Lectures 16-22

Overview of Senses

General vs. Special Senses

• General Senses: Receptors located in multiple organs. Examples include:

  • Touch

  • Pain

  • Body movement

• Special Senses: Receptors located in specialized sensory organs. Examples include:

  • Taste

  • Smell

  • Hearing

  • Balance

  • Vision

Functional Classification of Sensory Receptors

• Chemoreceptors: Detect chemicals, playing a role in taste, smell, and blood pH regulation.

• Photoreceptors: Respond to light, essential for vision.

• Mechanoreceptors: Detect physical forces, related to hearing, touch, and body movement.

• Thermoreceptors: Sense changes in temperature.

• Nociceptors: Respond to tissue damage and are responsible for pain perception.

General Senses and Neural Pathways

• Receptive Field: The area supplied by a single sensory neuron; precision determined by its size.

• Neuronal Pathways:

  1. First Order Neuron: Carries signal from sensory receptor to the CNS.

  2. Second Order Neuron: Crosses over and transmits the signal to the thalamus.

  3. Third Order Neuron: Sends signal to the primary somatosensory cortex.

Taste (Gustation)

• Lingual Papillae: Small bumps on the tongue that help grip food.

• Taste Buds: Contain gustatory receptor cells for taste detection; located within lingual papillae.

• Five Primary Taste Sensations:

  1. Salty

  2. Sweet

  3. Sour

  4. Bitter

  5. Umami (affected by both aroma and temperature)

Smell (Olfaction)

• Olfactory Neurons: Contain receptors that bind airborne chemicals.

• Olfactory Nerves: Bundles of axons from olfactory neurons.

• Olfactory Bulb: Structure where olfactory neurons synapse.

• Olfactory Tracts: Nerve fibers that connect the olfactory bulb to the brain.

Ear Anatomy and Hearing Mechanism

Outer Ear

• Auricle: Collects sound waves and helps determine the direction of sound.

• External Acoustic Meatus: Passage through the temporal bone for sound.

• Tympanic Membrane: Transmits sound vibrations to the middle ear.

Middle Ear

• Auditory Ossicles: Three small bones that transmit sound to the inner ear:

  1. Malleus: Hammer-shaped ossicle attached to the tympanic membrane.

  2. Incus: Anvil-shaped ossicle between malleus and stapes.

  3. Stapes: Stirrup-shaped ossicle attached to the oval window.

• Auditory Tube: Connects the middle ear to the throat; opens to equalize pressure.

Inner Ear

• Oval Window: Membrane where stapes attaches; involved in hearing/vestibular functions.

• Vestibule: Central chamber involved in equilibrium.

• Semicircular Canals: Detect head rotation.

• Cochlea: Snail-shaped structure involved in hearing.

• Round Window: Membrane at the end of the cochlea.

Cochlea Anatomy

• Ducts:

  1. Vestibular Duct: Contains perilymph; found behind the oval window.

  2. Cochlear Duct: Contains endolymph and the spiral organ (of Corti).

  3. Tympanic Duct: Contains perilymph; found behind the round window.

• Spiral Organ (Organ of Corti): Receptor organ for hearing within the cochlear duct.

• Hair Cells: Convert fluid movements into nerve signals.

• Stereocilia: Extensions that generate signals when bent.

• Tectorial Membrane: Overarches the stereocilia and interacts with the hair cells.

Eye Anatomy

Fibrous Layer

• Sclera: Tough outer layer of the eye.

• Cornea: Transparent structure that allows light to enter.

Vascular Layer

• Choroid: Rich in blood vessels; nourishes the eye.

• Ciliary Body: Smooth muscle that adjusts lens shape.

• Iris: Colored part of the eye surrounding the pupil.

• Pupil: Opening for light entry.

Neural Layer

• Retina: Inner layer sensitive to light; contains photoreceptors.

• Optic Disc: Blind spot where axons exit the eye; lacks photoreceptors.

• Macula: Area responsible for high-resolution color vision.

Optical Components

• Aqueous Humor: Fluid in front of the lens supporting eye shape and pressure.

• Lens: Focuses light onto the retina.

