Grey & White Matter in the Brain

Grey and White Matter

• Grey matter consists of cell bodies and is found in the horns (anterior, posterior, and lateral) of the spinal cord.
• The dorsal horn processes sensory (ascending) information, the lateral horn processes autonomic information, and the ventral horn processes motor (descending) information.
• White matter is composed of axons and forms columns or tracts.

White Matter Tracts

• Blue tracts are sensory and transmit pain and temperature information.
• Red tracts are motor and transmit voluntary movement information.
• Lateral spinothalamic tract transmits pain and temperature information.
• Anterior spinothalamic tract transmits touch information.
• Corticospinal tract transmits voluntary movement information.
• Medial tract transmits involuntary control information.

Regional Differences

• A: Cervical region
• B: Thoracic region
• C: Lumbar region
• D: Sacral region

Peripheral Nervous System

• Cranial nerves (III-XII) and spinal nerves are part of the peripheral nervous system.
• Cranial nerves enter and exit the CNS via the brainstem.
• Spinal nerves enter and exit the spinal cord.
• T1-L2 contain sympathetic NS axons, and S2-4 contain parasympathetic NS axons.

Dorsal and Ventral Roots

• Dorsal (afferent) roots transmit sensory information into the spinal cord.
• Ventral (efferent) roots transmit motor information from the spinal cord to the body.
• Dorsal and ventral roots form spinal nerves.

Dermatomes and Myotomes

• A dermatome is the area of skin innervated by a single spinal nerve.
• A myotome is a group of muscles innervated by a single spinal nerve.

Spinal Cord Injuries

• Paraplegia: paralysis of the lower limbs due to injury of the thoracic and lumbar cord.
• Quadriplegia/Tetraplegia: paralysis of upper and lower limbs due to injury of the cervical cord.
• C1-T1: paralysis of the diaphragm and respiratory muscles.
• C5: affects strength of deltoid and biceps.
• C7: affects strength of triceps, wrist flexors, and extensors.

Types of Injuries

• Anaesthesia: loss of all forms of sensation.
• Analgesia: inability to feel pain.
• Paralysis: loss of ability to move.
• Paresis: partial loss of voluntary movement.

Segmental Lesion

• Affects the horn, root, or spinal nerve.
• Results in altered/loss of sensation in dermatome, decreased/lost muscle power in myotome, and decreased/lost stretch reflex.
• Affects function of spinal cord segment only at the level of the lesion.

Vertical Tract Lesion

• Affects vertical tracts in the spinal cord.
• Results in altered/lost sensation below the level of the lesion, motor tract signs, and altered/lost control of BP, bladder, bowel control, and thermoregulation.
• Conveys ascending and descending information.
• Lesions interrupting vertical tracts result in loss of function below the level of the lesion.

Classification of Spinal Cord Injury

• Complete: no sensation and no voluntary movement below the spinal cord lesion, and no sensory or motor function in the lowest sacral region (S4-5).
• Incomplete: variable levels of sensation and/or movement in one limb compared to the other, and preservation of sensory and/or motor function in the lowest sacral segment.