Neuromotor Control of Speech and Movement (Lecture 4)
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| All motor activity is regulated by interaction among | higher and lower levels of the nervous system
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| HIGHER LEVELS of the nervous system | Cerebral cortex, Basal ganglia, Thalamus, Cerebellum
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| LOWER LEVELS of the nervous system | Brainstem and Spinal cord
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| In general, NEURAL impulses from higher levels may ________, ________, or ________ functions at the brainstem and spinal cord | initiate, inhibit, or facilitate
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| The 5 components of motor control | Final Common Pathway (LMN), Direct Control System (pyramidal, UMN, corticobulbar and corticospinal tracts), Indirect Control System (extrapyramidal), Basal Ganglia Control Circuit and Cerebellar Control Circuit
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| Final common pathway is also known as | lower motor neuron
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| Major players of the Lower motor neuron (efferent) | Alpha motor neurons,Gamma motor neurons, Neuromuscular junction, Muscle fibers (Extrafusal and Intrafusal), Sensory receptors and afferents, Muscle Spindles, Golgi Tendon Organs
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| Alpha and gamma-motor neurons receive motor impulses directly from | the motor centers in the forebrain and brainstem
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| Alpha motor-neurons (α-MNs) are | large lower motor neurons of the brainstem and spinal cord.
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| The primary output of α-MNs is to | extrafusal fibers of skeletal muscle and are directly responsible for initiating their contraction.
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| Other fibers from α-MNs synapse on Renshaw cells which are | inhibitory interneurons that synapse on the α-MN and limit its activity in order to prevent muscle damage
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| Alpha motor neurons receive input from a number of sources, including | upper motor neurons, sensory neurons, and interneurons.
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| Gamma motor neurons | innervate intrafusal muscle fibers of muscle spindles
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| The primary role of gamma lower motor neurons | to regulate the length of the muscle spindle fibers
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| Gamma motor-neurons are controlled by | synaptic input from the brainstem reticular formation and the vestibular system
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| The gamma-efferent fibers contract | the end portions of the intrafusal muscle fibers, passively stretching the central parts of the muscle spindles that are inside
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| As the spindles stretch, a surge of sensory input (afferent projections) is directed to the alpha motor neurons, which in turn | reflexively contracts the muscle mass (extrafusal muscle fiber)to progressively decrease the muscle length
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| Renshaw Cells (Interneurons) are | mostly inhibitory, association cells interconnecting cell bodies within sensory and motor neuron pools
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| The Renshaw cell receives axonal collaterals from nearby motor neurons, inhibiting the activity of the same or related adjacent alpha motor neurons to | cease muscle contraction
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| The recurrent inhibition by the Renshaw cell | facilitates and sharpens the activity of the projecting motor neuron
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| Muscle spindles | detect the degree and rate of change in muscle length and help maintain muscle tone
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| Muscles consist of | extrafusal and intrafusal fibers
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| Extrafusal fibers make up the large mass of the skeletal muscle; they are | attached to bone by fibrous tissue extensions called tendons and are controlled by alpha motor neurons
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| Intrafusal fibers, which contained in muscle spindles, are | attached to the extrafusal fibers and are controlled by gamma-motor neurons
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| True or False: Both ends of the intrafusal fibers contract, but the central region does not | true
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| Golgi tendon organs | innervate the tough tissues that attach muscles to bones and permits the muscle to stretch and prevents injury caused by excessive contraction
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| Muscle spindles are buried among | the extrafusal fibers of the muscle
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| Muscle spindles send information about muscle stretch to | the CNS
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| Intrafusal fibers are found in | muscle spindles
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| Gamma-motor neurons from CNS innervate | intrafusal fibers
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| One way to initiate a muscle contraction is through the stimulation of | alpha-motor neurons.
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| Activating alpha motor neurons causes | the extrafusal muscle fibers to contract. With contraction of the extrafusal fibers of the muscle, the intrafusal fibers become slack and consequently
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| To correct this impaired spindle sensitivity, the ______, ______, ______ reflexively discharge gamma-motor neurons | rubrospinal, reticulospinal, and vestibulospinal
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| Gamma-motor neurons,which contract the end portions of the intrafusal fibers | straighten the spindles and restore their sensitivity to muscle length(stretch).
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| The alpha motor neuron sends impulses to contract (shorten) the extrafusal muscle fibers via | the neuromuscular junction
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| Gamma-motor neurons prevent slackening of intrafusal fibers in response to | contraction of extrafusal fibers
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| Stimulated alpha-motor neuron contracts | extrafusal fibers
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| Activation of gamma-motor neuron contracts intrafusal fibers | restoring spindle sensitivity
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| The common element in all stretch reflexes is | that the stretched muscle contracts after a brief delay
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| Stretch or Myotactic Reflex | 1. Sensory from the stretched muscle spindles send afferent projections to activate the a-mns in L3 in the spinal cord. 2. The a-mns efferent fibers to the muscle cause a quick contraction of the extrafusal muscle fibers restoring it to resting position
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| Patellar Tendon reflex | Stretch or Myotactic Reflex
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| protective response to pain or painful stimuli seen when one touches a hot pan or steps on a nail | Withdrawl or Flexor Reflex
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| The neural mechanism of the limb-withdrawal reflex involves | pain receptors in the skin, afferent pain fibers, substantia gelatinosa, interneurons and alpha-motor neurons
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| True or False: A withdrawal reflex generally begins even before one is aware of the painful stimulus because the afferent information triggers a spinal response before the ascending signal of pain reaches the forebrain | True
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| Arm flexion | Example of Withdrawl or Flexor Reflex
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| Reciprocal inhibition is when | one muscle contracts while the paired muscle extends because it is inhibited from simultaneous contraction
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| Crossed Or Intrasegmetal Extensor Reflex is considered a genetically programmed protective behavior for survival because | it moves the entire body away from the painful stimulus
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| Crossed Or Intrasegmetal Extensor Reflex is a complex movement pattern in which | withdrawal(contract) of the limb on one side is accompanied by the activation of motor neurons to extend the agonistic muscle on the opposite side (ipsilateral) of the body
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| Large lesions result in LMN Syndrome in which | muscle fibers are disconnected from motor efferents and thus cannot receive descending cortical impulses and reflexive sensory input.
