Transcript The Nervous System

The Nervous System
BY LYDIA CHANG, LAUREN LEE, AND DIANA ZHENG
Evolution of the Nervous System
 Porifera: no nervous system
 Cnidaria: nerve net all throughout body—can react to stimuli from all
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sides
Platyhelminthes: cephalization; ganglia, eyespots, two main ventral
nerve cords
Rhynchocoela: dorsal nerve cord, two lateral nerve cords
Nematoda: ring of nervous tissue around pharynx attached to dorsal and
ventral nerve cords
Annelida: pair of brain-like cerebral ganglia and subpharyngeal ganglion
Mollusca: ranges from simple nervous system to relatively complex
systems that rival those of mammals
Arthropoda: cerebral ganglion (brain!); sense organs concentrated on
head
Echinodermata: decentralized nervous; no brain but have ganglia along
radial nerves in some species; sensory neurons within podia
Evolution of the Nervous System
 Vertebrates: very centralized and cephalized; well-developed
sensory organs; dorsal, hollow nerve cord (spinal cord)
 Lampreys and hagfishes: no myelin sheath
 Fish: enlarged cerebellum
 Amphibians: growing importance of forebrain, but midbrain
still important
 Reptiles/Birds: many connections between thalamus and
hemispheres
 Birds: larger cerebellum
 Mammals: brain completely dominated by cerebral
hemispheres; large surface area; controlled mainly by cortex;
large thalamus
The Human Nervous System
 Brain: about 2% human body mass
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Neocortex: outer layer of brain
Human cerebral cortex (aka pallium): flat sheets of cells in six
layers
Frontal lobe: reasoning, speech, motor cortex
Parietal lobe: speech, taste, reading, somatosensory cortex
Temporal lobe: hearing, smell, auditory
Occipital lobe: sight
Cerebellum: ballistic movements, balance, coordination, helps
in learning and remembering motor skills
From “Vertebrate Nervous System”
The Brain, cont’d
 Diencephalon: major integrating centers information, act as
relay stations for info flow
 Thalamus: main relay center for sensory information
 Hypothalamus: maintains homeostasis
 Brain stem: includes the pons, medulla oblongata
 transfers info between peripheral and central nervous systems
 helps coordinate large-scale body movements (e.g. running)
 nerve crossing: right side of brain controls left side of body and
vice versa
 Midbrain/RAS (reticular activating system): centers for
receiving and integrating several types of sensory info
 Corpus callosum: connects brain hemispheres
From Wikipedia
Evolutionary Trends
 More complex!
 This system is necessary for complexity and sophisticated
behaviors/responses to environment
 Increases chance of survival: more complex NS = more
complicated nerve connections, behaviors, movements
 The nervous system controls all other body systems!!
Except maybe skeletal
Neurons
 Neurons
 Sensory neurons
 Interneurons
 Motor neurons
How Neurons work
 Resting potential: negative relative to the outside
 Sodium-potassium pumps in the plasma membrane
 Transport sodium out of the cell and potassium into it
 Very few sodium channels
 Net negative charge inside cell
Action Potential
 Depolarization
 Rising phase of the action potential
 Falling phase of the action potential
 Undershoot: Potassium channels close to bring it
back to the concentration needed to be at resting
potential
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refractory period
Conduction of the Action Potential
 Action potential: a “wave” from dendrite to axon
 Speed is determined by axon diameter
 Evolutionary trend: Because vertebrate axons have
narrow diameters, vertebrates have adapted the
myelin sheath to enable more efficient conduction
 Nodes of Ranvier (nodes between gaps in myelin
sheath) allows for saltatory conduction
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current jumps from node to node
Synapses
 Electrical synapses: contain gap junctions to allow
electrical currents to flow from one neuron to
another
 Chemical synapses (most synapses):
neurotransmitter
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Examples of neurotransmitters: acetylcholine, biogenic
amines (serotonin)
Disorders and Diseases
 Cerebrovascular accident (stroke)
 Parkinson's disease:
 decreased stimulation of the motor cortex by the basal
ganglia caused by the insufficient formation and action of
dopamine
 Multiple sclerosis: immune system damages the
myelin
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When myelin is lost, the axons can no longer effectively
conduct signals
Works Cited and Consulted
 AP Bio book
 http://faculty.washington.edu/chudler/nsdivide.html
 http://parasitology.informatik.uni
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wuerzburg.de/login/n/h/0941.html
http://www.daviddarling.info/encyclopedia/V/vertebrat
e_nervous_system.html
http://infusion.allconet.org/webquest/PhylumMollusca.
html
http://www.mindcreators.com/Images/NB_Neuron.gif
http://en.wikipedia.org/wiki/File:Neurons_big1.jpg