Neural Basis of Motor Control. Chapter 4

Transcription

1 Neural Basis of Motor Control Chapter 4

2 Neurological Perspective A basic understanding of the physiology underlying the control of voluntary movement establishes a more comprehensive appreciation and awareness of capabilities and limitations of the people with whom a practitioner works. (Magill, pg 65)

3 Nervous System Nerves (Neurons) inside or outside the: Central Nervous System (Nerves inside) Brain and Spinal cord Peripheral Nervous System (Nerves outside CNS) Efferent nerves (motor) Afferent nerves (sensory)

4 Neural Activity The focus of this chapter will be how the nervous system controls voluntary, coordinated movement.

5 Concept 1: The Neuron Neuron are similar to other cells It has a cell membrane, a nucleus that contains genes, contains cytoplasm, mitochrondria, and organelles. It carries out basic cellar processes such as protein synthesis and energy production

6 Neuron: Basic Unit of CNS Neuron is a nerve Axon takes information away from the cell body (soma) - the neuron has only one Dendrites bring information to the cell body (soma) -neuron may have none to as many as 1000 dendrites

7 Summary of Differences Axons Take information away from the soma Generally only 1 axon per cell No ribosomes Can have myelin Branches further from the soma Dendrites Bring information to the soma Rough surfaces (dendritic spines) Many dendrites per cell Has ribosomes No myelin insulation Branches are near the soma

8 Concept 2: Types of Neurons Neurons are classified by direction that they send information: 1. Sensory (afferent) neurons sends information from sensory receptors (e.g. skin, eyes, ears) 2. Motor (efferent) neurons sends information AWAY from the CNS to muscles or organs. 3. Inter-neurons: send information between sensory and motor neuron; most are located in CNS.

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10 Sensory Neurons They are unipolar, that is, they have no dentrites and only one axon. Most sensory neuron are in the peripheral nervous system

11 Motor Neuron Two types Alpha motor neurons (predominately in spinal cord and referred to as the motor horn cells). Has many dendrites and long branch axons that connects directly to skeletal muscle fibers. Gamma motor neurons supplies a portion of skeletal muscle called intrafusal fibers.

12 Interneurons Originate and terminate in the brain or spinal cord They function as connections between axons descending from the brain. They synapse on motor neurons and axons from sensory nerves and spinal nerves ascending to the brain.

13 Concept 3: Central Nervous System Functions as the command center Comprises the the brain and spinal cord Integrates and organizes sensory and motor information to control movement

14 CNS Components most involved in Motor Control Cerebrum Diencephalon Cerebellum Brainstem

15 Cerebrum Divided into two the right and left cerebral hemispheres Each hemisphere is covering with gray matter of 2-5 mm thick, folded tissue of nerve cell bodies called the cerebral cortex The gray matter contains neurons that send signals from the cortex to other parts of the CNS (pyramidal cells) or non pyramidal cells. Each hemisphere of the cortex consist of four lobes Parietal Occipital Frontal Temporal

16 Sensory-Specific Areas (Figure 4.4 below) Proximity of primary sensory and motor cortex areas and their association areas allows interaction between perceptual and higherorder cognitive functions.

17 Diencephalon Diencephalon (contains the thalamus & Hypothalamus) lies between cerebrum and the brainstem Hypothalamus lies under the Thalamus controls the endocrine and the body homeostasis including temperature, hunger, thirst, and regulation of carbohydrate energy use. Thalamus is a relay station for sensory and motor information that transmits pulses from one cerebral hemisphere to another and interconnects the other areas of the brain, plays important roll in controlling attention, mood, & perception of pain. Hypothalamus Thalamus

18 Cerebellum 1. Attaches to the brain stem & Located behind the cerebral hemispheres 2. Regulates the accuracy & smoothness of movement. 3. Controls eye-hand movements 4. Movement timing 5. Posture Control 6. It detects errors and corrects errors in movement* cerebellum

