Title: BV4 / Modul 3 / Spinal motor functions

Q: What does locomotion allow us to do?
A: 1. Find food
2. Escape form predators
3. Search for a suitable habitat
4. Find mates

Q: What are the differnet modes of locomotion?
A: - FLying
- Jumping
- Swimming
- Crawling
- Running
- Walkning

Q: What is an important area for locomotion?
A: Is an important area for locomotion is the spinal cord, which is the 2nd largest part of the CNS

Q: What does the spinal cord form?
A: Formes different segments (left and right) - each of the segments contain a single autonomous network called the central pattern generators (CPG)

Q: What is CPG?
A: An autonomous network

Q: What does CPG stand for?
A: Central pattern generators

Q: How many CPG's d we have?
A: If we have 30 segments we understand that we will have 60 different CPGs - 2 per segment

Q: What are the CPG able to do?
A: The CPG are able to generate any type of movement, still the initiation of their operations is dictated by the brain by the supraspinal areas

Q: How is the CPG activates/how does it work?
A: 1. There is an initiation of movement from the brain which initiates the CPG
2. The CPG will perform recruitment of motorunits
3. As a result of this recruitment we will have a contraction of correspinfing muscle fibers - coordinated activity

Q: What is a motor unit?
A: We define a single motor neuron and the muscle fibers it innervates as a motor unit

Q: What is required to acheive an elegant movement?
A: In order to achieve an elegant movement we need coordinated activity between differnet muscles - Ex. walk - nice coordinate activity of flexors and extensor muscles, as well as the left and the right leg

Q: WHich are the descending systems with upper motor neurons?
A: - Motor cortex
- Brainstem centres

Q: What is the motor cortex responsible for?
A: Planning, initiating and directing voluntary movements

Q: What are the brainstem centres responsible for?
A: Rhythmic, stereotypes movements and postural control

Q: What are the basal ganglia responsible for?
A: Initiation of intended movement and supression of unwanted movement

Q: What is the cerebellum responsible for?
A: Coordination of ongoing movement

Q: Which are the spinal cord and brainstem circuits?
A: - Local circuit neurons
- Motor neuron pools

Q: What are local circuit neurons responsible for?
A: Sensorimotor integration and central pattern generation (receives sensory input)

Q: What are motor neuron pools responsible for?
A: Lower motor neurons (output to skeletal muscles)

Q: Which general types of motor neurons are there depending on location?
A: - Upper motorneurons
- Lower motorneurons

Q: What are upper motor neurons?
A: Upper motor neurons are located in the brain, especially in the cerebral cortex, which are directly projecting to the spinal cord

Q: What are lower motor neurons?
A: Lower motor neurons (real term of motor neurons come form lower motor neurons), which means that they are the neurons of the CNS that innervate different muscles

Q: What is a motor neuron?
A: Any neurons in the CNS that project outside to the periphery and contacts, innervates and eventually contract the muscle fibers is called motor neurons (Lower)

Q: Which shape can be seen in the spinal cord?
A: The spinal cord is in a butterfly form

Q: What is the grey matter/area in the middle of the spinal cord?
A: Grey area in the middle (butterfly) where all the spinalcord neurons exist, so the somas of these neurons are located in the gery matter area

Q: What is the white matter/area in the middle of the spinal cord?
A: We have the white matter that mainly contains axons and dendrites of neurons, either local of the spinal cord or axons descending from the brain

Q: What can the grey area be divided into?
A: - Dorsal horn area
- Ventral horn area

Q: What is teh purpose of the dorsal horn area?
A: Dorsal - is the location of neurons processing sensory information

Q: What is the purpose of the ventral horn area?
A: Ventral - neurons in charge of motor commands (CPG neuorns are located in the ventral horn area as well as the motorneurons)

Q: What is located in the ventral horn area?
A: CPG neurons are located in the ventral horn area as well as the motorneurons

Q: What are the CPG neuronal circuits able to do?
A: These neuronal networks are able to generate any movement without the presence of the brain

Q: What happens if we electrically stimulate a spinal cord (zebra fish)?
A: That although its
not living we have an activation of the CPG that generates movement (left and right coordination of muscles that allows the
animal to move in the water)

Q: What can the CPG do on their own?
A: Active
CPG can produce movement without necessarily the brain to exist

Q: For who does the CPG activation work, without the presence of the brain?
A: This exists in all the vertebraes (CPG)

