CHAPTER 3 NEUROSCIENCE aka BIOPSYCHOLOGY 1 Neurons cells in the nervous system that communicate with one another to I Neurons The Origin of Behavior A Discovery of How Neurons Function perform information processing tasks 2 Approximately 100 billion neurons in the brain 3 Neurons produce the underlying invisible physical component of visible behavior a Neurons came in many shapes and sizes and communicate without touching B Components of the Neuron 1 Cell Body Soma coordinates the information processing tasks and keeps 2 Dendrites receive information from other neurons and relay it to the cell the cell alive body speeds conduction a Myelin Sheath an insulating layer of fatty material around the axon that 3 Axon transmits information to other neurons muscles or glands 4 Synapse the junction between one neuron s axon and another neuron s b The myelin sheath is composed of glial cells a Glial Cells support cells found in the nervous system a Clean up dead tissue provide nutrients to neurons and provide myelin for axons dendrite or soma a Adults have between 100 and 500 trillion synapses C Major Types of Neurons 1 Sensory Neurons receive information from the external world and convey this information to the brain via the spinal cord movement 2 Motor Neurons carry signals from the spinal cord to the muscles to produce 1 Purkinje cells carry mostly motor information from the cerebellum to the rest 3 Interneurons connect sensory neurons motor neurons or other interneurons D Neurons Specialized by Location II The Electrochemical Actions of Neurons Information Processing A Electric Signaling Conducting Information within a Neuron 2 Pyramidal cells carry all kinds of information from the cerebral cortex 3 Bipolar cells carry visual information into the brain from the retina 1 Communication within and between neurons proceeds in two stages of the brain and spinal cord conduction and transmission together referred to as electrochemical action a First the signal is received and may initiate electrical conduction down the axon b Second the signal travels chemically across the synapse to the next neuron 2 Resting Potential the difference in electric charge between the inside and outside of a neuron s cell membrane 3 Charged molecules or ions flow across the cell membrane differentially to set up the resting potential a At rest there is a higher concentration of potassium K on the inside of the cell and sodium Na outside of the cell b The flow of ions across the cell membrane is controlled by opening and closing channels that are specific to each ion 4 The resting potential of a neuron is approximately 70 millivolts 5 Action Potential an electric signal that is conducted along the length of a neuron s axon to the synapse 6 Input must pass a threshold to activate an action potential 7 All or none that is an action potential s strength remains the same from the beginning to the end and is not influenced by further changes in input strength 8 Refractory period the time following an action potential during which a new action potential cannot be initiated 9 Bare segments of axon between sections of myelin are called the nodes of Ranvier which causes action potential to jump saltatory conduction and speeds conduction B Chemical Signaling Transmission between Neurons 1 Neurotransmitters chemicals that transmit information across the synapse to a receiving neuron s dendrites 2 Receptors parts of the cell membrane that receive neurotransmitters and initiate or prevent a new electric signal a Act like a lock and key system where only certain neurotransmitters can activate certain receptors 3 The sending or presynaptic neuron releases neurotransmitters into the synapse that are received by the postsynaptic neuron 4 Neurotransmitters are cleared from the synapse when they are finished binding to receptors via three different processes a Reuptake neurotransmitters are taken back into the presynaptic neuron through transporters still in the synapse b Enzymatic Degradation enzymes can destroy the neurotransmitter while c Autoreceptors can also detect if there is too much neurotransmitter being released and signal the presynaptic neuron to stop the release C Types and Functions of Neurotransmitters 1 Acetylcholine neurotransmitter involved in a number of functions including voluntary motor control 2 Dopamine neurotransmitter that regulates motor behavior motivation pleasure and emotional arousal 3 Glutamate major excitatory neurotransmitter involved in information transmission throughout the brain 4 GABA gamma aminobutyric acid primary inhibitory neurotransmitter in the brain 5 Norepinephrine neurotransmitter that influences mood and arousal 6 Serotonin a neurotransmitter involved in the regulation of sleep and wakefulness eating and aggressive behavior 7 Endorphins chemicals that act within the pain pathways and emotion centers of the brain D How Drugs Mimic Neurotransmitters of depression 1 Agonists drugs that increase the action of a neurotransmitter 2 l dopa increases dopamine and helps treat Parkinson s disease 3 Prozac increases serotonin by blocking reuptake which helps treat symptoms E Antagonists drugs that block the function of a neurotransmitter 1 MPTP destroyed dopamine producing neurons 2 Propanolol blocks the beta receptors for norepinephrine in the heart which helps with stage fright III The Organization of the Nervous System A Divisions of the Nervous System 1 Central Nervous System CNS brain and spinal cord 2 Peripheral Nervous System PNS connects the central nervous system to the body s organs and muscles a Somatic Nervous System a set of nerves that conveys information into and out of the central nervous system b Autonomic Nervous System a set of nerves that carries involuntary and automatic commands that control blood vessels body organs and glands a Sympathetic Nervous System a set of nerves that prepares the body for action in a threatening situation b Parasympathetic Nervous System helps the body return to a normal resting state B Components of the Central Nervous System 1 Spinal Cord coordinates breathing pain movement and other functions a Spinal Reflexes simple pathways in the nervous system that rapidly generate muscle contractions b The spinal cord is divided into four regions each controlling a different part of the body IV Structure of the Brain Generally simpler tasks are controlled by lower regions and complex functions by higher regions A The Hindbrain an area of the brain