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 are alpha motor neurones? State some other names given to alpha motor neurones.
Anterior horn cells, ventral horn cells or lower motor neurones
They are motor neurones that innervate the extrafusal fibres of skeletal muscle
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
Describe the arrangement of alpha motor neurones within the ventral horn.
Dorsal – flexors
Ventral – extensors
Medial – proximal
Lateral - distal
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 this rule 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 the 3 types of motor unit?
Slow (Type 1)
Fast fatigue-resistant (Type 2A)
Fast fatiguable (Type 2B)
Describe the structural and functional differences between slow and fast twitch muscle fibres.
Slow fibres have: Smallest diameter cell bodies Small dendritic trees Thinnest axons Slowest conduction velocity Fast fibres have: Larger diameter cell bodies Large dendritic cells Thicker axons Faster conduction velocity