All Pathways

What is the resting potential of a neuron?

-70 mV

What maintains the resting potential?

Na+/K+ ATPase pump (3 Na+ out, 2 K+ in)

What happens when a stimulus reaches threshold (-50 mV)?

Voltage-gated Na+ channels open, sodium rushes in

What happens during depolarization?

Membrane potential rises rapidly as Na+ enters the cell

What happens at the peak of an action potential (+35 mV)?

Na+ channels close, voltage-gated K+ channels open

What happens during repolarization?

Potassium leaves the cell, making the inside more negative

What happens during hyperpolarization?

Excess K+ leaves, causing potential to dip below -70 mV

What restores resting potential after hyperpolarization?

Na+/K+ pump reestablishes ion gradients

What is the refractory period?

Time when the neuron cannot fire another action potential until resting state is restored

What happens when an action potential reaches the presynaptic terminal?

Voltage-gated Ca2+ channels open

What does Ca2+ influx cause?

Vesicles fuse with presynaptic membrane

What is released into the synaptic cleft?

Neurotransmitters

What do neurotransmitters do?

Bind to receptors on the postsynaptic membrane

What happens after receptor binding?

Ion channels open, causing depolarization or hyperpolarization

How is the neurotransmitter signal terminated?

By reuptake, enzymatic breakdown, or diffusion

What enzyme breaks down acetylcholine?

Acetylcholinesterase

What happens if acetylcholine is not broken down?

Postsynaptic neuron remains activated and cannot repolarize

What does the sympathetic nervous system do to heart rate?

Increases it

What does it do to blood pressure?

Increases it

What does it do to the digestive system?

Inhibits digestion

What does it do to the lungs?

Causes bronchodilation

What does it do to pupils?

Dilates them

What does it do to bladder and urination?

Inhibits urination

What is the main neurotransmitter used by the sympathetic nervous system?

Norepinephrine

What does the parasympathetic nervous system do to heart rate?

Decreases it

What does it do to digestion?

Stimulates digestion

What does it do to the lungs?

Causes bronchoconstriction

What does it do to pupils?

Constricts them

What does it do to urination?

Stimulates urination

What is the main neurotransmitter used by the parasympathetic nervous system?

Acetylcholine

What is the first step in a reflex arc?

Sensory receptor detects a stimulus

What does the sensory neuron do in a reflex arc?

Transmits the signal to the spinal cord

What do interneurons in the spinal cord do in a reflex arc?

Process the signal and relay it

What does the motor neuron do in a reflex arc?

Transmits the response signal from the spinal cord

What is the final step in a reflex arc?

Effector organ (muscle or gland) carries out the response

Why are reflex arcs so fast?

They bypass the brain and are processed in the spinal cord

What is the correct pathway of filtrate through the nephron?

Bowman’s capsule → Proximal convoluted tubule → Loop of Henle (descending, then ascending) → Distal convoluted tubule → Collecting duct

What is the pathway of urine flow after leaving the collecting duct?

Collecting duct → Renal calyces → Renal pelvis → Ureter → Urinary bladder → Urethra

What are the four main steps of urine formation?

Filtration, Reabsorption, Secretion, Excretion

What happens during filtration in the kidney?

Blood plasma passes into Bowman’s capsule while large molecules (cells, proteins) remain in circulation

What happens during reabsorption in the kidney?

Essential molecules like glucose, ions, and water are reabsorbed into the blood

What happens during secretion in the kidney?

Additional wastes, ions, and drugs are secreted from blood into the nephron

What happens during excretion in the kidney?

Final urine leaves the body via urethra

What happens in the descending loop of Henle?

Permeable only to water; water leaves the filtrate, concentrating it

What happens in the ascending loop of Henle?

Impermeable to water; NaCl is actively reabsorbed, diluting the filtrate

What happens in the kidney when blood pressure is low?

Juxtaglomerular cells release renin → renin activates angiotensin → adrenal cortex releases aldosterone → more Na+ reabsorbed → water follows → blood volume and pressure increase

What is the effect of aldosterone on the nephron?

Increases Na+ reabsorption in distal tubule and collecting duct; water follows, increasing blood pressure

What is the effect of ADH (vasopressin) on the nephron?

Increases collecting duct permeability to water → more water reabsorbed → urine becomes concentrated

What effect do alcohol and caffeine have on ADH?

They inhibit ADH release, causing more dilute urine and dehydration

How do aquatic animals excrete nitrogenous waste?

As ammonia (NH3) or ammonium (NH4+)

How do mammals, sharks, and amphibians excrete nitrogenous waste?

By converting ammonia into urea

How do birds, reptiles, and insects excrete nitrogenous waste?

As uric acid

How do marine fish osmoregulate?

Their cells are hypotonic to seawater → they lose water → they drink constantly and urinate very little

How do freshwater fish osmoregulate?

Their cells are hypertonic to freshwater → they gain water → they rarely drink and urinate constantly

What is the pathway of food through the digestive system?

Mouth → Pharynx → Esophagus → Stomach → Small intestine (duodenum, jejunum, ileum) → Large intestine → Rectum → Anus

What is the pathway of food through the accessory organs?

Salivary glands → Pharynx → Esophagus → Stomach → Small intestine (with secretions from liver, gallbladder, pancreas)

What happens to carbohydrates in digestion?

Broken down into monosaccharides, absorbed into capillaries, and transported via hepatic portal vein to the liver

What happens to proteins in digestion?

Broken down into amino acids, absorbed into capillaries, and transported via hepatic portal vein to the liver

What happens to lipids in digestion?

Emulsified by bile salts, broken down by lipases into glycerol and fatty acids, absorbed into lacteals as chylomicrons

What is the pathway of blood through the heart?

Vena cava → Right atrium → Tricuspid valve → Right ventricle → Pulmonary semilunar valve → Pulmonary artery → Lungs → Pulmonary vein → Left atrium → Bicuspid (mitral) valve → Left ventricle → Aortic semilunar valve → Aorta → Body

What is the pathway of electrical conduction in the heart?

SA node → AV node → Bundle of His → Right and left bundle branches → Purkinje fibers

What is the systemic circulation pathway?

Left ventricle → Aorta → Arteries → Arterioles → Capillaries (exchange) → Venules → Veins → Vena cava → Right atrium

What is the pulmonary circulation pathway?

Right ventricle → Pulmonary artery → Lungs → Pulmonary vein → Left atrium

What is the pathway of air through the respiratory system?

Nose/mouth → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli

What is the pathway of oxygen transport in the blood?

Oxygen enters alveoli → Diffuses into pulmonary capillaries → Binds to hemoglobin in red blood cells → Transported to tissues → Diffuses into cells

What is the pathway of carbon dioxide transport in the blood?

CO2 produced in tissues → Diffuses into blood → Converted to bicarbonate in plasma or binds to hemoglobin → Transported to lungs → Diffuses into alveoli → Exhaled

What is the pathway of lymph flow?

Interstitial fluid → Lymphatic capillaries → Lymphatic vessels → Lymph nodes → Lymphatic ducts → Subclavian veins (into bloodstream)

What happens to pathogens in the lymph pathway?

They are filtered and destroyed by lymph nodes containing immune cells

What is the pathway of immune cell activation?

Antigen-presenting cell (APC) presents antigen → Helper T-cell recognizes antigen → Helper T-cell activates cytotoxic T-cells and B-cells → Cytotoxic T-cells kill infected cells; B-cells produce antibodies