Cell Signaling, Neurons, Action Potentials, and Muscles

What is the distribution of ions on the inside and outside of a neuron's membrane?

Na+ ions are outside and K+ ions are inside the cell

What is the charge difference of a polarized neuron at resting potential?

Outside is positive, inside is negative

Which type of hormones would have an intracellular receptor? Why?

Small or hydrophobic chemical messengers would have an intracellular receptor because they can readily cross the membrane and activate receptors. Examples include steroid and thryroid hormones

What type of ligand would have an extracellular receptor?

Water-soluble ligands because they can't readily cross the plasma membrane.

What is a transcription factor?

causes a gene to be turned on; may be the final activated molecule in the signaling pathway

What is a ligand gated ion channel? Where are they found? What ion do they let in to initiate an action potential?

It is found in the nervous system. When a ligand binds to the receptor protein, the receptor changes shape. The ligand gated ion channel allows some, such as Na+ and K+ to pass through and the diffusion of of ions through open channels triggers an electrical signal

What is the function of the sodium potassium pump? What specifically does it do and how does it do it?

It uses ATP to maintain K+ and Na+ gradients across the membrane.

Three Steps of Cell Signaling

Reception, Transduction, Response

Reception

A signal molecule binds to a receptor protein found in the plasma membrane, causing the receptor to change shape, which is often the initial transduction of the signal. The binding between the ligand/first messenger and the receptor is very specific.

Transduction

Multistep pathways that spread and amplify the signal throughout the cell. Fewer molecules can yield a larger cellular response, and multistep pathways can provide more opportunities for coordination and regulation. Activated receptors will activate the next protein until it reaches the one that will produce a response

Response

May occur in the cytoplasm or the nucleus, the signaling pathway ends in either turning on a gene to make a new protein or changing the activity of a pre-existing protein

Describe what a g protein coupled receptor is and how it works

It is a receptor found in the plasma membrane. When a G protein activates it, it moves horizontally to activate a membrane enzyme

Differentiate between first messenger (ligand) and second messenger.

Ligands are extracellular, small, and hydrophobic so they can readily cross the plasma membrane. Second messengers are small, non-protein, and water-soluble and spread across the cell by diffusion. They are released by the cell in response to the first messengers binding to a receptor

What properties do second messengers have? List two examples of second messengers.

They are small, non-protein, and water soluble and released in response to first messengers binding to a receptor. They are spread acorss the cell by diffusion. Examples include Ca2+ and cAMP

How do neurotransmitters affect postsynaptic cells?

ion channels in the postsynaptic membrane to open or close

What is myelination of a neuron?

the myelin sheath insulates the axon, which increases the action potential

How does a myelinated neuron transmit an action potential?

Nodes of Ranvier are gaps in the myelin sheath where voltage-gated Na_ channels are found, which is where action potentials are formed. The action potentials jump between nodes of ranvier

What direction does the information flow along a neuron?

It flows from the dendrites of the pre-synaptic cell and down its axon towards the synapse, the space between the neurons

What is the difference between paracrine and endocrine signaling?

In paracrine signaling, messenger molecules, or local regulators are secreted btravel to nearby cells

What happens during phosphorylation?

A phosphate group is added

What is a phosphorylation cascade?

a signaling pathway that involves both phosphorylation and dephosphorylation

What happens at the axon terminal to cause the neurotransmitter to be released?

depolarization of the terminal and (2) the presence of calcium ions (Ca2+) in the extracellular fluid

Sacromere

contracting unit of the muscle

Actin

thin filament

Myosin

thick filament

Presynaptic Cell

the cell passing a signal

Postsynaptic Cell

the cell receiving a signal

GABA

inhibitory postynaptic potential

Acetylcholine

excitatory postsynaptic potential

Hyperpolarization

too much K+ rushed out, cell is further from the threshold so there is no action potential

Saltatory Conduction

action potentials jump from a node of ranvier to another

What is the specific role of calcium during a muscle contraction? How does it get back into the SR?

Ca2+ binds to tropomyosin and moves it out of the way, revealing myosin binding sites. It is pumped back into the SR to lower the concentration in the sarcoplasm

How do myosin and actin interact during a muscle contraction?

myosin filaments reach out to grab actin filaments and bring them closer

What causes hyperpolarization? Can a neuron fire when it is hyperplolarized?

K+ channels open, so K+ diffuses out of the cell, making it more negative. It is further from the threshold, so it can not send a message

Differentiate between a sensory neuron and a motor neuron

Sensory Neurons is to send sensory signals from sensory organs to the central nervous system. Motor Nerves are responsible for sending motor commands from the central nervous system to the sensory organs to initiate actions.

Differentiate between protein kinase and protein phosphatase

Protein kinase adds a phosphate group and phosphatase removes a phosphate group, which turns off a signal. it also makes kinases available to be reused, enabling the cell to respond to the signal again

Describe the transmission of a message from a neuron to a muscle, starting with a stimulus and ending with the muscle contraction.

When the nervous system signal reaches the neuromuscular junction a chemical message is released by the motor neuron. The chemical message, a neurotransmitter called acetylcholine, binds to receptors on the outside of the muscle fiber. That starts a chemical reaction within the muscle.