COPY Comprehensive Human Sensory and Circulatory System Review

Mechanoreceptors

Receptors that respond to physical deformation (touch, pressure, vibration); differ by depth, adaptation speed, and receptive field size.

Rapidly adapting receptors

Respond primarily to changes in stimulus (on/off); ideal for detecting vibration or movement rather than sustained pressure.

Slowly adapting receptors

Continue firing during constant stimulation; important for detecting pressure and texture over time.

Free nerve endings

Unencapsulated receptors that detect pain, temperature, and crude touch; most widely distributed and least specialized.

Pacinian corpuscles

Large, encapsulated receptors that detect deep pressure and high-frequency vibration; adapt rapidly.

Merkel discs

Slowly adapting receptors responsible for fine touch and texture discrimination; small receptive fields.

Meissner corpuscles

Rapidly adapting receptors detecting light touch and low-frequency vibration; found in sensitive skin.

Ruffini endings

Slowly adapting receptors that detect skin stretch and sustained pressure.

Receptive field

The area of skin a receptor monitors; smaller fields provide greater sensory precision.

Sensory adaptation

The process by which receptors decrease responsiveness to constant stimuli, allowing focus on new inputs.

Gustation (taste)

Chemical sense detecting dissolved substances through taste buds.

Taste buds

Clusters of gustatory cells located on papillae; responsible for detecting taste stimuli.

Gustatory receptor cells

Specialized epithelial cells that release neurotransmitters in response to chemical stimuli.

Basal cells (taste)

Stem cells that replace gustatory receptor cells, which have a short lifespan.

Primary taste modalities

Sweet, sour, salty, bitter, and umami; each linked to different chemical stimuli.

Umami taste

Detects amino acids (protein-related substances); often tested conceptually.

Olfaction (smell)

Detection of airborne chemicals via receptors in the nasal epithelium.

Olfactory receptor neurons

Bipolar neurons that detect odorants; unique because they regenerate.

Olfactory transduction

Typically involves G-protein-coupled receptors and second messenger systems.

Olfactory bulb pathway

Signals travel directly to the brain without initial thalamic relay.

External ear

Includes auricle and auditory canal; funnels sound waves toward tympanic membrane.

Tympanic membrane

Vibrates in response to sound waves and transmits energy to ossicles.

Ossicles (malleus, incus, stapes)

Small bones that amplify and transmit sound vibrations to the inner ear.

Eustachian tube

Connects middle ear to nasopharynx; equalizes pressure across tympanic membrane.

Inner ear

Contains structures for hearing (cochlea) and balance (vestibular apparatus).

Cochlea

Spiral structure where sound waves are converted into neural signals.

Hair cells

Mechanoreceptors that convert mechanical vibrations into electrical signals.

Vestibule

Detects static equilibrium (head position relative to gravity).

Semicircular canals

Detect dynamic equilibrium (rotational movement).

Static equilibrium

Awareness of head position when still.

Dynamic equilibrium

Awareness of head movement and rotation.

Vision

Detection and processing of light through the eye.

Cornea

Provides most of the eye's refractive power.

Lens

Fine tunes focus by changing shape (accommodation).

Accommodation

Process of adjusting lens curvature to focus on near or distant objects.

Ciliary body

Controls lens shape via smooth muscle contraction.

Iris

Regulates pupil size to control light entry.

Pupil

Opening that allows light into the eye.

Retina

Layer containing photoreceptors and neural processing cells.

Rods

Photoreceptors for low-light vision; highly sensitive but low acuity.

Cones

Photoreceptors for color and detail; function best in bright light.

Optic nerve

Carries visual information from retina to brain.

Optic chiasm

Location where some visual fibers cross, allowing visual field processing.

Blind spot

Area where optic nerve exits; no photoreceptors present.

Heart

Muscular organ that pumps blood through pulmonary and systemic circuits.

Pulmonary circulation

Flow from heart to lungs and back; for oxygenation.

Systemic circulation

Flow from heart to body tissues and back.

Right atrium

Receives deoxygenated blood from systemic circulation.

Right ventricle

Pumps deoxygenated blood to lungs.

Left atrium

Receives oxygenated blood from lungs.

Left ventricle

Pumps oxygenated blood to the body; has thickest myocardium.

Atrioventricular (AV) valves

Prevent backflow from ventricles to atria.

Semilunar valves

Prevent backflow from arteries to ventricles.

Tricuspid valve

Located between right atrium and ventricle.

Mitral (bicuspid) valve

Located between left atrium and ventricle.

Pulmonary valve

Between right ventricle and pulmonary trunk.

Aortic valve

Between left ventricle and aorta.

Chordae tendineae

Fibrous cords that anchor AV valves.

Papillary muscles

Prevent valve prolapse during contraction.

Interatrial septum

Separates atria.

Interventricular septum

Separates ventricles.

Coronary arteries

Supply oxygenated blood to heart muscle.

Myocardium

Muscle layer responsible for contraction.

Endocardium

Inner lining of heart chambers.

Pericardium

Protective sac surrounding the heart.

Cardiac cycle

Sequence of contraction (systole) and relaxation (diastole).

Systole

Phase of contraction and blood ejection.

Diastole

Phase of relaxation and filling.

Heart sounds (S1, S2)

S1 = AV valve closure; S2 = semilunar valve closure.

Cardiac output (CO)

Volume of blood pumped per minute (HR × SV).

Stroke volume (SV)

Amount of blood pumped per beat.

Preload

Degree of ventricular stretch before contraction.

Afterload

Resistance the heart must overcome to eject blood.

Contractility

Strength of heart contraction independent of preload.

Blood pressure (BP)

Force of blood against vessel walls.

Systolic pressure

Pressure during ventricular contraction.

Diastolic pressure

Pressure during relaxation.

Pulse pressure

Difference between systolic and diastolic pressure.

Mean arterial pressure (MAP)

Average pressure driving blood flow; weighted toward diastole.

Peripheral resistance

Opposition to blood flow in vessels.

Vasoconstriction

Narrowing of vessels → increases resistance and BP.

Vasodilation

Widening of vessels → decreases resistance and BP.

Arteries

Carry blood away from heart; high pressure.

Veins

Return blood to heart; low pressure with valves.

Capillaries

Sites of exchange between blood and tissues.

Arterioles

Primary regulators of resistance and blood distribution.

Sympathetic nervous system

Increases heart rate, contractility, and BP.

Parasympathetic nervous system

Decreases heart rate.

Baroreceptors

Detect changes in blood pressure and adjust heart rate.

Chemoreceptors

Respond to oxygen, CO₂, and pH levels.

Renin-angiotensin system

Hormonal system that increases blood pressure.

ADH (antidiuretic hormone)

Increases water retention → increases blood volume.

Aldosterone

Promotes sodium and water retention → increases BP.

Hypertension

Chronic high blood pressure.

Atherosclerosis

Plaque buildup that narrows arteries.

Myocardial infarction

Heart attack caused by blocked coronary artery.

Shock

Failure of circulatory system to deliver adequate oxygen.

Hypovolemic shock

Caused by loss of blood volume.

Septic shock

Caused by infection leading to vasodilation.

Cardiogenic shock

Caused by heart pump failure.