli from the environment
How is the strength of a stimulus encoded in the reflex arc?
Both a and b
Study Notes
Reflex Arc
- Consists of 5 components: sensory receptor, afferent pathway, integrating center (CNS), efferent pathway, and effector organ (muscle or gland)
- Steps in a simple reflex arc:
- Activation of a receptor by a stimulus
- Activation of a sensory neuron: stimulation of dendrites produces graded polarization
- Information processing in the CNS
- Activation of a motor neuron: interneuron stimulates motor neurons that carry APs to periphery
- Response of a peripheral effector: motor neuron(s) release neurotransmitters at axon terminals, stimulating effector to respond
Afferent Division
- Consists of sensory receptors at peripheral endings of afferent neurons
- Respond to stimuli from external or internal environment
- Exist in various energy forms (modalities)
- Bring about graded potentials (receptor potentials) in receptor
- Receptor potential: sensory transduction process by which a stimulus is converted into an electrical signal
Coding of Stimulus Strength
- Stimulus intensity (strength) distinguished by:
- Frequency of APs generated in afferent neuron
- Number of receptors and afferent neurons activated within an area
- Stronger stimuli affect larger areas, and more receptors respond
Adaptation
- Decrease in receptor sensitivity with sustained stimulus strength
- Receptor “adapts” to stimulus by no longer responding to it to the same degree
- Decrease in AP frequency
Types of Receptors
- Tonic receptors:
- Always active
- Do not adapt or adapt slowly to sustained stimulus
- Provide continuous information about stimulus
- AP frequency reflects level of stimulation
- Phasic receptors:
- Normally inactive
- Adapt rapidly to sustained stimulus
- Become active for a short time
- Exhibit an off response when stimulus is removed
Acuity and Perception
- Receptive field: region of skin surface monitored by a sensory neuron
- Greater receptor density = smaller receptive field = greater acuity (discriminative ability)
- Lateral inhibition:
- Each activated signal pathway inhibits pathways next to it
- Stimulates inhibitory interneurons that pass laterally between ascending fibers
- Most strongly activated pathway in center of stimulus area inhibits less excited pathways at the peripheries
- Facilitates localization and sharpens contrast between wanted and unwanted information
Test your knowledge on the 5 components of a reflex arc - sensory receptor, afferent and efferent pathways, integrating center in the CNS, and effector organ. Also, quiz yourself on the steps involved in a simple reflex arc from activation of a receptor to response by the effector organ.
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