motor neuron

(noun)

A neuron located in the central nervous system that projects its axon outside the CNS and directly or indirectly control muscles.

Related Terms

  • spinal polio
  • paralysis
  • poliomyelitis
  • reflex arc
  • sensory neuron

Examples of motor neuron in the following topics:

  • Organization of Motor Neuron Pathways

    • There are upper and lower motor neurons in the corticospinal tract.
    • These are the upper motor neurons of the corticospinal tract.
    • These axons also synapse with lower motor neurons in the ventral horns.
    • The midbrain nuclei include four motor tracts that send upper motor neuronal axons down the spinal cord to lower motor neurons.
    • The lateral tract contains upper motor neuronal axons that synapse on the dorsal lateral lower motor neurons, which are involved in distal limb control.
  • Introducing the Neuron

    • There are three primary types of neuron: sensory neurons, motor neurons, and interneurons.
    • There are three major types of neurons: sensory neurons, motor neurons, and interneurons.
    • The structure of motor neurons is multipolar, meaning each cell contains a single axon and multiple dendrites.
    • Located in the CNS, they operate locally, meaning their axons connect only with nearby sensory or motor neurons.
    • Like motor neurons, they are multipolar in structure.
  • Organization of the Nervous System

    • The peripheral nervous system (PNS) consists of sensory neurons, motor neurons, and neurons that communicate either between subdivisions of the PNS or connect the PNS to the CNS .
    • The nervous system has three broad functions: sensory input, information processing, and motor output .
    • After information is processed, signals return to the PNS by way of motor neurons to muscles and glands, which respond with a motor output.
    • Central neurons, which in humans greatly outnumber the sensory and motor neurons, make all of their input and output connections with other neurons.
    • Electrical impulses travel along the axon of a neuron.
  • Sensory-Somatic Nervous System

    • The sensory-somatic nervous system is composed of cranial and spinal nerves and contains both sensory and motor neurons.
    • Motor neurons transmit messages about desired movement from the CNS to the muscles, causing them to contract.
    • Unlike the autonomic nervous system, which has two synapses between the CNS and the target organ, sensory and motor neurons have only one synapse: one ending of the neuron is at the organ and the other directly contacts a CNS neuron.
    • Motor neurons have cell bodies in the ventral gray matter of the spinal cord that project to muscle through the ventral root.
    • The cell bodies of motor neurons are found in the ventral portion of the gray matter of the spinal cord.
  • Overview of Motor Integration

    • A motor unit is comprised of a single alpha-motor neuron and all the muscle fibers it innervates.
    • A motor unit consists of a single alpha motor neuron and all of the corresponding muscle fibers it innervates; all of these fibers will be of the same type (either fast twitch or slow twitch).
    • The activation of more motor neurons will result in more muscle fibers being activated, and therefore a stronger muscle contraction.
    • Motor unit recruitment is a measure of how many motor neurons are activated in a particular muscle.
    • These small motor units may contain only 10 fibers per motor unit.
  • Classification of Neurons

    • Afferent neurons convey information from tissues and organs into the central nervous system (e.g. sensory neurons).
    • Efferent neurons transmit signals from the central nervous system to the effector cells (e.g. motor neurons).
    • Another way in which neurons are classified is by their effect on target neurons.
    • A neuron releases a neurotransmitter that binds to chemical receptors on the target neuron .
    • Other types of neurons include excitatory motor neurons in the spinal cord that release acetylcholine, and inhibitory spinal neurons that release glycine.
  • Motor Units

    • The motor unit is the functional unit of muscle contraction and includes the motor nerve fiber and the muscle fibers it innervates.
    • A motor unit consists of the motor neuron and the grouping of muscle fibers innervated by the neuron.
    • Thus, small motor units can exercise greater precision of movement compared to larger motor units.
    • Groups of motor units are innervated to coordinate contraction of a whole muscle and generate appropriate movement; all of the motor units within a muscle are considered a motor pool.
    • These multiple motor units of different sizes within a motor pool allow for very fine control of force either spatially or temporally.
  • Structural Diversity of Neurons

    • A typical neuron consists of a cell body and neuronal processes such as dendrites and axon.
    • These extensions are the conducting region of the neuron.
    • The cell body is the major biosynthetic center of the neuron.
    • Motor neurons receive signals from the brain and spinal cord to initiate muscle contractions and affect glands.
    • 1: Unipolar neuron, 2: Bipolar neuron, 3: Multipolar neuron, 4: Pseudounipolar neuron
  • Neurons

    • While some neurons have no dendrites, other types of neurons have multiple dendrites.
    • Neurons usually have one or two axons, but some neurons, like amacrine cells in the retina, do not contain any axons.
    • This insulation is important as the axon from a human motor neuron can be as long as a meter: from the base of the spine to the toes.
    • Dendrites from a single neuron may receive synaptic contact from many other neurons.
    • Multipolar neurons are the most common type of neuron.
  • Motor Areas

    • The motor areas of the brain are located in both hemispheres of the cortex.
    • The right half of the motor area controls the left side of the body, and the left half of the motor area controls the right side of the body.
    • Premotor cortex: Located anterior to the primary motor cortex and responsible for some aspects of motor control.
    • The majority of neurons in the motor cortex project to the spinal cord synapse on interneuron circuitry in the spinal cord.
    • $$Topography of the human motor cortex, including the premotor cortex, SMA, primary motor cortex, primary somatosensory cortex, and posterior parietal cortex.
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