Nerve Physiology

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Nerve Physiology by Mind Map: Nerve Physiology

1. Neuron

1.1. Structure

1.1.1. Soma (Cell Body)

1.1.2. Perikaryon (Cytoplasm) Nissl Bodies Neurofibrils Microtubules Neurofilaments Microfilaments

1.1.3. Cell Processes/Nerve Fibers Axon Parts Type by Length Dendrite Within CNS (LONG) Outside CNS (SHORT)

1.2. Types

1.2.1. Unipolar

1.2.2. Bipolar

1.2.3. Multipolar

2. Excitability

2.1. Capacity of cells or tissues to respond to stimuli

2.2. Characteristics for a Stimulus to be Effective

2.2.1. Nature or Kind Adequate Stimulus One form of energy to which given excitable cells are especially sensitive to

2.2.2. Strength Graded according to strength into threshold Liminal Minimal Maximal Supramaximal Response of single cells is maximal if stimulus reaches threshold ALL-OR-NONE LAW/LUCAS LAW

2.2.3. Rate of Change of the Strength of the Stimulus Stimulus must reach threshold value rapidly for tissue to visibly respond; DU BOIS-RAYMOND LAW

2.2.4. Duration Stimulus must be applied for a minimum period of time Rheobase Minimum current which produces a response when applied for an indefinite period Chronaxie Duration of current necessary for excitation when strength is twice the rheobase Utilization Time Minimum period of time needed for stimulus to produce excitations

3. Classification of Nerve Fibers

3.1. Function

3.1.1. Motor

3.1.2. Sensory

3.2. Myelin

3.2.1. Myelinated

3.2.2. Unmyelinated

3.3. Chemical Transfer

3.3.1. Cholinergic

3.3.2. Adrenergic

3.3.3. Histaminergic

3.3.4. Dopaminergic

3.3.5. Serotoninergic

3.4. Fiber Diameter

3.4.1. A Fibers Myelinated Somatic Afferent and Efferent Fast conduction speed and spike Slow absolute refractory period Less susceptible to hypoxia

3.4.2. B Fibers Myelinated Efferent Preganglionic Less conduction speed and spike Longer absolute refractory period Most susceptible to hypoxia

3.4.3. C Fibers sC Efferent Postganglionic Sympathetic Less conduction speed and spike Longest absolute refractory period Least susceptible to hypoxia drC Unmyelinated Afferent Least conduction speed and spike Longest absolute refractory period Least susceptible to hypoxia

4. Special Properties of Nerve Fibers

4.1. Cable Property

4.1.1. Weak stimulus = Exponential rise and fall of membrane potential

4.2. Accomodation

4.2.1. Prolonged subthreshold stimulus may decrease excitability

4.3. Block

4.3.1. Strong, slowly rising, depolarizing current can produce a decrease in excitability

5. Conduction Speed and Determinants

5.1. Physical Factors

5.1.1. Extent of depolarization induced increase in sodium permeability Greater permeability to sodium = Greater sodium influx = Greater rate of rise of action potential = Greater local current flow = Greater conduction speed

5.1.2. Reduction in amount of depolarization needed to reach threshold Locally depolarized nerve fiber > resting nerve fiber

5.1.3. Size of membrane capacitor per unit area Larger capacity = Lower speed

5.1.4. Resistivity of cell plasm Greater concentration of highly mobile ions = Lesser resistance = Greater current flow for given voltage

5.1.5. Temperature Higher temperature = Higher conduction speed

5.2. Geometry of Nerve Fibers

5.2.1. Fiber diameter Larger fiber diameter = Faster conduction speed = Less resistance

5.2.2. Myelin With myelin = Faster rate of conduction

6. Refractory Period

6.1. Absolute

6.1.1. Second stimulus will not produce action potential during spike potential

6.1.2. 0.04 - 2 msec in large myelinated fibers

6.2. Relative

6.2.1. Second stimulus, if stronger than prior stimulus and applied after a sufficient time, will produce an action potential

6.2.2. 10 - 30 msec after first stimulus

6.2.3. Full recovery of nerve fiber is ~100 msec after initial stimulus

7. Membrane Potential

7.1. Resting

7.1.1. Potassium Efflux

7.1.2. More permeable to K; easier to get out

7.1.3. Less permeable to Na; harder to get in

7.1.4. Depolarization (Making the inner surface more negative)

7.1.5. Sodium-Potassium Pump makes sure to maintain resting membrane potential (between -70 mV to -90 mV)

7.2. Graded

7.2.1. Local change is resting potential in either depolarizing (negative) or hyperpolarizing (positive) direction

7.2.2. Amplitude is variable and depends on the magnitude of the initiating event

7.2.3. Characteristics Response is graded; depends on magnitude of initiating event Can be summated Has no refractory period; no threshold Amplitude decreases over distance Duration varies with initiating event Can be depolarization or hyperpolarization Can be initiated by stimulus or neurotransmitter May occur spontaneously

7.2.4. Roles in Information Processing by Nerve Cells Synaptic Potential Excitatory Postsynaptic Potential (EPSP) Inhibitory Postsynaptic Potential (IPSP) End Plate Potential Miniature End Plate Potential (MEPP) Receptor Potential/Generator Potential Spontaneous Potential Pacemaker Potential (PP)

7.3. Action

7.3.1. A sudden switch from resting state to threshold

7.3.2. Occurence of Sodium Influx

7.3.3. Hodgkin Cycle More sodium comes in, more gates open up

7.3.4. Spike Potential

7.3.5. Hyperpolarization leading to Depolarization

7.3.6. Characteristics Response is all-or-none; amplitude independent of initiating event Cannot be summated Has a refractory period Has a threshold (+10 mV to +15 mV from resting potential; FIRING LEVEL) Amplitude is constant Duration is constant Depolarization without overshoot Initiated by an adequate stimulus

8. Membrane Channel

8.1. Voltage Gated

8.1.1. Controlled by membrane potential

8.2. Ligand Operated

8.2.1. Primary Controlled directly by neurotransmitters

8.2.2. Secondary Controlled indirectly by neurotransmitters and hormones via the 2nd messenger system

9. Axonal Transport

9.1. Anterograde

9.1.1. Slow Transports Neurofilament triplet Tubulin Actin Rate 1-5 mm/day Involves activities of Microtubules Neurofilaments Microfilaments Roles Renewal of axoplasm Provision of substrate for other transport system

9.1.2. Fast Transports Membrane-associated proteins Glycoproteins Rate 400 mm/day Involves activities of Smooth Endoplasmic Reticulum Roles Renewal of axolemma Renewal of synaptic constituents

9.2. Retrograde

9.2.1. Transports Endogenous Proteins Exogenous Proteins

9.2.2. Rate 250 mm/day

9.2.3. Roles Recycling of endogenous materials Sampling microenvironment of nerve terminals

10. Equilibrium Potential

10.1. Substance

10.1.1. If work is not needed to carry a small amount across the membrane, it is at equilibrium

10.2. Uncharged molecule

10.2.1. Internal concentration = External concentration

10.3. Ions

10.3.1. Both concentration and voltage difference across the membrane is calculated using the Nernst equation

10.4. Equilibrium Potentials for Specific Ions

10.4.1. Sodium +58 to +55 mV

10.4.2. Potassium -92 to -97 mV

10.4.3. Chloride -89 to -90 mV

10.4.4. Hydrogen -24 to -32 mV

10.4.5. Bicarbonate -23 to -32 mV

10.4.6. Calcium +129 mV