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NERVOUS SYSTEM Homeostasis controlled by • Nervous system • Endocrine system Divisions of the nervous system • Central nervous system (CNS) • Spinal cord • brain • Peripheral Nervous system (PNS) • Nerves that carry impulses to and from CNS Functions • Monitoring changes inside and outside of body – (stimuli) and gathers sensory input • Integration – processes and interprets the sensory input and makes decision about what is to be done • Effects a response by activating a muscle or gland – response is called motor output Neuron Nerve cell Parts of a neuron • Dendrite – carries impulses to the cell body • Axon – carries impulses from the cell body • Myelin sheath – protective layer formed by Schwann cells • Nodes of Ranvier – gaps between the sheaths ( not present in all neurons) • Axonal terminals – branches located at the terminal end of the neuron • Neurilemma – sheath of Schwann • Collateral branch – branch arising from the axon ( not present in all axons) • Oligodendrocytes – take the place of the Schwann cells in the CNS SUPPORTING CELLS neuroglia • Astrocytes – numerous projections with swollen ends that cling to neurons. Anchoring the neurons to their blood supply • Microglia – phagocytes that dispose of debris such as dead brain cells, bacteria, ect. • Ependymal cells = line cavities of the brain and spinal cord. Have cilia that beat to circulate the cerebrospinal fluid • Oligodendrocytes • Satellite cells – protective and cushion nerve cells TYPES OF NEURONS 1. Afferent • Also called sensory • Carry nerve impulses toward CNS 2. Efferent • Also called motor neuron • Carries impulses away from CNS 3. Interneuron • Also called association neuron • Connect motor and sensory neuron in neural pathways CONDUCTION OF A NERVE IMPULSE RESTING POTENTIAL • • • • • • • Membrane is polarized Not conducting an impulse -65mV to –70 mV Na+ greater concentration on outside K+ greater concentration on inside Overall charge is + on outside and – on inside Na/K pumps maintains this difference DEPOLARIZATION • Activates the neuron to transmit and action potential (AP) also called a nerve impulse • All or nothing response – AP is either propagated or not • Threshold must be reached –55mv • Na+ gates open and Na+ flows inside neuron • Voltage changes from –65 to +40 REPOLARIZATION • • • • Na+ gate closes K+ gate open and K+ flows to outside Voltage change from +40 to –65 Na/K pumps return Na+ and K+ back to normal • Thus neuron returns to resting potential REFRACTORY PERIOD • AP has passed • Na gate can’t open • Keeps AP from traveling in the wrong direction CROSSING THE SYNAPSE • Synapse – gap between the presynaptic and postsynaptic membrane • AP arrives at the presynaptic membrane • Presynaptic membrane becomes permeable to Ca++ • Vesicles move to the presynaptic mb. • They release neurotransmitter Myelinated neurons • Conduction occurs faster because the nerve impulses jump from node to node along the length of the fiber • Saltatory conduction – faster conduction in myelinated neurons External impairment of conduction • Alcohol, sedatives, and anesthetics block nerve impulses by reducing membrane permeability to sodium ions • Is no Na ions can enter the neuron then no AP will occur • Cold and pressure hinder impulse conduction because the interrupt blood circulation • Neurotransmitter diffuses across the synaptic cleft • At the postsynaptic mb. The neurotransmitter merges with receptor sites • AP starts at the postsynaptic mb • Neurotransmitters may be broken down by enzymes, washed away, or recycles • Axons may synapse with many other neurons 25 different neurotransmitters acetyocholine norepinephrine NERVE A bundle of axons also called nerve fibers REFLES ARC • Rapid predictable and involuntary responses to stimuli PERIPHERAL NERVOUS SYSTEM • Made up of nerves that lie outside the CNS • cell bodies (called ganglia) found outside the CNS • 2 structural types – cranial nerves – spinal nerves Cranial nerves • • • • • Carry impulses to and from the brain 12 pairs some are sensory some are motor some are mixed Spinal nerves • Carry impulses to and from spinal cord • all are mixed • 31 pairs Functional classification of PNS Sensory • Carries information to CNS from sense organs and sensory receptors • example: eye, Merkel discs Motor • Somatic - allows one to consciously control skeletal muscles • autonomic nervous system - regulates activity of smooth and cardiac muscles and glands 2 branches of the autonomic nervous system • Sympathetic nervous system • parasympathetic nervous system SYMPATHETIC • Controls body’s response to emergency situation and stress • increase blood glucose levels in blood • in heart rate • increases oxygen uptake • decrease activity of digestive system and urine output • dilates pupils • goosebumps/ perspiration PARASYMPATHETIC • • • • • Opposite normal no stress situations steadies heart rate constricts pupils no effect on sweat glands CNS PROTECTION • Meninges - connective tissue membranes around the brain • cerebrospinal fluid - cushions, – formed