Module 13.4 Sensation Part II: Role of the PNS in Sensation

Question 1

What is sensory transduction?

Answer 1

Sensory transduction is the process by which a stimulus is converted into an electrical signal. This involves the opening of sodium ion channels in the axolemma when a stimulus is detected by a sensory receptor, leading to a temporary depolarization known as a receptor potential. If enough sodium ions enter, the membrane potential may reach a threshold, causing voltage-gated sodium ion channels to open and propagate an action potential along the axon toward the CNS.

Question 2

What is the difference between rapidly adapting receptors and slowly adapting receptors?

Answer 2

Rapidly adapting receptors respond rapidly with high intensity to stimuli but stop sending signals after a certain time period, a process called adaptation. These receptors detect the initiation of stimuli but ignore ongoing stimuli. On the other hand, slowly adapting receptors respond to stimuli with constant action potentials that don’t diminish over time.

Question 3

What are the two forms of sensory receptors?

Answer 3

Sensory receptors exist in two forms: encapsulated nerve endings, which are surrounded by specialized supportive cells, and free nerve endings, which lack supportive cells.

Question 4

How are sensory receptors classified by the location of stimuli they detect?

Answer 4

Sensory receptors can be sorted by the location of stimuli they detect into exteroceptors, which are usually close to the body’s surface and detect stimuli originating from outside the body, and interoceptors, which are usually found within the body’s interior and detect stimuli originating from within the body itself.

Question 5

What are mechanoreceptors and what type of stimuli do they respond to?

Answer 5

Mechanoreceptors are encapsulated interoceptors or exteroceptors in the musculoskeletal system, skin, and in many other organs. They depolarize in response to anything that mechanically deforms the tissue where the receptors are found. Mechanically gated ion channels allow for sensory transduction from vibration, light touch, stretch, and pressure. user Classification of Sensory Receptors (4 of 10)

Question 6

What are thermoreceptors and what type of stimuli do they respond to?

Answer 6

Thermoreceptors are free nerve endings in the skin and mucous membranes that depolarize in response to changes in temperature.

Question 7

What are photoreceptors and what type of stimuli do they respond to?

Answer 7

Photoreceptors are located in the retina of the eye and depolarize in response to light.

Question 8

What are nociceptors and what type of stimuli do they respond to?

Answer 8

Nociceptors are free nerve endings in every body tissue except the brain. They depolarize in response to tissue damage.

Question 9

What are chemoreceptors and what type of stimuli do they respond to?

Answer 9

Chemoreceptors are located in the carotid and aortic bodies and in the medulla oblongata. They depolarize in response to changes in the concentration of specific chemicals.

Question 10

What are osmoreceptors and what type of stimuli do they respond to?

Answer 10

Osmoreceptors are located in the hypothalamus and depolarize in response to changes in the concentration of solutes in the blood or interstitial fluid.

Question 11

What are proprioceptors and what type of stimuli do they respond to?

Answer 11

Proprioceptors are located in muscles, tendons, and joints and depolarize in response to the degree of stretch.

Question 12

What are baroreceptors and what type of stimuli do they respond to?

Answer 12

Baroreceptors are located in the walls of most arteries, especially in the carotid sinuses and aortic arch. They depolarize in response to stretch caused by increased blood pressure.

Question 13

What are stretch receptors and what type of stimuli do they respond to?

Answer 13

Stretch receptors are located in the lungs and depolarize in response to the degree of lung inflation.

Question 14

What are the different types of sensory receptors classified by stimuli?

Answer 14

The different types of sensory receptors classified by stimuli include thermoreceptors, chemoreceptors, photoreceptors, and nociceptors.

Question 15

What is the function of thermoreceptors and where are they located?

Answer 15

Thermoreceptors are exteroceptors that depolarize in response to temperature changes. They are the most slowly adapting receptors and have separate receptors to detect hot and cold.

Question 16

How do chemoreceptors function?

Answer 16

Chemoreceptors can be either interoceptors or exteroceptors. They depolarize in response to binding to specific chemicals in body fluids or in the air, generating a receptor potential as sodium ion channels open.

Question 17

: What are the classes of mechanoreceptors?

Answer 17

The classes of mechanoreceptors include Merkel cell fibers, tactile corpuscles (Meissner corpuscles), Ruffini endings (bulbous corpuscles), lamellated corpuscles (Pacinian corpuscles), hair follicle receptors, and proprioceptors.

Question 18

What are the types of thermoreceptors and how do they function?

Answer 18

Thermoreceptors are usually small knobs at the end of free nerve endings in the skin. “Cold” receptors respond to temperatures between 10 °C and 40 °C (50–104 °F) and are located in the superficial dermis. “Hot” receptors respond to temperatures between 32 °C and 48 °C (90–118 °F) and are located deep in the dermis. Temperatures outside these ranges are detected by nociceptors, which is why extremes of temperature are interpreted as pain.

Question 19

What are the main components of first-order somatic sensory neurons?

Answer 19

First-order somatic sensory neurons are pseudounipolar neurons with three main components: the cell body, the peripheral process, and the central process.

Question 20

How does information flow in a first-order sensory neuron?

Answer 20

In a first-order sensory neuron, the peripheral process transmits an action potential from the sensory receptor to the neuron’s central process. The central process then transmits the action potential from the peripheral process to the posterior horn, eventually synapsing on a second-order neuron in the spinal cord or brainstem. The action potential propagated down the peripheral process does not generally reach the cell body; instead, it is usually transmitted to the central process in the area where the peripheral and central processes come into contact near the cell body.

Question 21

How are sensory neurons classified?

Answer 21

Sensory neurons are classified by two factors that determine the speed with which peripheral axons conduct action potentials: the diameter of the axon and the thickness of its myelin sheath. Large-diameter axons with thick myelin sheaths conduct the fastest impulses, while small-diameter axons with little myelin transmit action potentials the slowest.

Question 22

What are receptive fields in the context of sensory neurons?

Answer 22

Receptive fields are areas served by a particular neuron. A neuron with more branches innervates larger receptive fields. Body regions whose primary function is sensing the environment, such as the fingertips, contain many neurons with smaller receptive fields. In contrast, body regions that are not as involved in sensing the environment, like the skin of the forearm, have fewer neurons with larger receptive fields.

Question 23

What is the two-point discrimination threshold?

Answer 23

The two-point discrimination threshold is a method for measuring the relative size of receptive fields.

Question 24

What are dermatomes and how are they used clinically?

Answer 24

Dermatomes are different segments of the skin based on the spinal nerve that supplies the region with somatic sensation. Dermatomes can be combined to assemble a dermatome map, which represents all of the sensory pathways to different parts of the body. Dermatome maps can be used clinically to test the integrity of the sensory pathway to different parts of the body.

Question 25

What is referred pain?

Answer 25

Referred pain is a phenomenon whereby pain that originates in an organ is perceived as cutaneous pain. This occurs because many spinal nerves carry both somatic and visceral neurons, so visceral sensations travel along the same pathways as do somatic sensations. Referred pain is generally located along the dermatome for a particular nerve.