Chapter 4 Principles of Neural and Hormonal Communication

Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Outline • • Graded Potentials Action Potentials Synapses and integration Intracellular communication Signal Transduction Hormonal Communication Nervous vs. Endocrine System Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Communication is critical for the survival of the cells that compose the body. Two major regulatory systems of the body – nervous and endocrine - communicate with the cells/tissues/organs/systems they control. Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Neural Communication • Nerve and muscle are excitable tissues • Can undergo rapid changes in their membrane potentials • Can change their resting potentials into electrical signals – Electrical signals are critical to the function of the nervous system and all muscles Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Neural Communication • Membrane electrical states – Polarization • Any state when the membrane potential is other than 0 m. V – Depolarization • Membrane becomes less polarized than at resting potential – Repolarization • Membrane returns to resting potential after having been depolarized – Hyperpolarization • Membrane becomes more polarized than at resting potential Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Types of Changes in Membrane Potential Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Neural Communication • Two kinds of potential change – Graded potentials • Serve as short-distance signals – Action potentials • Serve as long-distance signals Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Graded Potential • Occurs in small, specialized region of excitable cell membranes • Magnitude of graded potential varies directly with the magnitude of the triggering event Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Portion of excitable cell Initial site of potential change Loss of charge Direction of current flow from initial site Chapter 4 Principles of Neural and Hormonal Communication * Numbers refer to the local potential in m. V Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning at various points along the membrane. Fig. 4 -4, p. 89

Current Flow During a Graded Potential Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Graded Potentials Examples of graded potentials: • • • Postsynaptic potentials Receptor potentials End-plate potentials Pacemaker potentials Slow-wave potentials Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Action Potentials • Brief, rapid, large (100 m. V) changes in membrane potential during which potential actually reverses • Involves only a small portion of the total excitable cell membrane • Do not decrease in strength as they travel from their site of initiation throughout remainder of cell membrane Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning Fig. 4 -7, p. 91

Action Potentials • When membrane reaches threshold potential – Voltage-gated channels in the membrane undergo conformational changes – Flow of sodium ions into the ICF reverses the membrane potential from -70 m. V to +30 m. V – Flow of potassium ions into the ECF restores the membrane potential to the resting state Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Action Potentials • Additional characteristics – Sodium channels open during depolarization by positive feedback. – When the sodium channels become inactive, the channels for potassium open. This repolarizes the membrane. – As the action potential develops at one point in the plasma membrane, it regenerates an identical action potential at the next point in the membrane. – Therefore, it travels along the plasma membrane undiminished. Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Action Potentials Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Action Potentials Permeability Changes and Ion Fluxes During an Action Potential Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Action Potentials The Na+/K+ pump gradually restores the concentration gradients disrupted by action potentials. • Sodium is pumped into the ECF • Potassium is pumped into the ICF Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Neuron • Once initiated, action potentials are conducted throughout a nerve fiber • Action potentials are propagated from the axon hillock to the axon terminals • Basic parts of neuron (nerve cell) – Cell body – Dendrites – Axon Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Neuron • Cell body – Houses the nucleus and organelles • Dendrites – Project from cell body and increase surface area available for receiving signals from other nerve cells – Signal toward the cell body Dendrite and cell body serve as the neurons input zone. Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Neuron • Axon – Nerve fiber – Single, elongated tubular extension that conducts action potentials away from the cell body – Conducting zone of the neuron – Collaterals • Side branches of axon – Axon hillock • First portion of the axon plus the region of the cell body fro m which the axon leaves • Neuron’s trigger zone – Axon terminals • Release chemical messengers that simultaneously influence other cells with which they come into close association • Output zone of the neuron Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Neuron Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Action Potentials • Two types of propagation – Contiguous conduction • Conduction in unmyelinated fibers • Action potential spreads along every portion of the membrane – Saltatory conduction • Rapid conduction in myelinated fibers • Impulse jumps over sections of the fiber covered with insulating myelin Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Contiguous Conduction Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Saltatory Conduction Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Saltatory Conduction • Propagates action potential faster than contiguous conduction because action potential does not have to be regenerated at myelinated section • Myelinated fibers conduct impulses about 50 times faster than unmyelinated fibers of comparable size • Myelin – Primarily composed of lipids – Formed by oligodendrocytes in CNS – Formed by Schwann cells in PNS Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Regeneration of Nerve Fibers • Regeneration of nerve fibers depends on its location • Schwann cells in PNS guide the regeneration of cut axons • Fibers in CNS myelinated by oligodendrocytes do not have regenerative ability – Oligodendrocytes inhibit regeneration of cut central axons Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Synapses • Junction between two neurons • Primary means by which one neuron directly interacts with another neuron (muscle cells or glands as well) • Anatomy of a synapse – Presynaptic neuron – conducts action potential toward synapse – Synaptic knob – contains synaptic vesicles – Synaptic vesicles – stores neurotransmitter (carries signal across a synapse) – Postsynaptic neuron – neuron whose action potentials are propagated away from the synapse – Synaptic cleft – space between the presynaptic and postsynaptic neurons Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning Fig. 4 -16, p. 103

