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Unit VIII: Animal Structure and Function, Part II
The Human Excretory and Nervous Systems
Excretory SystemNitrogen-containing wastes• toxic by-products of protein andnucleic 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 KidneyHuman Kidneys• two bean-shaped organs, one oneach 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 NephronFiltration 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
Reabsorption1. Proximal Tubule + HCO3
- (bicarbonate), H2O, NaCl, K+
2. Descending loop of Henle + H2O3. Ascending loop of Henle + NaCl4. Distal Tubule + NaCl, H2O, HCO3
-
5. 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 awayfrom the CNS + effectors
- voluntary and involuntary muscles
Autonomic Nervous SystemInvoluntary• smooth and cardiac muscle + sympathetic
- increases energy consumption and prepare for action
+ parasympathetic- enhance activity to gain and conserve energy
Neuron
cell body dendrites axon (hillock)myelin sheath Schwann cells nodes of Ranviersynaptic terminal synapse 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 Reflex1. Tap patellar tendon2. Sensory receptors sensestretch in quadriceps3. Sensory neurons conveyinfo. To spinal cord4. Synapses with motor neuron in spinal cord5. Motor neuron conveyssignal to quadriceps 6. Synapse with inter-neuron in spinal cord7. Interneurons inhibit othermotor neurons (hamstring)8. Prevents the hamstringfrom 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)
Action PotentialExcitable Cells• 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 PotentialAction potentials “travel” alongan axon because they are self-propagating• 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 causesinflux of Ca2+• Release of synapticvesicle contents• Neurotransmitter re-leased 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 BrainElectroencephalograph (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
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