Bio 14 Exam 2

homeostasis

A self-regulating process for maintaing internal stability while adjusting to changing external conditions

Direction of Homeostasis

1.) Sensors: Detect the issue to homeostasis

2.) Integrators: process info from multiple sensors

3.) Effectors: do something about the stimulus

Negative Feedback

A thing acts as its own signal to counteract something else, stabilizes systems

positive feedback

a thing acts as its own signal to do something even more, self-reinforcing. Generally not important to homeostasis

Examples of Homeostasis for thermoregulation of mammals

Isotonic

Solutions have equal solute concentration; no net movement of water (cell stays the same).

hypertonic

A solution with higher solute concentration than another; water moves out of the cell (cell shrinks).

Hypotonic

A solution with lower solute concentration; water moves into the cell (cell swells, may burst).

counter-gradient flow

when two fluids move in opposite directions, which helps maintain a constant gradient so transfer (like heat or oxygen) is more efficient. Uses energy to push molecules against the concentration gradient.

Osmosis

the passive movement of water across a selectively permeable membrane from an area of low solute concentration (high water) to high solute concentration (low water) until equilibrium is reached.

selective permability

Membrane proteins control what can and can’t cross, allows for solute gradients to form and allows for osmosis

Passive transport

No energy, facilitates flow down a gradient. Gradient flow mechanism

Active transport

Costs energy, counter-gradient flow mechanism

Human Thermregulation diagram

endotherms

internal heat generation regulated ot maintain temperature

ectotherms

can’t switch on internal heat, regulate temperature in other ways

homeotherms

keeps temperature very consistent

poikilotherms

tolerates some changes in temperature

Tempterature regulation across levels of organization

Internal communication

Chemical and electricity based communication within the body with chemical being slower and electric being faster

Chemical signals

Longer lasting, more general over the entire body, slower

Electric signals

Fast, short-lived, targeted to specific regions of the body

Hormone

A signal molecule that triggers a particular response in distant target cells, a type of chemical signal

Endocrine signals

Hormones carried by blood, a type of chemical signal

Blood glucose regulation

Blood Glucose Regulation (cellular level)

Key points about Blood Glucose Regulation

1.) insulin binds to a receptor on cell which amplifies the signal, positive feedback

2.) glucose transport proteins move towards cell membrane

3.) glucose enters the cell through glucose transport proteins via facilitated diffusion

Big Picture: neuron anatomy

Dendrite

short, branch-like extensions of a neuron that receive signals from other cells and carry them toward the cell body.

Axon

a long fiber of a neuron that sends signals away from the cell body to other neurons, muscles, or glands.

Cell body (soma)

the central part of a neuron that contains the nucleus and organelles; it processes incoming signals and maintains the cell’s basic functions.

Signal

Electricity or voltage difference. Signals are either on or off (binary).

Signal strength

Comes from frequency (action potentials)

action potential

a rapid, temporary change in a neuron’s membrane potential (electrical charge) that travels down the axon as a nerve signal. It occurs when the neuron reaches a threshold, causing Na⁺ to rush in (depolarization) followed by K⁺ moving out (repolarization). Occurs because of gated channels

Signal consequence

Depends on which cell receives signal and which cell sent it

Electric potential

Separation of charge, potential to do work.

Cell membrane potential

charge difference across the membrane

Resting potential

typical membrane potential the cell maintains

Chemical gradient

Cells have a chemical gradient of potassium and sodium ions. Lots of potassium ions on the inside and sodium ions on the outside. This creates a resting potential and a charge difference.

Communication Mode: Chemical

Signal: Hormones

Sender: Organs and Tissues

Receiver: Any cell w/ right hormone receptor

Medium/Route: Blood

Communication Mode; Electrical

Signal: Action potentials

Sender: Neurons and other “excitatory cells”

Receiver: Specific, connected cells primed to receive signal

Medium/Route: Axons + synapses

Voltage gated channels

protein channels in the cell membrane that open or close in response to changes in membrane potential (voltage).

• When the membrane reaches threshold, these channels open

• Voltage-gated Na⁺ channels open first → Na⁺ rushes in → depolarization

• Then voltage-gated K⁺ channels open → K⁺ leaves repolarization

Feedback in Neurons

Positive: transmitting down the axon

Negative: for repolarlization

presynaptic neuron

the neuron that sends the signal. It releases neurotransmitters from its axon terminal into the synapse.

Postsynaptic neuron

the neuron that receives the signal. It has receptors on its dendrites or cell body that bind those neurotransmitters and respond.

Action potential and release of neurotransmitters

Neurotransmitters

chemical messengers released by neurons that carry signals across the synapse to another neuron, muscle, or gland.

How they work (quickly):

1. Released from the presynaptic neuron

2. Cross the synapse

3. Bind to receptors on the postsynaptic cell

4. Either excite (increase chance of firing) or inhibit (decrease chance)

Examples:

• Dopamine → reward, motivation

• Serotonin → mood, sleep

• Acetylcholine → muscle movement

• GABA → inhibitory (calming)