exam 1 - LECTURE

Question 1

Features of the skeletal muscle neuromuscular junction?

 What transmitter is involved?

Answer 1

Transmitter Involved:

Acetylcholine (ACh) is the primary neurotransmitter released by motor neurons at the neuromuscular junction (NMJ).

When an action potential reaches the axon terminal of the motor neuron, ACh is released into the synaptic cleft, where it binds to receptors on the muscle fiber’s membrane (the motor end plate).

Question 2

Features of the skeletal muscle neuromuscular junction?

How reliable is the synapse?

Answer 2

Synapse Reliability:

The neuromuscular junction is a highly reliable synapse.

Every time a motor neuron releases ACh, it almost always leads to an action potential in the muscle fiber, ensuring muscle contraction.

Question 3

What is the motor end plate + motor neurons

Answer 3

The motor end plate is a specialized area of the muscle fiber’s membrane at the neuromuscular junction.

It contains nicotinic acetylcholine receptors (nAChRs), which bind ACh, leading to an influx of sodium ions (Na⁺) into the muscle cell, causing depolarization.

Smaller motor units (with slow-twitch fibers) are recruited first, allowing for fine, precise movements.
As more force is required, larger motor units (with fast-twitch fibers) are recruited.

This process is known as Henneman’s Size Principle.

Question 4

In order for crossbridge cycling to occur, the actin-myosin complex must be broken by what?

Answer 4

• The actin-myosin complex is broken when ATP binds to myosin, allowing the myosin head to detach from actin.

Question 5

Which of the following is TRUE about laminar flow in the circulatory system?
What is laminar flow?
When is it disrupted?
What is the relevance for measuring blood pressure?

Answer 5

Laminar Flow in the Circulatory System:
* Definition: Laminar flow refers to the smooth, orderly flow of blood through vessels.
* Disruption: It is disrupted by turbulence, often caused by high flow rates or vessel constrictions.
* Relevance to Blood Pressure: Turbulence (rather than laminar flow) is detected when measuring blood pressure via a cuff and stethoscope.

Question 6

Which of the following does NOT use ACh as its main neurotransmitter?

 What cell types have we seen that use Ach?

 What cell types have we seen that use other neurotransmitters?

Answer 6

Cell Types That Use Acetylcholine (ACh):

Motor Neurons at the Neuromuscular Junction (NMJ): Somatic motor neurons

Parasympathetic Neurons:

Preganglionic Parasympathetic Neuron

Postganglionic
Parasympathetic Neurons

Some Autonomic Ganglia:
The preganglionic neurons of both the sympathetic and parasympathetic systems release ACh to activate postganglionic neurons via nicotinic receptors.

CELLS THAT DONT USE ACH:

The sympathetic nervous system primarily uses norepinephrine (NE)

postganglionic sympathetic neurons

Question 7

What are the factors affecting the force generated by individual muscle fibers?

Answer 7

Fiber Length (Length-Tension Relationship):

(sarcomere length) at which muscle fibers generate the most force. This corresponds to the alignment of actin and myosin filaments, allowing for maximal cross-bridge formation.

Too Stretched or Too Compressed

Stimulation Frequency (Temporal Summation):

Twitch , Summation , to Tetanus

Muscle Fatigue: (Lactic acid buildup / excess K+)

Muscle Fiber: (fast twitch vs slow twitch)

Question 8

What causes summation and tetanus in individual muscle fibers?

Answer 8

Summation and Tetanus:
* These occur due to the frequency of action potentials. If stimuli are frequent enough, they cause sustained contraction (tetanus).

Question 9

What mechanism regulates the force generated by a whole muscle?

Answer 9

Motor Unit Recruitment (Spatial Summation):

Small motor units control fewer muscle fibers and
Large motor units control many muscle fibers and

Henneman’s Size Principle: Smaller motor units, which control slow-twitch fibers, are recruited first, and as more force is needed, larger motor units controlling fast-twitch fibers are recruited.

AND

Rate Coding (Temporal Summation):

Stimulation Frequency: The frequency at which motor neurons fire action potentials can affect the force output.

