Neurons Fires impulses called action potential Generate electricity from chemical events Ions are exchanged in chemistry to electricity process Fluid outside axons membrane is mostly positively charged ions fluids inside are mostly negatively charged ions This state is called the resting potential Axons surface is very selective about what it allows in and out selective permeability WHEN NEURON FIRES security parameters change First section opens its gates and positively charged sodium ions flood through the cell membrane This depolarizes that axon section causing another axon channel to open up and then another like a line of falling dominos During resting phase refractory period the neuron pumps the positively charged sodium ions back outside so that it can fire again In myelinated neurons the action potential speeds up by hopping from the end of one myelin to the next Process repeats up to 100 1000 times a second Most signals neurons receive are excitatory like pushing the neurons accelerator The ones that aren t excitatory are inhibitory like pushing its brakes When excitatory signals minus inhibitory signals exceed a minimum intensity or a threshold the combined signals trigger an action potential Corny but good way to look at it If the excitatory party animals outvote the inhibitory party animals the party is on The action potential then travels down the axon which branches into junctions with hundreds or thousands of other neurons or with the body s muscles and glands Increasing the level of stimulation above the threshold will not continue to increase impulses intensity Consider it as an All Or None response like guns neurons either fire or they don t A strong stimulus can trigger more neurons to fire and to fire more often However this does not affect to action potentials strength or speed Squeezing the trigger of a gun harder wont make a bullet go faster A synapse is the meeting point between neurons The synaptic space is the space between the axon terminal of one neuron and the receiving neuron It is almost impossible to see even with a microscope When an action potential reaches the terminals at the axons end it triggers the release of chemical messengers called neurotransmitters Within 1 10 000th of a second the neurotransmitter molecules cross the synaptic gap and bind to receptor sites on the receiving neuron Once bound the neurotransmitter unlocks tiny channels at the receiving site and electronically charged atoms flow in exciting the receiving neurons readiness to fire After that a process called reuptake occurs where the sending neuron reabsorbs the excess neurotransmitters How do neurotransmitters influence our motions and emotions A particular brain pathway may use only one or two neurotransmitters and particular neurotransmitters may affect specific behaviors and emotions However neurotransmitter systems don t operate in isolation they interact and their effects vary with the receptors that they stimulate Acetylcholine is one of the best known and understood neurotransmitters It plays a vital role in learning and memory and it is the messenger at every junction between motor neurons and skeletal muscle Motor neurons carry info from the brain and spinal cord to the body s tissues If ACh is blocked the muscles cannot contract and we become paralyzed Our bodies release several types of neurotransmitters similar to morphine in response to pain and vigorous exercise These are called endorphins and they help explain good feelings such as the painkilling effect of acupuncture and the indifference to pain in some severely injured people How Drugs and Other Chemicals Alter Neurotransmission Drugs and chemicals affect brain chemistry at synapses often by either exciting or inhibiting neurons firing Agonist molecules are substances that initiate a physiological response when combined with a receptor They are similar enough to a neurotransmitter to bind its receptor and mimic its effects Antagonist molecules also bind to receptors however they instead block a neurotransmitters functioning Ex of Antagonist Botulin The Nervous System Brain and Spinal Cord form the Central Nervous System Body s decision maker The Peripheral Nervous System is responsible for gathering info and for transmitting CNS decisions to other body parts Nerves link the CNS with the body s sensory receptors muscles and glands Info travels in the nervous system by three types of neurons Sensory Motor Interneurons There are the most interneurons PNS has two components Somatic and Autonomic Autonomic controls glands and the muscles of our internal organs Somatic enables voluntary control of skeletal muscles o Two systems within Autonomic System are the sympathetic and the pathetic The sympathetic arouses and expands energy The pathetic conserves energy and decreases heartbeat Brain enables humanity thinking feeling and acting Neural Networks are when the brains neurons cluster into working groups Neurons that fire together wire together o The spinal cord is a two way information highway connecting between the peripheral nervous and the brain Ascending neural fibers send up sensory info and descending fibers send back motor control information o The neural pathways governing our reflexes our automatic responses to stimuli illustrate the spinal cords work A simple spinal reflex pathway is composed of a single sensory neuron and a single motor neuron Example is the knee jerk response o Info travels to and from the brain by the way of the spinal cord The Endocrine System o The endocrine system s glands secrete another form of chemical messenger hormones which travel through the bloodstream and affect other tissues including the brain These hormones influence our interest in sex food and aggression o Endocrine and Nervous system are similar Chemically identical to neurotransmitters o Different in the fact that Endocrine system takes seconds or more to travel from the gland to the target tissue o Adrenal Gland On top of kidney releases epinephrine and norepinephrine These hormones increase heart rate and blood sugar o Pituitary Gland located in core of the brain and is controlled by the hypothalamus Releases Growth Hormones