Unit 2 Notes: Nerve Impulses

(1) Nerve Impulses What is it? Nerve Impulse = Electrical Current Messages sent to and from neurons Used to respond to stimuli Ultimately maintains homeostasis Nerve Impulse = Electrical Current Comes from the flow of positively charged ions Ions move across the neuron’s membrane

(2) Neuron Membranes & Ions Sodium & Potassium Pumps: In the membrane of neurons Only open when stimulated by neurotransmitter Na+ on the outside K+ on the inside Ions: Charged particles Sodium = Na+ = Positive Charge Potassium = K+ = Positive Charge Movement of Ion = Movement of Charges = Electrical Current

(3) Neuron Resting Potential Resting Potential: The natural charge distribution across a neuron’s membrane. K+ channel a little “loose”: Some K+ leaks OUT of the neuron Build up of MORE positive ions outside of the membrane Inside = More Negative, Outside = More Positive Membrane = Polarized = Imbalance

(4) Depolarization & Repolarization Depolarization: (Remove imbalance) Na+ pump opens  Na+ flows inward Depolarization  Temporary Balance REMEMBER: In this scenario, balance is NOT normal in this part of your body! Your body will FORCE repolarization! Repolarization: (Imbalance Again) K+ pump opens  TONS of K+ flows outward Repolarization REMEMBER: K+ needs to be in, and Na+ out!

http://upload. wikimedia http://upload.wikimedia.org/wikipedia/commons/2/2f/Action_potential_propagation_animation.gif

(5) Action Potential Action Potential = Movement of Na+ and K+ ions in and out (across) the neuron membrane. Process: Cycle of depolarization + repolarization Stimulus  Opening of Na+ Pumps  Movement Inward of Na+  Depolarization & Shutting of Na+ Pumps Depolarization  Opening of K+ Pumps  Movement Outward of K+  Repolarization & Shutting of K+ Pumps

http://www.youtube.com/watch?v=90cj4NX87Yk&NR=1

(6) Regaining Resting Potential Action Potential caused Na+ to be on the inside, and K+ to be on the outside. Change = NOT NORMAL Not Normal  Homeostasis kicks in! Na+ and K+ Pumps Actively Transport (using ATP) Na+ and K+ back out/in of the axon Na+ pushes out K+ pushes in Resting Potential regained

(7) Myelin & Action Potential Myelin = Insulation along axon Creates “gaps” between Na+ and K+ pumps in membrane… “Gaps”  electrical jumping Ions fly down to the next set of pumps Increases Speed of Current / Impulse

(8) Reflexes Rapid, Unpredictable and involuntary responses to stimuli. Reflex Arcs: Pathway which reflex messages are sent. 1- Stimulus & Receptor 2- Message sent in thru Sensory Neuron 3- Integration at CNS 4- Action message sent out Motor Neuron 5- Effector Organ responds

(9) Types of Reflexes Somatic: Autonomic: Stimulation of skeletal muscle Movement of limbs, torso, etc. Autonomic: Stimulation of smooth muscle, heart and glands Causes secretion of saliva, pupil dilation, etc.