Animals: Nervous system Neuron and connection of neurons Outline 1. Key concepts 2. An Overview and Evolution 3. Human Nervous System 4. The Neurons 5. The Electrical Signals 6. Communication between Neurons 7. Nervous System Organization 8. Key Terms 9. Conclusions Key Concepts: 1. Nervous systems are composed of neurons 2. Neurons are excitable cells 3. With stimulation, the polarity of charge across the membrane reverses from negatively charged inside the cell to being positively charged 1
Key Concepts: 4. Action potentials are changes in the polarity of the cell membrane 5. Information flow starts with action potentials, which self propagate along the plasma membrane 6. Chemical signals released from a neuron stimulate or inhibit the adjoining neuron, muscle cell, or gland cell 7. Information flow depends on integration of signals Nervous System Function Nervous systems perform 3 over lapping functions 1. Sensory input 2. Integration 3. Motor output Evolution of Neural Systems 1. No centralized processing a. Nerve net > Hydra b. ring > starfish 2. Beginning of centralized control: a. Ventral nerve cord: ganglia b. increasing cephalization c. increased sensory inputs 3. Full centralized control: Dorsal nerve cord, brain 2
Human Nervous System 1. Two basic parts: a. CNS: brain & spinal cord. b. PNS: sensory and motor nerves 2. Nervous system cells: a. neurons i. Sensory ii. Interneurons iii. Motor b. glial cells: i. Schwann (PNS) (myelin sheath) ii.oligodendrocytes (CNS) (myelin sheath) astrocytes (brain capillaries) Figure 48.7 50 µm Functions of The Nervous System 1. Receive information from internal/external environment or other nerve cells 2. Integrate the information and produce an appropriate output signal 3. Conduct the signal 4. Transmit the signal to other nerve cells, glands, or muscles 5. Coordinate and carry on metabolic activities 3
The Neurons 1. Non-myelinated a. Dendrites b. cell body c. axon hillock d. axon e. axon terminals 2. Myelinated: saltatory conduction Action Potential Propagation Along Sheathed Neurons 4
Neuron configuration fits function Functional Interactions of neurons 1. Simplest: Reflex Arc 2. Convergent 3. Divergent 4. Reverberating Mechanisms of neural activity 1. Electrical signals and membrane potentials a. Resting potential b. Action potential 2. Communication between neurons a. Synapses b. Neurotransmitters 5
The Nature of Neural Signals 1. Resting potential -70 mv. a. Stimulation 2. Action potential 3. Re-polarization 1. Resting potential: 2. Action Potential: 6
3. Repolarization Communication between Neurons Synapse the junction between neurons at which an electrical signal is converted into a chemical signal that can then stimulate another electrical signal. Neurotransmitters = chemical messengers Communication between Neurons The positively charged 1 st cell terminal triggers storage vesicles to release chemicals into the synaptic cleft (space between cells). Stimulatory neurotransmitters alter a neuron s permeability to Na+ ions (cause action potential). Inhibitory neurotransmitters alter a neuron s permeability to Cl - ions (less likely to produce an action potential). 7
Communication between neurons Communication between neurons Intercellular transmission: (synapse) electrical; chemical: excitatory vs. inhibitory 8
Nervous System Organization Central nervous system Peripheral nervous system Neuron Cell body Dendrites Axons Myelin sheath Schwann cells Oligodendrocytes Synapse Sensory neurons Interneurons Motor neurons Resting potential Action potential Depolarization Synaptic cleft Neurotransmitter Somatic nervous system Autonomic nervous system Parasympathetic division Sympathetic division In Conclusion 1. The nervous system consists of sensory neurons, interneurons, and motor neurons, which activate muscle and glands 2. A neuron s dendrites and cell body are input zones and the axon ending is the output zone 3. There is a voltage difference across the plasma membrane in a resting neuron 9
In Conclusion 5. An action potential is a reversal of the voltage difference across the membrane 6. When Na + channels open, allowing Na + to enter a cell, the voltage difference across the membrane reverses abruptly 7. Sodium/Potassium Pumps restore the gradients after an action potential 8. Neurotransmitters released into a synaptic cleft may excite or inhibit the cell s plasma membrane 10