Pyramidal cell

Pyramidal cells, or pyramidal neurons, are a type of multipolar neuron found in areas of the brain including the cerebral cortex, the hippocampus, and the amygdala. Pyramidal cells are the primary excitation units of the mammalian prefrontal cortex and the corticospinal tract. One of the main structural features of the pyramidal neuron is the conic shaped soma, or cell body, after which the neuron is named. Other key structural features of the pyramidal cell are a single axon, a large apical dendrite, multiple basal dendrites, and the presence of dendritic spines.^[1]

Pyramidal neurons are also one of two cell types where the characteristicsign, Negri bodies, are found in post-mortem rabies infection.^[2] Pyramidal neurons were first discovered and studied by Santiago Ramón y Cajal.^[3][4] Since then, studies on pyramidal neurons have focused on topics ranging from neuroplasticity to cognition.

One of the main structural features of the pyramidal neuron is the conic shaped soma, or cell body, after which the neuron is named. Other key structural features of the pyramidal cell are a single axon, a large apical dendrite, multiple basal dendrites, and the presence of dendritic spines.^[1]

The apical dendrite rises from the apex 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 and extends towards the cortical surface.^[1]

Basal dendrites arise from the base of the soma. The basal dendritic tree consists of three to five primary dendrites. As distance increases from the soma, the basal dendrites branch profusely.^[1]

Pyramidal cells are among the largest neurons in the brain. Both in humans and rodents, pyramidal cell bodies (somas) average around 20 μm in length. 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 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. Ramón y Cajal was also the first person to propose the physiological role of increasing 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, while the number increases away from it.^[4] The typical apical dendrite in a rat has at least 3,000 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 6,000.^[5]

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 (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.^[6]Transcription factors such as Ctip2 and Sox5 have been shown to contribute to the direction in which pyramidal neurons direct their axons.^[7]

Pyramidal cells in rats have been shown to undergo many rapid changes during early postnatal life. Between postnatal days 3 and 21, pyramidal cells have been shown to double the size of the soma, increase the length of the apical dendrite fivefold, and increase basal dendrite length thirteen-fold. Other changes include the lowering of the membrane's resting potential, reduction of membrane resistance, and an increase in the peak values of action potentials.^[8]

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 send and receive signals to and from many different neurons.

Pyramidal neurons, like other neurons, have numerous voltage-gated ion channels. In pyramidal cells, there is an abundance of Na⁺, Ca²⁺, and K⁺ channels in the dendrites, and some channels in the soma.^[9][10] Ion channels within pyramidal cell dendrites have different properties from the same ion channel type within the pyramidal cell soma.^[11][12] 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.^[13]

La capacidad de las neuronas piramidales para integrar información depende del número y la distribución de las entradas sinápticas que reciben. Una sola célula piramidal recibe aproximadamente 30 000 entradas excitatorias y 1700 entradas inhibitorias ( PPSI ). Las entradas excitatorias (PPSE) terminan exclusivamente en las espinas dendríticas, mientras que las entradas inhibitorias (PPSI) terminan en ^los tallos dendríticos, el soma e incluso el axón. Las neuronas piramidales pueden ser excitadas por el neurotransmisor glutamato [ ^{1 ] [ 14 ]} e inhibidas por el neurotransmisor GABA ^{[ 1 ]} .

Las neuronas piramidales se han clasificado en diferentes subclases según su respuesta de disparo a pulsos de corriente de 400 a 1000 milisegundos. Estas clasificaciones son las neuronas RSad, RSna e IB.

Las neuronas piramidales RSad, o neuronas de disparo regular adaptativas , disparan con potenciales de acción (PA) individuales , a los que sigue un postpotencial hiperpolarizante . El postpotencial aumenta de duración, lo que crea una adaptación de la frecuencia de disparo (AFD) en la neurona. ^{[ 15 ]}

Las neuronas piramidales RSna, o neuronas de disparo regular no adaptativas, disparan una serie de potenciales de acción después de un pulso. Estas neuronas no muestran signos de adaptación. ^{[ 15 ]}

Las neuronas piramidales IB, o neuronas intrínsecamente activas, responden a pulsos umbrales con una ráfaga de dos a cinco potenciales de acción rápidos. Las neuronas piramidales IB no muestran adaptación. ^{[ 15 ]}

Hay varios estudios que muestran que las propiedades morfológicas y eléctricas de las células piramidales podrían deducirse a partir de la expresión genética medida por secuenciación de células individuales . ^{[ 16 ]} Varios estudios proponen que las clasificaciones de células individuales en neuronas de ratón ^{[ 17 ]} y humanas ^{[ 18 ]} basadas en la expresión genética podrían explicar varias propiedades neuronales. Los tipos neuronales en estas clasificaciones se dividen en excitatorias, inhibitorias y cientos de subtipos correspondientes. Por ejemplo, las células piramidales de la capa 2-3 en humanos se clasifican como tipo FREM3 ^{[ 16 ]} y a menudo tienen una gran cantidad de corriente Ih ^{[ 19 ]} generada por el canal HCN .

Pyramidal neurons are the primary neural cell type in the corticospinal tract. 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.^[20]

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. Pyramidal cells within the prefrontal cortex appear to be responsible for processing input from the primary auditory cortex, primary somatosensory cortex, and primary visual cortex, all of which process sensory modalities.^[21] These cells might also play a critical role in complex object recognition within the visual processing areas of the cortex.^[3] Relative to other species, the larger cell size and complexity of pyramidal neurons, along with certain patterns of cellular organization and function, correlates with the evolution of human cognition.^[22]

The hippocampus's pyramidal cells are essential for certain types of memory and learning. They form synapses that aid in the integration of synaptic voltages throughout their complex dendritic trees through interactions with mossy fibers from granule cells. Since it affects the postsynaptic voltages produced by mossy fiber activation, the placement of thorny excrescences on basal and apical dendrites is important for memory formation. By enabling dynamic control of the sensitivity of CA3 pyramidal cells, this clustering of mossy fiber synapses on pyramidal cells may facilitate the initiation of somatic spikes.

The interactions between pyramidal cells and an estimated 41 mossy fiber boutons, each originating from a unique granule cell, highlight the role of these boutons in information processing and synaptic connectivity, which are essential for memory and learning. Fundamentally, mossy fiber input is received by pyramidal cells in the hippocampus which integrate synaptic voltages within their dendritic architecture. The location of prickly protrusions and the clustering of synapses influence sensitivity and contribute to the processing of information pertaining to memory and learning.^[23]

• Pyramidal tract
• Chandelier cells - innervate initial segments of pyramidal axons
• neurona de rosa mosqueta

• Pyramidal cell - Cell Centered Database
• Diagram
• Image
• Diagram (as part of slideshow)Archived 2016-11-02 at the Wayback Machine