• Vitreous Body: Gel-like substance filling the eye behind the lens.

Cells of the Retina

1. Rod Cells: For low-light vision; use rhodopsin as a photopigment.

2. Cone Cells: For color vision; use photopsins as photopigments.

3. Bipolar Cells: Connect rod/cone cells to ganglion cells.

4. Retinal Ganglion Cells: Transmit visual information to the brain.

Endocrine System Overview

Hormonal Functions

• Endocrine System: Composed of glands producing hormones influencing bodily functions.

• Hormones: Signal molecules released into the bloodstream affecting target cells.

• Feedback Loops: Regulate hormonal activity; types include positive and negative feedback.

Types of Hormones

1. Amino Acid-Derived Hormones

2. Steroid Hormones

   • Can cross cell membranes; may bind to DNA or use secondary messengers.

Hypothalamus and Pituitary Gland

1. Hypothalamus: Regulates the pituitary gland.

2. Pituitary Gland:

   • Anterior Pituitary: Produces hormones like FSH, LH, TSH, ACTH, GH, and PRL.

   • Posterior Pituitary: Stores ADH and OT produced by the hypothalamus.

Hormones of Specific Glands

• Pineal Gland: Produces melatonin.

• Thyroid Gland: Produces calcitonin and thyroid hormones (T3, T4).

• Parathyroid Glands: Secrete parathyroid hormone (increases calcium levels).

• Pancreas: Produces insulin (lowers blood glucose) and glucagon (raises blood glucose).

• Adrenal Glands:

  • Cortex: Produces corticosteroids, regulating various functions.

  • Medulla: Produces epinephrine and norepinephrine (stress response).

• Testes: Produce testosterone, influencing male characteristics.

Cardiovascular System Overview

Functions of the Cardiovascular System

1. Transports oxygen and nutrients.

2. Removes carbon dioxide and metabolic waste.

3. Delivers hormones.

4. Defends against pathogens.

5. Regulates body fluids and pH.

6. Maintains body temperature.

Blood Composition

• Blood Plasma: Liquid component, primarily water (92%).

• Formed Elements: Blood cells including erythrocytes, leukocytes, and platelets.

Blood Plasma Components

• Proteins:

  • Albumin: Maintains osmotic pressure.

  • Globulins: Involved in immune response.

  • Fibrinogen: Facilitates blood clotting.

  • Bilirubin: Produced from breakdown of red blood cells.

Erythrocytes (RBCs)

• Contain hemoglobin which binds oxygen and carbon dioxide.

• Percentage of hemoglobin saturated with oxygen indicates respiratory efficiency.

Immune Response Overview

Types of Immunity

1. Innate Immunity: Rapid, non-specific response using white blood cells and physical barriers.

2. Adaptive Immunity: Slower, specific response capable of remembering pathogens.

Cells of the Immune Response

• Macrophages/Dendritic Cells: Present antigens and initiate immune responses after engulfing pathogens.

• T Cells: Destroy infected or malignant cells; secrete signaling molecules to enhance responses.

• B Cells: Produce antibodies counteracting specific antigens.

Lymphatic System Functions

1. Return fluids to the bloodstream.

2. Transport immune cells.

3. Remove debris/pathogens from body tissues.

Respiratory System Overview

• Functions: Gas exchange, olfaction, speech production, and regulation of acidity.

Functional Classification

• Conducting Zone: Passageways that condition air but do not participate in gas exchange.

• Respiratory Zone: Alveoli where gas exchange occurs.

Anatomy of the Respiratory System

1. Nose/Nasal Cavity: Airway, filters, warms, and humidifies air.

2. Pharynx: Connects respiratory and digestive systems.

3. Larynx: Sound production, preventing food from entering trachea.

4. Trachea/Bronchi: Conduct air to lungs.

5. Lungs: Main organ for gas exchange composed of lobes.

6. Pleura: Serous membranes surrounding lungs separating them from thoracic wall.

Process of Breathing

• Inspiration: Diaphragm descends, increasing thoracic volume and decreasing lung pressure.

• Expiration: Diaphragm rises, decreasing thoracic volume and increasing lung pressure.