Neuromuscular and Spinal Cord Flashcards
What is the difference between EPSP (excitatory post-synaptic potential) and IPSP (inhibitory post-synaptic potential) in terms of membrane potential?
EPSP – makes the membrane potential less negative (bringing it closerto the threshold potential)
IPSP – makes the membrane potential more negative (hyperpolarisation)
You get graded effects – whether the neurone fires or not is dependent on the summation of inputs
Which proteins are involved in the release of acetylcholine at synapses?
SNARE proteins
What trigger 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
They are caused by the constant dumping of acetylcholine into the synapse
What is the difference between intrafusal and extrafusal muscle fibres?
Intrafusal – these are skeletal muscle fibres that serve as sensory organs (proprioceptors) that detect the amount and rate of change of length of a muscle
Extrafusal – standard skeletal muscle fibres that are innervated by alpha motor neurones and generate tension by contracting, thereby allowing for skeletal muscle movement
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
What is an important rule to remember regarding the connections between alpha motor neurones and muscle fibres?
One motor neurone can innervate several muscle fibres
But every muscle fibre can only be innervated by one motor neurone
Under what conditions can the rule muscle fibres can only be innervated by one motor neurone be broken?
Under pathological conditions (e.g. severed nerve), the axonal regeneration can result in the innervation of muscle fibres that are already innervated
Define motor unit.
A single motor neurone together with all the muscle fibres that it innervates - it is the 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 (e.g. extrinsic eye muscles) havea low innervation ratio (few fibres innervated by a single neurone)
Muscle that are required to generate a lot of power have a high innervation ratio because when the motor unit fires, it will cause the contraction of a large mass of muscle fibres thus generating power (e.g. quadriceps)
What are 2 methods by which the brain regulates the force that a single muscle can produce?
Recruitment – recruiting more motor units for the muscle contraction
Rate Coding – increasing the frequency of action potentials travelling down the nerves to the muscle fibres
What principle governs recruitment?
Size principle
Smaller units are recruited first, which are generally slow fibres
What are neurotrophic factors?
Factors produced within the nerves and are transported throughout the nerve to maintain the nerves integrity and function.
They are a type of growth factor that prevents neuronal death and promotes the growth of neurones after injury.
What happens to a slow fibre when a fast nerve is transplanted onto it and what does this show?
It becomes fast
This shows that the function of the muscle fibre is very much determined by the type of nerve that innervates it.
The action potentials can’t be the only thing being delivered to the muscles by the nerves.
How does muscle composition change with ageing?
Ageing is associated with a loss of type 1 and type 2 fibres with preferential loss of type 2 fibres
This means that a large proportion of muscle fibres in ages muscle are type 1
This loss of muscle is called sarcopenia
What tract is responsible for voluntary movements?
Pyramidal/Corticospinal tract
What is the role of extrapyramidal tracts?
It is responsible for automatic movements in response to stimuli (these are movements that your body makes without you being aware of it)
What is a reflex?
Automatic and often inborn response to a stimulus that involves a nerve impulse passing inward from a receptor to a nerve centre and then outwards to an effector (a muscle or gland) without reaching the level of consciousness
What are the components of a reflex arc?
Afferent signal
Relay neurone
Motor neurone
What are the two signals that are generated when the patellar ligament is tapped?
There is an excitatory signal going to the quadriceps
There is also an inhibitory signal going to the hamstrings (antagonist)
Why is there a difference in the time taken for these signals to reach the relevant muscles in patellar reflex?
The signal going to the quadriceps only has one synapse (monosynaptic) whereas the signal to the hamstrings goes via an inhibitory interneurone so there are two synapses.
This means that the signal to the quadriceps arrives slightly faster than the signal to the hamstrings.
Why do sensory nerves show a response at lower stimulus intensity than motor nerves?
They are more amenable to electrical stimuli because they’re larger
What names are given to the 2 polysynaptic reflexes?
Flexion withdrawal
Crossed extensor
