What is upper motorneuron?
-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?
2.Colliculospinal tract (also called Tectospinal)
3.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!
What is the reticulospinal tract like?
-axons go from reticular formation in the pons and medulla towards the spinal cord
-once at target spreads over to the other side, also interneurons
What is the reticulospinal tract for?
-acts on the motor neurons supplying the trunk and proximal limb muscles. It is involved mainly in locomotion and postural control
What is the colliculospinal tract like?
-neurons in the superior colliculus
-cross over in the brainstem contralaterally but termination the same (medial neurons on both sides) as the other two medial tracts
What information comes to the superior colliculus?
- sensory information that is integrated from vision, touch and hearing -and the colliculus= synthsis of 3D space around you -when you hear a noise andd turn towards it = that reflex is generated by the superior colliculus -info about vision and orienting yourself in space -visual looming= if the visual pattern in front gets bigger= falling, the colliculus signal= better do sth about posture
What is the function of colliculospinal tract?
-coordination of head and eye movements -the function of the tract is to mediate reflex postural movements of the head in response to visual and auditory stimuli
Is colliculospinal tract ipsilateral or contralateral?
-contralateral as it crosses in the brain stem
Is reticulospinal tract ipsilateral or contralateral?
What is the anticipatory maintenance of body posture?
-pre-emptive adjustment of posture so a movement that is about to be executed doesn't end badly -control of posture -reflex -very important for stability -we do this most of the time so the body doesn't have to correct when something goes wrong
What is the experiment with the sound signal and pulling on a bar?
-person holding onto a bar, a speaker above
-pull on the bar when you hear a sound -while doing that= detect electrical activity from muscle (EMG= electromyograms)
-the biceps is activated about 200ms after sounds, long after the calf is activated
-the calf= part of the motor pattern (if you pull on the bar and don't move the calf then your head will hit the wall)
-so you put more force into the calf -pre-emptive, anticipatory, -stability -posture control -reflex system
What do the mesencephalic and rostral pontine reticular formation do?
-modulates forebrain activity
What docaudal pontine and medullary reticular formation do?
-premotor coordination of lower somatic and visceral motor neuronal pools
What is the feedward and feedback mechanism of postural control?
How do we detect postural instability?
muscle spindles and vision
Where does lot of information to the brainstem comes from?
-from the voluntary motor centres in the cerebral cortex (motor cortex) -these pathways are creating the postural adjustment sets -brain stem and reticular formation= gets lot of input from cerebral cortex that is contructing motor plans
What do we do in the motor cortex?
-hat is where we plan our movements, think about consequences of movement --but part of that plan are the pre-emptive adjustments and these are made by the brain stem -motor cortex has the plan and send some info down to brain stem, that directs the pre-emptive adjustment accordingly
Which part of the brainstem gets lot of information form the cerebral cortex?
What is the functional division of the central gyrus?
-precentral gyrus area is more action related -postcentral less
What did the stimulation of precentral gyrus area evoke?
-the contralateral movement of the body
-mapped out as well, bits for legs, digits etc. -this is where motor cortex is
What did the stimulation of postcentral gyrus area evoke?
the more anterior= if stimulated (pre motor cortex)
-still can get movement, but need more stimulation and more complex movements= more muscles activated
-some contralateral some both ipsilateral and contralateral
-area of sequences of movements
What is the premotor cortex also called?
-motor association area -supplementary motor area
Why can you histologically recognise primary cortex in the brain?
-in white matter layer 5 and sometimes 6 there are big purple lumps= big cells, lot of dendrites
-expect these supply big axons
What are the big cells in the primary motor cortex called?
-40 microns across .-project from the brain through the brain stem all the way to the spinal cord to the motor neurons and interneurons
Where are the Betz cells?
-in layer 5 and sometimes 6 in primary motor cortex (also in motor association areas)
What are the two tracts of the lateral white matter?
1.corticospinal tract 2.corticobulbar tract (togetehr referred to as pyramidal tract) -axons mostly from the motor cortex
What is the corticobulbar tract?
-axons from motor cortex and terminate in the brain stem
-The muscles of the face, jaw, head and neck are controlled by the corticobulbar system, which terminates on motor neurons within brainstem motor nuclei.
