by lydia chang, lauren lee, and diana zheng the nervous system
TRANSCRIPT
BY LYDIA CHANG, LAUREN LEE, AND DIANA ZHENG
The Nervous System
Evolution of the Nervous System
Porifera: no nervous system Cnidaria: nerve net all throughout body—can react to stimuli from all
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 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 infoCorpus callosum: connects brain hemispheres
From Wikipedia
Evolutionary Trends
More complex!This system is necessary for complexity and
sophisticated behaviors/responses to environmentIncreases 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
DepolarizationRising phase of the action potentialFalling phase of the action potentialUndershoot: Potassium channels close to
bring it back to the concentration needed to be at resting potential refractory period
Conduction of the Action Potential
Action potential: a “wave” from dendrite to axon
Speed is determined by axon diameterEvolutionary 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 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 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 When myelin is lost, the axons can no longer
effectively conduct signals
Works Cited and Consulted
AP Bio bookhttp://faculty.washington.edu/chudler/nsdivide.htmlhttp://parasitology.informatik.uni-wuerzburg.de/
login/n/h/0941.htmlhttp://www.daviddarling.info/encyclopedia/V/
vertebrate_nervous_system.htmlhttp://infusion.allconet.org/webquest/
PhylumMollusca.htmlhttp://www.mindcreators.com/Images/
NB_Neuron.gif http://en.wikipedia.org/wiki/File:Neurons_big1.jpg