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Download Unit VIII: Animal Structure and Function, Part II
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Unit VIII: Animal Structure and Function, Part II The Human Excretory and Nervous Systems Excretory System Nitrogen-containing wastes • toxic by-products of protein and nucleic acid metabolism + ammonia - small and very toxic - no energy required - must be diluted + urea - 100,000 times less toxic - formed by combining CO2 and NH2 + uric acid - excreted in paste-like form - conserve even more water The Kidney Human Kidneys • two bean-shaped organs, one on each side of backbone + represent 0.5% body weight; + receive 20-25% of arterial blood pumped by the heart - renal artery/vein • each contains 1 million nephrons + ureter, bladder, urethra - 1300 ml/min blood enter via renal artery; 1299 ml/min blood exit via renal vein - produce 1 ml/min of urine The Nephron Filtration and Refinement • filtration + blood/body fluid exposed to filtering device - selectively permeable membranes - produces filtrate • reabsorption + selective transport of water and valuable solutes back into body fluids - glucose, salts, amino acids • secretion + solutes from body fluids are added to filtrate • excretion + discarding unwanted waste • Nephron Function • Filtration/Secretion Nephron as a filtering device • approx. 120 ml/min of plasma is filtered through Bowman’s capsule + body reabsorbs as much of the “good stuff” as possible Reabsorption 1. Proximal Tubule + HCO3- (bicarbonate), H2O, NaCl, K+ 2. Descending loop of Henle + H2O 3. Ascending loop of Henle + NaCl 4. Distal Tubule + NaCl, H2O, HCO35. Collecting Duct + Urea, H2O Hormonal Control Antidiuretic Hormone (ADH) • enhances fluid retention by making kidneys reclaim more H2O + osmoreceptors detect increase in osmolarity (solutes) of blood - promote thirst Hormonal Control (con’t) Renin-angiotensin-aldosterone system (RAAS) Organization of the Nervous System Nervous System • Central Nervous System (CNS) + brain and spinal cord • Peripheral Nervous System (PNS) + nerves outside of CNS - cranial nerves (12 pairs) + olfactory, optic, oculomotor, facial, auditory, trigeminal, etc. - cervical nerves (8 pairs) - spinal nerves (many pairs) + thoracic, lumber, sacral, coccygeal Peripheral Nervous System (PNS) Sensory/Afferent Div. • send impulses to the CNS + sense stimuli inside and outside the body Motor/Efferent Div. • send impulses away from the CNS + effectors - voluntary and involuntary muscles Autonomic Nervous System Involuntary • smooth and cardiac muscle + sympathetic - increases energy consumption and prepare for action + parasympathetic - enhance activity to gain and conserve energy Neuron cell body myelin sheath synaptic terminal dendrites Schwann cells synapse axon (hillock) nodes of Ranvier terminal branches Functional Organization of Neurons 3 Classes of Neurons • sensory neurons + convey impulse from sensory receptors to CNS • interneurons + integrate sensory input and motor output • motor neurons + convey impulses from CNS to effector cells • arranged in circuits of two or more types of neurons + simplest… reflex The Knee-jerk Reflex 1. Tap patellar tendon 2. Sensory receptors sense stretch in quadriceps 3. Sensory neurons convey info. To spinal cord 4. Synapses with motor neuron in spinal cord 5. Motor neuron conveys signal to quadriceps 6. Synapse with interneuron in spinal cord 7. Interneurons inhibit other motor neurons (hamstring) 8. Prevents the hamstring from contracting The Nature of Neural Signals Membrane Potential • the difference in voltage across the plasma membrane + arises from differences in ionic composition (Na+/K+ pump) - normal: positive outside; negative inside (-70mV) Excitable Cells Action Potential • cells that have the ability to change their membrane potentials + neurons and muscle cells - resting potential (unexcited) + change from resting potential can result in active electrical impulse + gated ion channels - special channels that allow cell to change membrane potential + hyperpolarization - increase in the electrical gradient + opens K+ channel; + increase outflow of K+; more negative + depolarization - reduction in the electrical gradient + opens Na+ channel + increase inflow of Na+; less negative - action potential + brief reversal of membrane polarity Graded Potentials and the Action Potential in a Neuron Propagation of the Action Potential Action potentials “travel” along an axon because they are selfpropagating • dominoes + neighboring region of the neuron will be depolarized • Access Excellence link Saltatory Conduction Saltatory Conduction • speeds the propagation of action potential + nodes of Ranvier: gaps between myelinated regions - action potentials “jump” from node to node Conversion of Signal: Electrical to Chemical • Depolarization causes influx of Ca2+ • Release of synaptic vesicle contents • Neurotransmitter released into cleft • Molecules bind to receptors • Opens ion channels Diversity of Nervous Systems The Brain Brain Facts • weighs about 3 lbs. (1.4 kg); about 2% of body weight • avg. brain has 100 billion neurons and 900 billion glial cells • basic brain pathways are developed in first 3 weeks How to Study the Brain Electroencephalograph (EEG) • measures electrical activity (brain "waves") + awake - quiet: slow alpha waves - intense mental activity: beta waves + asleep - sleep cycle + delta, REM sleep, delta • diagnosing brain disorders + epileptic seizures Imaging Techniques • • • • CT: X-ray Computed Tomography PET: Positron-Emission Tomography MRI: Magnetic Resonance Imaging Brain Briefings