ANPS 1190- Exam 2 flashcards

Neuron doctrine

the neuron is the main structural and functional unit of the nervous system

Neurons

the main info processing cell in the NS, the ability of the NS to process info is dependent on rapid intercellular communication between neurons

Glial cells

carry out diverse functions, including providing support for neurons: 

Astrocytes- diverse functions, regulation of extracellular space, vascular cells (make up blood vessles), only found in the CNS, analogous cell type, satellite cells, are found in the PNS, regulate the levels of chemicals (neurotransmitters), and ions (K⁺) in the environment surrounding neurons (at nodes of ranvier, synapses), surrounds blood vessels in the brain, helping to form the blood-brain-barrier

Microglia- immune cells of the NS, resident of immune cells of the CNS, but can also travel to the PNS following injury, through phagocytosis, microglia can remove foreign intruders (microbes), as well as debris after injury to the NS

Oligodendrocytes- myelinating cells of CNS, one of the 2 kinds of myelinating glia, myelination- dramatically increases the speed of electrical signaling in neurons, only found in CNS, processes reach out and wrap lipid-rich myelin around axons of multiple neurons

Schwann cells- myelinating cells of PNS, one of 2 kinds of myelinating glia, only found in the peripheral NS, wrap lipid-rich myelin around axons of a single neuron, one neuron has multiple schwann cells wrapping arounds its axon

Ependymal cells- produce cerebrospinal fluid

Astrocytes

diverse functions, regulation of extracellular space, vascular cells (make up blood vessles), only found in the CNS, analogous cell type, satellite cells, are found in the PNS, regulate the levels of chemicals (neurotransmitters), and ions (K⁺) in the environment surrounding neurons (at nodes of ranvier, synapses), surrounds blood vessels in the brain, helping to form the blood-brain-barrier

Microglia

immune cells of the NS, resident of immune cells of the CNS, but can also travel to the PNS following injury, through phagocytosis, microglia can remove foreign intruders (microbes), as well as debris after injury to the NS

Oligodendrocytes

myelinating cells of CNS, one of the 2 kinds of myelinating glia, myelination- dramatically increases the speed of electrical signaling in neurons, only found in CNS, processes reach out and wrap lipid-rich myelin around axons of multiple neurons

Schwann cells

myelinating cells of PNS, one of 2 kinds of myelinating glia, only found in the peripheral NS, wrap lipid-rich myelin around axons of a single neuron, one neuron has multiple schwann cells wrapping arounds its axon

Ependymal cells

produce cerebrospinal fluid

Dendrite

 info receiving component of the neuron, dendritic spines- tiny extensions on dendrites that increase surface area of plasma membrane, enables cell to receive more inputs, more dendrites/spines=more input

Axon

info transmitting component of the neuron

Axon hillock

the initial segment of the axon that extends from the cell body, this is where an action potential starts

Cell body

biosynthetic centric center of the cell, contains nucleus and other organelles. Primary site of protein synthesis in the neuron, also called soma, contains cytosol and organelles surrounding the nucleus, primary cite of other cellular metabolic processes, there is often prominent rER

Axon terminal

contains neurotransmitters, after the action potential spreads down the axon and reaches the axon terminal, neurotransmitters will be released into the synapse

Synapse

 includes a presynaptic neuron, the synaptic cleft and postsynaptic neuron

Neurons can be divided into four functional regions

Receptive region- dendrites and cell body receive signals

Impulse-generating region- action potential is generated at the axon hillock (aka trigger zone)

Conducting region- action potential travels down the axon

Secretory region- neurotransmitters are released from the axon terminal into the synapse

Morphology of neurons

multipolar, bipolar, pseudounipolar

The neuronal cytoskeleton is made up of

microfilaments (smallest), intermediate filaments (neurofilaments), microtubules (largest), these are important for axonal transport

Axonal transport

the cell body communicates with the axon terminal via this, neurons rely on bidirectional axonal transport, where cargo contained in a transport vesicle is shipped down a microtubule

Anteograde transport

movement of materials from cell body to axon terminals, neurotransmitters, new membrane, mitochondria, enzymes, vesicles

Retrograde transport

movement of materials from axon terminals to cell body, organelles for recycling, signaling molecules brought in at terminal, potentially hazardous molecules can be brought into terminals

Myelin

is a lipid-rich substance that insulates and protects the axon, myelination increases the speed of electrical impulses traveling along the axon, more myelin= faster electrical signaling (unmyelinated vs lightly myelinated vs highly myelinated), gives white matter its color

White matter

mostly myelinated axons

Grey matter

 mostly cell bodies, dendrites, and unmyelinated axons

Differences between neurons and glia

Neurons: basic functional unit of the NS, excitable cells that transmit electrical signals, don’t divide after developmental period

