Membrane Potential And Excitbility Flashcards
Ca2+ outside vs inside cell
Ca2+ kept very low inside cell, and high outside cell
*** Ca2+ kept under severe control
Na-K Pump
- uses ATP
- 3 Na out
- 2 K in
*** purpose/fn of Na|K ATPase is to establish Na|K gradient inside/outside the cell
Ca2+ Pump
- requires ATP
Ca2+ used for:
- conformational changes
Ohm’s Law
V=IR
I=VxG
Current = voltage x conductance
Amount of current you get = push (voltage) x how easy it is to go a->b (conductance)
Pores
Checks amino acids as filter
T|F At Nernst Potential there’s current for X ion?
F
- when at equilibrium, there is no current for the ion at equilibrium
Current can only occur when Voltage is
Different from NERST potential
Action Potential
Electrical signature responsible for all electrical activity in the body
Gating of Sodium Channels
(2 types)
M: ACTIVATION gate; opens
H: INACTIVATION gate; almost immediately closes; can’t open again until resets
- transitions between resting, activated, and inactivated states are dependent on membrane potential and time
BEFORE AP
- @ resting potential K+ at highest [inside], Na+ at highest [outside]
- Na|K pumps use ATP to maintain these gradients across the plasma membrane
Resting State
- more K channels open than Na
Depolarization
- some Na channels open depolarize game the membrane
- K channels are closed
Rising Phase of AP
- nearly all Na channels open, sharply raising the AP towards Ena
- K channels remain closed
Repolariziation
- Na close, K open, pulling membrane potential towards Ek
Undershoot
- overly depolarizes, pulling membrane potential towards Ek, past resting potential
- Voltage-gated K channels close to restore RP
Going to + NERST
Going to - NERST
+: Na|Ca
-: MUST be K
Na\K resets everything
Heart AP
AP held longer because Ca2+ helps hold K in
Catecholamines
Increase pacemaker rate by increasing cAMP which opens HCN channels increasing If sodium current during phase 4. That increases the slope of phase 4 thus the rate
CNS Overview
Brain & Spinal Cord
Afferent Division: sensory stimuli; visceral stimuli : input to CNS from periphery
Efferent Division: autonomic NS; somatic nervous system
Autonomic NS: sympathetic; parasympathetic NS : smooth|cardiac muscle; exocrine|endocrine glands
Somatic NS: motor neurons; skeletal muscle
Where is the ANS controlled?
- controlled centrally in brain regions including hypothalamus, midbrain, pons, medulla
ANS
Function|innervates
Function: Involuntary: sympathetic; parasympathetic; enteric
Innervates: cardiac muscles; smooth muscles; glandular epithelia
Somatic Motor Neuron
- originates from spinal cord
- directly innervates skeletal muscles
Autonomic Motor Neurons
-Preganglionic neuron ( most are myelinated): cell bodies in spinal cord
- postganglionic neuron (unmylinated): cell bodies in autonomic ganglia
Parasympathetic NS
- ganglion located close to target organ
- sympathetic chain ganglion: located in two sympathetic chains running alongside spinal cord
- short pre; v. Long post
Ganglion (Sympathetic Chain)
- located in two sympathetic chains running alongside spinal cord
- short pre, very long post
Sympathetic Subdivision also includes:
Innervation of adrenal medulla, which then secretes epi & norepi which are important for flight|flight reponse
Adrenal Medulla
Regulates release of epi|norepi
Ganglion
Intermediate before target organ
Reciprocal functions of the sympathetic|parasympathetic actions on the heart
- each target organ is reciprocally regulated by both symp|parasymp systems
Sympathetic Ganglia of the Heart
- located in symp chain
Parasymp ganglia are located
(Cardiac plexus)
Close to the target organ
SA node & AV node are innervates by
Both parasymp|symp systems
Dual innervation by symp|parasymp systems to target organs allows for
Balanced regulation of physiological functions
2 pathways originating from the hypothalamus important for body’s stress response
- sympatho-adrenal axis: releases epi|norepi = adrenaline rush during fight|flight
- HPA axis
Enteric Nerbous System inputs
Symp & parasymp
Enteric NS composed of
- local neural networks that receive inputs from both symp|parasymp systems
Enteric NS includes
- submucosa plexus
- myenteric plexus
Submucosal Plexus
Enteric NS
- groups of neurons located in submucosa of GI tract
Myenteric Plexus
Enteric NS
- groups of neurons located between 2 smooth muscle layers of GI tract
