Medicine Year 2 > Topic 11 - Pathways > Flashcards

Topic 11 - Pathways Flashcards

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1
Q

Describe slow transmission of noxious stimuli

A
  1. Dorsal root ganglion
  2. Dorsal horn (lamina I-VI)
  3. Paleospinothalamic tract
  4. Fibres to reticular formation, fibres to periaqueductal grey matter
  5. Fibres to hypothalamus
  6. Thalamus
  7. Cerebral cortex
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2
Q

Describe the function and location of hair follicle receptors

A
  • V sensitive to touch and pressure
  • Endings of sensory nerve fibres from plexus around hair follicle
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3
Q

What is the effect of cGRP and substance P?

A

cGRP: Dilation of blood vessels - redness

Substance P: Plasma extravasation - odema (wheal), release of bradykinin

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4
Q

Describe the 1st order neurons of the DCML

A
  • Ascending tract of gracile and cuneate fasciculi, synapse on dorsal column nuclei
    • Gracile - lower half of body - enters cord at lumbar level
    • Cuneate - upper half of body - enters cord at cervical level
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5
Q

Describe A beta afferent fibres

A
  • Slightly smaller diameter, myelinated
  • Moderate transmission speed
  • Mechanoreceptors in skin
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6
Q

Describe the path of the spinothalamic tract

A
  1. Primary afferent fibres
  2. Decussate via anterior white commissure - 1-2 spinal segments above point of entry
  3. Anteriolateral funiculus, outer to inner = sacral, lumbar, thoracic, cervical
  4. Spinal lemniscus - medulla, pons, midbrain, thalamus
  5. Thalamus to internal capsule to sensory cortex
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7
Q

What is the function of the anterior corticospinal tract?

A

15% of the corticospinal fibres - innervates the trunk/axial muscles

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8
Q

How can proprioception be impaired?

A
  • Vibration of tendons
    • Tonic activation of tendon reflex
    • Perception of increased length of muscle, muscle spindles activated
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9
Q

List the causes of pain associated with the cardiovascular system

A

Increased BP, HR or ischaemic heart disease

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10
Q

List causes of pain associated with the gastrointestinal system

A

Ileus, nausea, vomiting

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11
Q

Define a motor unit

A

Single motor neuron and all the muscle fibres it innervates

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12
Q

List the stages of nociception

A
  1. Transduction
  2. Transmission
  3. Modulation
  4. Perception
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13
Q

List causes of pain associated with the respiratory system

A

Cough, hyperventilation

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14
Q

Describe C afferent fibres

A
  • V small diameter, unmyelinated
  • V slow transmission speed
  • Temperature, pain, itch sensory receptors
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15
Q

Describe the location of the dorsal column medial lemniscus pathway

A

Dorsal funiculus - from medial to lateral arrangment is sacral, lumber, thoracic, cervical

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16
Q

Describe the fibre types involved in slow transmission of pain

A

C fibres, substance P is neurotransmitter

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17
Q

How do cutaneous receptors contribute to proprioception?

A

Those located over joints discharge during movement

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18
Q

Describe the type of pain which results from slow transmission of noxious stimuli

A
  • High threshold multimodal nociceptors
  • Dull, diffuse, prolonged pain
  • Produces spasm, guarding
  • Abolished by morphine
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19
Q

Describe the structure of the reticulospinal tract

A
  • Bilateral projections
    • Pontine tracts (extensors) - ipsilateral oral and caudal pontine reticular nuclei
    • Medullary tracts (flexors) - ipsilateral gigantocellular reticular nuclei of the medulla
  • Run entire length of cord
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20
Q

Describe the function of the spinothalamic pathway

A

Pain, temperature, crude touch

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21
Q

Describe the path of the DCML

A
  1. Primary afferent fibres
  2. Dorsal funiculus
  3. Dorsal column nuclei - gracile/cuneate nuclei
  4. Internal arcuate fibres
  5. Medial lemniscus
  6. Interal capsule
  7. Sensory cortex
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22
Q

Describe A delta afferent fibres

A
  • Smaller diameter, myelinated
  • Slower transmission speed
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23
Q

What is the function of the reticulospinal tract?

