Physiology Structure of the Nervous

Physiology

Structure of the Nervous System

The Nervous System is the most complex and extremely ordered of the various systems which make up the human body. It is the system concerned with the association and incorporation of a variety of bodily process and the responses and alterations of the organism to its surroundings. The nervous system as a whole comprises the Central Nervous System, which is made up of the brain and spinal cord, and the Peripheral Nervous System, whose nerve fibers bond all parts of the body with the central nervous system. The Peripheral Nervous System is further subdivided into two branches, the Somatic Nervous system and the Autonomic Nervous System. All these nerves are exterior to the Central Nervous System. The Somatic Nervous System controls musculoskeletal movement, and transports sensory messages from the body to the CNS. The Autonomic Nervous System has two divisions, the Sympathetic and the Parasympathetic, which control the spontaneous processes of the body, the viscera, and sense organs, glands and blood vessels. In evolutionary stipulations it is older than the CNS and its anatomical circuitry is mainly dispersed, creating a universal response, quite different from the highly specific pathways and response of the CNS. This comprehensive, widely dispersed structure allows it to mediate overall alterations in state. It is also part of the limbic system which has also been known as the mammalian or emotional brain (Schoenberg, Marsh & Lerner, 2011).

Central Nervous System

The Central Nervous System is made up of the brain and spinal cord. The main form of communication in the CNS is the neuron. The brain and spinal cord are very vital to life and functioning, so there are a number of defensive barriers that surround them. These include the skull and spine along with membrane tissues known as meninges. Additionally, both structures hover in a protective liquid known as cerebrospinal fluid in order to protect them (Nervous System, n.d.).

While neurons are the building blocks of the body's communication system, it is the system of neurons that permit indicators to move between the brain and body. These ordered networks, made up of one trillion neurons, constitute what is known as the nervous system. The human nervous system is made up of two parts. The first part is the central nervous system which includes the brain and spinal cord, and second part is the peripheral nervous system, which is composed of nerves and nerve networks throughout the body (Nervous System, n.d.).

The CNS is accountable for processing every feeling and thought that one experiences. The sensory information that is assembled by receptors all through the body then passes this information on to the central nervous system. The CNS also sends messages out to the rest of the body in order to manage movement, actions and reactions to the immediate environment (Nervous System, n.d.).

Peripheral Nervous System

The Peripheral Nervous System (PNS) is the part of the nervous system that contains all the nerves that lie outside of the central nervous system. The main role of the PNS is to join the CNS to the organs, limbs and skin. These nerves expand from the central nervous system to the furthest areas of the body. The nerves that make up the peripheral nervous system are in fact the axons or bundles of axons from neuron cells. In some instances, these nerves are very tiny but some nerve bundles are so big that they can be easily seen with the naked eye. The PNS is not sheltered by bone or the blood-brain barrier, leaving it bare to toxins and mechanical harms. The peripheral nervous system is separated into the somatic nervous system and the autonomic nervous system (Flaherty, 2011).

Autonomic Nervous System

The autonomic system is the part of the peripheral nervous system accountable for regulating involuntary body functions, such as blood flow, heartbeat, digestion and breathing. This system is additionally divided into two parts. The first is the sympathetic system that regulates the flight-or-fight responses. The second part is the parasympathetic system which helps uphold normal body functions and protects physical assets (El-Sheikh, Hinnant, & Erath, 2011).

Sympathetic Nervous System

The sympathetic nervous system sets in motion what is frequently known as the fight or flight response. Like other parts of the nervous system, the sympathetic nervous system functions by way of a series of interrelated neurons. Sympathetic neurons are regularly considered part of the peripheral nervous system (PNS), although there are many that lie inside the central nervous system (CNS) (Sherman, Bunyan, Creswell & Jaremka, 2009).

The sympathetic nervous system is accountable for up -- and down-regulating of many homeostatic mechanisms in living organisms. Fibers from the SNS innervate tissues in approximately every organ system, supplying at least some regulatory function to things as varied as pupil diameter, gut motility, and urinary production. It is possibly best known for arbitrating the neuronal and hormonal stress reaction normally known as the fight-or-flight response. This reaction is also known as sympatho-adrenal reaction of the body, as the preganglionic sympathetic fibers that end in the adrenal medulla secrete acetylcholine, which sets in motion the great discharge of adrenaline and to a lesser extent norepinephrine from it. Consequently, this reaction acts primarily on the cardiovascular system which is mediated directly by way of impulses conveyed through the sympathetic nervous system and in some way by way of catecholamines secreted from the adrenal medulla (Sherman, Bunyan, Creswell & Jaremka, 2009).

