Transcript Unit VIII: Animal Structure and Function, Part II

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
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CT: X-ray Computed Tomography
PET: Positron-Emission Tomography
MRI: Magnetic Resonance Imaging
Brain Briefings