2 The NeuronThe use of electrical signals to send messages rapidly through the bodyIs a nerve cell specialized in doing thisAll sensory info is processed via neurons (called nerve impulses).Structure of a neuronMost unusual looking of all cellsdendrites: the “antennae” , receive signals from other cellsCell body, much like that of a normal cellAxon: long membrane-covered extension of cytoplasm that conducts the nerve impulse.The ends of axons are axon terminals, this is where they communicate with each other
4 The insulated part…Myelin sheath: is a layer of insulation around the axon, allows impulses to move faster.Nodes of Ranvier: are gaps (where the myelin sheath is interrupted) where the axon is exposed to surrounding fluid.Nerve FunctionThere is a different “charge” on the inner surface of the cell and the fluid outside the cell.Membrane potential: is the difference in electrical charge across the cell membrane.It is expressed in voltage, just like a battery, but is very, very, small.Everything operates on ion channels, remember those proteins that allow ions to pass into or out of a cell, via the membrane?Even the slightest change/movement of ions affects the charge, and thus the signal.
6 Resting PotentialWhen a neuron is not conducting an impulse (said to be at rest).Roughly -70 millivolts (mV)The inside of the cell is negatively charged with respect to the outside.There is a greater concentration of Na+ ions outside than there are K+ ions inside. Remember the sodium potassium pump? This is very important in nerve impulses.
7 Action potentialA neuron is conducting an impulseA change from the negative charge at RP, to a more positive inside than outside.It moves very quickly down the axon.How does it work?A signal is received, which changes the membrane potential to become more positiveThe causes ion gates/channesl to open and sodium ions rapidly move into the axon.Briefly it gets up to +40 mVThis sudden reversal of polarity begins a chain reaction cause the gates to open down the entire length of the axon.The gates close immediately after the action potential has passedThis allows Na+ to flow back out, returning to a negative charge.
9 Communicationsynapse: the junction between two neuronsUsually do not touchGap is called a synaptic cleftPresynaptic neuron (sending signal), postsynaptic cell (receiving signal)As a signal arrives at the terminal, it can not cross the gapImpulse triggers the release of signal molecules, neurotransmitters, into the synaptic cleft.They are stored in vesicles, and there are many different types (example: dopamine)
12 Releases of neurotransmitters Released via exocytosisNT’s bind with post. Syn. Cell.They may open ion channels, or close themThis may excite or inhibit the activity of the post. Syn cellVery small amounts can cause changes in our moods, from ecstasy to depression. (norepinephrine and dopamine involve feelings, to low, we feel depressed)
13 Structures of the Nervous System CNS: central nervous system, brain and spinal cord, control center of the body, interprets and responds.PNS: peripheral nervous system, sensory and motor neurons, everything outside of spine and brain.The brain (see senses power point)PNSConnects brain and spinal cord to rest of the bodyTwo divisions: sensory division and motor divisionSensory div. directs sensory info to the CNSMotor div. carries out the responses to sensory information (and is also divided into two independent systems)
14 Motor divisions two parts SomaticMore of a “conscious” controlSkeletal musclesSome is involuntary, ie. Reflexes. (a self protective motor response) do not usually involve the brainAutonomicSmooth muscle (not conscious)Heart rate, blood flow, digestion, etc…Also divided into two division
15 Two divisions of the Autonomic nervous system (help maintain balance) ParasympatheticMost active under normal conditionsKeeps body functioning even during non activity (ex. Continuing to breath while you are asleep)SympatheticDominates during physical or emotional stress“fight or flight” responseNervousnessCan increase heart rate, blood flow, and breathing rateSee table 955 for a cool comparison of body reactions by each of the above.