neural tissue

vs
presynaptic facilitation by serotonin

nicotinic receptors are found at cholinergic synapses in the CNS, at parasympathetic and sympathetic autonomic ganglia, and at the neuromuscular junction.

da da da daaaa.....action potentials!

muscarinic receptors are metabotropic
(g-protein coupled receptors)
which trigger a series of intracellular events using second messengers.

in a
nutshell...

continu0us
propagation along
an unmyelinated axon travels
1 meter/sec (2 mph)

graded potentials are localized, are proportional to the intensity of the stimulus and diminish as the distance from the site of stimulation increases. they may initiate a specific function in a cell such as triggering an gland cell to release its hormone via exocytosis.

cell membrane potential relies on:
1. the ECF and ICF have different composition of ions
ECF has high Na+ and Cl-
ICF has high K+ and negatively charged proteins
2. plasma membranes are selectively permeable
ions must move across via ion channels

some channels are more "accessible" than others
ex: outgoing K+ channels are "leakier" than incoming Na+ channels
proteins can not cross the membrane which contributes to cell's (-) charge

neuropeptides

1. a stimulus starts a rapid change in voltage.

2. depolarization is caused by a the opening of sodium channels causing an influx of Na+ ions.
threshold is reached.

3. repolarization results from Na+ channel closing and a large efflux of K+ ions from activated K+ channels.

4. hyperpolarization is caused by the efflux of potassium ions and closing of the potassium channels.

5. the resting state is established when the membrane potential returns to the voltage before the stimulus.

cholinergic synapses are the most common, found at:
NMJ
CNS synapses
PNS neuron/neuron synapses
NMJ/NGJ in ANS parasympathetic division

adrenergic receptors

excitatory neurotransmitters initiate a post synaptic action potential by causing depolarization of the post synaptic cell producing an
EPSP = excitatory postsynaptic potential.
inhibitory neurotransmitters cause the post synaptic cell to hyperpolarize therefore suppressing an action potential producing an
IPSP = inhibitory post synaptic potential.
remember...
it is NOT the neurotransmitter that determines how the post synaptic cell will respond but rather the post synaptic receptor of that neurotransmitter.

changing the membrane potential

nicotinic vs muscarinic cholinergic receptors

propagation of an action potential

a chemical synapse is a gap between two neurons where a nerve impulse is relayed
chemically in the form of neurotransmitters.
chemical synapses are found at junctions between two neurons and between neurons and non-neuronal cells such as muscles (neuromuscular junction) or glands (neuroglandular junction).

gated ion channels can be:
1. ligand-gated channels
2. voltage-gated channels
3. mechanically-gated

the nerve impulse

electrochemical gradients
determine
how an ion moves across a membrane.
there is a:
1. chemical gradient = the difference in solute concentration across the membrane
2. electrical gradient = difference in charge across the membrane

membrane potential = a gradient that causes ions to passively move in a one direction.
1. (+) ions are attracted to the (-) side of the membrane
2. (-) ions are attracted to the (+) side of the membrane

electrochemical gradients

think threshold

all nicotinic receptors are ionotropic (ligand-gated ion channels)
nicotinic receptors respond to drugs such as nicotine, an agonist.

the adrenal medulla is the core of the adrenal gland. it participates in the flight or fight response by secreting epinephrine (adrenaline) and norepinephrine (noradrenaline)

a graded potential is a change in the membrane potential of a cell that remains localized. depolarization occurs in all directions from the site of where the stimulus was applied.

neurotransmitter function: direct vs indirect effects

sodium/potassium pumps are driven by the hydrolysis of ATP.

these pumps move sodium and potassium ions in opposite directions against their concentration gradients to balance the movement of these ions in/out of the cell through their channels. One cycle pumps 3 sodium ions out of the cell and 2 potassium ions into the cell.

biogenic amines

but first...some background

its all about the Na+ and K+ ions...

membrane potential

refractory
period

muscarinic receptors are found at cholinergic synapses in the CNS and at postganglionic parasympathetic nerve terminals.

K+ (potassium) is a positively charged ion. With an intracellular concentration of 120 mM and an extracellular concentration of 4 mM, it shows an equilibrium potential of -90 mV which means that K+ will reach electrochemical equilibrium when the cell is 90 mV lower than its environment.

adrenergic receptors (adrenoceptors) are metabotropic. they bind catecholamines such as
norepinephrine/noradrenaline and
epinephrine/adrenaline.

speeds:
type A - 120 m/sec
type B - 40 m/sec
type C - 1 m/sec

nodes are 1-2 mm apart

electrical synapses are
electrical and mechanical connections between two neurons found at a gap junction.
An electrical synapse has channel proteins between pre/postsynaptic neurons connecting the two neurons so the electrical signal can travel straight over the synapse.

saltatory
propagation along a myelinated axon travels 18-120 m/sec
(40-270 mph)

when a cell is at its resting potential of -70mv, it is said to be polarized.

a shift to this resting potential towards a less - potential by the movement of Na+ ions into the cell = depolarization

restoring the normal resting potential after depolarization is called

repolarization

an increase in the negativity of the resting potential = hyperpolarization

speaking of neuromodulation...
presynaptic inhibition by GABA

current =
a measurement of ions crossing the membrane

temporal vs spatial summation
a single excitatory post synaptic potential (ESPS) (0.5mv)won't provide enough stimulation to reach threshold generating an action potential but individual ESPSs can combine to reach threshold. This can occur 2 ways...

spatial summation = multiple presynaptic neurons release enough neurotransmitter to reach threshold
temporal summation = one presynaptic neuron releases neurotransmitter many times over a period of time to reach threshold

types of
propagation

cholinergic synapses release acelylcholine

equilibrium occurs when concentration gradient = electrical gradient

nicotinic muscarinic

other neurotransmitters and their functions

neurotransmitter imbalances

current = a measurement of ions crossing the membrane. the resistance of the membrane slows down ion exchange which causes the current to be weak.

the synapse

an ionotropic receptor is a membrane protein that responds to ligand binding by allowing ions to move across the membrane through an open ion channel.