5 - Spinal Reflexes Flashcards
Define a motor unit
= motor neuron together with its cell body in the dorsal horn, its motor axon and the set of muscle fibres it innervates
Contraction of 1 motor unit by a single action potential generates what?
Twitch
For smooth contraction, MU is activated by what to produce a type of which contraction?
MU is activated by a train of action potentials at a frequency high enough to produce a smooth fused contraction = tetanus/tetanic contraction (how healthy muscles normally contract, not a pathological condition)
What does a large activation of large motor unit produce?
Large Force
How are the force of contraction in muscle increase/decrease by?
Increase/decrease the force of contraction in muscle by recruiting more/less MU
Each motor axon fire at its tetanus fusion frequency or not at all.
Most muscles = Mixture of small and large motor unit.
Fine control of force = activate more or less small MU.
Full power = recruit the large MU
What is tetanus?
Contraction of a motor unit, smooth contraction, how normal healthy muscles work
Define a lower motor neuron
= A neuron with its cell body in the ventral horn of the spinal cord
What are the 3 main synaptic inputs to a lower motor neuron
Upper motor neurones from descending tracts in the spinal cord
Local interneurons (cells with all processes inside the CNS)
Local sensory nerve fibres via reflexes
What is the pathological condition if LMN is damaged?
Reduced tone or complete absence of tone = flaccid paralysis
Define an upper motor neuron
A neuron with its cell body in the brain that projects down the spinal cord in a descending tract to synapse with the cell bodies of the lower motor neurones
Some have their cell bodies in the brainstem, some in the motor cortex, basal ganglia or the cerebellum
What are the 2 systems of upper motor neurons and how do they relate to the spinal cord?
Pyramidal system – upper motor neurone cell bodies projecting directly from the motor cortex that travel via the corticospinal tract (pyramidal tract) to lower motor neurones
Extrapyramidal system – upper motor neurones with cell bodies in the brainstem that are regulated by the motor cortex
Spinal cord - lower motor neurones in ventral horn that project out via peripheral nerve to muscles
What is the pathological condition if the upper motor neuron is damaged?
= pathological increases in muscle tone and hyperactive reflexes = spasticity
Pathological types of reflexes indicating upper motor neuron injury include = cogwheel rigidity, exaggerated tendon reflexes, clonus reflexes, pendular reflexes etc.
What is meant by the babinski response?
Vagenskies response = (when scratching a baby’s foot, the toe will curl up but in normal adult, it curls down) ⇒ plantarflexion reflexion (downward push). Examination for spinal cord lesion in the foot will include scratching the base of the foot and if lesion is present in an adult, the toes will curl upwards.
Define muscle tone
Muscle tone (residual muscle tension or tonus) = the continuous and passive partial contraction of the muscles, or the muscle’s resistance to passive stretch during resting state.[1] It helps maintain posture and declines during REM sleep
Define spasticity
Spasticity = a condition in which certain muscles are continuously contracted. This contraction causes stiffness or tightness of the muscles and can interfere with normal movement, speech, and gait. Spasticity is usually caused by damage to the portion of the brain or spinal cord that controls voluntary movement.
What is meant by a monosynaptic reflex arc?
involuntary motor action triggered by sensory input
What are myotatic reflexes and what are they also called?
Myotatic reflexes are those that are elicited by tapping the tendon of a muscle. They are also called tendon jerk reflexes
Where are the reflexes stored and in what form?
Reflexes are stored in the dorsal and ventral grey matter of the spinal cord in the form of patterns of synaptic connections between inputs, outputs and interneurons
