pcb 3703 lec 17

What are the two types of PNS glial cells mentioned in the text?

Satellite cells and Schwann cells

Where are satellite cells typically arranged?

Around neuronal cell bodies in a ganglion

What are the two main functions of satellite cells?

Electrically insulate and regulate the exchange of nutrients and wastes

What is another name for a Schwann cell?

Neurolemmocyte

What is the physical structure of a Schwann cell?

An elongated, flat cell that ensheathes PNS axons with myelin

What is the functional result of Schwann cells ensheathing axons?

Allows for faster action potential propagation

How is myelination defined?

The process of wrapping an axon with myelin

What is myelin actually made of?

Several layers of membrane of glial cells

What gives myelin its glossy-white appearance?

High lipid content

What is the primary role of myelin on an axon?

It insulates the axon

Which glial cells form myelin in the PNS?

Schwann cells

Which glial cells form myelin in the CNS?

Oligodendrocytes

What is neuron function dependent on?

Transmission of intracellular electrical signals

How does the plasma membrane facilitate electrical signals?

By establishing ion concentration gradients

What are pumps in neuron membranes?

Membrane proteins that move substances against their concentration gradient

What do pumps require to function?

Cellular energy

Which specific pumps are found in neuron membranes?

Sodium-potassium pumps and calcium pumps

What are channels in neuron membranes?

Protein pores that allow ions to move down their concentration gradients

What happens when ion channels are open?

They allow a specific type of ion to diffuse

What are leak (passive) channels?

Channels that are always open for continuous diffusion

When do chemically gated channels open?

When a neurotransmitter binds to them

When do voltage-gated channels open?

When the membrane charge changes

What specific gates do voltage-gated Na+ channels possess?

Activation and inactivation gates

What triggers modality gated channels to open?

A specific type of sensory stimulus like temperature, pressure, or light

Where are modality gated channels primarily found?

Membranes of sensory neurons

Give an example of where modality gated channels respond to pressure.

Some receptor neurons of the skin

What channels and pumps are found across the entire plasma membrane of a neuron?

Leak channels and Na+/K+ pumps

What is the function of leak channels and pumps across the entire membrane?

To maintain resting membrane potential

What specific leak channels are mentioned for the entire membrane?

K+ leak channels

What structures make up the receptive segment of a neuron?

Dendrite and cell body

What type of channels are located in the receptive segment?

Chemically gated channels

What is another name for the initial segment of a neuron?

Axon hillock

What channels are located in the initial segment of a neuron?

Voltage-gated Na+ and K+ channels

What channels are located in the conductive segment (axon and its branches)?

Voltage-gated Na+ and K+ channels

What channels and pumps are located in the transmissive segment (axon terminals)?

Voltage-gated Ca2+ channels and Ca2+ pumps

What is another name for graded potentials in a postsynaptic neuron?

Postsynaptic potentials

What is a postsynaptic potential resulting in depolarization called?

An excitatory postsynaptic potential (EPSP)

What is a postsynaptic potential resulting in hyperpolarization called?

An inhibitory postsynaptic potential (IPSP)

Why can numerous postsynaptic potentials be generated simultaneously?

Because a postsynaptic neuron can bind many neurotransmitter molecules at once

What ion entry causes excitatory postsynaptic potentials (EPSPs)?

Na+ entry

What ion movements cause inhibitory postsynaptic potentials (IPSPs)?

K+ exit or Cl- entry

Where is the outcome of multiple EPSPs and IPSPs determined?

At the initial segment

What convergence happens at the presynaptic level for a single postsynaptic neuron?

Multiple presynaptic neurons synapse onto one postsynaptic neuron

What occurs at the axon hillock regarding EPSPs and IPSPs?

Summation of EPSPs and IPSPs

What defines spatial summation at the initial segment?

Multiple receptive regions receive neurotransmitter simultaneously

What defines temporal summation at the initial segment?

A single presynaptic neuron repeatedly releases neurotransmitter within a short period

Where does continuous conduction occur?

On unmyelinated axons

How do voltage-gated channels open during continuous conduction?

Charge opens channels, allowing charge to enter and spread to adjacent regions

Along what length of the axon does an action potential occur in continuous conduction?

Along the entire length of the axon

Where does saltatory conduction occur?

On myelinated axons

Where do action potentials occur during saltatory conduction?

