Anatomy of Brain

 Anatomy of Brain 

The cerebrum makes up most of the brain. It is located inside the skull. The brain is made up of two hemispheres (left and right) and five lobes. All lobes, except one, are named according to the bone of the skull on which they rest: frontal, parietal, temporal, occipital and, the exception we mentioned, insular. The insula lobe is hidden beneath the frontal, temporal, and parietal lobes. “Insula” means island; Indeed, the insula is an “island” of gray matter hidden beneath the surface of the brain.

 You can probably find the term “limbic lobe” in some text, however, this is not actually a lobe. It is a functional group of interconnected brain regions that together control emotions, memory, and spatial perception; therefore, we refer to it as the “limbic system.” The brain, together with the hippocampus, amygdala, olfactory bulb, and basal ganglia, make up the telencephalon.

 The most superficial layer of the brain is the cerebral cortex. This is a layer of gray matter that has multiple folds (sulci and gyri), and can be categorized structurally (cytoarchitecture of the cerebral cortex) or functionally (Brodmann areas). It is home to several areas such as the primary motor cortex and the primary somatosensory cortex, and it is these two that make up the homunculus.

 White matter connections extend between the gray matter of the cerebral cortex to other parts of the same cerebral hemisphere (association fibers), to the opposite hemisphere (commissural fibers) and to structures outside the cortex (projection fibers).

Subcortical structures

Subcortical structures are a group of diverse structures found deep within the brain. They include the diencephalon (thalamus, epithalamus, subthalamus, and hypothalamus), pituitary gland, structures of the limbic system, and basal ganglia.

 These structures have a wide variety of functions, for example:

•  The hypothalamus and pituitary gland are involved in the production of hormones and their regulation.

•  The limbic system (hippocampus, fornix, amygdala, insular cortex and others) is involved in memory, smell, emotional behavior and the general physiological balance of the human body (homeostasis).

•  The basal ganglia are a functional group of nuclei that together comprise a unit of the extrapyramidal motor system, modifying its motor activity.

 Brainstem

 The brainstem is the most caudal portion of the brain. It is composed of the midbrain, pons, and medulla oblongata (medulla oblongata). The cerebellum, pons, and medulla oblongata are usually grouped together under the name rhombencephalon. The importance of the brainstem lies in its functions; It basically works as our survival center:

 It contains all nuclei for the cranial nerves (except the first and second cranial nerves), being the somatic and autonomic provider of control of the head and neck.

 It contains the nuclei of the reticular formation.

 It contains the sympathetic and parasympathetic nuclei, providing vital centers that control functions such as breathing, heart rate and vascular movements.

 All pathways between the spinal cord and the cerebrum/cerebellum pass through the brainstem.

 Cerebellum

 The cerebellum lies between the cerebrum and the medulla of the brainstem. It plays an important role in regulating motor functions by participating in planning, modulation of motor activity, and coordination of the body while in motion.

 Like the cerebrum, the cerebellum has two hemispheres (left and right). They are connected by a midline mass known as the vermis. It also has three lobes: anterior, posterior and flocculonodular.

 The cerebellar cortex forms the outer layer of the cerebellum and is composed of gray matter. Some important structures of the cerebellum include its paired nuclei in its white matter and the cerebellar peduncles.

Spinal cord

 The spinal cord is located through the vertebral column. It is contiguous to the brainstem, extending from the foramen magnum of the occipital bone to the level of the L1/L2 vertebrae. This caudal part of the central nervous system transmits information to and from the periphery by interacting with the peripheral nervous system. However, the spinal cord is more than just a channel between the brain and the body - it also modifies and integrates the information that passes through it and participates in reflexes.

 The spinal cord consists of 5 segmented groups:

•  Cervical spinal cord - 8 segments (C1-C8) 
•  Thoracic spinal cord - 12 segments (T1-T12)
•  Lumbar spinal cord - 5 segments (L1-L5)
•  Sacral spinal cord - 5 segments (S1-S5)
•  Coccygeal spinal cord - 1 segment (Co1)

 Unlike the brain, the outer layer of the spinal cord is made up of white matter. It is divided into three cords (funicles); anterior, lateral and posterior, and contains pathways that travel between the brain and the periphery. The central mass of the spinal cord has butterfly-shaped gray matter containing neuronal cell bodies.

