The nervous system
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There are three main categories of neurons: sensory neurons, which conduct impulses to the spinal cord; interneurons, which interconnect sensory and motor neurons; and motor neurons, which conduct impulses from the spinal cord to effectors like muscles. Neurons are similar to other cells but have specialized extensions called dendrites and axons that allow them to communicate electrochemically. The three main parts of a neuron are the cell body, dendrites that receive signals, and a single axon that transmits signals. Glial cells support neurons and include oligodendrocytes, astrocytes, Schwann cells, and microglia. An action potential is the electrochemical signal transmitted along the axon.
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The nervous system
- 1. CELLS IN THE NERVOUS SYSTEM
- 6. NEURONS VS. OTHER CELLS IN THE BODY NEURONS ARE SIMILAR TO OTHER CELLS IN THE BODY BECAUSE: • Neurons are surrounded by a cell membrane. • Neurons have a nucleus that contains genes. • Neurons contain cytoplasm, mitochondria and other organelles. • Neurons carry out basic cellular processes such as protein synthesis and energy production. NEURONS DIFFER FROM OTHER CELLS IN THE BODY BECAUSE: • Neurons have specialized extensions called dendrites and axons. Dendrites bring information to the cell body and axons take information away from the cell body. • Neurons communicate with each other through an electrochemical process. • Neurons contain some specialized structures (for example, synapses) and chemicals (for example, neurotransmitters).
- 7. THREE GENERAL CATEGORIES OF NEURONS
- 8. THREE GENERAL CATEGORIES OF NEURONS
- 9. THREE GENERAL CATEGORIES OF NEURONS
- 10. THREE GENERAL CATEGORIES OF NEURONS SENSORY NEURON INTERNEURON MOTOR NEURON Long dendrites and Short dendrites and Short dendrites and LENGTH OF FIBERS short axon short or long axon long axon Cell body and Dendrites and the dendrite are cell body are outside of the Entirely within the located in the LOCATION spinal cord; the cell spinal cord or CNS spinal cord; the body is located in axon is outside of a dorsal root the spinal cord ganglion Interconnect the Conduct impulse to Conduct impulse to sensory neuron with FUNCTION an effector (muscle the spinal cord appropriate motor or gland) neuron
- 11. THE THREE DISTINCT PARTS OF THE NEURON
- 12. THE THREE DISTINCT PARTS OF THE NEURON
- 13. THE THREE DISTINCT PARTS OF THE NEURON
- 14. THE THREE DISTINCT PARTS OF THE NEURON
- 15. CELL BODY OR SOMA
- 16. CELL BODY OR SOMA
- 17. CELL BODY OR SOMA
- 18. DENDRITES
- 19. AXON
- 20. AXON
- 21. DENDRITES VS. AXON Take information away Bring information to the from the cell body cell body Rough Surface (dendritic Smooth Surface spines) Generally only 1 axon per Usually many dendrites cell per cell No ribosomes Have ribosomes Can have myelin No myelin insulation Branch further from the Branch near the cell cell body body
- 23. TWO TYPES OF GLIAL CELLS
- 24. TWO CLASSES OF MACROGLIA
- 25. SCHWANN CELL
- 26. MICROGLIA
- 27. ACTION POTENTIAL
- 28. ACTION POTENTIAL
- 29. ACTION POTENTIAL
- 30. ACTION POTENTIAL
- 31. ACTION POTENTIAL
- 32. ACTION POTENTIAL
- 33. ACTION POTENTIAL
- 39. CELLS IN THE NERVOUS SYSTEM
Editor's Notes
- When a neuron is not sending a signal, it is "at rest." When a neuron is at rest, the inside of the neuron is negative relative to the outside. Although the concentrations of the different ions attempt to balance out on both sides of the membrane, they cannot because the cell membrane allows only some ions to pass through channels (ion channels).
- The resting membrane potential of a neuron is about -70 mV (mV=millivolt) - this means that the inside of the neuron is 70 mV less than the outside.
- The resting potential tells about what happens when a neuron is at rest. An action potential occurs when a neuron sends information down an axon, away from the cell body. Neuroscientists use other words, such as a "spike" or an "impulse" for the action potential.
- The resting potential tells about what happens when a neuron is at rest. An action potential occurs when a neuron sends information down an axon, away from the cell body. Neuroscientists use other words, such as a "spike" or an "impulse" for the action potential. If the neuron does not reach this critical threshold level, then no action potential will fire. Also, when the threshold level is reached, an action potential of a fixed sized will always fire...for any given neuron, the size of the action potential is always the same. There are no big or small action potentials in one nerve cell - all action potentials are the same size. Therefore, the neuron either does not reach the threshold or a full action potential is fired - this is the "ALL OR NONE" principle.
- Because there are many more sodium ions on the outside, and the inside of the neuron is negative relative to the outside, sodium ions rush into the neuron. Remember, sodium has a positive charge, so the neuron becomes more positive and becomes depolarized.The action potential actually goes past -70 mV (a hyperpolarization) because the potassium channels stay open a bit too long.
- The vesicle membrane will fuse with the presynaptic membrane releasing the neurotransmitters into the synaptic cleft. Until recently, it was thought that a neuron produced and released only one type of neurotransmitter. This was called "Dale's Law." However, there is now evidence that neurons can contain and release more than one kind of neurotransmitter.
- Diffusion of Neurotransmitters Across the Synaptic CleftThe neurotransmitter molecules then diffuse across the synaptic cleft where they can bind with receptor sites on the postsynaptic ending to influence the electrical response in the postsynaptic neuron. In the figure on the right, the postsynaptic ending is a dendrite (axodendritic synapse), but synapses can occur on axons (axoaxonic synapse) and cell bodies (axosomatic synapse).When a neurotransmitter binds to a receptor on the postsynaptic side of the synapse, it changes the postsynaptic cell's excitability: it makes the postsynaptic cell either more or less likely to fire an action potential. If the number of excitatory postsynaptic events is large enough, they will add to cause an action potential in the postsynaptic cell and a continuation of the "message."
- Diffusion of Neurotransmitters Across the Synaptic CleftThe neurotransmitter molecules then diffuse across the synaptic cleft where they can bind with receptor sites on the postsynaptic ending to influence the electrical response in the postsynaptic neuron. In the figure on the right, the postsynaptic ending is a dendrite (axodendritic synapse), but synapses can occur on axons (axoaxonic synapse) and cell bodies (axosomatic synapse).When a neurotransmitter binds to a receptor on the postsynaptic side of the synapse, it changes the postsynaptic cell's excitability: it makes the postsynaptic cell either more or less likely to fire an action potential. If the number of excitatory postsynaptic events is large enough, they will add to cause an action potential in the postsynaptic cell and a continuation of the "message."
- Diffusion of Neurotransmitters Across the Synaptic CleftThe neurotransmitter molecules then diffuse across the synaptic cleft where they can bind with receptor sites on the postsynaptic ending to influence the electrical response in the postsynaptic neuron. In the figure on the right, the postsynaptic ending is a dendrite (axodendritic synapse), but synapses can occur on axons (axoaxonic synapse) and cell bodies (axosomatic synapse).When a neurotransmitter binds to a receptor on the postsynaptic side of the synapse, it changes the postsynaptic cell's excitability: it makes the postsynaptic cell either more or less likely to fire an action potential. If the number of excitatory postsynaptic events is large enough, they will add to cause an action potential in the postsynaptic cell and a continuation of the "message."