HSES 473 Exam 1

Differentiate between Depolarization and Repolarization.

-Depolarization: Moving the potential difference of the membrane towards 0, becoming less negative. -Repolarization: Moving the potential difference of the membrane back towards the resting membrane potential of -65mV after an action potential has occurred.

What is a twitch?

Force produced in response to a single action potential

Explain how the input of conductance (g) of a neuron affects the amount of current (I) needed to change the membrane potential a given amount (Ohm's Law).

Input conductance (g) is the neurons ability to conduct current that is applied. I=gV

What types of imaging techniques can be used to examine muscle activation?

MRI, PET-scan, Ultra Sound.

Name the three muscle fiber types. Define which fibers are slow twitch or fast twitch.

Type I - slow twitch Type IIa - fast twitch Type IIx - fast twitch

Explain the difference between voltage and ligand gated ion channels.

Voltage Gated: Change in membrane potential opens or closes the channels. Ligand Gated: A molecule has to bind to the receptor to open the channel. (neurotransmitters)

Explain the role of ligand gated vs. voltage gated ion channels in the process of AP generation at the neurmuscular junction.

Voltage gated: open calcium channels after AP (electrical) Ligand gated: deal with activated receptors (chemical)

What is the function of transverse tubules (t-tubules)?

they allow for the electrical signals to go deeper down into the muscle cells.

Units: -Potential Difference -Current -Conductance -Capacitance

- Voltage (Volts) (V) -Amps - Siemens (S) -Farad (F)

How does the Sodium Potassium pump maintain resting membrane potential? Is the pumping action an active or passive process?

-3 Na+ out, 2 K+ in -Active process

What is the approximate threshold (in mV) that must be reached during depolarization for a neuron to generate an action potential?

-50mV

What is the approximate potential difference (in millivolts) across the membrane of a neuron at rest?

-65mV

-Potential Difference (V) -Current (I) -Conductance (g) -Capacitance (C)

-Difference in the net electrical charges between 2 locations. - Rate at which electrical charges move. - The ease with which current flows (dependent upon the medium which its traveling). - The storage of electrical charge.

Name and describe the connective tissue layers in a muscle.

-Endomysium: connective tissue sheet that surrounds individual muscle fibers -Perimysium: connective tissue sheet that surrounds bundles (fascicles) of muscle fibers -Epimysium: connective tissue sheet that surrounds whole muscle

Describe the structure of a cell membrane. How does this structure contribute to the development of the resting membrane potential?

-Formed by a phospholipid bilayer -Hydrophilic heads -Hydrophobic talis -Selectively permeable -Impermeable to ions: Ion channels allow ions to flow through the membrane, which controls signal conduction.

Name and define the 4 properties of skeletal muscle

-Irritability: ability to respond to stimulus -Conductivity: capacity to propagate excitatory signals -Contractility: ability to modify its length -Adaptability: a limited growth and regenerative capacity

Describe the location (both inside and outside the cell) of ions involved in establishing the resting membrane potential of a neuron.

-Na+ and Cl- are located outside the cell -K+ is located inside the cell

Muscle force generated by the motor system is a function of what two processes?

1. The number of muscle units that are activated 2. The rate at which the motor neurons discharge action potentials

Define a motor unit.

A motor neuron and all the muscle fibers it innervates.

Define power.

Ability to generate high amounts of force in relatively short periods of time.

Which neurotransmitter is released at the neuromuscular junction to induce skeletal muscle contraction?

Acetylcholine (ACh)

What is an action potential?

An all or none event Transient reversal in the potential difference across the membrane that is transmitted rapidly along an excitable membrane.

What is electromyography?

An electrical observation of the function of muscle AP's.

Is the extracellular space of a neuron at rest more positive or negative than the intracellular space?

At rest it is more positive than the inside of the cell.

Explain the role of Ca2+, and it's regulation, in the process of muscle contraction.

Calcium binds to troponin, which opens up the binding sites on the actin filament.

Describe the flow of Na+ and K+ ions in the process of an action potential (include depolarization, repolarization, and afterhyperpolarization).

Depolarization: Voltage gated Na+ channels open, bringing Na+ into the cell, making the cell more positive. Repolarization: Voltage gated K+ channels open, bringing K+ out of the cell, making it less positive (more negative). Afterhyperpolarization: K+ channels stay open longer and the cell becomes hyperpolarized. Then the Sodium-Potassium pump kicks in, bring 3 Na+ in, and 2 K+ out.

What is the stretch shortening cycle?

