Auditory System Overview

Auditory System

• The outer ear collects and amplifies sound, directing it into the ear canal. It also helps determine sound direction and distance.
• The ear canal has a shape that amplifies certain frequencies and protects the eardrum from foreign substances. Earwax (cerumen) is produced to trap substances.
• The auditory ossicles (incus, malleus, stapes) transmit sound vibrations from the eardrum to the inner ear.
• The semicircular canals have a loop shape and maintain balance and spatial orientation. Each loop is oriented in a different plane—horizontal, anterior, and posterior.
• The cochlea is a fluid-filled structure that converts sound vibrations into neural signals sent to the brain.
• The auditory tube (Eustachian tube) connects the middle ear to the nasopharynx (upper part of the throat). It equalizes air pressure on both sides of the eardrum and drains fluid from the middle ear.
• The eardrum (tympanic membrane) is thin, cone-shaped, separating the external ear from the middle ear. Sound waves vibrating it triggers the malleus.
• The round window allows sound waves to dissipate.
• The oval window is where the stapes vibrates, setting up waves detected by hair cells that transmit information to nerve cells.

Cardiovascular System

• The cardiovascular system consists of the heart, blood vessels, and blood.
• The heart is a pump that moves blood throughout the body.
• Blood vessels are tubes that carry blood.
• Blood is a fluid that carries important gases.
• The heart has cardiac muscle cells called cardiomyocytes, allowing for contraction and relaxation.
• Two types of cells: Contractile cells: striated cells, use calcium to contract; Nodal cells: self-excitable, conduct APs, create heart beats.
• The heart valves prevent backflow of blood between chambers. Heart sounds ("lub" and "dub") are the closing sounds of these heart valves.
• The sinoatrial (SA) node is the pacemaker of the heart.

Cardiac Cycle

• The cardiac cycle describes the events of one complete heartbeat.
• It has five phases:
  • Isovolumetric ventricular systole: ventricles contract but cannot pump blood, volume doesn't change
  • Ventricular systole: blood moves into the aorta and pulmonary arteries
  • Isovolumetric ventricular diastole: ventricles relax but cannot fill, volume doesn't change
  • Late ventricular diastole: ventricles relax and fill with blood
  • Atrial systole: atrial contract, moving blood into ventricles
• EDV (End Diastolic Volume): amount of blood in ventricles before contraction
• ESV (End Systolic Volume): amount of blood remaining in ventricles after contraction
• SV (Stroke Volume): amount of blood pumped per heartbeat (EDV - ESV)

Blood Vessels

• The aorta is the largest artery in the body.
• Blood flows from arteries into arterioles and then into capillaries (smallest blood vessels).
• Blood enters venules and then veins.
• Blood vessels consist of three layers: Tunica externa (outermost), Tunica media (middle), Tunica interna (innermost) (aka endothelial cells).
• Arteries conduct blood away from the heart.
• Arterioles regulate blood flow and resistance.
• Capillaries are exchange vessels, allowing for gas, nutrient, and waste exchange.
• Venules and veins return blood to the heart.
• Blood pressure is highest in arteries and lowest in veins.

Blood Flow

• Blood flow is influenced by pressure gradients and resistance.
• Blood flow is needed to increase blood supply to active tissues and decrease it to inactive tissues
• Factors affecting resistance: Viscosity, length of vessel, radius of lumen
• Capillaries have single-cell-thick walls, facilitating exchange.
• Types of transport in capillaries: Transcellular transport (through cells) and Paracellular transport (between cells).

Vasoconstriction and Vasodilation

• Local regulation: changes in organ/tissue conditions (intrinsic mechanisms)
• Humoral regulation: substances traveling in blood (extrinsic mechanisms); hormones like epinephrine, angiotensin II, or ADH cause vasoconstriction.
• Neural regulation: sympathetic nervous system (extrinsic mechanisms) releasing norepinephrine constricting blood vessels.
• Factors affecting regulation include myogenic theory (changes in BP related to vasoconstriction/vasodilation) and metabolic theory (metabolites like oxygen and carbon dioxide affecting vessel diameter).
• Negative, feedback loop of baroreceptor reflex (stretch receptors) stabilizes blood pressure.

Kidney

• Nephrons are the functional units of the kidneys.
• Each nephron consists of a renal corpuscle and a tubule.
• The renal corpuscle is made of Bowman's capsule and glomerulus (a capillary bed).
• Filtration occurs in the renal corpuscle (water, salts, glucose, amino acids enter Bowman's capsule from blood in the glomerulus).
• Tubules reabsorb useful molecules (water, salts, nutrients) back into the blood.
• The remaining is excreted as urine.
• The kidney is responsible for maintaining water and salt balance in the body.
• Glomerular filtration rate (GFR): the volume of fluid filtered by glomeruli each minute.

Filtration

• Four forces influence glomerular filtration: Hydrostatic pressure in glomerular capillaries (high), colloid osmotic pressure in glomerular capillaries (low), hydrostatic pressure in Bowman's capsule (low), colloid osmotic pressure in Bowman's capsule (low).
• Net filtration pressure (NFP): difference between forces favoring and opposing filtration (NFP=([Hydrostatic pressure glomerular capillaries + Colloid Osmotic pressure Bowman's capsule) - (Hydrostatic pressure Bowman's capsule + Colloid Osmotic pressure glomerular capillaries)])

Glomerular Filtration Rate (GFR)

• GFR is the volume of filtrate formed per minute by the kidneys.
• Conditions influencing GFR: blood pressure, blood flow to the kidneys, and the size of the glomerulus.
• GFR is closely regulated by the juxtaglomerular apparatus (JGA) for homeostasis.
• GFR decreases in kidney disease and significantly lowers in kidney failure.

Tubule Transport

• Transport mechanisms in the tubule cells include channels, uniporters, symporters, and antiporters.
• Active Transport: requires energy (ATP). Moves substances against their concentration gradient.
• Facilitated Diffusion: uses transport protein. Moves substances passively with their concentration gradient.
• Passive Transport: moves along the electrochemical and concentration gradients.
• Tubules of the nephron have different functions and varying transport mechanisms to reabsorb water and solutes (nutrients) and secrete waste products (ions).

Explore the fascinating components of the auditory system in this quiz. From the outer ear to the cochlea, learn how sound is collected, amplified, and processed into neural signals. Understand the roles of various structures in hearing and balance.