Neuro 11 - Neuromuscular and Spinal Cord Flashcards
What is the difference between EPSP and IPSP in terms of membrane potential?
EPSP - makes the membrane less negative - bringing it closer to the threshold potential
IPSP - makes the membrane more negative - taking it further away from the threshold - Hyperpolarisation
Which proteins are involved in the release of acetylcholine at the synapses?
SNARE proteins
What triggers acetylcholine release?
Calcium influx
If you record the post synaptic membrane potential at any one time, you will see some small changes in membrane potential. What are these caused by?
Miniature end plate potentials
Caused by constant dumping of acetylcholine into the synapse
but not enough to cause an action potential
What is the difference between intrafusal and extrafusal muscle fibres?
intrafusal - skeletal muscle fibres that serve as sensory organs e.g. proprioceptors
Extrafusal - your bog standard skeletal muscle fibres that are innervated by alpha motor neurones and generate tension by contracting
What are alpha motor neurones?
motor neurones that innervate the extrafusal fibres of skeletal muscle
What is the name given to the sensory receptors in muscle that feedback to the CNS and allow an excitatory reflex to be generated?
Spindles
What is a motor neurone pool?
Collection of lower motor neurones that innervate a single muscle
Describe the arrangement of alpha motor neurones within the ventral horn?
Dorsal - flexors
Ventral - extensors
Medial - proximal
Lateral - distal
What is an important rule to remember regarding the connections between alpha motor neurones and muscle fibres?
1 motor neurone can innervate several muscle fibres
but 1 muscle fibre can only be innervated by 1 motor neurone
Under what conditions is the 1:1 muscle fibre:motor neurone debatable?
pathological conditions
e.g. severed neurone - can cause innervation of muscle fibres which are already being innervated
Define motor unit.
single motor neurone together with all the muscle fibres that it innervates
smallest functional unit that can generate force
Describe and explain the difference in innervation ratio across different muscles in the body using examples.
muscles that require very fine control have low innervation ratio e.g. maybe 1 fibre being innervated by 1 neurone
What are the three types of motor unit.
Slow - type 1
Fast Fatigue resistant - Type 2A
Fast Fatiguable - Type 2B
Describe the structural and functional differences between slow and fast twitch muscle fibres.
Slow - small diameter, smaller dendritic trees, thinnest axons, slowest condutions
What are the 2 methods by which the brain regulated the force that a single muscle can produce?
Recruitment - recruiting more motor units for contraction
Rate coding - increasing the frequency of action potentials occurring
What principle governs recruitment?
Size principle
smaller units recruited first aka slow ones
Describe the order of recruitment of motor units with increasing force generation.
Slow — Fast fatigue resistant – fast fatiguable
What are neurotrophic factors?
Factors produced within nerves and are transported throughout the nerve to maintain the integrity and function
Growth factor that prevents neuronal death
What happens to a slow fibre when a fast nerve is transplanted into it?
becomes fast
this shows that the function of a nerve is determined by the nerve that innervates it
action potentials are not the only thing being transported by the nerves
How easy is it to switch from one motor unit type to another?
type 2b to 2a is possible with training
slow to fast not normally possible
How does muscle composition change with ageing?
loss of type 1 and type2 with preference for type 2
sarcopenia
What tract is responsible for voluntary movements?
Corticospinal
What is the role of the extrapyramidal tracts?
automatic movements
