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Neurophysiology of Sensations Central Nervous System (CNS) Peripheral Nervous System (PNS) Cervical Thoracic Lumbar Sacral Cocygeal Components of the Nervous System Figure 11.1 Principle Parts of Nervous System • Central Nervous System (CNS) – Components: brain and spinal cord – Functions: receives, processes, and transfers information • Peripheral Nervous System (PNS) – Components: nerves outside CNS – Sensory neurons: carry information toward the CNS – Motor neurons: carry information away from CNS Types of Neurons in the Nervous System 1. Sensory Neuron 2. Interneuron 3. Motor Neuron Figure 11.2 Communication Cells of System • Neurons: Actual Communication Cells • Cell Body • Axon (one – away) • Dendrites (grow more with learning!) • Neuroglia: Support Cells of the Nervous System • Schwann Cells (PNS) • Oligodendrocyte (CNS) Neuroglia vs. Neurons • • • • Neuroglia divide. Neurons do not. Most brain tumors are “gliomas.” Most brain tumors involve the neuroglia cells, not the neurons. • Consider the role of cell division in cancer! How Neurons Function (Physiology) Irritability – ability to respond to stimuli Conductivity – ability to transmit an impulse The plasma membrane at rest is polarized Fewer positive ions are inside the cell than outside the cell Slide 7.17 Transfer of Information from Neuron to Target • Synaptic transmission –Release of neurotransmitter • Effects of neurotransmitter: – Electrical energy converted to chemical energy – cell –Role of postsynaptic neuron: integrate and process information –Role of postsynaptic muscle cell – must respond. –Nervous system has final and absolute control over skeletal muscle cells! Peripheral Nervous System: Relay Information between Tissues and CNS • Nerves: carry signals to and from CNS – Cranial nerves: connect directly to brain – Spinal nerves: connect to spinal cord • Sensory neurons: provide information to CNS Autonomic Functioning Parasympathetic – housekeeping activites Conserves energy Maintains daily necessary body functions Remember as the “D” division - digestion, defecation, and diuresis Slide Central Nervous System: Brain & Spinal Cord • CNS protection – Bone: skull and vertebrae – Meninges: dura mater, arachnoid, and pia mater – Cerebrospinal fluid: between arachnoid and pia – Blood-brain barrier: carries nutrients and waste for CNS • Spinal cord: relays information through nerve tracts in white matter Ventricles of the Brain and Circulation of Cerebrospinal Fluid Figure 11.12 Brain: Major Divisions • Hindbrain: coordinates basic, automatic, vital functions • Medulla oblongata: controls automatic functions of internal organs • Cerebellum: coordinates basic movements • Pons: aids flow of information • Midbrain: coordinates muscles related to vision & hearing • Reticular Formation - Wakefulness Brain: Processes and Acts on Information • Forebrain: receives and integrates information concerning emotions and conscious thought • Hypothalamus: helps regulate homeostasis • Thalamus: receiving, processing, and transfer center • Limbic system: neuronal pathways involved in emotions and memory • Cerebrum/cerebral cortex: higher Regions of the Brain Cerebral hemispheres Diencephalon Brain stem Cerebellum Figure 7.12 Slide 7.27 Cerebral Hemispheres (Cerebrum) The surface is made of ridges (gyri) and grooves (sulci) Figure 7.13a Slide Lobes of the Cerebrum Figure 7.15a Slide Specialized Areas of the Cerebrum Somatic sensory area – receives impulses from the body’s sensory receptors Primary motor area – sends impulses to skeletal muscles Broca’s area – involved in our ability to speak Slide 7.30 Specialized Area of the Cerebrum Figure 7.13c Slide Sensory and Motor Areas of the Cerebral Cortex Figure 7.14 Slide 7.31 Thalamus -Surrounds the third ventricle -The relay station for sensory impulses -Transfers impulses to the correct part of the cortex for localization and interpretation Slide 7.35 Hypothalamus Under the thalamus Important autonomic nervous system center Helps regulate body temperature Controls water balance Regulates metabolism Slide Hypothalamus An important part of the limbic system (emotions) The pituitary gland is attached to the hypothalamus Slide Hind Brain: Pons The bulging center part of the brain stem Mostly composed of fiber tracts Includes nuclei involved in the control of breathing Slide 7.40 Medulla Oblongata The lowest part of the brain stem Merges into the spinal cord Includes important fiber tracts Contains important control centers Heart rate control Blood pressure regulation Breathing Swallowing Vomiting Slide 7.41 Sleep: Midbrain Brain Activity continues during sleep! • Sleep center: reticular activating system (RAS) –Stages: based on electroencephalograms (EEGs) • Stage 1: transitional, random small waves on EEG • Stage 2: skeletal muscles relax, little eye or body movement, EEG shows sleep spindles Sleep • Stage 3: heart and respiration slower, EEG shows slow wave sleep • Stage 4: difficult to awaken, heart and respiration slowest, body temperature decreased • REM (rapid eye movement) Sleep: dreaming, EEG same as awake. Lack of REM = sleep deprivation • Sleep cycles through these stages, REM occurring every 90 minutes of so. Memory: Storing and Retrieving Information • Short term: working memory, information from previous few hours • Occurs in the Limbic System • Long term: information from previous days to years • Occurs in the Cerebral Cortex • Permanent Change to Neurons • “Builoding Dendrites Alzheimer’s Disease Progressive degenerative brain disease Mostly seen in the elderly, but may begin in middle age Structural changes in the brain include abnormal protein deposits and twisted fibers within neurons Victims experience memory loss, irritability, confusion and ultimately, hallucinations and