The Nervous System Chapter 38.1-38.5 Anatomy of a Neuron I. Dendrites II. Cell Body III. Axon Synaptic terminal 1
Neuron Connections dendrites cell body terminal cell body cell body terminals dendrites sensory detect stimuli and signal inters inter process information from sensory s and send signals to motor s motor control muscles and glands Action Potentials Potential = difference in electrical charge between inside and outside of cell An electrical signal which carries information within the When stimulus in the s trigger zone reaches threshold gated sodium channels open Voltage difference between inside and outside the cell decreases and starts the action potential 2
Electrical Events During an Action Potential 4 action potential resting potential threshold 1 2 3 less more negative negative 5 time (milliseconds) Fig. 38-2 extracellular fluid (+ charge, high concentration) Neuron at Rest resting + channel (always open) voltage-gated + channel (closed) Resting channel maintains negative charge in resting cell voltage-gated + channel (closed) cytoplasm (- charge, high + concentration) (a) The resting potential 3
Neuron is Stimulated + + action potential A voltage-gated + channel opens + influx creates positive charge in cell (b) The action potential First influx of + causes chain reaction + + Opens nearby + gates AP moves down The voltage-gated + channel closes The voltagegated + channel opens Opens nearby + gates + rushes out of cell Negative charge inside cell restored, causing + gate to close (c) The resting potential is restored 4
A Myelinated Axon An action potential jumps from node to node, greatly speeding up conduction down the Schwann cell node myelin myelin sheath Fig. 38-3 Action Potential Releases Neurotransmitters 1 An action potential is initiated synaptic vesicle 2 The action potential reaches the synaptic terminal of the presynaptic 3 The positive charge of the action potential causes the synaptic vesicles to release neurotransmitters synaptic terminal of presynaptic neurotransmitters 4 Neurotransmitters bind to receptors on the postsynaptic dendrite of postsynaptic synaptic cleft Copyright 2011 Pearson Education, Inc. 6 Neurotransmitters are taken back into the synaptic terminal, are degraded, or diffuse out of the synaptic cleft neurotransmitter 5 Neurotransmitter binding causes ion channels to open, and ions flow in or out receptor ions 5
Neurotransmitters Neurons use chemicals called neurotransmitters to communicate with other s, muscles, or glands. Acetylcholine (Ach) Controls motor function Stimulates digestion Maintains heart activity Regulates REM and short-term memory formation Anger control Alzheimer s patients show up to a 90% decrease of Ach activity in the brain Botox inhibits Ach release from s connecting to muscles 6
Norepinephrine Fight or Flight response Increases heart rate, blood pressure and alertness Triggers release of glucose from energy stores Increases blood flow to brain and muscles Halts digestive processes Associated with ADHD Adderall and Ritalin increase norepi and dopamine production Serotonin Controls overall sense of well-being Controls hunger THC decreases serotonin sensitivity Helps regulate sleep patterns Intimately tied to sensory perception Controls cognitive functions such as memory and learning abilities Linked to OCD, learning disabilities, and depression Prozac blocks the clearing of serotonin out of synapse 7
GABA Inhibitory effects of other neurotransmitters in the brain-quiets brain activity Binds to neurotransmitter receptors to block action Associated with anxiety disorders Valium enhances effects Like Dopamine, cannot pass the blood-brain barrier Glutamate Excitatory relative of GABA Is actually toxic to nerve cells and can destroy them in excess Lou Gehrig's Disease (ALS) is the excessive production of Glutamate Brain damage and stroke often lead to overproduction Blocks pain receptors Endorphins Create sense of well-being, involved in arousal Produced in the pituitary during periods of stress, while exercising, in pain, and during sex Triggers hibernation in bears: slows metabolism, heart rate and respiration Very similar in structure and function to opiates such as morphine and heroin 8
Dopamine Produced in the pleasure center of the brain whenever you do something you like Major player in drug addiction Inhibitory Neurotransmitter Blocks response from firing Too much = Schizophrenia Too little = Parkinson s Disease Can t inhibit Ach, which leads to incontrollable tremors Nervous System Organization ring of ganglia diffuse network of s (a) Hydra Fig. 38-6a 9
Nervous System Organization brain (b) Flatworm nerve cords cerebral ganglia (brain) (c) Octopus Fig. 38-6b, c Organization and Functions of the Vertebrate Nervous System Fig. 38-7 10
The Pain-withdrawal Reflex 2 The signal is transmitted by the pain sensory to the spinal cord dorsal root 1 A painful stimulus activates a pain sensory sensory spinal cord inter stimulus 5 The effector muscle causes a withdrawal response motor 4 The motor stimulates the effector muscle ventral root 3 The signal is transmitted to an inter and then to a motor Fig. 38-10 The Limbic System Emotions olfactory bulb limbic region of cortex cerebral cortex corpus callosum thalamus hypothalamus amygdala hippocampus Fig. 38-13 11