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University - Neuroscience > Reflexes and pain > Flashcards

Reflexes and pain Flashcards

1
Q

What is a reflex

A

A rapid, involuntary, stereotyped and co-ordinated response to a sensory stimulus

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2
Q

What is a pavlovian reflex

A

A learned reflex

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3
Q

What are somatic reflex (spinal reflex)

A

A reflex which involves muscles

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4
Q

What are features of spinal reflexes

A

Require stimulation

Are quick

Are involuntary - Suggests little input from CNS

Stereotyped - suggests simple circuit

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5
Q

What is the patellar reflex

A

Reflex used for stretching a muscle and ligament to hold and maintain body posture

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6
Q

How does the body react when it senses a stretch

A

Muscle spindles innervated by sensory fibres sense stretch –> spinal cord signals –> monosynaptic connection to motor neuron which fires AP, contracting the muscle –> A distinct inhibitory interneuron then inhibits the firing of the antagonist muscle, stopping it from contracting

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7
Q

What are muscle spindles

A

stretch detectors

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8
Q

Where are muscle spindles found

A

Striated muscle

Muscles involved in fine motor control

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9
Q

What are muscle spindles innervated by

A

(I)a sensory fibres
Provide feedback to the motor neurons innervating the surrounding muscle

Gamma motor neurons which stimulate the intrafusal (muscle) fibres to adjust the tension in the spindle as the extrafusal fibres contract. This makes sure that the muscle spindle is never slack

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10
Q

What is the golgi tendon organ

A

Another kind of proprioceptor

Detects muscle tension due to contraction not stretch (opposite of muscle spindles)

Activation of GTO sensory (I(b)) afferents leads to activation of inhibitory interneurons which inhibit alpha motor neurons that innervate the same muscle

Meaning the GTO is a negative feedback circuit that regulates muscle tension and protects the muscle

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11
Q

What is the flexor reflex

A

Withdrawal reflex to prevent injuries by withdrawing the limb

Activated by nociceptive sensory receptors (nociceptors)

Polysynaptic reflex despite speed of response (activation of multiple excitatory interneurons sustain response (Parallel after discharge)

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12
Q

What is a parallel after-discharge circuit

A

Different number of neurons in each circuit, so stimulus duration is created over an extended period of time

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13
Q

What is the flexor reflex 2 (crossed extensor reflex)

A

Because rapid withdrawal of limb may lead to imbalance, flexor reflexes often include a contralateral (opposite side)
element

Ipsilateral - flexor

Contralateral - extensor

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14
Q

What are central pattern generators

A

Local circuits that can generate the pattern of alternating flexion and extension

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15
Q

What is the difference between a monosynaptic and polysynaptic reflex

A

Mono involves one synapse between a sensory and motor neuron

Poly involves many interneurons

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16
Q

What is proprioception

A

The bodies sense of movement, action, and location

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17
Q

What are the major stimuli for the proprioceptive system

A

Mechanical stimuli and painful stimuli

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18
Q

Why do we need proprioception

A

Identify the shape and texture of objects

Monitor the internal and external forces acting on the body

Detect harmful circumstances

Have a sense of ourselves within our environment and so plan our actions accordingly

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19
Q

What are the Meissner corpsucles

A

Sensory receptors found on dermal papillae of skin (palms, eyelids, lips and tongue)

Modality: light touch and texture

Sensitive to 30-50Hz

Encapsulated nerve endings

Rapidly

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20
Q

What are Pacinian corpuscles

A

Dermis, joint capsules and viscera

Modality - deep pressure, stretch, tickle and vibration

Sensitive to 250-350 Hz

Rapidly adapting

Encapsulated nerve endings

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21
Q

What are Ruffini corpsucles

A

Dermis, subcutaneous tissue and joint capsules

Modality - Heavy touch, pressure, skin stretch and joint movements

Slowly adapting

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22
Q

What are merkel discs

A

Superficial skin

Modality - light touch, texture, edges and shapes

Slowly adapting

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23
Q

What are free nerve endings

A

Widespread in epithelia and connective tissues

Modality - pain, heat and cold

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24
Q

What is the difference between cellular and molecular receptors

A

Molecular detect ligands

Cellular receptors detect pressure, stretch or vibration (detects changes in the body or the environment)

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25
Q

What are the 2 modalities that sensory receptors take

A

Can be neurons (olfactory)

Or can synapse with a primary afferent neuron to relay sensory information to the CNS (photoreceptor)

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26
Q

What are the 2 different classes of mechanoreceptor response

A

Rapidly adapting or phasic - receptors give information about changes in the stimulus (Pacinian corpuscles)

Slowly adaption or tonic - respond as long as a stimulus is present (ruffini corpuscless)

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27
Q

How are primary afferent axons subtyped

A

According to conduction velocity which is proportional to diameter

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28
Q

What is the fastest primary afferent axon

A

A is fastest C is slowest

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29
Q

What is the largest primary afferent axon in muscles

A

Group 1

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30
Q

What are faster, pain fibers or proprioceptors

A

proprioceptors

31
Q

What does the medial Lemniscal tract do

A

Carries mechanoreceptive and proprioceptive signals to the thalamus

32
Q

What does the spinothalamic tract do

A

Carries pain and temperature signals to the thalamus

33
Q

What classification of neurons are dorsal root ganglions

A

First order - they detect the stimulus and transmit to spinal cord

34
Q

What do 2nd order neurons do

A

Relay from the spinal cord to the thalamus

35
Q

What do 3rd order neurons do

A

Carry signal from the thalamus to the cortex

36
Q

What does commissural mean when applied to 2nd order neurons

A

They cross the midline

37
Q

Where do 1st order axons synapse onto the second order neurons from upper body

A

Cuneate nucle

38
Q

Where do 1st order axons synapse onto the second order neurons from lower body

A

Gracile nucleus

39
Q

What is the gracile nucleus and cuneate nucleus known as

A

The dorsal column nuclei

40
Q

Where do 2nd order axons cross the midline and ascend into

A

The medial lemniscus

41
Q

Where do 3rd order axons synapse in the lower body

A

Medial cortical neurons

42
Q

Where do 3rd order axons synapse in the upper body

A

Lateral cortex

43
Q

What does each DRG innervate

A

A specific domain called dermatome (an area of skin)