death Slide 7.51 Traumatic Brain Injuries Concussion Slight brain injury No permanent brain damage Contusion Nervous tissue destruction occurs Nervous tissue does not regenerate Cerebral edema Swelling from the inflammatory response May compress and kill brain tissue Slide 7.49 Cerebrovascular Accident (CVA) Commonly called a stroke The result of a ruptured blood vessel supplying a region of the brain Brain tissue supplied with oxygen from that blood source dies Loss of some functions or death may result Slide 7.50 • NS has 3 main functional divisions; a) Sensory division of NS: • Detects changes in internal and external environments and informs the CNS about them. b) Motor division of NS: • Initiates and controls the activities of skeletal muscles • Controls the activities of plain muscles, cardiac muscles and even glands. c) Intellectual division of NS: • Consciousness, memory, learning, thoughts, emotions Centers Tracts Afferents Receptors 1) Def., • Sensation is a conscious perception of particular feeling caused by stimulation of certain type of receptor by its adequate stimulus. 2) Classifications: Sensations General Special Organic 1) Special sensations: • Vision, hearing, taste, smell and equilibrium 2) General sensations: • Arise from receptors distributed allover the body • Are classified into; a) Somatic sensations: from somatic structures e.g. skin b) Visceral sensations: from viscera 3) Organic senses: e.g. thirst, hunger and sexual desire Def, • These sensations arise from somatic structures of all the body i.e. skin and deep tissues e.g. sk ms Types: • They include according to their adequate stimulus: 1. Mechanoceptive sensations: 2 types; – Tactile e.g. touch, pressure, and vibration sensations. – Proprioceptive sensations e.g. sense of position and movement 2. Pain sensation. 3. Thermal sensation; cold and warm. Def., • Feeling produced by application of light mechanical pressure to the skin Types: • They include 2 types : 1. Crude touch 2. Fine touch Def., • Poorly localized touch sensation produced by touching the skin with diffuse ill defined object e.g. a piece of cotton or the touch of clothes. Receptors: • Free nerve endings • Hair end organs Pathway: • Ventral or anterior spinothalamic tract Def., • Highly localized touch sensation produced by application of a well localized object to the skin e.g. a tip of a pencil or a head of a pin or teeth of a comb. Receptors: • Meissner's corpuscles • Merkel's discs Pathway: • Dorsal column medial leminiscal system or gracile and cuneate tracts Types: • It includes : 1. Tactile localization: is the ability to localize the point of touch with eyes closed 2. Tactile discrimination : is the ability to perceive 2 points of touch with eyes closed as 2 separate points of touch 3. Stereognosis: is the ability to recognize a familiar object e.g. key with eyes closed Pressure: • It is a feeling produced by the application of heavy mechanical stimuli to the skin Vibration : It is a feeling of rhythmic pressure changes produced by the rapid repetitive stimulation of certain mechanoreceptors e.g. Pacinian and Meissner's corpuscles It is tested by use of tuning fork Pathway: both sensations are carried by Gracile and Cuneate tract Def : • Feeling produced by stimulation of proprioceptors in skeletal muscle and joints • Or It is the conscious perception of the position and movements of the different parts of the body, particularly the limbs and joints. • Types: a) Static or sense of position b) Dynamic or sense of movement of joints Pathway: Dorsal column medial leminiscal system or Gracile and Cuneate tract Significance: • The brain and other motor centers e.g. basal ganglia, cerebellum use this information in the control of posture and movements N.B. • Maintaining the body equilibrium or balance needs discharge from 3 kinds of receptors; 1. Proprioceptors of foot 2. Visual receptors 3. Vestibular receptors (Crista in semicircular canals and macula in utricle and saccule) in inner ear Crista Amuplaris Macula Def : •Unpleasant sensory and emotional experience associated with actual tissue damage. Significance: •Pain is a protective mechanism for the body. •It occurs whenever the tissues are damaged and it initiates protective reflex for removing the injurious stimulus Receptors: •Free nerve endings Pathway: lateral spinothalamic tract Types: • According to its source; 1. Cutaneous pain: pain comes from skin 2. Deep pain: pain comes from deep tissues e.g. skeletal muscle, joints, ligaments, and tendons and bone 3. Visceral pain: pain comes from viscera e.g. stomach • According to its characters; 1. Fast pricking pain 2. Slow burning pain Sensation Pain Crude touch Fine touch Deep pressure Vibration Proprioception Tool used Pin Receptors Free nerve endings Pathway or tract Lateral spinothalamic tract Cotton wool Free nerve endings Ventral and hair end organs spinothalamic tract compass or Meissner's Dorsal column pencil or coin corpuscles (gracile and Merkels disc cuneate tract) Different •Pacinian Dorsal column weights •Ruffini endings (gracile and cuneate tract) Tuning fork •Pacinian Dorsal column •Meissner’s (gracile and corpuscles cuneate tract) Finger or toe •Muscle spindle Dorsal column of the patient •Pacinian corpuscles (gracile and •Golgi tendon organs cuneate tract) Def. • Is the impairment of nerve functions due to high blood glucose Manifestations: Sensory Neuropathy - Symptoms Motor Neuropathy Symptoms Autonomic Neuropathy Symptoms Neuropathy - Signs Glove and stock Hypoesthesia Painless nature of diabetic foot disease CNS DEFINITIONS • Nucleus-collection of nerve cells inside the CNS • Ganglion-collection of nerve cell bodies outside the CNS • Centers- collections of cell bodies and dendrites in the CNS • Tracts-bundles of axons within the CNS Sensory nerve damage THANKS