Glia: “non-excitable”, undergo mitosis throughout life

Three general functions of the NS

 collect sensory input, integrate info, produce motor output

Collect sensory input

 collect sensory input, integrate info, produce motor output

Integrate info

interpret sensory input and determine proper response

Produce motor output

 activate effectors including muscles, organs, and glands

The NS is divided into structural and functional divisions

 info is sent to the CNS via the sensory division (afferent) of the PNS, the CNS system integrates info and stimulates a response by activating the motor division (efferent) of the PNS, motor responses can include control of voluntary movement via the somatic motor division or alteration of organ function via the autonomic (visceral motor) division

The autonomic division

 is divided into the:

Sympathetic NS- stimulates “fight or flight” response (increase hr and respiratory rate)

Parasympathetic NS- stimulates the “rest and digest” response (ex. Decrease hr, increase digestive function)

Comparison chart for the nervous system

PNS structures: nerve and a dorsal root ganglion

nerve- cable like bundle of parallel axons with their glia in the peripheral NS, ganglion- cluster of neuron cell bodies in the peripheral NS

Action potential

when stimulated, excitable cells can produce an electrical signal called this, nerve and muscle cells are excitable cells Electricity: “a phenomenon associated with stationary or moving electrical charges”, in the case of electrical signaling in neurons, ions move across the cell membrane to carry electrical charge

Ions carry electrical charge

 in a non-aqueous environment most ions will form ionic bonds and crystalize, in an aqueous environment (like the human body) most ions will dissociate, interacting with polar water molecules, ions are electrolytes and can carry electrical current in solution,  sodium (Na⁺), potassium (K⁺), and chloride (Cl^-) and calcium (Ca⁺²) are major ions relevant for physiology

Excitable membranes contain membrane proteins that determine a cell’s electrical behavior

transmembrane proteins are key to the electrical excitanility of neurons and muscle cells- leak ion channels, gated ion channels, receptor, ion pumps

Ion channel

an integral membrane protein that allows ions to pass through a pore between intracellular and extracellular environments (leakage ion channels, gated ion channels)

Receptor

an integral membrane protein that produces a physiological change in a cell after a logan (signaling molecule) bind

Selective permeability

 ion channels have pores that are selective for specific ions, ions can’t cross the cell membrane, based on cell size and charge, can be leakage channels which are always open, or gated channels which open and close, ion flows across membrane will change the membrane potential

Leakage channels

ion channels that are always open– leakage channels are ungated meaning they are always open, leakage channels are important for establishing the resting membrane potential, leak channels are selective for a specific ion

Gated ion channels

open and close in response to specific stimuli, allow ion movement only when open, control permeability for an ion, open channels allow passive movement of ions down their chemical and electrical gradient while the channel is open, voltage gated and chemically (ligand) gated

Voltage gated

open in response to a change in membrane voltage, highly concentrated in muscle and nerve tissue, voltage gated sodium channel, voltage gated potassium channel, closed under normal physiological conditions, but open with change in membrane voltage around the protein: voltage-gated sodium channels, potassium, and calcium channels

Chemically (ligand) gated)

 open in response to binding of an extracellular signal, many neurotransmitters will work via this mechanism, specific chemical binding, have selective binding site on extracellular side of plasma membrane, neurotransmitters are the ligands, receptor is specific for a particular NT, closed under normal physiological conditions, many drugs target ion channels

Ionotropic receptors

ligand-gated ion channels that open or close in response to an extracellular signal; open ion channels allow ions to move and carry charge across the membrane, when a neurotransmitter binds to this receptor, this opens an ion channel that allows specific ions to flow into or out of the cell, these types of receptors are called ligand-gated ion channels (chemically gated) and the flow of ions through the channel cause electrical changes in the neuron

Metabotrophic receptors

are membrane proteins that respond to an extracellular signal by altering the metabolism in the cell, many are G-protein coupled receptors, because when the neurotransmitter binds, it activates a G-protein, after the G-protein is activated, it can stimulate intracellular signaling pathways, when a neurotransmitter activates a metabotrophic receptor, the response is slower but more widespread and potentially longer lasting

Small molecule neurotransmitters/neuropeptides

most neurotransmitters fit into one of the two categories

Small molecule neurotransmitters

glutamate, GABA, glycine

Glutamate

generally excitatory, the principle excitatory NT in the brain

GABA

generally inhibitory, principle inhibitory neurotransmitter in the brain

Glycine

 inhibitory, major inhibitory neurotransmitter in the spinal cord+brain stem

Neuropeptides

small chains of amino acids made in the rER/golgi at cell body, substance P, endorphins (Endogenous opiates)

Life cycle of neurotransmitter

synthesis → packaging into vesicles →  release into the synapse →  binding to a post-synaptic receptor →  removal from the synapse

