In neuroscience

Neuroscience

Neuroscience is the scientific study of the nervous system. Traditionally, neuroscience has been seen as a branch of biology. However, it is currently an interdisciplinary science that collaborates with other fields such as chemistry, computer science, engineering, linguistics, mathematics,...

, granule cells refer to tiny neurons (a type of cell

Cell (biology)

The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

) that are around 10 micrometres in diameter. Granule cells are found within the granular layer of the cerebellum

Cerebellum

The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...

 (which is also known as layer 3, the inner most layer of cerebellar cortex with the middle layer being the Purkinje cell layer and the outermost being the Molecular layer), the dentate gyrus

Dentate gyrus

The dentate gyrus is part of the hippocampal formation. It is thought to contribute to new memories as well as other functional roles. It is notable as being one of a select few brain structures currently known to have high rates of neurogenesis in adult rats, .The dentate gyrus cells receive...

 of the hippocampus

Hippocampus

The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...

, the superficial layer of the dorsal cochlear nucleus

Dorsal cochlear nucleus

The dorsal cochlear nucleus , is a cortex-like structure on the dorso-lateral surface of the brainstem...

, and in the olfactory bulb

Olfactory bulb

The olfactory bulb is a structure of the vertebrate forebrain involved in olfaction, the perception of odors.-Anatomy:In most vertebrates, the olfactory bulb is the most rostral part of the brain. In humans, however, the olfactory bulb is on the inferior side of the brain...

.

Granule cells in different brain regions are both functionally and anatomically diverse: the main thing they have in common is smallness. For instance, olfactory bulb granule cells are GABA

Gabâ

Gabâ or gabaa, for the people in many parts of the Philippines), is the concept of a non-human and non-divine, imminent retribution. A sort of negative karma, it is generally seen as an evil effect on a person because of their wrongdoings or transgressions...

ergic and axonless, while granule cells in the dentate gyrus have glutamatergic projection axon

Axon

An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....

s. These two populations of granule cells are also the only major neuronal populations that undergo adult neurogenesis

Neurogenesis

Neurogenesis is the process by which neurons are generated from neural stem and progenitor cells. Most active during pre-natal development, neurogenesis is responsible for populating the growing brain with neurons. Recently neurogenesis was shown to continue in several small parts of the brain of...

, while cerebellar and cortical granule cells do not.

Cerebellar granule cell

Granule cell (cerebellum)

Granule cells of the cerebellum are among the smallest neurons in the brain. Cerebellar granule cells are also easily the most numerous neurons in the brain: in humans, estimates of their total number average around 50 billion, which means that they constitute about 3/4 of the...

s account for nearly half of the neuron

Neuron

A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...

s in the central nervous system

Central nervous system

The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

. Granule cells receive excitatory input from mossy fiber

Mossy fiber (cerebellum)

Mossy fibers are one of the major inputs to cerebellum. There are many sources of this pathway, the largest of which is the cerebral cortex, which sends input to the cerebellum via the pontocerebellar pathway. Other contributors include the vestibular nerve and nuclei, the spinal cord, the...

s originating from pontine

Pons

The pons is a structure located on the brain stem, named after the Latin word for "bridge" or the 16th-century Italian anatomist and surgeon Costanzo Varolio . It is superior to the medulla oblongata, inferior to the midbrain, and ventral to the cerebellum. In humans and other bipeds this means it...

 nuclei

Nucleus (neuroanatomy)

In neuroanatomy, a nucleus is a brain structure consisting of a relatively compact cluster of neurons. It is one of the two most common forms of nerve cell organization, the other being layered structures such as the cerebral cortex or cerebellar cortex. In anatomical sections, a nucleus shows up...

. Cerebellar granule cells send parallel fiber

Parallel fiber

Parallel fibers arise from granule cells in the cerebellar cortex. They form excitatory synapses onto the dendrites of Purkinje cells ....

s up through the Purkinje layer into the molecular layer where they branch out and spread through Purkinje cell

Purkinje cell

For the cells of the electrical conduction system of the heart, see Purkinje fibersPurkinje cells, or Purkinje neurons , are a class of GABAergic neurons located in the cerebellar cortex...

 dendritic

Dendrite

Dendrites are the branched projections of a neuron that act to conduct the electrochemical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project...

 arbors. These parallel fibers form thousands of excitatory Granule-cell-Purkinje-cell synapse

Granule-cell-Purkinje-cell synapse

Granule-cell–Purkinje-cell synapses or gcPc synapses are the junctions that form the synapse in the cerebellum between granule cells and Purkinje cells. These synapses are thought to be a storage site for the information that is required for motor coordination and their misfunctioning is involved...

s onto the intermediate and distal dendrites of Purkinje cells using glutamate as a neurotransmitter.

Layer 4 granule cells of the cerebral cortex receive driving inputs from thalamus

Thalamus

The thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...

and convey driving inputs largely to supragranular layers 2-3, but also to infragranular layers of the cerebral cortex.