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