Spinal cord compression - 129 Flashcards
Where do afferent neurons conduct to/from?
Conduct signals from sensory receptors INTO the CNS
Where do efferent neurons conducts to/from?
Conduct motor/effector signals from the CNS OUT to effectors, e.g. muscle
What is a ganglion?
A collection of neurons usually located outside the brain
What are the 5 components to each reflex circuit? (Regarding spinal reflexes)
1) sensory receptor 2) afferent path to CNS 3) synapse within CNS 4) efferent path from CNS 5) effector
What do inhibitory interneurons in the spinal cord allow for?
Contraction of agonist and simultaneous relaxation of the antagonist
Which root does sensory information pass through?
Dorsal root
Efferent information passes through which root in the spinal cord?
Ventral
What do muscle spindles do?
Detect changes in muscle length, stretch generates an action potential.
What is a myotatic reflex? What is the function of this reflex?
Stretch reflex.
Muscle lengthens -> muscle spindle is stretched and its nerve activity increases. Increases alpha motor neuron activity -> muscle fibers contract and resist stretching.
A secondary set of neurons causes opposing muscle to relax.
The reflex functions to maintain the muscle at a constant length.
What does tetanus toxin do?
Inhibit glycine release
What is responsible for making you drop heavy things? Why does this happen?
Golgi tendon organ. Has a higher threshold than muscle spindle and is activated by prolonged stretch, Ib afferent. Activation produces inhibition of homonymous muscle, preventing tendon damage
Do alpha motor neurones cause muscle contraction or spindle contraction?
Muscle contraction. The spindle is flaccid.
What causes muscle spindle contraction? What is the purpose of this?
Gamma motor neurons. It regenerates tension in the muscle
What cells are involved in recurrent inhibition?
Renshaw cells.
What are Renshaw cells?
inhibitory interneurones found in gray matter of spinal cord -> associated with an alpha motor neurone. They are excited by a-motor neurone, release glycine back onto the motor neurone, thus inhibiting firing. This allows synergistic muscles to contract together.
Where does descending motor control originate?
Pyramidal cells of motor cortex
What is apraxia?
Inability to produce a specific motor act even though sensory and motor pathways are intact - e.g. cannot execute a movement on request.
Name 2 descending tracts
Corticobulbar and corticospinal
What is the anterolateral system?
Ascending pathway that comprises 3 main pathways
What are the 3 main pathways of the anterolateral system?
Spinothalamic, spinoreticular and spinotectal
What are some classic signs and symptoms of a LMN lesion?
Hyporeflexia, fasiculations, muscle atrophy, denervation.
What are some classic signs and symptoms of an UMN lesion?
Paralysis, hyperreflexia, increased muscle tone, spasticity, babinski relex, bladder, bowel and sexual dysfunction
Where do corticospinal fibres most commonly decussate?
At the junction of the medulla and spinal cord
Where do fibres of the spinothalamic tract most commonly decussate?
In ventral white commissure. Pain and temperature axons usually cross within 1 segment of origin. Touch and pressure may ascend several segments before crossing.
