ࡱ> M 3bjbj== WWz/ltw@$ ׏d")E1)))))* )S$ZjL@ U-MZz<G0wpJ;);) Structure and functions of the Human Nervous system 1. The human nervous system Parts of the nervous system are responsible for various aspects of human behaviour either individually or working together Nervous system comprises of 2 main parts: central nervous system = made up of brain and spinal cord control room sending and receiving info to and from the body and the outside world peripheral nervous system = made up of neurons and organs that lie outside or beyond the brain and spinal cord 2 main parts the somatic and autonomous nervous system Central nervous system Brain and spinal cord are protected by bones and 3 strong membranes Outer membrane is called dura mater very strong and thick Middle membrane = arachnoid thick but more flexible Inner membrane is called pia mater = soft and flexible Brain and spinal cord are made up off 2 almost identical halves like mirror images Thus nerve tracts and structures found in one half will be found in other Spinal cord Spinal nerves Act like a cable connecting the brain with other parts of the body Extends from the brain down the length of the back Protected by bones forming the spinal column Spinal cord made up of columns of white matter = bundles fo axons covered with myelin Where the axon leaves the spinal cord they form nerves 30 pairs of nerves on each side of the spinal column Each nerve divides into a motor and sensory root Sensory root consists fo nerves that convey sensory info to the brain Sensory info is received form receptors in skin, skeletal muscles, tendons, joints and internal organs This info is conducted from sensory receptors to the brain along the sensory root of the spinal nerve Motor root consists of motor nerves that convey info from brain to the muscles and glands of the body Spinal nerves carry sensory and motor messages to and from the spinal cord and keep the body in communication with the brain Reflexes Spinal cord also produce basic forms of behaviour called reflexes Reflex = stereotype response that follows immediately after a certain stimulus is received E.g. touch a hot stove your hand jerks back without thinking The brain Estimated 10 billion neurons in the brain Space between the skull and brain is filled with fluid called cerebrospinal fluid Fluid is produced by the brain and surrounds the brain Floating in the fluid protects the brain being bumped about and injured Also protected by blood-brain barrier =keeps out certain harmful substances Brain is richly supplied with blood vessels These vessels carries NB substances like glucose and oxygen to brain and transport waste products like carbon dioxide from brain cells Passage of drugs more difficult in brain than in other parts of the body due to tiny blood vessels called capillaries that can not be penetrated by many substances Outer layer of brain = cerebral cortex Has wrinkled appearances because the surface has bumps and grooves called fissures Cerebral cortex composed of tissue made up by cell bodies that have a grey colour = that why it is called grey matter Brain consists fo 2 halves called cerebral hemispheres Two halves connected by thick band of fibres called the corpus callosum Corpus callosum allows two hemispheres to communicate with each other Left side mainly controls the right side and the right controls the left This is called contra lateral (contra = opposite & lateral = side) Some parts of body is controlled by same side of the brain = ipsilateral Evidence that 2 halves of brain is specialised for different types of function Left mainly involved in logical organisation, analysis of info, processing of info sequentially Left is also considered the language or verbal hemisphere Right half = process info holistically (bigger picture) and simultaneously (all at once) Right hemisphere considered to be more creative and concerned with spatial and non-verbal abilities Mostly we use both halves of the brain at the same time 1.3.1 The lobes of the brain Two hemispheres can be divided into smaller sections called lobes Different lobes have different main functions and are marked out by certain fissures on the surface of the cortex The occipital lobes Lies at the back of the brain Primary visual area of the cortex Thus the are where visual input is interpreted If there is a tumour or cell growth in this area the vision will be affected Also responsible to combine visual stimuli into meaningful patterns E.g. the ability to perceive that the eyes, nose and mouth make up a recognisable face Also where the integration of sensory experiences takes place The parietal lobes Made up of the somatosensory cortex Refers to bodily sensations such as touch, temperature, pressure and pain Parietal lobe receives info about these sensations Also receives info from muscles and joints which tells the brain about the bodys position in space Parietal lobes integrates all the somatosensory info received and provide feedback based on that info So the individual can know say what part of the body was touched, where feet and hands are in relation to the body to co-ordinate movements The temporal lobes Main functions is perception of sound Auditory info is projected to the temporal lobes where it is registered and interpreted E.g. helps us to understand spoken words and sound patterns like rain on a roof Left temporal lobe is language centre Damage to this area can negatively affect the ability to understand what is heard and use language effectively Right temporal lobe is concerned with no-verbal sounds and plays a role in speech The frontal lobes Regulates complex mental activities and behaviours Functions of frontal lobe are more generalised to produce integrated behaviour One of main functions is control of voluntary movement including the production of speech Motor area in frontal lobes ensure smooth performance in sequence of motor skills that make up complex behaviour like playing tennis If this part is damaged the person makes jerky uncoordinated movements and can struggle to stop