Brain control of movement Flashcards
Motor control is a hierarchy with 3 levels; what are they?
High - Strategy - association neocortex, basal ganglion
Middle - Tactics - Motor cortex, cerebellum
Low - Execution - Brain stem, spinal cord
In terms of motor control hierarchy’s and their functions; what is Strategy/Tactics/Execution?
Strategy = goal of the movement and the movement strategy to achieve this goal
Tactics = sequence of muscle contractions in space and time for an accurate goal
Execution = activation of motor neurons and interneurons for goal-directed movement
Which descending spinal tracts control voluntary muscles (1) and postural muscles (2)?
- Voluntary movements of distal muscles = LATERAL PATHWAYS
- Under direct cortical control
- Corticospinal tract (CST) control muscle tone and fine/precise movements of the distal parts of the limbs
(fingers and hands)
- 2/3 of CST axons from areas 4 and 6 of frontal motor cortex - the rest are somatosensory (touch/pressure/pain receptors)
- Right motor cortex controls left side & left motor cortex controls right side
- Rubrospinal tract (RST)
- Lesion to CST & RST = lose of fine movements of arms and hands + can’t move shoulders/elbows/wrists/ fingers independently
What happens if you have a lesion on CST alone?
- Same deficits but after a few months functions will reappear as they are taken over by RST
What are the 3 pairs of descending tracts within CST pathway?
- Corticobulbar tract
- Lateral corticospinal tract
- Anterior corticospinal tract
What’s the Corticobulbar tract within the CST pathway?
- Within the motor homunculus on the primary motor cortex, upper-motor neuron axons in the corticobulbar tract synapse on lower motor neurons in the nuclei of the cranial nerves III, IV, V, VI, VII, IX, XI & XII
= Conscious control of skeletal muscles controlling EYE/JAW/FACE/MUSCLES OF NECK AND PHARYNX
+ Innervates motor centres of medial and lateral pathways
- Lateral Corticospinal tract controls fine movement of ipsilateral limbs (fine finger movements)
- Anterior Corticospinal tract control movement of the trunk (abdominal area)
What’s the function of the Rubrospinal tract (RST)?
- Originates in the Red Nucleus of the Midbrain Tegmentum and descends via the Ventral Tegmental decussation
Function:
- Provide motor control over distal muscles of upper limbs – controlling tone of limb flexor muscles and inhibitory to extension extensions during of gait
Corticospinal tract axons control pools of spinal motor neurons, what does this mean and what is the consequence of this?
- The CST descends from the motor cortex in large pyramidal neurons which and monosynaptically excite pools of agonist spinal motorneurons
- A motor pool consists of all individual motor neurons that innervate a single muscle - each muscle fibre is innervated by one motor neuron BUT 1 motor neuron might innervate several muscle fibres
- Muscles responsible for fine movements are innervated by motor pools consisting of higher numbers of individual motor neuons
- The same pyramidal neurons branch via interneurons and inhibit pools of antagonist motorneurons
(allows for flexion and extension separately)
What are the Ventromedial pathways?
- Control posture and locomotion
- Regulates and fine-tine the lateral pathway
- Under brain stem control
- Consists of:
1. Tectospinal tract
2. Vestibulospinal tract
3. Potine reticulospinal tract
4. Medullary reticulospinal tract
What’s the Origin, termination and function of the Vestibulospinal tract (VST)?
Origin: Vestibular nuclei - at the border of pons and medulla oblongata
Termination: Lower motor neurons of anterior grey horns of spinal cord
Function: Receives information from Vestibulocochlear nerve which has receptors internal ear that monitor position and movement of the head
- Nuclei rsponses to changes in oreintation of head = send motor commands that alter the muscle tone, extension and position of the neck, eyes, head and limbs
- Primary goal = maintain posture and balance
What’s the Origin, termination and function of the Tectospinal tract (TST)?
Origin: Tectum (midbrain: roof of midbrand + superior and inferior colliculi)
Termination: Lower motor neurons of anterior grey horns (cervical spinal cord only)
Function: Superior Colliculi receives visual info and Inferior receives auditory semsations - motor axons descends via the TST and they cross to the opposite side immediately
- Direct reflex changes in the position of head/neck/upper limbs in response to bright lights/sudden movements/loud noises (ensure eyes remain stable as body moves)
What’s the Origin, termination and function of the Reticulospinal tract (RST)?
Origin: Reticular formation - network of nuclei in the brain stem
- Pontine reticular formation
- Medullary reticular formation
Pontine function: Their activity facilitates voluntary and reflex responses and influences muscle tone
Medullary function: inhibitory effect on voluntary and reflex responses of axial and limb muscles. The reticulospinal tracts are clinically important, not only because they influence muscle action and tone, but also because they influence the action of motor neurons of phrenic and intercostal nerves and thus control respiration.
- They have vasomotor effects and affect sweating and other autonomic responses.
- The major sources of inputs to the reticular formation include the cerebral cortex (especially the motor areas), the somatosensory pathway and the cerebellum (fastigial nucleus).
To carry out a voluntary movement what needs to occur?
- Input from the motor cortex through the lateral pathways
- Activates spinate motorneurons directly and frees them from reflex control by communicating with nuclei of ventromedial pathways
What are the steps invovled in carryout a voluntary movement?
- Mental image of body in space is generated by: Somatosensory (touch). proprioceptive (pain etc) and visual inputs to posterior parietal cortex (areas 5+7)
- Prefrontal and parietal cortex is where decisions are taken about what actions to take and their likely outcome
2a. Decision making neurons in the cortical Premotor area (PMA) fire before movement and continues through action (fire 1 sec before movement occurs)
2b. PMA mirror neurons fire when self or others perform specific actions - these are speific neurons in area 6 and they fire when movement is made/imagined/rehearsed mentally = allow for understanding of the actions or intentions of others
What selects and initiates willed movements?
Basal Ganglia
- Major subcortical input to the area 6 comes from the Ventral lateral nucleus in the dorsal thalamus
- Input to this is called VLo and comes from the Basal Ganglia
- Basal ganglia recieves inputs from the frontal, prefrontal and parietal cortex
- Information loop cycles from cortex through thalamus + basal ganglia and back to SMA in cortex
- Basal ganglia has a testing function - reviews how you’ve done things in the past and allows for the modification of certain movements - then goes back to pre motor area (Area 6)
