STRUCTURE ANDFUNCTIONS OF CELLSOF THE NERVOUSSYSTEM
Learning Objectives1. Name and describe the parts of a neuron and explain their functions2. Describe the supporting cells of the central and peripheral nervous systems and explain the blood-brain barrier.3. Briefly describe the neural circuitry responsible for a withdrawal reflex and its inhibition by neurons in the brain.4. Describe the measurement of the action potential and explain the how the balance between the forces of diffusion and electrostatic pressure is responsible for the membrane potential.5. Describe the role of ion channels in action potentials and explain the all-or-none law and the rate law.6. Describe the structure of synapses, the release of the neurotransmitter, and the activation of postsynaptic receptors.7. Describe postsynaptic potentials: the ionic movements that cause them, the processes that terminate them, and their integration.8. Describe the role of autoreceptors and axoaxonic synapses in synaptic communication and describe the role of neuromodulators and hormones in nonsynaptic communication
Cells of the Nervous Sytem3 Neurons Receive and transmit information Glia Support neurons Do NOT transmit information Endothelial Cells Capillaries
Cells of the Nervous System Neurons transmit information Classification Sensory Neurons Motor Neurons Interneurons
Neurons Multipolar neuron one axon and many dendrites most common in CNS Bipolar neuron one axon and one dendrite sensory systems Unipolar one stalk that divides into two branches Somatosensory system
Measuring Electrical Potentials ofAxons Electrode used to apply electrical stimulation and record electrical potentials. Microelectrode used to record activity of individual neurons.
Measuring Electrical Potentials of Axons Membrane Potential electrical charge across a cell membrane difference in electrical potential inside and outside the cell. Outside the cell Resting Potential membrane potential of a neuron at rest approximately -70 mV Inside the cell
The Membrane Potential: Balanceof Two Forces The force of electrostaticThe force of diffusion pressure Diffusion Electrolytes Molecules move Ions from regions of high Cations (+) to low Anions (-) concentrations Electrostatic pressure Like charges repel, opposite charges attract
The Membrane Potential: Balanceof Two ForcesExtracellular Fluid Intracellular Fluid High Concentration High Concentration Sodium (Na+) Potassium (K+) Chloride (Cl-) Low Concentration Low Concentration Sodium (Na+) Potassium (K+) Chloride (Cl-)
The Membrane Ion channel A specialized protein molecule that permits specific ions to enter or leave the cell. Voltage-dependent ion channel An ion channel that opens or closes according to the value of the membrane potential.
The MembraneSodium-Potassium Transporter a.k.a. sodium-potassium pump Moves Na+ and K+ across membrane 3 Na+ out 2 K+ in
Conduction of the Action Potential All-or-none law Rate Law Speed of signal Saltatory Conduction
Communication BetweenNeurons synaptic transmission the transmission of messages from one neuron to another through a synapse these messages are carried by neurotransmitters, chemicals diffuse across synapses.
Communication BetweenNeurons Presynaptic membrane Postsynaptic membrane Postsynaptic potentials
Communication BetweenNeurons Binding site Ligand A chemical that binds with the binding site of a receptor.
Structure of Synapses Types of synapses Axodendritic Axosomatic Axoaxonic
Release of Neurotransmitters Synaptic vesicles A small, hollow, beadlike structure found in the terminal buttons contains molecules of a neurotransmitter fuse with the membrane and then break open, spilling their contents into the synaptic cleft.
Activation of Receptors Neurotransmitter binds with postsynaptic receptor Opens neurotransmitter dependent ion channels (allows ions to flow in or out) Ionotropic receptor (fast and direct) Metabotropic receptor (slow and indirect) G Protein Second messenger
Postsynaptic Potentials Excitatory postsynaptic potential (EPSP) Depolarizes postsynaptic membrane Inhibitory postsynaptic potential (IPSP) Hyperpolarizes postsynaptic membrane Effect likelihood a neuron will fire an action potential
Termination of Postsynaptic Reuptake of neurotransmitter by transporter molecules Enzymatic deactivation Acetylcholine Acetylcholinesterase
Neural Integration Involves the effects of EPSP’s and IPSP’s on the likelihood a neuron will fire an action potential
Autoreceptors Presynaptic receptors respond neurotransmitters released by that neuron Metabotropic regulate internal processes like neurotransmitter synthesis
Axoaxonic Synapses Alter amount of neurotransmitter released Presynaptic inhibition Presynaptic facilitation
Nonsynaptic CommunicationNeuromodulators and hormones Neurotransmitters Neuromodulators Hormones Released endocrine glands and act on target cells