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63 Cards in this Set
- Front
- Back
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Nervous tissue consists of two types of cells
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Neurons and neuroglia
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Neurons
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Also known as nerve cell, neurons are responsible for the unique functions of the nervous system
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Neurolgia
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Which support, nourish and protect neurons
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NEURONS
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These are the nerve cells that carry messages form one part of the body to another. Although some are very short(in the brain), others are the longest cells in the body. One from the foot can stretch all the way to the brain. Functionally there are 3 types of neurons: Sensory, Interneurons and Motor Neurons
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Sensory Neurons
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Also known as afferent neurons, they carry information form various parts of the body to the central nervous system. They tell the brain or the spinal cord what is happening inside or outside of the body
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Interneurons
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These pass a message form one neuron to another neuron
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Motor Neurons
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Also known as efferent, these take a message FROM the brain or spinal cord TO the target cell and instruct it to do something
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Neurons consist of three parts
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Cell body, dendrites, axons
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Cell Body
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This part of a neuron contains the nucleus and the usual organelles(mitochondria etc
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Dendrites
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Are short, branched projection, emanating from the cell body. Each neuron has multiple dendrites. These are parts of a neuron that receive information
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Axons
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Each neuron has a single axon extending from the cell body. This propogates action potentials along hte neuron towards other cells(neurons, muscle fibres, or cells of glands). The ends of an axon divide into many processes called axon terminals, and attached to the ends are synaptic end bulbs that contain neurotransmitters. The synaptic end bulbs of a neuron form part of synapses-points of communication between neurons
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Neuroglia(support cells)
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Are non-neural cells that SUPPORT, nourish and protect the neurons of the CNS and PNS. Although they are regarded as support cells they actively participate in the operations of the nervous system. There are 6 different types of neuroglia, 4 are found in the CNS and 2 are found in the PNS. The most important neurogla are the schwann cells in the PNS and the oligodendrocytes in the CNS, both of these types form the myelin sheath(insulating layer)
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Myelin Sheath
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Neurons in the insulating layer are called the myelin sheath, and the axons that surronded by this layer are said to be myelinated (without sheath-unmyelinated). Several layers of cell membrane from either oligodendrocytes(CNS) or schwann celss(PNS wrap around axons to create the myelin sheath. A myelinated axon will have several neuroglial cell lined up next to each other and around it to form the sheath. There will be small gaps between the myelineating cells on the axon, these are called nodes of Ranvier
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Grey and white matter
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The amount of myelin present in different regions of the nervous system give it either a white or grey appearance
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White Matter
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WHITE matter is white in colour and so some regions of the brain and spinal cord appear white due to the presence of unmyelinated axons. White matter forms nerve tracts in the CNS and nerves in the PNS
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Grey matter
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Appears grey due to the absence of myelin. Grey matter contains neuronal cell bodies, dendrites, unmyelinated axons, axon terminal and neuroglia
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Organisation of the nervous system
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There are two main subdivisions of the nervous system-The central nervous system(CNS) and The peripheral nervous system(PNS), which is further divided into- The somatic nervous system, The enteric nervous system and the Autonomic nervous sytem, which is also further divided into the sympathetic and parasympathetic nervous systems
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Central nervous system
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The CNS consists of the brain and th spinal cord, both of which is enclosed and protected by bone and other structures. The CNS processes, integrates, stores, and responds to sensory information that is relayed from the peripheral nervous system. It is also the source of thoughts, emotions and memory
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Peripheral nervous system
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The PNS consists of all the nervous tissue outside the CNS, this includes the cranial nerves and their branches, the spinal nerves and their branches, ganglia and sensory receptors. The PNS can be divided into the somatic nervous system-SNS, the autonomic nervous system-ANS, and the enteric nervous system-ENS
