Betz cell in the context of "Primary motor cortex"

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⭐ Core Definition: Betz cell

Betz cells (also known as pyramidal cells of Betz) are giant pyramidal cells (neurons) located within the fifth layer of the grey matter in the primary motor cortex. These neurons are the largest in the central nervous system, sometimes reaching 100 μm in diameter.

Betz cells are upper motor neurons that send their axons down to the spinal cord via the corticospinal tract, where in humans they synapse directly with anterior horn cells, which in turn synapse directly with their target muscles. Betz cells are not the sole source of direct connections to those neurons because most of the direct corticomotorneuronal cells are medium or small neurons. While Betz cells have one apical dendrite typical of pyramidal neurons, they have more primary dendritic shafts, which can branch out at almost any point from the soma (cell body). These perisomatic (around the cell body) and basal dendrites project into all cortical layers, but most of their horizontal branches/arbors populate layers V and VI, some reaching down into the white matter. According to one study, Betz cells represent about 10% of the total pyramidal cell population in layer Vb of the human primary motor cortex.

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👉 Betz cell in the context of Primary motor cortex

The primary motor cortex (Brodmann area 4) is a brain region that in humans is located in the dorsal portion of the frontal lobe. It is the primary region of the motor system and works in association with other motor areas including premotor cortex, the supplementary motor area, posterior parietal cortex, and several subcortical brain regions, to plan and execute voluntary movements. Primary motor cortex is defined anatomically as the region of cortex that contains large neurons known as Betz cells, which, along with other cortical neurons, send long axons down the spinal cord to synapse onto the interneuron circuitry of the spinal cord and also directly onto the alpha motor neurons in the spinal cord which connect to the muscles.

At the primary motor cortex, motor representation is orderly arranged (in an inverted fashion) from the toe (at the top of the cerebral hemisphere) to mouth (at the bottom) along a fold in the cortex called the central sulcus. However, some body parts may be controlled by partially overlapping regions of cortex. Each cerebral hemisphere of the primary motor cortex only contains a motor representation of the opposite (contralateral) side of the body. The amount of primary motor cortex devoted to a body part is not proportional to the absolute size of the body surface, but, instead, to the relative density of cutaneous motor receptors on said body part. The density of cutaneous motor receptors on the body part is generally indicative of the necessary degree of precision of movement required at that body part. For this reason, the human hands and face have a much larger representation than the legs.

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Betz cell in the context of Upper motor neuron

Upper motor neurons (UMNs) is a term introduced by William Gowers in 1886. They are found in the cerebral cortex and brainstem and carry information down to activate interneurons and lower motor neurons, which in turn directly signal muscles to contract or relax. UMNs represent the major origin point for voluntary somatic movement.

Upper motor neurons represent the largest pyramidal cells in the motor regions of the cerebral cortex. The major cell type of the UMNs is the Betz cells residing in layer V of the primary motor cortex, located on the precentral gyrus in the posterior frontal lobe. The cell bodies of Betz cell neurons are the largest in the brain, approaching nearly 0.1 mm in diameter. The axons of the upper motor neurons project out of the precentral gyrus travelling through to the brainstem, where they will decussate (intersect) within the lower medulla oblongata to form the lateral corticospinal tract on each side of the spinal cord. The fibers that do not decussate will pass through the medulla and continue on to form the anterior corticospinal tracts.

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LINKED FROM (PARENTS)
← Primary motor cortex ← Upper motor neuron
LINKS TO (CHILDREN)
Pyramidal cell → Neuron → Grey matter → Primary motor cortex → Central nervous system → Μm → Upper motor neuron → Axon → Spinal cord → Corticospinal → Human → Synapse → Anterior horn (spinal cord) → Cell (biology) → Muscle → Apical dendrite → Pyramidal neurons → Soma (biology) → Basal dendrite → White matter →