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In neuroscience, the axolemma (from Greek lemma 'membrane, envelope', and 'axo-' from axon [1]) is the cell membrane of an axon, [1] the branch of a neuron through which signals (action potentials) are transmitted. The axolemma is a three-layered, bilipid membrane. Under standard electron microscope preparations, the structure is approximately ...
A motor neuron (or motoneuron or efferent neuron [1]) is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectly control effector organs, mainly muscles and glands. [2]
Neurilemma (also known as neurolemma, sheath of Schwann, or Schwann's sheath) [1] is the outermost nucleated cytoplasmic layer of Schwann cells (also called neurilemmocytes) that surrounds the axon of the neuron. It forms the outermost layer of the nerve fiber in the peripheral nervous system. [2]
Photomicrograph of Nissl bodies (two are indicated by arrows) in the cytoplasm of motor neurons in the anterior horn of the spinal cord; cresyl violet stain (purple) along with a luxol fast blue stain for myelin. Scale bar = 30 microns (0.03mm). Drawing of a motor neuron from the ventral horn of the medulla spinals of a rabbit.
The motor part of the spindle is provided by motor neurons: up to a dozen gamma motor neurons also known as fusimotor neurons. [4] These activate the muscle fibres within the spindle. Gamma motor neurons supply only muscle fibres within the spindle, whereas beta motor neurons supply muscle fibres both within and outside of the spindle.
A neuromuscular junction (or myoneural junction) is a chemical synapse between a motor neuron and a muscle fiber. [1] It allows the motor neuron to transmit a signal to the muscle fiber, causing muscle contraction. [2] Muscles require innervation to function—and even just to maintain muscle tone, avoiding atrophy.
The muscle fibers belonging to one motor unit can be spread throughout part, or most of the entire muscle, depending on the number of fibers and size of the muscle. [2] [3] When a motor neuron is activated, all of the muscle fibers innervated by the motor neuron are stimulated and contract. The activation of one motor neuron will result in a ...
When a reflex arc in an animal consists of only one sensory neuron and one motor neuron, it is defined as monosynaptic, referring to the presence of a single chemical synapse. In the case of peripheral muscle reflexes (patellar reflex, achilles reflex), brief stimulation to the muscle spindle results in contraction of the agonist or effector muscle