Y khoa, y dược - Chapter 5: The nervous system

Chapter 5 The Nervous System IntroductionThe nervous system is truly remarkable. Every thought, feeling or action reveals its fascinating activity; consequently, malfunction of the nervous system can have a devastating effect on life.      Compose a list of the conditions that you already know that affect the nervous system, add this to your portfolio The Nervous SystemThe nervous system is divided into the central nervous system (CNS), comprising the brain itself and the spinal cordthe peripheral nervous system (PNS), encompassing the cranial and spinal nerves. The CNS is an integrated command centre interpreting and responding to sensory impulses. The PNS is divided into sensory (afferent; carrying towards) and motor (efferent; carrying away) divisions. The BrainThe brain has the consistency of a soft-boiled egg, the wrinkled appearance of a walnut and no moving parts. It is housed and protected by the skull, or cranium. The brain weighs approximately 1500g and contains more than 100 billion neurons, the fundamental functional unit of the nervous system. The meninges cover, surround and protect the brain, and the spinal cord. They have three layers:The Dura materArachnoid membrane Pia mater The BrainThe brain is made up of visibly distinct regionsthe cerebrumthe brain stemthe cerebellumThe cerebral hemispheres are made up of four pairs of lobes: frontalparietal temporaloccipital In addition, the cerebrum also contains the diencephalon, which are composed of the thalamus, hypothalamus and epithalamus.Identify the Four Lobes of the BrainApplying Theory to Practice: Exercise What conditions have you heard of that are characterised by bleeding into the spaces between the meninges of the brain? What are the most likely causes of such bleeding?Cerebrospinal fluid (CSF), a clear, colourless, odourless liquid, surrounds the brain and the spinal cord. It acts as a shock absorber, floating and cushioning the brain and spinal cord from trauma. CSF is secreted from each of the four ventricles within the brain. Meningitis is inflammation of the meninges, most often caused by infection.Identify which type of infection affect the meninges and how would you expect the patient to present?Anatomy & PhysiologyThe cerebellum is located just below the occipital lobes and protrudes outwards.Continuous blood supply to the brain is crucial. The brain suffers irreparably to even short periods without oxygen and is totally dependent on glucose for metabolism. The brain is supplied with blood from the two pairs of arteries;the internal carotid arteriesthe vertebral arteriesThe Composition of BrainNeurons process all information and activity within the brain by conducting nerve impulses to, from and within the brain. All neurons have a cell body, with a nucleus, cytoplasmic material and dendrites and axons extending from it.Dendrites conduct nerve impulses towards the cell body whereas axons conduct impulses away from the cell body. FunctionNerve impulses occur as a result of the changes in cell membrane potential of each neuron. Alterations in the concentration of sodium and potassium on either side of the membrane stimulate the change in membrane potential. If the change in potential is great enough, an impulse is conducted. This is known as an action potential and is followed by a wave of depolarisation.Over 30 different neurotransmitters have been identified, these include: Acetylcholine NoradrenalineDopamineCerebrum The cerebral cortex governs higher mental function. It is responsible for conscious awareness, thinking, understanding and perception, language, memory, sensation, and movement. However, these functions are not necessarily associated with just one location, conscious behaviour often involves the whole cortex. The ThalamusThe thalamus, located within the diencephalon, acts as a relay station for sensory inputs. It adjusts and directs information to the correct area of the cerebrum for it to be received and responded to. It also has a role in focusing attention and collaborates with the reticular activating system (RAS) and the limbic system. The RAS governs the arousal of the brain and the limbic system allows recognition and expression of emotions. The HypothalamusControls autonomic nervous system activity via the brain stem centres Recognises and allows expression of emotions, as a major part of the limbic system Regulates biological rhythms and drives such as the sleep and wake cycle and sexual arousal Regulates body temperature and appetite Regulates water metabolism and thirst via osmoreceptors and hormone secretion of antidiuretic hormone from the pituitary gland Controls pituitary secretions of other hormones The Brain StemThe brain stem encompasses the midbrain, pons and medulla; it allows communication and conduction between the spinal cord, lower brain regions, cerebellum and the cerebral hemispheres. The brain stem is important in the RAS and consciousness as well as in autonomic regulation. The medulla plays a vital role in body homeostasis housing the cardiovascular and respiratory centres.The hypothalamus sends impulses (acting as messages) to the medulla to execute an instruction. CerebellumThe cerebellum is responsible for smooth, precise and coordinated motor activity; it also regulates posture and balance. All sensory inputs travel via the cerebellum giving information about the body and muscle activity. Information is relayed in pathways across the brain and fed-back to allow for synergy throughout the body. Neurological Assessment Neurological assessment skills are essential in nursing practice, assessment of consciousness being the most critical. Changing levels of consciousness indicate dysfunction and alterations in the normal transmission and processing of sensory information in the CNS.Neurological assessment should include: assessment of consciousness, limb power, pupillary and vital signs. The Glasgow Coma Scale (GCS) is used internationally to assess consciousness, it is comprised of three elements: Eye, Verbal, and Motor response. Head Injuries & Associated Risks Consider what the implications of a reduced conscious level may be for the well-being and health of a patient?The National Institute for Clinical Excellence (NICE) (2003) published guidelines for the management of head injuries. In their guidance, they