Neuroscience: Brain Stem and Spinal Cord Quiz

Quranic Verse

• The verse from Surah al-Zariyat states: "And in the earth are signs for those who have certainty (of faith)."
• The verse also says: "And within yourselves - then why do you not see?"

White Matter of the Spinal Cord

• Surrounds the central gray matter; contains short and long tracts.
• Divided into two halves.
• Each half is further divided into three columns: dorsal, lateral, and ventral.
• The dorsal column is split into the gracile fasciculus (medially) and the cuneate fasciculus (laterally), by the intermediate septum.

Brain Stem Structures and Features

• The brain stem connects the cerebrum to the spinal cord.
• It is located on the basilar part of the occipital bone (clivus).
• The brain stem comprises three main structures: midbrain, pons, and medulla oblongata.
• Each part of the brain stem is linked to the cerebellum by cerebellar peduncles (superior, middle, and inferior).

Cranial Nerves

• There are four cranial nerves that emerge from the medulla: hypoglossal (12th), glossopharyngeal (9th), vagus (10th), and accessory (11th).
• The glossopharyngeal, vagus, and accessory cranial nerves emerge from the posterolateral sulcus.
• The hypoglossal nerve originates from the anterolateral sulcus.
• The midbrain has one nerve: trochlear (4th).

Spinal Tracts (Ascending & Descending)

• **Ascending Tracts (Sensory):**These tracts carry sensory information from peripheral receptors to higher brain centers; they either:
  • Connect spinal cord to higher centers (long tracts).
  • Connect different segments of the spinal cord (short tracts).
• Descending Tracts (Motor): These tracts carry motor commands from the brain to the spinal cord via two motor neurons: upper motor neurons (UMNs) and lower motor neurons (LMNs).

Lesions of the Spinal Cord

• Spinal cord lesions can result in various neurological symptoms, depending on the location and extent of the damage.
• Different types of lesions affect different parts of the spinal cord.

Motor Neuron Signs

• Upper Motor Neuron (UMN) Lesion: Signs include disuse atrophy, no fasciculations, spastic paresis, hyperreflexia, and the Babinski sign (normal in infants).
• Lower Motor Neuron (LMN) Lesion: Signs include denervation atrophy, fasciculations, flaccid paresis, hyporeflexia, and the Babinski sign.

Poliomyelitis

• Poliomyelitis is a highly contagious viral infection caused by the poliovirus.
• It can cause severe nerve injury, irreversible paralysis, and breathing difficulties, possibly leading to death.

Lumbar Puncture

• Definition: introducing a needle into the subarachnoid space for drug injection or CSF sampling.
• Site: the needle is introduced between L3-L4.

Brain Stem Functions

• Pathways between cerebral cortex and spinal cord.
• Origin and emergence site of cranial nerves.
• Reticular formation for consciousness and regulation of cardiovascular and respiratory systems.

Medulla Oblongata

• Ventral surface:
• Ventral median fissure: divides the medulla into two halves; characterized by decussation (crossing over) of most pyramidal fibers.
• Pyramid: elevation on either side of the ventral median fissure (produced by the corticospinal tract).
• Olive: elevation lateral to the pyramid (produced by inferior olivary nucleus).

Pons

• Ventral surface:
• Basilar sulcus: divides the pons into two halves, containing the basilar artery.
• Pontocerebellar fibers: originate from pontine nuclei, cross the midline, and pass through the contralateral middle cerebellar peduncle to enter the opposite cerebellar hemisphere.

Midbrain

• Dorsal surface: Marked by four elevations: two superior colliculi (visual reflexes), two inferior colliculi (auditory pathway). The trochlear (4th) nerve emerges from the dorsal surface of the midbrain.