Neurophysiology Corresponding textbook pages: 436-440, 442-455 Organization Helps maintain homeostasis in the body Nervous system and endocrine system Nervous system is faster due to nerve impulses 1
Fig. 12.3 Peripheral nervous system Central nervous system 1 Sensory (afferent) neurons conduct signals from receptors to the CNS. 3 Motor (efferent) neurons conduct signals from the CNS to effectors such as muscles and glands. 2 Interneurons (association neurons) are confined to the CNS. Organization of Nervous system 2
The communicative role of Nervous System Neurons Function: Maintain communication through the use of electrical and chemical processes. Characteristics: Excitability Conductivity Secretion Functional Classes of Neurons Functional Cell of the nervous system Extremely excitable, and excite other cells Types: Sensory Motor Interneurons 3
Structure of a Neuron Soma or cell body Dendrites Axon hillock Axon Terminal Arborization Synaptic Knobs Nissl bodies Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Dendrites Nucleolus Soma Nucleus Axon Direction of signal transmission Node of Ranvier Terminal arborization Axon collater al Trigger zone: Axon hillock Internodes Myelin sheath Schwann cell Synaptic knobs Figure 12.4a Schwann cells Coat entire axon Found in the PNS Myelin Sheath Myelin Neurilemma Nodes of Ranvier 4
Fig. 12.4c Schwann cell nucleus Neurilemma (c) Myelin sheath The Resting Membrane Potential ECF Na + 145 m Eq/L K + 4 m Eq/L Na + channel ICF K + channel Na + concentrated outside of cell (ECF) K + concentrated inside cell (ICF) Na + K + 12 m Eq/L 150 m Eq/L Large anions that cannot escape cell Figure 12.11 12-10 5
Nerve Impulse Resting Membrane Potential When a nerve impulse is not conducting an impulse. Difference in Potential is usually -70mV. Threshold Potential The critical voltage point. Need to reach this point in order to send an impulse. Local potentials Local disturbances in the resting membrane potential Characteristics: Graded Decremental Reversible The process of Generating a local potential and Depolarization 6
Action Potential Action potential is the same as nerve impulse. A more dramatic change in potentials. Arrival of current at axon hillock depolarizes membrane Depolarization must reach threshold: critical voltage (about -55 mv) required to open voltage-regulated gates Voltage-gated Na + channels open, Na + enters and depolarizes cell, which opens more channels resulting in a rapid positive feedback cycle as voltage rises Potassium channels open, membrane becomes repolarized. Some characteristics of Action potential Characterization All or none law Nondecremental Irreversible 7
mv 8/22/2017 Fig. 12.13a +35 4 3 5 0 55 70 Local potential Depolarization Threshold 2 1 Resting membrane potential Repolarization 6 Action potential 7 Hyperpolarization (a) Time Signal Conduction 1. Unmyelinated Fibers Each region must depolarize and repolarize for an action potential to propagate 2. Myelinated Fibers Saltatory conduction Faster 8
Fig. 12.17 (a) Na + inflow at node generates action potential (slow but nondecremental) Na+ diffuses along inside of axolemma to next node (fast but decremental) Excitation of voltageregulated gates will generate next action potential here (b) Action potential in progress Refractory membrane Excitable membrane Synapse Region where a neuron carries info toward another structure like a muscle or a gland. 3 components: Axon of Presynaptic neuron Release of neurotransmitters. Synaptic cleft Post-synaptic neuron or other cells Binding of neurotransmitter to the receptors on postsynaptic membrane Generation of action potential 9
Fig. 12.20 Microtubules of cytoskeleton Axon of presynaptic neuron Mitochondria Postsynaptic neuron Synaptic knob Synaptic vesicles containing neurotransmitter Synaptic cleft Postsynaptic neuron Neurotransmitter receptor Neurotransmitter release 10