Week 1 part 2 Flashcards
What do lower motor nuerones command?
Muscle contraction
What neurones does the LMNs comprise of?
Alpha motor neurones - generate force
Gamma motor neurones - innervate sensory muscle spindle
Where do axons of the LMNs exit the spinal cord?
`In ventral roots (or via cranial nerves)
Each ventral root joints with a dorsal root to form what?
Mixed spinal nerve
What is the collection of alpha motor neurones that innervate a single muscle termed?
Motor neurone pool
Force of muscle contraction is graded by alpha motor nuerones by 2 principles - what are they?
- Frequency of action potential discharge
2. Recruitment of additional, synergistic motor units
What can be said about the positioning of LMN innervating axial muscles compared to distal muscles?`
Axial are more medial
What can be said about the positioning of LMN innervating flexors compared to extensors?
Flexors are dorsal
What are the three sources of input to an alpha motor neurone that regulate its activity?
- Central terminals of dorsal root ganglion cells whose axons innervate muscle spindles
- UMNs in motor cortex and brain stem
- Spinal interneurones
What do fast and slow muscle fibre types differ in?
How fast myosin ATPase splits ATP to probide energy
How is ATP derived in type I fibres?
Oxidative phosphorylation
How is ATP derived in type IIb fibres?
Glycolysis
In fast type muscle what size are the alpha motor neurones?
`Big
What motor neurone innervates intrafusal fibres in spindles?
Gamma motor neruone
What spinal level is assessed in supinator wrist?
C5-C6
What spinal level is assessed in Biceps?
C5-C6
What spinal level is assessed in triceps
C7
What spinal level is assessed in quadriceps
L3-L4
What spinal level is assessed in gastrocnemius (ankle)
S1
In what activities are static gamma motor neurones active?
When muscle length changes slowly and predictably
In what activitres are dynamic gamma motor neurones active?
Muscle length changes rapidly and unpredictably
What are golgi tendon organs in series with?
Extrafusal fibres
What are golgi tendon organs innervated by>?
Group Ib sensory afferents
What do golgi tendon orgabns do?
Act to regulate muscle tension to protect them from overload
What is the role of spinal interneurones?
Limb movement control of flexors and extensors
What mediates the inverse stretch reflex and reciprocal inhibition between extensor and flexor muscles?
Inhibitory interneurones
What do excitatory interneurones mediate?
The flexor reflex
The crossed extensor reflex
What reflex enhances postural support during withdrawel of foot from painful stimulus?
Crossed extensor reflex
What structures control strategy in motor control?
Neocrotical association areas basal ganglia
What structures conrol tactics in motor control?
Motor cortex
cerebellum
What strucutres control execution in motor control?
Brain stem
Spinal cord
Where do descending spinal tracts originate from?
Cerebral cortex and brain stem
What controls lateral pathways which are important for voluntary control of distal musculature (hands and fingers)?
Cerebral cortex
What controls ventromedial pathways which are important for control of posture and locomotion?
Brainstem
What is the major lateral pathway?
Corticospinal or pyramidal tract (longest tract)
In the corticospinal or pyrimidal tract where do most fibres decussate?
At the pyramidal decussation to form lateral corticospinal tract (from medullary pyramid_
What does left hemisphere control?
Right musculature
Name a minor lateral pathway?
Rubrospinal tract
Where do axons in rubrospinal tract decussate?
At ventral tegmental decussation (and descend the spinal cord ventrolateral to the lateral corticospinal tract, terminating in ventral horn)
Axons from the lateral vestibular nucleus (deiters) descend as far as?
The lumbar spinal cord (hold upright balanced posture)
Axons from the medial vestibular nucleus descend as far as the?
Cervical spinal cord (control nbeck and back muscles)
In relation to the tectospinal tract: where do cell bodies redide?
In superior colliculus (optic tectum) - receives direct input from retina
In relation to the tectospinal tract: where do axons decussate?
In dorsal tegmental decusssation
What two things arise from the reticular formation?
Pontine (medial) and medullary (lateral) reticulospinal tracts
What does the pontine reticulospinal tract ( descends ipsilaterally) help to maintain?
Standing posture due to contraction of extensors in lower limb
What side does the medullary reticulospinal tract descend?
Bilaterally - opposes action of medial tract
What are first order neurones that relay information to second order neurones in the CNS by chemical synaptic transmission?
Nociceptors
What fibres are mechanical/thermal nociceptors and mediate first, or fast pain?
Alpha delta fibres (thinly myelinated)
What fibres are nociceptors, unmyelinated and collectively respond to all nloxious stimuli (polymodal), mediate second or slow pain?
C-fibres
What is the term for when the rate of action potential discharge correlates with the intensity of the applied stimulus?
Frequency coding
What do type I Adelta fibres mediate?
First pain to intense mechanical stimuli
What do type II Adelta fibres mediate?