Q: What can we see if we focus on the muscle fibers of the same segment where CPG has motor activity?
A: If u focus on the muscles fibers of the same segment that the CPG/muslce activity there have a great alternation between the motor activity (important) bc the vertebrae (lamprey) nees to have left-right alternation of the CPG's

Q: What does the CPG produce in terms of left-right?
A: The CPG produce rhythmic activity and the one on the left and the one on the right side (CPG) don't have to be active simoultaneously but in alternation in order for the animal to perform its movements

Q: What can be seen in the CPG/motor activity if we induce effective locomotion pharmalogically?
A: We can induce effective locomotion pharmalogically using specific drugs and if u measure the activity between the left and the right side of specific segments u can see that u can have an activity of the motor neurons of the spinal cord of the same segments either we have left-right alterations due to our locomotor (ex. left/right leg)

Q: What type of network is the CPG and what is it responsible for?
A: The CPG is a structured single neuronal network that exists within the spinal cord that is responsible for the recruitment of corresponding motor units accoring to what we want the movement to be

Q: Where does the initiation of CPG come from?
A: The initiation of CPG come from the supraspinal areas (the brain)

Q: What are the CPG's in the spine called?
A: CPG dont exist on within the spinal cord, these are the locomotor CPG

Q: Which other CPG's do we have except for the locomotor CPG's in the spinal cord?
A: We
have another 2 CPG - both in the brain

Q: What is respective CPG in the brain responsible for?
A: - One is responsible for breathing, bc breathing that can be  modulated with speed is a rhythmic activity
- One is responsible for chewing, so when we eat and chew we activate the corresponing CPG which produces this rhythmic activity of the jaw that allows us to eat/chew the food we are eating

Q: WHich functions are CPG's important for?
A: - Locomotion
- Breathing
- Chewing

Q: What is meant by the CPG being an abstract form of network?
A: We dont know exactly how many neurons are involved in the CPG and the differnet types and connectivity that exists to generate the CPG

Q: Which types of neurons does teh CPG exist of?
A: From the inital lamprey, we know that the CPG exists of excitatory and inhibitory neurons, so in principle1 exist on the left and one on the right of side of each vertebrae segment

Q: What are the excitatory neurons importnat for in the CPG?
A: The excitatory neurons are important to excite the corresponding motor neurons, to provide input to the motor neurons in order to recruit

Q: What else do the excitatory neurons do in the CPG?
A: The excitatory neurons also excite inhibitory neurons that go to the contralateral side of the spinal cord/CPG in order to inhibit the contralateral CPG

Q: What do the excitatory and inhibitory neurons work in relation to each other in the CPG?
A: The CPG is like newtons cradle

Q: What is meant by the CPG's on both sides of a segment working as newton's cradle?
A: When the excitatory neurons stop on one side they initiate on the contralateral side of the CPG

Q: How is great alteration latered between the right and left side of the body, in terms of CPG?
A: To achieve a great alteraltion between the left and the right side, which is very important for us to locomote through walking or running, we can not activate the 2 CPG simoultaneously

Q: Are there situations when the CPG on both sides of the segment will be activated simoultaneously?
A: There are several differnt forms for movements where we need to activate the 2 CPG simoultaneously, ex. when we jump with both legs we need to perform simoultaneous activation of the 2 CPG (like in birds whe they are flying)

Q: Hos does it work when both CPG's (on both sides) are activated simoultaneously?
A: The inhibitory neurons can, if necessary, be inhibited, which will allow the 2 CPGs to be active simoultaneusly

Q: From where do the CPG's in the spinal cord receive input?
A: The 2 CPG receive specific input from the brainstem and other brain areas to become active

Q: WHat can be said about the organisation of CPG's?
A: We dont have a precise organisation of the CPG

Q: WHich type of neurons in the spinal cord participate in the CPG's?
A: The different types of interneurons in the mamallial spinalcord (all vertebrae), and espectially ventral part interneurons - all of these neurons participate in the CPG, except for the motorneurons, which recieve the final output from the CPG and are supposed to generate the contraction of the muscle fibers

Q: Are motor neurons involved in the CPG?
A: No, the motorneurons recieve the final output from the CPG and are supposed to generate the contraction of the muscle fibers

Q: WHat do the dorsal part interneuorns do?
A: The dorsal part inter neurons participate in sensory processing info

