NERVOUS SYSTEM CHAPTER 9 NERVE CELLS • ARE CALLED NEURONS • ARE THE STRUCTURAL AND FUNCTIONAL UNIT OF THE NERVOUS SYSTEM • THEY HAVE A CELL BODY USUALLY WITH ONE AXON AND SEVERAL DENDRITES • THE AXON TRANSMITS THE IMPULSE AND THE DENDRITES RECEIVE THE IMPULSE NERVE IMPULSE FLOW NERVOUS TISSUE • MASSES OF NEURONS THAT ARE SPECIALIZED TO REACT TO PHYSICAL AND CHEMICAL • CHANGES IN THE ENVIRONMENT. • NERVES ARE BUNDLES OF AXONS • NEUROGLIAL CELLS ARE SUPPORTING TISSUE FOR THE NERVOUS SYSTEM. (NEUROGLIAL LITERALLY MEANS NERVE GLUE) TWO MAIN DIVISIONS OF THE NERVOUS SYSTEM • CNS – CENTRAL NERVOUS SYSTEM – INCLUDES BRAIN AND SPINAL CORD • PNS – PERIPHERAL NERVOUS SYSTEM – ALL OF THE NERVES THAT CONNECT TO THE BODY PARTS NERVOUS SYSTEM FUNCTIONS • SENSORY – RECEIVE INFORMATION – CONNECTED TO RECEPTORS (SENSE ORGANS) • INTEGRATIVE – COMBINE AND MAKE DECISIONS • MOTOR – CAUSE ACTIONS – CONNECTED TO EFFECTORS (MUSCLES AND GLANDS) SENSORY • RECIEVES EXTERNAL INFORMATION THROUGH THE FIVE SENSES • ALSO MONITORS THE BODY’S INTERNAL CONDITIONS • THIS INFORMATION IS CONVERTED INTO IMPULSES AND TRANSMITTED TO THE BRAIN. INTEGRATIVE • INFORMATION IS BROUGHT INTO THE BRAIN AND COMBINED WITH MEMORY TO CREATE SENSATIONS AND ARE TRANSLATED INTO PERCEPTIONS. • CONSCIOUS OR SUBCONSCIOUS DECISIONS ARE MADE MOTOR • DECISIONS ARE CHANGED INTO IMPULSES TRANSMITTED TO THE MUSCLES AND GLANDS WHERE ACTIONS TAKE PLACE. HOMEOSTASIS • THE NERVES DETECT CHANGES EXTERNALLY AND INTERNALLY INTEGRATING NEW AND OLD INFORMATION THEY HELP MAINTAIN HOMEOSTASIS WITHIN THE BODY BY DIRECTING CHANGES TYPES OF NEUROGLIAL CELLS • MICROGLIAL CELLS – LOCATION – SCATTERED IN CNS – FUNCTION – SUPPORT NEURONS AND PHAGOCYTIZE BACTERIA AND CELLULAR DEBRIS • OLIGODENDROCYTES – – LOCATION – ON AXONS OF BRAIN AND SPINAL CORD – FUNCTION – PROVIDE MYELIN SHEATH FOR INSULATION • ASTROCYTES – LOCATION – FOUND BETWEEN BLOOD VESSELS AND NEURONS – FUNCTION – STRUCTURAL SUPPORT, REGULATES NUTRIENT CONCENTRATIONS, AND FORM SCAR TISSUE • EPENDYMAL CELLS – LOCATION AND FUNCTION – FORM MEMBRANES THAT COVER THE BRAIN AND LINE CAVITIES INSIDE OF THE BRAIN PARTS OF THE NEURON • AXON • DENDRITES • CELL BODY • NEUROFIBRILS • CHROMATOPHYLLIC SUBSTANCES • AXONAL HILLOCK • MYELIN • NEURILEMMA • NODES OF RANVIER STRUCTURAL TYPES OF NEURONS • BIPOLAR NEURONS • UNIPOLAR NEURONS • MULTIPOLAR NEURONS FUNCTIONAL TYPES OF NEURONS • SENSORY NEURONS -CARRY INFORMATION TO THE BRAIN -MOST = UNIPOLAR, SOME = BIPOLAR * INTERNEURONS -LOCATION ONLY BRAIN AND SPINAL CORD -ARE MULTIPOLAR AND CONNECT OTHER TYPES OF NEURONS • MOTOR NEURONS -CARRY INFORMATION