Chapter terms Class examples PSY 2012 0004 CHAPTER 2 BRAIN BEHAVIOR 9 1 2015 The Brain Neuron o All of your thoughts feelings and actions happen due to electrical impulses traveling along nerve cells within the brain o Neurons Nerve Cells o The brain has 100 billion neurons o Neurons carry and process information and activate muscles and glands o It takes a network of many neurons to perform simple actions o Networks of neurons produce intelligence and consciousness o No 2 neurons are alike similar to snowflakes but they have 4 basic parts Dendrites The roots that receive messages from other neurons hair on the head of a stick figure Soma AKA cell body The cell body that also receives messages from other neurons but it also sends messages of its own down a thin fiber Head of the stick figure Axon The thin fiber that transmits messages from the soma the body of the stick figure Axon terminal The branches of the axon that link up with the dendrites and somas of other neurons feet of the stick figure 1 Schwann cells Made up of myelin a fatty substance Marshmallows that makes travel more efficient throughout the cell lacking of myelin sheath can cause multiple sclerosis The Nerve Impulse o Each neuron contains electrically charged molecules called ions o Other ions lie outside of the cell o Some charges of the ions are positive and some are negative the charges vary in voltage o Each neuron in the brain has a charge of 70 millivolts Neurons have to have a negative charge because if they were positive we would be everywhere at once o Resting potential The electrical charge of an inactive neuron Raised and lowered by messages arriving from other neurons o The neuron threshold is 50 millivolts This means that the neuron will fire if the electrical charge rises to 50 millivolts o When the neuron reaches 50 millivolts an action potential or nerve impulse is sent down the axon The speed may vary but could be as fast as 200mph o During an action potential the axon membrane is pierced by tiny tunnels holes called ion channels o Normally these tunnels are closed by molecules that act like gatekeepers During an action potential the gates open an allow sodium ions Na to rush into the axon The tunnels begin opening near the soma and then gate after gate opens down the length of the axon as the action potential travels o An action potential is an all or nothing event 2 o After each nerve impulse the cell dips below its resting level and is less able to fire recovery o This is referred to as negative after potential Negative after potential occurs because as the tunnels open in the axon and sodium ions enter potassium ions K in the cell exit After everything settles the cell is recharged and ready for the next impulse If you have a seizure disorder cells may fire more than once Synapses and Neurotransmitters o The nerve impulse is primarily electrical This is why our brains respond to being electrically stimulated o Communicating between neurons is chemical o The small space between two neurons is called a synapse Messages pass over the synapse from one neuron to another Think of it as a parking space Certain neurotransmitters can only park in certain spaces o When an action potential reaches the tips of the axon terminals neurotransmitters are released into the synaptic gap area between the synapses o Neurotransmitters are chemicals that alter activity in neurons o When the neurotransmitters cross over the synapse they head towards a receiving area receptor site on the next neuron that is specialized just for them o There are receptor sites all over the nerve cell bodies and dendrites as well as on muscles and glands o Some neurotransmitters excite the neuron and some inhibit it If the neuron receives a number of exciting messages at the 3 same time it will fire If it receives a number of inhibiting messages at the same time it will not fire Synapses Neurotransmitter Examples o Acetylcholine Important for memories dementia can occur when there is a lack of acetylcholine Helps with energy and activating the system o Epinephrine o Norepinephrine Helps with anger o Serotonin o Dopamine Lack of serotonin can cause depression Lack of dopamine can cause Parkinson s disease Too much dopamine can cause schizophrenia Used to help with muscle control Helps with immune system o Histamine o Amino acids Protein Synapses and Neurotransmitters cont d o Neuropeptides regulate the activity of other neurons Enkephalins a neural regulator that relieves pain and stress natural opioid Receptor in our body for heroin makes it addictive Endorphins natural pain reducer 4 The Nervous System o Neurons are NOT the same as nerves Neurons are tiny cells Nerves are large bundles of axons bouquet of flowers o Many nerves are white because they contain axons coated with myelin fatty layer o There are gaps in the myelin which helps an impulse move faster by allowing action potentials leap from gap to gap Without the myelin we could not react in a timely manner o Neurilemma a thin layer of cells wrapped around most axons outside of the brain and spinal cord o Central Nervous System CNS Brain and spinal cord Neural networks are made up of a large number of neurons working together Each neural network is connected to other neural networks CNS runs all programing and hooks up with other systems that actually run the systems o Peripheral Nervous System Carries information to and from the CNS Somatic system Carries messages to and from the sense organs and skeletal muscles Autonomic system Carries messages to and from the internal organs and glands i e Heart rate digestion perspiration Fight or flight mode Sympathetic emergency system prepares the body for fight or flight during times of danger or high emotion 5 Parasympathetic quiets the body and returns it to a lower level of arousal o Spinal cord Connects the brain to other parts of the body When axons leave the spinal cord they form nerves 30 pairs of spinal nerves 1 pair that leaves the tip These carry sensory and motor messages to and from the spinal cord 12 pairs of cranial nerves leave the brain directly o Reflex arc response Reflex arc Occurs when a stimulus provokes an automatic A stimulus is detected by a sensory neuron The sensory neuron carries a message to the CNS The sensory neuron synapses with a connector neuron The connector neuron activates a motor neuron The motor neuron carries a message from the CNS to muscles and glands Effector cells in the muscle fibers