Study Guide Final

Special Senses

Accessory Structures, Cornea, Lens, and Humors of the Eye

• Accessory Structures: These include the eyelids, eyelashes, eyebrows, lacrimal apparatus, and extrinsic eye muscles. They provide protection, lubrication, and movement for the eye.

• Cornea: The transparent outer layer of the eye that helps focus light as it enters.

• Lens: A flexible structure that focuses light onto the retina. Its shape is adjusted by ciliary muscles to allow for near and far vision.

• Humors: The eye contains fluids called humors.

  • Aqueous humor: Fills the anterior cavity between the cornea and the lens.

  • Vitreous humor: Fills the posterior cavity between the lens and the retina, maintaining eye shape and supporting the retina.

Structural Components of the Three Layers of the Eye

• Fibrous Layer: The outermost layer.

  • Sclera: Provides protection and shape.

  • Cornea: Focuses light.

• Vascular Layer (Uvea): The middle layer.

  • Choroid: Contains blood vessels and pigment to absorb scattered light.

  • Ciliary Body: Controls lens shape, produces aqueous humor.

  • Iris: Controls pupil size, regulating light entry.

• Inner Layer:

  • Retina: Contains photoreceptors (rods and cones) that transduce light into neural signals.

Pathway of Light Through the Eye and Focusing

• Light passes through the cornea, aqueous humor, pupil, lens, and vitreous humor before reaching the retina.

• Refraction: The bending of light rays occurs primarily at the cornea and lens.

• The lens changes shape (accommodation) to focus light from objects at different distances.

Conversion of Light into a Neural Signal

• Phototransduction: Light striking the retina activates photoreceptors (rods and cones).

• Photoreceptors hyperpolarize in response to light, reducing the release of inhibitory neurotransmitters.

• This triggers a cascade of events in bipolar cells and ganglion cells, leading to action potentials in ganglion cells.

• Axons of ganglion cells converge to form the optic nerve, transmitting signals to the brain.

Blind Spot

• The optic disc is the area where the optic nerve exits the eye; it contains no photoreceptors, creating a blind spot.

• We don’t typically notice the blind spot because:

  • Each eye compensates for the other's blind spot.

  • The brain fills in the missing information.

Rods and Cones

• Rods:

  • More sensitive to light; function in dim light.

  • Provide black and white vision.

  • Concentrated in the periphery of the retina.

• Cones:

  • Require brighter light; function in daylight.

  • Provide color vision.

  • Concentrated in the fovea (center of the retina).

Mapping Visual Space on the Retina

• The image is inverted and reversed on the retina due to refraction.

• The brain corrects the image orientation during visual processing.

Structure and Function of the Ear

• Outer Ear: Collects sound waves.

  • Pinna (auricle): Directs sound into the auditory canal.

  • Auditory Canal: Transmits sound to the tympanic membrane.

• Middle Ear: Amplifies sound waves.

  • Tympanic Membrane (eardrum): Vibrates in response to sound.

  • Ossicles (malleus, incus, stapes): Transmit and amplify vibrations to the oval window.

• Inner Ear: Converts sound waves into neural signals and maintains balance.

  • Cochlea: Contains receptors for hearing.

  • Vestibular Apparatus: Contains receptors for balance.

Properties of Sound

• Loudness: Determined by the amplitude of the sound wave.

• Pitch: Determined by the frequency of the sound wave.

• Location: Determined by the timing and intensity differences between the two ears.

Sound Transduction

• Sound waves cause the tympanic membrane to vibrate, which moves the ossicles.

• The stapes transmits vibrations to the oval window, causing pressure waves in the perilymph of the cochlea.

• These pressure waves cause the basilar membrane to vibrate.

• Hair cells on the basilar membrane are deflected, opening mechanically gated ion channels.

• Ion influx depolarizes the hair cells, causing them to release neurotransmitters and stimulate auditory nerve fibers.

Vestibular Apparatus

• Semicircular Canals: Detect rotational movements.

• Otolith Organs (utricle and saccule): Detect linear acceleration and head position.

