Part 4 Motor Functions of the Nervous system I Motor Unit and final common pathway
Part 4 Motor Functions of the Nervous System I Motor Unit and Final Common Pathway
Ventra root Ventral Lower he orn Mixed motor spinal Muscle neurons nerve fib er
1. Motor unit
1. Motor Unit
Alpha motor neuron every striated muscle has encapsulated Gamma moto muscle fibers neuron scattered throughout the muscle called muscle spindles Extrafusal muscle fibers Extrafusal and muscle fibers intrafusal fibers
•Every striated muscle has encapsulated muscle fibers scattered throughout the muscle called muscle spindles. •Extrafusal and intrafusal fibers
Alpha motor neuron The extrafusal muscle fibers are innervated by alpha motor Gamma motor neuron neuron The intrafusal muscle fibers are innervated by gamma motor Extrafusal neurons muscle fibers Intrafusal muscle fibers
The extrafusal muscle fibers are innervated by Alpha motor neuron The intrafusal muscle fibers are innervated by Gamma motor neurons
Motor units o A motor unit is a single motor neuron(a motor) and all(extrafusal)muscle fibers it innervates o Motor units are the physiological functional unit in muscle(not the cell) All cells in motor unit contract synchronously
Motor units ⚫ A motor unit is a single motor neuron (a motor) and all (extrafusal) muscle fibers it innervates ⚫ Motor units are the physiological functional unit in muscle (not the cell) ◼All cells in motor unit contract synchronously
Motor units and innervation ratio (A) (B) Motor neuron in spinal cord Innervation ratio Fibers per motor neuron Extraocular muscle 3: 1 Gastrocnemius 2000: 1 Muscle fibers innervated by a single motor neuron PUe织g164 o 2001 Sinauer Associates, Inc
Motor units and innervation ratio Purves Fig. 16.4 Innervation ratio Fibers per motor neuron Extraocular muscle 3:1 Gastrocnemius 2000:1
(B) Motor neuron in spinal cord · The muscle cells of a motor unit are not grouped but are interspersed among cells from other motor units Muscle fibers innervated by · The coordinated a single motor movement needs neuron the activation of several motors
•The muscle cells of a motor unit are not grouped, but are interspersed among cells from other motor units •The coordinated movement needs the activation of several motors
organization of motor subsystems DESCENDING SYSTEMS upper Motor Neurons Motor Cortex BASAL GANGLIA Planning, initiating, and Gating proper initiation directing voluntary movements of movement Brainstem Centers CEREBELLUM Basic movements and Sensory motor postural control coordination Local circuit neurons Re Motor neuron pools flex coordination Lower Motor Neurons SPINAL CORD AND BRAINSTEM CIRCUITS SKELETAL MUSCLES o 2001 Sinauer Associates, Inc
organization of motor subsystems
Input from spinal Sensory input interneurons from muscle spindles Input from upper motor neurons in the brain Alpha motor neuron
