Neuronal Communication (Part 1)

determines if an action potential is produced or not

the net effect of the interaction between graded potentials

how do GPCRs affect post synaptic ion channels

they are transducers that indirectly affect ion channels

saltatory conduction

the propagation of action potentials along myelinated axons from one node of ranvier to the next, increasing the conduction velocity of action potentials

synapse

the region where an axon terminal communicated with its postsynaptic cell

What 2 major factors affect speed of AP in neurons

(1) the diameter of the axon and (2) the resistance of the axon membrane to ion leakage out of the cell. The larger the diameter of the axon or the more leak-resistant the membrane, the faster an action potential will move. Saltatory conduction thus is an effective alternative to large-diameter axons and allows rapid action potentials through small axons.

AP conduction in unmyelinated axons

1.

NT release at the synapse

1. AP depolorizes axon terminal 2. Voltage gated Ca2+ channels open, Ca2+ enters 3. Ca2+ triggers exocytosis 4. NT diffuses across synaptic cleft and binds with receptors on postsynaptic cell 5. Postsynaptic cell has response

2 factors that influence membrane potential

1. Concentration gradients of ions across the membrane. Normally, sodium (Na* ), chloride (Cl+ ), and calcium (Ca2* ) are more concentrated in the extracellular fluid than in the cytosol. Potassium (K* ) is more concentrated in the cytosol than in the extracellular fluid. 2. Membrane permeability to those ions. The resting cell membrane is much more permeable to K* than to Na* or Ca2* . This makes K* the major ion contributing to the resting membrane potential.

AP sequence of events

1. RMP 2. depolarizing stimulus 3. membrane depolarizes to threshold. Na+ channels open quickly. K+ channels open slowly. 4. Rapid Na+ entry depolarizes cell 5. Na+ channels close. SLower K+ channels open. 6. K+ moves from cell to ECF 7. K+ channels stay open and more K+ leaves. Hyperpolorization 8. K+ channels close 9. cell returns to RMP

AP conduction in myelinated axons

AP jump from one node of ranvier to next only the nodes have Na+ channels

absolute vs relative refractory period

Absolute: Na+ inactivation gate closes, activation gate still open Relative: Na+ inactivation gate reopens and activation gatecloses [de-inactivation] - ready to participate in AP again During the relative refractory period, a stronger than normal stimulus is needed to elicit neuronal excitation. After the absolute refractory period, Na+ channels begin to recover from inactivation and if strong enough stimuli are given to the neuron, it may respond again by generating action potentials.

Microglia

Act as phagocytes, eating damaged cells and bacteria, act as the brains immune system

How GPCRs act at the presynaptic neuron

Alter the function of voltage gated ion channels and modulate NT release

chemically gated ion channels

Chemically gated ion channels in most neurons respond to a variety of ligands, such as extracellular neurotransmitters and neuromodulators or intracellular signal molecules.

EPSP vs IPSP

EPSP is a depolarization (Na+ entering the cell). IPSP is a hyperpolarization (Cl- entering the cell)

Concentration of K+ in and out of cell

Extracellular - 5mM Intracellular- 150mM

metabotropic receptors

G-protein coupled receptors that activate heterotrimeric G-proteins; G-proteins dissociate to control ion channel activity or bind to other effector proteins

Effect that hypokalemia have on neurons

If blood K* concentration falls too low (hypokalemia), the resting membrane potential of the cells hyperpolarizes, moving farther from threshold. In this case, a stimulus strong enough to trigger an action potential when the resting potential is the normal +70 mV does not reach the threshold value (Fig. 8-19d). This condition shows up as muscle weakness because the neuron

mechanically gated channels

Mechanically gated ion channels are found in sensory neurons and open in response to physical forces such as pressure or stretch.

Astrocytes

Provide structural and metabolic support for neurons. blood brain barrier

tonic control

Regulates physiological parameters in an up-down fashion. The signal is always present but changes in intensity.

Where on neuron does integration occur

Soma integrates all incoming info and det's the net signal strength

Schwann cell

Supporting cells of the peripheral nervous system responsible for the formation of myelin. Each cell forms myeline around a segment of one axon

conductance

The ease with which ions flow through a channel

Explain Na+ channels

There are 2 gates: activation and inactivation. 1. at RMP activation gate is closed and inactivation gate is closed 2. Depolarization: AG opens. IG already open. 3. Na+ enters cell 4. at 30mV IG closes 5. during repolarization caused by K+ leaving cell, gates reset to their orig position

Oligodendrocytes

Type of glial cell in the CNS that wrap axons in a myelin sheath.

voltage-gated ion channels

Voltage-gated ion channels respond to changes in the cell's membrane potential. These channels play an important role in the initiation and conduction of electrical signals.

dendrites and soma

have responses that receive incoming neurotransmitter signals

resting membrane potential primarily determined by

[K+] gradient and the cell's resting permeability to Na+, K+, and Cl-

graded potential

a membrane potential that varies in magnitude in proportion to the intensity of the stimulus travel short distances and lose strength as they travel

normokalemia

a normal range of K+ in the blood; subthreshold graded potentials will not trigger action potentials

excitatory post-synaptic potentials

a small, local depolarization that make it easier for a neuron to fire

inhibitory post-synaptic potentials

a small, local hyperpolarization that make it harder for a neuron to fire

effect of subthreshold graded potential in normokalemia

a subthreshold GP creates no AP but a suprathreshold will

depolarizes the axon terminal

action potential

ligand-gated ion channel

an extracellular site and membrane-spanning ion channel; made of multiple individual protein subunits

