Neurons, Synapses and Signaling Chapter 48
Warm Up Exercise What types of cells can receive a nerve signal?
Nervous Organization Neurons- nerve cells. Brain- organized into clusters of neurons, called ganglia. Central Nervous System- includes the brain and the spinal cord. Peripheral Nervous System- all of the neurons extending from the brain and the spinal cord.
Types of Neurons Sensory Neurons- transmit information from the senses to processing centers in the brain or ganglia. Interneurons- neurons in the brain that analyze and interpret sensory input. Motor Neurons- transmit signals for muscle and gland activity.
Neuron Structure and Function Cell Body- contain the organelles and nucleus. Dendrites- branched extensions that receive signals from other neurons. Axon- extension from the cell body that transmits signals to other cells. Synapse- junction between neurons. Neurotransmitters- chemical messengers that pass information between neurons. Glial Cells- supporting cells that insulate the axons of neurons and regulate fluid surrounding neurons.
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Ion Pumps and Resting Potential Membrane Potential- the difference in voltage between the inside and outside of the cell membrane. Resting Potential- the membrane potential of a resting neuron is -60 to -80 mv. Formed by a high concentration of K + ions inside the cell, and high Na + ions outside the cell.
Sodium-Potassium Pumps Sodium-Potassium Pumpsmaintain resting potential in the cell membrane. Transport 3 Na + ions out for every 2 K + ions in. In addition to the Sodium- Potassium pump, ions diffuse across the concentration gradient. Many K + channels are open, allowing for a large amount of K + to move out of the cell, few Na + channels are open allowing little flow inside, leading to a negative membrane potential inside.
Warm Up Exercise Explain how a nervous response is transmitted through a series of neurons? How does the sodium-potassium pump maintain a membrane gradient?
Ion Gated Channels Ion Gated Channels- ion channels that open or close in response to stimuli. The opening and closing of ion gated channels alters the membrane potential. Hyperpolarization- an increase in the magnitude of the membrane potential. Depolarization- a reduction in the magnitude of the membrane potential.
Graded and Action Potentials Graded Potential- a shift in the membrane potential; is a response to hyperpolarization or depolarization Action Potential- a massive change in membrane voltage, caused by depolarization. Action potentials can be regenerated to spread along the axon at a constant magnitude.
Graded Potentials and Action Potentials kk
Voltage Gated Ion Channels Voltage-Gated Ion Channels- open and close when the membrane potential passes a particular level. Action potentials occur when depolarization increases the membrane potential to a certain level, called the threshold.
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Warm Up Exercise Explain what happens in hyperpolarization and depolarization? Which ions move in which direction? Describe what happens in an action potential.
Action Potentials Refractory Period- downtime when a second action potential cannot be initiated. Occurs because of the inactivation of the sodium channelsduring the falling phase and early part of the undershoot.
Action Potentials Saltatory Conduction- how the action potentials jumps from node to node along the axon.
Communication With Other Cells Electrical Synapses- contain gap junctions which allow electrical currents to flow from one neuron to the next. Chemical Synapses- release a chemical neurotransmitter between cells.
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Chemical Synapse Presynaptic neuron synthesizes neurotransmitter and packages in synaptic vesicles. The arrival of action potential at axon/synaptic terminal depolarizes plasma membrane, opening voltage-gated channels, which allow Ca 2+ to diffuse into the synaptic terminal, which forces vesicles to fuse with membrane causing the release of neurotransmitter into the synaptic cleft. Neurotransmitters diffuse across the cleft and binds to and activates a specific membrane receptor (called a ligand-gated ion channel).
Ligand-Gated Ion Channels Ligand-Gated Ion Channel- located in postsynaptic cell- binding of neurotransmitter to this receptor opens the channel and allows specific ions to diffuse across the postsynaptic membrane, resulting in a postsynaptic potential. Excitatory Postsynaptic Potential (EPSP)- occurs when channel is permeable to both Na+ and K+. Causes depolarization. Inhibitory Postsynaptic Potential (IPSP)- occurs when channel is permeable to either K+ or Cl-. Causes hyperpolarization.
Summation of Action Potentials Temporal Summation- two EPSP s occur at a single synapse in rapid succession- in this case the EPSP s add together. Spatial Summation- two EPSP s produced simultaneously at different synapses on the same postsynaptic neuron- EPSP s added together.
Exit Slip In multiple sclerosis, myelin sheaths harden and deteriorate. How would this affect the nervous system function?
Warm Up Exercise What is meant by the term saltatory conduction? Explain the difference between an electrical and chemical synapse. Discuss how a presynaptic cell transmits a chemical impulse once it receives the action potential near the axon terminal.
Neurotransmitters Acetylcholine- causes the opening of potassium channels in cardiac muscle membrane. Leads to hyperpolarization, which reduces the rare at which the heart pumps (inhibitory). Dopamine and Serotonin Epinephrine and Norepinephrine
Organization of Human Brain Cerebrum- the center for voluntary movement, learning, emotion, memory, etc. Divided into right and left hemispheres, connected by the corpus callosum. Cerebellum- coordinates movement and balance.
Organization of Human Brain Diencephalon Thalamus Hypothalamus Pineal Gland Pituitary Gland Brainstem- receives signals from sensory neurons Midbrain Pons Medulla Oblongata
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