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Pyramidal neurons (pyramidal cells) are a type of neuron
Neuron

Neurons are responsive cell in the nervous system that process and transmit information by electrochemical Signal . They are the core components of the brain, the vertebrate spinal cord, the invertebrate ventral nerve cord, and the peripheral nerves....
 found in areas of the brain including cerebral cortex
Cerebral cortex

The cerebral cortex is a structure within the brain that plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness....
, the hippocampus
Hippocampus

The hippocampus is a brain structure located inside the medial temporal lobe of the cerebral cortex, and therefore is part of the telencephalon ....
, and in the amygdala
Amygdala

The are almond-shaped groups of neurons located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotions, the amygdalae are considered part of the limbic system....
. Pyramidal neurons are the primary excitation units of the mammalian prefrontal cortex
Prefrontal cortex

The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the primary motor cortex and premotor cortex areas....
 and the corticospinal tract
Corticospinal tract

The corticospinal or pyramidal tract is a collection of axons that travel between the cerebral cortex of the brain and the spinal cord.The corticospinal tract mostly contains motor axons....
. Pyramidal neurons were first discovered and studied by Santiago Ramón y Cajal
Santiago Ramón y Cajal

Santiago Ram?n y Cajal was a Spanish people histology, physician, pathologist and Nobel laureate. His pioneering investigations of the microscopic structure of the brain were so original and influential that he is considered by many to be the greatest neuroscientist of all time....
. Since then, studies on pyramidal neurons have focused on topics ranging from neuroplasticity
Neuroplasticity

Neuroplasticity refers to changes that occur in the organization of the brain as a result of experience. The coining of the term plasticity in regards to neuronal process is attributed to Polish neuroscientist Jerzy Konorski....
 to cognition
Cognition

Cognition is the science term for "the process of thought."Its usage varies in different ways in accord with different disciplines: For example, in psychology and cognitive science it refers to an information processing view of an individual's psychological Functionalism s....
.

Features One of the main structural features of the pyramidal neuron is the triangular shaped soma
Soma (biology)

The soma, or cyton or perikaryon, is the bulbous end of a neuron, containing the cell nucleus. The word soma is Greek language, meaning "body"; the soma of a neuron is often called the "Cell body"....
, or cell body, after which the neuron is named.






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Encyclopedia


Pyramidal neurons (pyramidal cells) are a type of neuron
Neuron

Neurons are responsive cell in the nervous system that process and transmit information by electrochemical Signal . They are the core components of the brain, the vertebrate spinal cord, the invertebrate ventral nerve cord, and the peripheral nerves....
 found in areas of the brain including cerebral cortex
Cerebral cortex

The cerebral cortex is a structure within the brain that plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness....
, the hippocampus
Hippocampus

The hippocampus is a brain structure located inside the medial temporal lobe of the cerebral cortex, and therefore is part of the telencephalon ....
, and in the amygdala
Amygdala

The are almond-shaped groups of neurons located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotions, the amygdalae are considered part of the limbic system....
. Pyramidal neurons are the primary excitation units of the mammalian prefrontal cortex
Prefrontal cortex

The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the primary motor cortex and premotor cortex areas....
 and the corticospinal tract
Corticospinal tract

The corticospinal or pyramidal tract is a collection of axons that travel between the cerebral cortex of the brain and the spinal cord.The corticospinal tract mostly contains motor axons....
. Pyramidal neurons were first discovered and studied by Santiago Ramón y Cajal
Santiago Ramón y Cajal

Santiago Ram?n y Cajal was a Spanish people histology, physician, pathologist and Nobel laureate. His pioneering investigations of the microscopic structure of the brain were so original and influential that he is considered by many to be the greatest neuroscientist of all time....
. Since then, studies on pyramidal neurons have focused on topics ranging from neuroplasticity
Neuroplasticity

Neuroplasticity refers to changes that occur in the organization of the brain as a result of experience. The coining of the term plasticity in regards to neuronal process is attributed to Polish neuroscientist Jerzy Konorski....
 to cognition
Cognition

Cognition is the science term for "the process of thought."Its usage varies in different ways in accord with different disciplines: For example, in psychology and cognitive science it refers to an information processing view of an individual's psychological Functionalism s....
.

