Voluntary Movement. Ch. 14: Supplemental Images

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1 Voluntary Movement Ch. 14: Supplemental Images

2 Skeletal Motor Unit: The basics Upper motor neuron: Neurons that supply input to lower motor neurons. Lower motor neuron: neuron that innervates muscles, including skeletal muscle fibers involved in movement. 1. Alpha motor neuron: Aα fiber innervates extrafusal muscle fibers 2. Gamma motor neurons: Aγ fibers innervates intrafusal muscle fibers Motor Unit: one lower motor neuron and all muscle fibers that it innervates. 1. Innervation ratio: Extraocular =1:10; Hand = 1:100; Gastrocemius in knee = 1: Proportional to size of muscle 3. Trade off between control and total force Extrafusal muscle fibers: 1. Workhorse fibers all of the force of muscle 2. ACh at neuromuscular endplate: endplate potential that leads to All-or-none fiber contraction. 3. Sherrington (1925) Final common pathway a. Lower motor neuron influenced by many sources b. Sums influences on neuron to determine if Action Potential occurs, releasing ACh at endplate Grading a muscle contraction 1. Number of motor units activated 2. Rate of action potentials of a motor neuron (rate modulation): higher rate = more force

3 Hierarchy of Movement Motor Unit Reflexes: Monosynaptic reflex arc (e.g. patellar) Polysynaptic reflexes (e.g. cross-extensor reflex) Rhythmic Motor Patterns: once initiated, the sequence of relatively stereotyped repetitive movements can continue in automatic manner (e.g., walking) combines characteristics of reflexes with voluntary (initiation, termination) movement. central pattern generators (Ch 13) Voluntary movement: purposeful, goal-drected movement Often learned movements which improve with practice and requires less attention, e.g., combing hair, swinging a bat, driving a car, swimming, using eating utensils, etc, etc, etc. Cortical control over movement.

Duration of each movement Phasic (transient, discrete movements) Static (e.g.

4 Voluntary movement Organization of voluntary movement general sequence Planning, strategy: Purpose/motivation Order of movement (each set of movement prepares body for next set) Direction Rate of movement Strength Timing One movement relative to another Duration of each movement Phasic (transient, discrete movements) Static (e.g., stabilize joints) Initiate (start) movement Postural adjustments (+ feedback) Medial limb movement (+ feedback) Distal limb (+feedback) Adjustments at EVERY point Stop movement

5 Voluntary movement (cont.): hierarchical organization Non-proprioceptive sensory input , 6 Proprioceptive Sensory input

6 General Organization of Spinal Cord Ascending pathways Lateral spinothalamic tract Descending pathways 14.2

Direction of movement depends on population of cells Individual cells have directional preference Population vectors Requires feedback

7 Primary Motor Cortex: M1/Area 4/Precentral gyrus Amount of force Different cells for extensors, flexors Cells are active BEFORE contraction AP rate increases and decreases as load increases or decreases. Direction of movement depends on population of cells Individual cells have directional preference Population vectors Requires feedback for ongoing corrections Minor discrepancies modifies cells within population Major discrepancies - changes population of cells ALL cells are modified by Other cortices Basal ganglia Cerebellum

Premotor Motor Cortex: Area 6 Proximal and axial muscles initial phases of orienting body and limbs Set-related neurons Preparation of motor response: cells activated when subject is given

8 Premotor Motor Cortex: Area 6 Proximal and axial muscles initial phases of orienting body and limbs Set-related neurons Preparation of motor response: cells activated when subject is given information to perform a task with specific location Relatively simple tasks. Cells active before execution of movement, continues until movement is complete. Does NOT appear to encode fine detailed movement Stimulus triggered movement Spontaneous movement Cell AP responses are modified by Other motor cortices Basal ganglia Cerebellum 14.7

Descending pathways: Reticulospinal pathways 14.6 14.

extensors of legs to maintain length and tension of muscles (e.g., vestibular).

9 Descending pathways: Reticulospinal pathways Posture and antigravity muscles of limbs Pontine: Enhances antigravity reflexes by facilitating extensors of legs to maintain length and tension of muscles (e.g., vestibular). Medullary: Inhibits antigravity reflexes (opposite effect) to allow change as needed (e.g., to begin movement). Cortex keeps these two antagonistic systems in balance.