A
  • Modulate activity of alpha motor neurons
  • Important in maintenance of balance and posture
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24
Q

Describe the parts of the corticobulbar pathway

A
  1. Midbrain - basis pedunculis
  2. Pons - trigeminal motor nucleus, facial motor nucleus
  3. Medulla - nucleus ambiguous - vagus and hypoglossal nuclei
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25
Describe the mechanism of the triple response
1. Mild mechanical trauma 2. Damage to BVs - release of potassium and prostaglandins 3. Plasma releases bradykinins 4. Platelets release 5-HT (serotonin) 5. Potassium, bradykinin and 5-HT - free nerve endings activated, signal travels up spinothalamic pathway 6. Surrounding nerve endings also stimulated - cGRP and substance P released from C fibres, act on mast cells to release histamine 7. Histamine activates fibres again - reinforcement of signals
26
List the causes of pain associated the CNS
Anxiety, depression, sleep impairment
27
Meissner's corpuscle - function and location
* Light touch * In dermal papillae * Unmyelinated
28
Describe the 3rd order neurons of the DCML
Axons from the thalamus synapse with neurons on the ventral nuclear group, sends axons to sensory cortex
29
Describe the function of the corticobulbar pathway
* Motor control (voluntary) - bilateral innervation of the cranial nerve nuclei * 2 neuron white matter motor pathways connecting the motor cortex in the cerebral cortex to the medullary pyramids * Primarily involved in carrying out the motor function of the non-oculomotor cranial nerves
30
List the causes of pain associated with muscles
Restless (O2), immobility (DVT)
31
Describe the function of the corticospinal pathway
Motor pathway starting at cerebral cortex, terminates on lower motor neurons + interneurons in the spinal cord, controlling movements of the limbs and trunk
32
List metabolic causes of pain
* Increased catabolism * Cortisone, glucagon, GH, catecholamines * Decreased anabolism * Insulin, testosterone * Decreased plasminogen * Increased coagulation, DVT
33
Describe the fibre types involved in transmission of noxious stimuli
* Thermal - warm = C, cold = A delta * Nociceptor - polymodal (mechano/heat/chemical) = C, mechanical = A delta * Mechanoreceptors - slow and fast adapting = A beta
34
Define ischaemic pain
* Lack of adequate blood supply to active tissues e.g. due to build up of atheroma in intima of arteries * Pain of angina + referred pain
35
List the ascending pathways
* Dorsal column medial lemniscus pathway * Spinothalamic pathway
36
Describe the process of activation of muscles by peripheral nerves
1. Initiation of action potential (voluntary or as result of electrical stimulation) 2. Conduction of action potential along nerve fibre 3. Release of neurotransmitter (acetyl choline) into neuromuscular junction 4. Brief increase in intracellular concentration of calcium ions 5. Activation of contractile molecular machinery in fibre, requires use of ATP of energy source 6. Brief contraction (twitch)
37
Describe gate control theory
* In response to pain, rub area where pain is localised * Activates touch/pressure receptors - A beta fibres to dorsal column * Give off collaterals to stimulate inhibitory neurons in Lamina II of dorsal horm * Interneurons (inhibitory) release GABA, which inhibits sensory pain signals * Leads to decreased pain perception
38
List the parts of the corticospinal tract
1. Midbrain - basis pedunculi 2. Pons 3. Medulla 4. Pyramidal decussation (crosses over) 5. Lateral or anterior corticospinal tracts
39
Describe A alpha afferent fibres
* Myelinated * Large diameter * Fast transmission speed * Proprioceptors in skeletal muscle
40
List the types of pain modulation
1. Spinal - gate control theory 2. Supra-spinal - conditioned pain modulation
41
Describe the role of muscle spindle sensory endings in proprioception
* Primary + secondary sensory endings * Sensitive to stretch of muscle + signal changes in length - gives information about joint position * Primary - high dynamic sensitivity, respondsto changing length and tapping/vibrating tendons * Opposing muscles at a joint (e.g. flexors and extensors) provide complementary information about joint angles
42