The ANS includes
- sympathetic and parasympathetic divisions
The sympathetic division mobilizes the body for ___________ and controls the _________
- mobilizes the body for activity
- controls the “fight|flight” response
The sympathetic system also innervates the ___________ ___________, which secretes…
- innervates the adrenal medulla
- which secretes epi|norepi important for the fight|flight response
The parasympathetic division…
- relaxes the body; rest|digest
Ying|Yang Regulation
Symp|parasymp
The Enteric NS contains the _______ & _____ and is controlled by both the ________ & __________ divisions
- myenteric plexus & submucosal plexus
- sympathetic|parasympathetic divisions
Wiring the autonomic NS
- reiprocal regulation between symp|parasymp
2 main synapse types:
- electrical: faster
- chemical: allow for more levels of regulation by using diff NT & different receptors
Electrical Signals
- v. Fast (cardiac)
Trafficking Pathways in the Nerve Terminal
- precursors of synaptic vesicles get loaded with neurotransmitters, then dock at active zone and become primed to be released in response to an action potential
- vesicles undergo endocytosis to be recycled & reused
- pre-synaptic vesicles loaded with NT; AP releases vesicles into space
- recycle vesicles back in after signal completion
NT vs Hormone
NT: acts locally at the synapse
Hormone: released into blood and can affect distant organs
Some substances can be both (norepi)
What defines a neurotransmitter?
- must be present in the presynaptic neuron
- must be released in response to presynaptic depolarization
- specific receptors for the substance must be present on the postsynaptic cell
Neurotransmitter
- substances synthesized in the presynaptic neuron (MUST be present in presynaptic neuron)
- released in response to an AP
- act on specific receptors on postsynaptic cells
NT Important for peripheral NS
- Acetylcholine
- Norepi
3 Catecholamines
- adrenaline
- noradrenaline
- dopamine
NT release at the synaptic terminal
- NT release is in response to an AP which triggers Ca2+ influx
Chemical Synapse effect on time
- process of synaptic transmission at the chemical synapse causes a slight time delay
What is significant about the delay with chemical synapses
Acts as regulation
2 Broad Types of Postsynaptic Receptors
- ionotropic
- metabotropic: regulate target response through secondary messenger pathways
Ionotropic Rececptor
- Nicontinic
- all postganglionic neurons; adrenal medullary cells and neuromuscular junctions of the skeletal muscle: causes excitation
Nicotinic Acetylcholine Receptors
(NAchR)
- specifically activated by nicotine
- IONOTROPIC
- permeable to Na|K (and sometimes Ca)
Nicotine Poisoning
- where receptors are located
- what can nicotine affect
- nAchRs: located on skeletal muscles, post ganglion is neurons & adrenal medullary cells
- nicotine can affect the somatic, symp|parasymp NS depending on dosage
- e cigs can cause nicotine poisoning
Metabotropic Receptors
- GPCR signaling pathways: can lead to different downstream pathways depending on specific G proteins bound to the receptors
Muscarinic Acetylcholine Receptors
(MAchRs)
- Metabotropic
- have different subtypes: can activated different downstream pathways depending on which Gproteins bound
- mainly expressed on target organs of parasympathetic pathways
mAchRs
- agonist vs antagonist
- agonists will mimic the actions of the parasympathetic system
- antagonists will inhibit the parasympathetic system
Parasympathetic System Overall Effect
- decreased heart rate
- decreased BP
- increased digestion
- contracts bladder wall muscles
Rest|Digest
Adrenergic Receptors
- all activated by epi|norepi
- lead to diverse intracellular signaling pathways
Types of Adrenergic Receptors
- a1: smooth muscle contraction
- a2: inhibition of transmitter release; smooth muscle contraction
-B: heart muscle contraction; smooth muscle relaxation; glycogenolysis
Adrenergic Receptor Antagonists
- mainly expressed in sympathetic target organs
- will counter the action of the sympathetic system
- NE
Somatic NS (illustration)
Somatic NS ——————————-Ach
Parasympathetic Nervous System (illustration)
Parasymp NS ———————-Ach [ganglion] ————-Ach
Sympathetic Nervous System (illustration)
Symp NS —-Ach [Ganglia] —————————— NA
— Ach [Ganglia] ——————————Ach
—Ach [Ganglia] Adrenal Gland - - - - - -> ADR
