deck_3650054 Flashcards
UMN LMN study
Lower Motor Neurons vs Upper Motor Neurons
LMNs directly synapse on the muscle and have cell bodies in the ventral horn of the spinal cord. Two types: gamma (for sensory) and alpha motor neurons (axons go to skeletal muscles). UMN synapse onto LMN or local circuitry neurons and have cell bodies in the motor cortex and brainstem.
What are the 4 motor systems?
Basal Ganglia - gating proper initiation of movementCerebellum - sensory motor coordination of ongoing movementUMN - motor cortex - voluntary movements brainstem - basic movements and postural control
With increased motor unit size, alpha motor neurons exhibit:
Increased cell body size dendritic complexity short term EPSP potentiation with repeated activation axonal diameter (i.e faster conducction) number of axonal branches (i. e more muscle fibers innervated) Decreased Input resistance excitability Ia EPSP amplitude PSP decay constant Duration of after-hyperpolarization
Describe the stretch reflex circuit
Regulation of muscle lengthα-MN innervate extrafusal muscle fibersγ-MN innervate intrafusal muscle fibersTypes of intrafusal muscle fibers Nuclear bag -static (type II sensory neuron) -dynamic (type Ia sensory neuron) Nuclear chain (type II sensory neuron)
Describe the Golgi Tendon Organ Reflex Circuit
Regulation of muscle forceThought to a) protect the muscle by causing it to relax when exceptionally large forces are generated and b) maintain a steady level of force, counteracting effects that diminish muscle force such as fatigue.GTO innervated by Ib sensory neuron
What are Central Pattern Generators (CPGs)?
CPGs are neural networks that produce rhythmic patterned outputs with little to no sensory feedback or external motor commandsDNTM: Can generate fairly complex, stereotypical movements such as walking without voluntary motor control, using only local spinal cord CPGs.
Describe the corticobulbar tract
Corticobulbar tractMotor cortex (related to head/face) -> internal capsule -> descend with corticospinal fibers -> different motor nucleisTermination - Cortex to BRAINSTEMFunctionArises from areas related to head and faceControls turning of head/neck
Describe the motor cortex
The Corticospinal and Corticobulbar TractsStarts: posterior frontal lobeknown as primary motor cortexInputs:-Basal ganglia, cerebellum-Sensory regions of parietal lobeSpecial cells:Betz cells in layer 5 (largest cells in CNS)Function: Mediate planning and initiation of complex temporal sequences of voluntary movement
Describe the lateral corticospinal tract
Cortex -> internal capsule -> cerebral peduncles -> pons -> medulla (CROSS OVER!!!) -> descend down spinal cordTermination - Target LMN in lateral portion of anterior horn (LMN)FunctionLMNs responsible for innervation of distal musclesAllow for precise skilled movements and synergisticc movement of limb
Functional Organization of the Primary Motor Cortex
1930s – Sherrington and Penfield Motor cortex contains spatial map of the contralateral body1960s– more refined method (smaller magnitude of electrical current)Small currents initiate excitation of several muscles (and suppression of others1970s: spike-triggered averagingCorrelate muscle activity with discharge of single upper motor neuronsMotor map is less precise than sensory map – This allows for dynamic and flexible way of encoding higher order parameters that coordinate activation of multiple muscle groups
The premotor cortex
Receives input from parietal lobe and prefrontal area Projections: Over 30% of axons in corticospinal tract arise from neurons in premotor cortexDifference between premotor and primary motor cortex?Strength of their connections to lower motor neuronStudy-Monkey trained to reach different directions depending on visual cue– premotor area fires before monkey receives signal to activity Encode intention to perform movement
The premotor cortex contains mirror neurons. describe
- Premotor areas fires Mirror Motor Neurons2. Responds less when same actions pantomimed without presence of behavioral goal (ie object to be grasped)3. Can fire to goal-directed behavior even if final stage of action is hidden from view (because they understand the goal!Therefore, these neurons encode intentions and involved in imitation learning
What are the Motor Control Centers in the Brainstem?
Vestibular complex: -Maintenance of balanceReticular formation: -Regulation of posture Red nucleus:-Flexor movement in upper limbs-Source of learning signals for cerebellumSuperior Colliculus: -Orientation of visual gaze-Responsible for orienting head and neck during eye movements
What is the difference between medial and lateral vesibular nuclei?
Medial Vestibular Nuclei-Terminates bilaterally in medial ventral horn-Regulates head position by reflex activation of neck muscles in response to semicircular canalsLateral Vestibular Nuclei-Terminates along medial lower motor neuronal pools, govern proximal limbs-Activators limb extensors to stabilize balance and upright posture
Describe the reticular formation in the brainstem
Complicated network of circuits– therefore, many functionsMotor: temporal and spatial control of limb and trunk movementThe reticular formation with the Vestibular Nuclei - maintains posture, responds to disturbance of body position and stability