Acetylcholine

synthesized from choline, and acetyl coenzyme A by an enzyme in the presynaptic terminal and then loaded into a synaptic vesicle, released from all somatic motor neurons, many neurons of the ANS, and many CNS neurons, the impact of Ach depends on which type of receptor it binds to, mechanism of removal from synapse, broken downby the enzyme acetylcholinesterase, neurons typically syntehsize and release only one small molecule neurotransmitter and are named for the dominant transmitter released (ex. Cholinergic, serotonergic, dopaminergic)

Nicotinic acetylcholine receptor

ionotropic, effect of Ach binding: Na+ influx/depolarization

Muscarinic acetylcholine receptor (metabotropic)

effect of Ach binding: Activation of a G-protein stimulates intracellular signaling that leads to calciu, release from intracellular organelles

The neuronal membrane can be broken down into 4 functional segment

Receptive region: dendrites and cell body, impulse-generating region- axon hillock, conducting region- axon, secretory region- axon terminals

The different functional segments have different complements of ion channels

Membrane potential (Vm)

refers to the difference in electrical potential (voltage) across the cell membrane, membrane potential=V_inside-V_outside

The resting membrane potential (Rm)

is the difference in electrical potential (voltage) across the cell membrane at rest

All human cells are said to be polarized at rest

Neurons= -60 - -80mV, Muscle= -90mV, red blood cells= -7mV

The resting membrane potential (Rm) of a typical neuron is -70mV

because the charge on the inside of the membrane (negative) is the opposite charge of the outside of the membrane (positive), we say that the cell is electrically polarized

Polarize

 to separate into uneven groups

The human body is_____ but the plasma membrane _______

electrically neutral, properties allow for the generation of a membrane potential

Phospholipids

phosphate head (polar)- hydrophilic, hydrocarbon tail (nonpolar)-hydrophobic

The phospholipid bilayer is impermeable to

ions allowing for storage of charge, functions as a capacitor- a device that can store electrical charge

The cell membrane is selectively permeable

only certain molecules can freely cross the cell membrane, ions and polar molecules cannot freely cross through the cell membrane, they require transmembrane proteins like ion channels and pumps to move into or out of the cell

What makes the resting potential ~ -70mV?

Unequal distribution of charge across the cell membrane due to the movement of ions

1. Sodium/potassium pump

2. Potassium efflux through leakage channels

3. Movement of other ions

4. Intracellular organic anions (A-)

What are ions

atoms that have an electrical charge resulting from gaining or loosing electrons, when they pass through the cell membrane they change the membrane potential

Cation

positively charged ion

Anion

negatively charged ion

Depolarization

 if Na+ moves into the cell, the membrane potential becomes more less negative (more positive) (depolarizing current)

Hyperpolarization

 if K+ moves out of the cell, the membrane potential becomes more negative (less positive) (hyperpolarizing current)

Currents (I)

 the flow of electrical charge measured in amperes (A), in cells charge is carried by ion movement

The sodium potassium pump

uses ATP to move 3 sodium ions out of the cell and 2 potassium ions into the cell

By pumping 3 sodium ions extracellularly and 2 potassium ions intracellularly, this pump sets up the concentration gradient for sodium and potassium across the cell membrane, slight accumulation of a + charge extracellularly and - charge intracellularly

K+ efflux occurs through passive transport

they can be “pumped” in energetically unfavorable ways that require ATP, they can “flow” energetically favorable ways based on electrical and chemical driving force

Electrical driving force

 the force that results from attraction between positive and negative charges

Chemical driving force

the force that results from movement of ions from high concentration to low concentration

How can you predict which way an ion will flow

Equilibrium potentials allow you to predict the direction of ion movement, the voltage of the cell membrane at which an ion is at electrochemical equilibrium. Tells you which direction and ion “wants” to flow, based on electrical and chemical driving forces. An ion will always flow in a qay that drives the membrane potential towards the equilibrium potential for that ion.

If the membrane is permeable to a particular ion

 that ion will flow in a way that drives the membrane potential towards its equilibriu potential, which tells you how an ion wants to flow, based on electrochemical driving forces, the actual flow of an ion across the cell membrane depends on the permeability of the cell to that ion, which is determined by the presence of ion channels ion flow=driving force X permeability

The neuronal cell membrane displays selective ion pemeability

neurons are highly permeable to K+ relative to other ions due to abundant K+ leakage channels, high permeability to K+ allows K+ to leave the cell, driving the voltage of the cell towards the equilibrium potential for K+ (Kk= -80mV), as a result the resting membrane potential (-70mV) is very close to Ek

What are the most important determinants of the resting membarne potential

 Na/K pump, and high permeability to potassium

Resistance (R)

hindrance to charge flow by substances through which current must pass measured in ohms (Ω ), in cells, resistance comes from basic property of the plasma membrane, resistance is the inverse of permeability, more permeability=less resistance

Voltage potential (𝛥V)

measure of potential energy generated by separated electrical charges measured in volts (V), separation is most often a physical barrier (in cells, this is the plasma membrane), in cells we refer to this as membrane potential

Bioelectricity is governed by Ohm’s law