alpha motor neuron

Examples of alpha motor neuron in the following topics:

• 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.

• Spinal Reflexes

  • This increases alpha motor neuron activity, causing the muscle fibers to contract and thus resist the stretching.
  • There, they synapse with interneurons, which in turn, excite or inhibit alpha motor neurons to the muscles of the contralateral limb.
  • It is polysynaptic, and causes the stimulation of sensory, association, and motor neurons.
  • The sensory neuron then synapses with interneurons that connect to motor neurons.
  • Some motor neurons send inhibitory impulses to the extensors so flexion is not inhibited—this is referred to as reciprocal innervation.

• Proprioceptive Sensations

  • They convey length information to the central nervous system via sensory neurons.
  • The Golgi organ should not be confused with the Golgi apparatus—an organelle in the eukaryotic cell—or the Golgi stain, which is a histologic stain for neuron cell bodies.
  • Although muscle tension is increasing during the contraction, alpha motor neurons in the spinal cord that supply the muscle are inhibited.
  • Mammalian muscle spindle showing typical position in a muscle (left), neuronal connections in spinal cord (middle), and expanded schematic (right).
  • The spindle is a stretch receptor with its own motor supply consisting of several intrafusal muscle fibers.

• 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.

• 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.

• 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.

• 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.

• 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

• 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.

• Classification of Nerves

  • These classifications apply to both sensory and motor fibers.
  • The A group is further subdivided into four types (A-alpha, A-beta, A-delta, and A-gamma fibers) based on the information carried by the fibers and the tissues they innervate.
  • A-alpha fibers are the primary receptors of the muscle spindle and golgi tendon organ.
  • A-gamma fibers are typically motor neurons that control the intrinsic activation of the muscle spindle.
  • Demonstrates the faster propagation of an action potential in myelinated neurons than that of unmyelinated neurons.