Exercise Physiology (Exam 1)

Chapter 3… (Neural Control of exercising muscle)

What is the structure and function of cell body?

• Contains receptors for neurotransmitters

• Receives impulses (have receptors)

What is the structure and function of dendrites?

• Contains receptors for neurotransmitters

• Receive impulses (have receptors)

What is the structure and function of the axon?

• sends action potentials that starts at the axon hillock

• has end branches (terminals) with neurotransmitters.

Anatomy of a neuron

What are the functions of the plasma membrane?

• a boundary separating the cytoplasmic (intracellular) substances from the extracellular environment of the cells.

• A main function to transport substances (ions, nutrients, gases) into and out of the cell.

• it has receptors (proteins) for chemical substances (neurotransmitter and hormones)

what is the plasma membrane composed of?

• fats

what does the lipid bilayer do?

• moves lipid soluble molecules

• Soluble = dissolve or mix in

what are the different kinds of plasma membrane proteins?

• peripheral

• Integral

What is the difference between a channel and a carrier (transporter)

• They both are proteins in the membrane AKA facilitators and helpers

• Channels = Ions

• Carriers (transporters) = Glucose + Amino Acids

What is resting membrane potential?

• negative ions along inside of cell membrane + positive ions along outside

• potential energy difference at rest is -70 mV

Resting potential exists:

1. concentration of ions different inside and outside

• extracellular fluid high Na+ and low K+

• intracellular fluid high K+ and low Na+

2. membrane permeability differs for Na+ and K+

What is open and closed at resting potential?

• All voltage gated Na+ and most voltage gated K+ channels are closed

• - 70mv

Movement through the plasma membrane – what can and cannot cross, and why?

• The plasma membrane is selectively permeable, meaning it maintains homeostasis even though inside and outside compositions differ.

• K⁺ is higher inside the cell (intracellular fluid), while Na⁺ is higher outside the cell (extracellular fluid).

• Lipid-soluble molecules (O₂, CO₂, fatty acids) diffuse directly through the lipid bilayer.

• Large, non-lipid-soluble molecules (glucose, amino acids) and ions cannot diffuse freely and require transport proteins to cross the membrane.

What do both simple and facilitated diffusion rely on?

• movement (diffusion) relies on using a concentration gradient

What is simple diffusion?

• the passage of lipids (free fatty acids) through the plasma membrane

• High to low concentration

What is facilitated diffusion?

• uses membrane proteins

• goes from high to low concentration

• uses channels or carriers (Facilitators or helpers)

• facilitates movement of Ions + electrolytes

• moves molecules or electrically charged molecules across the plasma membrane

What is important to remember for channels?

• they are gated meaning the the neurotransmitter must bind to a receptor.

what are leak and gated ion channels?

Gated ion channels: opened or closed by certain stimuli

• open in response to small molecules that bind to receptor proteins

What is ATP

• Adenosine Triphosphate = the primary form of energy in the body

• ATPase cleaves one phosphate to create energy for the cell to use.

What kind of active transport are Action potentials?

• Primary active transport

What is the purpose of ATP in action potentials?

• ATP is not used during depolarization or repolarization.

• ATP is used by the Na⁺/K⁺ ATPase to maintain ion gradients (3 Na⁺ out, 2 K⁺ in) after action potentials occur.

• These gradients allow future action potentials to happen, but ATP does not directly cause an action potential.

Does Na⁺ concentration inside the cell ever become higher than outside during an action potential?

No.
Only a very small amount of Na⁺ enters during an action potential, so overall Na⁺ concentrations do not significantly change.

What gradients does the Na⁺/K⁺ pump work against?

• Na⁺ pumped out: against both concentration and electrical gradients.

• K⁺ pumped in: against the concentration gradient (with the electrical gradient).

How does Na⁺ interact with its concentration and electrical gradients during Na⁺/K⁺ pump activity?

• Na⁺ concentration gradient: Na⁺ is high outside and low inside, so Na⁺ naturally wants to enter the cell.

• Na⁺ electrical gradient: Na⁺ is positive and the inside of the cell is negative, so Na⁺ naturally wants to enter the cell.

• Na⁺/K⁺ pump action: moves Na⁺ out of the cell.

• Therefore, Na⁺ is pumped against both the concentration gradient and the electrical gradient.

How does K⁺ interact with its concentration and electrical gradients, and how does the Na⁺/K⁺ pump move K⁺?

• K⁺ concentration gradient: K⁺ is high inside and low outside, so K⁺ naturally wants to leave the cell.

• K⁺ electrical gradient: K⁺ is positive and the inside of the cell is negative, so K⁺ naturally wants to enter the cell.

• Na⁺/K⁺ pump action: moves K⁺ into the cell.

• Therefore, K⁺ is pumped against its concentration gradient but with its electrical gradient.

characteristics of Action Potentials

resting potential of Action Potential

• Resting potential

• -70mV

• Na+ + K+ channels are closed

Phase 1 of action potential

Depolarization

• acetylcholine binds to the receptor

• channels open - the negativity inside the cell is lost

• Na+ facilitate diffuses into the cell

Phase 2 of action potential

1. Na+ channels close

2. K+ channels open and facilitated diffuses out of the cell

Phase 3 of action potential

returning to resting potential

• hyper polarization occurs because the K+ channels take longer to close compared to the Na+ channels.

• this is where primary active transport comes in so that the cell can return

• the resting membrane potential is reestablished after the voltage gated ion channels close. the sodium potassium pump is used to reestablish the resting membrane potential.