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| Clinical signs of LMN Syndrome occur | unilateral to the lesion for both reflexes and voluntary motor movements
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| flaccid paralysis, absent reflexes, muscular fibrillation (spontaneous firing)/ fasciculations, atrophy (silence of firing and shrinking of the muscle), paresis are clinical signs of | LMN Syndrome
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| Sudden onset of paralysis of all ipsilateral upper and lower facial muscles; a LMN syndrome that paralyzes the entire side of the face | Bell's palsy
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| Glossopharyngeal nerve (CV IX) serves | both sensory and motor functions
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| Direct, voluntary skilled movement | DIRECT ACTIVATION PATHWAY (Pyramidal System)
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| Corticospinal and Corticobular tracts are associated with | DIRECT ACTIVATION PATHWAY (Pyramidal System)
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| One of the major descending pathways originating in the motor cortex of the brain to terminate at the α-MNs of the spinal cord | The corticospinal tract
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| Provides a mechanism for the cerebral cortex mediate voluntary movements of the skeletal muscles | The corticospinal tract of the DIRECT ACTIVATION PATHWAY (Pyramidal System)
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| Where 90% of the corticospinal fibers cross and form the lateral corticospinal tract | at the medulla
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| Where 10% of the coriticospinal fibers cross in the spinal cord before synapsing on the ventral horn with alpha motor neuron and internuncial cells is called | the anterior corticospinal tract
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| Cortex-Corona Radiata-Post. limb of internal capsule-Pes Pedunculi-Ventral pons-Pyramids of the medulla-a. Lateral corticospinal tract (90%)-b. Anterior corticospinal tract (10%)-Synapse alpha motor neurons to regulate muscle activity | ORDER OF CORTICOSPINAL TRACT
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| Originates in the cortex and terminates in the bulbar area (medulla and adjacent brainstem areas) | The corticobulbar tract
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| It controls skilled and fine movements but exclusively for the head and face | The corticobulbar tract
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| Fibers arise from the lower 1/3 of the motor cortex-Corona Radiata-through genua of internal capsule-Pes Pedunculi-Cross midline, (decussate) at vaious points-Terminate on specific motor nuclei in brainstem | ORDER OF CORTICOBULBAR TRACT
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| Maintains balanced posture, smooth and coordinated movement, muscle tone, supportive to voluntary movement, regulates reflexes | INDIRECT ACTIVATION PATHWAY (Extrapyramidal System)
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| Multiple synapses before providing input to LMN, EVENTUALLY INFLUENCES GAMMA MOTOR NEURONS | INDIRECT ACTIVATION PATHWAY (Extrapyramidal System)
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| Damage results in increased tone, increased reflexes, spasticity and loss of skilled movements | INDIRECT ACTIVATION PATHWAY (Extrapyramidal System)
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| Speech: unilateral UMN dysarthria and spastic dysarthria is result of damage to | INDIRECT ACTIVATION PATHWAY (Extrapyramidal System)
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| Vestibulospinal, Corticorubral, and Corticoreticular Tracts are associated with | INDIRECT ACTIVATION PATHWAY (Extrapyramidal System)
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| Vestibular nuclei(on floor of 4th ventricle)-terminate on Alpha Motor Neurons and Gamma Motor Neurons | order of the Vestibulospinal tract of Indirect Activation pathway
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| Function: keeps head stable | Vestibulospinal tract of Indirect Activation pathway
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| Cortex–red nucleus (midbrain)-it becomes the rubrospinal tract-spinal or Cranial Nerve | order of the Corticorubral Tract of the Indirect Activation Pathway
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| Function: Keeps upright against gravity | Corticorubral Tract of the Indirect Activation Pathway
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| Projects from cortex (motor, premotor and sensory areas) to midbrain to reticular formation | Corticoreticular Tract of the Indirect Activation Pathway
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| A field of cells in midbrain, pons and medulla crucial for muscle tone | The reticular formation
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| Results in increased muscle tone | Stimulation of facilitory reticular areas (midbrain, pons, medulla)
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| Results in decreased muscle tone | Stimulation of inhibitory reticular area (lower medial medulla)
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| Reticulospinal tract synapses on | gamma motor neurons in cranial and spinal nerve nuclei
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| It regulates swallowing by integrating the sensorimotor functions of the trigeminal nerve (CN V), facial nerve (CN VII), glossopharyngeal nerve (CN IX), vagus nerve (CN X) and hypoglossal nerve (CNXI) | Reticulospinal tract of Indirect Activation Pathway (Extrapyramidal System)
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| Gives movement force, timing and precision | Cerebellar Circuit
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| Refines movement | Basal Ganglia Circuit
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| Akinesia, Bradykinesia, Decreased excursion of movement, Tremor? result from | too much inhibition (hypokinetic) in the Basal Ganglia Circuit
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| Athetosis, Ballism, Chorea, Dyskinesia | Too much excitation (hyperkinetic) in the Basal Ganglia Circuit
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| Ataxia, Dysdiadochokinesis, Ataxic dysarthria, Dysmetria, Intention tremor, Hypotonia, Rebounding, Disequilibrium | Cerebellar issues
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