one movement and start another Very NB function is to maintain attention and concentration, abstract thinking, reasoning and planning & regulate emotions and behaviour Damage can result in changed behaviour 1.3.2 Major structures of the brain Neocortex is the outer layer of the brain Below the neocortex are number of structures that make up the subcortex Brain can be divided into 3 sections: hindbrain, midbrain & forebrain The hindbrain Part of the brain that is at the back of the brain Oldest part of the brain & many of the structures also found in other species 3 main structures in hindbrain: Name of structureDescriptionFunctionMedulla oblongataExtension of spinal cord consists of grey matter surrounded by white matter (nerve fibres) Groups of neurons in medulla acts as reflex centres for processes ensuring survival Front of the medulla are 2 bumps called pyramids formed by crossing of motor nerve tracts Inside medulla is network of cell bodies = reticular formation which extends upwards into the brain Reflex centres for breathing and heart rate Motor nerve tracts maintain brains contra lateral control of muscles Reticular formation stimulates the brain keeping it active and alert also prevents it form over-stimulation by regulating inputPonsStructure that acts as bridge between medulla and other brain structuresAlso regulates sleep and wakefulnessCerebellumSometimes called small brain because it looks like a miniature cerebral cortexMain function is to co-ordinate motor movement by regulating posture, balancing muscle tone and muscle co-ordination By integrating and comparing info received from body can make the necessary adjustment for co-ordinated movements The midbrain Very small part of the brain Actually continuation of the pons Has 2 structures: Tectum : 2 structures : reflex centre for vision = superior colliculus Reflex centre for hearing = inferior colliculus Tegmentum: structures are mainly involved in regulation of motor movement The Forebrain Major structures are thalamus, hypothalamus, basal ganglia and limbic system StructureDescriptionFunctionThalamusConsists of collection of nerve nucleiMain function = act as relay station for sensory info thus receives sensory info and then it sends info to the appropriate structures or areas o the cortexHypothalamusBelow the thalamus Has many nerve nucleiInvolved in regulating the internal environment of the body like temperature, digestion etc. Involved in regulating states of sleep and wakefulness Involved in regulating of emotionsBasal gangliaThree large groups of neurons Axons from some of the neurons project to motor areas fo the cerebral cortex and midbrainRegulates slow, smooth movements like walkingLimbic systemMade up of several structures: hippocampus, amygdala, septum and limbic cortexRegulates motivated behaviour, emotions and memory (examples p. 79) 1.4 General principles of brain functioning 1.4.1 Hierarchical functioning Brain functions are organised hierarchically Thus more complex or higher structures control lower structures Functions of structures hierarchically higher are more complex than lower ones Higher structures also depends on input form lower ones E.g. complex attention is function of frontal lobes but to regulate attention lobes are dependent on input form reticular formation Example of a feedback loop Feedback loop = are the basis for adjusting functions to demands from the environment 1.4.2 Specificity and plasticity Function of brain is both specific and plastic Means certain structures may be connected in specific way like structures concerned with memory But brain is also capable of plasticity = being changeable than new connections can be formed in the brain E.g. child an adult brain has same amount of neurons but during development the connections between neurons are formed in response to the stimulation of the environment then regarded as more plastic 1.4.3 Lateralisation of functions Means the location of functions are predominantly in one hemisphere more than in the other The higher up in the hierarchical structure is the more lateralised its function is E.g. consider the different roles of the thalamus(lower structure) to the cerebral cortex (higher structure) in language All sounds are received by thalamus but only the verbal sounds are projected to the left temporal cortex and non-verbal sounds to the right temporal cortex Means cerebral cortex is more literalised than sub cortical structures 1.5 Peripheral nervous system ( Made up of 2 sub systems: somatic (bodily) nervous system autonomic nervous system 1.5.1 Somatic nervous system Has 2 components: sensory and one is motor Refers to the nerves that conduct info from the sensory receptors in the body to the central nervous system (sensory or efferent nerves) & from central nervous system to the skeletal muscles of the body (motor or afferent nerves) 1.5.2 Autonomic nervous system Controls processes that regulate our internal organs and glands for body to function evenly Has 2 divisions: a) sympathetic = stimulates the organs b) parasympathetic = slow things down again to restore and sustain normal functioning E.g. sympathetic nervous system increases heart rate when you have to run away form danger and parasympathetic restores heart rate to normal when danger is over See other examples in table 1 p. 81 Autonomic nervous system is designed to bring state of homeostasis or balance in the body Usually the 2 systems work in relation to one another constantly adjusting to bring optimal function in face of demands placed on the individual Sometimes one system dominates Person with sympathetic dominance is likely to be in state of tension with dilated pupils, sweaty hands, poor concentration emotional intensity etc. Parasympathetic dominance likely to be under-aroused, poorly motivated, may have respiratory or digestive difficulties Person who is automatically balanced will have moderate level of tension, reacting appropriately and concentration, motivation and 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