world , with the midbrain , the pons and the medulla oblongata , the emergence locus for almost all cranial nerves with their respective nuclei and the regulating center for some basic functions such as cardiac and respiratory functions , �inally , all nervous tracts from and to the forebrain pass by the brain stem . Behind , the cerebellum with a cerebrum-like but a smaller structure , delimiting the fourth ventricle ; while the coordination and control of motor responses , equilibrium and unconscious proprioception are known functions of the cerebellum , its role in cognition and other emotional aspects are still beyond our understanding .
Continuing the medulla oblongata from the bottom , the spinal cord , the last part of the CNS , is a cylindrical bundle that extends for about forty-seven centimeters , organized in segments ( each segment corresponds to the vertebrae of the spinal nerve exit ), the spinal cord is the main direct center of command for limbs skeletal muscles by means of the motoneurons ( contained in the anterior column ) that receive the superior nervous impulses along with the peripheral input from the muscles and the sensory organs , and the relay of the majority of the peripheral sensory input through the different tracts heading towards the brain .
Giving the fragility of the nervous tissue , this last represents one of the most well-protected organs in the body , with some solid bony structures ( skull and the vertebral column ), a three layered membrane assures more �lexible reinforcement of the bones ( dura mater , pia mater and arachnoid mater ), �inally , the CNS is also provided with a shock absorbing apparatus ( the �luid core ) �illed with the cerebrospinal �luid , which has for a role , nutrition and immunity of the nervous system also .
Peripheral Nervous System / Autonomic Nervous System
Outside the CNS , some nervous structures exist , englobing the nerves ( a pack of neural �ibers -axons- enclosed in a connective sheath along with some blood vessels , assuring a bidirectional impulse transport from and to the CNS ) cranial ( originating from the brain stem to innervate the cranial side of the body ) or spinal ( originating from the fusion of the anterior and posterior spinal roots ) they can be , the ganglia ( housing neural somas and synapses ) which are assimilated to peripheral regional treating centers and the peripheral sensory organs ( scattered in different organs and tissues ) along with the effectors ( glands and muscles mainly ). All these structure are regrouped under the name of the Peripheral Nervous System .
This third division is , in reality , more of a functional division , the ANS combines structure from both the CNS ( Limbic system , hypothalamus and the lateral column of the spinal cord ) and the PNS ( ganglia and nerves ), with its two branches , sympathetic and parasympathetic , it regulates unconsciously the heart and respiratory rates , digestion rhythm and the general state of our bodies ( overall excitation , pupillary diameter adjustments ) basing on the visceral feed-back ( mechanic , osmotic , barometric and chemo-receptors in smooth muscles , heart and the different organs ) and nature of our surroundings , determining the classic reactions of “ Fight and Flight ” or “ Feed and breed ”. The ANS is implicated on many other functions , unclear for the most , but the latest results suggest a role in systemic nervous coordination and even , cognition .
5