1 Coordinated Purposeful Movements Voluntary Motor Function: * Posture Control (maintaining a position) * Goal Directed Movements * Rhythmic Movements Reflexes: Rapidly executed automatic and stereotyped response to a given stimulus

2 Functional basis of the voluntary movement control Decision Making Decision Processing Decision Execution Level 1 Level 2 Level 3 Joint angles and torques Load Sensory information 1.Decision making: Planning Based on the task (will) and memory 3.Decision execution: Execution - Executing the movement, and - Informing the upper control level 2.Decision processing: Programming Interpreting the descending commands and processing them

3 Receptors & Sensory Information Mechanoreceptors: Cochlear hear cells, Vestibular System Kinesthesia: Proprioceptors, Exterocepts (Somatosensory System) Photoreceptors: Visual Information (direct) 1. Sensory Feedback 2. Defining the ambiance Manipulating the sensory information!

4 Table 5.3 (1) Page 144 Hypothalamus Brain stem Cerebral cortex Thalamus (medial) Basal nuclei (lateral to thalamus) Cerebellum Spinal cord Midbrain (Mesencephalon) Pons Medulla oblongata Brain components Cerebral cortex Basal nuclei Thalamus Hypothalamus Cerebellum Brain stem (midbrain, pons, and medulla) Diencephalon

5 Hierarchical organization of the motor system Cerebral Cortex Motor Area Brain Stem Spinal Cord Basal Ganglia Cerebellum Thalamus Sensory Receptors Muscle Contraction and Movement Other Sensory Input Sensory Information Table 5.3 (1) Page 144 Hypothalamus Brain stem Cerebral cortex Thalamus (medial) Basal nuclei (lateral to thalamus) Cerebellum

6 Hierarchical Organization: Decentralized Control Parallel Processing: Production and Control of Discrete types of Movements, e.g., Reaching while Controlling the Posture Posture Control: Medial neuronal system of BS Distal muscles of limbs: Lateral neuronal system of BS Eye and Head movement Control : BS

7 Cerebral Cortex Area: Primary motor cortex (M1) Premotor Cortex (PM) Supplementary motor area (SMA) Premotor area & SMA: Coordinating and planning sequences of movements & receive information and project it to the primary motor cortex (to BS) Somatotopic map!

8 A Hierarchical Structure for motor control system Limbic System Associative Cortex Motor Cortex Basal Ganglia Sensory System Cerebellum Spinal Cord Musculo-skeletal System Plan Need Movement Afferent pathway Efferent pathway Planning Programming Execution ?

9 Pathways: The centers and tracts that link the brain with the rest of the body Sensory pathways (Afferent): Distribute information from peripheral receptors to processing centers in brain Motor pathways (Efferent): Begin at CNS centers concerned with motor control and end at the effectors they control

10 Usual sensory and motor pathways (no reflex arc is considered)

11 Limbic System: * A functional grouping * Includes nuclei and tracts along the border between the cerebrum, diencephalons and mesencephalon Functions of the Limbic System: * Establishing emotional states * Linking the conscious, intellectual functions of the cerebral cortex with the unconscious and automatic function of the brain stem * Facilitating memory storage and retrieval Limbic System Motor Cortex Basal Ganglia Sensory System Cerebellum Spinal Cord Musculo-skeletal System Plan Need Movement ? Associative Cortex

12 Decision Making Decision Processing Decision Execution Level 1 Level 2 Level 3 Commands to muscles Joint angles and torques Load Proprioceptive and other sensory information A proposed internal structure of the three levels involved in performing a voluntary movement Load Antagonist Agonist Interneurons Decision Making  -MN  -MN Supra-spinal Intra-spinal (reflex loops)

13 Muscle fibers and Motor Neurons Two types of muscle fibers: 1. Intrafusal muscle fibers 2. Extrafusal muscle fibers (main body of the muscle) Two types of motor neuron: 1. α-motor neurons Innervate the extrafusal muscle fibers. When the alpha nerve fires the motor unit generates tension and/or shortens. 2. γ-motor neurons Innervate the intrafusal muscle fibers. When the gamma nerve fires the intrafusal muscle fiber generates tension and/or shortens.

14 Two types: 1. Muscle Spindle Apparatus 2. Golgi Tendon Organ Proprioceptors

15 Function: Sensing a)Changes in muscle length: Spatial position b) Rate of change in muscle length: Stretch reflex Muscle Spindle

16 Two kinds of sensory neurons (afferents) I. Primary afferents (Ia): fast or dynamic endings – Rate of stretch – Function: react to oppose stretch II. Secondary afferents (II): slow or static endings – Final length of muscle – Function: maintain muscle tone, posture, positional awareness

17 Muscle Tone: A Resting tension Some motor units are always active. The contraction does not produce movement, but do tense and firm the muscle. Remark: the identity of the stimulated motor units changes constantly. The effect of changes in muscle spindle length on muscle tone

18 Golgi Tendon Organs  Monitors tension developed in muscle and prevents damage during excessive force generation  Ib fibers supply the receptors. Tension Firing pattern in the Ib fiber

19 Alpha-Gamma Coordination Voluntary Contraction

20 Reflexes Processing Site A. Spinal Reflex : Many segments interact to produce a coordinated, highly variable motor response B. Cranial Reflex Directed by nuclei in brain e.g., the reflex movements in response to a sudden loud noise Reflex motor behavior occurs automatically, without instructions of higher centers

21 Complexity of the Circuit I. Monosynaptic Reflex (stretch reflex ): One sensory neuron One interneuron One motor neuron II. Polysynaptic Reflex (scratch reflex) One sensory neuron Multiple interneurons Multiple motor neurons Different reflexes: Stretch reflex, Withdrawal or Flexion reflex, Tonic reflex, Golgi tendon reflex, Crossed extensor reflex, etc. Disynaptic reflex Trisynaptic reflex {

22  Quick stretch of muscle distorts nuclear bag (muscle spindle)  Afferent signal via primary sensory nerve (Ia)  Monosynapse in spinal cord with α-motor neuron  Efferent signal via α-motor neuron  Muscle contraction results to oppose stretch  Reciprocal innervation Collateral Ia synapses inhibitory interneurons Inhibitory interneuron sends efferent signal to antagonist → relaxation of antagonist muscle I. Stretch Reflex Patellar reflex (knee jerk)

23 II. Withdrawal or Flexion Reflex (Disynaptic)  Protective reflex  Longer latency than stretch reflex  Complex nature (coordination of several joints)  Reciprocal inhibition  Nonlinear

24 III. Tonic Stretch Reflex (monosynaptic) Contributes to muscle tone Stabilizes muscle length when it is under constant load Result: Skeletal muscle length regulation, → Posture regulation

25 IV. Golgi Tendon Reflex  Disynaptic reflex  Afferent fiber: Ib  Synapses are based on reciprocal inhibition  Complements the tonic stretch reflex  Skeletal muscle length regulation → Postural Control Rectus femoris (extensor)

26 Mechanism of postural control during standing: RF starts to fatigue Patelar tendon force decreases Activity in Ib declines Normal inhibition of the MN supplying RF will be removes Muscle will be stimulated to contract more IV. Golgi Tendon Reflex Rectus femoris (extensor)

27 V. Crossed Extensor Reflex  Contralateral reflex arc (crossed extensor reflex) occurs on the opposite side of stimulus  The two occur simultaneously With 250 msec delay between Flexion and extension Function: maintaining posture and balance