Eccentric contraction, followed by concentric contraction Ex: Squatting and swinging arms before performing a vertical jump

Explain the difference between an electrical synapse and a chemical synpase

Electrical Synapse: Uses ions to conduct action potentials via gap junctions Chemical Synapse: Uses neurotransmitters, which binds to post synaptic ligand-gated receptors to conduct action potentials.

A post-synaptic neuron can receive currents from a pre-synaptic neuron that make the post-synaptic cell more or less likely to fire an action potential. Explain what excitatory post-synaptic potentials and inhibitory post-synaptic potentials are.

Excitatory post-synaptic potentials (EPSP): response to depolarizing current. Should result in an AP. Inhibitory post-synaptic potentials (IPSP): response to hyperpolarizing current. Could, but might not result in an AP, makes it harder for an AP to occur.

Do myelinated neurons propagate action potentials faster or slower than unmyelinated neurons?

Faster, unmyelinated neurons don't conduct action potentials as quickly. (MS)

You are trying to determine which initial starting position will allow you to achieve the highest vertical jump. If you start in a squatted position and jump vertically, will you produce more, or less, force than if you had performed a countermovement jump? What are the mechanisms involved in increasing force production (and allowing you to jump higher) when a countermovement jump is performed?

Force produce = less -Increased time to develop force -Storage and release of elastic energy -Force potentiation (force from individual cross-bridges is enhanced as a consequence of the preceding stretch) -Stretch reflex (capacity of additional sensory feedback associated with the forced lengthening of the muscle at the beginning of the stretch-shortening cycle)

What happens to the myelin sheath as a result of multiple sclerosis? Will the propagation of action potentials be impaired in a patient diagnosed with MS?

In patients with MS their neurons myelin sheath's are attacked. The process of propagating an action potential is slower in patients with MS.

How does the neuron size affect input conductance of a neuron? How does the relationship between neuron size and input conductance affect the ease of changing the membrane potential? What is the importance of this in terms of generating action potentials?

Input conductance is directly proportional to the neuron size and density of resting ion channels. Smaller neurons have a smaller input conductance (g), which means there is a larger change in membrane potential for a given current (I) in smaller neurons. Since the voltage threshold is similar in neurons of all sizes, the smallest neurons will achieve the required change in potential to reach threshold with the smallest current first, and discharge an action potential first.

The force a muscle can produce is influenced by sarcomere length, and the corresponding overlap of the myofilaments. What sarcomere length (e.g., shorter length, intermediate length, or long length) allows for optimal intramuscular tension, and therefore maximum force production?

Intermediate length, too short and they are already contracted and can't form as many cross bridges, too long and they are too stretched out to form cross bridges.

What is presynaptic inhibition? How are interneurons involved in this process?

Interneuron decreases amount of neurotransmitter released by innervated neuron.

Which positively charged ion tends to "leak" from inside a neuron to the extracellular space through resting ion channels? Does the inside of the neuron become more negative or positive as a result of this outward ion "leak"?

K+ ions leak through potassium leak channels, making the inside of the cell more negative.

How does neuron size affect the input capacitance of a neuron? How does the relationship between neuron size affect the ease of changing the membrane potential? What is the importance of this in terms of generating action potentials?

Larger neurons require a great amount of capacitive current to charge the capacitor; therefore it takes them longer to realize a significant amount of iconic current and the corresponding change in membrane potential. They take longer to generate an action potential.

What is electrotonic conduction? Explain how dendrite diameter and length affects the transmission of current.

Membrane conductance from extracellular to intracellular (across the membrane) and axial conductance along the length of the neuron. Transmission of current decreases with length and increases with diameter.

Explain the relationship between motor neuron size and the properties of the motor neuron.

Motor neurons are activated in order of increasing size.

In what order (size principle) are motor units recruited during a voluntary muscle contraction?

Motor units are recruited from smallest to largest.

What is axonal transport, and why is this process important in neurons?

Movement of products form cell body of a neuron to the neurotransmitter release sites (orthograde), as well as moved back to the cell body (retrograde).

What is the function of muscle spindles and Golgi tendon organs? What neurons do these receptors utilize to provide proprioceptive input to the spinal cord?

Muscle spindle: provides feedback about the rate of muscle lengthening via 1a afferent neurons. Golgi Tendon Organs: Use 1b sensory neurons, measures the change in muscle tension.

Under what conditions is neuromuscular transmission from the alpha motor neuron to the muscle cell potentially impaired? Include pharmacological, poisonous, and disease possibilities.

Pharmacological: Drugs that bind to ACh receptors instead or prevent the breakdown of ACh can be used to paralyze muscle cells for surgical procedures. Poisonous: Snake venom (alpha bunguotoxin) reduces the ability of the nerve terminal to release ACh. Disease: A disease that affects the neuromuscular junction

What does rate coding refer to?

