16-+SensesCV

Senses

Overview

• Human Anatomy and Physiology I focuses on understanding the human senses, which are vital for interaction with the environment.

Sensory Modalities

Classification of Sensory Modalities

• Sensory modalities refer to various forms of sensory stimuli classified based on subjective experiences. Examples include:

  • Vision

  • Smell

  • Taste

  • Hearing

  • Mechanosensation

  • Temperature

  • Pain

Sensory Receptors

• Sensory receptors are specialized nerve endings that transform different forms of stimulus energy (like light, sound, or pressure) into electrical signals that the nervous system can interpret.

• These receptors are further categorized into Special Senses and Somatic (General) Senses.

Action Potentials and Neuronal Response

Action Potentials Characteristics

• Action potentials in sensory neurons operate on an all-or-none principle, meaning that all action potentials fired by a sensory neuron are identical in amplitude (height).

• The frequency of action potentials increases with increased stimulus intensity, meaning a stronger stimulus will elicit a higher firing rate of action potentials.

Response Thresholds

• Different sensory neurons exhibit varying thresholds for response:

  • Low threshold neurons respond to mild stimuli, indicating a weak sensory signal.

  • High threshold neurons respond to strong stimuli, indicating a stronger sensory signal.

Somatosensory Receptors

Types of Receptors

• Somatosensory receptors include:

  • Free nerve endings

  • Tactile (Merkle) Disc

  • Hair receptor

  • Tactile (Meissner) corpuscle

  • End bulb (Krause)

  • Bulbous corpuscle (Ruffini Ending)

  • Pacinian (Lamellar) corpuscle

  • Muscle spindle

  • Tendon organ

Receptive Fields

Definition and Function

• A receptive field is the area within which a sensory neuron detects stimuli.

• Size of receptive fields can vary:

  • Example 1: A large receptive field may result in less precise spatial localization of stimuli.

  • Example 2: Smaller receptive fields provide greater spatial resolution allowing for finer discrimination of stimuli.

Referred Pain

Concept

• Referred Pain refers to pain perceived at a location other than the site of the painful stimulus, often due to the convergence of neural pathways in the central nervous system (CNS).

The Anatomy of the Eye

Key Components

• Structures of the eye include:

  • Conjunctiva: A thin, clear membrane covering the inner surface of the eyelid and the sclera that assists with lubrication.

  • Iris: Controls the size of the pupil and thus the amount of light entering the eye.

  • Pupil: The opening that allows light to enter.

  • Sclera: The white outer coat of the eyeball.

Lacrimal Apparatus

• Involved in tear production:

  • Composition includes lacrimal ducts, lacrimal sac, and nasolacrimal duct.

  • Explanation on why the nose runs when one cries is linked to the drainage of tears into the nasal cavity.

Photoreceptors and Color Vision

Types of Photoreceptors

• Humans possess two types of photoreceptors:

  • Rods: Active in low-light conditions; do not mediate color vision.

  • Cones: Function in bright light and mediate color vision.

Fovea and Macula Lutea

• Fovea centralis contains only cones and is responsible for sharp central vision.

• The macula lutea is a part of the retina that contains high concentrations of cones.

Trichromatic Color Vision

• Humans have trichromatic vision because they can perceive color through three types of cones sensitive to different ranges of wavelengths (S, M, L for short, medium, and long wavelengths).

Auditory System

Key Components of Hearing

• The anatomy of the ear consists of:

  • Outer Ear: Auditory canal.

  • Middle Ear: Tympanic membrane, ossicles (Malleus, Incus, Stapes).

  • Inner Ear: Cochlea and vestibular apparatus.

Sound Wave Physiology

• Sound occurs through air pressure variations that create areas of high and low pressure.

• Frequency determines pitch:

  • High frequency (short wavelength) = high pitch.

  • Low frequency (long wavelength) = low pitch.

Auditory Receptors

• Inner Hair Cells (IHCs) are the primary auditory receptors, while Outer Hair Cells (OHCs) serve as mechanical feedback amplifiers.

• Depolarization of hair cells occurs when tip-links connected to stereocilia stretch, leading to the creation of electrical signals.

Chemical Senses

Olfaction - The Sense of Smell

• Olfactory Mucosa: Contains millions of olfactory neurons and is responsible for the sense of smell. Olfactory nerve bundles pass through the cribriform plate.

Gustation - The Sense of Taste

• There are five primary tastes:

  • Salty

  • Sour

  • Sweet

  • Bitter

  • Umami (savory).

• Each taste cell contains one type of receptor and synapses onto sensory neurons. Flavor perception is a complex process involving the integration of taste, aroma, texture, and other sensory inputs.