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Types of Nervous Systems. Cephalization. The concentration of neurons in a brain located in the head. Bilateral symmetry Allows for a concentration of sensory organs in the head. Flatworms—simple brain and 2 nerve cords. Vertebrate Nervous System. Central nervous system (CNS) Brain - PowerPoint PPT Presentation
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Types of Nervous Systems
Cephalization
• The concentration of neurons in a brain located in the head.– Bilateral symmetry– Allows for a concentration of sensory organs in the
head.– Flatworms—simple brain and 2 nerve cords
Vertebrate Nervous System
• Central nervous system (CNS)– Brain – Dorsal nerve cord
• Peripheral nervous system (PNS)– Nerves-– Ganglia-clusters of
nerve cells
Information pathway
Vertebrate Nerve cells
• Neuron-Functional cell • Glia-Supporting cell– Astrocytes-CNS, maintain
blood/brain barrier– Oligodendrocytes-
insulation in CNS– Schwann cells-insulation
in PNS
Anatomy of a Neuron•Cell body~ nucleus and organelles•Dendrites~ impulses from tips to neuron•Axons~ impulses toward tips•Myelin sheath~ supporting, insulating layer made of schwann cells•Synaptic terminals~ neurotransmitter releaser•Synapse~ neuron junction
Reflex Arc
Membrane Potentials• Membrane potential (voltage differences across the plasma membrane)• Intracellular/extracellular ionic concentration difference• K+ diffuses out (Na+ in); large anions cannot follow….selective permeability
of the plasma membrane• Net negative charge of about -70mV
Resting Potential• Nontransmitting neuron• -60 to -80 mV• Na+ and K+diffuse down concentration gradient• Neurons at rest are more permeable to K+ and less permeable to Na+-more
ungated ion channels open
Action potentials• Signals conducted by neurons• Gated channels-open and close in response to stimuli– Na+ and K+ voltage gated channels control action
potential– Depolarization (inside of the cell becomes less negative)
opens Na+ gated channels– Opening of K+ gates causes hyperpolarization (inside of
cell becomes more negative)
Conduction of Action Potentials
• Na+ influx in rising spase depolarizes adjacent section of the membrane, bringing them to threshold.
Speed of Action Potentials• Axon diameter (larger = faster; 100m/sec)• Nodes of Ranvier (concentration of ion channels);
saltatory conduction; 150m/sec
Synaptic communication
• Presynaptic cell: transmitting cell• Postsynaptic cell: receiving cell• Synaptic cleft: separation gap• Synaptic vesicles: neurotransmitter
releasers• Ca+ influx: caused by action potential;
vesicles fuse with presynaptic membrane and release….
• Neurotransmitter
Vertebrate PNS
The Vertebrate Brain• Forebrain– cerebrum~memory, learning,
emotion– cerebral cortex~sensory and
motor nerve cell bodies – corpus callosum~connects left and
right hemispheres – thalamus; hypothalamus
• Midbrain – inferior (auditory) and superior
(visual) colliculi• Hindbrain
– cerebellum~coordination of movement
– medulla oblongata/ pons~autonomic, homeostatic functions