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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
What are the 2 modalities that sensory receptors take
Can be neurons (olfactory) Or can synapse with a primary afferent neuron to relay sensory information to the CNS (photoreceptor)
26
What are the 2 different classes of mechanoreceptor response
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)
27
How are primary afferent axons subtyped
According to conduction velocity which is proportional to diameter
28
What is the fastest primary afferent axon
A is fastest C is slowest
29
What is the largest primary afferent axon in muscles
Group 1
30
What are faster, pain fibers or proprioceptors
proprioceptors
31
What does the medial Lemniscal tract do
Carries mechanoreceptive and proprioceptive signals to the thalamus
32
What does the spinothalamic tract do
Carries pain and temperature signals to the thalamus
33
What classification of neurons are dorsal root ganglions
First order - they detect the stimulus and transmit to spinal cord
34
What do 2nd order neurons do
Relay from the spinal cord to the thalamus
35
What do 3rd order neurons do
Carry signal from the thalamus to the cortex
36
What does commissural mean when applied to 2nd order neurons
They cross the midline
37
Where do 1st order axons synapse onto the second order neurons from upper body
Cuneate nucle
38
Where do 1st order axons synapse onto the second order neurons from lower body
Gracile nucleus
39
What is the gracile nucleus and cuneate nucleus known as
The dorsal column nuclei
40
Where do 2nd order axons cross the midline and ascend into
The medial lemniscus
41
Where do 3rd order axons synapse in the lower body
Medial cortical neurons
42
Where do 3rd order axons synapse in the upper body
Lateral cortex
43
What does each DRG innervate
A specific domain called dermatome (an area of skin)
44
Where does each region of the dermis arise
The somite
45
What are somites
Structures that give rise to the underlying musculature and skeleton
46
What is a dermatome
an area of skin in which sensory nerves derive from a single spinal nerve root
47
How do you measure the size of a receptive field
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
What is a receptive field
The area each sensory neuron innervates
49
where are receptive fields largest and smallest
Legs and arms Fingers, lips - More cortex is dedicated to regions were receptive field is small
50
Where is the somatotopic map preserved
Coronal plane of the postcentral gyrus Different sensory modalities are localised on the sagittal axis
51
What are Brodmann areas
Different sensory modalities which are localised on the sagittal axis
52
What is cortical map plasticity
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
What specificity theory
Pain is a distinct sensation, detected and transmitted by specific receptors and pathways to distinct pain areas of the brain
54
What is convergence theory
Pain is integrated, plastic state represented by a pattern of convergent somatosensory activity within a network
55
How fast are lightly myelinated Ad fibres
20m/s Mechano-sensitive Mechanothermosensitive
56
How fast are unmyelinated C fibres
2m/s | Polymodal - mechanical, thermal and chemical
57
What are the two categories of pain
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
What do Aa or Ab receptors do
Proprioceptive or mechanoreceptive Never elicit the pain sensation
59
How is fast pain mimicked
Direct simulation of A delta fibre nocicpetors
60
How is slow pain mimicked
Stimulation of C fibre nocicpetors
61
How is capsaicin receptor activated
In nociceptive A delta and C fibres at 45C and by capsaicin --> active component in chillis
62
How do nociceptors work
By detecting the release of chemicals from stressed cells
63
What are the 2 components that carry information to the brain
Sensory discriminative - signals location, intensity and type of stimulus - Spinothalamic tract Affective - motivational - signals unpleasantness and enables autonomic activation "fight or flight"
64
What does measurement of activity in the somatosensory cortex indicate
The region does respond to pain and that response correlates to intensity of pain
65
What is proof of the specificity theory
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
What is some evidence against the specificity theory
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
What is hyperalgesia
Increased response to a painful stimulus Result of lowered nociceptor thresholds which heightens the pain response as a result of prostaglandins
68
What is allodynia
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
What is hyperpathia
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
What is central sensitisation
When central pathways are damaged, diabetes, MS or after a stroe
71
What is phantom limb pain
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
What is referred pain
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
What is central modulation of pain
Severe pain can often be perceived as no pain Indicates that mechanisms exist, voluntary or involuntary, to overcome even severe pain
74
What is pain of modulation
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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