Neurology: 13 Muscle spindle, Golgi tendon organ and Reflexes – Flashcards
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*Highest level* of the motor system?
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*Pre command* level
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*Middle level* of the motor system?
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*Projection* level
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*Lowest level* of the motor system?
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*Segmental* level
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What are the *functions* of the *precommand level*?
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Programs and instructions (modified by feedback)
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What are the *anatomical parts* of the *precommand level*?
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1. Cerebellum 2. Basal Nuclei
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What are the *functions* of the *projectional level*?
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Conveys instructions to spinal cord motor neurons and sends a copy of that information to higher levels.
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What are the *anatomical parts* of the *projectional level*?
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1. *Motor cortex* (pyramidal pathways) 2. *Brain stem nuclei* (vestibular, red, reticular formation
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What are the *functions* of the *segmental level*?
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Contains central pattern generators (CPGs)
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What are the *anatomical parts* of the *Segmental level*?
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spinal cord
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What three things *feedback* onto the precomand level?
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1. Sensory input 2. Projection level 3. Segmental level
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What two areas feed into *motor output*?
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1. Projection level 2. Segmental level
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Function of *renshaw cells*?
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inhibitory interneurons found in the gray matter of the spinal cord. Inhibits itself
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What levels have large ventral horns?
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C5-T1 and L2-S2
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What is a *motor unit*?
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single motoneuron and the muscle fibers that it innervates.
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What is a *motoneuron pool*?
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a set of motoneurons inverting fibers within the same muscle
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What are the two types of motoneurons?
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1. Alpha motoneurons 2. Gamma motoneurons
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What do alpha motoneuron innervate?
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extrafusal skeletal muscle fibers
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What do gamma motoneurons innervate?
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specialized intrafusal muscle fibers, (a component of the muscle spindles)
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What are the proprioceptors in skeletal muscles?
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muscle spindles
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What do muscle spindles monitor?
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the length of skeletal muscles and participate in stretch reflexes
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Intrafusal muscle fibers of muscle spindles are of what two types?
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1. nuclear bag fibers 2. nuclear chin fibers
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Both types of muscle spindles are present in every cell, but which one is more plentiful?
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*More nuclear chain fibers* then nuclear bag fibers
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Nuclear bag fibers look like what?
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large, with nuclei accumulated in a central region
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Nuclear chain fibers look like what?
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small, with nuclei arranged in rows
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What innervates the central region of both the nuclear bag and chain fibers?
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A single group 1a afferent nerve and group II afferent nerves.
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Group II afferent nerves are primarily on which muscle spindle?
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nuclear chain fibers
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Motor innervations by gamma motoneurons have what two types?
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1. dynamic 2. static
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*Dynamic* gamma motoneurons synapses where?
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on nuclear bag fibers in "plate endings"
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*static* gamma motoneurons synapses where?
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on nuclear chain fibers in "trail ending" which spread over long distances
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steps of muscle contraction in response to *muscle stretch*
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*Stretch of muscle --> stretch of muscle spindle* --> distortion of primary sensory endings at the center of intrafusal fiber --> action potential generation in 1a fibers --> stimulation of alpha-motor neurons in the spinal cord --> muscle contraction
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steps of muscle contraction in response *of gamma motor neurons*
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*activation of gamma-motor neurons --> contraction of ends of the spindle --> stretch of central part of muscle spindle* --> distortion of primary sensory endings at the center of intrafusal fiber --> action potential generation in 1a fibers --> stimulation of alpha-motor neurons in the spinal cord --> muscle contraction
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gamma motor neurons are primarily influenced by what? and not by what?
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*descending fibers* NOT by primary sensory fibers
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what is alpha-gamma motor coactivation?
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gamma motor discharge increases along with increased discharge of alpha motor neurons
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Golgi tendon organ (GTO) is what?
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specialized receptor that is located between the muscle and the tendon
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Golgi tendon is made of what?
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capsule containing numerous collagen fibers, in series with the muscle
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Golgi tendon is innervated by what fibers?
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primary afferents --> *Group Ib fibers* that are weaved between the collagen fibers
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What is the golgi tendon organ reflex?
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muscle contracts shortening the extrafusal muscle fibers --> activating the golgi tendon organs --> group Ib afferent fibers synapse on inhibitory interneurons in the spinal cord --> inhibiting alpha motoneuron (tension on tendon is reduced)
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What is a reflex?
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a fast, involuntary, unplanned sequence of actions that occurs in response to a particular stimulus
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when integration takes place in the spinal cord gray matter the reflex is what?
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a spinal reflex- stretch reflex example: patellar reflex
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when integration takes place in the brain stem rather than the spinal cord it is what?
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a cranial reflex -- pupillary light reflex example: the tracking movements of the eyes as you read this
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what autonomic (visceral) reflexes?
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generally not consciously perceived; involves responses of smooth muscle, cardiac, and glands example: urination, digestion
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what are somatic reflexes?
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most aware of the reflex example: contraction of skeletal muscles
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what are the two groups of reflexes?
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1. monosynaptic reflex 2. polysynaptic reflex (two or more synapses)
