The Nervous System

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TheNervous System

Thenervous system is made up of two main parts i.e. the peripheral andcentral nervous systems. It generally performs three main tasks i.e.sensoryinputthat involves gathering information using synapses, glia and neurons.It then performs integrationof data andthen motoroutput.The nervous system comprises of synapses and neurons, which formwithin the neurons connecting them to the epicenter throughout theentire body and other neurons. The neurons function on inhibition orexcitation. Their function is also dependent on the communicationthey have with each other.

Thenerves convey impulses from the sensory receptors to the spinal cordand brain. Information is then processed i.e. integrated within thebrain and then conducted to the glands and muscles, also known asmotor input. Glia cells located in the tissues assist in myelination,extracellular fluid and ionic regulation. The nervous system is anintricate structure with the components involved being complex aswell. Understanding how information is conveyed from one region toanother needs deep knowledge of the components involved. The paperwill outline communication aspects of the nervous system based on thecomponents involved. It will be mainly based on the two components ofthe nervous system i.e. the central nervous system (CNS) and theperipheral nervous system (PNS). Additionally, it is vital to haveunderstand the structure and purpose of the neurons in processing andconveyance of signals [ CITATION AmW11 l 1033 ].

THENEURONS

Theneurons are specialized in processing and conveyance of cellularsignals. They occur in various shapes, electrochemical properties andsizes due to the diverse functions they perform. Sensory afferentneurons transmit data from organs and tissues into the centralnervous system. On the other hand, efferent neurons convey signalsfrom the CNS towards the effector cells hence the name motor neurons.Interneurons link neurons within particular sections of the CNS.

Theexcitatory neurons excite the targeted postsynaptic neurons makingthem to function. Somatic and Motor neurons are examples ofexcitatory neurons. Spinal motor neurons that synapse on cellmuscles, utilize acetylcholine for neurotransmission. Inhibitoryneurons impede the target neurons and are also called short axonneurons. Modulatory neurons arouse more intricate effects referred toas neuromodulator. The brain neurons discharge inhibitoryneurotransmitters much more than the excitatory neurotransmittershence the reason why individuals do not have all the memories as wellas all the sensual stimuli concurrently. Most of the informationwithin the brains is regularly inhibited [CITATION Mar09 l 1033 ].

THECENTRAL NERVOUS SYSTEM

Thecentral nervous system is basically the control epicenter of theentire body and is the largest part of the nervous system. Itregulates higher thought, body movements as well as organ function.It comprises of the spinal cord and brain.

Figure1: Generation and propagation an action potential

NerveImpulse

Stimulationof nerve means the resting potential also changes. Examples ofstimuli include electricity, pressure, chemicals among others.Various neurons are sensitive to various stimuli though most of themcan sense pain. Sodium ion channels are opened up by the stimuli. Theprompt shift in polarity, which travels along the fiber nerve isknown as Action Potential and has several stages i.e. thedepolarization, repolarization and refractory phases [ CITATION Dav13 l 1033 ].

TheBrain

Itentails nerve centers tasked with the coordination of motor andsensory structures of the body. The stem of the brain contains thelower nerve centers i.e. pons, medulla and midbrain. Other componentsinclude the cerebrum, cerebellum and the limbic system [ CITATION Pin10 l 1033 ].

Limbicsystem

Thelimbic system combines primitive emotions and higher mentalfunctionalities into one structure. It is commonly referred to as theemotional nervous system. Apart from the emotional responsibilities,it is also responsible for our higher mental functionalities likememory formations as well as learning. The system clarifies whythings such as eating are pleasurable whereas medical conditions likehigh blood pressure are due to mental stress. The limbic systemcomprises of the amygdala, hippocampus, thalamus, hypothalamus,fornix and par-hippocampus and cingulate gyrus [ CITATION Lil10 l 1033 ].

Memoryand learning

Memorycan be described as the mental aptitude of recalling and retainingpast experiences. It is the act of remembering. Learning on the otherhand involves retaining and using past memories. Technically, thetechnique of memory cannot be entirely understood. The brain sectionsare mostly likened to the particular kinds of memory. For instance,hippocampus is implicated in spatial and declarative learning. Theamygdala is associated with emotional memory. However, it is notadequate to define memory and learning to be entirely dependent onparticular brain regions. Memory and learning are also attributed tovariance in the neuronal synapses facilitated by long-term depressionand potentiation [ CITATION Lal13 l 1033 ].Thereexists three main kinds of memory

  1. Sensory Memory that act as buffers for stimuli by senses. They retain the exact copy of what is heard or seen.

  2. Short Term Memory that involve temporary recall of the info under development.

  3. Long Term Memory that is utilized for information storage over a longer period. It entails three activities i.e. storage, deletion and retrieval.