AWAY FROM THE BRAIN TO THE EFFECTORS NERVE IMPULSE • THE NERVE IMPULSE IS CAUSED BY ELECTROCHEMICAL CHANGES IN THE CELL MEMBRANE. • NERVE IMPULSES FOLLOW THE ALL OR NONE RESPONSE LIKE THE MUSCLE FIBERS. • NERVE IMPULSES TRAVEL FROM AXON TO DENDRITE • THE AXONS DO NOT TOUCH THE DENDRITES! • THE GAP BETWEEN THE AXON AND THE DENDRITE ENDINGS IS CALLED THE SYNAPSE • NEUROTRANSMITTERS DIFFUSES ACROSS THE SYNAPTIC GAP CARRYING THE NERVE IMPUSLE. NEUROTRANSMITTERS • EXCITATORY TRANSMITTERS TRIGGER IMPULSES • INHIBITORY TRANSMITTERS LESSEN THE CHANCE THAT AN IMPULSE WILL BE TRANSFERRED. • ACETYCHOLINE – CONTROLS SKELETAL MUSCLES • NOREPINEPHRINE – CREATES A SENSE OF FEELING GOOD • SEROTONIN – WORKS WITH SLEEP PATTERNS • ENDORPHINES – REDUCES PAIN • NEUROTRANSMITTERS ARE DECOMPOSED BY ENZYMES OR REABSORBED BY THE NERVE CELLS TO STOP THE IMPUSLE. NERVE • A NERVE IS A CORDLIKE BUNDLE OF FIBERS HELD TOGETHER BY LAYERS OF CONNECTIVE TISSUE. TYPES OF NERVES • SENSORY NERVES CONDUCT IMPULES INTO THE BRAIN AND SPINAL CORD • MOTOR NERVES CARRY IMPULSES TO THE MUSCLES AND GLANDS • MIXED NERVES ARE COMPOSED OF BOTH SENSORY AND MOTOR FIBERS REFLEXES • ARE INVOLUNTARY ACTIONS • ARE SUBCONSCIOUS RESPONSES TO CHANGES OF STIMULI INSIDE OR OUTSIDE OF THE BODY – EXAMPLES: SNEEZES, BLINKING, SWALLOWING, VOMITING, BLOOD PRESSURE, HEART RATE, DIGESTION, KNEE JERK, AND MANY OTHERS Meninges Membranes located between the brain and the bones. There are three layers * dura mater -outermost -white fibrous connective tissue -contains many blood vessels and nerves -continues down and covers the spinal cord • arachnoid mater -thin, weblike membrane that contains no blood vessels -The middle membrane -Covers spinal cord • pia mater -thin inner layer that contains many nerves and blood vessels -Hugs the brain and spinal cord supplies them with nourishment SPINAL CORD • A SLENDER COLUMN OF NERVES THAT EXTEND FROM THE BASE OF THE BRAIN. • IT IS SURROUNDED BY THE VERTEBRAE • IT ENDS NEAR THE 2ND LUMBAR VERTEBRAE STRUCTURE OF THE SPINAL CORD • MADE OF 31 SEGMENTS WHICH PRODUCES A PAIR OF SPINAL NERVES FUNCTION OF SPINAL CORD • PROVIDES TWO WAY COMMUNICATION BETWEEN BRAIN AND BODY • CARRIES NERVE IMPULSES FROM SENSE ORGANS TO THE BRAIN AND FROM THE BRAIN TO THE EFFECTORS BRAIN STRUCTURE • THREE MAIN PARTS: CEREBRUM, CEREBELLUM, AND BRAINSTEM • THE BRAINSTEM HAS NERVE PATHWAYS THAT CONNECT VARIOUS PARTS OF THE BRAIN AND REGULATES CERTAIN VISCERAL ACTIVITIES. CEREBRUM • THE CEREBRUM IS THE LARGEST PART AND IS ASSOCIATED WITH SENSORY AND MOTOR FUNCTIONS AND PROVIDES HIGHER MENTAL FUNCTIONS, INCLUDING MEMORY AND