Q: What can be said about the ratio of neurons in the brain compared to the spinal cord?
A: While the brain contains 100 miljon neurons the spinal cord contains a small fraction of this

Q: HOw many neurons are there in the human spinal cord?
A: 13,5 million neurons

Q: Which other movements can the CPG generate?
A: Beside the CPG generating rhythmic movements, such as jumping, locomotion, walking etc, we can have movements that aren't rythmic

Q: What are examples of movements generate dby the CPG that aren't rhythmic?
A: These movements use parts of the CPG neurons and the motor neurons, such as the strech reflexes

Q: HOw does the strech reflex work?
A: By streching the tendon we strech the spindles within the muscles fibres, the result is that the Ia (1a) afference which are nerouns of the spindles transmitt this impulse of activity within the spinal cord  and they make monosynapic conducts with alfa motor neurons in the ventral horn of the same segment in order for these motor neurons to contract the muscles

Q: What happens simoultaneously as the strech reflex?
A: To achive the strech reflex we need to make sure that the antagonistic muscles wont be contracted, which is done by the same Ia fiber that whilst connecting to the alfa-motor neuron on that level they also project to inhibitory neurons that innervate the alfa-motor neurons of the antagonistic fibers - they ensure that these a-motor neurons won't fire AP's

Q: Is the reciprokal reflex of the other leg, happening simoultaneously as the strech reflex, involvning the CPG?
A: This movement is not involving the CPG since its not rythmic, and also any reflex overrides any activity of the CPG, since the reflexes are important to protect us from further damages as such they have an override activity

Q: WHat is true about reflexes and CPG?
A: They are not involvning CPG's, since they aren't rhythmic - any reflex overrides the activity of the CPG

Q: What happens when u walk and step on something sharp?
A: First thing that happens when u walk and step on someting sharp is that u will stop walking, seize down the CPG, and at the same time afferences arrive in the spinal cord and we have a flexon cross extension reflex

Q: Where do the afferences transmitt info whne the flexion-cross-extension reflex happens?
A: The afference transmitt info to sensory neurons in the spinal cord - this will conduct the motor neurons differentially (flexor and extensor muscles) in order to allow us to lift our leg from the stimulus by exciting the flexon and inhibiting the extensor muscle
- However, if we are standing we will fall down, so in order to prevent that from happening what also happens is that the neurons go to the contralateral side and perform this contralaterally

Q: What do the neurons stimulate in the flexion cross extension reflex, briefly?
A: They inhibit the flexor and stimulate the extensor - ensuring that the other leg will be on the ground

Q: Why does the CPG's stop working when we have the flexion-cross-extension reflex?
A: We avoid painful stimuls while we remain standing - however we cant continue walking - we will stop, so the CPG will pause up to a certain level or it will stop based on what will happen

Q: What type of movement is a reflex?
A: Reflexes are a non-rhythmic movements that utilize the spinal cord network and the motor neurons

Q: What is the descending system of the brain?
A: Which
brain areas and structures are producing/initiating the CPG or any network
within the spinal cord are called the descending system of the brain

Q: WHat does the descending system of the brain consist of?
A: Consists of upper motor neurons, altough these arent the real motor neurorns, still we use that term coz they directly connect to the motor neurons or the spinal networks in order to generate movements

Q: Which 2 areas contain the upper motor neurons?
A: - Cerebral cortex (Motor cortex)
- HIndbrain/brainstem: Tectospinal nucleus, rubrospinal nucleus, reticulospinal nuclei, vestibulospinal nuclei

Q: Which area sin the brainstem/hindbrain contain upper motor neurons?
A: - Tectospinal nucleus
- Rubrospinal nucleus
- Reticulospinal nuclei
- Vestibulospinal nuclei

Q: What do the upper motor neurons look like in the motor cortex?
A: Here we have the corticospinal neurons, which are neurons that project directly to the spinal cord, while during this part provide an important input to the reticular formation, to the hindbrain nuclei

Q: Where do corticospinal neurons project?
A: Project directly to the spinal cord from the cortex

Q: What do the hindbrain nuclei containing upper motor neurons project?
A: All the nuclei mentioned contain neurons that project directy to the spinal cord, either directly to the motor neurons or the CPG

