BioElectricity Local Currents (graded Potential) Action Potentials

Question 1

Electricity and Bioelectricity

Electricity and Bioelectricity

Answer 1

Electricity - Flow of electrons
* Force is an electrical gradient

Bioelectricity - Flow of ions
* Force is a chemical gradient and eletrical gradient combined

Question 2

Transmembrane Potential

Transmembrane Potential

Answer 2

• Driving force for ion flow across the cell membrane
• Extracellular fluid - higher concetration of NA ions and CL ions and Ca2+ ions
• Intracellular Fluid - higher concentration of K ions and Proteins (A-)
• Concentration gradient maintained by active transport of sodium ions out of cell and postassium ions into cell
• NA/K ATPase exchange pump

Question 3

Gated Ion Chanels

Gated Ion Chanels
(on/off switched for bioelectricity)

Answer 3

Pathway for ion flow across the cell membrane
* Chemically gated (Neurotransmitters and Hormones)
* Voltage gated
* Mechanically Gates ( presure on cell membrane)

Gated chanels open in response to various signals (stimuli)
* Ions flow across membrane by difsuiion down their concentration gradient
* Typically stay open only Briefly

Question 4

Bioelectricity

Bioelectricity

Answer 4

Ion Flow across a membrane requires:
* Chemical and or electrical concentration gradient (driving force)
* Transmembrane poteantial
* Pathway
* Ion chanel through the membrane

Ion flow through the cytoplasm or interstitial fluid (local current) requires:
* Chemical and or electrical concentration gradient (driving force)

Question 5

Local Current - Graded Potential

Local Current - Graded Potential

Answer 5

Driving force is concentration gradient created by ions coming across membran through open chanels
* ions travel a short distance through cytoplasm or or interstitial fluid
* Cytoplasm and interstitial fluid have high resistance to ion flow
* Depolarization or hyperpolarization effect decreases with distance from open chanel

Question 6

Bioelectricity and conduction of electrical signals in nervoussystem

Bioelectricity and conduction of electrical signals in nervoussystem

Answer 6

local currents (graded potentials) transmit bioelectric signals over short distances
* Typical of dendrites and cell bodies in NS

Action Potentials need to transmit bioelectric signals over long distances
* Typical of Axons
* Typical of long dendrites of unipolar and Bipolar sensory neurons
* Unique to excitible cells
* An unstoppable chain reaction of small local currents

Question 7

Action Potential of Voltage Gated Chanels

Action Potential of Voltage Gated Chanels

Answer 7

Sodium ion Channel
* Open rapidly in response to depolarization (-60mV threshold)
* Inactivate or close rapidly after opening and can not reopen until return to resting rate
* Absolute refractory period - can not reopen

Potassium Ion Channel
* Open slowley in response to depolirization (at +30mV)
* Close slowley after repolarization

Question 8

Action Potentials

Action Potentials

Answer 8

Steps involved:
* Membrane depolarization stimulus occurs
* Sodium Channel activates - NA ions flow into cell, duter depolarizing
* Sodium chanel innactivation - NA ions stop flowing
* Potasium channel activates - K+ ions flow out of the cell, repolarizing and then hyperpolarizing the membrane
* Return to normal permeability - Both channels are inactivated

Question 9

Action Potentials

Action Potentials

Answer 9

Ion Restoration
* Only a small amount of sodium ions and potassium ions cross the membrane
* Transmembrane potential (like a battery) can power many action potentials before becoming depleated
* Sodium-Potassium ATPase exchange pump maintains transmembrane potential over time but is not needed each action potential

Question 10

Action Potentials

Action Potentials

Answer 10

Generation of action potential follows all or none principle
* Requires threshold depolarization to initiate an action potential
* Threshold depolarization - amount of depoloarization needed to open voltage gted sodium chanels
* Threshold depolarization comes from local current spreading throughout the cytoplasm

Question 11

Action Potentials

Action Potentials

Answer 11

Continuous Propagation
* Unmylenated axons
* Propagation of action potential along entire membrane in series of small steps

Saltatory Propegation
* Myelinated axons
* Porpagation of action potential from node to node, skipping internodal membrane

