Ch 4850 Introducingyour best friend the Neuron Neuron basic structural unit Cell body soma contains nucleus amp organelles Dendrite receives stimuli Axon sends nerve impulses ID: 434690
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Slide1
The Nervous SystemCh. 48-50Slide2
Introducing…..your best friend, the Neuron
Neuron = basic structural unitCell body (soma):
contains nucleus & organellesDendrite: receives stimuli
Axon: sends nerve impulsesSlide3
Types of Neurons
Sensory neurons: receive stimuli (to brain)
Motor neurons: stimulate target cells (from brain)
Interneurons (brain/spinal cord): receive sensory input, evaluate, send response to motor neuronsSlide4
Nerve Impulse
Also called “action potential”Signal that travels through neurons
Electrochemical signalTravels across the
membraneSlide5
Membrane Polarization
Membrane = POLARIZEDDifference in electrical charge inside & out
Inside
is more negative (Pump: 3Na+out, 2K+ in AND K+ leaks out)High
Na+ outside, high K+ insideNa+/K+ pump counteracts
leaking“resting potential
” = approx. -70 millivoltsSlide6
Action Potential
Stimulus causes gated Na+ channels to openNa+ rushes INTO the cell
Depolarizes membrane (-70mV → +30mV)
Causes more Na+ gates to open (depolarization travels along membrane)
This is an all-or-nothing
event (like a gun firing). The stimulus must be above a certain THRESHOLD level to cause an action potential (otherwise no depolarization)Slide7
Repolarization
Na+ gates closeDepolarization causes gated K+ channels to open
K+ rushes OUT of the cellRepolarizes membrane
K+ gates are SLOW to close, letting out extra K+ to cause HYPERpolarization (-80mV)Slide8Slide9
Action potentials travel in ONE DIRECTION along the axonSlide10
Myelination
Myelin sheath insulates axonComposed of Schwann cellsNodes of Ranvier = gaps of unsheathed axon inbetween Schwann cellsSaltatory conduction = action potential jumps from node to node (can only occur where membrane is unsheathed)Slide11
Salutatory ConductionSlide12
Refractory Period:To be or not to be?Slide13
Let’s re-cap! What happens when K+ leaves the cell?Slide14
Refractory Period
Membrane is polarized, BUT too much K+ on outside, Na+ inside of the membrane
Hyperpolarization prevents the cell from reaching threshold for a new action potential (no response to new stimuli)
Na+/K+ pumps restore ions to original polarization (Na+ pumped out, K+ pumped in)When original polarization (resting potential) is restored, neuron can respond to stimuli (reach threshold & trigger action potential)Slide15
Synapse (synaptic cleft)
Gap separating adjacent neuronsPresynaptic cell (message coming from)Postsynaptic cell (message going to)Neurotransmitter = chemical that travels across synapse for transmission of impulse
Acetylcholine – used at neuromuscular junctions
Epinephrine, norepinephrine, dopamine, serotonin – used between neurons in the brainGABA (gamma aminobutyric acid) – inhibitory among neurons in brainSlide16
Synaptic Transmission
Action potential reaches end of axonGated Ca+ channels open
Ca+ enters cell
Ca+ causes synaptic vesicles to merge with membrane & release neurotransmitters into synapseNeurotransmitter binds to postsynaptic receptors (with specificity)Postsynaptic membrane is excited or inhibited
EPSP (excitatory) – Na+ gates open, depolarizationIPSP (inhibitory) – K+ gates open, hyperpolarization
Neurotransmitter is degraded and recycledSlide17
The Synapse: A Chemical PARTY Slide18
SUMMATION
Multiple axons synapse on a single neuron
Different combinations of EPSP
’
s and IPSP
’
s may or may not lead to AP
’sSlide19
Bozeman Nervous Systemhttp://www.youtube.com/watch?v=UabDiuTtU0M