Parasympathetic Nervous System

The Parasympathetic system is the part of the Autonomic Nervous System (ANS) that is responsible for the body's capability to convalesce and return to a balanced state known as homeostasis after enduring pain or stress. It is frequently called relax and renew. The Parasympathetic functions in opposition to the Sympathetic nervous system. When the sympathetic system triggers in response to some sort of stressor, the parasympathetic reacts in turn to bring the body back to a state of equilibrium. The Parasympathetic system is constantly active at a low level, but levels of action increase when it is essential to bring the body back to a balanced state from a state of high Sympathetic activity (Dulleck, Ristl, Schaffner & Torgler, 2011).

The primary Parasympathetic nerve is the vagus nerve, which is also known as cranial nerve X. When active, the Parasympathetic system slows down heart rate, dilates blood vessels, activates digestion, and stores energy. Different from the Sympathetic system, the Parasympathetic response does not automatically perform all of these functions at once, but selectively, as warranted (Dulleck, Ristl, Schaffner & Torgler, 2011).

There appears to be a direct link between the PNS and a person's mood. Ones PNS can go into overdrive leading to depression, despair, withdrawal and feelings of shame.

A person's energy goes inward and they become more introspective. The parasympathetic and sympathetic nervous systems work together. At a point of balance they may be both operating, that is, neither is overriding. When the SNS is in motion a person feels stressed or excited. Ultimately there is a compensatory reaction of the PNS. The PNS brings the nervous system down. When the parasympathetic nervous system moves into overdrive people experience it as fear provoked states such as the freeze response or shame. What helps to alter these states is the regulating function of a higher cortical center in an area of the brain called the pre-frontal cortex which is right between the eyes and above (Dulleck, Ristl, Schaffner & Torgler, 2011).

Somatic Nervous System

The somatic system is the part of the peripheral nervous system accountable for carrying sensory and motor information to and from the central nervous system. The somatic nervous system gets its name from the Greek word soma, which means body. The somatic system is in charge of transmitting sensory information as well as for voluntary movement. This system is made up of two major types of neurons: sensory neurons or afferent neurons that carry information from the nerves to the central nervous system, and motor neurons or efferent neurons that carry information from the brain and spinal cord to muscle fibers all through the body (Ihlen & Vereijken, 2010).

The somatic nervous system manages all voluntary muscular systems inside the body, with the exception of reflex arcs. The fundamental route of nerve signals within the efferent somatic nervous system comprises a progression that begins in the upper cell bodies of motor neurons within the precentral gyrus which approximates the primary motor cortex. Stimuli from the precentral gyrus are conveyed from upper motor neurons and down the corticospinal tract, via axons to control voluntary muscles. These stimuli are transmitted from upper motor neurons through the ventral horn of the spinal cord, and across synapses to be received by the sensory receptors of alpha motor neurons of the brainstem and spinal cord (Ihlen & Vereijken, 2010).

Upper motor neurons release a neurotransmitter, acetylcholine, from their axon terminal knobs, which are obtained by nicotinic receptors of the alpha motor neurons. In turn, alpha motor neurons communicate the stimuli received down their axons via the ventral root of the spinal cord. These indications then proceed to the neuromuscular connections of skeletal muscles. From there, acetylcholine is released from the axon terminal knobs of alpha motor neurons and received by postsynaptic receptors of muscles, thereby communicating the stimulus to contract muscle fibers (Ihlen & Vereijken, 2010).

Psychological Influences

Research on patient's brains scanned by Positron Emmision Tomography have designated that the kind of thoughts people have influence the balance of brain chemicals, so by learning to think more positively and sensibly one can influence brain chemistry in a positive way, but other factors like an unloved, unsupported childhood can influence brain chemistry and physiology in such a way that it makes people less able to cope with stress in adulthood. If people think mainly negatively their brains secrete chemicals that can undermine their psychological and physiological health, whereas if they think more positively they can cause chemicals to be secreted that boost their psychological and physical well-being (Nervous system, n.d.).

People also need to be aware that they are not exact carbon copies of each other. People have subtle biochemical and physiological differences that partly influence how they react to stress. For instance, each person's nervous system can react quite differently to any given stimuli or situation. Some people's nervous systems are more sensitive than others; more easily set off by stress, and may also take longer to switch on the relaxation mode, once the stress response has done its job. There can also be dissimilarities in the amount of stress hormones that people secrete in response to a stressor. People who have more of a tendency to being what is known as Type A personality are more reactive to stress and can produce up to forty times more cortisol, they can produce four times as much adrenalin and also pump three times more blood to their muscles than the more laid back Type B personality. This does not mean however that there is nothing that the more biologically reactive Type A's can do to reduce their stress. Research on Type A personalities who had suffered a heart attack showed that if they were taught stress management techniques then they could radically reduce their risk of a second heart attack when compared to Type A personalities who had not been taught stress management techniques (Nervous system, n.d.).