Anatomy of the Central Nervous System

Coverings and Blood Supply of the Central Nervous System

• The brain and spinal cord are protected by the skull and vertebral column.
• The central nervous system (CNS) is enveloped by three membranes: dura mater, arachnoid mater, and pia mater.
• Dura Mater: The outermost layer, tough and fibrous, forming a loose bag around the CNS.
• Cranial Dura: Fuses with the periosteum in some regions, creating compartments in the cranial cavity through dural reflections.
• Key structures include the falx cerebri (between cerebral hemispheres) and tentorium cerebelli (above cerebellum).
• Dural venous sinuses serve as channels for venous drainage, located on the cranial cavity floor and along dural attachments.
• Arachnoid Mater: Thin, translucent membrane beneath the dura, separated by the subdural space.
• Pia Mater: Innermost layer, closely adherent to the brain and spinal cord surface; follows contours closely.
• The subarachnoid space between arachnoid and pia contains cerebrospinal fluid (CSF).
• Blood supply to the brain comes from internal carotid and vertebral arteries, forming the circulus arteriosus (circle of Willis).
• The spinal cord receives blood from vertebral arteries and segmental vessels (radicular arteries).
• The middle meningeal artery is the main vascular supply to the meninges.

Anatomy of the Spinal Cord

• Housed within the vertebral canal, the spinal cord is continuous with the brainstem (medulla oblongata).
• Contains 31 pairs of spinal nerves, facilitating communication between the CNS and peripheral structures.
• Spinal nerves split into dorsal (posterior) roots carrying sensory afferent fibers and ventral (anterior) roots carrying motor efferent fibers.
• The spinal cord does not extend the full length of the vertebral canal in adults, ending near L1-L2, with lumbar and sacral nerves forming the cauda equina.
• The cord structure includes a central core of grey matter with dorsal and ventral horns; grey matter has a characteristic 'H' shape.
• Dorsal horns: Site of sensory neuron termination; ventral horns: Contain motor neurons; lateral horns (in thoracic/upper lumbar): Contain sympathetic preganglionic neurons.
• White matter consists of ascending and descending tracts; principal ascending tracts include dorsal columns, spinothalamic tracts, and spinocerebellar tracts.
• The lateral corticospinal tract is crucial for voluntary movement control.

Anatomy of the Brain

• Dominated by cerebral hemispheres, characterized by a grey matter cortex and white matter core with embedded grey matter regions.
• Two hemispheres separated by the longitudinal fissure, accommodating the falx cerebri and containing the corpus callosum for inter-hemispheric communication.
• Ventricular System: CSF circulates through the fourth ventricle, cerebral aqueduct, and third ventricle, communicating with lateral ventricles.
• Brainstem: Includes medulla oblongata, pons, and midbrain; crucial for vital functions and links between the brain and spinal cord.
• Contains cranial nerve nuclei for sensory and motor functions related to the head and neck via 12 pairs of cranial nerves.
• Cerebellum: Attached to the brainstem, responsible for motor coordination, featuring a grey matter cortex and white matter branching structure.
• Diencephalon: Comprising epithalamus, thalamus, subthalamus, and hypothalamus, crucial for sensory regulation and the autonomic nervous system.
• The hypothalamus links to the pituitary gland, influencing neuroendocrine function.
• The cerebral cortex has convolutions (gyri and sulci) maximizing surface area, divided into frontal, parietal, temporal, and occipital lobes according to skull bones beneath.### Brain Structure and Lobes
• The parietal lobe is located posterior to the central sulcus and is separated from the temporal lobe by the lateral fissure.
• The tip of the temporal lobe is referred to as the temporal pole; the occipital lobe is situated posteriorly, ending at the occipital pole.
• Boundaries between parietal, temporal, and occipital lobes lack distinct sulci on the lateral surface, but are separated by the parieto-occipital sulcus on the medial surface.
• The cingulate sulcus runs parallel to the corpus callosum on the medial surface, outlining a cortex region known as the limbic lobe.

Functional Areas of the Cortex

• The frontal lobe contains the precentral gyrus, which is the primary motor cortex responsible for voluntary movement control.
• Each hemisphere of the primary motor cortex represents the opposite half of the body in a somatotopic manner due to decussation of motor neurones at the brainstem and spinal cord.
• The parietal lobe features the postcentral gyrus, or primary somatosensory cortex, where modalities of touch, pressure, pain, and temperature are consciously perceived.
• The primary visual cortex is situated in the occipital lobe, primarily above and below the calcarine sulcus.
• The primary auditory cortex resides in the temporal lobe, specifically the superior temporal gyrus.
• The limbic lobe, mainly consisting of the cingulate gyrus, hippocampal formation, and amygdala, is involved in emotional behavior and memory.

Structural Organization of the Cerebral Hemisphere

• The cerebral hemisphere has a C-shaped configuration due to the temporal lobe's migration, with the lateral ventricle also taking on this shape, having extensions into the frontal, occipital, and temporal lobes.
• The outer layer consists of grey matter (cerebral cortex), while beneath lies a complex mass of white matter (nerve fibers), including the corona radiata and internal capsule.
• The basal ganglia, also known as basal nuclei or corpus striatum, consists of the caudate nucleus, putamen, and globus pallidus, playing a key role in controlling movement, posture, and muscle tone.

Brain Division and Sensory Pathways

• The brain is divided into hindbrain, midbrain, and forebrain, with the hindbrain comprising the medulla oblongata, pons, and cerebellum.
• The forebrain includes the diencephalon (thalamus and hypothalamus) and the cerebral hemisphere, which contains several nuclei called the basal ganglia.
• The brain houses cavities (ventricles) containing cerebrospinal fluid (CSF), produced by the choroid plexus.
• There are 12 pairs of cranial nerves facilitating communication with the head structures and linking the two cerebral hemispheres via the corpus callosum.

Sensory Information Processing

• Sensory information is transmitted through afferent nerve fibers in cranial and spinal nerves, divided into special and general senses.
• Special senses (olfaction, vision, taste, hearing, vestibular function) are carried by cranial nerves.
• General senses include touch, pressure, pain, temperature, and proprioception, with pathways relaying information via spinal and cranial nerves.
• A three-neurone sequence transmits general sensory information to the cerebral cortex:
  • The first-order neurone enters the CNS and synapses with the second-order neurone in the spinal cord or brainstem.
  • The second-order neurone decussates and ascends to the thalamus, where it connects with the third-order neurone.
  • The third-order neurone projects to the somatosensory cortex in the postcentral gyrus.

This quiz explores the anatomy of the central nervous system, focusing on its coverings and blood supply. Learn about the protective membranes, including the dura mater, and the relationship between the brain, spinal cord, and their bony structures. Test your knowledge on these vital aspects of CNS anatomy.