What is the trigger zone

axon hillock all or non location for NET signal of AP

Why do AP's appear to jump from one node of Ranvier to next

because only the nodes have Na+ voltage gated channels

chemically-gated channels

bind chemical ligands

Glial cells

cells in the nervous system that support, nourish, and protect neurons

slow axonal transport

conveys axoplasm in one direction only - from the cell body toward the axon terminals. moves materials down axon and supplies new axoplasm needed for developing or regenerating neurons Used for things like enzymes and cytoskel. proteins

where in neuron does the input signal occur

dedrites and soma that have receptors to rcv incoming NT signals

Where are graded potentials found?

dendrites and cell body

neuron structure

dendrites, cell body, axon, myelin sheath, Schwann cells

intensity of a neurotransmitter

depends on the frequency of action potentials (more action potentials = stronger intensity)

opens voltage-gated Ca2+ channels

depolarization

Factors that affect speed of AP

diameter resistance to leakage

influences speed of action potential

diameter of axon and resistance of axon membrane to ion leakage out of the cell

lysosomes

digest old membrane components

Concentration of Na+ in and out of cell

extracellular- 145mM intracellular - 15mM

true or false, different action potentials can differ in strength

false

do ligand-gated ion channels control fast or slow responses?

fast

oligodendrocytes

form neuronal myelin sheaths in CNS; highly fatty myelin acts as an electrical insulator

What det'd stimulus intensity

frequency of AP

nodes of ranvier

gaps in myelin sheath along the axon between two Schwann cells

type of signal in graded potential vs action potential

graded - input signal AP- Regenerating conduction signal

decrease in strength as they spread out from the point of origin

graded potentials

ionotropic receptors

have two functional domains: an extracellular site that binds neurotransmitters, and a membrane-spanning domain that forms an ion channel both domains funct as a ligand gated ion channel (LGIC) Control fast responses

exocytosis

how neurotransmitters are relased

hyperkalemia

increased K+ in the blood; subthreshold graded potentials can trigger action potentials because the membrane has been brought closer to the threshold

function of voltage gated channels

init and regenerate AP VG Na+ channels are located in trigger zone and axon

voltage-gated channels

initiate and regenerate the action potential; are located in the trigger zone and in the axon

neurotransmitter binding

initiates a response in the postsynaptic cell

soma

integrates all of the information (determines net signal strength)

divergence

one presynaptic neuron branches to affect a larger number of postsynaptic neurons.

creates electrical signals

ion movement

do larger or smaller axons produce faster action potentials?

larger

convergence

many presynaptic neurons provide input to influence a smaller number of postsynaptic neurons

effect of subthreshold while someone has hyperkalemia

membrane is closer to threshold. So a subthreshold stimulus would trigger AP

G-protein coupled receptors

metabotropic receptors that activate heterotrimeric G proteins The alpha subunit interacts with GDP to GTP G protein dissociates to control ion channel activity or bind to other effector proteins that make 2nd messengers slow response

fastest type of axon

myelinated

patients with hyperkalemia

need more anesthesia because their threshold baseline is higher than it should be

Relationship between graded and action potention

net effect of graded potentials det's if a neuron produces AP

is the threshold voltage the same for all channels

no

only these have Na+ voltage-gated channels

nodes of ranvier

depolarization is this type of feedback cycle

positive

Output signal occurs at

pre-synaptic axon terminal

refractory period of the previously depolarized membrane

prevents backward action potential conduction

graded potentials

produced by stimulation of responses on dendrites and soma

Describe what happens to the Na+ and K+ channels

see slide 45 - Refractory period

mechanically-gated channels

sense distortion in their immediate membrane environment

voltage-gated channels

sense voltage changes in their immediate membrane environment

What affect does hyperkalemia have on neuron AP's

shifts the resting membrane potential of a neuron closer to threshold and cause the cells to re action potentials in response to smaller graded potentials

do GPCRs control fast or slow responses?

slow

neurotransmitters are synthesized and packaged here

soma

Satellite cells

surround neuron cell bodies in PNS

axon

the action potential is regenerated here until it arrives at the presynaptic axon terminal

axon hillock (trigger zone)

the all-or-none location for initiation of action potentials

resting membrane potential

the electrical potential difference across the plasma membrane of an unstimulated living cell measured in millivolts (mV) closest to the equillibrium potential for K+

what happens to the signal of graded potentials as they move

they decrease

G-proteins

transduers that indirectly couple GPCR-NT binding to the regulation of postsynaptic ion channels

neurotransmission

transmitting information via a neurotransmitter-initiated signal

calcium entry triggers

triggers exocytosis of synaptic vesicle contents

fast axonal transport

uses proteins that function as motors to move materials along the surfaces of microtubules in both directions in the axon either in an anterograde direction or in a retrograde direction

microtubule network

where fast axonal transport occurs

Schwann cells

wrap around axon and form insulating myelin sheaths in the PNS