lab midterm

negative feedback loop

counteracts or reverses a change to bring the body back to homeostasis. This is the most common type of feedback loop in the body.

To stabilize conditions and maintain equilibrium.

• ex: Body temperature regulation, blood sugar regulation, blood pressure control.

purpose of negative feedback loop

positive feedback loop

amplifies/enhances a change rather than reversing it. These loops push the body further from its normal state temporarily, for a necessary function.

To intensify a process until a specific event is completed.

• ex: Blood clotting, childbirth, lactation.

purpose of positive feedback loop

the body’s ability to maintain stable internal conditions

• Importance: Keeps the body functioning properly despite external changes

What is homeostasis, and why is it important?

When blood sugar is high, insulin lowers it. When blood sugar is low, glucagon raises it.

(Brings levels back to normal)

How does a negative feedback loop maintain blood sugar levels?

Labor contractions → release of oxytocin → stronger contractions

(Process keeps increasing until birth)

Why is childbirth an example of a positive feedback loop?

The response would continue & intensify, which could be dangerous/harmful to body

What would happen if a positive feedback loop continued without stopping?

Osmosis

Water moves from an area of low solute concentration (more water) to an area of high solute concentration (less water).

Semipermeable Membrane

The dialysis tubing allows water to pass but not sucrose.

Tonicity

Determines the direction of water movement based on solute concentration.

Diffusion

Movement of solutes (particles) from high → low concentration

• ex: Oxygen moving from lungs into blood

Electrolytes

ions in solution that conduct electricity

• Importance: Maintain fluid balance, Help nerve signals, & Enable muscle contraction

semipermeable membrane

a barrier that allows certain molecules (usually small) to pass through while blocking others.

• ex: The cell membrane acts as this, regulating what enters and exits the cell.

Hypertonic Solution

A solution with a higher solute concentration than the inside of the cell. Water moves out of the cell, causing it to shrink (crenation in animal cells, plasmolysis in plant cells)

Hypotonic Solution

A solution with a lower solute concentration than the inside of the cell. Water moves into the cell, causing it to swell and possibly burst (lysis in animal cells, turgid in plant cells).

Isotonic Solution

A solution with an equal solute concentration as inside the cell. No net water movement occurs, and the cell remains the same size.

motor unit

consists of a single motor neuron and all the muscle fibers it innervates. When the motor neuron sends an action potential, all the connected muscle fibers contract simultaneously.

It extends from the spinal cord and branches to multiple muscle fibers. At the neuromuscular junction, the neuron releases a neurotransmitter to stimulate muscle contraction. More motor units recruited = greater muscle force.

How Does a Motor Unit Innervate Muscle Fibers?

Calcium ions (Ca²⁺) enter, triggering the release of acetylcholine into the synaptic cleft.

What Ion Moves Into the Axonal Ending to Trigger Neurotransmitter Release?

Calcium ions (Ca²⁺) bind to troponin, exposing binding sites on actin, allowing myosin to form cross-bridges and generate contraction.

What Ion Initiates the Sliding Filament Mechanism in Skeletal Muscle? 

electromyogram (EMG)

a recording of electrical activity produced by skeletal muscles during contraction. 

muscle twitch

a single, brief contraction followed by relaxation.

It consists of:

1. Latent period – Time between stimulus & contraction onset. 

2. Contraction period – Muscle shortens.

3. Relaxation period – Muscle returns to resting state.   

4. Myogram Appearance: A single peak with distinct phases. 

Treppe

the 'staircase effect,' where successive twitches increase in strength due to increased calcium availability. 

• Myogram Appearance: A staircase-like increase in tension with repeated stimuli.

Muscle fatigue

occurs when a muscle cannot maintain contraction due to ATP depletion, lactic acid buildup, or ion imbalances. 

synapse

a junction between a neuron and another cell where neurotransmitters transmit signals.

because it can respond to electrical stimuli (nerve impulses) and generate an action potential, leading to contraction.

How is Muscle Tissue Excitable? 

Isotonic contraction

Muscle changes length while maintaining tension (e.g., lifting a weight). 

• Concentric: Muscle shortens (lifting a dumbbell). 

• Eccentric: Muscle lengthens (lowering a dumbbell).

Isometric contraction

Muscle generates tension but does not change length

• ex: holding a weight steady

Amplitude

the height of the EEG waves, which represents the strength of electrical activity in the brain.

Frequency

how many times a wave cycles (goes up & down) per second.

Awake, alert, attentive, in the frontal lobe 

What are beta waves, and when are they most commonly observed? 

Beta and/or gama 

Which type of brain waves would you expect to dominate when someone is taking an exam?

Alpha

If someone is meditating or in a relaxed state, what brain waves would you expect to see?

Alpha block occurs

Why do alpha waves disappear when a person starts doing mental calculations?

Sleep disorders or epilepsy

What would an EEG be useful for diagnosing? 

Gama

• HINT DEEP CONCENTRATION

If a person is in deep concentration while solving a puzzle, what brain wave pattern would likely be observed?

reflex arc

the pathway taken by nerve impulses to produce an automatic response without conscious thought.

Action potential occurs 

What happens when a neuron reaches the threshold potential? 

For an action potential to occur it has to reach threshold potential (-55mv). If the stimulus is not strong enough to depolarize the membrane potential to threshold the neuron will return to its resting membrane potential of -70mv. 

What is the 'all-or-nothing' principle of action potentials?

No because it would not reach threshold potential

If a neuron is at -60 mV, will an action potential occur? Why or why not?

sodium (Na+ ) channels open, and sodium rushes into the cell causing the membrane potential to become more positive

During an action potential, what ion moves into the cell during depolarization? How does membrane potential change if it is depolarized? 

Potassium (K+) leaves during this, causing the membrane potential to become negative and return back to resting membrane potential 

What ion leaves the neuron during repolarization?

Prevents back to back action potentials from being fired. 

Why is the refractory period important for neuron function? 

Excitatory post Synaptic Potential (EPSP)

makes it more likely to fire an action potential 

inhibitory post synaptic potential (IPSP)

causes the MP to repolarize, makes it less likely to fire an action potential.