Structure



Features

One of the main structural features of the pyramidal neuron is the triangular shaped soma
Soma (biology)

The soma, or cyton or perikaryon, is the bulbous end of a neuron, containing the cell nucleus. The word soma is Greek language, meaning "body"; the soma of a neuron is often called the "Cell body"....
, or cell body, after which the neuron is named. Other key structural features of the pyramidal cell are a single axon
Axon

An axon or nerve fiber is a long, slender projectionof a nerve cell, or neuron, that conducts action potentialaway from the neuron's cell body or soma....
, a large apical dendrite
Apical dendrite

An apical dendrite is a dendrite that emerges from the apex of a pyramidal cell. Apical dendrites are one of two primary categories of dendrites, and they distinguish the pyramidal cells from spiny stellate cells in the cortices....
, a basal dendrite
Basal dendrite

A basal dendrite is a dendrite that emerges from the base of a pyramidal cell that receives information from nearby neurons and passes it to the soma, or cell body....
, and the presence of dendritic spines.
Apical Dendrite
The apical dendrites arise from the apex
Apex

Apex may refer to:...
 of the pyramidal cell's soma. The apical dendrite is a single long thick dendrite that branches several times as distance from the soma increases.

Basal Dendrite
The basal dendrites arise from the base of the pyramidal cell's soma. The basal dendritic tree consists of three to five primary dendrites. As distance increases from the soma, the basal dendrites branch profusely.

Size


Pyramidal cells are among the largest neurons in the brain. In humans, pyramidal cell somas average from 10 to 50 micrometers in diameter, but cell body diameters up to 100 micrometers have been recorded. Pyramidal dendrites typically range in diameter from half a micrometer to several micrometers. The length of a single dendrite is usually several hundred micrometers. Due to branching, the total dendritic length of a pyramidal cell may reach several centimeters. The pyramidal cell’s axon is often even longer and extensively branched, reaching many centimeters in total length.

Dendritic Spines


Dendritic spines receive most of the excitatory impulses (EPSPs) that enter a pyramidal cell. Dendritic spines were first noted by Ramón y Cajal in 1888 by using Golgi's method
Golgi's method

Golgi's method is a nervous tissue staining technique discovered by Italy physician and scientist Camillo Golgi in 1873. It was initially named the black reaction by Golgi, but it became better known as the Golgi stain or later, Golgi method....
. Ramón y Cajal was also the first person to propose a physiological role of dendritic spines: increase the receptive surface area of the neuron. The greater the pyramidal cell's surface area, the greater the neuron's ability to process and integrate large amounts of information. Dendritic spines are absent on the soma, and the number of spines increases away from it. The typical apical dendrite in a rat has at least 3000 dendritic spines. The average human apical dendrite is approximately twice the length of a rat's, so the number of dendritic spines present on a human apical dendrite could be as high as 6000.

Growth and development


Differentiation


Pyramidal specification occurs during early development of the cerebrum. Progenitor cells are committed to the neuronal lineage in the subcortical proliferative ventricular zone (VZ) and the subventricular zone
Subventricular zone

Subventricular zone is a paired brain structure situated throughout the lateral walls of the lateral ventricles. Along with the subgranular zone of dentate gyrus, the subventricular zone serves as a source of neural stem cells in the process of adult neurogenesis....
 (SVZ). Immature pyramidal cells undergo migration to occupy the cortical plate, where they further diversify. Endocannabinoids (eCBs) are one class of molecules that have been shown to direct pyramidal cell development and axonal pathfinding. Growth factors such as Ctip2 and Sox5 have been shown to contribute to the direction in which pyramidal neurons direct their axons.

Early postnatal development


Pyramidal cells in rats have been shown to undergo many rapid changes during early postnatal
Postnatal

Postnatal is the period beginning immediately after the childbirth of a child and extending for about six weeks. The period is sometimes incorrectly called the postpartum period, which refers to the mother and, less commonly, puerperium....
 life. Between postnatal days 3 and 21, pyramidal cells have been shown to double in the size of the soma, increase in length of the apical dendrite by five fold, and increase in basal dendrite length by thirteen fold. Other changes include the lowering of the membrane’s resting potential
Resting potential

Relatively static membrane potential of quiescent cells is called resting membrane potential , as opposed to the specific dynamic electrochemical phenomenona called action potential and graded membrane potential....
, reduction of membrane resistance, and in increase in the peak values of action potential
Action potential

An action potential is a self-regenerating wave of electrochemical activity that allows nerve cells to carry a signal over a distance. It is the primary electrical signal generated by nerve cells, and arises from changes in the permeability of the nerve cell's axonal Cell membranes to specific ions....
s.

Signaling


Like dendrites in most other neurons, the dendrites are generally the input areas of the neuron, while the axon is the neuron’s output. Both axons and dendrites are highly branched. The large amount of branching allows the neuron to receive and send signals to many different neurons.

