Nerve Tissue Overview
- Nerve tissue is a highly cellular network specialised for communication.
- It is distributed throughout the body as an integrated communications network.
- The primary role of nerve tissue is to transmit electrical signals from sensory receptors to effector organs, such as muscles and glands, thereby controlling their activity.
- It is responsible for crucial bodily functions, including internal controls (homeostasis), mental activity, movement, and general behavioural patterns.
- Nerve tissue consists mainly of two types of cells: nerve cells (neurons) and glial cells.
- Neurons are the functional units, typically featuring numerous long processes for signal transmission.
- Glial cells have shorter processes and serve to support, protect, insulate, nourish, and defend neurons, participating in many neural activities.
Histogenesis (Development) of Nerve Tissue The development of nerve tissue, known as histogenesis, is a complex process originating early in embryonic life:
- Embryonic Origin: The nervous system develops from the ectoderm, the outermost of the three early embryonic layers.
- Timing: This developmental process commences during the third week of gestation.
- Neural Plate Formation: The initiation is marked by signals from the underlying axial structure, the notochord, which induces the ectoderm on the mid-dorsal side of the embryo to thicken, forming the epithelial neural plate.
- Neural Tube Formation: The lateral edges of the neural plate then fold upwards, growing towards each other medially. These neural folds fuse within a few days to form the neural tube.
- The neural tube gives rise to the entire Central Nervous System (CNS), which includes the brain and spinal cord, as well as most glial cells within the CNS.
- Neural Crest Formation: As the neural folds fuse and the neural tube detaches from the overlying surface ectoderm, a population of cells known as the neural crest separates from the neuroepithelium and becomes mesenchymal.
- Neural crest cells undergo extensive migration and differentiate into all the cells of the Peripheral Nervous System (PNS), including sensory neurons,
postsynaptic autonomic neurons, Schwann cells, and the cells of the adrenal medulla. They also contribute to other non-neuronal tissues, such as melanocytes and mesenchymal elements in the head and neck.