Neuromere
[1] There are three classes of neuromeres in the central nervous system – prosomeres (for the prosencephalon), mesomeres (for the mesencephalon) and rhombomeres (for the rhombencephalon) that will develop the forebrain, midbrain, and hindbrain respectively.
[1] Neuromeres can then be divided up so that each segment is carrying different and unique genetic traits, expressing different features in development.
[2] Although researchers have long since recognized the different signs of differentiation during embryonic development, it was widely thought that neuromeres held no relation to the structure of the nervous system.
These genes determine the basic structure and orientation of an organism after the embryonic segments have formed.
[1] The genes that are being expressed fall into two categories, extracellular signaling proteins and intracellular transcription factors.
[1] The genes are able to perform different tasks at different times depending on the environment that may or not be changing as well as when they are being activated and expressed.
During development, the neural tube is considered as the precursor to the spinal cord and the rest of the central nervous system.
These rhombomeres are also associated with the neural crest that supplies the pharyngeal arches, a set of visible tissues that are in line with the developing brain and give rise to the head and neck.
The spinal cord is the main pathway for information connecting the brain and peripheral nervous system.
The human spinal cord extends from the foramen magnum and continues through to the conus medullaris near the second lumbar vertebra, terminating in a fibrous extension known as the filum terminale.
The cervical enlargement, located from C3 to T2 spinal segments, is where sensory input comes from and motor output goes to the arms.
The lumbar enlargement, located between L1 and S3 spinal segments, handles sensory input and motor output coming from and going to the legs.
The pia mater continues as an extension called the filum terminale, which anchors the spinal cord to the coccyx.
The cauda equina forms as a result of the fact that the spinal cord stops growing in length at about age four, even though the vertebral column continues to lengthen until adulthood.
This results in the fact that sacral spinal nerves actually originate in the upper lumbar region.
Ventral roots consist of axons from motor neurons, which bring information to the periphery from cell bodies within the CNS.
The gray matter, in the center of the cord, is shaped like a butterfly and consists of cell bodies of interneurons and motor neurons.
Within the CNS, nerve cell bodies are generally organized into functional clusters, called nuclei.
There are 33 spinal cord nerve segments in a human spinal cord: 8 cervical segments forming 8 pairs of cervical nerves (C1 spinal nerves exit spinal column between occiput and C1 vertebra; C2 nerves exit between posterior arch of C1 vertebra and lamina of C2 vertebra; C3-C8 spinal nerves through IVF above corresponding cervica vertebra, with the exception of C8 pair which exit via IVF between C7 and T1 vertebra) 12 thoracic segments forming 12 pairs of thoracic nerves (exit spinal column through IVF below corresponding vertebra T1-T12) 5 lumbar segments forming 5 pairs of lumbar nerves (exit spinal column through IVF, below corresponding vertebra L1-L5) 5 sacral segments forming 5 pairs of sacral nerves (exit spinal column through IVF, below corresponding vertebra S1-S5) 3 coccygeal segments joined up becoming a single segment forming 1 pair of coccygeal nerves (exit spinal column through the sacral hiatus).
The netrins act as chemoattractants to decussation of pain and temperature sensory neurons in the alar plate across the anterior white commissure, where they then ascend towards the thalamus.