recommend that patients with a GCS less than or equal to 8 should be referred immediately for management of their airway and breathing. Patients with a reduced conscious level will have a significant risk of obstruction of the airway and aspiration.Using your experience of different hospital environments, consider which settings would be the most appropriate for a patient with a reduced conscious level? Patient ScenarioMark James, a 35-year-old, is admitted to the emergency department by ambulance with sustained seizures. He has been continually fitting for 15 minutes. On arrival he is unconscious and displaying rhythmic jerking movements of his whole body.Airway: a nasopharyngeal airway has been inserted by paramedicsBreathing: respiratory rate 31, oxygen saturation 98% on 15L oxygen via a reservoir bag mask Circulation: pulse 124 regular. BP 146/89, Blood sugar 9.8 mmol/l Disability: GCS 4/15 E-1, V-2, M-1. Pupils 5mm reacting bilaterally Environment: body temperature is recorded as 36c, there are no signs of external injury The paramedic crew informs you that they administered 5mg of diazepam rectally when they arrived at the patient’s house, without therapeutic effect. Past Medical History includes: Epilepsy, depression Mr James’s girlfriend informed the paramedic crew that he had not been taking his usual anti-epileptic medication recently Assessment & Analysis of Patient Presentation Mr James’s presentation indicates that he is in status epilepticus, a term used clinically when generalised seizures occur without improvements in conscious level between seizures, or when a seizure is sustained for more than 30 minutes. At the point of presentation, the seizure had been in progress for 15 minutes. Despite intervention with the administration of diazepam the seizure had been sustained. It is rare that a single convulsive seizure, in adults, lasts longer than a few minutes and it is accepted that early diagnosis and treatment is important in this form of epilepsy. It is usual for treatment for status epilepticus to be initiated before 30 minutes elapses as this condition has a high mortality and morbidity risk, it is therefore treated as a medical emergency. EpilepsyEpilepsy is characterised by a sudden abnormal burst of electrical stimulation, interrupting normal neuronal conduction and normal cerebral function. Seizures lead to temporary impairment of consciousness, movement, sensation and memory.Different epilepsies differ pathophysiologically, but there are common characteristics, these include alterations of synaptic and neuron properties, changes in ion channels and increased neuronal excitability and synchronization.Any type of seizure can proceed to become status epilepticus.ExerciseThere are various classifications to the severity of a seizure; identify common presentations and the potential cause.Alcohol is frequently associated with seizures, why?Tonic-clonic seizures involve bilateral extension of limbs followed by synchronous jerking movements. There is often a cry before the seizure, a fall to the ground followed by incontinence, tongue biting, foaming at the mouth and loss of consciousness. There is a post-ictal phase and when patients wake they have muscle tenderness, transient confusion and exhaustion. Cerebral Vascular Accident / StrokeStroke is defined as a sudden loss of brain function leading to a neurological deficit that lasts for 24 hours or more. Stroke occurs when blood flow to a local area of the brain is interrupted, leading to oxygen deprivation of the tissue (ischaemia), and eventually cell death or infarction.Neurons that die are irreparable, neurons that lie just outside the infarcted area, an area known as the penumbra, are often also damaged but these neurons may recover.PathophysiologyStrokes are either ischaemic or haemorrhagic:Ischaemic strokes account for 85% of all strokes. Cerebral blood flow is interrupted due to either an embolus or thrombosis. Haemorrhagic strokes accounts for 15% of all strokes and involves rupture of a blood vessel. It is further divided into intracerebral haemorrhage (ICH), or subarachnoid haemorrhage (SAH).Haemorrhagic stroke is linked closely to hypertension. The Spinal Cord Protected and hidden within the vertebral column, the spinal cord is a long mass of nerve tissue. The spinal cord is continuous with the medulla oblongata and extends beyond the cranium, through the foramen magnum of the occipital lobe, into the vertebral column extending down until the level of the first or second lumbar vertebra. It is approximately 42 - 45 cm long and 1.8 cm thick, but tapers towards its end. The Spinal CordSpinal NervesThere are 31 pairs of spinal nerves relaying nerve impulses between the body areas they serve and the spinal cord Each nerve attaches via its root to the cord, and leaves the spinal region through openings between the vertebrae, known as intervertebral foramina. The spinal cord has two enlargements along its length, known as the cervical and lumbar enlargements. The enlargements allow innervation of the upper and lower limbs; the cervical enlargement innervating the upper limbs the lumbar enlargement innervating the lower limbsDeveloping & Delivering Expert Care: For any patient with an actual or suspected spinal cord injury, care should be taken to ensure the spine remains in anatomical alignment in order to reduce the risk of further damage to the spinal cord. This is achieved by positioning patients in a neutral anatomical position. During moving or positioning the whole spine must be kept in the neutral position. A coordinated manoeuvre known as a log roll is performed using a minimum of four people. ConclusionDeveloping a fundamental understanding of the form and function of the nervous system, alongside knowledge and appreciation of common disorders, is essential to nursing practice. As nurses we are empowered to use our knowledge, understanding and skill to care for patients expertly and compassionately. Irrespective of the location or specialty, a nurse will engage with patients who are living with chronic neurological disorders or who are experiencing acute problems. Having analysed and explored these disorders, the nurse will be in a better position to understand the pathophysiology, to appreciate the challenges and difficulties that a patient faces and ultimately be insightful when caring for patients.