• Hair cells in these organs are deflected by movement, similar to those in the cochlea.

CNS Vestibular Processing Centers

• Vestibular information is integrated in the vestibular nuclei of the brainstem.

• Outputs project to:

  • Cerebellum: Coordination of movement.

  • Motor nuclei: Reflexive eye movements and postural adjustments.

  • Thalamus: Conscious awareness of spatial orientation and movement

Types of Deafness

• Conductive Deafness: Impaired sound transmission through the outer or middle ear (e.g., otitis media).

• Sensorineural Deafness: Damage to the inner ear or auditory nerve.

• Otitis Media: Middle ear infection.

• Tinnitus: Ringing in the ears.

• Meniere’s Syndrome: Inner ear disorder causing vertigo, tinnitus, and hearing loss.

Chemical Senses

• Taste (gustation): Detection of chemicals dissolved in saliva.

• Smell (olfaction): Detection of airborne chemicals.

• Taste and smell receptors transduce chemical signals into neural signals, which are interpreted by the brain.

Endocrine System

Endocrine vs. Exocrine Glands and the Nervous System

• Endocrine System:

  • Releases hormones into the bloodstream.

  • Slower, longer-lasting effects.

  • Widespread effects on multiple target organs.

• Exocrine Glands:

  • Secrete products into ducts that lead to specific locations (e.g., sweat glands, salivary glands).

• Nervous System:

  • Uses electrical signals (action potentials) and neurotransmitters.

  • Fast, short-lived effects.

  • Localized effects.

Endocrine Disorders

• Hyperfunction: Excessive hormone production.

• Hypofunction: Insufficient hormone production.

• Altered Tissue Responsiveness: Target tissues do not respond properly to hormones.

• Primary Disorders: Problem with the gland itself.

• Secondary Disorders: Problem with the pituitary gland.

• Tertiary Disorders: Problem with the hypothalamus.

• Diagnosis: Hormone level measurements, stimulation/suppression tests, imaging.

Humoral, Neural, and Hormonal Stimulation

• Humoral Stimulation: Hormone release caused by altered levels of certain critical ions or nutrients (e.g., $Ca^{2+}$$$Ca^{2+}$$).

• Neural Stimulation: Hormone release caused by neural input (e.g., adrenal medulla).

• Hormonal Stimulation: Hormone release caused by another hormone (e.g., tropic hormones from the pituitary).

Factors Governing Hormone Levels and Negative Feedback

• Rate of Synthesis and Release: How much hormone is being produced.

• Rate of Degradation and Elimination: How quickly the hormone is broken down or removed from the body.

• Negative Feedback: Rising hormone levels inhibit further hormone release.

Chemical Classes of Hormones

• Amino Acid Derivatives:

  • Examples: epinephrine, norepinephrine, thyroid hormones.

  • Can be water-soluble or lipid-soluble.

• Peptide Hormones:

  • Examples: insulin, growth hormone.

  • Water-soluble.

  • Bind to receptors on the cell surface.

• Steroid Hormones:

  • Examples: cortisol, testosterone, estrogen.

  • Lipid-soluble.

  • Synthesized from cholesterol.

  • Bind to intracellular receptors.

Mechanisms of Hormone Action

• Water-Soluble Hormones:

  • Bind to receptors on the cell membrane.

  • Activate intracellular signaling pathways (e.g., second messengers like cAMP).

  • Rapid effects.

• Lipid-Soluble Hormones:

  • Diffuse through the cell membrane.

  • Bind to intracellular receptors in the cytoplasm or nucleus.

  • Alter gene transcription.

  • Slower, longer-lasting effects.

Pituitary Gland

• Connected to the hypothalamus via the infundibulum.

• Posterior Pituitary: Stores and releases hormones produced by the hypothalamus (ADH and oxytocin).

• Anterior Pituitary: Produces and releases its own hormones, regulated by hypothalamic hormones.

• Feedback Loops: Hormones from target glands feed back to the pituitary and hypothalamus.

Posterior Pituitary Hormones

• Antidiuretic Hormone (ADH): Promotes water retention by the kidneys.