REASONING • THE CEREBRUM IS DIVIDED INTO LEFT AND RIGHT HEMISPHERES WHICH ARE CONNECTED BY THE CORPUS CALLOSUM • THE THIN OUTER LAYER OF THE CEREBRUM IS CALLED THE CORTEX • THE SURFACE IS COMPOSED OF CONVOLUTIONS SEPARATED BY THE SULCUS(THIN GROOVES) • THERE IS A LONGITUDINAL FISSURE BETWEEN THE LEFT AND RIGHT SIDES OF THE CEREBRUM. • A TRANSVERSE FISSURE SEPARATES THE CEREBRUM FROM THE CEREBELLUM • THE CEREBRUM IS DIVIDED INTO LOBES NAMED BY THE BONE THE ARE LOCATED UNDER: – FRONTAL LOBE – PARIETAL LOBE – TEMPORAL LOBE – OCCIPITAL LOBE – INSULA – A LOBE THAT IS LOCATED DEEP WITHIN THE CEREBRUM CEREBRAL CORTEX THE CEREBRAL CORTEX HAS MOTOR AREAS, SENSORY AREAS, AND ASSOCIATION AREAS. DOMINANT HEMISPHERE • ONE HEMISPHERE OF THE CEREBRUM IS USUALLY DOMINANT • 90 % OF THE POPULATION IS LEFT HEMISPHERE DOMINANT FOR LANGUAGE-RELATED ACTIVITIES OF SPEECH, WRITING, READING AND COMPLEX VERBAL, ANALYTICAL, AND COMPUTATIONAL PROBLEMS. VENTRICLES • ARE INTERCONNECTED CAVITIES THAT CONTAIN CEREBROSPINAL FLUID WHICH COMPLETELY SURROUNDS THE BRIAN Cerebrospinal fluid • Clear watery fluid located in the subarachnoid space. – (between the pia mater and the arachnoid mater) – It cushions the brain and spinal cord – ALSO MAINTAINS CHEMICAL CONCENTRATIONS IN THE CENTRAL NERVOUS SYSTEM. DIENCEPHALON • PARTS – THALAMUS IS THE CENTRAL RELAY FOR SENSORY IMPULSES – HYPOTHALAMUS: – REGULATES – HEART RATE AND ARTERIAL BLOOD PRESSURE – BODY TEMPERATURE – WATER AND ELECTROLYTE BALANCE – CONTROL OF HUNGER AND BODY WEIGHT – SLEEP AND WAKEFULNESS – OPTIC TRACTS - CONTROLS VISION – INFUNDIBULUM – CONNECTS PITUITARY AND HYPOTHALAMUS – PITUITARY GLAND – CONTROLS GROWTH – MAMMILARY BODIES – INVOLVED WITH THE PROCESSING OF RECOGNITION MEMORY – PINEAL GLAND – PRODUCES MELATONIN WORKS WITH SLEEP/WAKEFULNESS BRAINSTEM • A BUNDLE OF NERVOUS TISSUE THAT CONNECTS THE CEREBRUM AND THE SPINAL CORD • PARTS OF BRAINSTEM: – PONS – MIDBRAIN – MEDULLA OBLONGATA MIDBRAIN • CONTAINS CENTERS FOR VISUAL REFLEXES • CONTAINS CENTERS FOR AUDITORY REFLEXES PONS • RELAYS SENSORY IMPULSES FROM THE PERIPHERAL NERVES TO THE BRAIN CENTERS MEDULLA OBLONGATA • CARDIAC CENTER – IMPULSES TO THE HEART • VASOMOTOR CENTER – IMPULSES TO BLOOD VESSELS FOR VASODILATION AND VASOCONSTRICTION • RESPIRATORY CENTER – WORKS WITH RATE, RHYTHM, AND DEPTH OF BREATHING • ALSO CONTROLS OTHER REFLEXES: • VOMITING, SNEEZING, COUGHING, ETC… CEREBELLUM • THE CEREBELLUM COORDINATES VOLUNTARY MUSCULAR MOVEMENTS. • INTEGRATES SENSORY IMPULSES ON BODY POSITION AND INITIATES MOVEMENT OF BODY PARTS. PERIPHERAL NERVOUS SYSTEM • CONSISTS OF THE NERVES THAT