Neurons

____ are cell types of the nervou system

neurons

what establish the resting membrane potential

ion pumps and ion channels

what causes changes in voltage across a membrane

opening and closing of ion channels

changes in ____ induce signaling between neurons

voltage

what are two ways signaling can be achieved

1. direct passing of electrical current

2. intermediate chemically mediated step

what is the purpose of glia for neurons

provide essential support, protection, and maintenance for neurons.

are glia electrically active

NO

glia have a ____ membrane potential

negative

what are four types of glia cells

1. astrocytes

2. oligodendrocytes and Schwann cells

3. microglia

4. ependyma cells

what is the purpose of astrocytes

essential element of the blood brain barrier

what is the importance of the blood-brain barrier

limits compounds that can access the brain (protects from infection) but also limits therapeutic drug delivery to the brain

what are five ways to overcome the blood-brain barrier

1. small molecule optimization (modify properties to improve passive diffusion)

2. direct delivery (bypass BBB via olfactory delivery)

3. lipid carriers (encapsulate and deliver drugs)

4. receptor and antibody shuttles (antibodies that bind to transport systems)

5. focused ultrasound

which type of glia wrap many layers of membranes around axons

Schwann cells and oligodendrocytes

what does multiple sclerosis attack

myelin of neuron

what is the consequence of multiple sclerosis on neurons

electrical nerve impulses travel slowly, become scrambled, or stop completely,

what characterizes multiple sclerosis

scarring in the white matter tracts of brain

purpose of microglia

brain and spinal cord's primary defense and maintenance crew

which glia are considered phagocytotic cells

Microglia

what are the main signaling units of the nervous system

neurons

what are the 5 externally recognizable parts of neurons

• soma (cell body)

• axon

• dendrites

• presynaptic release sites

• postsynaptic targets

where is most of a neuron’s organelles found in

soma (cell body)

what are the purpose of dendrites

highly branched extensions that receive signals from other neurons

what is the axon

longer extension that conducts electrical impulses away from the cell body

what are synapses

specialized junction that allows a neuron to pass an electrical or chemical signal to another neuron

what are the two kinds of synapses

electrical synapses

chemical synapses

what are dendrodendritic synapses

specialized connections where the dendrites of two different neurons communicate directly with each other

axon hillock

the cone-shaped region of a neuron’s cell body (soma) where it tapers and connects to the axon

what are held in the axon hillock

• voltage gated sodium channels

• action potential originates here

what is neuro-electricity

the electrical phenomena, voltages, and signals generated and used by the nervous system

what ion diffuses inside inside the cytoplasm and which diffuses out to the extracellular fluid

in - sodium

out - potassium

what is the membrane equilibrium potential of sodium? potassium?

sodium = + 60mv

potassium = - 90 mv

what determines the membrane potential inside and outside a cell

the ratio of ion concentrations inside vs out and not the absolute concentration of ions

is the resting membrane more permeable to sodium or potassium

potassium

how is the resting balance maintain around -70 mv

resting membrane is much more permeable to potassium than to sodium = potassium's outward diffusion dominates, keeping the resting membrane potential close to −70 mV rather than staying down at -90 mv (potassium resting potential)

compare the resting leak of potassium and sodium in a cell

• abundant potassium leaks

• sparse sodium leaks

resting membrane potentials are _____ (negative or positive)

negative

why does the membrane potential of potassium significantly outweigh sodium

the cell membrane has far more open potassium leak channels than sodium channels at rest

what would happen if the permeability to sodium were suddenly increase

sodium ions to rush into the cell, leading to depolarization of the membrane potential (making the inside of the cell more positive).

what are the stages of an action potential

• resting stage

• rising stage (depolarization)

• peak

• falling phase (repolarization)

