Neuromuscular & Spinal Cord Flashcards
EPSP?
Excitatory Post Synaptive Threshold
Brings potential CLOSER to firing threshold
IPSP?
Inhibitory Post Synaptic Threshold
Brings potential FURTHER from firing threshld
Summation?
Graded effects of EPSP + IPSP
NMJ?
Specialised synapse BETWEEN the: o motor neurone AND o motor end plate (muscle fibre cell membrane)
mEPPs?
Miniature End-Plate Potentials
At rest, individual vesicles release ACh at a very LOW rate causing mEPPs
Alpha motor neurones?
These are the LMNs of the brainstem & spinal cord - hence innervate skeletal muscle fibres
What contains ALL the alpha motor neruones innervating a single muscle?
Motor neuron pool
Somatotropic arrangement of alpha-neurones in the SC
In the ventral horn!
o Posterior = flexor
o Anterior = extensor
o Medial lateral = proximal
o Postolateral = distal
Motor Unit?
Single motor neurone
+
all the muscle fibres it innervates
i.e. stimulation of ONE motor unit causes contraction of ALL the muscle fibres in that unit
How many motor neurones innervate EACH muscle fibre?
ONE distinct motor neurone
i.e. two DIFFERENT MNs CANNOT innervate the same muscle fibre
Innervation ratio?
Number of muscle fibres innervated by a MN
i.e. lower the number = MORE precise the movement
3 types of Motor Units?
o SLOW (S, Type I)
o Fast, Fatigue Resistant (FR, Type IIA)
o Fast, Fatiguable (FF, Type IIB)
Type I Motor Unit?
SLOW
o smallest soma
o small dendritic trees
o thinnest axons
o SLOWEST conduction velocity
Type IIA Motor Unit?
FAST, FATIGUE RESISTANT
o larger soma
o larger dendritic trees
o thicker axons
o FASTER conduction velocity
Type IIB?
FAST, FATIGUABLE
o larger soma
o larger dendritic trees
o thicker axons
o FASTER conduction velocity
(same as Type IIA essentially!)
How are the 3 motor unit distributed?
Are NOT discretely located but spread out (OneNote!!)
What 3 properties are the 3 different motor unit types classified by?
- Tension generated
- Speed of contraction
- Fatiguability
What 2 regulative mechanism in in place to regulate the force that a single muscle can produce?
- Recruitment
2. Rate coding
How does ‘Recruitment’ regulate force production?
Governed by the ‘Size Principle’
o SMALLER units are recruited FIRST (generally slow twitch units)
o As MORE FORCE is required, more units are recruited
This allows for FINE CONTROL when low force is required
How does ‘Rate Coding’ regulate force production?
via. rate of FIRING
o SLOW units fire at a LOWER frequency
o As the firing rate INCREASES, FORCE by the UNIT INCREASES
In regards to ‘Rate Coding’ when does summation occur?
When the units fire at a frequency TOO FAST to allow the muscle to RELAX between arriving APs
What are neurotrophic factors?
Type of GF
Characteristics of neurotrophic factors?
o Prevent neuronal death
o Promote growth of neurones after injury
Relationship between motor units, fibre characteristics & nerves?
Motor unit & fibre characteristics are DEPENDENT on the NERVE which INNERVATES them
i.e. if fast twich muscle (FDL or FHL) and a slow muscle (SOL) are CROSS-INNERVATED:
o the SOL becomes FAST
o the FDL becomes SLOW
