The nervous system is divided into the central nervous system (CNS—brain and spinal cord) and the peripheral nervous system (PNS—nerves and ganglia extending outward). While neurons transmit electrical signals, the nervous system relies on a diverse population of non-neuronal support cells known collectively as glial cells. Glial cells provide structural support, supply nutrients, and maintain the chemical balance necessary for proper neuronal function.
Identifying Satellite Cells: Location in the PNS
Satellite cells are a type of glial cell found exclusively within the Peripheral Nervous System (PNS). Their specific anatomical placement is within the ganglia, which are clusters of neuron cell bodies situated outside the CNS. These flat, small cells form a delicate envelope that completely encases the cell bodies, or somas, of peripheral neurons. This arrangement is consistently found in sensory ganglia, such as the dorsal root ganglia (DRG) near the spinal cord, and in autonomic ganglia.
The Specific Roles of Satellite Cells
The primary role of satellite cells is to maintain homeostasis within the immediate environment of the peripheral neuron cell body. This involves the careful control of the chemical microenvironment necessary for stable electrical signaling. Satellite cells are known for their ability to buffer ions, particularly potassium ions, which are released by the neuron during electrical activity. The uptake of excess potassium prevents its accumulation in the extracellular space, which could disrupt the neuron’s normal excitability.
They also possess transporters that regulate neurotransmitter concentrations, such as glutamate, ensuring signaling molecules are cleared efficiently after a neuron fires. Beyond chemical regulation, satellite cells provide physical protection and structural support for the neuron bodies within the ganglion structure. They also mediate the supply of nutrients from the blood vessels into the neuron. In response to nerve injury, these cells become reactive, releasing signaling molecules that influence the neuron’s response to damage and may play a part in chronic pain.
Satellite Cells and the Glial Cell Family
Satellite cells and Schwann cells are the two main types of glial cells in the PNS. Both originate from the embryonic neural crest but serve distinct anatomical segments of peripheral neurons. Schwann cells produce the myelin sheath that insulates the long axons of peripheral nerves, facilitating rapid signal transmission. In contrast, satellite cells focus their support on the neuron’s cell body within the ganglia.
Functionally, satellite cells are often compared to astrocytes, the most abundant glial cell type found in the CNS. Astrocytes perform similar homeostatic tasks in the brain and spinal cord, such as buffering ions and regulating the extracellular fluid. However, astrocytes have a distinct, star-like morphology and interact with blood vessels to form part of the blood-brain barrier. This feature is not fully replicated by the flattened satellite cells in the PNS ganglia.