Sensory Receptors 1

Question 1

What are sensory receptors?

Answer 1

-Nerve endings, specialised non-neural structures

Question 2

What do sensory receptors do?

Answer 2

• They are transducers that convert different forms of energy into frequency of AP
• Inform the CNS about the internal and external environment

Question 3

Sensory modality

Answer 3

A type of stimulus activating a particular receptor e.g. touch, pressure, pain, temperature, light

Question 4

Adequate stimulus

Answer 4

They type of energy a receptor normally responds to

Question 5

What are sensory receptors sensitive to?

Answer 5

Highly sensitive to one specific energy form but can be activated by other intense stimuli

Question 6

What are the types of sensory receptors?

Answer 6

• Mechanoreceptors
• Proprioceptors
• Nociceptors
• Thermoreceptors
• Chemoreceptors
• Photorececeptors

Question 7

Mechanoreceptors

Answer 7

• Stimulated by mechanical stimuli- pressure, stretch or deformation
• Detect many stimuli- haring, balance, blood pressure and skin sensations of touch and pressure

Question 8

Proprioceptors

Answer 8

Mechanoreceptors in joints and muscles that signal information related to body or limb position

Question 9

Nociceptors

Answer 9

Response to painful stimuli- tissue damage and heat

Question 10

Thermoreceptors

Answer 10

Detect cold and warmth

Question 11

Chemoreceptors

Answer 11

Detect chemical changes e.g pH, pO2 and pCO2

Question 12

Photoreceptors

Answer 12

Respond to particular wavelengths of light

Question 13

What are cutaneous mechanoreceptors and proprioceptor good examples of?

Answer 13

The principles of peripheral sensory processing

Question 14

What does transduction in all sensory receptors involve?

Answer 14

Opening and closing of ion channels

Question 15

What does an adequate stimulus cause/

Answer 15

A graded membrane potential change called a receptor potential or a generator potential

Question 16

Membrane deformation

Answer 16

The adequate stimulus in cutaneous mechanoreceptors and proprioceptors

Question 17

What does membrane deformation activate?

Answer 17

Stretch sensitive ion channels causing ion flow across the membrane

Question 18

What does a stimulus cause?

Answer 18

Local current to flow to where the membrane has voltage gated ion channels that generate action potentials

Question 19

Where does the local current flow to in myelinated sensory neurons?

Answer 19

The start of myelination

Question 20

Describe the receptor potential.

Answer 20

Graded to stimulus intensity

Question 21

Frequency coding of stimulus intensity.

Answer 21

The larger the stimulus, the larger the receptor potential and the higher the frequency of AP in a sensory nerve

Question 22

What also reflects the stimulus intensity?

Answer 22

The number of receptors activated

Question 23

What is the information a touch receptor in the skin responds to dependent on?

Answer 23

The properties of nerve endings and of accessory, non-neuronal structures

Question 24

What happens for some mechanoreceptors if the stimulus persists?

Answer 24

APs persist

Question 25

Adaption

Answer 25

Some mechanoreceptors adapt to a maintained stimulus and only signal change- the onset of stimulation

Question 26

Why do some mechanoreceptors only signal at the onset of stimulus?

Answer 26

- Stimulus is enough to cause an above threshold generator potential, which triggers APs - The generator potential declines rapidly and APs cease - They respond only to change or a novel event

Question 27

What do rapidly/ moderately adapting receptors include?

Answer 27

- Pacinian corpuscles | - Meissners corpuscles

Question 28

What are examples of slow-adapting receptors?

Answer 28

- Merkels discs | - Ruffini endings

Question 29

Why do nociceptors not adapt?

Answer 29

They are free nerve endings that detect painful stimuli and it is important to not ignore painful stimuli

Question 30

What is a pacinian corpuscle?

Answer 30

A myelinated nerve with a naked nerve ending, enclosed by a connective tissue capsule of layered membrane lamellae separated by fluid

Question 31

How does the Pacinian corpuscle respond?

Answer 31

- A mechanical stimulus deforms the capsule and nerve ending - Stretching the nerve ending opens ion channels - Na influence causes local depolarisation (generator potential) - APs are generated and fire at the myelinated nerve

Question 32

Describe adaption in the pacinian corpuscle?

Answer 32

- Stimulus is on - Fluid redistribution in the capsule rapidly dissipates stimulus, removes mechanical stretch of nerve ending and the AP stops firing - Withdrawal of the stimulus means the capsule springs back and the AP starts firing again

Question 33

What happens if the lamellae is removed?

Answer 33

Much of the adaption is lost

Question 34

What happens when the capsule is removed?

Answer 34

- Bare nerve ending loses much adaption | - Continues to produce a receptor/ generator potential

Question 35

What does the non-neural accessory structure do?

Answer 35

It is critical to how the sensory receptor works and in general enhances sensory function

Question 36

Receptive field

Answer 36

A somatic sensory neuron is activated by stimuli in a specific area e.g a touch-sensitive neuron in the skin responds to pressure within a defined receptive field

Question 37

What does our ability to tell 2 points on the skin apart depend on?

Answer 37

- Receptive field size - Neuronal convergence - Determined by 2 point discrimination test

Question 38

hat do sensory neurons with neighbouring receptive fields exhibit?

Answer 38

Neuronal convergence= multi presynaptic neurons input on a smaller number of post-synaptic neurons

Question 39

What does convergence of primary sensory neurons allow?

Answer 39

Simultaneous sub-threshold to sum at the secondary neuron, forming a large secondary receptive field and initiating AP

Question 40

What does convergence and large secondary receptive field indicate/

Answer 40

A relatively insensitive area

Question 41

2 point discrimination test

Answer 41

Distance between points adjusted until just perceive 2 points rather than 1

Question 42

Where has a very small 2-point threshold?

Answer 42

Fingers and lips

Question 43

Where has a large 2 point threshold?

Answer 43

Back and limbs

Question 44

Acuity

Answer 44

The ability to locate a stimulus on the skin and differentiate it from another closeby

Question 45

How can we precisely determine the location of a stimulus?

Answer 45

- Lateral inhibition - Information from afferent neurons with sensory receptors at edge of stimulus is strongly inhibited, compared with information from stimulus centre

Question 46

What does lateral inhibition do?

Answer 46

Enhances the contrast between relevant and irrelevant information

Question 47

Where does lateral inhibition occur/

Answer 47

In the spinal cord for cutaneous information

Question 48

Describe sensory signals in the brain.

Answer 48

- All sensory information goes to the brain - Relayed through thalamus to somatosensory cortex - Cortical body map is distorted - Most sensitive areas occupy biggest cortical space

Question 49

Merkel receptors

Answer 49

Sense steady pressure and texture

Question 50

Meissners corpuscle

Answer 50

responds to flutter and stroking movements

Question 51

Pacinian corpuscle

Answer 51

Senses vibration

Question 52

Ruffini corpuscle

Answer 52

Responds to skin stretch

Question 53

Sensory nerves

Answer 53

Carry signals to spinal cord

Question 54

Free nerve endings of nociceptors

Answer 54

Responds to noxious stimuli