Question 10

Systole accounts for what % of the cardiac cycle (at rest)?

Answer 10

• Systole accounts for roughly 1/3 of the cardiac cycle at rest.

Question 11

Cardiac Cycle: STEP 1 - PHASE 2 (closed)

Answer 11

STEP 1 - PHASE 2 (closed)

Isovolumetric Contraction

Systole begins

Question 12

Cardiac cycle STEP 2 - PHASE 3 (OPEN)

Answer 12

Ventricular Ejection

Full systole

Question 13

Cardiac Cycle STEP 3 - PHASE 4 (CLOSED)

Answer 13

Isovolumetric Relaxation

diastole begins

Question 14

Cardiac Cycle STEP 4 - PHASE 1 (OPEN)

Answer 14

Ventricular filling
full diastole

Question 15

Systole

Answer 15

Systole (Contraction Phase):

During systole, the heart’s ventricles contract, pumping blood into the arteries:

Left Ventricle: Pumps blood into the aorta (systemic circulation).

Right Ventricle: Pumps blood into the pulmonary artery (pulmonary circulation).

AV valves (mitral and tricuspid) close and semilunar valves (aortic and pulmonary) open

Question 16

Diastole

Answer 16

Diastole is when the heart relaxes, allowing the ventricles to fill with blood.

The semilunar valves close

The AV valves open

Atrial contraction occurs at the end of diastole, completing ventricular filling before the next systole begins.

Question 17

What are the differences between fast-twitch and slow-twitch muscle fibers?

Answer 17

Fast-Twitch vs. Slow-Twitch Muscle Fibers:
* Fast-Twitch: Quick, powerful contractions, fatigue quickly, rely on anaerobic metabolism.
* Slow-Twitch: Slower contractions, fatigue-resistant, rely on aerobic metabolism.

Question 18

What is MAP for a patient with a diastolic pressure of X and a systolic pressure of Y?

Answer 18

Mean Arterial Pressure (MAP):
* MAP = Diastolic Pressure + 1/3 (Systolic Pressure - Diastolic Pressure).

Question 19

In pacemaker potentials in cardiac muscle cells, what is the correct sequence of events that takes place following an action potential? Which channels open when?

Answer 19

• The sequence includes the opening of funny channels (If) to allow influx of Ca slowly

calcium channels (I_Ca) (T - TYPE THENN THRESHOLD REACHES TO L -TYPE TO OPEN!!!

potassium channels (I_K) for repolarization.

Question 20

How do autonomic inputs change the rate of pacemaker potentials? Which channels are affected by what neurotransmitters?

Answer 20

• Parasympathetic (ACh): Slows heart rate by increasing K+ permeability.
• Sympathetic (NE): Increases heart rate by increasing Ca2+ and Na+ influx.

Question 21

What are the properties of Purkinje fibers in the heart? (contractile? conduction? pace makers?)

Answer 21

Conduction Specialized: Purkinje fibers are specialized for rapid conduction of electrical impulses rather than for contraction. They spread action potentials quickly

Low Pacemaking Ability: Although Purkinje fibers have some inherent pacemaker activity, their primary function is conduction, and their pacemaking capability is much slower than the SA or AV nodes.

Purkinje fibers deliver the action potential to the ventricular muscle, enabling the ventricles to contract simultaneously and forcefully

Question 22

Which ventricle has thicker walls?

Answer 22

• The left ventricle has thicker walls due to the higher pressure needed to pump blood to the systemic circulation.

Question 23

What are the possible pathways for pre-ganglion sympathetic nerve fibers that enter the sympathetic chain? We described 3 pathways.

Answer 23

Synapse at the Same Level

Ascend or Descend the Chain

Bypass the Chain (Splanchnic Nerves)

Question 24

How do you calculate stroke volume? What are end diastolic volume and end systolic volume?

Answer 24

• Stroke Volume = End Diastolic Volume (EDV) - End Systolic Volume (ESV).

Question 25

How do you calculate Cardiac Output (CO)?

Answer 25

• CO = Stroke Volume × Heart Rate