19 Important Subcortical Component Basal ganglia plays critical role in planning and initiating movement, control of antagonist muscles during movement, and the control of force. Basal ganglia People with Parkinson s disease and cerebral palsy affect the basal ganglia s functions People with basal ganglia limitations experience: Bradykinesia (slow movements) Akinesia (reduced amount of movements) Tremor Muscular rigidity

20 Concept 4: The Brain Stem Consists of the pons, medulla or medulla oblongata, and reticular formation

21 Pons 1. Pons considered to be part of the brainstem. 2. Top of the brain stem 3. Bridge between cerebral cortex and cerebellum 4. Connects the two hemispheres of the cerebellum 5. Acts as a relay for the auditory system and movement 6. Involved in controlling chewing, swallowing, salivating, and respiration 7. Plays a role in balance Pons

22 Medulla or Medulla Oblongata 1. Considered to be part of the brainstem 2. Serves as regulatory agent for various internal physiologic processes such as heart beat, respiration, and gastrointestinal functions. 3. Site where sensory (ascending) and motor neural (descending) pathways cross over the body midline and merge on their way to the cerebellum and cerebral cortex. medulla

23 Reticular Formation Located just above pons and contains the reticular formation which is considered to be part of the brainstem) Plays a major role in arousal, consciousness, states of sleep, and relaxation Primary role is as an integrator of sensory and motor neural impulses, that is, inhibits or increases neural impluses which in turn influences skeletal muscle activity. Reticular

24 Concept 5: Limbic system Limbic system controls behaviors including emotions, motivation, and learning which provides impetus for goal directed movement in environmental contexts. Pleasure center of the brain. Consists of the frontal and temporal lobes of cerebral cortex, thalamus, hypothalamus, and interconnections nerves of CNS

25 Hummm! How does this all relate to learning a motor skill? video/jennifer-raymond.html

26 Two major portions of the spinal cord are the gray and white matter. Concept 6: Spinal Cord Gray matter is butterfly shape, central part of spinal cord, containing 2 pairs of horns. Dorsal horn involve cells are involved in transmitting sensory information. Ventral horns contain Alpha Motor Neuron whose axons terminate on skeletal muscles. Spinal cord contains interneurons call Renshaw cells. Nerve fibers descend from the brain terminate on interneurons which influence Alpha Motor Neuron activity.

27 Concept 7: Transportation of sensory information to the brain Sensory neural pathway (ascending track) Passes through the spinal cord to brain stem to thalamus to the sensory areas of cerebral cortex and to the cerebellum There are different specific ascending tracks: Vision has it s own track to the cerebral cortex Audition has it own track to the cerebral cortex Sensory information has it own tracks to the cerebral cortex. Ascending tracks cross at the brain stem from one side of the body to another which means information from one side of the body is received in the opposite side of the brain. Next Slide

28 Concept 8: Transportation of Movement information from the Brain to the Muscles Motor neural pathway. Transport of movement information (descending track) that will execute the movements: Two distinct pathways that function together Pyramidal (corticospinal tract) Transmits neural information that arises from the cerebral cortex with axons projecting into the spinal cord that cross over to the opposite side of the body. Primarily associated with fine motor skills (mostly discrete in nature or what neural scientists call fractionated movements). Extrapyramidal (brainstem pathways) Transmits neural information that arises in the brainstem with axons descending into the spinal cord with many of fibers not crossing over to the opposite side of the body Chiefly found in the reticular formation of the pons and medulla. Primarily associated with postural control and muscle control of flexion and extension of hands and fingers.

29 Concept 9: Motor Unit The end of transmission of motor neural information is the motor unit. Commonly defined as the Alpha motor neuron and muscle fibers it innervates (motor unit) Connection between an Alpha motor neuron and skeletal muscle occurs at the neuromuscular junction located at the middle of the muscle. This synapse allows nerve impulses to be transmitted so he muscle contracts and movement occurs. Alpha Motor Neuron

30 Concept 10: Performing a Voluntary Motor Skills Neural system is hierarchical organized. 1. One needs to have cognitive intent to move. 2. Various structures work both hierarchically (top-down or down-up) and in parallel (same time). 3. Different neural activity occurs when we perform different skills.

31 THE END