Receptor Mechanisms - 37

Front 1

5 characteristics of Generator Potentials?

Back 1

1. Local: not propagated-electrotonic spread short distance – exponential decay
2. Graded
3. No refractory Period
4. Decrements with distance
5. Little affected by local anesthetics, e.g. Procaine

Hint 1

LoNG DeL

Front 2

What are sensory receptors?

Back 2

Specialized structures that are capable of responding to external or internal environment

Front 3

What are 2 important features of receptors?

Back 3

1. They are biological or sensory transducers: transform different forms of energy into electrical energy

2. Each receptor is especially sensitive to one form of energy.

Front 4

What is adequate stimulus?

Back 4

The form of energy (light, touch, etc.) to which the receptor is most sensitive

Front 5

Define Sensory unit?

Back 5

A single primary afferent fiber including its peripheral branches and central terminals

Front 6

Define Stimulus?

Back 6

Stimulus: stimulus energy serves as trigger to release energy stored at cell membrane as concentration gradient

Front 7

What is the stimulus energy used for?

Back 7

Stimulus energy serves only as a trigger to release energy previously stored across the cell membrane, presumably in the form of ion electrochemical gradients and neurons do not use it to produce electrical signals.

Front 8

Why do sensory neurons use stored energy ?

Back 8

Using the stored energy in the receptor membrane allows the sensory neuron to produce an extremely high degree of amplification of the stimulus.

Front 9

what does afferent fibers mean?

Back 9

means they enter the spinal cord dorsally.

Front 10

How are sensory stimuli transformed into nerve
impulses?

Back 10

Stimulus causes local flow of current in receptor and if there is a high receptor response, one or more Action Potentials will be elicited from sensory fibers

Front 11

Describe the transducer process or the process of excitation at receptor endings?

Back 11

A stimulus will cause a local change in permeability and this will generate a current (charge transfer)and you get an action potential.

Front 12

What happens when a Generator Potential is depolarized above threshold?

Back 12

The cell will generate spikes repetitively as long as the Generator Potential can maintain the depolarization above threshold.

Front 13

The rate of spike firing varies directly with what?

Back 13

The magnitude of the Generator Potential depolarization

Front 14

What is the difference between how receptors and parent nerve fibers code information?

Back 14

1.The receptor codes information by means of amplitude modulation

2. The parent nerve fiber codes information by frequency ( nerve impulses) modulation.

Front 15

What is the relationship between:

1. Generation potential and
Stimulus
2. Generation potential and
Impulse

Back 15

1. The greater the strength of the stimulus, the greater the size (or amplitude) of the generator potential (GP).
2. The greater the size of the GP, the greater the number of impulses that traverses nerve fiber per unit time.
3. A bigger stimulus strength, get bigger GP, more AP. Then when GP is big enough, you get a barrage of impulses traveling in that nerve fiber. That’s what we as neurophysiologists use to evaluate responses of system we’re stimulating. Can hear neuron AP popping.

Front 16

Define Receptive Field?

Back 16

That area within which a stimulus of sufficient intensity and quality will evoke a discharge of impulses in the sensory unit

Front 17

What are the three types of receptors?

Back 17

1. Exteroceptors (external)
2. Teleceptors (distant)
3. Enteroceptors (internal)

Hint 17

TEnEx

Front 18

What are the differences btw the three types of receptors?

Back 18

Exteroceptors (external) and teleceptors (distant)provide the CNS with information about the outside world but Enteroceptors (internal)
monitor changes inside the body

Front 19

compare the receptors in joint, golgi tendon organs, pacinian corpuscles and muscle spindle

Back 19

The receptors are simple in joints, more complicated in golgi tendon organs and pacinian corpuscles, and more complex in muscle spindle.

Front 20

What are the 9 classifications of receptors?

Back 20

1. Mechanoreceptors -
mechanical deformation

2. Thermoreceptors –
temperature

3. Nocireceptors – harmful,
noxious

4. Electromagneticreceptors – light

5. Chemoreceptors - chemical

6. Exteroceptors – from
external environment

7. Interoceptors – from
internal environment

8. Proprioceptors – from
within; – position of
body parts,- postural

9. Teleceptors – at a
distance, e.g. eye

Hint 20

CEMENT PIT

Front 21

Distinguish between:
1. Superficial
2. Visceral
3. Special

Back 21

1. Superficial – skin;
external

2. Visceral – deep pressure,
pain

3. Special – vision,
olfaction, auditory,
taste, linear – rotation
and linear acceleration

Hint 21

Special - TRAVeL Out

Front 22

Discuss the Law of Specific Nerve Energies ?