Only at neurofibril nodes

Why are voltage-gated channels concentrated at neurofibril nodes?

To facilitate saltatory conduction

What happens after Na+ enters at a neurofibril node?

It starts a rapid positive current down the inside of the myelinated region

Why does saltatory conduction appear to jump?

Because the action potential occurs only at successive nodes

What are two advantages of saltatory conduction over continuous conduction?

It is much faster and uses less ATP to maintain resting membrane potential

Where are neurotransmitters synthesized and stored?

Synthesized by neurons and stored in vesicles in axon terminals

What triggers the release of neurotransmitters from vesicles?

Action potential triggering calcium entry into the axon terminal

What happens after a neurotransmitter is released from vesicles?

It binds to a receptor in a target cell

What is the ultimate effect of neurotransmitter binding to a target cell?

It triggers a physiologic response in the target cell

Approximately how many different neurotransmitters have been named?

Approximately 100

What are the four main chemical classes of neurotransmitters?

Acetylcholine, biogenic amines, amino acids, and neuropeptides

How does acetylcholine's structure compare to other transmitters?

Its structure differs substantially from other transmitters

How are biogenic amines synthesized?

By slightly modifying an amino acid

Catecholamines, such as dopamine, are made from which amino acid?

Tyrosine

Indolamines, such as serotonin, are made from which amino acids?

Histidine or tryptophan

What are three common amino acid neurotransmitters?

Glutamate, glycine, and GABA

What are neuropeptides?

Chains of amino acids, 2 to 40 amino acids long

What are two examples of neuropeptides mentioned?

Endorphins and substance P

How are neurotransmitters classified by their effect on membrane potential?

As excitatory transmitters or inhibitory transmitters

Why can some neurotransmitters excite some targets and inhibit others?

Depending on the specific receptor present on the target cell

How do direct neurotransmitters function?

They bind to receptors that are chemically gated channels for immediate postsynaptic potential

How do indirect neurotransmitters function?

They bind to receptors that involve G-proteins and second messengers

Which neurotransmitter is the best characterized?

Acetylcholine (ACh)

Where is acetylcholine used in the PNS?

To stimulate skeletal muscle

Where is acetylcholine used in the CNS?

To increase arousal

What are the building blocks from which ACh is synthesized?

Acetate and choline

Where is synthesized ACh stored?

In synaptic vesicles

What triggers the release of ACh into the synaptic cleft?

An action potential

How is ACh cleared from the synaptic cleft?

By being broken down into acetate and choline by acetylcholinesterase

What happens to acetate and choline after ACh breakdown?

They are taken up by the presynaptic cell for recycling

What determines ACh's effect on a target cell?

The specific receptor present

What are the two major receptor types for acetylcholine?

Nicotinic and muscarinic receptors

What type of receptors are nicotinic receptors?

Inotropic receptors that open ion channels and cause EPSPs

What type of receptors are muscarinic receptors?

Metabotropic receptors that activate a G protein second messenger system

Can muscarinic receptor activation result in an EPSP or IPSP?

Yes

What are four ways neurotransmitters are removed from the synaptic cleft?

Enzymatic degradation, presynaptic reuptake, diffusion/glia absorption, or drug action

How do selective serotonin reuptake inhibitors (SSRIs) work?

By influencing neurotransmitter removal to treat depression

What are neuromodulators?

Chemicals that alter responses of local neurons

What is facilitation in neuromodulation?

Modulation that causes a greater response in the postsynaptic neuron

What is inhibition in neuromodulation?

Modulation that causes a weaker response

What is nitric oxide classified as in terms of its nature?

A short-lived, nonpolar gas

Where is nitric oxide made and released in the brain?

By postsynaptic neurons

What is the proposed function of nitric oxide in the brain?

To strengthen memory by increasing release of neurotransmitters

What is an effect of nitric oxide in the peripheral nervous system (PNS)?

Blood vessel dilation

Which receptors do endocannabinoids influence?

The same receptors that marijuana influences

What are the physical properties of endocannabinoids?

Small, nonpolar molecules

Where are endocannabinoids made and released?

By postsynaptic neurons

What is the effect of endocannabinoids on presynaptic release?

Decreases presynaptic neurotransmitter release

What physiological functions do endocannabinoids influence?

Memory and appetite

What are the four major regions of the brain?

Cerebrum, diencephalon, brainstem, and cerebellum