Describe sensory transduction in nociception
* Free nerve endings (nociceptors) in skin, bone, muscle, internal organs, blood vessels (not brain) * Mechanical, thermal and chemical stimuli converted to electrical signals
43
How is the gate control theory of pain modulation implimented clinically?
TENS machine used to treat pain
44
Describe the structure and function of the tectospinal pathway
* Important in maintenace of balance and posture * Origin - contralateral superior colliculus (crossed) * Projects to cervical spinal segments only - innervates muscles of neck * Modulates activity of alpha and gamma motor neurons
45
Describe the function and location of Pacinian corpuscles
* Large onion-like structure in dermis and hypodermis * Sensitive to mechanical and vibratory pressure
46
Describe the location of the spinothalamic pathway
Lateral - lateral funiculus Anterior - ventral funiculus
47
Define nociception
Neural mechanism for detecting potentially tissue harming stimuli
48
Describe peripheral nerve stimulation
* Each individual muscle fibre innervated by branch of a motor axon * Neuronal action potential activates all muscle fibres innervated by the motor neuron and its axonal branches
49
List the types of proprioceptors
1. Slowly and rapidly adapting receptors in joint capsules and ligaments 2. Cutaneous receptors 3. Muscle spindle sensory endings
50
What is the general function of the involuntary motor pathways
Maintaining muscle tone - balance and posture
51
Which type of afferent fibres contribute to the spinothalamic tract
A delta or C fibres
52
Describe the 2nd order neurons of the DCML
Ascending internal arcuate fibres, cross at sensory decussation to form medial lemniscus which connects w/ thalamus
53
What is the general function of ascending and descending pathways
* Ascending = sensory * Descending = modulate activity (motor)
54
What is the function of the dorsal column medial lemniscus pathway?
Fine touch, vibrations, two-point discrimination, proprioception
55
Describe gamma motor fibres
* Myelinated - smaller diameter, slower conduction velocity * Fusimotor - to intrafusal muscle, detect amount and rate of change in length of muscle
56
Describe C motor fibres
* Unmyelinated * Motor - sympathetic postganglionic
57
Describe the order of events in the triple response
1. Red reaction - where mechanical trauma occurred 2. Wheal - oedema, pale 3. Red flare - mottled reddening of skin
58
Describe the functions of the anterior and lateral parts of the spinothalamic pathway
* Anterior - crude touch, pressure * Lateral - pain and temperature
59
What is the white reaction/triple response?
Response to mild mechanical trauma
60
Describe alpha motor fibres
* Myelinated - large diameter, fast conduction velocity * Skeletomotor - to extrafusal muscles
61
What is the difference between somatic and referred pain?
Somatic pain follows dermatomes, referred pain doesn't
62
Describe the function and location of Merkel discs
* Found in basal epidermis and hair follicles * Mechanical pressure, position, deep static touch features e.g. shapes and edges
63
Define proprioception and describe the features of proprioception
* Signals contributing to conscious and subconscious mechanisms of motor control * Position sense = conscious awareness of the relative position of body parts in space * Kinaesthesia - sense of: * Speed of movement * Direction of movement
64
Which type of afferent fibres contribute to the DCML
A beta
65
List proprioceptive receptors in joint capsules/ligaments - fast or slow?
* Ruffini endings - slow * Paciniform endings - rapid * Golgi endings - slow * Free nerve endings - slow
66
How is the strength of a muscle contraction increased?
* Recruitment - more motor axons firing * Summation - increased frequency of firing action potentials * Muscle doesn't completely relax between contractions, so next contraction is stronger
67
Are golgi tendon organ receptors involved in proprioception?
Signal muscle tension which can vary for same joint position, therefore unlikely to contribute to position sense
68
How is heaviness/sense of effort detected?
Centrally, determined by brain based on amount of motor output required
69
Which type of fibres are cutaneous and subcutaneous mechanoreceptors?