Where does the corticospinal tract begin?
--goes from contralateral cortex, these axons would be in the subcortical white matter
What is the corticospinal tract like?
-begins in layer 5 of motor cortex (in the pyramidal cells) and supplementary motor cortex, also Betz cells -then go to brain stem, in caudal medulla about 90% of the axonal fibres cross over (pyramidal decussation or medullary pyramid)
-10% stay on the same side and go down on the ventral side and down the medial pathway
-the 90% then continue down in the lateral pathway and innervate lower motor neurons
What do the 90% of corticospinal tract do?
-the ones that cross over in the caudal medulla -lateral corticospinal tract -fine voluntary movement control (fingers etc)
What do the 10% of corticospinal tract do?
-the ones do not cross over in the caudal medulla -ventral corticospinal tract --so these corticospinal continue down the medial pathway -probably the voluntary control of axial muscle
How does voluntary movement happen?
plan the movements in the cortex and get going by sending to brain stem and spinal cord
What is the simplistic topographic map of the motor cortex?
-some points not exact
-the ones we need most= have more space, for tool use, facial expression
What is the more modern topographic map of movement in the primary motor cortex?
-we see broad regions -not so exact -do not want to go to more detail
What was the monkey movement experiment=purposeful movement?
-small amounts of current applied to motor cortex of a monkey
-blue cross= where the hand was at the start, red dot where the hand ended up after stimulation
B)-doesn't matter where the hand was at forst then teh hand ends up at the face= this neuron saying move the hand towards the face
C)hand always comes to the chest -movements that mean sth to the animal -purposeful movements
What do motor maps represent?
-map of what we do with our body
-map of function
-what are cerebral neurons representing= movements, meaningful
What was the handle moving monkey experiment?
-experiment= monkey has a handle, when light on in 0 , 80, 180, 270 degress around it pull in that direction -record what is happening with neurons when lights in different position -when movement in particular direction= neurons never quiet, before and after a particular movement then really active! -the opposite of those direction then it is quiet, it is active over range of motions -can tuning curve= broad, over which frequencies do they repond (not frequencies but direction of movement) -somehow groups of neurons with wide tuning curves produce sharp and exact movemnts
What is the frontal eye field?(macaque brain)
frontal eye field= voluntary control, where you decide to look at
-part of complex planning
What are the mirror motor neurons?
-have someone show monkey a task -monkey does the task -motor neuron activated both when observing and doing -that is how we learn
Where are the mirror motor neurons?
-in ventral-anterior sector of lateral premotor cortex
How are we sure that the mirror motor neurons are involved in learning?
-when using a different tool the neuron is quiet -do the movement without seeing still activated -proved that you do not need the visual cue to activate it
What do cerebral cortical neurons represent?
-individually do not represent anything, it is only in the groups or ensembles where you can see they encode precise movements
What is the Babinski sign?
-the extensor plantar response
-if trace something along the bottom of the foot= spread your toes and extend
-what babies do
What is the normal plantar response?
-toes down (flexion)
Why do babies show the Babinski?
if a baby does it= the opposite, dorsal flexion, and the toes spread out -as babies get older they develop the same pattern -showing that the brain influences the flow of information from spinal cord into the motor neuorns -when you do not walk, the brain hasn't made the connection yet and the spinal circuit is different
What happens with Babinski sign when there is brain damage?
= infantile reflex comes back as the circuits are unmasked now, the inhibition is turned off -if get this Babinski sign as an adult= sth in the normal inhibition of the spinal cord is not working
What are the signs of upper motor neurons syndrome (lesion)?
-spastic paralysis (stiffness)=happens because muscle is contracted
-increased muscle tone
-clonus(clamped up muscle)
-Babinski's sign (infantile)
-loss of fine voluntary movements
What are the signs of lower motor neuron syndrome (lesion)?
-weakness or flaccid paralysis
-decreased superficial reflexes
-decreased muscle tone
-when muscle is weakened and not used gets more easy to excite (spontaneous stimulation)
-muscle needs innervation otherwise atrophy -hypoactive deep reflexes
-severe muscle atrophy
-fasciculations and fibrillations