Lecture 13- Upper Motorneuron Flashcards
What is upper motorneuron?
- functional definition
- any neuron that controls the excitability of the lower motorneuron
What parts of the brain are considered upper motorneuron?
the descending systems-motor cortex, brainstem centers and basal ganglia and cerebellum (the last two do not directly feed into the motor neurons)
What is the role of motor cortex in movement?
planning, initiating and directing voluntary movements
What is the role of brainstem centers in movement?
basic movements and postural control -often involuntary
What is the role of basal ganglia in movement?
gating proper initiation of movement
What is the role of cerebellum in movement?
sensory motor coordination of ongoing movement
What is the input from the brain into the spinal cord most like?
-most of the input from the brain is actually inhibitory -most of the nervous system at any time is inhibiting the nervous system -if you want sth done, then removing the inhibitory signal= disinhibition -the motor pathway mostly= inhibition, if damaged= lose inhibition and difficult to move! -reflexes get abnormally strong when the inhibition is compromised
What happens to reflexes when the motor pathway is damaged?
-if damage in the brain, then reflexes get much stronger as the inhibition is not there
What are the two types of white matter in the spinal cord?
- lateral white matter
- medial white matter (in the middle is grey matter which they innervate)
What is the white matter in the spinal cord?
-myelinated axons of neurons coming from the brain
What axons are the lateral white matter in the spinal cord?
-axons coming from the motor cortex in the brain
What axons are the medial white matter in the spinal cord?
-axons from brainstem
What do the axons in the spinal cord that come from the brain synapse with?
-mostly synapse with interneurons except for some in the medial white matter synapse directly with motor neurons but that is unusual
What is the mapping of the white matter and spinal cord neurons?
-lateral white matter = lateral pathways= have axons that excite neurons that are distal -medial white matter excite interneurons that synapse with neurons that innervate medial structures -medial to lateral organisation is really important and it is an overall principle
Where do the axons of the white matter terminate in the spinal cord?
-at all levels some do
What do the upper motor neurons in the cerebral cortex excite?
-the axons are the lateral white matter -excite lower motor neurons in lateral ventral horn -these then excite distal limb muscles(skilled movements)
Are upper motor neurons from the cerebral cortex ipsilateral or contralateral?
-contralateral -cross over the midline (some of them)
Why is it an advantage that the upper motor neurons from cerebral cortex are contralateral?
-control distal muscle that make skilled, fine movements so do not want both sides doing the same thing at once
What do upper motor neurons in the brainstem excite?
-the medial white matter are the axons -excite lower motor neurons in medial ventral horn -those excite axial and proximal limb muscles (posture and balance)
Are upper motor neurons from the brainstem ipsilateral or contralateral?
- tend to be ipsilateral (come down on the same side)
- then spread to both sides
Why is it an advantage that upper motor neurons from the brainstem are ipsilateral?
-excite lower motor neurons that control axial and proximal limb muscles -those are for posture and balance control and we want these to cooperate
What is the overview of upper motor neuron connections with lower motor neuron?
-
What are the 3 tracts projecting from the brainstem to the spinal cord?
- Reticulospinal tract
- Colliculospinal tract (also called Tectospinal)
- Lateral and medial vestibulospinal tracts
- these are the axons that are the medial white matter, controlling axial muscle for posture
What are the 3 components of the brain stem?
-medulla -pons -midbrain
Where is the vestibular nucleus?
-part of the brain stem -it is in the middle of the pons
What are the lateral and medial vestibulospinal tracts?
- tract from brain stem to spinal cord (medial white matter)
- goes from the vestibular nucleus, from there projections to spinal cord
- the neurons come down and stay on the same side and some excite interneurons to excite the other medial side
- the lateral mainly sends the information
What is the vestibulospinal tract for?
-the vestibular nucleus gets information about the position of head and relays motor commands to alter muscle tone, extend, and change the position of the limbs and head with the goal of supporting posture and maintaining balance of the body and head. -coordinate head and trunk movement
Where is the reticular formation?
- brain stem, spread out, is in the midbrain, pons and medulla
- big cells, spread out, big dedritic branches,
- called reticular neurons
- spreads through the medulla, pond and goes right up to the midbrain
Which parts of the reticular formation are important for motor control?
-pons and medulla
Is the vestibulospinal tract ipsilateral or contralateral?
-ipsilateral, spreads to the other side once it reached its target -it is the medial white matter so ipsilateral!