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MD2002 > Sensory Receptors > Flashcards

Sensory Receptors Flashcards

1
Q

Briefly explain the function of sensory receptors.

A

Changes sensory stimuli (touch, temperature etc) into nerve signals that are then conveyed to and processed in the CNS.

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2
Q

What are examples of mechanoreceptors enabling

1. Skin tactile sensibilities and 2. Deep tissue sensibilities ?

A
    • Free nerve endings
    • Expanded tip endings (e.g. Merkel’s discs)
    • Spray endings (e.g. Ruffini’s endings)
    • Encapsulated endings (e.g. Meissner’s corpuscles and Krause’s corpuscles)
    • Hair end-organs
    • Free nerve endings
    • Expanded tip endings
    • Spray endings (e.g. Ruffini’s endings)
    • Encapsulated endings (e.g. Pacinian corpuscles)
    • Muscle endings
    • Muscle spindles
    • Golgi tendon receptors
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3
Q

Which layers of skin are included under skin tactile sensibilities ?

A

Epidermis and dermis

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4
Q 
State whether each of the following is a slow-adapting or fast-adapting mechanoreceptor, and which sensation each one senses. 
A) Meissner corpuscule
B) Merkel's corpuscule
C) Pacinian corpuscule
D) Ruffini corpscule
A

A) Meissner corpuscule: rapidly-adapting. TOUCH and PRESSURE.
B) Merkel’s corpuscule: slow-adapting. TOUCH and PRESSURE.
C) Pacinian corpuscule: rapidly-adapting. VIBRATION and DEEP PRESSURE.
D) Ruffini corpscule: slow-adapting. SKIN STRETCH

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5
Q

What kind of receptors are free nerve endings ? Are they rapidly-adapting or slow-adapting ?

A

Some nociceptors, some thermoreceptors, some mechanoreceptors.
Free nerve endings are slow-adapting

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6
Q

What is a possible difference regarding receptors between hairy and glabrous skin ?

A

Hairy skin will have hair receptors whilst glabrous skin might have Meissner’s corpuscles

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7
Q

Give the main features of Pacini’s corpuscles, including:

  • size
  • shape
  • location
  • function
  • type of sensory fiber and presence in hairy and/or glabrous skin types
  • rapidly or slow-adapting, and why
  • Activation treshold
A
  • largest mechanoreceptor – 2mm long
  • Onion like encapsulation of nerve endings;
  • Found in deep layers of dermis; detects high frequency (40-500Hz) vibration;
  • Aβ fibres; glabrous & hairy skin types.
  • Rapidly adapting due to a slick viscous fluid between the layers – more later on adaptation
  • Has a low activation threshold ie is sensitive
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8
Q

Give the main features of Meissner’s corpuscles, including:

  • size and basic components
  • shape
  • location
  • function
  • type of sensory fiber and presence in hairy and/or glabrous skin types
  • rapidly or slow-adapting
  • Activation treshold
A
  • Encapsulated nerve endings similar to Pacini’s but much smaller; Stacks of discs interspersed with nerve branch endings;
  • Found between dermal papillae; detects touch, flutter &low frequency vibration (2-40Hz);
  • Aβ fibres; glabrous (non-hairy) skin types
  • rapidly-adapting
  • Has a low activation threshold so is sensitive
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9
Q

Give the main features of Merkel’s disks, including:

  • basic components
  • shape
  • location
  • function
  • type of sensory fiber and presence in hairy and/or glabrous skin types
  • rapidly or slow-adapting
A
  • Non-encapsulated nerve endings; consist of a specialised epithelial cell + nerve fibre
  • Found just under the skin surface in for example the finger tips – good discrimination. Multiple branches often found in an ‘Iggo Dome’.
  • detect static touch and light pressure; work with Meissner’s corpuscles to help determine texture
  • Aβ fibres; all skin types.
  • Slowly adapting

-

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10
Q

Give the main features of Ruffini corpuscle, including:

  • basic components
  • location
  • function
  • presence in hairy and/or glabrous skin types
  • rapidly or slow-adapting
  • how they work
A
  • encapsulated nerve endings
  • located in the deeper layers of the skin as well as tendons and ligaments
  • responds to skin stretch
  • in all skin types but especially abundant in hands and fingers as well as soles of feet
  • nerve ending weave between collagen fibres which activate the nerve when they are pulled longitudinally
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11
Q

Give the main features of skin hair cell receptors, including:

  • basic components
  • location
  • function
A
  • mechanosensitive receptor wrapped around its follicle.
  • present in hairy skin
  • detect both the muscular movements of the hair (erector muscle) and the external displacements of the hair
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12
Q

Name the mechanoreceptors for:

  1. Hearing
  2. Equilibrium
  3. Arterial Pressure
A
  1. Hearing = Sound receptors of cochlea
  2. Equilibrium = Vestibular receptors
  3. Arterial Pressure = Baroreceptors of carotid sinuses and aorta
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13
Q

What are different things that chemoceptors can sense ? For each one, name a specific receptor (e.g. Taste- receptor of taste buds).