Back 22

It shows that each nerve tract sends info along nerve pathway to CNS and terminates in a specific point in CNS so that modality specificity (type of sensation appreciated or sensed) is determined by where it lands in CNS, based on connection in CNS.

Front 23

How is Modality specificity determined?

Back 23

It is determined centrally, meaning that sensation is experienced by specified termination of tract in CNS

Front 24

There are specific pathways to brain sites and their
intensity can be varied by what 2 means?

Back 24

1. altering frequency of
impulses
2. number of receptors
excited

Front 25

Discuss the LAW OF PROJECTION?

Back 25

It shows that you can
stimulate pathway from receptor to CNS at any point
and there is perception of sensation interpreted or referred to location of the receptor. For example, we can stimulate cortical receiving station for hand and for an amputee, it will be the phantom limb.

-It is a modification of law of specific nerve energies. The pathway goes all the way up to CNS. For example,a guy in a hospital had his toes amputated,but his toe itches! How is that possible? This is because the nerve fiber travels all the way up to higher centers and the law of projection tells us that the information goes back down to toe telling the patient to scratch it even though the leg is amputated.
- What could have happened to nerve pathway addressing this? Nerve pathway at end where cut could have been irritated by some infectious process, anywhere along that pathway, up or down.

Front 26

How do 2 types of receptors detect 2 different types of stimuli?

Back 26

The receptors can differentiate different types of stimuli because different stimuli correspond to different receptors which terminate at different places in the CNS and you can also have receptor fields overlapping, accounting for exciting more fibers, giving you different types of response in system.

Front 27

Discuss Pacinian corpuscles?

Back 27

-It is an “onion-like capsule” of connective tissue around myleinated sensory nerve fibers. The first node of Ranvier is inside the capsule but the second node of Ranvier is just outside the capsule.
-It is a viscoelastic structure (filled with fluid) located deep in the muscle and used for proprioception.
-It is a pressure receptor so if you apply pressure to the capsule, there is mechanical displacement of nerve terminal, and stretching it brings about opening up of channels and associated permeability of sodium ions and you get depolarization. Therefore, application of pressure will lead to a Generator Potential (GP). The bigger the stimulus, the bigger the GP so it is graded. This is the “ON” response of the rapidly adapting pacinian corpuscle. However, if you remove the stimulus, you get the subthreshold response (“OFF” response) from the pacinian corpuscle.

Front 28

How are impulses moved?

Back 28

Impulses are moved by saltatory conduction along the nerve fiber.

Front 29

Regarding the source of Generator Potentials, what will happen in these 3 scenarios?

1. Remove the capsule
2. If you block the 1st Node
of Ranvier
3. If you section the
sensory nerve (and allow
the nerve to degenerate

Back 29

1. Remove capsule – you will
still get a generator
potential (GP) and an
action potential (AP)
2. Block the 1st Node of
Ranvier – you will get a
generator potential (GP)
and no action potential
3. Section sensory nerve
and allow nerve to
degenerate – no generator
potential (GP)because the
source of the GP is in
the nerve terminal

Front 30

Define Receptor Adaptation?

Back 30

When a maintained stimulus of constant strength is applied to a sense organ, the frequency of spikes in the sensory nerve declines over a period of time

Front 31

What are 3 characteristics of Receptor Adaptation?

Back 31

1. Adaptation in the nerve fiber is in response to adaptation in the GP.

2. Adaptation varies with the type of sense organ.

3. Receptors are categorized as “slowly adapting” (tonic) or “rapidly adapting” (phasic)

Front 32

What are Rapidly adapting receptors?

Back 32

1. They have generator potentials with both transient (dynamic) and static phases but, they generate spikes only during the transient phase.

