Sensory Systems

Question 1

what is each type of sensory information associated with?

Answer 1

a specific receptor type responding to a specific sensory modality

Question 2

What are examples of sensory receptors?

Answer 2

Mechanoreceptors

Chemoreceptors

Thermoreceptors

Nociceptors

Proprioceptors

Question 3

How does the nerve endings of different sensory receptors differ?

Answer 3

May have free nerve endings or complex structures

Question 4

What are examples of sensory receptors that have free nerve endings?

Answer 4

Nociceptors

Cold receptors

Question 5

What are examples of complex structures at the end of sensory receptors?

Answer 5

Pacininan corpuscle

Meissner’s corpuscle

Question 6

What is the specific area that sensory receptors respond to stimulus over called?

Answer 6

Receptive field

Question 7

How do sensory receptors tranduce their adequate stimulus?

Answer 7

Into depolarisation, the receptor (generator) potential

This evokes firing of action potentials for long distance transmission

Gives information on modality, intensity and location of the stimulus

Question 8

what do all sensory receptors transduce their adequate stimulus into?

Answer 8

a depolarisation, the receptor (generator) potential

Question 9

what does the size of generator potential encode for?

Answer 9

intensity of stimulus

Question 10

what does generator potential evoke?

Answer 10

firing of action potentials for long distance transmission

Question 11

what does the frequency of action potentials encode for?

Answer 11

encodes intensity of stimulus

Question 12

What does the receptive field encode?

Answer 12

Location of stimulus

Question 13

What determines acuity?

Answer 13

Density of innervation and size of receptive fields

Question 14

What are action potentials from sensory receptors transmitted to the CNS by?

Answer 14

Axons

Question 15

Cutaneous sensation is mediated by 3 types of primary afferent fibres; what are they?

Answer 15

Aβ = large myelinated (30-70 m/s) touch, pressure, vibration

Aδ = small myelinated (5-30 m/s) cold, “fast” pain, pressure

C = unmyelinated fibres (0.5-2 m/s) warmth, “slow” pain

Question 16

What are Aß fibres also known as?

Answer 16

Large myelinated

Question 17

What is the speed of Aß fibres?

Answer 17

30-70m/s

Question 18

What kinds of sensory information is transmitted by Aß fibres?

Answer 18

Touch, pressure, vibration

Question 19

What are Aσ fibres also known as?

Answer 19

Small myelinated fibres

Question 20

What is the speed of Aσ fibres?

Answer 20

5-30m/s

Question 21

What kind of information is transmitted by Aσ fibres?

Answer 21

Cold, “fast” pain, pressure

Question 22

What are C fibres also known as?

Answer 22

Unmyelinated fibres

Question 23

What is the speed of C fibres?

Answer 23

0.5-2m/s

Question 24

What kind of information is transmitted by C fibres?

Answer 24

Warmth, “slow” pain

Question 25

What are the 2 types of primary afferent fibres that mediate proprioception?

Answer 25

Aa and Aß (such as muscles spindles, golgi tendon organs etc)

Question 26

What do proprioceptors give information about?

Answer 26

Position and movement

Question 27

What do all primary afferent fibre types enter the spinal cord through?

Answer 27

Dorsal root ganglia (or cranial nerve ganglia for the head)

Question 28

What fibres transmit information from mechanoreceptors?

Answer 28

Aa and Aß fibres

Question 29

Explain the pathway of mechanoreceptor (Aa and Aß fibres)?

Answer 29

1) Project straight up through ipsilateral dorsal columns 2) Synapse in cuneate and gracile nuclei 3) The 2nd order fibres cross over midline in the brain stem and project to reticular formation, thalamus and cortex

Question 30

Where do mechanoreceptor fibres cross the midline?

Answer 30

Brainstem

Question 31

What do mechanoreceptor fibres project up the spinal cord through?

Answer 31

Ipsilateral dorsal columns

Question 32

What fibres do thermoreceptors use?

Answer 32

Aσ and C fibres

Question 33

What fibres do nociceptive receptors use?

Answer 33

Aσ and C fibres

Question 34

Explain the pathway of thermoreceptive and nociceptive fibres?

Answer 34

1) Synapse in the dorsal horn 2) The 2nd order fibres cross over the midline in the spinal cord 3) Project up through the contralateral spinothalamic (anteriolateral) tract to reticular formation, thalamus and cortex

Question 35

What do mechanoreceptors detect?

Answer 35

Touch, pressure, stretching and motion

Question 36

What do nociceptive receptors detect?

Answer 36

Pain

Question 37

Where do thermoreceptive fibres cross the midline?

Answer 37

Spinal cord

Question 38

Where do nociceptive fibres cross the midline?

Answer 38

Spinal cord

Question 39

How are thermoreceptive fibres transmitted up the spinal cord?

