Chapter 48 Neurons 12 03 2015 FIG 48 3 Nervous impulses travel about 300 mph Sensory input detect stimuli conduction of signal PNS integration brain process signal in CNS motor output muscle or gland PNS All vertebrates have three classes of neurons Sensory neurons receptors activated by a receptor Detecting change in internal or external environment Inter neurons where signals are processed Motor neurons motor output that has body do what signal wanted it to do FIG 48 4 typical neuron Axon takes signal away to other neurons or muscles Synapse space between two neurons Dendrites receive the signals Pre synaptic and post synaptic cell Schwann cell non nervous cells in peripheral nervous system about half of the vertebrate system layers of myelin wrapped around the axon Myelin directs the impulse down the axon Reinforce protect insulate assist neurons in other ways Makes it better to conduct the impulse MS destroys the myelin sheath Nodes of ranvier space between Schwann cells Neuroglia act like connective tissue Oligodendrocytes central nervous system works like schwann cell Astrocytes structures associated with blood brain barrier Vertebrates Longitudinal nerve cord is single not paired Spinal cord is dorsally located not ventral Spinal cord is hollow not solid The division of ganglia collection of cell bodies of neurons in the peripheral nervous system is not as apparent The brain is used more than the spinal cord more important than Table 48 1 Impulse electrical signal that depends on the flow of ions across the membrane of a neuron All cells have an electrical membrane potential or voltage Positive on outside negative on inside Membrane potential ranges from 50 100 mega volts 70 is resting potential three major ions in impulse sodium o mostly outside cell potassium o mostly inside cell chlorine o mostly outside cell large anions inside cell such as proteins charged things have a problem moving across membrane because of these charged ions protein channels help facilitate movement across the membrane FIG 48 7 KNOW There are more open channels for potassium more permeable than others Potassium will move out Makes the inside more negative Sodium will move it Makes the inside more positive All cells have sodium potassium pumps to deal with this so that the membrane potential is not shifted Only two types of cells can change their membrane potentials in response to a stimuli nerve cells muscle cells known as excitable cells gated channels allow for the change of membrane potential when a stimulus is recognized it will open the gates when not excited it is at a resting potential if potassium channels are opened hyperpolarizing the neuron if sodium channels are opened depolarizing the membrane graded potentials voltage changes because strength of stimuli opens more channels each cell has a threshold that will be graded against if depolarization reaches the threshold the cell will responded with what is called an action potential action potential rapid change in the membrane potential of an excitable cell caused by stimulus trigger selective opening or closing of voltage gated ion channels all or none if it reaches threshold it will fire to the max if not it won t fire at all FIG 48 11 1 resting state 70 2 stimulus received and sodium channels are opened and depolarization occurs 50 becoming more positive 3 action potential 50 4 falling phase of action potential potassium channels are open and getting more negative 5 undershoot below resting potential refractory period too negative so another impulse can t be sent until returns to resting state 6 sodium potassium pump brings it back to resting potential 70 weak and strong stimuli based on the frequency of the action potential two things affect the speed of the action potential resistance to the flow larger diameter of the axon the faster impulse will travel saltatory conduction looking at myelinated fibers will travel faster on the myelinated fibers electrical synapse chemical synapse most common way to jump the synapse FIG 48 15 impulse comes down presynaptic neuron opens calcium channels calcium makes the neurotransmitters move and dump depolarizing post synaptic neuron ligand gated ion channels in between the two axons excitatory postsynaptic potential EPSP sodium depolarizes inhibitory postsynaptic potential IPSP potassium chlorine temporal summation time two excitatory neurons sent very close together are added up and an action potential is created spatial summation Table 48 2 Neurotransmitters Acetylcholine GABA gamma aminobutyric acid major inhibitory transmitter in the brain 12 03 2015 12 03 2015