Languageand speech

Semanticmemory is involved with language. Articulation and formation ofspeech are characterized in the motor areas. The broca’s andwernicke’s areas are concerned with speech formation and languageanalysis. Broca’s section assembles motor of writing and speech.Therefore, it assists one to

  • Perfectly understand the language

  • Write perfectly

  • Seldom speak spontaneously

TheWernicke section entails the visual and auditory associations’cortex. It is responsible for the formation and analysis of language.Therefore, a problem in this section one is

  • Unable to name objects

  • Unable to understand meaning of words

  • Unable to appropriate articulate speech

THEPERIPHERAL NERVOUS SYSTEM

Theperipheral nervous structure has thirty one pairs of spinal nervesand twelve cranial nerves. It is divided further into somatic andautonomic. It is a mode of communication between the various parts ofthe human body and the central nervous parts by the help of the nerveof impulses whose role is to control the functions of the body. Thereare one coccygeal, twelve thoracic, eight cervical, five sacral andfive lumbar in the sets of the spinal nerves. Their main function isto regulate the rest of the body. The function of the cranial nervesregulate the work of the head’s anatomic structures and only ten ofthe cranial nerves are from the brainstem. Somatic nervous system hasefferent fibers responsible for contraction of the muscles andafferent fibers which receives information from the exterior sources.Generally, somatic system deals with voluntary control of receptionof the external stimuli and movements of the body by the action ofthe skeletal muscles [CITATION Kal08 l 1033 ].

Autonomicsystem deals with visceral organs such as the intestines, stomach,gland, and the heart. It controls the systems that keep the humanbody well and alive like digestion, breathing and heartbeatregulation. It consist of parasympathetic and sympathetic divisions,both having same nerve pathways and do work with no conscious effort,however both divisions have differing effects on tissues. Autonomicsystem regulates homeostasis by controlling relative input from everydivision. Cranial Nerve X is one of the important nerves of theparasympathetic system. Sympathetic nervous system activates theflight or fight response also denoted to as sympathetico-adrenalreaction of the body. This nervous system is looked at an autonomicregulation system since it operate without conscious thought.Parasympathetic nervous system increases gland and intestinalactivity, slows heart rate and relaxes sphincter muscles existent inthe gastrointestinal tract [ CITATION Eys10 l 1033 ].

Sympatheticnerves originate from the vertebral column and its cells begin in thelumbar and thoracic regions of the spinal cord hence havethoracolumbar outflow. Its axon nerves leave ventral branches ofspinal nerves and separate as white rami which connects to twoelongated ganglia. This axons travel long distances in order to reachthe target glands and organs and this is accomplished since each axonlink with an axon of another cell. The ends of the axons make a linkacross space that is the synapse. Synapses are made in the ganglia,the ganglia includes superior cervical ganglion and sympathetictrunks and mesenteric ganglia [ CITATION Bra05 l 1033 ].

Insomatic nervous system, messages have bidirectional flow. Afferentmessages bring about sensations like pain heat or cold while theefferent messages can trigger variations in various parts of thebody. The target synapse activated either by the adrenaline or thenoradrenaline physiologically is mediated by the adrenergic receptor.The first synapse activated by acetylcholine physiologically ismediated by the nicotinic receptors. Parasympathetic nervous systemreciprocates the effects of sympathetic system. Effects aresynergistic in some tissues when both systems innervate this tissues[ CITATION AmW11 l 1033 ].

Theparasympathetic nervous system has one acetylcholine acting asneurotransmitter and it acts on the nicotinic and muscarinicreceptors. Preganglionic nerves releases the acetylcholine whenstimulated which then act on the nicotinic receptors of thepostganglionic nerve, this nerve hence release the acetylcholinewhich stimulate muscarinic receptors of the organ being targeted.Three types of the muscarinic receptors with the first being locatedat the neural system, the second is in the heart which acts bybringing the heart to normal after the actions performed by thesympathetic nervous system, the third is located in various parts ofthe body and causes bronchoconstriction and vasoconstriction.

References

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