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神经生物学ppt课件:7神经系统对运动的调节.ppt
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    Central Nervous System Control of Movement

    XING, GUOGANG(邢国刚), MD. Ph.D.

    北京大学 神经科学研究所

    Neuroscience Research Institute, Peking University

    Email address: ggxing@bjmu.edu.cn

    Introduction

    * 生命在于运动......

    * 运动是动物维系个体生存和种族繁衍的基本功能之一

    How does a coordinated movement achieved ?

    The motor control hierarchy have three levels

    * The highest level- strategy

    > Represented by the association areas of neocortex and basal ganglia of the forebrain

    > Is concerned with strategy:

    ?a The goal of the movement and the movement strategy that best achieves the goal

    The motor control hierarchy have three levels

    * The middle level-tactics

    > Represented by the motor cortex and cerebellum

    > Is concerned with tactics

    -The sequences of muscle contractions

    ?Arranged in space and time

    ? Required to smoothly and accurately achieve the strategic goal

    The motor control hierarchy have three levels

    * The lowest level- execution

    >Represented by the brain stem and spinal cord

    >Is concerned with execution

    -Action of the motor neuron and interneuron pools that generate the goal-directed movement and make any necessary adjustments of posture

    Overview

    * 脊髓内的"下运动神经元(Lower neurons)?±￡?除了受到脊髓内局部环路的影响外，还受到大脑皮层运动区及脑干中许多"上运动神经元(Upper neurons)?±的支配和协调

    * 基底神经节和小脑则向那些上运动神经元提供某种感觉、认知或感性的信息，使运动更加精确和协调

    

    Part 1

    Spinal Control of Movement

    Introduction

    * "running around like a chicken with its head cut off"

    * The rhythmic movements could be elicited in the hind legs of cats and dogs long after their spinal cords had been severed from the rest of the central nervous system

    -Charles Sherington & Graham Brown (English)

    -The importance of circuitry within the spinal cord for the coordinated control of movements

    Spinal circuitry control of movement

    Spinal motor neurons

    * Alpha motor neurons

    Innervate skeletal muscle (extrafusal muscle)

    Function: directly command muscle contract

    * Gamma motor neurons

    Innervate muscle spindle(intrafusal muscle)

    Function: regulating the muscle spindle

    * Interneurons

    Allows coordinated motor programs to be generated

    * Final common pathway

    (directly command muscle contract)

    ? Compare: Upper motor neurons

    The Lower Motor Neurons

    - Alpha motor neurons

    * Alpha motor neurons are directly responsible for the generation of force by muscle

    * Motor unit: one alpha motor neuron and all of the muscle fibers it innervates collectively make up motor unit, the elementary component of motor control

    * Motor neuron pool: The collection of alpha motor neurons that innervates a single muscle

    The motor unit is an alpha motor neuron and all of the muscle

    Muscle innervation by lower motor neurons

    The cervical enlargement of the spinal cord contains the motor neurons that innervate the arm muscles

    The lumbar enlargement contains neurons that innervate the muscles of the leg

    支配上肢的神经元集群位于颈膨大处，支配下肢的则在腰膨大处

    The distribution of lower motor neurons in the ventral horn

    Motor neurons controlling flexors lie dorsal to those controlling extensors

    Motor neurons controlling axial muscles lie medial to those controlling distal muscles

    支配躯干部肌肉的神经元位于脊髓前角灰质最内侧，由此向外排列的神经元则支配肢体由近及远分布的肌肉

    * Muscle weakness and paralysis-所支配的骨骼肌瘫痪、肌张力下降、腱反射消失(软瘫)

    * 肌萎缩、纤维颤动或肌束颤动

    * 见于如肌萎缩侧索硬化症(amyotrophic lateral sclerosis, ALS)：Selective damage to alpha motor neurons(degeneration)-脊髓?-运动神经元的进行性溃变为主

    SPINAL CONTROL OF MOTOR UNITS

    How the activity of the motor neuron

    is itself controlled ?

    The function of gamma motor neurons

    The Gamma loop

    * Changing the activity of the gamma motor neurons changes the set point of the myotatic feedback loop

    * The Gamma loop

    * Gamma motor neuron ? intrafusal muscle fiber ?Ia afferent ? alpha motor neuron ? extrafusal muscle fibers

    * Alpha and gamma motor neurons are simultaneously activated by descending commands from the brain

    Significance of the reverse myotatic reflex

    * In extreme circumstances, this reflex arc protects the muscle from overload

    * The normal function is to regulate muscle tension within an optimal range

    > As muscle tension increases, the inhibition of the alpha motor neuron slows muscle contraction

    > As muscle tension falls, the inhibition of the alpha motor neuron is reduced, and muscle contraction increases

    * This type of proprioceptive feedback is thought to be particularly important for the proper execution of fine motor acts, such as the manipulation of fragile objects with the hands, which require a steady but not too powerful grip

    Spinal interneurons

    * Most of the input to the alpha motor neurons comes from interneurons of the spinal cord

    * Interneurons receive synaptic input from primary sensory axons, descending axons from the brain, and collaterals of lower motor neuron axons

    * The interneurons are themselves networked together in a way that allows coordinated motor programs to be generated in response to their many inputs

    Reciprocal inhibition of flexors and extensors of the same joint

    Circuitry of the crossed-extensor reflex

    The generation of spinal motor programs for walking

    * Headless chickens; behavior

    * A complete transectionof a cat?ˉs spinal cord at the mid-thoracic level leaves the hind limbs capable of generating coordinated walking movements

    Central pattern generators within the spinal cord

    * The circuit for the coordinated control of walking must reside within the spinal cord

    * In general, circuits that give rise to rhythmic motor activity are called central pattern generators

    * How do neural circuits generate rhythmic patterns of activity?

    - The simplest pattern generators, are single neurons whose membrane properties endow them with pacemaker properties (pacemaker neurons)......（后略) ......