Lectures 6-10 Flashcards
What is the definition of the motor unit?
a somatic efferent plus all the muscle fibres it supplies
What is the neruomuscular junction?
The interface between the neuronal and muscular compartments
What is a fasciculus comprised of?
muscle fibres, and then myofibril
What kind of muscle fibres are somatic?
skeletal
What is the sheath of the myofibril?
the endomysium
What surrounds the fascicle
the perimysium
What runs between muscle fascicles?
The neurovascular bundle
Name 5 types of skeletal muscle
Convergent Strap Circular Fusiform Pennated (Unipennate, Bipennate, Multipennate
What is in the middle of the H zone?
the m line
What kind of lower motoneurones are there?
alpha, beta, or gamma
What three things do the characteristics of the motor unit allow for?
unifrorm force throughout muscle
It allows the nervous system to control the rate and speed of contraction
Muscle to contract within the central axis of the attachments of the muscle
What determines the motor unit properties?
The type of efferent supplying it
What is a stretch reflex?
The connection between the lower motoneurone and an afferetnt of muscle length sense organ
monosynaptic stretch reflex (synapse between sensory and motor neruones)
What is the sginificance of the muscle stretch reflex?
the template nerual circuit for all motor units, and allows for minimal neural circuits
Which motor units are recruited first?
those with the smallest cell bodies and the lowest threshold for firing action potentials (lowest force)
Larger units are recruited on a progressively increasing scale of firing threshold.
How many molecules of ACh are requireed to open an AChR?
2
Where are Na+ VGC’s found in the NMJ?
deep in the folds of the post-synapse
What happens to the EPP?
The end plate potential decays as it gets further away from the end plate
How is Ca2+ released from the SR?
DHP receptors (Ca2+ VGC) detect the action potential in the t-tubule and open the Ca2+ Ryanodine release channels
What is Myesthenia Gravis?
an autonimmune disease of nAChR, at the NMJ.
It is treated using AChE inhibitors.
What are the 3 components of the motor unit?
The motoneurone
The NMJ
The skeletal muscle fibres
What are damaged muscle symptoms akin to?
lower motoneurone signs
What happens in reinnervation?
Sometimes nerves may reinnervate other effector organs
What is Polio Myelitis?
Polio virus infection of neurone soma of the ventral horn
What are the two variants of Polio?
1 - kills upper and lower motoneurones
2 - kills lower motoneurones
What is Motoneurone disease?
spontaneous genetic apoptosis of motoneurones, although extraocular motoneurone and anal sphincter motoneurones are unaffected
What does Botulinum Toxin do?
It can make food toxic - paraysis and death.
It de[letes the presynaptic terminal of the NMJ
What can Botulinum Toxin be used for?
controlling muscle spasms
What are nerve gases?
organophosphates, blocking AChE in NMJ
What are the 4 properties of a good LA?
Reversible
Blocks Ap in nociceptive neurones
What is nociception, and what is their significance with LA?
sensory receptors generate AP’s to the brain, their Na+ VGC’s are targeted
What are the common features of LA’s?
have an aromatic ring (makes it lipid soluble)
an ester(faster)/amide linkage
an amide end group
What are the lengths of duration of Procaine, Lidocaine, Prilocaine, and Bupivacaine?
Procaine - short (too short for modern use)
Lidocaine - medium
prilocaine - medium
Bupivacaine - long
What happens to the equilibrium when the environment is more alkaline?
the PoE will shift left, decreasing the amount of ionised LA (therefore, at pH 7.41, we have more of the ionised form)
What does the LA block?
The ionised LA blocks open channels (NA+ VGC’s) from within the axon
What effect does inflammation or infection have on LA
It decreases the pH, decreasing LA+, and hence reducing its effectiveness
Which motoneurones are the most easily affected by LA?
A-delta and C as they have the smallest diameter
What might injection of LA into blood vessels cause?
cadiac arrest or vessel dilation
What might be administered with LA’s to minimise risks of side-effects?
vasoconstrictors (they also increase duration of action)
Are reflexes somatic or autonomic?
BOTH
What 3 functions do reflexes serve?
protection
postural control
homeostasis
Expand on the term integration in the reflex arc
Interneurones in the CNs are inhibitory neurones.
They enable modulation - permiting somatic overriding of reflexes.
They allow the brain to know what is going on in the reflex
What is a myotatic reflex?
simple stretch reflexes
Use muscle spindles (stretch receptive), more stretches stimulate greater muscle contraction
Inhibitory interneurones reduce contraction of antagonistic muscle
What kind of reflex arc would a myotatic reflex use?
monosynaptic
What happens to Golgi tendon organs?
How do they work?
They are stretched as the tendon is stretched
The interneurone releases inhibitory transmitter to the motoneruone, reducing contraction.
What kind of reflex would Golgi tendon organs stimulate?
polysynaptic, inverse myotatic reflexes
What are golgi tenon organs important for?
preventing damage due to overwork and permits fine control in the hands
Do all somatic reflexes use prioprioreceptors?
No, not the withdrawal effect
What is the crossed extensor reflex
With the withdrawal reflex, posture may also be adjusted to combat forward momentum, for example.
NMJ: What does Ca2+ trigger in the pre-synaptic knob?
Binds to Ca2+ sensor called a synaptogram, stimulating a conformational change and hence vesicle fusion