First pain to heat (sensitive to capsaicin)
What subclassification of Cfibre - contributes to heat pain and location of stimulus and shows sensitisation to repeated stimuli?
C-MH
What subclassification of Cfibre - responds to noxious mechanical stimuli, insensitive to heat and capsaicin?
C-M
What subclassification of Cfibre - responds to notious heat, sensitive to capsaicin, mediates heat hyperalgesia, does not contribute to location and requires a sensitivity to mechanical stimulation in the context of inflammation?
C-H
What subclassification of Cfibre - is normally insensitive to both mechanical and heat stimuli but aquires sensitivity following sensitisation by inflammatory mediators?
C-MiHi (silent)
What nociceptor terminal is the site of Ca dependent transmitter release (glutamate) and is targeted by endogenous molecules that regulate activity?
Central terminal
What nociceptor terminal is the site of release of molecules that influence local tissue environment (e.g. substance P causes vasodilation and extravasation of plasma proteins, calcitonin gene related pepetide causes vasodilation), and is targeted by endogenous molecules that regulate sensitivity?
Peripheral terminal
What signalling direction is by nociceptors?
Bidirectional
Where are primary afferent cell bodies (apart from trigeminal system) located?
In dorsal root ganglia
Where do axons of primary afferent cell bodies terminate?
Centrally in dorsal horn of spinal cord in various laminae of Rexed (I-V)
Where do nociceptive C and Adelta fibres mostly terminate superficially?
In lamiae I and II (also V for Adelta)
What can be said about cells that only receive input from Adelta fibres?
They are proprioceptive
What pain originates from stretching, twisting, inflammation and ischaemia but not cutting or burning?
Visceral pain
Where do terminals of visceral nociceptors terminate?
In laminae I and V but not II
Where does referred pain from the heart go?
T1 - T5
Where is gallbladder pain referred to?
C4
What does the spinoreticular tract transmit?
Slow C-fibre pain
What tract in the anterolateral system is invoved in autonomic responses to pain, arousal, emotional response and fear of pain?
Spinoreticular tract
In relation to the spinothalamic tract: where do prohjection neurones originating from lamina I (fast Adelta pain) terminate?
In posterior nucleus of thalamus
In relation to the spinothalamic tract: where do projection neurones originating from lamina V terminate?
In posterior and ventroposterior nucleus of the thalamus
In relation to the slow pathway (spinoreticular tract) where are signals from the thalamus relayed by thalamocortical neurones to?
Limbic area of forebrain
What pathway registers the emotional/motivational component of pain?
Spinoreticualr tract
What does stimulation of non-nociceptive afferents (e.g. Abeta fibres) activate?
Lamina II inhibtory interneurones that suppress firing of projection neurone
In relation to controlling spinal gates: with physiological influence what opens and closes the gate?
Opens - C/Adelta dibres active
Closes - Abeta fibres active
Name three important brainstem regions for pain modulation?
- Periaqueductal grey - excitation produces profound analgesia
- nucleus raphe magnus
- locus coeruleus
Name three mechanisms involved in suppression of nociceptive transmission of dorsal horn?
- Diret presynaptic inhibition
- Direct post synaptic inhibition
- Indirect inhibition
What inhibition is being described here (suppression of nociceptive transmission of dorsal horn): inhibition of neurotransmitter release from nociceptors. Works via GPCR suppressing the opening of vltage gated calcium channels and calcium influx?
Direct presynaptic inhibition
What inhibition is being described here (suppression of nociceptive transmission of dorsal horn): works via GPCR opening K channels in the projection neurone causing hyperpolarisation and reduced excitability?
Direct post synaptic inhibition
What inhibition is being described here (suppression of nociceptive transmission of dorsal horn): works by activation of inhibitory interneurons (enkephalinergic) thay suppress transmission of both pre- and post synaptic mechanisms?
Indirect inhibition - opoid agonsit drugs mimic the activity of enkephalinergic interneurones
What is opoid action mediated by?
GPC opiod receptors
What are the four classes of opiod receptors>
- mu
- delta
- kappa
- ORL
What opiod receptor is responsible for most analgesic action of copoids but has some major adverse effects such as depression, constipation, euphoria, sedation and dependence?
Mu
What opiod receptor contributes to analgesia bt activation can be proconvulsant?
Delta
What opiod receptor contributes to alagesia at the spinal and peripheral level and activation associated with sedation, dysphora and hakllucinations?
Kappa
What opiod receptor when activated produces an anti-opoid effect?
ORL
What should pethidine not be used together with?
MAO inhibitors
Is codeine given orally or IV?
Oral
What patients should not be given tramadol - weak u-receptor agonist?
Epileptics
What drug - antagonist - is used to reverse opoid toxicity?
Naloxone
What limits selective COX-2 inhibitor use?
Prothrombotic
