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35 Cards in this Set
- Front
- Back
Lower motor neurons
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-Somatic motor neurons in the ventral horn of the spinal cord
-Directly command muscle contraction -Final common pathway |
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Upper motor neurons
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-Brain
-Supply input to spinal cord. |
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Spinal nerve
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-Axons of lower motor neurons form ventral roots. Ventral roots join with dorsal roots to form these nerves.
-In notches btw vertebrae |
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Mixed spinal nerves
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-Nerves contain both sensory and motor fibers
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Alpha Motor Neurons
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-Directly trigger the generation of force by muscles
-Combine with other AMN and muscle fibers to form a motor unit |
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Motor neuron pool
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-Motor neuron = alpha motor neurons + muscle fibers
-Collection of AMNs that innervates a single muscle |
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What are the 2 ways that the CNS controls muscle contraction?
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1. Varying action potential firing rate
2. Recruiting additional synergistic motor units |
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What are the 3 sources of inputs to an alpha motor neuron?
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1. Dorsal root ganglion cells
2. Upper motor neurons in motor cortex/brain stem 3. Interneurons in spinal cord (largest source) |
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Hypertrophy v. Atrophy
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Hypertrophy: Exaggerated growth of muscle fibers
Atrophy: Degeneration of muscle fibers |
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Excitation Contraction Coupling
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-Action potential release Ca2+ from an organelle inside muscle fiber -> contraction of the fiber.
-Relaxation occurs when Ca2+ levels are lowered |
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Sarcolemma
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-Excitable cell membrane enclosing muscle fibers
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Myofibrils
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-Cylindrical structures within muscle fibers which contract in response o an AP sweeping down sarcolemma.
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Sarcoplasmic Reticulum
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-Surrounds myofibrils
-Extensive intracellular sac that stores Ca2+ |
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T Tubules
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-Network of tunnels
-Inside fiber -Inside out axons, continuous with extracellular fluid. |
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Tetrad
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-Voltage-sensitive cluster of four calcium channels in the T tubule
-Linked to calcium release channel in the SR. |
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Calcium Release Channel
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-Linked to tetrad
-Ca2+ flows through = myofibril contracts |
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Z Lines
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-Divides myofibril into segments by disks
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Sarcomere
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-Segment comprised of 2 Z lines and the myofibril between.
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Thin filaments
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-Series of bristles anchored to each side of Z line
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Thick filaments
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-Series of fibers
-Between and among the two sets of thin filaments |
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How does muscle contraction occur?
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-The thin filaments slide along the thick filaments, bringing adjacent Z lines towars one another
-aka Sarcomere is shorter |
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Actin and myosin
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-Myosin binds to actin and undergo a conformation change that causes pivoting.
-Thick filament moves with respect to thin filament -Myosin heads disengage and uncock so that the process can repeat itself = myosin heads walk along actin filaments. |
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Troponin
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-Prevents myosin from interacting with actin when muscles are at rest
-Covers actin binding sites. |
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Muscle spindles
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-Deep in skeletal muscles
-Stretch receptor -Several types of specialized skeletal muscle fibers contained in a fibrous capsule |
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Proprioreceptors
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-Component of somatic sensory system that is specialized for body sense or proprioception which informs us about how our body is positioned and moving space.
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Myotatic Reflex
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-When a muscle is pulled on it tends to contract.
-Stretch reflex |
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Monosynaptic Myotatic reflex arc
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-The Ia axon and the AMNs on which it synapses constitute this
-One synapse separates the primary sensory input from the motor neuron input. |
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Intrafusal fibers
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-Contained within muscle spindle
-Modified skeletal muscle fibers in fibrous capsule |
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Extrafusal fibers
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-Outside spindle, and form bulk of muscle
-receive motor innervation by another type of lower motor neuron called a gamma motor neuron. |
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Gamma Motor Neurons
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-Innervate extrafusal fibers at 2 ends of muscle spindle
-Causes a contraction of two poles of the spindle, thereby pulling on the noncontractile equatorial region and keeping the Ia axons active. |
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Gamma Loop
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Gamma Motor Neuron->intrafusal muscle fiber->Ia afferent axon->alpha motor neuron->extrafusal muscle fibers
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Golgi tendon organ
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-Sensor in skeletal muscle
-acts like a strain gauge -Monitors muscle tension or force of contraction -In series (not in parallel) |
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Reciprocal inhibition
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-the contraction of one set of muscles accompanied by the relation of the antagonist muscles. (Walking)
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Crossed extensor reflex
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-activation of extensor muscles and the inhibition of flexors on the opposite side
-stepping on tack |
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Central pattern generators
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-Rhythmic motor activity
e.g. walking |