What factors determine the strength of muscle contraction generated by a single motoneurone supplying striated muscle? Does this apply to C.N.S. synapses?

Sanjay Manohar (Oxford 2015)

Somatic = voluntary = striated = skeletal muscle

Key experiments to describe:
	Sherrington 1920
	 - definition motor unit = alpha motoneuron + fibre
	 - mn pool - neurones innervating 1 muscle
	Sherrington 1906 - stroking foot of dog - temporal summation
	Ramsay and Street 1939
	 - semitedinosus of frog; tetanic stimulus
	 - isometric force measure -> length-tension curve	Eccles 1941 - endplate potentials
	Fatt & Katz 1951   
	 - minature EPP = fluctuations 100th size of response to AP
	 - smaller with curare, larger with pyridostigmine = cholinergic
	 - calcium depletion reduces EPP but not mEPP; Na depletion reduces both.
	Eccles 1960 crossed innervation study

	Gordon Huxley & Julian 1965
	 - sliding filament theory
	 - interference microscopy
	 - sarcomeres 2 microns long.

What affects force:
motor unit size (number of fibres)
neuron's firing rate
length of fibre
fibre type
number of receptors
calcium release
receptor blockade
    Myasthenia - nachr blocker
    alpha bungarotoxin (blocker, venom)
    botulinum toxin (prevents release)
fatigue; duration of stimulation
    order (smaller first, Henneman's size principle)

Muscle                            CNS
MEPP without input                 EPSP/IPSP with input
reliable AP                        unreliable AP
Ca/Mechanical summation            EPSP summation

80 ns twitch, tetany, fusion       probability of AP
"Motor unit"                       Many input cells
 = no inputs to sum                dendrites sum inputs
large complex endplate             small dendritic spine
temporal integration by calcium    shorter time
force is graded                    firing rate is graded
nAChR                              many receptors and transmittors

fast twitch                       slow twitch
type 2                            type 1
larger motor unit                 smaller
adapting                          nonadapting
anaerobic                         aerobic
high frequ input 30/60Hz          lower frq 10-20 hz
large diameter axon               smaller
power                             posture
white                             red - myoglobin