2. The threshold of the spike generator increases with time after the onset of stimulation

3. Usually respond only at the onset of a stimulus = “ON” response. Response at the cessation of a stimulus = “OFF” response.

Front 33

What is “accommodation”?

Back 33

Increase in threshold with time

Front 34

Slowly adapting receptors
Found in the carotid sinus, muscle spindles, receptor for cold and pain.

If pain and cold receptors were rapidly adapting, they undoubtedly would lose some of their warning value. Likewise, carotid and aortic receptors operate continuously in regulating blood pressure, and rapid adaptation would limit their precision of operation.

Back 34

Slowly adapting receptors
Found in the carotid sinus, muscle spindles, receptor for cold and pain.

If pain and cold receptors were rapidly adapting, they undoubtedly would lose some of their warning value. Likewise, carotid and aortic receptors operate continuously in regulating blood pressure, and rapid adaptation would limit their precision of operation.

Front 35

Where are Slowly adapting receptors found?

Back 35

They are found in:
1. carotid sinus
2. muscle spindles
3. cold receptor
4. pain receptor

If pain and cold receptors were rapidly adapting, they undoubtedly would lose some of their warning value. Likewise, carotid and aortic receptors operate continuously in regulating blood pressure, and rapid adaptation would limit their precision of operation.

Hint 35

CoMP Crashed

Front 36

Why are pain and cold receptors not rapidly adapting?

Back 36

If pain and cold receptors were rapidly adapting, they would lose some of their warning value.

Front 37

Why are carotid and aortic receptors not rapidly adapting?

Back 37

carotid and aortic receptors are not rapidly adapting because they operate continuously in regulating blood pressure, and rapid adaptation would limit their precision of operation.

Front 38

Compare phasic (rapid) adapating to tonic (slowly) adapting in terms of GP and AP?

Back 38

1. In phasic or rapid adapting, with regards to GP, there is a response related to stimulus strength and there is a nice burst of activity that then goes to extinction

2. In tonic or slow adapting receptor, you stimulate and maintain the stimulus and there is a burst of info that continues over time because the AP keeps firing.

Front 39

What are the three basic types of cutaneous mechanoreceptors?

Back 39

1. touch receptors.
2. pressure receptors.
3. vibration receptors.

Hint 39

TV Program

Front 40

What are cutaneous Touch Receptors?

Back 40

-They are sometimes referred to as velocity detectors and they are very extensive throughout surface of the body
- Their density varies with locations, e.g. finger tips, lips , oral cavity body (axial surface), hair follicle
- They undergo rapid adaptation and signal change of state

Front 41

What are pressure receptors
?

Back 41

-They serve as intensity or displacement detectors where they indicate stimulus duration

-They are slowly adapting and their discharge rate is proportional to stimulus intensity
- They are numerous in both hairy and glabrous skin where they respond primarily to pressure or maintained stimuli

Front 42

What are vibration receptors?

Back 42

-They serve as vibration or acceleration detectors and they are rapidly adapting

- They are located in hairy or glabrous skin, deep structures/pressure sensitive areas

-Their lowest threshold is in the finger tips, lips, scanty=trunk

-They may generate 1:1 response to tuning fork meaning it is a high fire system

-examples of the Receptor:
a) pacinian corpuscle
b) touch pressure receptor

Front 43

What are proprioceptors?

Back 43

- They are involved in position sense of body and body parts

-The receptor is located in joints, tendons (golgi), muscles(spindles)

-They are slowly adapting and they function as movement detector.

-Their discharge rate is proportion to joint position with movement at rest

Front 44

What is unique about extraocular eye muscles of some animals?

Back 44

They have no muscle spindles.

Front 45

Describe the muscle receptors
in mammals?

Back 45

-Muscle receptors in mammals is mainly the muscle spindle and the golgi tendon organ

Front 46

What is Weber-Fechner Principle?

Back 46

GRADATIONS OF STIMULUS STRENGTH DISCRIMINATE APPROXIMATELY PROPORTIONAL TO LOG OF STIMULUS INTENSITY

Front 47

What is spike discharge frequency?

Back 47

Indicator of stimulus intensity

Front 48

What is Pattern Theory?

Back 48

Firing at different frequencies in response to different energies so there is variation of firing frequency or pattern that determines quality of sensation experienced