- Neurophysiology 2
- nerve fibres
- A (myelinated)
- alpha
- 15um
- 100m/s
- afferent subtypes
- 1A
- from muscle spindles: dynamic (bag 1) & static (bag 2) nuclear bag and nuclear chain fibres (connect at annulospiral endings)
- 1B
- efferent
- connect to extrafusal (extra-fast!) muscle fibres to cause contraction (NMJ)
- beta
- 10um
- 50m/s
- afferent
- efferent
- connect to intrafusal fibres of muscle spindles to control contraction
- gamma
- 5um
- 25m/s
- efferent
- connect to the intrafusal fibres of muscle spindles (again, dynamic (bag 1) & static (bag 2) nuclear bags and nuclear chain fibres to control contraction
- delta
- 3um
- 20m/s
- afferent
- synapse in laminae 1 and 5 of the dorsal horn
- B (myelinated)
- pre-ganglionic autonomic
- 2um
- 10m/s
- C (unmyelinated)
- post-ganglionic autonomic
- 1um
- 1m/s
- synapse in dorsal horn laminae II - III (substantia gelatinosa)
- SAME DAVE
- sensory afferent, motor efferent, dorsal afferent, ventral efferent
- mechanoreceptors
- Meissner’s corpuscles
- Merkel’s disks
- Pacinian corpuscles
- proprioception and vibration
- Ruffini endings
- Messi has a great touch, Merkel puts pressure of the EU, Paice has a vibrator, pain is rough
- reflex arcs
- monosynaptic
- stimulation of muscle, group 1a afferent neurone transmits impulse through the dorsal root to the ventral horn, synapses with alpha motor neurone, which transmits impulse to muscle.
- EPSP
- (excitatory post-synaptic potential)
- excitatory transmitter = glutamate
- IPSP
- (inhibitory post-synaptic potential)
- inhibitory transmitter = glycine (opens Cl channels and hyper polarises membrane)
- e.g. knee jerk reflex
- L2-L4
- femoral nerve
- absence = Westphal’s sign
- polysynaptic
- sensory receptors
- mechanoreceptors
- chemoreceptors
- thermoreceptors
- photoreceptors
- nociceptors
- brainstem death testing
- no reversible cause
- drugs, hypothermia, electrolyte, cardiovascular, endocrine
- deeply unconscious
- apnoeic
- reflexes PCV PCG
- pupillary light reflex
- sensory II, motor III
- light shone in eyes
- corneal blink reflex
- sensory V, motor VII
- cornea brushed w. swab
- vestibulo-ocular reflex
- sensory VIII, motor III, IV, VI
- 50mL of ice cold saline into ears
- ‘COWS’
- cold - opposite, warm - same
- due to endolymph movement
- pain response
- sensory V, motor VII
- stimulus to supra-orbital ridge
- cough reflex
- sensory X, motor X
- bronchial catheter passed to the carina
- gag reflex
- sensory IX, motor X
- pharynx stimulated with spatula
- I, XI and XII not tested as don’t have a reflex arc
- apnoea test
- increase FiO2 to 1, do ABG, reduce MV until ETCO2 reaches 6, maintain apnoiec oxygenation, observe for respiratory activity for 5 mins, confirm increase in PaCO2 of more than 0.5kPa
- must all be done twice
- 2 competent clinicians, one of them a consultant
- can then become a DBD (donor after brain death) as opposed to DCD (donor after cardiac death)
- NMJ
- disease
- MG
- IgG autoantibodies to acetylcholine receptors at the NMJ
- worse towards end of day
- worsens with activity
- Tx: pyridostigmine + atropine, plasmapheresis in crisis thymectomy
- anaesthesia: resistant to sux, sensitive to non-depolarising NMB’s (give 10% of dose)
- Lambert-Eaton
- IgG autoantibodies inhibit VG Ca channels on presynaptic membrane
- improves with activity
- often paraneoplastic (small cell carcinoma)
- Tx: treat the cancer, pyridostigmine, steroids, diaminopyridine, plasmapheresis, IVIG
- Action potential
- Presynaptic
- AP opens voltage gated Ca channels
- 125 vesicles of Ach migrate and release 10,000 molecules into the synapse each
- synaptic cleft = 30 - 50 nm wide
- synaptic delay 0.5 ms
- summation
- temporal
- repeated potentials in single neurone add up
- spatial
- summation of potentials from different dendrites add up (or subtract with IPSPs)
- muscle
- skeletal
- functions
- movement
- posture and joint stability
- heat production
- structure
- fascicles
- myofibres (surrounded by sarcolemma)
- myofibrils
- sarcomeres
- lines
- H band
- length of myosin that does not overlap with actin
- I band
- length of actin that does not overlap with myosin
- Z line
- junction between actin filaments
- M line
- junction between myosin filaments
- A band
- contraction
- H and I bands shorten
- A stays the same
- filaments
- thin
- actin arranged in a doublehelical structure
- tropomyosin coiled around in grooves
- secured by troponin (‘the nail’)
- and covers the myosin binding site on actin
- thick
- Movement
- pre-central gyrus impulse —> descends through internal capsule —> decussates in the cortico-spinal tract (with input from cerebellum) —> travels through anterior horn cell —> travels to alpha motor neurone
- excitation-contraction coupling
- Ach activates VG Na channels at NMJ and down T-tubule of sarcolemma and causes depolarisation and opening of VG Ca channels
- depolarisation for 5-10ms
- Ca activates ryanodine receptor on SR and releases more calcium (CICR)
- sliding filament theory
- Ca binds to troponin C on actin
- Troponin C interacts with troponin I, which interacts with troponin T to move tropomyosin and expose myosin binding site on actin
- 1) ATP binds to myosin head —> myosin releases actin
- 2) ATP —> ADP + phosphate + energy cocks myosin into high energy conformation
- 3) phosphate realeased from myosin —> pushes on actin
- 4) ADP released
- duration of contraction 7.5 - 100ms
- repeats
- Ca channels on SR actively reuptake Ca
- energy
- 2 seconds
- 10 seconds
- ATP from phosphagens (e.g. creatine phosphate)
- 1 minute
- ongoing
- types
- I
- slow twitch
- high mitochondria, myoglobin and surface to volume ratio
- darker
- oxidative metabolism
- resistant to fatigue
- II
- IIa
- fast twitch
- also high mitochondria, myoglobin and surface to volume ratio
- IIb
- fastest
- few mitochondria, low myoglobin and SA to vol ratio
- light appearance
- anaerobic
- easily fatigued
- ‘Usain wants IIb the fastest’
- smooth
- no ordered sarcomeres
- minimal T-tubules and SR
- calmodulin causes myosin and actin binding slowly
- heart
- functional syncytium
- more mitochondria
- CICR is more important
- 150 - 200ms