lecture recording on 18 March 2025 at 11.17.22 AM

Olfactory System

The olfactory nerve is the first cranial nerve and plays a crucial role in the sense of smell.
Carries action potentials from specialized sensory neurons in the olfactory epithelium, situated in the nasal cavity, to the brain.
Anatomical Pathway: The axons of olfactory sensory neurons travel through the cribriform plate of the ethmoid bone, which acts as a barrier between the nasal cavity and the cranial cavity. This structure is critical as it protects the brain while allowing olfactory information to pass through.
Action potentials generated in response to odorant molecules bind to olfactory receptors, triggering a neural signal that is transmitted to the olfactory bulb.
The olfactory bulb is responsible for processing these signals; it then synapses directly with the primary olfactory cortex located in the temporal lobe of the brain. Notably, this pathway bypasses the thalamus, a usual relay station for sensory information, indicating the direct route and significance of smell in everyday life.

The olfactory system is unique in its close connections to the limbic system, which includes structures such as the amygdala and hippocampus that are essential for memory and emotional responses.
This connection explains why certain scents can evoke strong emotional reactions and vivid memories, making olfaction a powerful sensory modality.

Sensation begins when a stimulus (e.g., a specific smell, temperature change from snow or heat from the sun) is detected by a specialized receptor in the sensory organs.
When a receptor detects a stimulus, it generates action potentials. The intensity and duration of the stimulus can also influence the frequency of action potentials.

Action potentials travel along afferent (sensory) neurons, through the spinal cord, and to the brain via specialized ascending tracts. This pathway is critical for transmitting sensory information from the periphery to central processing areas of the brain.

Perception refers to the conscious awareness and interpretation of sensory information. It involves complex processes within the brain that allow us to recognize and understand stimuli (e.g., identifying a stop sign or acknowledging a sound, such as music).
Different brain regions work together in this process, integrating sensory input to create a coherent understanding of our environment.

Problem: A patient reports difficulty in sensation, specifically an inability to feel touch on their skin.
Explanation: This may be due to significant damage to touch receptors caused by third-degree burns, resulting in the loss of sensory function in affected areas.

Problem: A patient presents with acute blindness, having intact optic nerves but unable to see.
Explanation: This condition indicates damage to the visual cortex of the brain, disrupting the process by which visual signals are interpreted, leading to a loss of perception of visual stimuli despite functioning eyes.

Problem: A patient experiences severe limitations, unable to feel anything below the waist.
Explanation: This condition arises from a severed spinal cord, which interrupts the conduction pathways necessary for sensory signals to reach the brain, resulting in a complete loss of sensation in the lower body.

General Senses: These are widely distributed throughout the body and include various modalities such as temperature, touch, pain, and proprioception (awareness of body position).
Special Senses: These are localized to specific organs in the head and include vision, hearing, equilibrium, taste (gustation), and smell (olfaction). Each special sense has dedicated pathways and processing areas in the brain.

Adaptation refers to the decrease in sensitivity to a continuous or unchanging stimulus over time. For example, individuals may no longer notice the cold sensation of water after remaining submerged for an extended period.
This phenomenon is significantly relevant in environments with constant stimuli, such as factories with loud machinery sounds or areas with persistent alarms, highlighting the body's ability to prioritize sensory input.

Nociceptors: Specialized for the detection of pain (nociception) in response to potentially harmful stimuli (extreme temperatures, physical damage).
Chemoreceptors: Detect specific chemical substances, essential for the senses of taste and smell, responding when chemicals bind to receptor ligands.
Mechanoreceptors: Respond to mechanical changes in the environment, such as touch, pressure, or vibration, providing critical information about physical interactions.
Thermoreceptors: Detect variations in temperature, allowing the body to respond appropriately to thermal changes.
Photoreceptors: Specialized for light detection; these receptors facilitate vision by converting light into neural signals.

Action potentials are initiated when gated channels in sensory neurons open in reaction to stimuli, leading to depolarization. Each type of receptor has a distinct function that corresponds to the type of stimuli it detects:
- Nociceptors: Responsible for identifying pain.
- Thermoreceptors: Specialized in detecting temperature variations.
- Mechanoreceptors: Critical for sensing physical changes in the environment (touch, pressure).

It is essential to review all vocabulary and concepts related to sensory systems, focusing on general and special senses.
Completing a comprehensive chart detailing the types of receptors, their anatomical structures, and corresponding functions is advised to facilitate deeper understanding and retention of the material.