Chapter 48 49 NEURONS AND NERVOUS SYSTEM I Overview Organization Invertebrates Simple have nerve nets Complex brain and nerve cord Vertebrates Central nervous system CNS contains brain and spinal cord I Overview Information Processing 3 stages Sensory input from outside Integration in brain Motor output in muscle body part neurons carry information into and out of the CNS which make up the peripheral nervous system PNS Figure 48 3 Sensory input Integration Sensor Motor output Effector Peripheral nervous system PNS Central nervous system CNS I Overview Neurons A nerve cell The fundamental unit of the nervous system Receive and transmit information I Overview Neurons Cell body Dendrites Highly branched extensions that receive signals from other neurons Axon Contains organelles A single extension that transmits the signal to other cells It branches at the end Synapse Junction to another cell where information is transmitted usually via neurotransmitters I Overview Neurons Synapse Presynaptic cell Transmitting neuron Postsynaptic cell Receiving neuron muscle gland Figure 48 4 Dendrites Stimulus Axon hillock Nucleus Cell body Presynaptic cell Axon Signal direction Synapse Neurotransmitter Synaptic terminals Postsynaptic cell Synaptic terminals I Overview Glial Structural support for neurons Insulate axon Nourish neuron Regulate extracellular fluid II Ion Pumps and Channels Membrane Potential Voltage across membrane because inside cell is negatively charged and outside of cell is positively charged II Ion Pumps and Channels Resting Potential When a neuron is not transmitting a signal Ionic gradients More sodium outside than inside Less potassium outside than inside Due to sodium potassium pump ATPase II Ion Pumps and Channels Resting Potential Membrane ion channels always open Ions move across membrane through ion channels and create a resting potential Many ion channels for potassium and not many for sodium Gated ion channels Open or closed depending on Change in membrane potential Binding of a chemical to channel Stretching of membrane Figure 48 7 Key Na K Sodiumpotassium pump Potassium channel OUTSIDE OF CELL Sodium channel INSIDE OF CELL III Action Potential When the membrane potential changes by massive amounts an action potential is generated III Action Potential Making them happen Depolarization The plasma membrane becomes depolarized it changes its charge Normally the inside of the membrane has a negative charge and the outside of the membrane has a positive charge When depolarized the inside of the membrane is slightly more positively charged than the outside of the membrane III Action Potential Making them happen How Gated sodium channels open so sodium ions enter cell Return to resting potential by closing sodium channels and opening potassium channels Figure 48 11 5 Key Na K 3 Rising phase of the action potential Membrane potential mV 50 OUTSIDE OF CELL 100 Sodium channel Potassium channel Action potential 3 0 50 2 Depolarization 4 Falling phase of the action potential Threshold 2 1 4 5 Resting potential Time INSIDE OF CELL Inactivation loop 1 Resting state 5 Undershoot 1 III Action Potential Conducting Them Successive Depolarizations Successive depolarizations occur down the length of an axon Sodium rushing through open gated channels causes neighboring gated channels to open Gated potassium channels open right behind the depolarizaiton zone Figure 48 12 3 Axon Plasma membrane Action potential 1 Cytosol Na K Action potential 2 Na K K Action potential 3 Na K III Action Potential Conducting Them Speed Fatter axon faster travel Myelin sheath an insulating layer around an axon will increase the speed IV Communication Through Synapse Electrical Synapse Direct flow of electrical current between cells through gap junctions Chemical Synapse A neuron releases chemical neurotransmitters into synaptic cleft IV Communication Through Synapse Postsynaptic Potential Arises from direct transmission of signal across synapse Ligand gated channels on receiving neuron open and let sodium ions in Excitatory postsynaptic potential Inhibitory postsynaptic potential Neurotransmitter binds to ligand gated ion channel to generate these Counter each other opposites Figure 48 15 Presynaptic cell Postsynaptic cell Axon Synaptic vesicle containing neurotransmitter 1 Postsynaptic membrane Synaptic cleft Presynaptic membrane 3 K Ca2 2 Voltage gated Ca2 channel Ligand gated ion channels 4 Na IV Communication Through Synapse Communication done by Neurotransmitters Acetylcholine Is excitatory Nicotine binds to same receptor stimulant Botulism blocks it Biogenic Amines Norepinephrine Dopamine Serotonin IV Communication Through Synapse Communication done by Neurotransmitters Amino Acids Proteins Glutamate for long term memory GABA increases membrane permeability to chloride ions Glycine Endorphins decrease pain perception Gases Nitric oxide Carbon monoxide Table 48 2 V Vertebrate Nervous System Central Nervous System Brain and spinal cord Both are highly cooridnated V Vertebrate Nervous System Peripheral Nervous System Nerves Ganglia Cranial nerves from the brain Spinal nerves from the spinal cord Clusters of nerve cell bodies Somatic nervous system Voluntary movements skeletal muscle Figure 49 4 Central nervous system CNS Brain Peripheral nervous system PNS Cranial nerves Spinal cord Ganglia outside CNS Spinal nerves V Vertebrate Nervous System Peripheral Nervous System Autonomic nervous system Involuntary smooth and cardiac muscle Sympathetic fight flight response Parasympathetic calming response Enteric digestive tract pancreas gall bladder control secretion and peristalsis Note can be regulated by sympathetic and parasympathetic as well Figure 49 7 Central Nervous System information processing Peripheral Nervous System Efferent neurons Afferent neurons Sensory receptors Autonomic nervous system Motor system Control of skeletal muscle Internal and external stimuli Sympathetic division Parasympathetic Enteric division division Control of smooth muscles cardiac muscles glands Figure 49 8 Sympathetic division Parasympathetic division Action on target organs Action on target organs Constricts pupil of eye Dilates pupil of eye Stimulates salivary gland secretion Inhibits salivary gland secretion Constricts bronchi in lungs Cervical Sympathetic ganglia Relaxes bronchi in lungs Slows heart Accelerates heart Stimulates activity of stomach and intestines Inhibits activity of stomach and intestines Thoracic