Neuromuscular and Spinal Cord Control of Movement Flashcards
What mechanism causes the graded effects of neuronal transmission
Summation
- The degree of summation will determine how readily a neurone can ….
reach threshold to produce an AP
3 steps of activation at a NMJ:
- When an AP arrived at the MNJ, Ca2+ influx causes ACh release
- ACh binds to receptors on the motor end plate
- Ion channel opens- Na+ influx causes an AP in the muscle fibre
What causes MINIATURE END-PLATE POTENTIALS
At rest, individual vesicles release ACh at a very low rate in a motor neuron
What is the motor unit:
NAME GIVEN TO A SINGLE MOTOR NEURON TOGETHER WITH ALL THE MUSCLE FIBRES THAT IT INNERVATES- IT IS THE SMALLEST FUNCTIONAL UNIT WITH WHICH TO PRODUCE FORCE
Stimulation of one motor unit causes contraction of how many fibres
all the muscle fibres in that unit
THE ALPHA MOTOR NEURON is the….
lower motor neurons of the brainstem and the spinal cord (the last neurons before the muscle fibre)
THE ALPHA MOTOR NEURON is located in…
the ventral horn of the spinal cord
motor neuron pool contains …
all alpha motor neurons innervating a single muscle
The 3 different motor unit types are:
Slow S type 1
Fast fatigue resistant, FR TIIA
Fast fatiguable FF, TIIB
Which motor unit has the largest diameter cell bodies, dendritic tress, axon thickness, and fastest conduction velocity
FF TIIB
2 mechanisms by which the brain regulates the force that a single muscle can produce?
RECRUITMENT
RATE CODING
Explain recruitment in regulating force produced by a motor neuron
- Motor units are not randomly recruited- there is an order to this
- Governed by the ”SIZE PRINCIPLE”- smaller units are recruited first (these are generally the slow twitch units)
- As more force is required, more units are recruited
- This allows for fine control e.g. writing, under which low force levels are required
Which type of motor unit is recruited first
Smaller units and so generally slow twitch
Explain rate coding in regulating force produced by a motor neuron
- A motor unit can fire at a range of frequencies Slow units fire at a lower frequency
- As the firing rate increases, the force produced by the unit increases
- Summation occurs when units ire at frequency too fast to allow the muscle to relax between arriving APs
Which type of motor unit has the lowest firing frequency
Slow twitch T1
- Summation occurs when units are at frequency too fast to …
allow the muscle to relax between arriving APs
Motor unit and fibre characteristics are dependent on …
the nerve which innervated them
If a fast twitch muscle and a slow muscle are cross innervated (their innervation is switched) what happens to speed of twitching
the slow becomes fast and the fast becomes slow
Type I to II muscle fibre switching is possible in cases of … example of when this occurs.
severe deconditioning or spinal cord injury
Microgravity during spaceflights results in shift from slow to fast muscle fibre types
- Ageing is associated with loss of type I and II fibres but also preferentially loss of what type of fibre. What is evidence of this
type II
evidenced from slower contraction times
REFLEX definition:
AN AUTOMATIC AND OFTEN INBORN RESPONSE TO A PERIPHERAL STIMULUS THAT INVOLVES A NERVE IMPULSE PASSING INWARD FROM A RECEPTOR TO A NERVE CENTRE AND THEN OUTWARD TO AN EFFECTOR (AS A MUSCLE OR GLAND) WITHOUT REACHING THE LEVEL OF CONSCIOUSNESS
Reflex response size is proportional to …
the size of the stimulus
Describe the reflex pathway starting with the sensory receptor
Sensory receptor -> sensory neuron -> (interneuron -> inhibits antagonistic muscle) motor neuron -> effector
What is a Volley, e.g. afferent volley or effect volley
collection of APs
What detects stretch in the reflex arc
Muscle spindle
What is the Hoffman reflex
- Stimulate the nerve that you want to stimulate the muscle of interest electrically
- Stimulate a mixed nerve right in the centre and it will send signals up to the spinal cord and down to the muscle
- This allows you to achieve the same identical stimulation each time
- Should result in a quick response resulting from immediate motor activation, and a slower response resulting from sensory and THEN motor activation (the second is called the Hoffman reflex)
What test can enable us to work out which part of the NS is damaged
Hoffman Reflex
Explain crossed extensor reflex
If you step on a plug, Not only is a response on the ipsilateral side to the stimulus required e.g. moving your foot off of the plug, but a response on the contralateral side is needed e.g. repositioning your other leg to stay balanced This is what we mean by crossed extensor
How do you enhance the kneejerk reflex
ching our teeth or making a fist when having our patellar tendon tapped
what is the Jendrassik manoeuvre
enhance the kneejerk reflex by clenching our teeth or making a fist when having our patellar tendon tapped- this is called the JENDRASSIK manoeuvre
Explain the Jendrassik manoeuvre
- Higher centres of the CNS exert inhibitory and excitatory regulation upon the stretch reflex
- Inhibitory control dominates in normal conditions (N)
- Decerebration reveals the excitatory control from supraspinal areas
- Rigidity and spasticity can result from brain damage giving over-active or tonic stretch reflex
HIGHER CENTRES INFLUENCE REFLEXES BY: (5)
1) activating alpha motor neurone activating inhibitory interneurons activating propriospinal neurons activating gamma motor neurons activating terminals of afferent fibres
HIGHER CENTRES AND PATHWAYS INVOLVED in reflexes are? (4)
Cortex
Red nucleus
Vestibular nucleus
Tectum
Pathway the cortex controls in reflexes? and this does?
Corticospinal (fine control of limb movements and body adjustments)
Pathway the Red nucleus controls in reflexes?
Rubrospinal (automatic movements of arm in response to posture/balance changes)
Pathway the Vestibular nucleus controls in reflexes?
vestibulospinal (altering posture to maintain balance)
Pathway the Tectum controls in reflexes?
tectospinal (head movements in response to visual information)
HYPER-REFLEXIA is a classic symptom of ….
upper motor neurone disorders e.g. stroke
CLONUS definition? Often seen in?
series of involuntary, rhythmic muscular contractions and relaxations (often seen in upper motor neurone disorders)
BABINSKI SIGN is… often seen in people with ….
Stimulation on sole of foot with blunt instrument leads to an uncontrolled upward extension of the hallux (toe) in people with upper MN disorders
Hyporeflexia is associated with XXXX diseases
lower motor neurone