Q: What can be said about the cross activity of upper motor neurons in the motor cortex and the nuclei of the hindbrain?
A: In particular important is the cross activity by which they provide addiotional input form one to the other - the important input the hindbrain area receives is also from the corticospinal tract from corticospinal neurons, while they project directly, they project indriectly though this areas indirectly to the spinal cord and modulate the activity in all of these hindbrain areas

Q: From where does the input to the hindbrain nuclei come from?
A: The important input the hindbrain area receives is also from the corticospinal tract from corticospinal neurons
- While they project directly, they project indirectly though these areas, indirectly to the spinal cord and modulate the activity in all of these hindbrain areas

Q: Which locations can the descending axons have where they corss the spinal cord?
A: There are 2 locations:
- One in the lateral white matter
- One in the medial white matter

Q: Which descending axons are in the lateral white matter in teh spinal cord?
A: Axons from the motor cortex

Q: Which descending axons are in the medial white matter in teh spinal cord?
A: Axons cross from predominantely the brainstem areas

Q: What is the importance of the location of the descending axons in the spinal cord?
A: The importance of this location is related with which neurons, either motor neurons or CPG are innervating - so they are going to be closer which is meaningful for using muscles to perform their activityes

Q: What is the motor cortex responsible for, and how does hat affect the locations of its descending axons in the spinal cord?
A: The motor cortex is responsible for planning, execution and  especially of coordination of muscles that are performing elegant movements, such as the fingers - they are (their pathway) very close to motor neurons innervating the distal muscles in the spinal cord (their pathway in the spinal cord/lateral white matter)

Q: What is the brainstem responsible for, and how does hat affect the locations of its descending axons in the spinal cord?
A: The brainstem neurons are responsible for the generation of principal locomotion and therefore they are preferred to be closer to the motor neurons that innervate our limbs (forelibs or hindlimbs), by descending in the medial white matter of the spinal cord

Q: How do the upper motor neurons of the cerebral cortex project their neurons to the spinal cord?
A: The upper motor neurons of the cerebral cortex dont project ipsilaterally to the spinal cord instead contralaterally through the lateral white matter, and they project to the lower motor nerons (principal motor neurons) in the lateral ventral horn that are responsible for distal limb muscles performing skilled movements

Q: Where do teh upper motor neurons of the cerebral cortex project to the lower motor neurons?
A: They project to the lower motor nerons (principal motor neurons) in the lateral ventral horn, that are responsible for distal limb muscles performing skilled movements

Q: How do the upper motor neurons of the brainstem project their axons to the lower motor neurons?
A: The upper motor neurons in the brainstem project through/close to the middle line of the spinal cord ipsilaterally, however when they reach the motor neuron pools they can also project contralaterally  and ipsilaterally

Q: How can the upper motor neuron' axons of the brainstem project when reaching the motor neuron pools in the spinal cord?
A: When they reach the motor neuron pools they can also project contralaterally  and ipsilaterally

Q: Which lower motor neurons do the upper motor neurons of the brainstem prefer?
A: They prefer the lower motor neurons of the medial parts of the ventral horn (proximal limb muscles), that are responsible for the posture, balance and locomotion

Q: WHat are the lower motor neurons in the medial parts of the ventral horn responsible for?
A: They are responsible for the posture, balance and locomotion

Q: WHat can be concluded from the topographic  organisations of the projections of upper motor neurons to the spinal cord?
A: By the topographic organisation of thee projections we can understand how important and what is exactly the contribution of the cerebral cortex neurons vs the brainstem neurons in the activation of corresponding muscle fibers of the motor axons that allow us to perform

Q: Which cells are located in the 5th primary motor cortex layer?
A: Betz-cells

Q: What are betz-cells?
A: Upper motor neurons that receive and process information in the primary motor cortex and they project directly to the spinal cord but also to the brainstem nuclei

Q: To where do betz-cells project?
A: They project directly to the spinal cord but also to the brainstem nucle

Q: Where are betz-cells located in the M1?
A: 5th primary motor cortex layer

Q: How do the betz-cells (neurons) project?
A: These neurons dont go ipsilaterally, they go contralaterally to innervate the corresponding motor neuons and muscle fibers - meaning that any lesion damage on the left side of the brain results in deficits in the muscles on the contralateral side

Q: What does it imply that the Betz-cells project their axons contralaterally to the spinal cord and brainstem?
A: That any lesion damage on the left side of the brain results in deficits in the muscles on the contralateral side