A 
•  Taste
–  Receptors of taste buds
•  Smell
–  Receptors of olfactory epithelium
•  Arterial oxygen
–  Receptors of aortic and carotid bodies
•  Osmolality
–  Neurons in or near supraoptic nuclei
•  Blood CO2
–  Receptors in or on surface of medulla and in aortic and carotid bodies
•  Blood glucose, amino acids, fatty acids 
–  Receptors in hypothalamus
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14
Q

What is the difference between a receptor and generator potential ?

A

Generator Potential: Potential caused by a stimulus to a nerve ending
Receptor Potential: Potential caused by a stimulus to a receptor cell

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15
Q

What is the immediate effect following stimulation of a receptor ?

A

Change in the membrane electrical potential (this change = RECEPTOR POTENTIAL.)

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16
Q

What is receptor/generator potential ?

A

“graded response to a stimulus that may be DEPOLARIZING or HYPERPOLARIZING”

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17
Q

What different things can create a receptor potential ?

A
  • MECHANICAL deformation which stretches the receptor membrane and also opens ion channels.
    – Application of a CHEMICAL to the membrane which opens ion channels.
    – Change in membrane TEMPERATURE which changes the permeability of the membrane.
    – Effects of ELECTROMAGNETIC radiation (eg light) on visual receptor which changes receptor membrane characteristics allowing ions to flow through membrane channels.
18
Q

What is the maximum amplitude of most sensory receptor potentials ? When would this occur ?
What is the maximum voltage recorded in action potentials ? When would this occur ?

A 
100 millivolts (mV), at an extremely high intensity of sensory stimulus
Around the same (100 mV), when the membrane becomes maximally permeable to sodium ions.
19
Q

What is the relation between a receptor potential and action potential ?

A

When the receptor potential rises above the threshold for eliciting action potentials in the nerve fiber attached to the receptor, then action potentials occur.
The more the receptor potential rises above the threshold level, the greater becomes the action potential frequency.

20
Q

What is the structure of the nerve fiber in a Pacinian Corpuscle ? Explain the main features of the receptor potential of the Pacinian Corpuscle.

A

Tip unmyelinated, then fibre myelinated shortly before leaving corpuscle.

  • Mechanial compression of layers results in deformed area in central fibre
  • Ion channels open up, increasing permeability
    • ions can diffuse inside the fibre
  • That increases amount of + charge inside fibre (i.e. increase receptor potential)
  • Receptor potential induces current flow which spreads along fiber until reach node of Ranvier
  • At the first node of Ranvier, depolarises fibre membrane (set off AP which can travel up the fiber)
21
Q

Explain the relationship between stimulus intensity and the receptor potential, especially with respect to the Pacinian Corpuscle.

A

Amplitude of receptor potential changes because of progressively stronger mechanical compression applied to central core of Pacinian Corpuscle.

22
Q

For a non-damaging sensory stimulus, what is the the intensity of the stimulus coded by ? Give an example for this.

A

By the frequency of action potentials in the sensory nerve (which is itself influence by extent in increase in receptor potential above the threshold).
E.g. light touch, no AP firing (not enough for treshold)
As pressure increases, more and more rapid firing of AP (so frequency of AP firing feeds us info about pressure being applied)

23
Q

Nerve fibres transmit ONLY impulses, so how do we “know” the modality (i.e. if it’s vibration, touch, pain etc.) ?

A

-Nerves terminate at specific point in CNS and the type of sensation felt is determined by the point in the NS to which the fibre leads (e.g. pain from the leg is delivered to a particular part of the CNS which is different to, but near, stretch or vibration signals from the leg.)

24
Q

What is the label-line principal ?

A

Pathways carrying sensory information centrally are specific, forming a “labelled line” regarding a particular stimulus

25
Q

Using your knowledge of sensation modality, how does phantom limb sensation arise ?

