Lecture 10: The Motor System Flashcards
What is the Prefrontal Cortex?
PFC is defined as those areas of the frontal lobe that do not result in movement following electrical stimulation
Also associated with executive functions such as planning, decision-making, judgment, social cognition, etc…
What is the Hierarchy of Motor Control?
- Premotor Cortex
- Supplementary Motor Cortex
- Primary Motor Cortex
All 3 located in the frontal lobes, project directly to the spinal cord via the corticospinal tract
What is the Basal Ganglia’s Function?
Receive input from many cortical areas (not just motor cortex)
Projects to the thalamus and then to cortical areas cortex involved in motor planning and modulating muscle force
What is the Cerebellum Function?
Receives input from the spinal cord
Projects to both the brainstem and thalamus
Improves movement accuracy by comparing descending motor commands with information about resulting motor action
What do the brain structures inside include?
- Reticular Activating System (RAS)
- Vestibular Nuclei
- Inferior Olivary Complex
Peripheral neurons that make synaptic connections in the spinal cord create spinal reflexes involving?
An afferent nerve signalling the activity of a stretch receptor in either muscle or tendon
2a) An efferent nerve synapsing with an agonist skeletal muscle
3b) An inhibitory interneuron, located in the spinal cord gray matter, interposed between sensory and motor neurons, that results in reciprocal inhibition of the related antagonist muscle
What are the 2 kinds of Myofbrils?
Actin and Myosin
What are Actins?
Actins are helical strands of protein molecules that wrap around the myosin strands
What is Myosin?
Myosin has cross bridges protruding out in a spiral pattern at right angles from the long axis toward neighboring Actins
Where are Lower Motor Neurons found and Where do they Synapse?
Where: Lower Motor Neurons arise in the spinal cord segment and pass through the ventral root on their way to the target muscle fibers
Synapse: Lower motor neurons synapse with muscle at the muscle’s neuromuscular junction
What are Muscle Spindles?
Encapsulated stretch receptors (aka intrafusal fibers) are in the non-contractile muscle belly. They sense the degree of stretch caused by the muscle contractile intrafusal fibers contracting from both ends of the muscle toward the middle
Muscle spindles cannot sense the force created by the extrafusal fibers – only the degree of stretch created by their contraction
What is a Golgi Tendon Reflex?
Monosynaptic ipsilateral circuit producing a fast inhibition of muscle in response to increased muscle force
What is a Flexor Withdrawal Reflex?
Polysynaptic reflex resulting in withdrawal of a limb from a noxious stimulus
What is Crossed Extensor Reflex?
Polysynaptic, contralateral reflex causing the flexors in the withdrawing limb to contract and the extensors to relax while, at the same time in the other limb, the opposite occurs (e.g the flexors relax and the extensors contract)
What is the Corticospinal Tract?
The primary motor pathway in the central nervous system
What is a Dorsolateral Corticospinal Tract?
Originates in the precentral gyrus and, following decussation in the medullary pyramids descends contralaterally to control fine muscle movements of the contralateral arm and leg (esp. Digits, wrist, and elbow – think typing and tap dancing
What is the Ventromedial Corticospinal Tract (aka Anterior Corticospinal Tract)?
Originates in the precentral gyrus and descends ipsilaterally to decussate at their terminating spinal segment to control the more central axial and girdle muscles of the trunk, neck, and shoulders (e.g sit-ups and belly dancing)
What are the 3 Vocalization and Masticatin behaviours?
- Laryngeal Activity
- Respiratory Movement
- Supralaryngeal (Articulatory) Activity
What are the 5 types of Abnormal Muscle Control?
- Flaccidity
- Ridigitidy
- Spasticity
- Hypokinesis
- Hyperkinesia
What is Faccidity?
The affected limb is floppy due to damage to one or more lower motor neurons
What is Rigidity?
Due to lesions of the extrapyramidal tract (rubrospinal or vestibulospinal tracts, basal ganglia)
What is Spasticity?
Due to lesions of the pyramidal tract (upper motor neurons e.g corticospinal tract)
What is Hypokinesis?
ecreased ability to produce body movement typically caused by abnormal basal ganglia activity (Parkinsonism)
What is Hyperkinesia?
Exaggerated, unwanted motor movements (Tourettes, Huntington’s Chorea)
What are the Symptoms of Upper Motor Neuron Damage?
- Voluntary movements involving affected muscles are absent or weak
- Increased muscle tone (spasticity) resulting in rigidity
- Altered reflexes
- Reduced muscle tone (flaccidity)
- Weak stretch reflex
What did Georgepoulos?
Recorded activity of neurons in the motor cortex while a monkey moved a lever in different directions
What did Giacomo Rizzolatti do?
First discovered mirror neurons in the rostral division of the ventral premotor region (F5) in macaques
What are Mirror Neurons?
Enable communication between a sender and a receiver
Mirror neurons are generally located in the left hemisphere
Have a role in self-action, perception of action, self-awareness, and awareness of the intention and actions of others
What does the Medial Prefrontal Cortex control?
Movement control guided by internal motivations and states
What does Lateral Prefrontal Cortex control?
Movement control guided by external stimuli
What are the two Basal Ganglia Pathways?
- Direct Pathway (Positive Feedback Loop)
- Indirect Pathway (Negative Pathway Loop)
What is the Direct Pathway (Positive Feedback Loop)?
Cortex to putamen to Globus Pallidus internal (Gpi) to Thalamus and back to excite cortical activity
What is the Indirect Pathway (Negative Feedback Loop)?
Cortex to Putamen to Globus Pallidus external (Gpe) to Subthalamic Nucleus to Globus Pallidus internal (Gpi) to Thalamus and back to inhibit cortical activity
What are the 7 deficits associated with Cerebellar Lesions?
- Ataxia
- Dysmetria
- Dysdiadochokinesia
- Asynergia
- Hypotonia
- Nystagmus
- Action Tremor (aka Intention Tremor)