A beta
70
List the types of cutaneous and subcutaneous mechanoreceptors
1. Meissner's corpuscle 2. Merkel disc 3. Hair follicle receptor 4. Pacinian corpuscle 5. Ruffini ending
71
Describe the structure and function of the vestibulospinal pathway
* Originates from ipsilateral lateral vestibular (Dieter's) nucleus * Important in maintenance of balance and posture * Runs entire length of cord * Modulate activity of alpha motor neurons
72
List the types of noxious stimuli and the receptors they stimulate at nociceptor terminals
* Heat - TRPV1 + 2 * Acid - ASIC + TRPV2 * Cold - TRPM8 + TRPAT * Mechanosensation - ASIC (?) + TRPM8 * Irritants - TRPAT
73
Describe the types of efferent (motor) fibres
1. Alpha 2. Gamma 3. C fibres
74
Describe descending modulation of pain
* Periaqueductal and periventricular grey matter cause release of neurotransmitters e.g. noradrenaline and serotonin in dorsal horn lamina II * Stimulates inhibitory neurones, secretes endorphins, enkephalins, dynorphins (endogenous opoids) to inhibit action potentials of sensory pain pathway
75
Define pain
Unpleasant sensory and emotional experience associated with actual or potential tissue damage
76
Define dermatographia
Strong response to mild mechanical trauma
77
Describe the function and location of Ruffini endings
* Bulbous corpuscle * Slowly adapting mechanoreceptors in cutaneous tissues (between dermal papillae and hypodermis) * Sensitive to skin stretch, kinaesthetic control of finger position/movement * Mechanical deformation of joints * Long acting thermoreceptors
78
Describe the type of pain which results from fast transmission
* High threshold thermo/mechanoreceptors * Sharp, short, localised pain - reflex withdrawal * Not abolished by morphine
79
Describe the structural organisation of ascending pathways
* 1st neuron * Primary sensory neuron * Periphery * 2nd neuron * Second sensory neuron * Spinal cord/brainstem * 3rd neuron * Tertiary sensory neuron * Thalamus
80
List causes of pain associated with the genitourinary system
Urinary retention, uterine inhibition
81
How does tetanic contraction occur?
If frequency of firing of action potentials increased enough that muscle can't relax between - tonic contraction
82
List the types of afferent fibres
1. A alpha 2. A beta 3. A delta 4. C
83
List the descending pathways
* Voluntary * Corticospinal * Corticobulbar * Involuntary * Tectospinal * Vestibulospinal * Reticulospinal
84
What is the function of the lateral corticospinal tract?
85% of the corticospinal fibres - innervates distal muscles for fine motor control
85
Where is the skin most sensitive in the triple response?
* Skin most sensitive in red inner area - scratched surface of skin so nociceptors closer to surface, nociceptors have increased sensitivity due to mediators e.g. bradykinin * Skin least sensitive to pain in wheal - oedema means nociceptors are further from surface of skin
86
Describe fast transmission of noxious stimuli
* A delta fibres, glutamine is neurotransmitter 1. Dorsal root ganglion 2. Dorsal horn (lamina I-VI) 3. Neospinothalamic tract 4. Thalamus 5. Cerebral cortex
87
Define two point discrimination
The ability to determine that two nearby objects touching the skin are truly two distinct points, not one
88
What determines two point discrimination?
The density of peripheral endings of sensory receptors - to activate two separate receptors and be perceived as two distinct points the stimuli must fall within separate receptive fields. Where receptive fields are small (high density of receptors) this can happen for more closely spaced stimuli.
89
Which areas of the body have high two point discrimination?
Fingers \< arm \< trunk
90
What are skin tension lines and what is their clinical significance?
* Skin tension lines = topological lines drawn on the body which correspond to the natural orientation of the collagen fibres in the dermis, generally perpendicular to the orientation of the underlying muscle fibres * Important for surgical procedures - cut along tension lines for better healing of incisions e.g. caesarean * If cut perpendicular to lines, wound will gape and cause more scarring e.g. sternotomy in open heart surgery
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