physiology

Homeostasis

The body’s ability to maintain stable internal conditions despite external changes.

Dynamic Equilibrium

A state where variables fluctuate within a narrow range to maintain stability.

Variable

A factor that is being regulated (e.g., temperature, pH).

Receptor

Senses changes (stimuli) and sends information to the control center.

Control Center

Determines the set point and sends signals to respond to changes.

Effector

Carries out the response to restore homeostasis.

Negative Feedback

Reduces or opposes the initial stimulus to return the system to normal.

Positive Feedback

Enhances the initial stimulus, pushing the system further from the set point.

Nervous System

Provides communication for regulation in homeostasis.

Endocrine System

Works alongside the nervous system to help regulate homeostasis.

Homeostatic Reflexes

Involuntary and often unconscious responses that maintain homeostasis.

What is the main difference between negative and positive feedback mechanisms?

Negative feedback reduces the effect of the stimulus, while positive feedback enhances it.

What are the three components of a homeostatic mechanism?

Receptor, Control Center, Effector.

Give one example of negative feedback.

Regulation of blood glucose: insulin lowers blood sugar levels after a meal.

Give one example of positive feedback.

During labor, oxytocin increases uterine contractions until birth.

Plasma Membrane

The outer membrane of the cell that controls what enters/exits.

Fluid Mosaic Model

Describes the membrane as a fluid structure with proteins embedded.

Phospholipid

A molecule with a hydrophilic head and hydrophobic tail.

Hydrophilic

Water-loving; dissolves in water.

Hydrophobic

Water-fearing; does not dissolve in water.

Amphipathic

Molecules with both hydrophilic and hydrophobic regions.

Integral Proteins

Span the membrane, function as receptors or transporters.

Peripheral Proteins

On the surface; act as enzymes or for cell shape changes.

Selectively Permeable

The membrane's ability to allow certain molecules to pass while blocking others.

Criteria for Passive Transport

Does not require energy, includes diffusion and osmosis.

What does 'amphipathic' mean?

A molecule has both polar (water-attracting) and nonpolar (water-repelling) regions.

What are the three main components of the plasma membrane by weight?

Proteins (62%), lipids (35%), carbohydrates (3%).

Diffusion

Movement of molecules from high to low concentration due to random motion.

Osmosis

Diffusion of water across a membrane.

Aquaporins

Channels in the membrane that allow water to pass.

Osmolarity

Number of solute particles in a solution (osmol/L).

Tonicity

The ability of a solution to change a cell's shape by altering water volume.

Isotonic

Equal solute concentration; no net water movement.

Hypotonic

Lower solute concentration; water enters the cell, causing swelling.

Hypertonic

Higher solute concentration; water leaves the cell, causing shrinking.

Osmotic Pressure

The pressure created by water moving due to osmosis.

What kind of solution would cause a red blood cell to shrink?

A hypertonic solution.

What is the osmolarity of 1 M NaCl?

2 Osm (because it dissociates into Na+ and Cl–).

Why does urea make a solution hypotonic even if it's isoosmolar?

Urea is a penetrating solute, so it enters the cell, and water follows.

How does water move during osmosis?

From low solute (high water) to high solute (low water) concentration.

Passive Transport

Movement that does not require energy.

Active Transport

Requires energy (ATP); moves substances against a gradient.

Facilitated Diffusion

Carrier or channel proteins help large or polar molecules cross.

Carrier Proteins

Specific proteins that help with transport.

ATPase Pump

Active transporter like the sodium-potassium pump.

Facilitated diffusion uses what?

Uses a carrier protein for molecules too large or polar.

What is the function of the sodium-potassium pump?

Pumps 3 Na⁺ out and 2 K⁺ in to maintain cell electrochemical gradient.

Is glucose transported via diffusion or active transport?

Facilitated diffusion.

Exocytosis

Moving substances out of the cell via vesicles.

Endocytosis

Moving substances into the cell.

