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Transcript
Peripheral nervous system (PNS) Central nervous system (CNS) Cranial nerves and spinal nerves Communication lines between the CNS and the rest of the body Brain and spinal cord Integrative and control centers Sensory (afferent) division Somatic and visceral sensory nerve fibers Conducts impulses from receptors to the CNS Somatic sensory fiber Motor (efferent) division Motor nerve fibers Conducts impulses from the CNS to effectors (muscles and glands) Somatic nervous system Somatic motor (voluntary) Conducts impulses from the CNS to skeletal muscles Skin Visceral sensory fiber Stomach Autonomic nervous system (ANS) Visceral motor (involuntary) Conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands Skeletal muscle Motor fiber of somatic nervous system Sympathetic division Mobilizes body systems during activity Sympathetic motor fiber of ANS Structure Function Sensory (afferent) division of PNS Motor (efferent) division of PNS Parasympathetic motor fiber of ANS Parasympathetic division Conserves energy Promotes housekeeping functions during rest Heart Bladder Capillary Neuron Astrocyte Myelin sheath Process of oligodendrocyte Nerve fibers Neuron Microglial cell Fluid-filled cavity Ependymal cells Brain or spinal cord tissue Satellite cells Cell body of neuron Schwann cells (forming myelin sheath) Nerve fiber Dendrites (receptive regions) Cell body (biosynthetic center and receptive region) Neuron cell body Nucleolus Nucleus Nissl bodies Axon (a) (impulse Impulse generating and conducting direction region) Axon hillock Neurilemma Dendritic spine Node of Ranvier Schwann cell (one internode) Terminal branches Axon terminals (secretory region) Schwann cell plasma membrane Schwann cell cytoplasm Axon 1 A Schwann cell envelopes an axon. Schwann cell nucleus 2 The Schwann cell then rotates around the axon, wrapping its plasma membrane loosely around it in successive layers. Neurilemma Myelin sheath (a) Myelination of a nerve fiber (axon) 3 The Schwann cell cytoplasm is forced from between the membranes. The tight membrane wrappings surrounding the axon form the myelin sheath. Receptor Neurotransmitter chemical attached to receptor Na+ Na+ Chemical binds K+ Closed K+ Open (a) Chemically (ligand) gated ion channels open when the appropriate neurotransmitter binds to the receptor, allowing (in this case) simultaneous movement of Na+ and K+. Na+ Na+ Membrane voltage changes Closed Open (b) Voltage-gated ion channels open and close in response to changes in membrane voltage. Voltmeter Plasma membrane Ground electrode outside cell Microelectrode inside cell Axon Neuron The concentrations of Na+ and K+ on each side of the membrane are different. Outside cell The Na+ concentration is higher outside the cell. K+ (5 mM ) Na+ (140 mM ) The K+ concentration is higher inside the cell. K+ (140 mM ) Na+ (15 mM ) Inside cell The permeabilities of Na+ and K+ across the membrane are different. Suppose a cell has only K+ channels... K+ loss through abundant leakage channels establishes a negative membrane potential. K+ leakage channels K+ K+ K+ K+ K+ K+ Na+ K K+ Na+ K+ K+ Na+ K+ K+ Na+ Na+-K+ ATPases (pumps) maintain the concentration gradients of Na+ and K+ across the membrane. Cell interior –90 mV Now, let’s add some Na+ channels to our cell... Na+ entry through leakage channels reduces the negative membrane potential slightly. Cell interior –70 mV Na+-K+ pump Cell interior –70 mV Finally, let’s add a pump to compensate for leaking ions. Na+-K+ ATPases (pumps) maintain the concentration gradients, resulting in the resting membrane potential. The concentrations of Na+ and K+ on each side of the membrane are different. The Na+ concentration is higher outside the cell. The K+ concentration is higher inside the cell. Outside cell (5 mM ) Na+ (140 mM ) K+ (140 mM ) Na+ (15 mM ) K+ Inside cell Na+-K+ ATPases (pumps) maintain the concentration gradients of Na+ and K+ across the membrane. The permeabilities of Na+ and K+ across the membrane are different. Suppose a cell has only K+ channels... K+ K+ K+ K+ K+ leakage channels Cell interior –90 mV K+ loss through abundant leakage channels establishes a negative membrane potential. Stimulus Depolarized region Plasma membrane (a) Depolarization: A small patch of the membrane (red area) has become depolarized. Spread of depolarization: The local currents (black arrows) that are created depolarize adjacent membrane areas and allow the wave of depolarization to spread. SHINGLES