motor 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.