Sensory perception involves the processing of stimuli through the nervous system.
All stimuli, including light and sound, are converted (transduced) by sensory receptors and processed via different pathways.
Responses to stimuli are executed through motor outputs such as moving away from danger or seeking food.
Sensory Reception: Begins when a stimulus is detected by sensory receptors.
Example: Bright light entering through a window.
Transduction: Conversion of stimulus into an action potential by the peripheral nervous system.
Transmission: The action potential is sent through the spinal cord to the brain.
Perception: The final stage where the brain interprets the stimulus.
Example: Touching a hot stove might not be consciously perceived until after reaction.
Reflex actions can occur without conscious perception, often through a rapid process known as a reflex arc.
Example: Pulling away from a hot surface occurs without conscious thought, but is still a perception mechanism.
Sensory pathways start with sensory reception and involve different types of receptors.
Five major types of sensory receptors:
Mechanoreceptors: Detect physical deformation (e.g., touch, hearing).
Chemoreceptors: Respond to chemical stimuli (e.g., taste, smell).
Electromagnetic receptors: Detect light (e.g., vision).
Thermoreceptors: Sense temperature changes.
Pain receptors (nociceptors): Respond to harmful stimuli.
Action potentials represent nerve impulses transmitting signals through neurons.
Conditions of resting state:
Neuron membrane is polarized, with inside being negatively charged (~-70mV).
Initiation of an action potential occurs when a stimulus causes the membrane potential to reach a threshold (~-55mV), resulting in depolarization.
Signals travel along the axon of the neuron, similar to ripples in a pond.
Action potentials can be graded, meaning that stronger stimuli generate higher frequency of action potentials.
Example: Stronger smell or pressure results in more frequent action potentials compared to gentler stimuli.
Different sensory modalities (e.g., sight, hearing, taste) have separate neural pathways.
Example of synesthesia, where sensory modalities overlap, causing mixed perception.
Sensory organs are complex structures or groups of cells that include:
Eyes: For vision, detecting light and color via rods and cones.
Ears: For hearing and balance, utilizing mechanoreceptors.
Nose: For smell, using chemoreceptors.
Skin: For touch, detecting pressure and temperature.
Taste buds: For taste, sensing five primary taste categories (sweet, sour, salty, bitter, umami).
Taste (Gustation): Sensing of molecules via tasteants, with ability to perceive multiple flavors from one taste bud.
Smell (Olfaction): Involves detection of odorant molecules binding to olfactory receptors in the nasal cavity, transmitting signals to the olfactory bulb for perception.
The relationship between taste and smell enhances the overall perception of flavor.
Understanding of sensory perception systems prepares for further exploration into the muscular and skeletal systems, particularly how sensory input influences motor responses.
Movement and muscle contraction are dependent on sensory input and require coordination involving the nervous system.