Rate at which the motor neurons discharge action potentials.

What is the relationship between conductance and resistance?

Resistance (R)= 1/g Resistance is the reciprocal of conductance

Are slow twitch fibers more, or less, fatigue resistant in comparison to fast twitch fibers?

Slow twitch fibers are more fatigue resistant than fast twitch fibers. They are more of an endurance muscle. They can last a longer period of time without fatigue.

How does motor neuron size, and the related motor neuron properties, affect the activation and behavior of that motor neuron?

Smaller motor neurons can reach threshold to fire an action potential quicker than larger motor neurons

Diagram the steps in the cross bridge cycle, including the role of ATP in the process.

Step 1 cross bridge formation: phosphorylated myosin head attaches to an actin myofilament Step 2 the power stroke: 1) ADP and Pi are released from the myosin head 2) Shape change pulls the actin towards the M line Step 3 cross bridge detachment: ATP attaches to myosin, breaking the cross bridge Step 4 cocking of the myosin head: attached ADP is hydrolyzed by myosin ATPase into ADP + Pi, bringing it back to a high-energy state

The force exerted by a muscle during a voluntary contraction depends on what three things?

The # of activated motor units The contractile properties of the motor units The mechanical characteristics of the connective tissues to which the contractile proteins are attached

What is the function of the SR in the process of muscle contraction?

The SR stores the Ca2+ that is released in order for the muscle contraction to occur.

What gene is affected (i.e., gene mutation) in Duchenne Muscular Dystrophy? How does this gene mutation affect muscle, and what symptoms do a patient experience as the disease progresses?

The absence of the dystrophin gene. Dystrophin links the filaments of the muscle to the sarcolemma, which helps produce the force of muscle contraction. Symptoms: Muscle wasting and weakening, eventually patients are wheelchair bound, around the age of 12

During intense exercise, why does the plasma K+ concentration increase?

The accumulation of action potentials occurring causes K+ to be flushed out of the cell for depolarization of the cell.

You are struggling to curl a very heavy dumbbell. How does the dumbbell's external force (i.e., load) affect the contraction velocity of your biceps muscle? What would happen to the contraction velocity of your biceps muscle if you lifted a very light dumbbell instead?

The contraction velocity is much slower, but would be quicker if you were lifting a lighter dumbbell.

Larger diameter axons have greater axial conductance than small diameter neurons. As result of their size, will conduction velocity tend to be faster or slower in large diameter neurons?

The larger diameter of the axons, the faster the velocity.

What is occuring during the afterhyperpolarizatin phase of the action potential? Is the membrane potential during this period more or less negative than the resting membrane potential prior to depolarization?

The membrane potential is less negative than the resting membrane potential as "too much" K+ has been pumped out of the cell, causing a refractory period, where there can't really be any action potentials fired. Then the Sodium-Potassium pump works to restore the membrane potential to the resting value.

Explain how the information in an AP on the sarcolemma is translated to muscle force production at the level of the myofibrils.

The neuron releases ACh and AP is transferred to the sarcolemma. The AP travels down the sarcolemma and down the T-tubules, where it passes to the SR. This causes the Ca2+ gates to open, and Ca2+ diffuses out of the SR and amongst the myofilaments, where it binds to troponin, opening the binding sites on actin.

Explain the role of, and relationship between, the thick and then myofilaments during a muscle contraction.

The thin filament is actin, and the thick filament is myosin. The two myofilaments are the structures that attach to each other and move to generate force.

Are slow twitch fibers capable of producing more, or less, force in comparison to fast twitch fibers?

They typically generate less force compared to fast twitch fibers.

Peak power is obtained at intermediate loads and intermediate velocities. True or False?

True, Too light of a load too quick, but not enough force Too heavy of a load too slow

Are slow twitch fibers innervated by small or large motor neurons? What about fast twitch fibers? How does the size of the motor neuron innervating each fiber type affect contraction speed?

Type I: small neurons Type IIa: large neurons Type IIx: large neurons Small neurons have a slow contraction speed, and larger neurons have a faster contraction speed.

Ohm's Law

V=IR -----> I=gV R= resistance g=conductance

Where are the motor neuron cell bodies located (be specific)?

Ventral horn of spinal cord, or brain stem

Describe the role of Calcium in the process of neurotransmitter release from a presynaptic membrane.

When an AP is propagated on a presynaptic cell, voltage gated calcium channels release calcium into the cell, causing exocytosis of vesicles containing neurotransmitter, then the neurotransmitter diffuses across the synaptic cleft to bind to receptors on the post synaptic membrane and active those receptors.

What is motor unit synchronization?

When several motor units fire at once.