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Colden - Sensory Receptors
Sensory Receptors and Transduction

Additional Physiology Flashcards




What are the four basic categories of stimuli that can lead to action potentials?
1) mechanical

2) thermal

3) chemical

4) electromagnetic
How does a stimulus eventually cause firing of an action potential?
1) an adequate stimulus causes a change in membrane conductance

2) the change in membrane conduction causes a receptor potential (or generator potential)

3) if the receptor potential is depolarizing and large enough then an action potential will be fired
How does stimulus strength and duration affect action potential firing?
Different situations

1) A weak stimulus will cause a sub-threshold receptor potential which will not lead to an action potential

2) a normal stimulus will cause a super-threshold receptor potential which will fire an action potential

3) a stimulus that is either longer or stronger will increase the rate of action potential firing
What are the five main types of somatic sensory receptors?
Mechanoreceptors - touch, hearing

Photoreceptors - vision

Chemoreceptors - smell,taste

thermoreceptors - temperature

nocireceptors - pain
What are the main classifications of sensory receptors?
Exteroceptors - concerned with the external environment (includes all “five senses”).

Interoceptors - concerned with the internal environment (e.g., temperature, chemical composition, stretching of tissue)

Proprioceptors - concerned about the position of the body in space (e.g., muscle spindles, joint receptors).
What are the different types of mechanoreceptors?
Pacinian Corpuscles
-Subcutaneous layers of nonhairy skin & in muscle
-Pressure, vibration

Meissner’s Corpuscles
-Fingertips, nonhairy skin
-Tactile discrimination

Hair Follicle Receptors
-Hairy skin
-Detect velocity & direction of movement across skin

Merkel’s Disks
-Nonhairy skin
-Detect vertical indentations of skin

Ruffini’s Corpuscles
-Dermis of hairy skin & in joint capsules
-Detect stretch & joint rotation

Tactile Disks
-Hairy skin
-Similar to Merkel’s Disks
What is the difference in how a sensory cell is influenced versus a nerve cell?
A nerve cell is influenced by a transmitter

A sensory cell is influenced by a stimulus
What is a pacinian corpuscle?
It is a mechanoreceptor that detects pressure and vibration

It is present in skin and some mucous membranes.

The free nerve ending is encanspulated by CT
How does sensory transduction work in a pacinian corpuscle?
Pressure and vibration cause compression and stretch the Na+ channels.

More Na+ enters and creates a receptor potential.

The receptor potential causes an action potential to be fired at the 1st node of ranvier
How does adaptation work in pacinian corpuscles?
If constant pressure is being applied, the pacinian corpuscle can adapt to it and no longer react

When pressure is 1st applied, a receptor potential generates action potentials. Eventually the receptor potential will decay below threshold level and stop causing the firing of ap's.

The pressure being released has the same effect as the pressure being 1st applied to let the body know when the pressure is released.

Pacinian corpuscles use rapid adaptation
What is the mechanism of the rapid adaptation of the pacinian corpuscle?
When pressure is 1st applied the nerve ending is stretched and this generates the receptor potential.

The pressure is maintained and the nerve ending can adjust and the receptor potential decays.

Once the pressure is released, the nerve ending changes back and another receptor potential is generated
What are the different attributes of sensory properties?
Modality- different forms of energy are transformed by the nervous system into different sensations or sensory modalities.

Intensity or amount of a sensation depends on the strength of the stimulus.

The duration of sensation is defined by the relationship between the stimulus intensity and the perceived intensity.

Location - two important measurements of the awareness of the spatial aspects of sensory experience are:
1) the ability to locate the site of stimulation
2) the ability to distinguish two closely spaced stimuli
What are the different sensory modes related to modality?
vision, hearing, smell, taste, touch (pressure and temperature), pain, muscle length and tension, joint movement and position, pain, linear and rotational acceleration
Explain frequency code of stimulus intensity
For an individual pacinian corpuscle, increased levels of pressure lead to increased rates of action potential firing

Increased levels of pressure lead to a larger receptor potential which will fire more action potentials before it decays
Explain population code of stimulus intensity
Increased pressure will lead to an increased number of pacinian corpuscles being "recruited" which leads to more action potentials being fired

So for example instead of 2 pacinian corpuscles reaching threshold and firing action potentials, increased pressure causes 4 to fire
What is the difference between phasic receptors and tonic receptors?
Phasic receptors rapidly adapt because the receptor potentials decay quickly
ex - Pacinian Corpuscle

Tonic receptors slowly adapt because the receptor potentials slowly decay
ex - Pain receptor

Remember the decaying of the receptor potential determines how many action potentials will be fired
Explain the purpose of inhibitory receptive fields?
First there are small and large receptive fields.

In a small receptive field it is easy to pinpoint location because there is only one first order neuron leading to a second order neuron.

In a large receptive field there are multiple neurons so it's necessary to have inhibitory receptive fields which help pinpoint location
What are the two somatosensory pathways?
The dorsal column system involves fine touch, pressure, and proprioception.

The anterolateral system involves pain, temperature, and light touch

Both pathways follow the pathway of receptor to spinal cord to brain stem to thalamus to somatosensory cortex

The anterolateral system crosses the midline in the spinal cord

The dorsal column system crosses the midline in the brain stem
What is the overall take away from the somatosensory homunculus?
The hand (and fingers) is the most sensitive area while the face is less sensitive and the back even less so.
How would action potential firing be slowed down by a stimulus?
It is important to remember that is possible for a stimulus to cause a hyperpolarizing receptor potential which would slow down the rate of action potential firing.
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