BRANCH OUT FROM THE CNS AND CONNECT TO THE OTHER BODY PARTS • INCLUDES THE CRANIAL NERVES AND THE SPINAL NERVES • IT CAN BE DIVIDED INTO TWO PARTS – SOMATIC NERVOUS SYSTEM: – CONSISTS OF CRANIAL AND SPINAL NERVES CONNECTING CNS TO THE SKIN AND SKELETAL MUSCLES – OVERSEES THE CONSCIOUS ACTIVITIES – AUTONOMIC NERVOUS SYSTEM: – CONSISTS OF FIBERS, ORIGINATING IN THE BRAINSTEM, THAT CONNECT TO THE INTERNAL ORGANS – CONTROLS UNCONSCIOUS ACTIVITIES CRANIAL NERVES • THERE ARE 12 PAIRS OF CRANIAL NERVES. • Cranial Nerve:     Major Functions: • I Olfactory        smell • II Optic        vision • III Oculomotor        eyelid and eyeball movement • IV Trochlear       turns eye downward and laterally • V Trigeminal        chewing face & mouth touch & pain • VI Abducens        turns eye laterally • VII Facial        controls most facial expressions secretion of tears & saliva taste • VIII Vestibulocochlear(auditory)        hearing and equillibrium sensation – IX Glossopharyngeal        taste senses carotid blood pressure – X Vagus        senses aortic blood pressure slows heart rate stimulates digestive organs taste – XI Spinal Accessory       controls trapezius & sternocleidomastoid controls swallowing movements – XII Hypoglossal       controls tongue movements SPINAL NERVES • 31 PAIRS OF SPINAL NERVES – 8 PAIRS OF CERVICAL – 12 PAIRS OF THORACIC – 5 PAIRS OF LUMBAR – 5 PAIRS OF SACRAL – 1 PAIR OF COCCYGEAL SPINAL NERVES • THEY ARE MIXED NERVES THAT ORIGINATE FROM THE SPINAL CORD. • THEY DO NOT HAVE NAMES BUT ARE LABLED BY THE LEVELS OF THE SPINE FROM WHICH THEY ARISE. – C1, C2, C3 ETC… PLEXUSES • INTERWOVEN BUNDLES OF NERVES • THREE MAJOR: – CERVICAL LOCATED IN NECK REGION – BRACHIAL LOCATED DEEP IN SHOULDER – LUMBOSACRAL LOCATED IN LOWER BACK AUTONOMIC NERVOUS SYSTEM • FUNCTIONS CONTINUOSLY WITHOUT CONSCIOUS EFFORT • CONTROLS AUTOMATIC BODY FUNTIONS • REGULATES HEARTBEAT, BLOOD PRESSURE, BREATHING RATE, BODY TEMPERATURE, AND OTHER BODY ACTIVITIES TO MAINTAIN HOMEOSTASIS • ALLOWS RESPONSE TO EMOTIONAL STRESS AND ALLOWS THE BODY TO MEET THE DEMANDS OF STRENUOUS PHYSICAL ACTIVITY • THE BRAIN AND SPINAL CORD MOSTLY CONTROL THE ANS EVEN THOUGH IT IS CONSIDERED AN INDEPENDENT SYSTEM WITHIN THE NERVOUS SYSTEM DIVISIONS OF THE ANS • 1. SYMPATHETIC DIVISION – PREPARES THE BODY FOR ENERGY EXPENDING STRESSFUL OR EMERGENCY SITUATIONS (THE FIGHT OR FLIGHT RESPONSE) • 2. PARASYMPATHETIC DIVISION – CONTROLS DURING ORDINARY RESTFUL SITUATIONS NEUROTRANSMITTERS SECRETED BY THE ANS • ACYTLCHOLINE – REMEMBER CONTROLS MUSCLE CONTRACTION • NOREPINEHRINE – REMEMBER IT CREATES A SENSE OF FEELING GOOD