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Somatic nervous system
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The motor responses of the SNS can be consciously controlled, and so the SNS in responsible for VOLUNTARY control. It consists of sensory neurons that transmit information mainly formt he external environment to the CNS and motor neurons that transmit nerve impulses from the CNS to the SKELETAL MUSCLES ONLY
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Autonomic nervous system
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The ANS is responsible for the INVOLUNTARY neural control, because its motor responses aren\rquote t normally under conscious control. It consists of sensory neurons that transmit information mainly from the internal environment to the CNS, and motor neurons that transmit nerve impulses from the CNS to SMOOTH MUSCLES, CARDIAC MUSCLE and GLANDS. It has two branches- the sympathetic and parasympathetic divisions
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ANS sympathetic division
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Has generally stimulating actions. This division supports exercise and emergency actions, often known as the fight or flight responses
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ANS parasympathetic division
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Generally the relaxing action, this division is involved in the rest and digest activities
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Enteric nervous system
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ENS is sometimes knwon as the brain of the gut, as it is located in the gastrointestinal tract. It was considered to be part of the ANS as its function is INVOLUNTARY, but it has since been found that many of its nerons act independantly of the ANS. It consists of Sensory neurons which monitor chemical changes and stretching within the GITract, and motor neuron which control the contraction of smooth muscle in the wall of the GITract, secretions of the GITract and activity of hormone secreting cells in the GITract
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Nerve impulse conduction
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Conduction of nerve impulses occurs either by1)continuous conduction or 2)saltatory conduction. The speed at which the nerve impulses are conducted depends upon a number of things including the diameter of the neuron and whether it\rquote s myelinated. Neurons can be classified into types according to their speed of transmission. They are Type A fibres Type B fibres and Type C fibres
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Continuous conduction
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This is the SLOWEST method of nerve impulse conduction, and is very much like a domino effect-as when Na+(Sodium) flow into the neuron it causes sodium channels in the adjacent areas to open-and this continues along the length of the axon. This type of conduction takes place in unmyelinated axons and fibres
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Saltatory conduction
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Is much FASTER and only occurs on myelinated axons. During saltatory conduction nerve impulses appear to \lquote leap\rquote rapidly from one node on Ranvier to the next, hence this method is much faster
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Nerve impulse conduction-Type A fibres
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These are the LARGER DIAMETER axons and all type a fibres are myelinated. Impulses are conducted at rapid speeds. This includes the axons that propogate impulses associated with touch, pressure, position of joints and some thermal sensation. Also those that conduct impulses to skeletal muscle
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Nerve impulse conduction-Type B fibres
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These have SMALLER DIAMETER than type a fibres, but are still myelinated. Impulses are conducted at speeds that are slower than type a fibres, but more rapid than type c fibres. This includes the axons that conduct sensory nerve impulses from internal organs to the brain and spinal cord, and the axons of autonomic motor neurons that extend from the brain and spinal cord to autonomic ganglia
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Nerve impulse conduction-Type C Fibres
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Have the SMALLEST DIAMETER and are unmyelinated, as a result nerve impulses are conducted along these axons very slowly. This includes axons that conduct some sensory impulses for pain, touch, pressure, heat and cold from the skin and pain impulses from internal organs. Also autonomic motor fibres that extend from autonomic ganglia to the heart, smooth muscle and glands
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Functions of the spinal cord
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-Propogate sensory nerve impulses from peripheral parts of the body to the brain\par-Propogates motor nerve impulses from the brain towards the peripheral parts of the body-Integrates information arriving at the spinal cord-Processes information and produces spinal cord reflexes when appropriate
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General structure of the spinal cord-Protective structures
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The central nervous system has a very limited ability to repair itself, therefore its important to protect the brain & the spinal cord as much as possible. Bone tissue(cranium and vertebrae) surround the CNS & membranes that cover the surface of the brain & spinal cord. These membranes are called meninges, there are 3 layers. From superficial to deep they are; Dura Mater, Arachnoid Mater and Pia Mater. Cerebrospinal fluid also protects the CNS
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Dura Mater Dura-tough Mater-Mother