Question 12

Continuous Propagation of an AP

Continuous Propagation of an AP

Answer 12

1. Threshold level of local current spreads to AP initation site
2. AP is initiated in small segement of axon
   * Voltage gated NA+ ion chanels open, and NA+ ions flow in, Channels inactivate
   * Voltage Gated K+ ion channels ope, K+ flows out of the cell casuing repolarization which closes the potasium channel
3. High Concentration of NA+ ions produce local current that spread down cytoplasm, bringig adjacent segemnt of axon to threshold
4. AP is initiated in the adjacent small segement of axon
5. Propagation
   * Cycle is repeated - local current spreading from each action potential creates an AP in the next adjcent segment

Question 13

Saltatory Propagation of an AP

Saltatory Propagation of an AP

Answer 13

1. Threshold level of local current spreads to AP initation site
2. AP is initiated in small segment of axon
3. High concentration of NA+ ions produces local current that spread relativley down cytoplasm, bringing adjacent noed of axon to threshold
4. AP is initiated in these adjacent nodes
5. Porpagation
   * Cycle is repeated, local current spreading from each action potential creates an AP in the next adjacent nodes

Question 14

Clasification of Nerve Fibers

Clasification of Nerve Fibers

Answer 14

Large Fibers
* Type A Fibers: Largest Diamater, mylinated, fastest (140m/s)
* Motor Neurons to skeletal muscles
* Fastest Sensory informartion

Slower, small fibers
* Type B Fibers: Small diamater, myleinated, moderate speed (18m/s)
* Type C Fibers: Small diamater, unmylenated slowest (1m/s)
* Efferent neurons sending action potentials to smooth, caridac muscle, and gland cells
* Slow sensory information

Question 15

Synapse

Synapse

Answer 15

Synapse - cell to cell
* Presynaptic cell
* Postsynaptic cell
* Neuron, muscle, or gland (fat cells)

Eletrical synapses or Chemical synpses

Question 16

General Properties of Synapses

General Properties of Synapses

Answer 16

Eletrical synapses
* Rare in nervous system
* Pre- and postsynaptic cells are bound by interlocking membrqane proteins (gap junctions)
* Ion current flows directly from presynaptic cell to postsysnaptic cell

Question 17

General Properties of Synapses

General Properties of Synapses

Answer 17

Chemical Synapses
* Neurotransmitter released from axon terminal to postsymanptic neuron
* Neurotransmitter difueses across synptic cleft (synaptic gap)
* Neurotransmitter binds to receptors of chemically gated ion channel
* Neurotransmitter is removed from celft by diffusion, reuptake, and or degredation (enzyme ex: AchE)

Question 18

Mechansims of chemically gated ion channels

Mechansims of chemically gated ion channels

Answer 18

Direct acting - fast
* Neurotransmitter binds to receptor site that is part of the gated channel

Indirect Acting - Slow
* Neurotransmitter bindws to receptor that cpntrolls gated channel via intracellular secondary messenger
* G-Protein Coupled Receptor
* Primary Messenger - neurotransmitter
* Secondary Messenger - Intracellular Molecule, often Cyclic AMP or Cyclic GMP

Question 19

Effect on Postsynaptic cell

Effect on Postsynaptic cell

Answer 19

Excitatory Post-synaptic Potential (EPSP)
* Gated channel opens for NA+ ion
* Depolarining synaptic potential
* Bringing axon hillock closer to threshold
* Promotes action potential initiation

Inhibitory Post-synaptic Potential (IPSP)
* Gated Chaneel opens for potassium or chloride ion channels
* Hyperpolarizing synaptic potential
* Supress action potential initiation

Question 20

Information Processing

Information Processing

Answer 20

Simplest level of information processing occurs at the cellular level
* Excitatory and Inhibitory potentials are integrated and determine weither or not an action potential in intitated

EPSP and IPSP local ion currents combine through summation
* Temporal Summation (time)
* Spatial Summation (Space)

Question 21

Neurotransmitters

Neurotransmitters

Answer 21

PNS Neurotransmitters
* Acetylcholine (ACh) - Cholinergic synapses
* Norepinephrine (NE) - Adrenergic Synapses

Question 22

Cholinergic Synapses

Cholinergic Synapses

Answer 22

• Presynaptic cell contains vesicles of acetylcholine (ACh)
• Postsynaptic cell has chemically gated ion channels and receptors for ACH
• Synaptic cleft has AChE enzyme that breaks down ACH

