Neruons and Action Potentials Physiology

Define resting membrane potential

Baseline electrical potential that can be measured across the cell membrane

What is the resting membrane potential for the average cell

-70 mV

Define voltage

The electrical difference across a membrane

How do intra and extracellular ion concentrations influence membrane potential

Potassium, sodium, and calcium are all positive ions. High amount of potassium inside cell, high amount of sodium and calcium outside cell. Sodium has biggest impact and extracellular electrical potential is higher/more positive than inside

How does sodium potassium ATPase contribute to resting membrane potential

Uses ATP to pump 3 sodium out and w potassium in

Which ions’ equilibrium potential is closest to the resting membrane potential

K= -90 mV

Na= 60-70 mV

Resting membrane potential is closest to potassium because of potassium leak channels that make the membrane more permeable to potassium than sodium

What is equilibrium potential

The membrane voltage where there is no NET ion movement. It is unique to each individual ion.

Depends on electrical valance and concentration in intra vs extracellular fluid

What are the upper and lower limits of membrane potential and how do they compare to other ions

Negative limit= -90 mV

Positive limit= +70 mV

Inside this limit ions follow concentration gradient, outside this limit ions follow electrical gradient

What deterimes membrane potential

The permeability of ions at rest.

Concentration of ions

Their valence

What happens if equilibrium potential is or is not equal to membrane potential

If equal no net movement of ions, if unequal then net movement of ions shifts membrane closer to ions equilibrium potential

Depolarization vs hyper vs repolarization

Depolarization= membrane potential becomes less negative

Hyperpolarizatoin= membrane potential becomes more negative

Repolarizatoin= membrane potential goes from positive to negative

Graded potential vs Action potential location, magnitude, channel sasociation, and ions

Graded potentials (PSP)= result from opening of ligand-gated ion channels. Excitatory neurotransmitters elicit excitatory post synaptic potentials. Ligand gated Potassium channels are mane ion associated with hyperpolarization and ligand gated sodium are associated with depolarization

Action potentials (AP)= result from opening of voltage gated ion channels once PSP summation is enough to bring membrane potential to threshold. Sodium channel opening is main ion contributing depolarizatoin

What stages can voltage gated sodium channels have

Open, inactive, closed

Open occurs at threshold, inactive is time mediated and happens spontaneously right after opening, closed happens when resting membrane potential is obtained again

What stages can v gated potassium channels have

Open at threshold, closed once resting membrane potential is reached

What stage are sodium and potassium at during each phase of AP

Stage 5 resting: Vgated Na are closed, Vgated K are closed, K leak are open

Stage 2 Depolarization (after threshold): Vgated Na are open, Vgated K are closed, K leak are open

Stage 3 Repolarization: Vgated Na are inactive, Vgated K are open, K leak are open

Stage 4 Hyperpolarization: Vgated Na are closed, Vgated K remain open, K leak are open

Define neuron

Nerve cells/Neurons are major functional unit of the nervous system

Dendrite, cell body(soma), axon, axon hillock, axon terminals

Dendrites are branched extensions of a neuron that conduct impulses from other cells toward the cell body, cell body/soma contains organelles, axon is a long process that conducts impulses away from the cell body toward other cells, axon hillock is the area of origin of the axon from the cell body, axon terminals are the terminal portions of axon brancehs

Define synapse, synaptic cleft, synaptic vesicles, post and pre synaptic membranes

Presynaptic membrane is portion of the axon terminal that forms synapse with target cell, postsynaptic membrane is the portion of target cell that forms a synapse with the neuron. Synaptic cleft is space between. Synaptic vesicles contain neurotransmitters

Temporal vs spatial summation

Temporal occurs when high frequency from one presynaptic neuron

Spatial is from multiple adjacent neurons simultaneously stimulate the postsynaptic cell

How do psp generated in dendrites influence AP at axon hillock

Graded potentials spread from the postsynaptic membrane towards the soma and axon, however their magnitude decreases as distance from the synapse increases, so synapses nearest to the axon hillock have the greatest impact.

All or nothing AP pheneom

AP do not sum together, however frequency of AP generation can change

What is absolute refractory period

Occurs when no stimulus regardless of magnitude can generate a subsequent AP. Is due to inactive sodium channels

What is relative refractory period

Occurs when a greater stimulus (graded potentials is needed to reach threshold and generate AP. Due to hyperpolarization because of slow closing of sodium channels

How do AP propagate in unmyelinated axons

Large influx of sodium occurs at axon hillock, depolarizing local region of membrane, this results in depolarization and AP of adjacent part of membrane.

Why is AP unidirectional

Because of inactive period of Vgated sodium channels

How do AP propagate in myelinated axons

Transmembrane movement ions only occurs at nodes of Ranvier and APs jump from node to node. Faster than unmyelinated axons.

How do myelination and axon diameter affect speed of conduction

Highly myelinated large diameter axons are fastest, unmyelinated small diameter axons are slowest

Define, nerve, ganglion, nucleus and glial cells

Nerve= cord like bundle of axons from multiple neurons. Cranial nerves emerge from brain or brain stem, spinal nerves emerge from spinal cord.

Nucleus= collection of neuronal cell bodies within of the brain or spinal cord.

Ganglion= collection of neuronal bodies outside of brain or spinal cord

Glial cells= supporting cells of the nervous system. Astrocytes, oligodendrocytes, and microglia.

Central vs peripheral nervous system

CNS is the brain and spinal cord

PNS is cranial and spinal nerves, carry signals to and from CNS

Efferent vs afferent nerves

Efferent (motor) nerves are peripheral nerves that carry impulses away from the CNS. Cell bodies located inside CNS.

-Somatic nerves are efferent nerves that carry impulses to skeletal muscle

-Visceral nerves are efferent nerves that carry impulses to cardiac muscle, smooth muscle, and glands

Afferent (sensory) nerves are peripheral nerves that carry impulses towards the CNS. Cell bodies located outside CNS

Autonomic nervous system

Consists of specific portions of CNS and PNS, responsible for involuntary control. Has the sympathetic and parasympathetic divisions

Parasympathetic vs sympathetic nervous system

Both are a part of the ANS

Parasympathetic=peace=rest and non-stress activities (digestion, reproduction)

Sympathetic=stress=times of stress, (fight, flight, or freeze)

What factors contri