Senses

Definition: Cellular structures or individual cells that detect external and internal stimuli, playing a critical role in sensory perception.
Function: Perform transduction by converting stimulus energy into changes in membrane potential, generating graded receptor potentials when activated, and communicating with sensory neurons.

General Senses: Cover cutaneous receptors, proprioceptors, etc.
Special Senses: Include gustation (taste), olfaction (smell), hearing, equilibrium (balance), and vision.

Adequate Stimulus: The specific stimulus a receptor responds best to, requiring the least energy to activate. For example, light serves as the adequate stimulus for photoreceptors.
Law of Specific Nerve Energies: Activation of a specific sensory receptor and its neural pathway leads to the perception of a single type of sensation, irrespective of how the receptor is stimulated (e.g., pressure can sometimes lead to a visual sensation).

Photoreceptors: Respond to light.
- Examples: Rods and cones in the retina.
Chemoreceptors: Respond to chemical stimuli in body fluids or external environment.
- Examples: Taste cells, olfactory cells, aortic and carotid bodies, osmoreceptors.
Nociceptors: Respond to extreme temperatures, chemicals, and mechanical damage.
- Examples: Free nerve endings that signal pain.
Thermoreceptors: Respond to temperature changes.
- Examples: Also free nerve endings that are sensitive to heat and cold.
Mechanoreceptors: Respond to mechanical forces, pressure, or vibrations.
- Examples: Hair cells in the inner ear, cutaneous receptors, proprioceptors.

Tonic Receptors: Non-adapting receptors that maintain a consistent response frequency and magnitude of action potentials as long as the stimulus is present.
- Examples: Nociceptors and photoreceptors.
Phasic Receptors: Adapting receptors; their response frequency decreases when stimuli are constant. They may also discharge briefly after stimuli are removed, resulting in an “afterimage.”
- Examples: Olfactory cells, thermoreceptors, and pressure mechanoreceptors.

Definition: The area of the body supplied by a particular sensory neuron.
Size and Sensitivity: The convergence of neurons can increase receptive field size, affecting sensory discrimination. Smaller receptive fields allow for greater sensitivity and discrimination, illustrated by the two-point discrimination threshold test.

Type (Modality): The nature of the stimulus.
Type of Receptor Stimulated: Influences the neural pathway activated.
Intensity of Stimulus: Measured by the number of receptors activated and the frequency of action potentials.
Location of Stimulus: Related to the area of the primary somatosensory cortex that is stimulated.
Duration of Stimulus: Linked to the length of neural stimulation to the brain.

Somatic Senses: Sensory information from skin, muscles, tendons, joints, and internal organs.
Visceral Senses: Sensory information from internal organs.
Special Senses: Such as gustation, olfaction, hearing, equilibrium, and vision.

Fine Touch, Pressure, Temperature, and Pain: Receptors derived from the dendrites of sensory neurons, mainly mechanoreceptors.

Definition: Specialized mechanoreceptors that provide information about body position and movement.
Types:
- Muscle Spindles: Located within muscles; respond to muscle stretch, stimulating contraction to avoid tears.
- Golgi Tendon Organs: Located in tendons; respond to excessive tension, inducing muscle relaxation to prevent tendon injury.
- Joint Receptors: Located in joint capsules; provide information regarding joint activity.

Stimulus: Molecules dissolved in saliva, acting as chemical stimuli.
Receptor: Taste receptor cells located within taste buds, classified as chemoreceptors.
- Microvilli interact with dissolved food molecules, sending signals to sensory neurons.

Stimulus: Odorant molecules which are also chemical stimuli.
Receptor: Olfactory receptor cells found in olfactory epithelium; these are also chemoreceptors and are involved in the detection of airborne molecules.

Structure: Modified epithelial cells with stereocilia arranged in increasing heights; the tallest cilium is known as the kinocilium.
Function: Bathed in endolymph rich in K+. Bending of stereocilia depolarizes or hyperpolarizes hair cells based on the direction of movement, affecting neurotransmitter release.

Stimulus: Sound waves acting on hair cells which are mechanoreceptors.
Neural Pathway: Action potentials generated in hair cells are sent to the brain, responding to varying frequencies and amplitudes (sound intensity) of the sound waves.

Vestibular Apparatus: Comprises semicircular canals, utricle, and saccule to detect rotational and linear acceleration. Hair cells act as mechanoreceptors, signaling body movements.

Light Detection: The human eye detects wavelengths of visible light which correspond to color perception. Given wavelengths create different colors.
Pathway of Light: Light travels through the pupil to the retina, which consists of multiple cell layers including ganglion cells, bipolar cells, and photoreceptors.
Retina Anatomy: Contains rods (for night vision and peripheral vision) and cones (for color vision and visual acuity).
Visual Pathway: Involves processing visual information whether it involves right or left visual fields, optic nerves, and the corresponding cortical areas of the brain.