Cerebral Cortex and Sensory Tracts

Cerebral Cortex

• Somatic sensory area I and II are located on the postcentral gyrus.
• The somatic sensory areas are crucial for processing sensory information, including touch, temperature, pressure, and pain. Damage to these areas can lead to specific sensory deficits.

Sensory Tracts

• Sensory information is transmitted to the brain through various tracts.
• Dorsal Columns (Lemniscal System) transmits fine touch, proprioception, and vibration.
• Spinothalamic Tract transmits pain, temperature, itch, and crude touch.
• Dorsal Pathway: The dorsal pathway is responsible for carrying information about fine touch, proprioception, and vibration. It crosses over at the level of the medulla.
• Spinothalamic Pathway: The spinothalamic pathway carries information about pain, temperature, and crude touch. It crosses over in the spinal cord.

Sensory Representation on the Cortex

• Sensory information is represented on the cortex in a somatotopic map, known as the homunculus.
• This map is upside down with a larger representation for areas with a higher density of sensory receptors.

Touch

• Touch is transmitted through both the Dorsal Columns (fine touch) and the Ventral Spinothalamic Tract (crude touch).
• Proprioception is transmitted via the Dorsal Columns and mainly sent to the cerebellum.

Pain and Temperature

• There are two types of temperature receptors: those below body temperature and those above body temperature.
• Mild adaptation occurs for temperature receptors, but not above 40oC and below 20oC.
• Pain is sensed by free nerve endings and can be either sharp and sudden (Aδ fibers) or slow and dull (C fibers).
• Pain receptors are found in superficial and deep tissues and are not extensive in deeper tissue.
• Pain is a protective mechanism for the body, but pain receptors adapt very little, meaning that prolonged stimulation can increase pain.

Features of Pain

• Pain can be either superficial (localized) or deep/visceral (poorly localized).
• Visceral pain may be referred to different areas of the body.

Pain Pathways

• The fast pain pathway relays sharp, sudden pain through Aδ fibers and involves the neospinothalamic tract.
• The slow pain pathway relays dull, aching pain through C fibers and involves the paleospinothalamic tract.

Pain Control

• The brain has its own analgesic system that utilizes opioid receptors and naturally occurring opioids like endorphins, dynorphins, and enkephalin.
• The peri-aqueductal gray area, raphe magnus nucleus, and dorsolateral horn are crucial for pain inhibition.
• Pain control mechanisms include local suppression, lateral inhibition, and descending inhibition.

Referred Pain

• Referred pain is pain experienced in a part of the body distant from the source of the pain.
• Headaches are often a form of referred pain.

Dermatomes

• A dermatome is a skin area innervated by sensory fibers from a single nerve root.
• Dermatomes are essential for mapping the distribution of sensory nerve function.

This quiz focuses on the functions and pathways of the cerebral cortex, particularly the somatic sensory areas. It covers key aspects of sensory information transmission, including the dorsal columns and spinothalamic tracts, as well as the concept of sensory representation on the cortex.