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Is composed of dense irregular connective tissue. Between the dura mater and the wall of the vertebral cavity (Skull) is a space called the epidural space, this is filled with fat and connective tissue and provides additional cushioning
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Arachnoid Mater Arachnoid-like a spider Mater-mother
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Is composed of delicate collagen and elastin fibres that are arranged like a spiders web. Between the dura mater and the arachnoid mater is a space called the subdural space, this is filled with interstitial fluid
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Pia Mater Pia-Delicate Mater-mother
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Is composed of thin, transparent connective tissue containing collagen and elastic fibres. The pia mater is attached to the surface of the spinal cord and the brain. Between the pia mater and the arachnoid mater is a space called the subarachnoid space, this contains the cerebrospinal fluid(CSF)
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Spinal Cord
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The spinal cord and the brain comprise of the Central Nervous System. The spinal cord connects to the brain through a large hole in the base of the skull, called the FORAMEN MAGNUM, and is enclosed and protected by the bones that make up the vertebral column. It acts as a communication link between the brain and the Peripheral Nervous System. 31 pairs of spinal nerves emerge from the spinal cord and are part of the Peripheral Nervous System
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Cerebrospinal fluid (CSF)
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Cerebrospinal fluid is a clear liquid that protects the CNS from chemical and physical injury. It also functions to carry oxygen, glucose and other chemicals to neurons and neuroglia. This fluid continually circulates through cavities in and around the brain and the spinal cord in the subarachnoid space
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External Spinal Cord Anatomy
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In adults the spinal cord extends from the medulla oblongata at the base of the brain, to the superior border of the second lumbar vertebrae. Therefore the spinal cord is shorter than the vertebral column-as a result the nerves that arise from the base of the spinal cord hang down in the vertebral cavity from the base of the spinal cord, before exiting at a lower point. These are called Cauda Equina.The spinal cord enlarges in two regions -superior and inferior enlargementSpinal cord-Superior enlargement
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Spinal cord-Inferior enlargement
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Also called the lumbar enlargement. Nerves that carry the information to and from the lower limbs arise for this location
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INTERNAL spinal cord anatomy
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A cross section of the spinal cord reveals an araangement of grey and white matter. The grey matter is surrounded by the white matter
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White Matter
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Consists of bundles of myelinated axons. The white matter of the spinal cord is divided into 3 regions called COLUMNS; the DORSAL, VENTRAL and LATERAL columns. Within these columns are bundles of axons called tracts, which share a common origin or destinatioin adn carry similar information. These tracts are either Sensory(ascending) or MOTOR(descending) tracts. Sensory tracts carry impulses to the brain and motor tracts carry impulses back down the spinal cord
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Grey Matter
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The grey matter of the spinal cord looks like a letter H or a butterfly, and is surrounded by the white matter. Grey matter is composed of nueron dendrites and cells bodies, unmyelinated axons, and neuroglia. Grey matter is responsibile for receiving and integrating incoming and outgoing information.The grey matter on each side of the spinal cord is divided into three regions calle HORNS. The dorsal horn contains interneurons and incoming axons of sensory neurons. The anterior horn contains cell bodies of somatic motor neurons and the lateral horn contains cell bodies of autonomic motor neurons
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Spinal nerves
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31 pairs of spinal nerves emerge form different points of the spinal cord and are part of the PNS. These nerves and their branches connect the CNS to sensory receptors, muscles and glands. They are grouped as follows-8 cervical pairs-thoracic pairs-5 lumbar pairs-5 sacral pairs-1 coccygeal pair
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The BRAIN
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The brain is surrounded and protected by the cranium, meninges & CSF. It contains about 100billion neurons and about 1000 trillion synapses! The brain is the organ in which sensations are register, integrated and store, allowing us to make decision & take action that are appropriate. Also the brain is responsible for emotions, itellect, memory & behaviour. Different regions are specialised, but may also work together is some shared functions
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Blood brain barrier
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The blood brain barrier (BBB) refer to structural adaptations in the capillaries of the brain and neuroglia htat help to protect the brain from harmful substances and pathogens, by denying them entry into the brain. From the blood ciculation substances that are necessary and important can enter easily(eg glucose) whilst other may be denied, or only able to enter very slowly. It isn\rquote t effective against lipid-soluble substance including alcoholand anaesthetics
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Parts of the Brain
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The principle parts of the brain include:Brain stem,Diencephalon, Cerebrum, Cerebellum.