10 Descending pathways: Vestibulospinal and tectospinal 14.4 Posture of head and neck Vestibulospinal: Several vestibular nuclei in brain stem keep head balanced during movement and turns head as needed. Tectospinal: Helps coordinate eye movement (superior colliculus function) with head movement (tectospinal).

Descending pathways: Corticospinal and rubrospinal tracts 14.3 Fine Movement of Arms and Fingers Corticospinal (pyramidal): Contralateral Areas 4 and 6.

11 Descending pathways: Corticospinal and rubrospinal tracts 14.3 Fine Movement of Arms and Fingers Corticospinal (pyramidal): Contralateral Areas 4 and % decussate (cross) at posterior medulla. Terminate on alpha motor neurons and interneurons mostly flexor activation. Rubrospinal: Complements corticospinal pathways.

Basal Ganglia Terminology Basal Ganglia includes all of the following - Caudate nucleus Putamen Globus pallidus (palidum) - external, internal Subthalamus Substantia nigra Subgroupings Striatum =

12 Basal Ganglia Terminology Basal Ganglia includes all of the following - Caudate nucleus Putamen Globus pallidus (palidum) - external, internal Subthalamus Substantia nigra Subgroupings Striatum = caudate nucleus + putamen Lenticular nucleus = putamen + globus pallidus Corpus striatum = caudate n. + lenticular n. + internal capsule (crosshatch of gray and white fibers) Direct Pathway Indirect Pathways

13 Direct Pathway (Motor Loop) Flow of information through basal ganglia for point-topoint adjustments in execution of ongoing motor signals Motor cortices putamen globus pallidus VA\VL motor cortices No Movement no AP no AP high AP = tonic inh. no AP unaltered Ongoing movement Topographic increase in AP Specific +AP specific - AP = release of inh. Specific +AP Specific +AP Other Input Selected excitation that modifies motor signals Selected release of inhibition Enhanced or modified movement

12 Combined +/- Excites selected cells of GP which

14 Basal Ganglia: Indirect Motor Loops Ventrolateral n. Substantia Nigra Subthalamus Combined +/- Excites selected cells of GP which INCREASES inhibition of VL n. of thalamus (and decreases behavior)

15 Posterior and Anterior Spinocerebellar Pathways Human upright position

Cerebellum (Latin="little brain") Functions Coordinating reflexive and voluntary movement, particularly if Movements are rapid Require accurate aiming and timing Automatic, not at level of awareness

16 Cerebellum (Latin="little brain") Functions Coordinating reflexive and voluntary movement, particularly if Movements are rapid Require accurate aiming and timing Automatic, not at level of awareness Maintain equilibrium Generating and planning movements Some motor learning (Classical conditioning; well-practiced, automatic responses) Cognitive functions Behavioral Examples Playing instruments Athletic skills Typing Writing Speaking

17 Medial Zone: Vermis ( worm -spinocerebellum) Vestibular input/postural control Deep nuclei Lateral & Intermediate zones Similar but not same circuitry. Output through deep nuclei Superior cerebellar peduncles (brachium conjunctivum) VL/VA n. of thalamus Motor cortices Flocculonodular node Vestibulocerebellum Vestibular input/eye movement Deep nuclei Cortical Zones (Nolte, 1993)

18 Deep nuclei (Nolte, 1999) All output from cerebellar cortex goes through deep nuclei. Nuclei: Fastigial Interposed nuclei Globose n. Emboliform n. Dentate

19 Principal Cerebellar - Cortical Relationship Per caption: principal circuit by which deep nuclei influence cortically controlled movement. PD: Pyramidal Decussation RST: Rubrospinal tract

Biological Bases of Behavior. 8: Control of Movement

Biological Bases of Behavior. 8: Control of Movement Biological Bases of Behavior 8: Control of Movement m d Skeletal Muscle Movements of our body are accomplished by contraction of the skeletal muscles Flexion: contraction of a flexor muscle draws in a