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Nervous System “Chapter 13” General Outcomes

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Nervous System “Chapter 13” General Outcomes NERVOUS SYSTEM “CHAPTER 13” GENERAL OUTCOMES • In this unit, you will… • Explain how the nervous system controls physiological processes • Explain how the endocrine system relates to homeostasis QUESTIONS • Questions 1-5 page 406. • The human nervous • system is a complex • system composed of • many subsystems • that all work together • to maintain • homeostasis in the • body NERVOUS SYSTEM • 1998 Michael J. Fox announced leaving TV because of Parkinson’s Disease. • He noticed a twitch in a finger in 1991. • Getting worse it make acting difficult. • Parkinson’s Disease is a progressive degenerative nerve disorder that affects muscle activity. • Cells in two areas of the brain, the substantia nigra and locus cerlus degenerate and die. These cells secrete dopamine and norepinephrine. Any reduction in these chemicals affect movement. • Symptoms include muscle tremors, slow body movements, rigidity in joints and inability to gain balance. • The cause is not known. In 15% of cases heredity plays a role. ACTIVITY ORGANIZATION OF THE NERVOUS SYSTEM • Has two divisions: 1) Central Nervous System 2) Peripheral Nervous System • Central nervous system consists of the nerves of the brain and spinal cord and acts as a coordinating center for incoming and outgoing info. • The peripheral Nervous system consists of nerves that carry infomation between organs of the body and the central nervous system. • It can be further divided into somatic and autonomic nerves. • Somatic nervous system controls skeletal muscle, bones, and skin. Sensory somatic nerves relay info about the environment to the CNS while motor somatic nerves initiate the appropriate response. (voluntary) • The autonomic nervous system contains special motor nerves that control the internal organs of the body. (involuntary) FUNCTIONS OF THE NS • The nervous system gathers and processes information from the external and internal environments and then relays a response to the necessary areas of the body. ANATOMY OF A NERVE CELL • Two cells found in the nervous system: glial cells and neurons • Glial Cells – often called neuroglial cells, and non conducting cells and are important for structural support and metabolism of the nerve cells. • Neurons – are the functional units of the nervous system. Conducts nerve impulses. All neurons contain dendrites, cell bodies and axons. • Dendrites – receive information, either from the environment or from other neurons. Like all living cells, neurons contain a nucleus. Dendrites conduct nerve impulses towards the cell body. • Axon – extension of cytoplasm that carries nerve impulses away form the cell body. A neuron has only one axon, though it may form branches. In humans the axon is very thin, more that 100 can be placed in a piece of hair. • Myelin Sheath – insulated covering over the axon of a nerve cell. White coat of fatty protein. • Schwann Cells – special type of glial cell that produces the myelin sheath. • Nodes of Ranvier – regularly occurring gaps between sections of myelin sheath along the axon. Nerve impulses jump from one node to another. Thereby speeding up movements of impulses. Move much faster along myelinated than non. Speed is also affected by the diameter of an axon. Larger means faster. • Neurilemma – delicate membrane that surrounds the axon of some nerve cells. Promotes regeneratin of damaged nerve cells. This explains why feeling returns to your finger after a paper cut. NEURON TYPES OF NEURONS • Sensory neurons –known as afferent, relay info received by sensory receptors about the internal and external environment to the central nervous system. The cell bodies are located in clusters called ganglion located outside the spinal cord. • Interneurons – link neurons to other neurons. Found only in the brain and spinal cords, known as associated neurons connect sensory neurons to motor neurons. • Motor neurons –known as efferent relay info to effectors, which is the cell or organ that responds to the stimulus. Muscles, organs and glands are effectors because they produce responses. • Questions 1-4 page 410 REPAIRING DAMAGED NERVES • Emerging work with stem cells provide hope. • Sweden 25 yr. Thomas Westburg sustained a serious spinal cord injury while snowmobiling. Four nerves were torn in from the spinal cord in the area of the neck. The injury left his shoulder, arm and hand paralyzed. Surgeons reattached two nerves. New nerves began to grow. He recovered 40% of movement. • Stem cells are cells that have not yet specialized into tissue such as skin, nerve cells. THE REFLEX ARC • If you touch a hot stove, how does your body tell you it is hot? • Heat is detected by temperature receptors in your skin and a nerve impulse is carried to the