A

Phantom limb sensation arises when sensory neurons from absent limbs are spontaneously active, and can be mimicked by electrical stimulation

26
Q

Some sensory receptor types adapt rapidly to constant stimuli; what effect does this have on their receptor potential ?
What about slow-adapting receptor ?

A

Their receptor potential does also adapt rapidly (so slowing down and stopping of AP, even though stimulus may still be there)

AP will carry on for a long time (not much adaptation)

27
Q

Give 2 examples of rapidly-adapting receptors and 2 examples of slowly-adapting receptors.

A

Rapidly-adapting receptors: Pacinian Corpuscle and Hair Receptor

Slowly-adapting receptors: Joint Capsule Receptors and Muscle Spindle

28
Q

What are the factors which determine the precision of localisation of a particular stimulus ?

A
  1. Size of the individual nerve fibre receptive field (smaller one, can localise more specifically)
  2. Density of sensory units (increased density means higher frequency of APs and better localisation because more receptor terminals which will generate APs)
  3. Amount of overlap in nearby receptive fields (increased overlap helps localise more specifically, because then more terminals stimulated and hence more APs)
29
Q

Which of these two usually has a shorter average distance of two point discrimination: Lips or skin of the back ? Why ?

A

Lips

Because smaller receptive field

30
Q

What are the causes of variations in the results of the two point discrimination test ?

A
  • Receptive field size
  • Receptor density
    in the area
31
Q

Do the results of the two point discrimination test represent sensitivity to stimulus ?

A

NO

32
Q

What is lateral inhibition ? How does this affect localisation of stimulus ?

A

Information from afferent neurons whose receptors are at edge of a stimulus are strongly inhibited compares to information form the stimulus’ centre
It aids in enabling localisation of stimulus.

33
Q

How does size of receptive field impact two point discrimination ?

A

The smaller the receptive field is, the better the linear discrimination between stimuli is

34
Q

Why are not all areas of the body given high linear discrimination ? Give an example of a body part without high linear discrimination

A

High linear discrimination needs more sensory fibres/neurons to cover the area with small receptive fields
There is no requirement for the TORSO to be able to have that level of discrimination, and the extra neurons would present a space problem in the spinal cord

35
Q

What are some space savers in the spinal cord, other than the absence of extra sensory fibres/neurons for high linear discrimination in the torso ?

A

Multiple same modality sensory neurons with overlapping fields all project to a single ascending neuron

36
Q

Are sensory receptors better at determining absolute levels of stimulus intensity or detecting changes in space or with time, using comparisons ?

A

Sensory receptors are poor at determining absolute levels of stimulus intensity.
They are better at detecting changes in space or with time, and often work using comparisons.

37
Q

Outline the main features of neural pathways of the somatosensory system.

A
  • Primary afferent (first order neuron) terminates in spinal chord or the brain stem
  • At synapase between first and second order neurons, substance P or glutamate is neurotransmitter used
  • Second order neuron projects to the thalamus
  • Third order neuron projects to the brain (somatosensory cortex)
38
Q

Where in the brain is the primary sensory cortex located ?

A

In a strip posterior to the post central sulcus of the brain.

39
Q

True or False: Sensory information is projected in a topographical manor to this area, with areas of lower discrimination having a larger proportion of the space.

A

False: Sensory information is projected in a topographical manor to this area, with areas of HIGHER discrimination having a larger proportion of the space.

40
Q

How may one determine where neuronal lesions may lie, especially in the context of sensory receptors ?

A

Loss of sensation in specific, discrete areas can be used to determine where neuronal lesions may lie (use sensory dermatome maps)

41
Q

True or False: Spinal nerves are arranged in pairs.

A

True (31 pairs total, 8C, 12T, 5L, 5S, 1C)

42
Q

Name the basic kinds of sensory receptors, and their main function.

A
  1. Mechanoreceptors, which detect mechanical compression or stretching of the receptor or of tissues adjacent to the receptor;
  2. Thermoreceptors, which detect changes in temperature, with some receptors detecting cold and others warmth;
  3. Nociceptors (pain receptors), which detect physical or chemical damage occurring in the tissues; Free nerve endings.
  4. Electromagnetic receptors, which detect light on the retina of the eye; Vision via rods and cones.
  5. Chemoreceptors, which detect taste in the mouth, smell in the nose, oxygen level in the arterial blood, osmolality of the body fluids, carbon dioxide concentration, and other factors that make up the chemistry of the body

MD2002 (77 decks)

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