The most important exception is the hagfish, which is often thought of as the most primitive type of vertebrate. Nearly all vertebrate species possess a pineal gland. Its shape resembles a tiny pine cone, and it is located in the epithalamus, near the centre of the brain, between the two hemispheres, tucked in a groove where the two halves of the thalamus join. It produces the serotonin derivative melatonin, a hormone that affects the modulation of sleep patterns in the circadian rhythms and seasonal functions. The pineal gland, also known as the pineal body, conarium or epiphysis cerebri, is a small endocrine gland in the vertebrate brain.
Beberapa vertebrata yang lebih maju, termasuk buaya, kekurangan kelenjar pineal kerana mereka telah hilang sepanjang perjalanan evolusi. The lancelet Branchiostoma lanceolatum, yang terdekat dengan relatif vertebrata, juga tidak mempunyai kelenjar pineal yang dikenali. Walau bagaimanapun, di hagfish, terdapat struktur "bersamaan pineal" di diencephalon dorsal. Pengecualian yang paling penting adalah hagfish, yang sering dianggap sebagai jenis vertebrata yang paling primitif. Hampir semua spesies vertebrata mempunyai kelenjar pineal. Bentuknya menyerupai kon pain kecil, dan terletak di epithalamus, berhampiran pusat otak, di antara dua hemisfera, terselip di alur di mana kedua-dua bahagian thalamus bergabung. Ia menghasilkan melatonin derivatif serotonin, hormon yang mempengaruhi modulasi pola tidur dalam irama sirkadian dan fungsi bermusim.
The axon will be able to regenerate itself at a rate of 3 cm per month, generally indicating a return to a physiological state in roughly three months.Pineal gland Kelenjar pineal, juga dikenali sebagai badan pineal, conarium atau epiphysis cerebri, adalah kelenjar endokrin kecil di otak vertebrata. In that case, they will be a loss of neural transmission which will be causing a diminished response in the distal part of the nerve. A sort of lesion called axonotmesis can happen, where the axon of the nerve is damaged while the integrity of the perineurium and epineurium is preserved. The perineurium, as the epineurium, has a clinical importance following a trauma, like a fracture. In contrast, the epineurium is a tough and mechanically resistant tissue which is not easily penetrated by a needle. The perineurium is a smooth, transparent tubular membrane which may be easily separated from the fibers it encloses. The tight junctions provide selective barrier to chemical substances. Perineurial cells are sometimes referred to as myoepithelioid due to their epithelioid and myofibroblastoid properties including tight junctions, gap junctions, external laminae and contractility. The perineurium is composed of perineurial cells, which are epithelioid myofibroblasts. The perineurium is composed of connective tissue, which has a distinctly lamellar arrangement consisting of one to several concentric layers. This grouping structure is analogous to the muscular organization system of epimysium, perimysium and endomysium. Several fascicles may be in turn bundled together with a blood supply and fatty tissue within yet another sheath, the epineurium. Fascicles, bundles of neurons, are surrounded by the perineurium. In the peripheral nervous system, the myelin sheath of each axon in a nerve is wrapped in a delicate protective sheath known as the endoneurium. The perineurium is composed from fibroblasts. This bundles together axons targeting the same anatomical location. The perineurium is a protective sheath that surrounds a nerve fascicle.
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