Q: What is an example of contralateral innervation?
A: When the moneky moves its right arm we have high activation of these upper motor neuron of the left side of the cortex while the right side of the cortex remains silent during these movements

Q: HOw is adrenergic input provided to the spinal chord?
A: The superior colliculus, the locus coerulus and the raphe nucleus that provide the locus coerulus with adrenergic (?) input in the spinal cord

Q: HOw is serotonergic input provided to the spinal chord?
A: Raphe's nucleus provides serotonergic input to the spinal cord

Q: WHich nuclei form the mian parts of communication between the brainstem areas and spinal cord?
A: - Tectospinal tract
- Rubrospinal tract
- Vestibulospinal tracts
- Reticulospinal tracts

Q: What is the tectospinal tract between?
A: From superior colliculus to the spine

Q: What is the vestibulospinal tract between?
A: From vestibular nuclei to the spine

Q: What is the reticulospinal tract between?
A: From the pontine reticular formation to the spinal cord

Q: What is the rubrospinal tract between?
A: From nucleus ruber to the spinal cord

Q: What is the MLR?
A: Mesencephalic locomotor region

Q: Where is the MLR located?
A: This area is not in the hindbrain it's in the mesencephalon and located in a specific area in the mesencephalon and we found that this area is important for locomotuion

Q: What is the MLR area important for?
A: Locomotion

Q: WHat happens if the MLR is stimulated?
A: By electrically stimulating this area they saw that the animal always start locomoting

Q: To what does the MLR provide a strong imput?
A: This is a very imprortant area that provides a strong input to the reticular formation nuclei

Q: WHat happens if there is strong input from the MLR (to the reticular formation nuclei)?
A: They recieve a strong initiation input in order to transmitt this input eventually to the spinal cord networs and to activete the CPG from these MLR's

Q: WHat in the spinal cord can the MLR's indirectly activate?
A: The CPG

Q: What determines the mode of locomotion in animals?
A: The strength of the input that the MLR provides to the reticular formation neurons dictates the mode of locomotion the animals will extruit

Q: WHat happens if the stimulation intensity from the MLR is low and then becomes stronger and stronger?
A: If stimulation intensity is low the animals will perform slow walking, if we increase this stimulation these animlas will start walking faster, meaning that the CPG will also start recruiting the intermediate motor neurons
If we stimulate more they are galopping, trotting: the 2 faster modes of locomotion of animals with forelimbs

Q: What happens if the stimulation instensity increases form the MLR in the CPG?
A: The CPG will also start recruiting the intermediate motor neurons

Q: WHy is the input from the MLR to the reticular formation important?
A: The stimulation
is and the input the MLR provides to the reticular foration - it govers almost
directly how many motor units in ths step-wise recruitment from slow to
intermediate to fast will happen based on single input form the MLR

Q: What can be said about the MLR and locomotion?
A: The
MLR, altough it doesnt project directly to the spinal cord, is one of the most
important regions of the brain that control the locomotion

Q: What are the cortico-and rubrospinal tracts important for?
A: 1. Transmission of commands for skilled movements (like finger movements)
2. Corrections of motor patterns generated by the spinal cord

Q: What is the reticulospinal tract important for?
A: 1. Activation of the CPG for the activation of spinal motor program for stepping and other stereotypic movements (rhythmic motor programs)
2. These neurons although they project directly to the spinal cord, their activity is still detected by the MLR
3. Control of upright body posture

Q: What are the vestibulospinal tract important for?
A: Generation of tonic activity in antigravity muscles

Q: Why is the vestibulospinal tract important for the generation of tonic activity in antigravity muscles?
A: This
is based on the vestibular system that allows us to balace out bodies with our
surrounding envrionment, as such we have antigravity control all the time -
this requires a lot of efferency from our motor system although we dont think
about it

Q: What does the CPG constantly do?
A: The CPG constantly recruits slow motor units, muscle fibers and motor neurons in order to allow to contract the corresponding muscles that allow us to stand

Q: What would happen if the CPG system failed?
A: If this system fails then we collapse, we cant even maintain the tonic activity of the muscles

Q: How does activation of locomotion happen in several steps?
A: 1. Cerebral cortex - desicion
2. Striatum - activated
3. Globus pallidus - inhibited (tonically active at rest)
4. Mesencephalic locomotor region - disinhibited
5. Reticular formation - activated
6. Reticulospinal neurons
7. Locomotor CPG in the spinal cord