spinal cord. The sensory neuron passes the impulse to an interneuron, which relays the impulse to a motor neuron, which causes the muscle to contract. This happens in less than a second. All this happens before the info is sent to the brain. • Reflexes are involuntary and often unconscious. • The simplest nerve pathway is the reflex arc • Tapping tendon in the knee, light on pupil REFLEX ARC • A reflex arc: – Is the simplest nerve pathway – Is involuntary – Occurs w/o brain coordination PATELLAR REFLEX “KNEE-JERK RESPONSE” Questions 1-6 page 414 ACTIVITY ELECTROCHEMICAL IMPULSE • Julius Bernstein suggested that nerve impulses were an electrochemical message created by the movement of ions through the nerve cell membrane. • Action potential – the voltage difference across a nerve cell membrane when the nerve is excited. • Resting potential – voltage difference across a nerve cell membrane when it is not transmitting a nerve impulse. (Usually negative) • The plasma membrane of almost all cells has an electrical potential of about -70 mV. In neurons this is called the resting potential. Both sides have a rich supply of positive and negative ions. There is a higher concentration of potassium ions (K) inside the cell and a higher concentration of sodium ions (Na) outside the cell. The movement of K is responsible for the electrical potential. • Plasma membrane is composed of a phospholipid bilayer. Plasma membranes are selectively permeable, ions cannot cross through simple diffusion. Instead they enter through facilitated diffusion, passing through gated channels. There are more K than Na so K diffuses out of the cell. • As K leave it transfers its positive charge outside the cell. The neg. charged ions are trapped inside an so an electrical charge builds up across the membrane ELECTROCHEMICAL IMPULSE RESTING POTENTIAL • Sodium potassium pump – a transporter in the cell membrane that moves potassium ions into the cytoplasm while simultaneously removing sodium ions from the cytoplasm to the external fluid. • Active transport – movement of substances across cell membranes that uses energy. • Polarized membrane – membrane charged by unequal distribution of positively charged ions inside and outside the nerve cell. SODIUM POTASSIUM PUMP THE ACTION POTENTIAL • A nerve impulse is an action potential, When a neuron receives a stimulus, the cell membrane becomes more permeable to sodium than potassium. The sodium ions rush into the cell by diffusion and by charge attraction. The rapid inflow of sodium reverses the charge on both sides of the membrane. • This charge reversal is referred to as depolarization. Once the voltage inside the cell becomes positive the sodium channels slam closed, stopping the inflow. The potassium channels open and potassium diffuses out of the cell and the outside of the cell becomes positive. ACTION POTENTIAL • Repolarization – process of restoring the original polarity. • Hyperpolarization – inside of the nerve cell has a greater negative charge then the resting membrane caused by excessive diffusion of potassium ions out of the cell. • Refractory period – recovery time required before a neuron can produce another action potential. ACTION POTENTIAL PHASES MOVEMENT OF THE ACTION POTENTIAL • Dominos falling, one after another. • When axons are myelinated, nerve impulses travel by salutatory conduction. Action potential jump from node to node. SUCCESSIVE ACTION POTENTIALS ACTION POTENTIAL • A nerve impulse is a series of action potentials • In myelinated neurons, APs only occur at the • Nodes of Ranvier • The threshold potential refers to the minimum stimulus required to generate an AP in a neuron (this can vary amongst different neurons) • APs are “all-or-none” meaning • When the threshold potential is reached (usually around -55mV), special protein channels in the membrane open allowing Na+ to rush inside the axon • This causes the inside of the neural membrane to now contain more positives than the outside (thus reversing the normal charge distribution) • This reversal of charge is called depolarization • The Na+/K+ pump then restores the original resting potential • There is a short refractory period when the membrane cannot depolarize QUESTIONS • Questions 1-4 page 418 THRESHOLD LEVELS AND THE ALL OR NONE RESPONSE • Threshold level – minimum level of a stimulus required to produce a response. • Stimuli below the threshold level do not initiate a response. • All or none response – neurons either fire maximally or not at all. THRESHOLD LEVELS SYNAPTIC TRANSMISSION • Small spaces between neurons are known as synapses. • Small vesicles containing chemicals called neurotransmitters are located at the end of the plates of axons. They are chemical messenger released by the presynaptic neuron that binds to the receptors on the postsynaptic neuron. • The neurotransmitters
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