• Oxytocin: Stimulates uterine contractions during childbirth and milk ejection.

Anterior Pituitary Hormones

• Growth Hormone (GH): Promotes growth and metabolism.

• Thyroid-Stimulating Hormone (TSH): Stimulates thyroid hormone release.

• Adrenocorticotropic Hormone (ACTH): Stimulates adrenal cortex hormone release.

• Follicle-Stimulating Hormone (FSH): Stimulates follicle development and sperm production.

• Luteinizing Hormone (LH): Stimulates ovulation and testosterone production.

• Prolactin (PRL): Stimulates milk production.

Thyroid Gland

• Located in the neck.

• Thyroid Hormone (T3 and T4): Regulates metabolism, growth, and development.

• Calcitonin: Lowers blood calcium levels.

Disorders Associated with Growth Hormone, Thyroid Hormone, and Adrenal Medulla Dysfunction

• Growth Hormone:

  • Gigantism/Acromegaly: Excessive GH.

  • Dwarfism: Insufficient GH.

• Thyroid Hormone:

  • Hyperthyroidism: Excessive TH (e.g., Graves' disease).

  • Hypothyroidism: Insufficient TH (e.g., Hashimoto's thyroiditis).

• Adrenal Medulla Dysfunction:

  • Pheochromocytoma: Tumor of the adrenal medulla, causing excessive catecholamine release.

Adrenal Gland

• Located on top of the kidneys.

• Adrenal Medulla: Secretes epinephrine and norepinephrine (catecholamines).

• Adrenal Cortex: Secretes corticosteroids (mineralocorticoids, glucocorticoids, and androgens).

Pancreas and Blood Glucose Regulation

• Pancreas: Endocrine and exocrine functions.

• Insulin: Decreases blood glucose levels by promoting glucose uptake by cells.

• Glucagon: Increases blood glucose levels by stimulating glycogen breakdown in the liver.

Type I and Type II Diabetes

• Type I Diabetes: Autoimmune destruction of pancreatic beta cells, resulting in insulin deficiency.

• Type II Diabetes: Insulin resistance and impaired insulin secretion.

Organs in Reproductive Endocrinology

• Ovaries (females): Produce estrogen and progesterone.

• Testes (males): Produce testosterone.

• Hormone Functions: Sexual development, reproductive function, and secondary sex characteristics.

Parathyroid Gland and Ca2+ Homeostasis

• Parathyroid Gland: secretes parathyroid hormone (PTH), which increases blood $Ca^{2+}$$$Ca^{2+}$$ levels.

• PTH (Parathyroid Hormone):

  • Increases $Ca^{2+}$$$Ca^{2+}$$ reabsorption in the kidneys.

  • Stimulates osteoclast activity to release $Ca^{2+}$$$Ca^{2+}$$ from bone.

  • Increases $Ca^{2+}$$$Ca^{2+}$$ absorption in the intestine (indirectly via vitamin D activation).

• Disorders:

  • Hyperparathyroidism: Elevated $Ca^{2+}$$$Ca^{2+}$$ levels.

  • Hypoparathyroidism: Low $Ca^{2+}$$$Ca^{2+}$$ levels.

Thymus

• Hormonal Role: secretes thymosin and thymopoietin, which promote T-cell development.

• Immune Role: Site of T-cell maturation.

Stages of the Stress Response

• Alarm Phase: Initial response; epinephrine release (fight or flight).

• Resistance Phase: Long-term response; cortisol release.

• Exhaustion Phase: Prolonged stress; depletion of resources leading to organ system failure.

Endocrine Response to Stress

• Short-Term Stress: Increased heart rate, blood pressure, and energy mobilization.

• Long-Term Stress: Immune suppression, increased blood glucose levels, and sodium and water retention.

Endocrine and Paracrine Signaling

• Endocrine Signaling: Hormones travel through the bloodstream to distant target cells.

• Paracrine Signaling: Chemicals act on nearby cells (e.g., eicosanoids).

• Eicosanoids:

  • Locally acting signaling molecules derived from fatty acids.

  • Examples: prostaglandins, leukotrienes.