Neuromuscular and spinal cord final Flashcards
Synapses between
Neurones and neurones
Neurones and muscle
Contact ratio for which N-N N-M:
1000: 1
1: 1
1: 1 N-M
1000: 1 M-M
Presynaptic terminal is also known as
bouton
Synaptic cleft length
10-50nm
How can the membrane potential of the post synaptic neurone be altered
It can be made less negative – i.e. be brought closer to threshold for firing; this is an excitatory post synaptic potential (EPSP)
OR
It can be made more negative – i.e. be brought further away from threshold for firing; this is an inhibitory post synaptic potentials (IPSP)
EPSPs and IPSPs can also summate
NMJ
A specialised synapse between the motor neuron and the motor end plate, the muscle fibre cell membrane
Activation of the neuromuscular junction
What happens at rest
When an action potential arrives at the MNJ, Ca2+ influx causes ACh release. ACh binds to receptors on motor end plate.
Ion channel opens – Na+ influx causes action potential in muscle fibre.
At rest, individual vesicles release ACh at a very low rate causing miniature end-plate potentials (mEPP)
Alpha motor neuron-innervate? from ?
Activation causes
lower motor neurons of the brainstem and the spinal cord
They innervate the (extrafusal) muscle fibres of the skeletal muscles
muscle contraction
Alpha motor neuron in anterior ventral horn where are flexors, extensors, proximal, distal in
Flexors are found more dorsally
Extensors found more anteriorly
Proximal musculture, alpha motor neurones found medially
Distal musculuture, alpha motor neurones found laterally
Motor unit consists of
Motor neuron and muscle fibres it innervates
Types of motor unit
Type 1:S-Slow, Low tension
Type 2A: FR- Fast, Fatigue resistant, moderate tension
Type 2B: FF- Fast, fatiguable, High tension
Dendritic trees of each
Slow type: Small dendritic tree Fast, fatigue resistant: Larger dendritic tree Fast, fatiguable: Larger dendritic trees
Two ways in which brain regulates the force a single muscle can produce
Recruitment
Rate coding
What is size principle in recruitment
What does this allow
Smaller units are recruited first (these are generally the slow twitch units). S->FR->FF
As more force is required, more units are recruited.
This allows fine control (e.g. when writing), under which low force levels are required.
Rate coding
Summation in rate coding occurs when to allow
As the firing rate increases, the force produced by the unit increases.
Summation occurs when units fire at frequency too fast to allow the muscle to relax between arriving action potentials.
Neutrophic factors are
Function
Type of growth factor
Prevent neuronal death and promote growth of neurons after injury
Does motor neurone have an effect on the properties of the muscle which it innervates
yes. If a fast twitch muscle and a slow muscle are cross innervated, the soleus becomes fast and the FDL becomes slow.
Reflex
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
An involuntary coordinated pattern of muscle contraction and relaxation elicited by peripheral stimuli.
Components of a reflex arc
- SENSORY RECEPTOR
- SENSORY NEURON– dorsal root ganglion =cell body of sensory neuron And into dorsal horn of Spinal cord
- INTEGRATING CENTER-One or more regions within the CNS that relay impulses from sensory to motor neurons
- MOTOR NEURON from ventral horn, ventral root
- EFFECTOR
Monosynpatic (Stretch) reflex
- Stretching stimulates SENSORY RECEPTOR
- Within dorsal horn info goes up to brain (but no input from brain) and INTEGRATING CENTER to motor etc. cause contraction
Relax antagonistic muscle
Inhibitory interneuron
Receives input from sensory neuron
Hoffmann (H-) Reflex= electrically stimulated monosympatic reflex
3 different conditions in which fibre types can change properties
1) Following training: Type2b to Type 2a
2)severe deconditioning or spinal cord injury. –Type I to II
Microgravity during spaceflight results in shift from slow to fast muscle fibre types
3)Ageing associated with loss of type I and II fibres but also preferential loss of type II fibres. This results in a larger proportion of type I fibres in aged muscle (evidence from slower contraction times).
List 3 Extrapyramidal tracts
Rubrospinal tract
Reticulospinal tract
Vestibulospinal tract
Olivospinal tract
Rubrospinal tract function
From where to where
Automatic movements of arm in response to posture/balance changes
Red nucleus in midbrain to spinal cord
Reticulospinal tract function
Coordinate automated movements of locomotion and posture (e.g to painful stimuli)
Vestibulospinal tract function
Regulates posture to maintain balance and facilitates mainly alpha motorneurones of the postural, anti-gravity (extensor) muscles
Polysynaptic reflex-Flexion withdrawal
Stimulation of flexor muscle to allow withdrawal of leg
More than one motor unit and involved in innervation of several muscles stimulation
sometimes stimulation occurs above and below level of stimulation of spinal cord to promote contraction of muscle
excitatory innervation
Crossed extensor
Inhibition across midline for relaxation of antagonistic muscle to maintain gait – crossed extensor
Example of supraspinal reflex
Jendrassik manoeuvre
Clench teeth or making a fist when having patellar tendon tapped will make reflex action stronger
Supraspinal reflex acton upon which reflex
What normally dominates in normal conditions
Decerebration results in
Higher centres of CNS exert inhibitory and excitatory regulation upon stretch reflex.
Inhibitory control dominates in normal conditions
Decerebration reveals the excitatory control from supraspinal areas– no inhibitory input
Rigidity and spasticity can result from brain damage giving over-active or tonic stretch reflex
Supraspinal reflexes: Higher centres activate what to influence reflexes
Activating alpha motor neurons-ventral horn
inhibitory interneurons
Activating propriospinal neurons-proprioceptive info
Activating gamma motor neurons-interfusal to tense or not– innate from afferent input
Activating terminals of afferent fibres
Supraspinal reflexes: Higher centres and pathways involved
Higher centres & pathways involved are:
Cortex – corticospinal (fine control of limb movements, body adjustments)
Red nucleus – rubrospinal (automatic movements of arm in response to posture/balance changes)
Vestibular nuclei – vestibulospinal (altering posture to maintain balance)
Tectum – tectospinal (head movements in response to visual information).
Extrafusal muscle fibers
Under control of alpha motor neurones voluntary contraction of muscle
have sensory axons and respond to changes in lengths of muscle fibres and gamma motor neurones supply intrafusal- reacting to activity of muscle itself
What if the knee is extended and the muscle goes slack?
The spindle is shortened to maintain its sensitivity
THIS IS THE GAMMA REFLEX LOOP
Hypereflexia- inhibition of
stroke
loss of descending pathway inhibition
babinski sign–toes should curl not splayed
clonus
Hyporeflexia
associated with what
Below normal or absent reflexes
Mostly associated with lower motor neuron diseases