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Brain stem
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The brain stem is part of the brain between the spinal cord and the diencephalon and consists of the following areas; Medulla oblongata, Pons, Midbrain, Reticular formation
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Brain stem-Medulla oblongata
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Is continous with the spinal cord and contains ascending and descending nerve tracts. Medullary neuclei regulate heartbeat, respiration, blood vessel diameter, swallowing,vomiting, coughing, sneezing and hiccupping
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Brain stem-Pons
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Is superior to medulla oblongata, and contains the pneumotaxic and apneustic areas, which work with the medulla oblongata to control respiration
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Brain stem-midbrain
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Is superior to the pons and relays motor impulses form the cerebral cortex to the pons and sensory impulses from the spinal cord to the thalamus. The midbrain is involved in eyeball co-ordination, movement of the head and trunk, and control of movement
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Brain stem-Reticular formation
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Is a netlike arrangement of grey and white matter that extends thorughout the brainstem. The reticular formation has both sensory and motor function, including alerting the cerebral cortex of incoming sensory signals. The reticular activating system help to wake us up and keep us conscious
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Cerebellum
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The cerebellum is the second largest part of the brain, and has three parts that control balance, gross motor coordination and fine motor coordination. The cerebellum regulates posture and balance, and corrects discrepancies between intended and acutal movement
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Diencephalon
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Is located between the brainstem and the cerebrum and consists of a number of distinct parts:-Epithalamus-Thalamus-Hypothalamus-Circumventricular organs
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Diencephalon-Epithalamus
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Contains the pineal gland, which secretes melanonin(a hormone involved in sleep/awake cycles and the setting of the bodys biological clock
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Diencephalon-Thalamus
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Functions as a relay centre. It direct incoming information to the appropriate part of the brain
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Diencephalon-Hypothalamus
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Controls and integrates ANS activities(involuntary), as well as controlling the release of hormones from the anterior pituitary gland. The hypothalamus us involved in emotional and behavious patterns, carcadian rhythms, body temperature, food intake, and wake and sleep patterns
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Diencephalon-Circumventricular organs
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Are able to montior chemical changes in the blood because they lack the blood-brain barrier. The circuventricular organs are involved in regulatin blood pressure, fluid balance, hunger and thirst
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Cerebrum
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Is the largest portion of the brain, refered to as the seat of intelligence, it gives us the ability to read, write and speak, imagine and remember. It consists of an outer rim of grey matter known as the cerebral cortex. It is divided into left and right hemispheres. These hemispheres contain basal ganglia nd the limbic system, each hemisphere is futher divided into lobes
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Cerebrum-Cerebral cortex
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Consists of an outer rim of grey matter, which contains billions of neuron. The cerebral cortex is folded into ridges called SULCI(sulcus) or FISSURES. Deep to the cerebral cortex in cerebral white matter
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Cerebrum-Hemispheres
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The cerebrum is divided into left and right hemisphers by the longitudinal fissure. The left hemisphere is sometimes called the thinking brain, and is used for logical reasoning, usch as solving maths equations. The right hemisphere may be known as the feeling brain and is used more for intuition and creativity. Some people tend to use one side more than the other
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Cerebrum-Basal ganglia
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Deep within each hemisphere are three masses of grey matter(nuceli) that are collectively called the basal ganglia. The basal ganglia are important in coordinating motor movements and posture
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Cerebrum-Limbic system
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The limbic system is often called the emotional brain because it is involved in the range of emotions such as apleasute, affection, fear and anger. One area called the AMYGDALA is responsible for rage. Other functions include a role in olfaction(smell) and memory
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Cerebrum-Lobes
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Each hemisphere is then further divided into lobes-Frontal lobes are involved in voluntary motor function, motivation, agression and mood-Parietal lobes contain the major sensory areas-Occipital lobes contain the visual areas-Temporal lobes receive oflactory(smell) and auditory(hearing) input, and involved in memory, abstract thought and judgement.Scattered throughout the lobes are areas which contain neurons for particular functions. eg understanding language or recognition
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