by choroids plexuses, – fluid continually moves through ventricles and between the brain and spinal cord, – 1/2 cup of fluid SPINAL CORD • • • • • 17 inches long 2 way connection with brain ends at lumbar vertebrae #2 rest of column filled with spinal fluid has gray and white matter • Caudal equina – collection of spinal nerves that extend from the end of the spinal cord • Paralysis – result of injury to cord • Severity due to location on spinal cord GRAY MATTER • Contains cell bodies and nonmyelinated fibers • contains portions of sensory and motor neurons WHITE MATTER • Myelinated axons of interneurons that run to the brain and from one side of the SC to the other side ( called tracts) PARTS OF THE BRAIN http://www.psych.ualberta.ca/~ITL/br ain/ Ventricles • Interconnecting cavities filled with CSF • 4: 4th, 3rd, and 2 lateral ventricles Medulla Oblongata • Regulates heart beat, blood pressure, and breathing, • Has reflex centers for swallowing, coughing, sneezing, hiccupping and vomiting • Has nerve tracts between the spinal cord and brain Pons • Works with medulla to regulate breathing rate • Mostly a fiber tract MIDBRAIN • Relay station for tracts passing between the cerebrum and the spinal cord or cerebellum • Has reflex centers for visual, auditory, and tactile responses • Contains the cerebral peduncles and corpora quadrigemina CEREBELLUM • Maintains normal muscle tone, posture, balance • Ensures that all of the skeletal muscles work together to produce smooth and coordinated movements • Essential for skills such as playing the piano or hitting a baseball. hypothalamus • Forms floor of the 3rd ventricle • Maintains homeostasis by regulating hunger, sleep, thirst, body temperature and water balance. • Sex, pain , and pleasure centers are located here • Part of the limbic system • Called emotion visceral brain • Regulates the pituitary gland therefore it is the link between the nervous system and the endocrine system THALAMUS • Serves as a relay station for sensory impulses traveling upward to other parts of the brain to the cerebrum • Involved in arousal and higher mental functions such as memory and emotion • Gives one a crude awareness of whether the sensation will be pleasant or not Pineal gland • Secretes the hormone melatonin • At night the pineal gland produces melatonin - causes one to fall asleep LIMBIC SYSTEM • • • • System of tracts and nuclei Surround the brain stem Called emotional brain Blends higher mental functions and primitive emotions into a whole • Area that makes eating and sexual behavior seem pleasant Parts of limbic system • • • • • Hippocampus Amygdala Thalamus Hypothalamus Frontal lobe hippocampus • Area through which incoming sensory signals generate particular limbic response • example Amygdala • Associated with fear conditioning and associating danger with sensory stimuli • May be responsible for controlling human aggression Frontal lobe • Keeps limbic system in check • It uses reason to keep us from acting out strong feelings • Alcohol suppresses the frontal lobe and the limbic system takes over RETICULAR FORMATION • Nuclei and fibers that extend the length of the brain stem • Reticular activating system • Controls the sleep/wake cycle • Severe damaged can cause one to be comatose CEREBRUM CEREBRUM • Largest portion of the brain • Divided into left and right cerebral hemispheres • Surface has gyri – elevated ridges of tissue • Sulci – shallow grooves • Fissures – deeper grooves • Divided into lobes • Lobes named after cranial bones • Gray matter • Center for association, integration, and learning CORPUS CALLOSUM • Bridge of nerve tracts that connect the right and left hemispheres • Tracts cross – left controlled by right side of brain • White matter – tracts that carry information from 1 part of cerebrum to another part • Basal nuclei – relay stations that help to regulate motor activities – islands of gray matter found deep within the white matter LOBES • • • • Occipital – vision Temporal – hearing Frontal - olfactory and higher learning Parietal Functional areas of the cerebral cortex • Somatic sensory area – Impulses from the body’s sensory receptors, except for the special senses, are localized and interpreted in this area of the brain • Primary motor area – Allows us to consciously move our skeletal muscles GENERAL INFORMATION Falling in love • Pleasure center in the hypothalamus • Brain neurotransmitters – norepinephrine and dopamine • They give brain a pleasure flush (cousins of amphetamines) • Falling in love – pleasure center is bathed with dopamine and norepinephrine BLOOD BRAIN BARRIER • Composed of least permeable capillaries in the body • Prevents urea and most drugs from entering the brain tissue • Useless against fats, respiratory gases • Keeps internal environment of brain very controlled DISEASES/DISORDERS • • • • • • • • Multiple sclerosis Huntington’s chorea Parkinson’s disease Meningitis Hydrocephalus Concussion Contusion Cerebral edema • • • • • • • • • CVA TIA Alzheimer’s disease Quadriplegic Paraplegic Type A personality Cerebral palsy Spina bifida