Brain cells make up the
functional tissue of the brain. The rest of the brain tissue is structural or connective called the
stroma which includes
blood vessel
The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away ...
s. The two main types of cells in the
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a ve ...
are
neuron
A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. ...
s, also known as nerve cells, and
glial cell
Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cells in the central nervous system (brain and spinal cord) and the peripheral nervous system that do not produce electrical impulses. They maintain homeostasis, form myel ...
s also known as neuroglia.
Neurons are the
excitable cells of the brain that function by communicating with other neurons and
interneurons (via
synapses), in
neural circuits and
larger brain networks. The two main neuronal classes in the
cerebral cortex
The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consistin ...
are excitatory projection neurons, and inhibitory interneurons; around 70-80 per cent are neurons, and 20-30 per cent inhibitory interneurons.
Neurons are often grouped into a cluster known as a
nucleus where they usually have roughly similar connections and functions.
Nuclei are connected to other nuclei by
tracts of
white matter
White matter refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distributi ...
.
Glia are the supporting cells of the neurons and have many functions not all of which are clearly understood, but include providing support and nutrients to the neurons. Glia are grouped into
macroglia of
astrocyte
Astrocytes (from Ancient Greek , , "star" + , , "cavity", "cell"), also known collectively as astroglia, are characteristic star-shaped glial cells in the brain and spinal cord. They perform many functions, including biochemical control of e ...
s,
ependymal cell
The ependyma is the thin neuroepithelial ( simple columnar ciliated epithelium) lining of the ventricular system of the brain and the central canal of the spinal cord. The ependyma is one of the four types of neuroglia in the central nervous syst ...
s, and
oligodendrocyte
Oligodendrocytes (), or oligodendroglia, are a type of neuroglia whose main functions are to provide support and insulation to axons in the central nervous system of jawed vertebrates, equivalent to the function performed by Schwann cells in the ...
s, and much small
microglia. Astrocytes are seen to be capable of communication with neurons involving a signalling process similar to
neurotransmission
Neurotransmission (Latin: ''transmissio'' "passage, crossing" from ''transmittere'' "send, let through") is the process by which signaling molecules called neurotransmitters are released by the axon terminal of a neuron (the presynaptic neuron), ...
called
gliotransmission.
Cell types
Brain cell types are the functional
neuron
A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. ...
s, and supporting
glia
Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cells in the central nervous system (brain and spinal cord) and the peripheral nervous system that do not produce electrical impulses. They maintain homeostasis, form myel ...
.
Neurons
Neurons, also called nerve cells, are the functional
electrically excitable cell
Membrane potential (also transmembrane potential or membrane voltage) is the difference in electric potential between the interior and the exterior of a biological cell. That is, there is a difference in the energy required for electric charges ...
s of the brain. They can only function in collaboration with other neurons and
interneurons in a neural circuit.
There are an estimated 100 billion neurons in the human brain.
Neurons are
polarised cells that are specialised for the conduction of
action potential
An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...
s also called nerve impulses.
They can also synthesise membrane and protein. Neurons communicate with other neurons using
neurotransmitters released from their
synapses, and they may be inhibitory, excitatory or
neuromodulatory
Neuromodulation is the physiological process by which a given neuron uses one or more chemicals to regulate diverse populations of neurons. Neuromodulators typically bind to metabotropic, G-protein coupled receptors (GPCRs) to initiate a second ...
.
Neurons may be termed by their associated neurotransmitter such as excitatory
dopaminergic neurons and inhibitory
GABAergic neurons.
Cortical interneurons only make up around a fifth of the neuronal population but they play a major role in modulating cortical activity needed for cognition and many aspects of learning and memory. Cortical interneurons vary in shape, molecular make-up, and electrophysiology; they function collectively to maintain the balance between excitation and inhibition in the cortex primarily through the use of GABA. Disruption of this balance is a common feature of neuropsychiatric disorders such as
schizophrenia
Schizophrenia is a mental disorder characterized by continuous or relapsing episodes of psychosis. Major symptoms include hallucinations (typically hearing voices), delusions, and disorganized thinking. Other symptoms include social wit ...
. A cause of the disruption can occur in
prenatal development through the
exposure to chemicals and environment.
In the
cerebral cortex
The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consistin ...
different neurons occupy the different
cortical layers and include the
pyramidal neurons and
rosehip neurons. In the
cerebellum Purkinje cell
Purkinje cells, or Purkinje neurons, are a class of GABAergic inhibitory neurons located in the cerebellum. They are named after their discoverer, Czech anatomist Jan Evangelista Purkyně, who characterized the cells in 1839.
Structure
T ...
s and interneuronal
Golgi cells
In neuroscience, Golgi cells are inhibitory interneurons found within the granular layer of the cerebellum. They were first identified as inhibitory in 1964.
It was also the first example of an inhibitory feedback network, where the inhibitory ...
predominate.
Glia
Glial cells are the supporting cells of the neurons.
The three types of glial cells are
astrocyte
Astrocytes (from Ancient Greek , , "star" + , , "cavity", "cell"), also known collectively as astroglia, are characteristic star-shaped glial cells in the brain and spinal cord. They perform many functions, including biochemical control of e ...
s,
oligodendrocyte
Oligodendrocytes (), or oligodendroglia, are a type of neuroglia whose main functions are to provide support and insulation to axons in the central nervous system of jawed vertebrates, equivalent to the function performed by Schwann cells in the ...
s, and
ependymal cell
The ependyma is the thin neuroepithelial ( simple columnar ciliated epithelium) lining of the ventricular system of the brain and the central canal of the spinal cord. The ependyma is one of the four types of neuroglia in the central nervous syst ...
s, known collectively as
macroglia, and the smaller
scavenger cells known as
microglia. Glial stem cells are found in all parts of the adult brain.
Glial cells greatly outnumber neurons and apart from their supporting role to neurons, glia – astrocytes in particular have been acknowledged as being able to communicate with neurons involving a signalling process similar to
neurotransmission
Neurotransmission (Latin: ''transmissio'' "passage, crossing" from ''transmittere'' "send, let through") is the process by which signaling molecules called neurotransmitters are released by the axon terminal of a neuron (the presynaptic neuron), ...
called
gliotransmission.
They cannot produce an
action potential
An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...
as generated by a neuron but in their large numbers they can produce chemicals expressing excitability that exert an influence on neural circuitry.
The star-like shape of the astrocyte allows contact with a great many synapses.
References
Central nervous system neurons
Glial cells
Neurons
{{Nervous tissue