Voluntary control and descending pathways Flashcards
organisation of the motor system, descending motor pathways to spinal cord, functions of brain stem
What is the significance of spinal cord circuitry in locomotion?
Spinal cord circuitry alone can produce a locomotor rhythm.
What happens if the connection between the cerebral cortex and spinal cord is removed in a cat?
The cat can still locomote on a treadmill.
what do lower motor neurons do?
LMNs = alpha MNs
directly innervate muscle
What are the three basic inputs to motor neurons?
- Sensory input (e.g., from muscle spindles)
- Input from spinal cord circuitry
- Descending input from pre-motor neurons
What are pre-motor neurons also known as?
Upper motor neurons (UMMs).
How does the old textbook model explain motor control?
The frontal lobe establishes a goal, the motor cortex formulates a plan, and the brain stem and spinal cord execute muscle commands.
known as ‘Serial model of motor control’
True or False: If a person loses their cerebral cortex, they would be completely unable to undertake any action.
False.
What did the studies on cats with removed cerebral cortex reveal?
The cats could still walk, run, jump, and feed themselves despite lacking a motor cortex, proving the serial model wrong
What evolutionary significance does the lamprey (parasite) have in understanding motor control?
Lampreys can perform core life functions with only a partial cerebral cortex, suggesting sophisticated motor control evolved before the cortex and can be done without.
What is the parallel model of motor control?
The cerebral cortex and brain stem both influence spinal cord activity, rather than a strict serial pathway.
brain stem + cortex : UMNs, spinal cord: LMNs
What are the two main descending pathways ?
the routes through which the cerebral cortex and brain stem influence the spinal cord
- lateral pathway
- ventromedial pathway
lateral pathway origin and what it does
originates in cortex, controls distal muscles
ventromedial pathway origin and what it does
originates in the brainstem, controls proximal muscles of limbs and axial muscles of trunk
2 major cortical pathways
- corticospinal tract (cortex directly influencing spinal cord)
- corticobulbar tract (cortex influencnig brainstem)
what is the corticospinal tract
(pyramidal tract)
- most importnt lateral tract in humans
where does the corticospinal tract decussate
the medulla
where does the corticospinal tract originate
premotor neurons in cortex
- poterior frontal lobe
- parietal lobe
What does the ventromedial pathway primarily control?
Proximal muscles and axial muscles of the trunk.
what is the corticalbulbar tract
cortical projection to brainstem
What anatomical feature gives the corticospinal tract its alternative name, the pyramidal tract?
The pyramids in the medulla that resemble a pyramidal shape.
What is the main origin of the lateral descending pathway?
The cerebral cortex.
What is the main origin of the ventromedial pathway?
The brain stem.
the 3 main ventromedial tracts in the brainstem
- vestibulospinal tract
- reticulospinal tract
- tectospinal tract
what is the vestibulospinal tract
premotor neurons in vestinular nuclei
what is the reticulospinal tract
premotor neurons n reticular formation
what is the tectospinal tract
premotor neurons in superior colliculus
What can be observed in a control monkey during a motor control task?
The monkey displays highly dexterous reaching and grasping movements.
major lateral brainstem pathway
rubrospinal tract: premotor neurons in red nucleus
small in humans
Fill in the blank: The _______ tract starts in the cortex and ends in the spinal cord.
corticospinal
Fill in the blank: The _______ tract is the cortical projection to the brain stem.
corticobulbar
What are the main functions of the corticobulbar tract?
It influences brain stem activity.
What is the main function of the corticospinal tract?
Motor control, particularly skilled movements of the limbs and fingers.
The corticospinal tract is crucial for voluntary motor control.
What surgical procedure was performed on the monkeys in the study?
Pyramidotomy.
A pyramidotomy involves severing the corticospinal tract at the level of the pyramids.
What abilities were preserved in monkeys after a pyramidotomy?
- Intact running
- Intact walking
- Intact climbing
- Grasping using the whole hand.
Despite severe lesions, many basic motor functions remained unaffected.
What was observed about the monkeys’ reaching behavior after the pyramidotomy?
Reaching was more hesitant and less skilled, impaired independent finger movements
Monkeys lost dexterity and could only use whole hand grasping to retrieve pellets
What is a significant implication of the findings regarding independent finger movements?
Independent finger movements are crucial for many human activities, such as knitting and playing instruments.
This highlights the unique function of the motor cortex.
How do the corticospinal tract neurons connect to the spinal cord?
They can synapse directly onto motor neurons or indirectly via interneurons.
Direct connections are more prominent in primates compared to rodents.
What role do the ventromedial pathways play in motor control?
They are crucial for posture control, locomotion, and basic movement control.
These pathways are evolutionarily ancient and important for fundamental mammalian behavior.
What was the result of the lateral brain stem tract lesion in monkeys?
Monkeys had intact posture and locomotion but impaired ability to grasp objects.
This indicates the role of lateral brain stem pathways in extremity control.
What was the effect of the ventromedial brain stem tract lesion?
Impaired posture and locomotion but preserved ability to grasp.
This shows that ventromedial pathways are essential for maintaining posture.
Summary of Lawrence & Kuypers monkey experiments
evolutionary pathways
What is the significance of the accidental discovery made by Lawrence and Kuipers?
It suggests that even minimal remaining corticospinal connections can allow for recovery of motor function.
(from incomplete lesions)
This has implications for rehabilitation after neurological damage.
What are the major functions of the brain stem in motor control?
- Control posture
- Control locomotion
- Control reaching and grasping
- Orienting to salient objects.
Each function is vital for coordinating complex movements.
different types of orienting movements
- eyes (humna)
- pinnae (ears)(bats)
- whiskers (moles)
- head (owls)
What is the role of the superior colliculus in orienting movements?
- integrates visual and motor information from retina
- produces saccadic eye movements
circuit basis of orienting eyes
- visual stimuli come in
- brain stem contains pre-motor neurons
- activate SC
- activates PPRF (paramedian pontine reticular formation) and drives motor neurons in eye muscles
What are iDREADDs?
Inhibitory Designer receptors exclusively activated by designer drugs
These are artificially created receptors used to manipulate neuronal activity in research.
What happens when CNO (designer agonist) binds to inhibitory DREADDs?
It opens potassium channels, leading to neuronal inhibition as MP decreases
This mechanism allows for precise control of neuron activity in experimental settings.
What behavior was studied in relation to orienting and prey capture?
The orientation of a mouse towards a cricket in a box.
This illustrates the role of brain stem motor control in predatory behavior.
In which part of the brain did Hoy et al. express iDREADDS in?
Superior colliculus.
What is the purpose of the red fluorescent tag attached to the iDread molecule?
To visualize neurons expressing the iDREADDS
What was the first experiment conducted to test the effectiveness of CNO?
Recording the firing rate of neurons before and after CNO injection.
What was the result of injecting CNO in terms of neuronal firing rate?
A 40% decrease in firing rate on average.
What behavior was observed when injecting mice with CNO and placing them in an arena with a cricket?
The mouse showed a very slow orienting response and moved away from the cricket.
What type of neuron expressed iDREADDS in the mouse used for the behavior experiment?
NF neurons.
True or False: The method of inhibiting neurons with CNO was ineffective.
False.
Fill in the blank: The integration of visual and motor information is done on a _______ level.
cellular
Who is one of the key figures mentioned that has written important papers on the topic?
McArthur.
What type of movements are discussed in relation to visual perception?
Eye movements and coordination of motor movements.
What is the lateral geniculate nucleus associated with?
Visual structure.
What was the conclusion drawn about the hunting behavior of the mouse injected with iDread?
It grossly interfered with the hunting behavior.