44
Q

Where does each region of the dermis arise

A

The somite

45
Q

What are somites

A

Structures that give rise to the underlying musculature and skeleton

46
Q

What is a dermatome

A

an area of skin in which sensory nerves derive from a single spinal nerve root

47
Q

How do you measure the size of a receptive field

A

The ability to discriminate between two sharp points at different distances

If subject feels two then the distance between the points is larger than the receptive field

48
Q

What is a receptive field

A

The area each sensory neuron innervates

49
Q

where are receptive fields largest and smallest

A

Legs and arms

Fingers, lips - More cortex is dedicated to regions were receptive field is small

50
Q

Where is the somatotopic map preserved

A

Coronal plane of the postcentral gyrus

Different sensory modalities are localised on the sagittal axis

51
Q

What are Brodmann areas

A

Different sensory modalities which are localised on the sagittal axis

52
Q

What is cortical map plasticity

A

The disappearance of one part of a system will lead to an increased devotion to other parts of that system in the cortical map of the brain

53
Q

What specificity theory

A

Pain is a distinct sensation, detected and transmitted by specific receptors and pathways to distinct pain areas of the brain

54
Q

What is convergence theory

A

Pain is integrated, plastic state represented by a pattern of convergent somatosensory activity within a network

55
Q

How fast are lightly myelinated Ad fibres

A

20m/s
Mechano-sensitive
Mechanothermosensitive

56
Q

How fast are unmyelinated C fibres

A

2m/s

Polymodal - mechanical, thermal and chemical

57
Q

What are the two categories of pain

A

Fast pain - sharp and immediate, micked by direct stimulus of Ad fibre nociceptors

Slow - more delated, diffuse and longer lasting, mimicked by stimulation of C fibres

58
Q

What do Aa or Ab receptors do

A

Proprioceptive or mechanoreceptive

Never elicit the pain sensation

59
Q

How is fast pain mimicked

A

Direct simulation of A delta fibre nocicpetors

60
Q

How is slow pain mimicked

A

Stimulation of C fibre nocicpetors

61
Q

How is capsaicin receptor activated

A

In nociceptive A delta and C fibres at 45C and by capsaicin –> active component in chillis

62
Q

How do nociceptors work

A

By detecting the release of chemicals from stressed cells

63
Q

What are the 2 components that carry information to the brain

A

Sensory discriminative - signals location, intensity and type of stimulus - Spinothalamic tract

Affective - motivational - signals unpleasantness and enables autonomic activation “fight or flight”

64
Q

What does measurement of activity in the somatosensory cortex indicate

A

The region does respond to pain and that response correlates to intensity of pain

65
Q

What is proof of the specificity theory

A

Several receptors both cellular and molecular that respond specifically to pain (alpha subset of Ad and C fibers)

Specific pathways that convey pain

Regions of the CNS that are specifically and distinctly activated in response to pain

66
Q

What is some evidence against the specificity theory

A

Pain perceived is not always proportional to intensity of stimulus

Modulation by other stimuli (e.g. acupuncture)

Perception of pain in severed limbs (phantom limbs)

Referral of pain from viscera to skin

Placebo effect

67
Q

What is hyperalgesia

A

Increased response to a painful stimulus

Result of lowered nociceptor thresholds which heightens the pain response as a result of prostaglandins

68
Q

What is allodynia

A

Painful response to a normally innocuous stimulus

Relay neurons become sensitive to non-nociceptive inputs (mechanical) –> normally innocuous stimuli can be perceived as painful

69
Q

What is hyperpathia

A

Varient of hyperalgesia and allodynia

Fibre loss/damage resulting in a raising of the detection threshold. However when the detection threshold is reached, patients report explosive pain

70
Q

What is central sensitisation

A

When central pathways are damaged, diabetes, MS or after a stroe

71
Q

What is phantom limb pain

A

Illusion that limb is present can happen in children born without limbs (suggesting that central maps may be partly pre-formed.)

Attempts to block known pain pathways usually fail, suggesting that this pain may also be centrally represented

Suggests that the pain we experience may, in part, be a central representation of what we expect pain to be

72
Q

What is referred pain

A

Pain due to damage in the viscera is often perceived as coming from another location (heart attack is preceded by pain in left shoulder)

Not well understood but thought to reflect convergence of visceral afferents onto the same pathways as cutaneous afferents in the CNS

Useful in clinical settings

73
Q

What is central modulation of pain

A

Severe pain can often be perceived as no pain

Indicates that mechanisms exist, voluntary or involuntary, to overcome even severe pain

74
Q

What is pain of modulation

A

Experiments stimulating certain regions of the midbrain produced pain relief

Stimulation of the periaqueductal grey activates brainstem nuclei that modulate the activity of the dorsal horn

The dorsal horn activates enkephalin releasing interneurons which presynaptically inhibit nociceptive fibres

Can also be local:
Rubbing an injury - local local inhibition by mechanoreceptors (Ab fibres) of nociceptive (C fibre) inputs in the spinal cord

University - Neuroscience (9 decks)

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