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