Neuronal Physiology Handouts PDF

NEURONAL PHYSIOLOGY Sherwood Chapter 4  LECTURE OBJECTIVES What does a neuron look like and how are they linked together? How do neurons initiate electrical signals and what are their characteristics? Graded potentials Action potentials How do neurons tra...

NEURONAL PHYSIOLOGY Sherwood Chapter 4  LECTURE OBJECTIVES What does a neuron look like and how are they linked together? How do neurons initiate electrical signals and what are their characteristics? Graded potentials Action potentials How do neurons transfer these electrical signals to other neurons? Working of the synapse Neurotransmitters and neuropeptides Effect of drugs/diseases on synaptic activity  Sherwood Fig 4-7 STRUCTURE OF THE NEURON DENDRITES - Also known as input zone AXON TERMINALS - Increase surface area - Also known as output zone - Carry signals towards cell body - Releases neurotransmitters - Contains receptors for neurotransmitters - Initiate graded potentials AXON HILLOCK - Also known as trigger zone (action potentials) - Abundant voltage gated sodium channels AXON/NERVE FIBER CELL BODY - Single elongated tubular structure Nucleus & cell organelles - May be covered in myelin sheath - Conducts signals away from cell body  Sherwood Fig 4-18 NEURONAL LINKAGE By converging input, a single cell is influenced by thousands others By diverging output, a single cell influences thousands of other cells  http://philschatz.com/anatomy-book/resources/1220_Resting_Membrane_Potential.jpg http://www.nibb.ac.jp/annual_report/2004/img/230-01.jpg GRADED POTENTIALS Local changes in RMP EXAMPLES that occur in varying - Receptor potentials grades/strength - Postsynaptic potentials - Pacemaker potentials - Slow wave potentials Stimulus leads to influx of sodium ions: a small depolarization A small hyperpolarization is also a graded potential CHARACTERISTICS OF GRADED POTENTIALS The magnitude & duration of the Resting potential graded potential Graded potentials is proportional to the magnitude & duration of the Magnitude triggering event of stimulus Stimulus applied  Sherwood Fig 4-2 CHARACTERISTICS OF GRADED POTENTIALS Graded potentials spread by passive current flow in all directions  Sherwood Fig 4-3 CHARACTERISTICS OF GRADED POTENTIALS Graded potentials die out over short distances  Sherwood Fig 4-16 CHARACTERISTICS OF GRADED POTENTIALS 1+1=2 1-1=0 Graded potentials can undergo summation & initiate action potentials  https://ka-perseus-images.s3.amazonaws.com/0e6eb6f7a24b3e8b2cc37908130e7f85481313f4.png Sherwood Fig 4-4 ACTION POTENTIALS Brief, rapid, large changes in RMP: inside becomes more positive! DIFFERENT FROM GPs: - Magnitude & duration always same: 1msec - Do not die; serve as long distance signals  Sherwood Fig 4-5 ACTION POTENTIALS Arise due to changes in membrane permeability to ions due to conformational changes of voltage-gated sodium and potassium channels  Sherwood Fig 4-6 ACTION POTENTIALS Inactivation gate Activation gate of VGSCs close of VGPCs open VGSCs activation gate close, Activation inactivation gate gate of open VGSCs open Activation gate of VGPCs close Activation gates closed Na+-K+-ATPase restores balance  Sherwood Fig 4-8 CHARACTERISTICS OF ACTION POTENTIALS Once initiated, AP are conducted throughout the axon Contiguous conduction in unmyelinated neurons  Sherwood Fig 4-9 CHARACTERISTICS OF ACTION POTENTIALS Action potentials are propagated in one direction only  Sherwood Fig 4-10 REFRACTORY PERIOD VGSCs are in VGSCs are in closed and not closed and VGPCs are open capable of capable of opening stage opening stage  Sherwood Fig 6-3 CHARACTERISTICS OF ACTION POTENTIALS The frequency of action potentials depends on the strength of the stimulus  CHARACTERISTICS OF ACTION POTENTIALS Action Potentials occur in all or none fashion The speed of action potentials depends on the diameter of nerve fiber & myelination