 Meninges

 The meninges comprise three membranous layers: dura mater, arachnoid mater, and pia mater, which surround the brain and spinal cord.

The meninges protect the CNS structures, form separations and provide spaces. The separations created by the meninges divide the cerebrum and cerebellum and separate their hemispheres (falx cerebri, tentorium cerebellum, falx cerebellum, sellar diaphragm). The meningeal spaces contain the dural venous sinuses and cisterns filled with cerebrospinal fluid (CSF). Study the anatomy of the meninges with our learning resources.

 Ventricles and cerebrospinal fluid (CSF)

 The ventricles are interconnected cavities located deep in the brain. They are filled with cerebrospinal fluid, which functions to protect the brain and spinal cord, provide nutrients, and remove waste. There are four cerebral ventricles:

•  Two lateral ventricles - below the hemispheres of the brain.

•  Third ventricle – between the two thalami.

•  Fourth ventricle - located above the pons and medulla oblongata, below the cerebellum.

 Cerebrospinal fluid is produced by the cells of the choroid plexuses found between the walls of these ventricles. It then circulates through the ventricles through the foramina located between them. From the fourth ventricle, cerebrospinal fluid enters a system of subarachnoid cisterns, flows through the subarachnoid space of the brain and spinal cord until it is finally absorbed into the venous system of the CNS.

 Brain irrigation

 The blood supply to the brain comes from two main sources: the internal carotid and the vertebral arteries. The internal carotid forms the anterior circulation of the brain, supplying the anterior and middle portions of the brain. The vertebral arteries provide blood supply to the posterior region of the brain, brainstem, and cerebellum (posterior circulation). These two circulations anastomose at the base of the brain, forming a vascular network known as the circle of Willis.

Venous blood from the brain is drained through a system of superficial and deep veins. The superficial cerebral veins drain the cortex, while the deep veins drain the deep surfaces. Both groups eventually drain into the dural venous sinuses, which are enlarged venous channels found in the dura mater. The venous sinuses drain into the internal jugular vein.

 Peripheral nervous system

 The peripheral nervous system consists of 12 pairs of cranial nerves, 31 pairs of spinal nerves, and all their branches. Spinal nerves arise from segments of the spinal cord and innervate the body. Cranial nerves originate from the brainstem, predominantly innervating the head and neck region. Functionally, the PNS can be divided into the somatic nervous system and the autonomic nervous system (sympathetic and parasympathetic).

 cranial pairs

 The cranial nerves originate from the nuclei of the brain. They emerge from the foramina and fissures of the skull to provide motor and sensory innervation to the head and neck. Only the vagus nerve descends through the body below the level of the neck to innervate abdominal and thoracic viscera.

 The numerical order of these nerves is 1 to 12 and is determined by their order of exit from the skull (from rostral to caudal).

12 cranial pairs

•  Cranial nerve 1 Olfactory nerve (I cranial nerve) 
• Cranial nerve 2 Optic nerve (II cranial nerve) 
• Cranial nerve 3 Oculomotor nerve (III cranial nerve) 
• Cranial nerve 4 Trochlear or pathetic nerve (IV cranial nerve) 
• Cranial nerve 5 Trigeminal nerve (V cranial nerve) )
• Cranial nerve 6 Abducens or abducens nerve (VI cranial nerve)
• Cranial nerve 7 Facial nerve (VII cranial nerve)
• Cranial nerve 8 Vestibulocochlear nerve (VIII cranial nerve)
• Cranial nerve 9 Glossopharyngeal nerve (IX cranial nerve)
• Cranial nerve 10 Vagus nerve (X cranial nerve) 
• Cranial nerve 11 Accessory or spinal nerve (XI cranial nerve)
• Cranial nerve 12 Hypoglossal nerve (XII cranial nerve)