Pyramidal neurons, like other neurons, have numerous voltage-gated ion channels
Voltage-gated ion channel

Voltage-gated ion channels are a class of Transmembrane protein ion channels that are activated by changes in electrical potential difference near the channel; these types of ion channels are especially critical in neurons, but are common in many types of cell ....
. In pyramidal cells, there are an abundance of Na+, Ca2+, and K+ channels in the dendrites, and some channels in the soma. Ion channels within pyramidal cell dendrites have different properties from the same ion channel type within the pyramidal cell soma. Voltage-gated Ca2+ channels in pyramidal cell dendrites are activated by subthreshold EPSPs and by back-propagating action potentials. The extent of back-propagation of action potentials within pyramidal dendrites depends upon the K+ channels. K+ channels in pyramidal cell dendrites provide a mechanism for controlling the amplitude of action potentials.

The ability of pyramidal neurons to integrate information depends on the number and distribution of the synaptic inputs they receive. A single pyramidal cell receives about 30,000 excitatory inputs and 1700 inhibitory (IPSPs) inputs. Excitatory (EPSPs) inputs terminate exclusively on the dendritic spines, while inhibitory (IPSPs) inputs terminate on dendritic shafts, the soma, and even the axon. Pyramidal neurons use glutamate as their excitatory neurotransmitter
Neurotransmitter

Neurotransmitters are chemistry which relay, amplify and modulate signals between a neuron and another cell . Neurotransmitters are packaged into vesicles that cluster beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to receptors in the membrane on the postsynaptic side of...
, and GABA
Gabâ

Gab? or gabaa, for the Cebuano people , is the concept of a non-human and non-divine, imminent Retributive justice. A sort of negative karma, it is generally seen as an evil effect on a person because of their wrongdoings or transgressions....
 as their inhibitory neurotransmitter.

Firing Classification of Pyramidal Neurons

Pyramidal neurons have been classified into different subclasses based upon their firing responses to 400-1000 millisecond current pulses. These classification are RSad, RSna, and IB neurons.
RSad Pyramidal Neurons
RSad pyramidal neurons, or adapting regular spiking neurons, fire with individual action potential
Action potential

An action potential is a self-regenerating wave of electrochemical activity that allows nerve cells to carry a signal over a distance. It is the primary electrical signal generated by nerve cells, and arises from changes in the permeability of the nerve cell's axonal Cell membranes to specific ions....
s (APs), which are followed by a hyperpolarizing
Hyperpolarization (biology)

Hyperpolarization is any change in a cell membrane potential that makes it more polarized. That is, hyperpolarization is an increase in the absolute value of a cell's membrane potential....
 afterpotential
Hyperpolarization (biology)

Hyperpolarization is any change in a cell membrane potential that makes it more polarized. That is, hyperpolarization is an increase in the absolute value of a cell's membrane potential....
. The afterpotential increases in duration which creates spike frequency
Action potential

An action potential is a self-regenerating wave of electrochemical activity that allows nerve cells to carry a signal over a distance. It is the primary electrical signal generated by nerve cells, and arises from changes in the permeability of the nerve cell's axonal Cell membranes to specific ions....
 adaptation
Neural adaptation

Neural adaptation or sensory adaptation is a change over time in the responsiveness of the sensory system to a constant Stimulus . It is usually perception as a change in the stimulus....
 (SFA) in the neuron.

RSna Pyramidal Neurons
RSna pyramidal neurons, or non-adapting regular spiking neurons, fire a train of action potentials after a pulse. These neurons fail to show any signs of adaptation.
IB Pyramidal Neurons
IB pyramidal neurons, or intrinsically bursting neurons, respond to threshold
Threshold

Threshold may refer to:...
 pulses with a burst of two to five rapid action potentials. IB pyramidal neurons show no adaptation.

Function


Corticospinal tract


Pyramidal neurons are the primary neural cell type in the corticospinal tract
Corticospinal tract

The corticospinal or pyramidal tract is a collection of axons that travel between the cerebral cortex of the brain and the spinal cord.The corticospinal tract mostly contains motor axons....
. Normal motor control depends on the development of connections between the axons in the corticospinal tract and the spinal cord. Pyramidal cell axons follow cues such as growth factors to make specific connections. With proper connections, pyramidal cells take part in the circuitry responsible for vision guided motor function.

Cognition


Pyramidal neurons in the prefrontal cortex are implicated in cognitive ability. In mammals, the complexity of pyramidal cells increases from posterior to anterior brain regions. The degree of complexity of pyramidal neurons is likely linked to the cognitive capabilities of different anthropoid species. Because the prefrontal cortex receives inputs from areas of the brain that are involved in processing all the sensory modalities, pyramidal cells within the prefrontal cortex may process many different types of inputs. Pyramidal cells may play a critical role in complex object recognition within the visual processing areas of the cortex.

See also


  • Cerebral cortex
    Cerebral cortex

    The cerebral cortex is a structure within the brain that plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness....
  • Pyramidal tract


External links