Question 23

Function of Cholinergic Synapse

Function of Cholinergic Synapse

Answer 23

• Action potential reaches axon terminal
• Depolirization by AP opens calcium ion channels in axon terminal, allowing CA to flow in
• Calcium Ions cause vesicles to undergo exocytosis, releasing acetylcholine into synaptic celft
• ACh drifts across synaptic celft, binds to receptors, causing ion channels to opne

Question 24

Function of Cholinergic Synapse

Function of Cholinergic Synapse

Answer 24

• Synaptic delay - time required for calcium influx, neurotransmitter release and difussion, and gated ion channel opening (few miliseconds)
• ACh is broken down by AChE - Choline reabsorbed by presynaptic neurons and recycled
• Synaptic fatigue occurs when stores of ACh are exhausted

Question 25

# **Neurotransmitters** **Neurotransmitters**

Answer 25

* **ACh - Primarley Direct** * **Serotonin - Primarley Direct** * **Aspartate - Direct or Indirect** * **Gamma-Aminobutyric Acid (GABA) - Direct or indirect** * **Glycine - Direct**

Question 26

# **Neurotransmitters** **Neurotransmitters**

Answer 26

* **Norepinephrine - Indirect** * **Epinephrine - indirect** * **Dopamine - Indirect** * **Histamine - Indirect** * **Glutamine - Indirect** * All pepties listed - indirect * **Adenosine - indirect**

Question 27

# **CNS Neurotransmitters** **CNS Neurotransmitters**

Answer 27

* **Acetylcholine** * **Monoamines (biogenic Amines):** * Norepinephrine, Epinephrine, Dopamine, Serotonin * **Amino Acids:** * Glutamate, Glycine, Gamma Aminobutyric Acid (GABA) * **Neuropeptides:** * Substance P, Endorphins, Enkephalins * **Purines** * ATP/GTP * **Gasses and Lipids**

Question 28

# **Neurotransmitters and postynaptic effect** **Neurotransmitters and postynaptic effect**

Answer 28

* **Postsynapptic receptor properties determine effect of neurotransmitter on postsynaptic cell** * ACh produces EPSPs at some synapses and IPSPs at other synapses due to different types of postynaptic receptors **Ammount of neurotransmitter released into synaptic cleft and how long it remains determines amount of IPSPs and EPSPs current in postsynaptic cell**

Question 29

# **Understanding effects of drugs on synaptic function** **Understanding effects of drugs on synaptic function**

Answer 29

**Drugs that bind to the postsynaptic receptor:** * Agonists (mimetics) - mimic effect of neurotransmitter-receptor * Antagonists (blocking agents) - block effect of neurotransmitter * Many neurotransmitters have more than one type of postsynaptic receptor **Affect removal of NT from synaptic cleft**

Question 30

# **Cholinergic Synapses Postsynaptic Receptors** **Cholinergic Synapses Postsynaptic Receptors**

Answer 30

**Nicotinic Cholinergic receptors (direct Acting)** * Skeletal Muscles, Autonomic Ganglia * Excitatory * Agonist = **Nicotine** * Antagonist = **Curare** **Muscarinic Cholinergic Receptors (indirect: G-Protein coupled Receptors)** * Excitatory or Inhibitory * Visceral Muscles, Cardiac Muscles, CNS * Agonist = **Muscarine** * Antagonist = **Atropine**

Question 31

# **Adrenergic Synapses Postsynaptic Receptors** **Adrenergic Synapses Postsynaptic Receptors**

Answer 31

**Alpha Adrenergic receptors** * **Alpha 1 - Excitatory effect:** on smooth muscles of blood vesels of skin and viscera, cause constriction * **Alpha 1 Blockers - reduce hypertension** **Beta Adrenergic Receptors** * **Beta 1 - excitatory on cardiac muscle** * Beta 1 blockers reduce heart rate * **Beta 2 - Inhibitory on smooth musles or respitory tract, cause relaxation** * beta 2 blockers cause respitory constriction (**Agonists)**

Question 32

# **Removal of Neurotransmitter from the Synaptic Cleft** **Removal of Neurotransmitter from the Synaptic Cleft**

Answer 32

1. Diffusion, Degredation, reuptake (transport proteins bring NT into pre-synaptic cell of glial cell) * **Cholingeric Synapses** * Acetylchonline Esterase degrades ACh * **Monoamine synapses (norepinephrine, Epinerphrine, dopamine, seratonin)** * Monoamine oxidase degredation * Slective reuptake into presynaptic terminal