Nervous System is composed of Central Nervous System (CNS) and peripheral nervous system (PNS). Creative Biomart provides recombinant proteins and other molecular tools for your research about nervous system development.
Central Nervous System Structure
Understanding the organization and biology of the nervous system is essential to formulating materials-based solutions to the challenges in nerve repair and regeneration. The Central Nervous System (CNS) is composed of the brain and spinal cord and is responsible for conducting and interpreting signals between the brain and the body. The peripheral nervous system (PNS) connects the CNS to the rest of the body. Though the two systems are intricately connected, each possesses a unique environment which results in drastically different responses to traumatic injury. This difference is primarily attributable to the presence of Schwann cells in the PNS, which rapidly infiltrate the injury region and secrete growth-promoting cytokines, thus rendering the PNS more permissive for regeneration. The lack of Schwann cells, glial scar formation and the presence of growth inhibitory proteoglycans combine to generate an environment that is not conducive to regeneration in the CNS.
There are two primary cell types in the CNS: neurons and glia. Neurons form specific contacts (synapses) with each other via their axons and dendrites to create neuronal networks. They secrete chemical messengers known as neurotransmitters at their synapses, which propagate electrical signals. Glial cells, such as astrocytes and oligodendrocytes, support, nourish and protect neurons. Oligodendrocytes form myelin sheaths around axons, which increase the conduction velocity of action potentials. Myelin contains approximately 70% lipids and 30% proteins including myelin basic protein, myelin oligodendrocyte glycoprotein and myelin-associated glycoprotein. Astrocytes promote oligodendrocyte myelinating activity, form the blood brain barrier, modulate neurotransmitter uptake and release, and maintain synaptic plasticity. Microglial cells are also present in the CNS; they scavenge cell debris and secrete molecules that affect the immune and inflammatory response. In addition to supporting and nurturing neurons, glia also plays an important role in the response to trauma and regeneration.
The tissue of the CNS is composed of two distinct regions: white matter and grey matter. White matter contains myelinated axon tracts and glial cells, and constitutes the communication networks between grey matter regions. The high lipid content of myelin gives this tissue its white appearance. The grey matter contains neuronal soma, glial cells and has a high capillary density. Its function is to route motor and sensory stimuli to interneurons via chemical synapse activity in order to generate a response. Interneurons are cells which act as intermediaries between afferent neurons, which conduct impulses from the body toward the CNS, and efferent neurons, which conduct impulses away from the CNS towards the body. The tissue in both the brain and the spinal cord is covered by three layers of connective tissue: the dura mater, arachnoid mater, and pia mater, collectively referred to as the meninges. The subarachnoid space, between the arachnoid and pia mater, is filled with cerebral spinal fluid. The role of the meninges is to protect the CNS. The ECM of the CNS is composed of hyaluronan, adhesive glycoproteins such as tenascin, laminin, netrin and reelin, and proteoglycans such as neurocan, versican and brevican. It serves to organize the CNS structure, guide axon growth and development, and store growth factors and cytokines. Additionally, the ECM modulates the mechanical properties of the CNS.
Peripheral nervous system (PNS)
During development, neurons in the peripheral nervous system (PNS) must project axons over vast distances to form connections with their appropriate peripheral targets. In order to accomplish this daunting task, developing neurons rely on growth and guidance from a variety of extracellular cues expressed by the surrounding environment and distal targets. As developing axons extend into the periphery, they encounter a plethora of target-derived signals, which they must interpret properly in order to accomplish proper axonal guidance, maturation, survival, target innervation, and synapse formation.
The cues that guide axons of the developing PNS have been extensively studied. One common theme is that extracellular cues from the environment and/or distal targets bind to receptors on developing neurons to regulate functions including differentiation, survival, and target innervation. For example, sensory neurons of the DRG and trigeminal ganglia depend on target-derived neurotrophins for survival. Neurotrophins, including NGF, BDNF, NT3, and NT4, are produced in limited amounts by target cells and bind to members of the Trk family of receptors. In addition to the role of neurotrophins in survival, a number of extracellular guidance factors are also critical for axonal growth and target innervation. One example is the semaphorins, a class of secreted or transmembrane guidance cues that bind to the neuropilin and plexin receptors and regulate axon guidance. Loss of semaphorin signaling leads to defects in axon pathfinding and defasciculation of axonal tracts of neurons in both the CNS and PNS.