Acetylcholine is used as a neurotransmitter. Lower motor neurons originate in the brainstem ( cranial nerve nuclei) and the spinal cord (anterior horn) and project to innervate muscles and glands throughout the body.Upper motor neurons travel down specific pathways, including the pyramidal, extrapyramidal, rubrospinal, tectospinal and reticulospinal tracts. Glutamate is used as a neurotransmitter. Upper motor neurons originate primarily in the cerebral cortex (primary motor cortex) and extend towards the brainstem or spinal cord, where they synapse.Each type of motor neuron utilizes different neurotransmitters to relay their signals. Motor neurons are divided into either upper or lower motor neurons. Their nerve fibers are considered to be the longest in the human body. Motor neurons are the most common structure for neurons. Häusser), Oxford University Press.Motor neurons, also known as efferent neurons, are nerve cells responsible for carrying central nervous system signals towards muscles to cause voluntary or involuntary movement through the innervation of effector muscles and glands. Here are some dimensions of simple dendritic spines as determined through serial electron microscopy.įiala J.C., Harris K. Electron microscopy must be used to determine the geometry of spines. This makes them difficult to study through light microscopy. Simple spines are very small, often less than 1 micron in diameter. Therefore, spines may play an important role in learning and memory. For these cells, more than 90% of their excitatory synapses occur on dendritic spines. These spines are frequent on the dendrites of the principal cells of most brain regions, notably on the pyramidal cells of cerebral cortex and the Purkinje cells of the cerebellar cortex. Perhaps the most common synaptic specialization of dendrites is that which Spanish anatomist Ramon y Cajal referred to as 'espinas', since they resembled the thorns on a flower stem.

Right: Reconstruction from serial electron microscopy. Spiny dendrites from hippocampal pyramidal neuron. Here are some examples of synaptic specializations of dendrites. These structures are often sites of synaptic contact and therefore can be referred to as synaptic specializations. Other neurons exhibit enlargements, protrusions, or other structural specializations along dendrites, or frequently, at the ends of dendrites. Here are some examples of patterns of dendritic arborization.ĭendrites of some neurons are smooth, tapered processes, such as in motor neurons of the spinal cord. The arbor formed by the dendrites of a neuron often has a characteristic shape as determined by the spatial domains into which the dendrites ramify. Thus, the dendrites of a neuron provide a surface for receiving synaptic inputs from other neurons. These synapses can occur on the cell bodies or the axons of other neurons, but most frequently they occur on dendrites. Axons typically make synapses with other neurons through specialized enlargements near their terminals. Neurons communicate through specialized junctions called synapses. Here are the dimensions of dendrites for a few types of neurons. In contrast, axons can extend to distant targets, more than a meter away in some instances.ĭendrites are rarely more than about a millimeter long and often much shorter. The dendrites branch and terminate in the vicinity of the cell body. A neuron typically has many dendrites and one axon.

Dendrite labeled