Structure and Functions of Neurons

Cell body (Soma) contains the

nucleus

The Axon

sends messages

Dendrites

receives messages from adjoining cells

Terminal Buttons

contain neurotransmitters

Resting membrane potential

the difference in voltage between the inside and outside of \n the axon membrane

Axon Voltage measures___ inside

-70 mV

What determines membrane \n potential?

\n Balance between Diffusion and Electrostatic pressure

Diffusion

molecules diffuse from regions of high concentration to low concentration (high → low)

Electrostatic pressure

force exerted by attraction or repulsion of ions

Cations

positive charge (+)

Anions

negative charge (-)

4 important ions:

• Organic ions (A-)

• Chloride ions (Cl-)

• Potassium ions (K+)

• Sodium ions (Na+)

Sodium potassium pump in membrane kicks out ___ and takes in __.

- Kicks out 3 Na+ ions

- Takes in 2 K+ ions

Sodium potassium pump in membrane keeps-

Na+ located outside cell at rest

depolarization

Reversal of membrane potential from negative \n to positive (neg. → pos.)

Ionic basis of the Action Potential:

NA+ in: (upswing of spike)

K+ out: (downswing of spike) \n Return to resting potential

The action potential is a

“all or none” event

Cable properties of the axon:

Give sub-threshold stimulation → decremental conduction

myelinated neurons (neurons with a myelin shealth) allows:

- Action potential (AP) to jump from node-to-node

- Speeds up conduction

- Energy efficient

“synapse”:

a physical gap between pre- and post-synaptic membranes of neurons

Communication between neurons:

Action potential → Terminal button (contains synaptic vesicles) → Synaptic vesicles (contain neurotransmitter) → Synapse

Neurotransmitter Release Process:

- Vesicles “docked” near presynaptic membrane \n - Action potential at the terminal opens CA++ channels \n - CA++ ions open a fusion pore \n - Vesicles release transmitter into the synapse \n - Transmitter diffuses across gap to the postsynaptic membrane receptors

- Vesicles “docked” near __? __ \n - Action potential at the terminal opens CA++ channels \n - CA++ ions open a fusion pore \n - Vesicles release transmitter into the synapse \n - Transmitter diffuses across gap to the postsynaptic membrane receptors

presynaptic membrane

- Vesicles “docked” near presynaptic membrane \n - Action potential at the terminal opens ? \n - CA++ ions open a fusion pore \n - Vesicles release transmitter into the synapse \n - Transmitter diffuses across gap to the postsynaptic membrane receptors

CA++ channels

- Vesicles “docked” near presynaptic membrane \n - Action potential at the terminal opens CA++ channels \n - CA++ ions open a __ ? __ \n - Vesicles release transmitter into the synapse \n - Transmitter diffuses across gap to the postsynaptic membrane receptors

fusion pore

- Vesicles “docked” near presynaptic membrane \n - Action potential at the terminal opens CA++ channels \n - CA++ ions open a fusion pore \n - Vesicles release transmitter into the __ ? __ \n - Transmitter diffuses across gap to the postsynaptic membrane receptors

synapse

- Vesicles “docked” near presynaptic membrane \n - Action potential at the terminal opens CA++ channels \n - CA++ ions open a fusion pore \n - Vesicles release transmitter into the synapse \n - __ ? diffuses across gap to the __ ? receptors.

- transmitter, postsynaptic membrane

Postsynaptic Receptors

- Neurotransmitter “binds” to post-synaptic \n receptors (“lock and key”) \n - Receptor activation opens ion channels \n - Ions enter, producing depolarization or \n hyperpolarization \n - Ions create a “post-synaptic potential”

- Neurotransmitter “binds” to _? (“lock and key”) \n - Receptor activation opens ion channels \n - Ions enter, producing depolarization or \n hyperpolarization \n - Ions create a “post-synaptic potential”

Postsynaptic receptors

- Neurotransmitter “binds” to post-synaptic receptors (“lock and key”) \n - Receptor activation opens _? \n - Ions enter, producing depolarization or hyperpolarization \n - Ions create a “post-synaptic potential”

ion channels

- Neurotransmitter “binds” to post-synaptic receptors (“lock and key”) \n - Receptor activation opens ion channels \n - Ions enter, producing _? or _? \n - Ions create a “post-synaptic potential”

depolarization or hyperpolarization

- Neurotransmitter “binds” to post-synaptic receptors (“lock and key”) \n - Receptor activation opens ion channels \n - Ions enter, producing depolarization or hyperpolarization \n - ? create a “_?_ potential”

• Ions, post-synaptic

Postsynaptic receptors control ion channels in 2 ways:

• directly, indirectly

Directly

(ionotropic receptors)

Indirectly

using second messenger systems (metabotropic receptors)

Ionotropic Receptors:

The ion channel opens when a molecule of neurotransmitter attaches to the binding site.

Post syaptic Potentials (PSP)’s are either-

excitatory (EPSP) or inhibitory (IPSP)

Opening NA+ ion channels is-

(EPSP) Excitatory post synaptic potential

Opening Cl- ion channels is-

(IPSP) Inhibitory Post synaptic potential

Termination of Synaptic Transmission is accomplished via:

Reuptake or Enzymatic deactivation

Reuptake:

Molecules of a neurotransmitter that has been released into the synaptic cleft are transported back into the terminal button

(transmitter is transported back into the presynaptic neuron)

Enzymatic deactivation:

an enzyme destroys the transmitter molecule

- Acetylcholine (ACh) \n - AChE – enzyme, destroys ACh

EPSP →

depolarization

IPSP →

hyperpolarization

Effects of excitation or inhibition on behavior?

Need details on the neural circuits to predict \n effects on behavior

Excitation of excitatory neurons can →

increase behavior

Excitation of inhibitory neurons can →

decrease behavior

Inhibition of inhibitory neurons can →

increase behavior

Autoreceptors are located

pre-synaptically

Autoreceptors respond to the neuron’s _?

OWN transmitter

Autoreceptors regulate amount of _? a neuron __?_.

- transmitter \n - releases (feedback mechanism)

To Activate autoreceptor →

decrease transmitter release

To Block autoreceptor →

\n increase transmitter release

(AP) Stimulate resting neuron →

__?_channels open →

Na+ enters cell →

cell is depolarized →

impulse travels down axon

Na+

(AP) Stimulate resting neuron →

Na+ channels open →

Na+ enters cell →

cell is _? →

impulse travels down axon

depolarized

(AP) Stimulate resting neuron →

Na+ channels open →

Na+ enters cell →

cell is depolarized →

impulse travels down _?

axon