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
Under which conditions can fibre types change properties?
o Training:
Type IIB –> Type IIA
o Deconditioning/SC injury:
Type I –> Type II
o Ageing:
Loss of Type I & II (preferential loss of Type II so larger proportion of Type I)
i.e. hence why slower contraction times
What are Extrapyramidal Tracts associated with?
Concerned with AUTOMATIC MOVEMENTS in response to stimuli (modify motor function)
What somatotopic representation is associated with the coticospinal tracts in the SC?
1a - LATERAL CS.T
1b - ANTERIOR CS.T
1a has sacral, lumbar, thoraci and cervical regions
Pathway of reflex reaction?
- Sensory receptor
- Sensory neurone
- Integration in interneurone
- Motor neurone
- Effector muscle
Experiment to see how many synapses within a reflex arc?
A volley (an AP travelling past recording equipment)
The difference in time from the afferent volley to the IC efferent recording
(generally one synapse = 0.7ms)
Monosynaptic (stretch) reflex?
e.g. knee-jerk reflex
When the patella ligament is hit:
- sensory stretch receptors activated
- sends impulse to integrating centre
- both to an INHIBITORY & EXCITATORY neurone to 2 different muscle groups
What is beneficial about the Hoffman (H-) Reflex?
Done so electronically (rather than mechanically) via. patella hammer
SO
any difference in response due to person NOT human error
What are the 2 waves seens in the Hoffman (H-) Reflex?
INITIAL M-wave
o direct response of muscle to the stretch with NO synpases (inital twitch after knee being hit)
H-reflex
o response of muscle a few ms later as the response has travelled through a few synapses (multiple fibres) - sensory neurone response exciting the motor neurone again
Describe the H wave seen in the Hoffman (H-) Reflex
o it ACTIVATES at LOWER stimuli strengths BUT is SLOWER to fire
o DECREASES at HIGHER stimuli strength as motor cells get activates that fire AGAINST the normal flow & CANCEL out the AP
Polysynaptic Reflexes - flexion withdrawal?
Reflexes that cross the spinal cord to the other side such that the other limbs do something to keep us upright
Called:
FLEXION withdrawal AND
CROSSED extensor
i.e. withdrawal of one leg in a reflex action & extensor of the other leg in the same reflex arc to ensure balance (gait)
Jendrassik Manoeuvre?
Can influence reflex action with supraspinal control
i.e. clench teeth while knee jerk - will get a GREATER RESPONSE
Explain the supraspinal control of reflexes
Higher centres of the CNS exert INHIBITORY & EXCITATORY REGULATION upon the stretch reflex
o INHIBITORY control DOMINATES in normal conditions
What can affect the supraspinal control of reflexes?
Decerebration
Leads to hyperreflexia & spasticity (over-active or tonic stretch reflex)
Gamma Reflex Loop?
(along with gamma motor neurones)
Ensure the muscle NEVER remains slack and so can remain SENSITIVE to stretch movements
Gamma neurones SHORTEN the spindle to maintain its sensitivity
What is found synonymously with alpha motor neurones?
Gamma motor neurones!
So found together & fire together when needs be
Why is hyperreflexia seen in stroke patients?
Loss of descending inhibition