• Hyperpolarization

• return to resting stage

what is the threshold potential required to send an action potential

about -55

what happens in the depolarization stage of an action potential

• Reaching the threshold causes voltage-gated sodium (Na⁺) channels to open

• positive sodium ions rush rapidly into the cell

• influx of positive ions drives the membrane potential from its resting state (around −70 mV) up past zero to a peak

what kind of feedback loops are exhibited by action potentials

positive feedback during their rising phase (depolarization)

(Na⁺ ions rush into the cell, making the inside more positive = further depolarizes the membrane = causes even more voltage-gated Na⁺ channels to open)

negative feedback during their falling phase (repolarization)

(K⁺ ions flow out of the cell = removing positive charge = brings the membrane potential back down toward the resting state, often overshooting before stabilizing)

what happens in the repolarization stage of an action potential

• The fast voltage-gated sodium channels close and become inactivated, stopping the influx of positive sodium ions

• Slower voltage-gated potassium channels open in response to the depolarization

• Positively charged potassium ions rush out of the cell down

• loss of positive ions from the interior makes the inside of the cell negative again

why does Hyperpolarization happen

Delayed closing of potassium (K⁺) channels as these channels close slowly

how are sodium and potassium channels gated

voltage gated channels

why do membrane potential changes occur

because neurons contain ion channels that open or close in response to stimuli

how is energy stored in electrochemical gradients harvested

selectively altering membrane permeability to ions not at their electrochemical equilibrium

why can electrical signaling be fast

because ion channels can open and close quickly

why can’t you have consecutive action potentials across a neuron

cell goes through a phase of hyperpolarization where the inside of the cell becomes more negative than its normal resting state which would need a larger stimuli to start another action potential

what prevents action potentials from traveling backwards

, which is caused by the temporary inactivation of voltage-gated sodium (Na⁺) channels immediately behind the moving signal.

compare electrical and chemical synpases

An electrical synapse passes ionic current directly through physical gap junctions

chemical synapse converts electrical signals into chemical neurotransmitters to cross a fluid-filled gap

what kind channels does electrical signals travel down in an electrical synapses

channel made from connexons

how do you make a connexon

6 connexins

what does 1 connexon make

1 hemichannel

what does 2 connexons make

gap junction channel

can electrical synapses be ionotropic or metabotropic or both

NO - is not considered any of these

are chemical synapses ionotropic or metabotropic

can be either

compare ionotropic or metabotropic

ionotropic - ligand-gated ion channels made up of multiple protein subunits (typically three to five) that form a central pore

metabotropic (G-protein-coupled receptors) - single-unit, membrane-bound proteins that do not contain an ion pore

what are ionotropic and metabotropic receptors

the two primary neurotransmitter receptors

where is information transmitted from and where is it received

received - postsynaptic cell

transmitted - presynaptic cell

what are two ways a synaptic terminal of one neuron can pass information across the synapse

1. direct passage of electrical current via gap junction

2. chemical messengers (neurotransmitters)

is ionotropic or metabotropic fast? slow?

Ionotropic Receptors - Fast

Metabotropic Receptors - Slow

which type of receptor has an ion channel built into it

ionotropic receptor

how do ionotropic receptors work? Metabotropic Receptors work?

ionotropic receptor

• A chemical messenger binds directly to binding site of the receptor.

• binding causes an physical conformational change that open channel’s gate.

• Ions rush through the pore down their electrochemical gradient.

Metabotropic Receptors

• A neurotransmitter binds

• triggers shape change that activates G-protein

• activated G-protein dissociates and eventually open or close ion channels

why are Metabotropic Receptors slower

due to time needed for ligand to diffuse to receptor AND multiple chemical steps before channel is modified

does a Metabotropic Receptor or Ionotropic receptor last longer

Metabotropic Receptor

does Metabotropic Receptor or Ionotropic receptor modify the excitability of neurons

Metabotropic Receptor

is Metabotropic Receptor or Ionotropic receptor direct? indirect?

Ionotropic receptors use a direct mechanism

Metabotropic receptors use an indirect mechanism