Neurons in the shape of a pyramid
Pyramidal neurons are neural cells found in nearly all mammals’ cerebral cortexes, as well as in birds, fish, and reptiles. They are also common in subcortical structures like the hippocampus and the amygdala. They got their name due to their specific teardrop or rounded pyramid shape.
The structure of these cells looks like a tree. The body of these neurons is called soma and resembles the tree base. Multiple extensions called dendrites grow from the soma, just like roots. On the other end, a singular long extension called an axon resides like a tall tree trunk with little branches at the top. The dendrites, covered in small protrusions called dendritic spines, receive signals from other neurons. On the other hand, the axon sends signals to other neurons. Such a structure allows pyramidal neurons to form complex communication networks within the brain like a forest, allowing us to learn and create memories (1, 2).
The brain has two prominent families of neurons. First are excitatory neurons, which release the neurotransmitter glutamate. Excitatory means that they stimulate other neurons to transmit electrical signals. The second type consists of inhibitory neurons, which release gamma-aminobutyric acid (GABA). Their function is to calm or suppress the activity of other neurons. Pyramidal neurons are the most numerous members of the excitatory family in the brain areas. They comprise of about 70% of all neurons in the mammalian cerebral cortex (3).
Synaptic plasticity — how the brain stores information and creates memories
The most impressive structures of pyramidal neurons are the dendritic spines. They are the primary synaptic input sites, meaning they receive the most signals from other neurons. Each spine contains a synapse. It is a tiny gap where neurotransmitters are released to propagate the neural signal. The number and shape of these spines can change in response to learning and making memories. This phenomenon is known as synaptic plasticity (4).
Pyramidal neurons, especially the hippocampal ones, are crucial in creating and storing memories. If the experience is significant or repeated, the connections between these neurons strengthen in a process known as long-term potentiation. Such link strengthening makes it easier for signals to pass along these pathways in the future, forming the basis of memory (5, 6). New dendritic spines might also be created when a memory is formed, or existing ones might grow larger to strengthen the synaptic connection (7).
The Long-Distance Messengers of the Nervous System
Like many other neurons, pyramidal neurons transform synaptic inputs into a patterned output of action potentials. What sets them apart is their sheer number of so-called projection neurons. Pyramidal neurons often project their axons for long distances, sometimes outside the brain. The corticospinal pyramidal neurons, known as Betz cells, are one of the longest neurons in the human body (8). These neurons start in the brain’s motor cortex and send their axons down the spinal cord, which makes them over a meter long in tall individuals. These neurons carry motor commands from the brain to the body’s muscles, and their long axons allow for direct, rapid communication between the brain and the spinal cord (9, 10).
While pyramidal neurons are long, most of the neuron’s length comes from the axon. The soma, where the nucleus and most of the neuron’s other organelles are located, is much smaller, typically around 20–30 micrometers in diameter for pyramidal neurons. The dendrites also extend much shorter distances than the axon, typically only a few millimeters (1, 11).
Pyramidal Neurons in Disease
What if pyramidal neurons do not work as they should? Faulty pyramidal cells are a cause of major brain disorders. For example, in epilepsy, the hyperexcitability of pyramidal neurons starts and propagates epileptic seizures. Pyramidal neurons can generate rapid electrical activity bursts, and as they spread through neural networks, they lead to the uncontrolled firing patterns characteristic of epilepsy (12).
In the case of Alzheimer’s disease, the accumulation of β-amyloid plaques and neurofibrillary tangles causes the death of pyramidal neurons in the cerebral cortex and hippocampus. It can result in synaptic loss and cognitive decline, which is common in patients with Alzheimer’s (13).
In schizophrenia, a chronic psychiatric disorder characterized by hallucinations and delusions, there are visible changes in the dendritic spines of pyramidal neurons. These changes can disrupt the communication between neurons and contribute to the disorder’s symptoms (14).
In these diseases, pyramidal neurons play a unique yet crucial role in disease pathology. Understanding these neurons’ mechanisms can offer valuable insights into treating and managing these neurological disorders.