Answer 39

Contralateral spinothalamic (anteriolateral) tract to reticular formation, thalamus, and cortex

Question 40

How are nociceptive fibres transmitted up the spinal cord?

Answer 40

Project up through the contralateral spinothalamic (anteriolateral) tract to reticular formation, thalamus, and cortex

Question 41

what is brown-sequard syndrome?

Answer 41

a rare neurological condition characterized by a lesion in the spinal cord which results in weakness or paralysis on one side of the body and a loss of sensation on the opposite side

Question 42

below the level of injury in brown sequard syndrome what is experienced on the contralateral side?

Answer 42

Loss of pain and temperature

Question 43

below the level of injury in brown sequard syndrome what is experienced on the ipsilateral side

Answer 43

Loss of vibration, motor function, deep touch and proprioception

Question 44

Different transmission for sensory information explains consequences of spinal cord injuries, what does damage to dorsal columns cause?

Answer 44

Loss of touch, vibration, proprioception below lesion on ipsilateral side

Question 45

different transmission for sensory information explains consequences of spinal cord injuries, what does damage to anteriolateral quadrant cause?

Answer 45

Loss of nociceptive and temperature sensation below lesion on contralateral side

Question 46

Where is the ultimate terminate of all sensory receptor fibres?

Answer 46

Somatosensory cortex (S1) of the postcentral gyrus

Question 47

What are the endings of sensory fibres grouped according to?

Answer 47

Location of the receptors, forming sensory homunculus

Question 48

What are the steps of processing in sensory pathways?

Answer 48

Adaptation Convergence Lateral inhibition

Question 49

What is the adaptation step of processing in sensory pathways?

Answer 49

Decline in the electrical response of a receptor neuron over time in spite of the continued presence of an appropriated stimulus of constant strength Is apparent as a gradual decrease in frequency of spikes generated within the receptor neuron

Question 50

What are the 2 kinds of adapting that sensory receptors can display?

Answer 50

Rapidly adapting Slowly adapting

Question 51

What are consequences of convergence occuring when processing sensory information?

Answer 51

Saves on neurons But reduced acuity May underlie referred pain

Question 52

What is the lateral inhibition step of processing in sensory pathways?

Answer 52

Activation of one sensory input causes synaptic inhibition of its neighbours

Question 53

What are consequences of lateral inhibition in sensory receptors?

Answer 53

Gives better definition of boundaries Cleans up sensory information

Question 54

What is perception?

Answer 54

The ability to see, hear or become aware of something through the sense, or the way something is interpreted

Question 55

What are examples of the different kinds of pain?

Answer 55

Sharp, stabbing vs diffuse, throbbing Fast (initial pain) vs slow (delayed) pain Acute vs chronic pain Visceral pain Referred pain Phantom limb pain

Question 56

What is signal transduction?

Answer 56

Transmission of molecular signals from a cell’s exterior to its interior

Question 57

What is signal transduction in nociceptors activated by?

Answer 57

Low pH, heat (via ASIC, TRPV1 etc) Local chemical mediators (such as bradykinin, histamine, prostaglandins)

Question 58

What are examples of local chemical mediators that activates signal transduction in nociceptors?

Answer 58

Bradykinin, histamine, prostaglandins

Question 59

Explain the processing of nociceptive pathways?

Answer 59

1) Segmental controls (such as gate theory control of pain where activity in Aa/ß fibres activates inhibitory interneurons) 2) Inhibitory interneurons release opiod peptides (endorphins) that inhibit transmitter release from Aσ/C fibres, “closing the gate” 3) Descending controls, the same inhibitory interneurons are also activated by descending pathways from PAG and NRM, hence also “closing the gate” 4) Transmitted to thalamus

Question 60

What is the medical term for the inability to feel pain?

Answer 60

Analgesia

Question 61

What is the “gate control theory of pain”?

Answer 61

Non-painful stimulus input closes the nerve “gates” to painful input, which prevents pain sensation form travelling to the central nervous system

Question 62

What can analgesia be achieved with?

Answer 62

Non-steroidal anti-inflammatory drugs (NSAIDs) Local anaesthetics Transcutaneous electrical nerve stimulation (TENS) Opiates

Question 63

How do NSAIDs achieve analgesia?

Answer 63

1) Prostaglandins sensitive nociceptors to bradykinin 2) NSAIDs inhibit cyclo-oxygenase which converts arachidonic acid to prostaglandins 3) So NSAIDs work well against pain associated with inflammation

Question 64

How do local anaesthetics achieve analgesia?

Answer 64

Block Na+ action potential and therefore all axonal transmission

Question 65

What is an example of an opiate?

Answer 65

morphine

Question 66

How do opiates achieve analgesia?

Answer 66

Reduce sensitivty of nociceptors Block transmitter release in dorsal horn (hence epidural administration) Activate descending inhibitory pathways