Make Up Neuro Blok 3 Juli 2014 dr I Njoman Widajadnja, M.Kes (Fis Olahraga)

Excitable Tissues: Nerves Muscle Cardiac muscle Skeletal muscle Smooth muscle

Neuron: Functional unit of nervous system, with excitability and conductivity characteristics The number of neurons in the CNS = = 10 billion Glial cells (neuroglia): Non conductive cells which protect, maintain, and support the nervous system The number of glial cells = 10 – 50 x of neurons

THE HISTOLOGY OF NEURON Dendrite Cell body/ soma Axon hillock Axon Myelin sheath Synaptic knobs/ terminal buttons/ axon telodendria

(pseudounipolar) Pyramidal

Dendrites & soma  receptive segment Axon closest to axon hillock  initial segment Axon  conductive segment Axon terminal  transmissive segment

Stimulus: Any change in the environment that is strong enough to initiate an action potential Action potential: An electrical signal that propagates along the surface of the membrane of a neuron Graded potential: A small deviation from the resting membrane potential that occurs caused by the different ion channels of all neuron, ligand-gated or mechanically gated channels open or close  hyperpolarizing or depolarizing graded potential

hyperpolarizing graded potential  inside more negatif Depolarizing graded potential  inside less negatif Receptor potential (sensory receptors) Post-synaptic potential (mainly in dendrites & soma): Excitatory post-synaptic potential (EPSP) Inhibitory post-synaptic potential (IPS

Action potential  generator potential/ receptor potential “Receptor”  - sensory receptor - proteins bind to hormones/ neurotransmitters Sensory receptors: Transducers which alter various energy in the environment changed into action potentials in neurons Sensory organs = receptor + non neural cells

Mechanism: Stimulus  receptor/ generator potential (EPSP like; does not spread, graded, local)  if are reach firing level/ neuronal threshold  action potential

CharacteristicsGraded PotentialAction Potential Origin Dendrites/ SomaTrigger zone of an axon Channels Ligand-gated/ mechanically gated Voltage-gated (Na + and K + ) Conduction Local, not propagated Propagated Amplitude  Stimulus intensity (1 mV – 50 mV) All-or-none (100 mV) Duration Longer (msec – min) Shorter (0.5 – 2 msec) Polarity Hyperpolarizing/ Depolarizing Depolarizing  Polarizing Refractory period Not presentPresent

Ion Channels, macam dan gradien timbulnya 1.Leakage (bocor) channels  K + leakage channels > Na + leakage channels 2.Voltage-gated channels  open/ close in response to a change in membrane potential  Na +, K +, Ca + 3.Ligand-gated channels  open/ close in response to a specific chemical stimulus (neurotransmitter, hormones, ions) directly or indirectly (second messenger system)  Na +, Ca + inward, K + outward 4.Mechanically gated channel  open/ close in response to mechanical stimulation (vibration, pressure, stretching)  auditory receptors, stretch receptors of internal organs, touch receptors of skin

THE PHYSIOLOGY OF NEURON in Rest Recording with an electrode inside an axon  resting membrane potential/ polarization  typically -70 mV (the potential difference between the inside and outside of the axon, the inside being more negative than the extra-cellular fluid)

Resting membrane potential  small build-up of negative ions along the inside of membrane, and positive ions along the outside Neurons  range: -40 to -90 mV (ranges of membrane potential of cells: +5mV to -100 mV) Resting membrane potential

ECF  Na + and Cl - ICF (cytosol)  K + and phosphates (attached to ATP and amino acids) Factors causing the negativity inside neurons: 1.Leakage (bocor) of K + to ECF 2.Negative ions inside neurons cannot leave cells (attached to proteins/ larger molecules) 3.Na + /K + ATPase pumps (3 Na + out for 2 K + in)  contributes only -3 mV

Synapses Axodendritic Axosomatic Axoaxonic Synapses Electrical synapses  gap junctions  connexons Chemical synapses  neurotransmitters

Excitatory Post-Synaptic Potentials (EPSP) Partial depolarization which decreases membrane potential/ increases neuronal excitability Cation channels open (Na +, K +, Ca +2 ) Na + enters cells > Ca +2 inflow or K + outflow Local depolarization  action potential, but facilitating action potential

Inhibitory Post-Synaptic Potentials (IPSP) The increase of negative potential inside cells  -90 mV (hyperpolarizing post-synaptic potential) Opening of Cl - or K + channels (Cl - enter to the cells and K + exit from the cells), or Na + and Ca +2 channels are closed Cells body/ soma integrates EPSP and IPSP An example of excitatory and inhibitory system  skeletal muscles motor neuron Examples of inhibitory system organization: Negative feedback (Renshaw cell), spinal motor neuron Cerebral cortex, limbic system, cerebellum

Spatial summation Temporal summation Repeated stimulation of one pre-synaptic neuron on a post- synaptic neuron Simultaneous stimulation of many pre-synaptic neurons on one post-synaptic neurons

References 1. Ganong WF (2005). Review of Medical Physiology, 22 nd ed. Chapter 2, Pages: 51-60; Chapter 4, Pages: Guyton AC & Hall JE (2006). Textbook of Medical Physiology, 11 th ed. Chapter 5, Pages: 57-71; Chapter 45, Pages: Carola R, Harley JP, Noback CR (1990). Human Anatomy & Physiology. Chapter 11, Pages: Tortora GJ & Derrickson BD (2006). Principles of Anatomy and Physiology. Chapter 12, Pages: