physiology

Objective 1: Homeostasis

📘 Key Vocabulary

• 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.

📝 Key Concepts

• All organ systems contribute to homeostasis.

• Nervous and endocrine systems provide communication for regulation.

• Homeostatic reflexes are involuntary and often unconscious.

❓Practice Questions

Q1: What is the main difference between negative and positive feedback mechanisms?
A1: Negative feedback reduces the effect of the stimulus (returns the system to normal), while positive feedback enhances it (amplifies the change).

Q2: What are the three components of a homeostatic mechanism?
A2: Receptor, Control Center, Effector.

Q3: Give one example of negative feedback.
A3: Regulation of blood glucose: insulin lowers blood sugar levels after a meal.

Q4: Give one example of positive feedback.
A4: During labor, oxytocin increases uterine contractions until birth.

🧪 Objective 2: Solubility and Cell Membranes

📘 Key Vocabulary

• 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 (e.g., phospholipids).

• Integral Proteins – Span the membrane, function as receptors or transporters.

• Peripheral Proteins – On the surface; act as enzymes or for cell shape changes.

📝 Key Concepts

• The membrane is selectively permeable.

• Integral proteins allow water-soluble molecules to pass.

• Membranes contain antigens, receptors, and play a key role in cell recognition.

❓Practice Questions

Q1: Why can’t hydrophobic molecules dissolve in water?
A1: They are nonpolar and not attracted to water's polar molecules.

Q2: What does “amphipathic” mean?
A2: A molecule has both polar (water-attracting) and nonpolar (water-repelling) regions.

Q3: What are the three main components of the plasma membrane by weight?
A3: Proteins (62%), lipids (35%), carbohydrates (3%).

🌊 Objectives 3 & 4: Diffusion, Osmosis, Tonicity

📘 Key Vocabulary

• 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.

📝 Key Concepts

• Smaller, nonpolar, lipid-soluble molecules diffuse easily.

• Ions and large polar molecules need channels or carriers.

• Tonicity depends on whether the solute is penetrating or nonpenetrating.

❓Practice Questions

Q1: What kind of solution would cause a red blood cell to shrink?
A1: A hypertonic solution (>0.3 Osm).

Q2: What is the osmolarity of 1 M NaCl?
A2: 2 Osm (because it dissociates into Na+ and Cl–).

Q3: Why does urea make a solution hypotonic even if it's isoosmolar?
A3: Urea is a penetrating solute, so it enters the cell, and water follows.

Q4: How does water move during osmosis?
A4: From low solute (high water) to high solute (low water) concentration.

🚚 Objective 5: Membrane Transport

📘 Key Vocabulary

• Passive Transport – Movement that does not require energy (includes diffusion, osmosis).

• 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.

📝 Key Concepts

• Passive = no energy; Active = energy required.

• Facilitated diffusion uses carrier proteins but still moves substances down a gradient.

• The Na+/K+ ATPase pump maintains ion gradients essential for nerve function.

❓Practice Questions

Q1: How does facilitated diffusion differ from simple diffusion?
A1: Facilitated uses a carrier protein for molecules too large or polar.

Q2: What is the function of the sodium-potassium pump?
A2: Pumps 3 Na⁺ out and 2 K⁺ in to maintain cell electrochemical gradient.

Q3: Is glucose transported via diffusion or active transport?
A3: Facilitated diffusion.

📦 Objective 6: Vesicular (Bulk) Transport

📘 Key Vocabulary

• 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.

📝 Key Concepts

• Used for large particles or large volumes of fluid.

• Requires ATP.

• Endocytosis involves vesicle formation.

• Phagocytes (like white blood cells) use phagocytosis to remove invaders.

❓Practice Questions

Q1: What is the difference between phagocytosis and pinocytosis?
A1: Phagocytosis engulfs solids; pinocytosis engulfs fluids.

Q2: Which transport method moves neurotransmitters out of neurons?
A2: Exocytosis.

📚 Summary Table

OBJECTIVE 7: Neuron Structure & Nervous System Functions

✅ Key Concepts

Functions of the Nervous System:

1. Sensory Input – Detects internal and external stimuli.

2. Integration – Processes and interprets sensory input.

3. Motor Output – Activates muscles/glands to respond.

Divisions of the Nervous System:

• 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).

🧾 Vocabulary

❓ Practice Questions

1. Q: What are the three main functions of the nervous system?
   A: Sensory input, integration, and motor output.

2. Q: What is the difference between the somatic and autonomic nervous system?
   A: Somatic controls voluntary skeletal muscles; autonomic controls involuntary actions like heart rate and digestion.

3. Q: What neurotransmitter is associated with the parasympathetic division?
   A: Acetylcholine (ACh).

🧩 OBJECTIVE 8: Neural Regeneration

✅ Key Concepts

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.

• Inhibitors: Glial scars, lack of guiding Schwann cells, and growth-inhibiting proteins in CNS myelin.

🧾 Vocabulary

❓ Practice Questions

1. Q: What conditions are necessary for neuron regeneration in the PNS?
   A: Damage must be away from the cell body and Schwann cells must remain intact.

2. Q: Why is CNS neuron regeneration limited?
   A: Glial scars block growth and oligodendrocytes do not support regeneration.

⚡ OBJECTIVE 9: Neurophysiology & Resting Membrane Potential

✅ Key Concepts

• Resting Membrane Potential (RMP): ~-70 mV

• More Na⁺ outside, more K⁺ inside.

• Maintained by Na⁺/K⁺ ATPase pump (3 Na⁺ out, 2 K⁺ in).

• Membrane is more permeable to K⁺ (via leak channels).

🧾 Vocabulary

❓ Practice Questions

1. Q: What ions are involved in the resting membrane potential?
   A: Sodium (Na⁺) and Potassium (K⁺).

2. Q: What does the Na⁺/K⁺ pump do?
   A: Pumps 3 Na⁺ out and 2 K⁺ in to maintain the RMP.

3. Q: Why is the inside of a resting neuron negative?
   A: More K⁺ leaves than Na⁺ enters, and large anions remain inside.

🚦 OBJECTIVE 10: Graded vs. Action Potentials

✅ Key Concepts

Graded Potentials:

• Short-lived, local changes in membrane potential.

• Can be depolarizing or hyperpolarizing.

• Magnitude depends on stimulus strength.

• May lead to an action potential if strong enough.

Action Potentials:

• All-or-none electrical impulse along the axon.

• Requires threshold (~ -50 mV).

• Has 3 phases: Depolarization, Repolarization, Hyperpolarization.

• Maintained by voltage-gated ion channels.

🧾 Vocabulary

❓ Practice Questions

1. Q: What causes a graded potential to become an action potential?
   A: If the graded potential reaches threshold (~20 mV depolarization).

2. Q: What ion movement causes depolarization?
   A: Sodium (Na⁺) influx.

3. Q: What is the difference between graded and action potentials?
   A: Graded potentials vary in size and die out; action potentials are all-or-none and self-propagating.

📡 OBJECTIVE 11: Action Potential Propagation

✅ Key Concepts

• Unmyelinated (C-Fibers): AP moves segment by segment (slow).

• Myelinated (A/B-Fibers): Saltatory conduction (AP jumps between Nodes of Ranvier) – much faster.

• Absolute Refractory Period: No new AP possible (Na⁺ channels open/inactive).

• Relative Refractory Period: Stronger stimulus needed (some K⁺ still open).

🧾 Vocabulary

❓ Practice Questions

1. Q: What allows saltatory conduction?
   A: Myelin sheaths and Nodes of Ranvier.

2. Q: When can no new action potential be initiated?
   A: During the absolute refractory period.

3. Q: What factors affect impulse speed?
   A: Myelination and axon diameter.

✅ Summary Chart: Graded vs. Action Potentials

OBJECTIVE 12–13: Synaptic Transmission

✅ Key Concepts

1. What Is a Synapse?

• Synapse: The junction where an impulse is transmitted from one neuron to another (or to a muscle/gland).

  • Presynaptic neuron: Sends the signal.

  • Postsynaptic neuron: Receives the signal.

  • Synaptic cleft: Small gap between them.

🔁 Chain of Events in Chemical Synaptic Transmission

a. Action Potential reaches axon terminal.
b. Voltage-gated Ca²⁺ channels open → Ca²⁺ floods in.
c. Ca²⁺ causes vesicles containing neurotransmitters (NTs) to fuse with membrane → NTs released by exocytosis.
d. NTs bind to receptors on postsynaptic membrane → opens ligand-gated ion channels.
e. Depending on NT and receptor, it can cause:

• EPSP (Excitatory postsynaptic potential)

• IPSP (Inhibitory postsynaptic potential)
  f. NTs are cleared by:

1. Reuptake (into presynaptic cell)

2. Enzymatic breakdown

3. Diffusion away

🧠 EPSPs vs IPSPs

• EPSPs help trigger an action potential at the axon hillock.

• IPSPs inhibit action potential generation.

🔄 Spatial vs. Temporal Summation

📘 Vocabulary

❓ Practice Questions

1. Q: What causes synaptic vesicles to release neurotransmitters?
   A: Influx of Ca²⁺ into the axon terminal.

2. Q: What type of potential is created by sodium influx?
   A: EPSP (depolarizing graded potential).

3. Q: Name three ways neurotransmitters are removed from the synaptic cleft.
   A: Reuptake, enzymatic breakdown, diffusion.

4. Q: What is the difference between spatial and temporal summation?
   A: Spatial: different locations; Temporal: rapid signals over time.

🧪 OBJECTIVE 14: Neurotransmitter Receptors & Drug Effects

✅ Key Concepts

Neurotransmitter Receptors Types:

Receptor Behavior Can Change!

• Desensitization = Receptors stop responding.

• Number of receptors can increase or decrease.

💊 Drug Effects

📘 Vocabulary

❓ Practice Questions

1. Q: What is the difference between channel-linked and G-protein linked receptors?
   A: Channel-linked are fast and direct; G-protein linked are slow and indirect.

2. Q: What happens when a reuptake inhibitor is used?
   A: Neurotransmitter stays longer in the synaptic cleft → prolonged effect.

3. Q: What type of receptors do norepinephrine and epinephrine act on?
   A: G-protein linked alpha and beta adrenergic receptors.

🧬 OBJECTIVE 15: Neurotransmitter Examples

✅ Key Neurotransmitters

🧠 Receptor Summary

❓ Practice Questions

1. Q: What neurotransmitter is low in Parkinson’s disease?
   A: Dopamine.

2. Q: Which neurotransmitter is linked to depression and targeted by SSRIs?
   A: Serotonin.

3. Q: What is the role of endorphins?
   A: Reduce pain perception and induce pleasure.

4. Q: What is the effect of glutamate after brain injury?
   A: Excess glutamate can cause neuron damage (excitotoxicity).

🧠 Helpful Mnemonics

• "NAG SED" — Norepinephrine, Acetylcholine, Glutamate = Excitatory
  Serotonin, Endorphins, Dopamine = Mostly Inhibitory (but context matters)

• "ACE the test" for Acetylcholine:

  • Activates Contraction in Effector muscles

OBJECTIVE 16: Senses / Tactile Sensation

✨ Sensory System Overview

• A sensory system includes:

  • Sensory receptors: detect stimuli

  • Neural pathways: carry signals

  • Brain areas: interpret signals = Sensation (when conscious)

🔍 I. Sensory Reception

• Receptors: Convert stimuli → graded potentials → action potentials

  • Graded potentials: travel short distances

  • Action potentials: self-propagate long distances

📌 Classification of Sensory Receptors

By Location/Stimulus:

By Type of Stimulus:

✅ OBJECTIVE 20–21: Vision / Photoreception

👁 Photoreceptors in Retina

• Rods: Black & white, dim light, peripheral vision

• Cones: Color, bright light, sharp vision

• Location:

  • Fovea centralis: only cones (sharpest vision)

  • Peripheral retina: mostly rods

⚙ Vision Chemistry

• Rods: Rhodopsin

  • Made of scotopsin (protein) + cis-retinal

  • Light → cis to trans retinal → pigment bleached → signal

• Cones: Iodopsin

  • 3 types: red (600 nm), green (550), blue (450)

  • Genetic basis = on X chromosome → red-green colorblindness (more common in males)

🧠 Visual Pathway

• Light → Retina (photoreceptors → bipolar → ganglion cells)

• Ganglion axons form optic nerve

• Cross at optic chiasm

  • Left optic tract → right visual field, vice versa

📷 Optics & Refraction

• Cornea bends light most (constant curvature)

• Lens: Adjustable curvature (accommodation)

  • Convex lens: converges light (used for hyperopia)

  • Concave lens: diverges light (used for myopia)

👓 Focusing

Near Vision (within 20 ft):

• Lens bulges (more curved)

• Pupils constrict

• Eyes converge

• Parasympathetic (oculomotor nerve) active

Distance Vision:

• Lens flattens

• Pupil dilates (mydriasis)

• Sympathetic control active

Disorders:

💡 Light/Dark Adaptation

• Light adaptation: rods OFF, cones ON (1 minute)

• Dark adaptation: cones OFF, rods ON (20–30 min)

🔦 Light Reflex

• Afferent (sensory): Optic nerve (CN II)

• Efferent (motor): Oculomotor nerve (CN III)

✅ OBJECTIVE 20–23: Hearing & Equilibrium

🔊 Hearing Basics

• Sound = waves of pressure (vibrations)

• Pitch = frequency (Hz), Loudness = amplitude (dB)

🦻 Ear Anatomy

• Eustachian tube equalizes pressure

🔁 Cochlea & Hearing

• Basilar membrane vibrates → hair cells bend → graded potentials

• Organ of Corti = hearing receptor

  • Base → high pitch

  • Apex → low pitch

🦻 Hearing Loss

• Hearing aids: amplify sound

• Cochlear implants: direct nerve stimulation

✅ OBJECTIVE 24: Equilibrium (Balance)

🔄 Vestibular System

• Input from:

  • Inner ear (semicircular canals, vestibule)

  • Eyes (vision)

  • Proprioceptors (body position)

🧠 Static Equilibrium (Head Position)

• Maculae in utricle & saccule

  • Detect linear movement

  • Hair cells embedded in otolithic membrane

  • Movement → otoliths shift → hair cells bend → signal

🔁 Dynamic Equilibrium (Rotation)

• Crista ampullaris in semicircular canals (3 planes)

• Cupula = gel mass with hair cells

• Rotation → endolymph moves → hair bends → CN VIII signal

👀 Vestibular Nystagmus

• Eye movement linked to head rotation → vertigo

✅ OBJECTIVE 25: Taste (Gustation) & Smell (Olfaction)

👅 Taste

• Taste buds: located on papillae of tongue

  • 3 cell types: supporting, receptor (sensory), basal (regenerate)

• Five primary tastes:

  • Sweet (tip), salty (sides), sour (sides/back), bitter (back), umami (savory)

👃 Smell

• Olfactory epithelium (roof of nasal cavity)

• Chemoreceptors in mucus detect odorants

• Olfactory neurons regenerate (every 60 days)

• Direct link to limbic system (emotion/memory)

✅ OBJECTIVE 26: Pain

⚠ Nociceptors

• Free nerve endings

• Triggered by:

  • Mechanical deformation

  • Extreme temperature

  • Chemicals (bradykinin, prostaglandins, H⁺)

🔄 Types of Pain

• Referred pain: visceral pain perceived as somatic

🧠 Pain Pathways

• Both send branches to reticular formation → alertness

🧬 Pain Management

• Endorphins: natural opioids

• Therapies: acupuncture, meditation, hypnosis

• Medications:

  • Analgesics (aspirin, ibuprofen): reduce perception

  • Anesthetics: block sensation