Recognizing and appreciating the labs working in this space
- State Key Laboratory of Membrane Biology, School of Life Sciences, Peking-Tsinghua Center for Life Sciences, and PKU-IDG/McGovern Institute, Peking University, China, https://www.med.tsinghua.edu.cn/en/info/1334/1263.htm
- Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway, https://www.med.uio.no/imb/english/people/aca/huah/index.html
- Department of Neuroscience and Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas, https://www.bcm.edu/research/baylor-research/faculty-recognition/howard-hughes-medical-institute-investigators
- Institut de Neurobiologie de la Méditerranée (INMED) INSERM U1249, Aix-Marseille University, Marseille, France, https://www.inmed.fr
- Oxford Centre for Computational Neuroscience, Oxford, UK, https://www.oxcns.org/
- Laboratory of Systems Neuroscience, National Institute of Mental Health, Bethesda, MD, https://www.nimh.nih.gov/research/research-conducted-at-nimh/research-areas/clinics-and-labs/lbc
References:
- Spruston N. Pyramidal neurons: dendritic structure and synaptic integration. Nature Reviews Neuroscience. 2008;9(3):206–21.
- Bekkers JM. Pyramidal neurons. Current biology. 2011;21(24):R975.
- Wang Y, Ye M, Kuang X, Li Y, Hu S. A simplified morphological classification scheme for pyramidal cells in six layers of primary somatosensory cortex of juvenile rats. IBRO reports. 2018;5:74–90.
- Wang M, Yu X. Experience-dependent structural plasticity of pyramidal neurons in the developing sensory cortices. Current Opinion in Neurobiology. 2023;81:102724.
- Lømo T. Discovering long‐term potentiation (LTP)–recollections and reflections on what came after. Acta Physiologica. 2018;222(2):e12921.
- Magee JC, Grienberger C. Synaptic plasticity forms and functions. Annual review of neuroscience. 2020;43:95–117.
- Runge K, Cardoso C, De Chevigny A. Dendritic spine plasticity: function and mechanisms. Frontiers in synaptic neuroscience. 2020;12:36.
- Rivara CB, Sherwood CC, Bouras C, Hof PR. Stereologic characterization and spatial distribution patterns of Betz cells in the human primary motor cortex. The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology: An Official Publication of the American Association of Anatomists. 2003;270(2):137–51.
- Gerfen CR, Economo MN, Chandrashekar J. Long distance projections of cortical pyramidal neurons. Journal of neuroscience research. 2018;96(9):1467–75.
- Fishell G, Hanashima C. Pyramidal neurons grow up and change their mind. Neuron. 2008;57(3):333–8.
- Konur S, Rabinowitz D, Fenstermaker VL, Yuste R. Systematic regulation of spine sizes and densities in pyramidal neurons. Journal of neurobiology. 2003;56(2):95–112.
- Biagini G, D’Arcangelo G, Baldelli E, D’Antuono M, Tancredi V, Avoli M. Impaired activation of CA3 pyramidal neurons in the epileptic hippocampus. Neuromolecular medicine. 2005;7:325–42.
- Disterhoft JF, Wu WW, Ohno M. Biophysical alterations of hippocampal pyramidal neurons in learning, ageing and Alzheimer’s disease. Ageing research reviews. 2004;3(4):383–406.
- Garey L, Ong W, Patel T, Kanani M, Davis A, Mortimer A, et al. Reduced dendritic spine density on cerebral cortical pyramidal neurons in schizophrenia. Journal of Neurology, Neurosurgery & Psychiatry. 1998;65(4):446–53.
About the author:
DR. AGA SZMITKOWSKA
Content Editor The League of Extraordinary Celltypes, Sci-Illustrate Stories
Aga did her Ph.D. in Biochemistry at the CEITEC/Masaryk University in Brno, Czech Republic, where she was a part of the Laboratory of Genomics and Proteomics of Plant Systems. She is a passionate public speaker and science communicator. After graduation, she became a freelance content coordinator and strategist in a start-up environment focused on lifestyle and longevity.
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