Chapter 12 Objectives

Central Nervous System: Brain, Meninges & Cranial Nerves: Chapter 12

Brain Anatomy

The brain is the central organ of the nervous system, responsible for processing sensory information, coordinating voluntary and involuntary actions, and enabling cognition, emotion, and memory. It is divided into several major regions, each with specialized functions.

Cerebrum

• Cerebral Hemispheres: The cerebrum is divided into left and right hemispheres, connected by the corpus callosum. Each hemisphere controls the opposite side of the body.

• Sulci and Fissures:

  • Central sulcus: Separates the frontal and parietal lobes.

  • Lateral sulcus: Separates the temporal lobe from the frontal and parietal lobes.

  • Longitudinal fissure: Divides the two cerebral hemispheres.

• Gyri:

  • Precentral gyrus: Contains the primary motor cortex, responsible for voluntary movement.

  • Postcentral gyrus: Contains the primary somatosensory cortex, responsible for processing sensory information from the body.

• Lobes of the Cerebrum:

  • Frontal lobe: Involved in reasoning, planning, movement, and problem-solving.

  • Parietal lobe: Processes sensory information such as touch, temperature, and pain.

  • Occipital lobe: Responsible for visual processing.

  • Temporal lobe: Involved in auditory processing and memory.

• White Matter: Composed of myelinated axons that connect different brain regions.

• Gray Matter: Contains neuron cell bodies, dendrites, and axon terminals; site of synaptic processing.

• Corpus Callosum: Large bundle of nerve fibers connecting the two cerebral hemispheres.

• Fornix: A C-shaped bundle of nerve fibers involved in memory formation.

Diencephalon

• Septum Pellucidum: Thin membrane separating the lateral ventricles.

• Choroid Plexus: Network of capillaries producing cerebrospinal fluid (CSF).

• Thalamus: Relay station for sensory and motor signals to the cerebral cortex.

  • Intermediate Mass: Connects the two halves of the thalamus.

• Hypothalamus: Regulates homeostasis, including temperature, hunger, and endocrine functions.

• Pituitary Gland: Major endocrine gland; connected to the hypothalamus by the infundibulum.

• Mammillary Bodies: Involved in memory processing.

• Pineal Gland (Epithalamus): Secretes melatonin, regulating sleep-wake cycles.

Cerebellum

• Arbor Vitae: Tree-like arrangement of white matter within the cerebellum, important for coordination and balance.

Brainstem

• Midbrain: Contains the corpora quadrigemina (superior and inferior colliculi), involved in visual and auditory reflexes.

• Pons: Relays signals between the cerebrum and cerebellum; involved in sleep and respiration.

• Medulla Oblongata: Controls vital autonomic functions such as heart rate and breathing.

• Spinal Cord: Connects the brain to the peripheral nervous system.

Ventricular System

• Lateral Ventricles: Paired cavities within each cerebral hemisphere containing CSF.

• Third Ventricle: Located in the diencephalon; connects to the lateral ventricles via the interventricular foramina.

• Cerebral Aqueduct: Connects the third and fourth ventricles.

• Fourth Ventricle: Located between the brainstem and cerebellum; continuous with the central canal of the spinal cord.

Protection of the Brain: Meningeal Layers, Septa, and Sinuses

The brain is protected by three connective tissue membranes called meninges, as well as specialized partitions (septa) and venous sinuses that drain blood from the brain.

Meningeal Layers

• Dura Mater: Tough, outermost layer with two sublayers:

  • Periosteal Layer: Attached to the inner surface of the skull.

  • Meningeal Layer: Closer to the brain tissue.

• Subdural Space: Potential space between dura mater and arachnoid mater.

• Arachnoid Mater: Middle, web-like meningeal layer.

• Subarachnoid Space: Contains cerebrospinal fluid and blood vessels.

• Arachnoid Granulations: Protrusions that allow CSF to drain into the venous system.

• Pia Mater: Thin, delicate inner layer adhering closely to the brain surface.

Dural Septa

• Falx Cerebri: Separates the two cerebral hemispheres.

• Falx Cerebelli: Separates the two cerebellar hemispheres.

• Tentorium Cerebelli: Separates the cerebrum from the cerebellum.

Venous Sinuses

Venous sinuses are channels that drain venous blood from the brain into the internal jugular veins.

Sinus Name	Location/Function
Superior sagittal sinus	Runs along the top of the falx cerebri; drains blood from the cerebral hemispheres
Inferior sagittal sinus	Runs along the lower edge of the falx cerebri
Straight sinus	Formed by the union of the inferior sagittal sinus and great cerebral vein
Transverse sinus	Runs horizontally along the tentorium cerebelli
Confluence of sinuses	Junction of several sinuses at the internal occipital protuberance
Occipital sinus	Located in the attached margin of the falx cerebelli
Sigmoid sinus	S-shaped sinus that drains into the internal jugular vein

Cranial Nerves

There are 12 pairs of cranial nerves, each with specific sensory, motor, or mixed functions. They emerge directly from the brain and brainstem and are numbered I to XII.

Number	Name	Function	Type
I	Olfactory	Smell	Sensory
II	Optic	Vision	Sensory
III	Oculomotor	Eye movement, pupil constriction	Motor
IV	Trochlear	Eye movement (superior oblique muscle)	Motor
V	Trigeminal	Sensory from face, motor to muscles of mastication	Both
VI	Abducens	Eye movement (lateral rectus muscle)	Motor
VII	Facial	Facial expression, taste (anterior 2/3 of tongue)	Both
VIII	Vestibulocochlear	Hearing and balance	Sensory
IX	Glossopharyngeal	Taste (posterior 1/3 of tongue), swallowing	Both
X	Vagus	Parasympathetic control of heart, lungs, digestive tract	Both
XI	Accessory	Motor to sternocleidomastoid and trapezius muscles	Motor
XII	Hypoglossal	Motor to tongue muscles	Motor

• Mnemonic for Names/Order: Oh Oh Oh To Touch And Feel Veronica’s Gucci Vest, Ah Heaven!

• Mnemonic for Function (Sensory/Motor/Both): Sister Said Marry Money But Mary’s Brother Said Bad Business My Man!

Comparison: Human vs. Sheep Brain

• Size and Shape: The human brain is larger and more rounded, while the sheep brain is smaller and elongated.

• Olfactory Bulbs: More prominent in sheep, reflecting their reliance on smell.

• Cerebral Cortex: More convoluted in humans, allowing for greater cognitive abilities.

Example: The precentral gyrus in both human and sheep brains contains the primary motor cortex, but its size and complexity are greater in humans, supporting advanced voluntary movements.

Additional info: The ventricular system is essential for the production, circulation, and drainage of cerebrospinal fluid, which cushions the brain and removes metabolic waste.