Phagocytosis

Cell 'eating' large particles.

Pinocytosis

Cell 'drinking' fluid droplets.

What is the difference between phagocytosis and pinocytosis?

Phagocytosis engulfs solids; pinocytosis engulfs fluids.

Which transport method moves neurotransmitters out of neurons?

Exocytosis.

Sensory Input

Detects internal and external stimuli.

Integration

Processes and interprets sensory input.

Motor Output

Activates muscles/glands to respond.

CNS (Central Nervous System)

Brain & spinal cord – control center.

PNS (Peripheral Nervous System)

Cranial & spinal nerves.

Sensory Division (Afferent)

Sends info to CNS.

Motor Division (Efferent)

Sends instructions from CNS.

Somatic

Voluntary (skeletal muscles).

Autonomic

Involuntary (smooth/cardiac/glands).

Parasympathetic

Rest & digest (uses ACh).

Sympathetic

Fight or flight (uses epi/norepi).

What are the three main functions of the nervous system?

Sensory input, integration, motor output.

What is the difference between the somatic and autonomic nervous system?

Somatic controls voluntary skeletal muscles; autonomic controls involuntary actions.

What neurotransmitter is associated with the parasympathetic division?

Acetylcholine (ACh).

PNS Regeneration

Possible if the cell body is intact.

Wallerian degeneration

Clears damaged distal axon.

Schwann cells

Form a regeneration tube and secrete nerve growth factor (NGF).

CNS Regeneration

Typically does not occur.

Reasons for limited CNS regeneration

Glial scars block growth and oligodendrocytes do not support regeneration.

Resting Membrane Potential (RMP)

The electrical potential across the cell membrane at rest, typically around -70 mV.

Na⁺ and K⁺ ions

Sodium ions are more concentrated outside the cell, and potassium ions are more concentrated inside the cell.

Na⁺/K⁺ ATPase pump

Maintains the resting membrane potential by pumping 3 Na⁺ out and 2 K⁺ in.

What ions are involved in the resting membrane potential?

Sodium (Na⁺) and Potassium (K⁺).

What does the Na⁺/K⁺ pump do?

Maintains resting membrane potential.

Why is the inside of a resting neuron negative?

More K⁺ leaves than Na⁺ enters, and large anions remain inside.

Graded Potentials

Short-lived, local changes in membrane potential.

Action Potentials

All-or-none electrical impulse along the axon.

Threshold for Action Potential

Approximately -50 mV.

What causes a graded potential to become an action potential?

If the graded potential reaches threshold.

What ion movement causes depolarization?

Sodium (Na⁺) influx.

What is the difference between graded and action potentials?

Graded potentials vary in size and die out; action potentials are all-or-none and self-propagating.

Unmyelinated (C-Fibers) propagation

Action potential moves segment by segment (slow).

Myelinated (A/B-Fibers) propagation

Saltatory conduction where action potential jumps between Nodes of Ranvier (much faster).

Absolute Refractory Period

No new action potential possible (Na⁺ channels open/inactive).

Relative Refractory Period

Stronger stimulus needed for a new action potential (some K⁺ channels still open).

What allows saltatory conduction?

Myelin sheaths and Nodes of Ranvier.

When can no new action potential be initiated?

During the absolute refractory period.

What factors affect impulse speed?

Myelination and axon diameter.

Synapse

The junction where an impulse is transmitted from one neuron to another.

Presynaptic neuron

Sends the signal in a synapse.

Postsynaptic neuron

Receives the signal in a synapse.

Synaptic cleft

Small gap between presynaptic and postsynaptic neurons.

Chain of events in chemical synaptic transmission starts with?

Action Potential reaches axon terminal.

What opens voltage-gated Ca²⁺ channels?

Action potential reaching the axon terminal.

Ca²⁺ function in synaptic transmission

Ca²⁺ influx causes vesicles with neurotransmitters to fuse with the membrane.

EPSP

Excitatory postsynaptic potential.