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Chapter # 9 Nervous System A. Introduction 1. The nervous system is the control center and communication network within the body. It monitors the sate of the body, processes the information, and initiates a response. _________ function – monitor ___________ function – ability to process the information _________ function – initiating a response B. Divisions of the Nervous system • 1. Central Nervous System (CNS) – ___________ and spinal cord – Located along midline of body – All sensory impulses go to______, all motor impulses _______________ from the CNS • 2. Peripheral Nervous System (PNS) – Include the nerves____________ the CNS • Cranial nerves – originate from the brain to supply head and neck • Spinal nerves – originate from the spinal cord to supply body below the head – a. ___________ System – voluntary (conscious) nervous system – b. _____________System – involuntary (unconscious) nervous system » Sympathetic - “fight or flight" response » Parasympathetic – “rest-repose” C. Nerve Tissue • Nerve tissues primary function is to conduct impulses. • There are two categories of cells – Neuroglia and neurons 1. Neuroglia • Cells that help __________and maintain the neurons. • These cells make up ____ of the brain and spinal cord. – Astrocytes – Ependymal cells – Microglia – Oligodendrocytes – Schwann cells Supporting cells A. Classification of Neuroglial Cells 1. Neuroglial cells ____spaces, ______ neurons, provide structural frameworks, produce myelin, and carry on phagocytosis. Four are in the CNS and the last in the PNS. 2. Microglial cells are small cells that _____________ bacterial cells and cellular debris. CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3. Oligodendrocytes form _______ in the brain and spinal cord. 4. 5. 6. Astrocytes are near blood vessels and support structures, aid in metabolism, and respond to brain injury by filling in spaces. Ependyma cover the inside of ventricles and form choroid plexuses within the ventricles. Schwann cells are the _______ producing neuroglia of the peripheral nervous system. 2. Neurons • The structural and functional units of the nerve tissue. • a. Structure: – ___________ – contains nucleus and cytoplasm – ______________ – thin branching extensions of the cell body – _____ – carries impulses away from the cell body. Also called a nerve fiber – 1. Myelinated vs unmyelinated • myelin sheath created by the _________ cells form a protective covering around the axon. This creates white matter • _____________________ – gap between myelin sheath • Unmyelinated lacks the schwann cells and creates gray matter b. Types of Neurons • 1. Structural differences – ___________ – many dendrites arising from the cell body, and a single axon. – CNS to muscle – _________ – single dendrite and single axon from cell body in opposite directions. – Eyes, ears, nose. – ___________– single nerve fiber extending from the cell body branching to spinal cord and other to periphery. Skin to spinal cord • 2. Functional differences – ___________neurons – (afferent neurons) carry nerve impulses from a peripheral part of the body to the CNS. unipolar – ____________ neurons – (interneurons) located within the CNS. They form a link between neurons. Multipolar – ________ neurons – (efferent neurons) carry nerve impulses from CNS to parts of the body. Multipolar c. Function • A nerve impulse is similar to the flow of electricity through an insulated wire • 1. _______ Potential – at rest a neuron has an uneven distribution of ions across its membrane – It has a higher concentration of _________ outside the membrane than inside. Making the inside more negative – The sodium-potassium pump will pump Na+ out and K+ in. – A neuron that has a resting potential is called __________. 2. Action Potential • Neurons have excitability (respond to change in environment) • A stimulus great enough to alter the resting membrane potential will cause the membrane to change and become permeable to Na+. • _______ will move into the membrane and cause the charge to become more positive. • This is called _________________. • Immediately after the depolarization, the K+ flow out of the axon to repolarize the axon. • This is called an _______________ or nerve impulse. 3. Conduction of Nerve Impulse • The action potential spreads from one points along the length of the neuron. • The speed of a nerve impulse is extremely rapid (1/1000 second) and does not vary in ______________________neurons. • _______ conduction is found in myelinated fiber. The impulse jumps from one ______________ to the next 4. All or None Response • If a stimulus is strong enough to cause an action potential the nerve will conduct the __________________ of the nerve fiber. • ___________stimulus – minimum strength required to initiate an action potential. – Increasing the strength of the stimulus has no effect on action potential. – Sub-threshold stimuli cannot initiate an impulse but can have a cumulative affect called summation. 5. Transmission of Impulses from cell to cell • Junction between neurons is called a synapse. – ______________neuron – neuron that sends the impulse to the synapse – __________ neuron – neuron that receives the impulse. – The presynaptic neuron ends with a synaptic end bulb, which contain synaptic vesicles which contain __________________. – The neurotransmitters cross the synaptic cleft to the post synaptic neuron Figure 9.08 Synaptic Transmission at a Chemical Synapse 6. Excitatory vs. Inhibitory transmission • A transmission involving neurotransmitters that increase the postsynaptic membrane permeability to Na+ is called an ________ transmission. – Examples: Acetylcholine and Norepinephrine • A transmission that decreases the permeability to Na+ is called an ________ transmission. – Examples: Endorphins and GABA 7. Processing at the synapse • A post synaptic neuron may have thousands of presynaptic neurons affecting it. The overall effect on the postsynaptic membrane is determined by the sum of the effects from excitatory and inhibitory neurotransmitters HEALTH CLINIC • Chemicals and their influence – Stimulants – Depressants – Antidepressants – Psychedelic drugs – Analgesics D. The Central Nervous System • Contains the brain and spinal cord 1. The Spinal Cord • The spinal cord is a long bundle of nerves that extended from the base of the brain to about the ___________ lumbar vertebra • It provides the connection between the brain and peripheral nerves a. Protective Coverings • The spinal cord is protected by the: – Vertebral Column – ___________ – ____________fluid (CSF) – liquid cushion that provides for shock absorption – Meninges – 3 layers of membranes around brain • ___________ – outer layer • Arachnoid – middle layer • __________ – inner layer – The space between the arachnoid and pia mater is filled with CSF b. Structure • The cord consists of _____ segments, and each contain a pair of spinal nerves • Its cross section contains white and gray matter – 1. Gray matter distribution – contains unmyelinated fibers and neuron bodies. – It occupies the center of the cord in the shape of an ______. – It consists of the posterior gray horns (sensory) and the anterior gray horns (motor) – 2. White matter distribution – contains ___________ fibers and surrounds the gray matter c. Function • 1. Conduction pathways – descending (motor) and ascending (sensory) tracts • 2. Reflex center – A spinal reflex is a rapid signal the bypasses the higher brain centers for reduced response time. – a. ____________ – involves a sensory receptor, sensory neuron, reflex center in spinal cord and motor neuron – b. Somatic – stimulate skeletal muscle – Visceral – stimulate or inhibit visceral organs (heart rate, breathing, vomiting, sneezing, coughing) 2. The Brain • Divided into 3 regions – __________ – Cerebrum and diencephalon – __________– smallest – ___________ – pons, medulla oblongata, and cerebellum CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brain A. The brain is the largest, most complex portion of the nervous system, containing 100 billion multipolar neurons. B. The brain can be divided into the ________ (largest portion and associated with higher mental functions), the diencephalon (processes sensory input), the ___________ (coordinates muscular activity), and the ____________ (coordinates and regulates visceral activities). a. Protective covering – Cranium – bone – CSF – fluid around brain – Meninges – membranes around brain and spinal cord ( pia mater, arachnoid and dura mater) b. Cerebrospinal fluid and ventricles of the brain – 1. _______________ - cavities in the brain that produce CSF – 2. CSF production and circulation - fluid flows within arachnoid space and then returned to blood stream c. Cerebrum • Largest structure of the brain • Contains _____________ attached by the corpus callosum • External region is called the cerebral _______ (gray matter), underlying is white matter • Function: controls complex thought, voluntary movement, language, reasoning and perception CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4. 5. The lobes of the brain are named according to the bones they underlie and include the frontal lobe, parietal lobe, temporal lobe, occipital lobe, and insula. A thin layer of gray matter, the cerebral cortex, lies on the outside of the cerebrum and contains 75% of the cell bodies in the nervous system. d. Diencephalon • Contains the __________and _____________. • Located inferior to the corpus callosum. • This together with the cerebrum make up the forebrain 1. Thalamus • Largest portion of the diencephalon • Acts as a relay station for most sensory impulses on their way to the cerebral cortex and voluntary motor impulses traveling out 2. Hypothalamus • Located below the thalamus • Controls the __________ nervous system – Body temperature – Emotions – Hunger – Thirst e. Midbrain • -Above the pons between the hindbrain and forebrain • ___________ sensory information from the spinal cord to the forebrain. – Relay for rapid eye, head and trunk movements f. Pons • Bridge between spinal cord and brain g. Medulla Oblongata • At the top of the __________ • Controls breathing, heart rate, and blood pressure. • Brainstem – – midbrain – Pons – medulla h. Cerebellum • At the lower rear • Divided into 2 hemispheres • Controls movement, __________, posture • “automatic pilot” for the motor responses, keeps muscle movements smooth E. The Peripheral Nervous System • The peripheral nervous system provides a ________________________ pathway for impulses traveling between the CNS and the other parts of the body. • It consists of nerves, ganglia, and sensory receptors 1. Organs of the PNS • a. Nerves and ganglia – a nerve is a true organ, composed of many tissues. ( nerve vs. nerve fiber) – _____________ – carry impulses to CNS – __________ – carry impulses away from the CNS – Mixed – contain fibers from both sensory and motor neurons • Ganglia – cluster of neuron cell bodies located outside the CNS • b. ___________________ – structures that are specialized to respond to stimuli. – Simple (touch, pain, temperature) to complex ( eyes, ears) 2. Cranial Nerves • Nerves attached directly to the brain • There are 12 pair of cranial nerves that extend through the cranium to supply head and neck. • See page 265 • • • • • • • • • • • • • Cranial Nerve CN# Brain Region Major Functions Olfactory 1 Cerebral Cortex Smell Optic 2 Limbic System Vision Oculomotor 3 Midbrain Eyelid & eyeball movement; pupil dilation Trochlear 4 Pons Control downward & lateral eye movement Trigeminal 5“ Chewing; sensation of face & mouth Abducens 6“ Control lateral eye movement Facial 7“ Control most facial expressions; secretion of tears & saliva; taste; ear sensation Auditory 8 Medulla Hearing; balance Glossopharyngeal 9“ Taste; swallowing; sensation from tongue, tonsil, pharynx, carotid blood pressure Vagus 10“ Sensory, motor and autonomic functions of viscera - glands, digestion, heart rate, breathing rate, aortic blood pressure Spinal Accessory 11“ Controls muscles used in head movement Hypoglossal 12“ Controls tongue movements 3. Spinal Nerves • There are 31 pair that attach directly to the spinal cord, one pair each segment. 4. Somatic System • Part of the PNS that controls ________________ activities. • The sensory component receives information from skin organs and sensory organs. • The motor neuron always terminate in ___________, which are skeletal muscle. 5. Autonomic System • Part of the PNS that is under ________________ control. • Sensory pathway leads to hypothalamus, brain stem or spinal cord. • Motor neurons are complex. a. Sympathetic division • Processes that uses energy. • Called the ___________________system b. Parasympathetic division • Processes that conserve energy. • Called the ___________________ system