Synapses Signal at synapse either excites or inhibits the postsynaptic neuron • Two types of synapses – Excitatory synapses – Inhibitory synapses Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning Table 4 -2, p. 105

Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning Table 4 -3, p. 108

Neurotransmitters • Vary from synapse to synapse • Same neurotransmitter is always released at a particular synapse • Quickly removed from the synaptic cleft • Some common neurotransmitters – – – – – Acetylcholine Dopamine Norepinephrine Epinephrine Serotonin Histamine Glycine Glutamate Aspartate Gamma-aminobutyric acid (GABA) Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Synaptic inputs (presynaptic axon terminals) Dendrites Cell body of postsynaptic neuron Axon hillock Myelinated axon Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning Fig. 4 -15, p. 102

Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning Fig. 4 -16, p. 103

Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning Fig. 4 -17, p. 104

Neuropeptides • Large molecules consisting of from 2 to 40 amino acids • Synthesized in neuronal cell body in the endoplasmic reticulum and Golgi complex • Packaged in large, dense-core vesicles present in axon terminal Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Comparison of Classical Neurotransmitters and Neuropeptides Characterist Classical Neuropeptides ic Neurotransmitters Size Small, one amino acid or similar chemical Large, 2 to 40 amino acids in length Site of Synthesis Cytosol of synaptic knob Endoplasmic reticulum and Golgi complex in cell body, travel to synaptic knob by axonal transport Site of Storage In small synaptic vesicles in axon terminal In large dense-core vesicles in axon terminal Site of Release Axon terminal, may be cosecreted with neurotransmitter Speed and Duration of Action Rapid, brief response Slow, prolonged response Site of Action Subsynaptic membrane of postsynaptic cell Nonsynaptic sites on either presynaptic or postsynaptic cell at much lower concentrations than classical neurotransmitters Effect Usually alter potential of postsynaptic cell by opening specific ion channels Usually enhance or suppress synaptic effectiveness by long-term changes in neurotransmitter synthesis or postsynaptic receptor sits (act as neuromodulators) Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Neuronal Integration • Multiple EPSP and IPSP’s from numerous synapses converge on one neuron. • These signals can cause different changes in the postsynaptic neuron – Cancellation – Spatial summation – Temporal summation Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Threshold = approx -55 mv Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning Fig. 4 -18, p. 106

Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning Fig. 4 -19, p. 109

Presynaptic inputs Convergence of input (one cell is influenced by many others) Postsynaptic neuron Presynaptic inputs Divergence of output (one cell influences many others) Postsynaptic neurons Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning Arrows indicate direction in which information is being conveyed. Fig. 4 -20, p. 111

The Retina Example of convergence and divergence Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Synaptic Drug Interactions • Possible drug actions – Altering the synthesis, axonal transport, storage, or release of a neurotransmitter – Modifying neurotransmitter interaction with the postsynaptic receptor – Influencing neurotransmitter reuptake or destruction – Replacing a deficient neurotransmitter with a substitute transmitter Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Examples of drugs that alter synaptic transmission • Cocaine – Blocks reuptake of neurotransmitter dopamine at presynaptic terminals • Strychnine – Competes with inhibitory neurotransmitter glycine at postsynaptic receptor site • Tetanus toxin – Prevents release of inhibitory neurotransmitter GABA, affecting skeletal muscles Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Chemical Messengers • Four types of chemical messengers – Paracrines • Local chemical messengers • Exert effect only on neighboring cells in immediate environment of secretion site – Neurotransmitters • Short-range chemical messengers • Diffuse across narrow space to act locally on adjoining target cell (another neuron, a muscle, or a gland) Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Chemical Messengers – Hormones • Long-range messengers • Secreted into blood by endocrine glands in response to appropriate signal • Exert effect on target cells some distance away from release site – Neurohormones • Hormones released into blood by neurosecretory neurons • Distributed through blood to distant target cells Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Chemical Messengers • Extracellular chemical messengers bring about cell responses primarily by signal transduction – Process by which incoming signals are conveyed to target cell’s interior • Binding of extracellular messenger (first messenger) to matching receptor brings about desired intracellular response by either – Opening or closing channels – Activating second-messenger systems • Activated by first messenger • Relays message to intracellular proteins that carry out dictated response Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Hormones • Endocrinology – Study of homeostatic activities accomplished by hormones • Two distinct groups of hormones based on their solubility properties – Hydrophilic hormones (Proteins, peptides) • Highly water soluble • Low lipid solubility – Lipophilic hormones (Steroids) • High lipid solubility • Poorly soluble in water Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Fig. 4 -21, p. 112

Table 4 -4, p. 114

Fig. 4 -22, p. 115

Fig. 4 -23, p. 116

Fig. 4 -24, p. 118

Fig. 4 -25, p. 119

Fig. 4 -26, p. 122

Comparison of Nervous System and Endocrine System Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood © 2007 Brooks/Cole-Thomson Learning

Action Potential

Neuron

Voltage Gated