Brain Anatomy Pdf Free Download

The brain is a complex organ that controls thought, memory, emotion, touch, motor skills, vision, breathing, temperature, hunger and every process that regulates our body. Together, the brain and spinal cord that extends from it make up the central nervous system, or CNS.

Weighing about 3 pounds in the average adult, the brain is about 60% fat. The remaining 40% is a combination of water, protein, carbohydrates and salts. The brain itself is a not a muscle. It contains blood vessels and nerves, including neurons and glial cells.

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Gray and white matter are two different regions of the central nervous system. In the brain, gray matter refers to the darker, outer portion, while white matter describes the lighter, inner section underneath. In the spinal cord, this order is reversed: The white matter is on the outside, and the gray matter sits within.

The brain sends and receives chemical and electrical signals throughout the body. Different signals control different processes, and your brain interprets each. Some make you feel tired, for example, while others make you feel pain.

The cerebrum (front of brain) comprises gray matter (the cerebral cortex) and white matter at its center. The largest part of the brain, the cerebrum initiates and coordinates movement and regulates temperature. Other areas of the cerebrum enable speech, judgment, thinking and reasoning, problem-solving, emotions and learning. Other functions relate to vision, hearing, touch and other senses.

The spinal cord extends from the bottom of the medulla and through a large opening in the bottom of the skull. Supported by the vertebrae, the spinal cord carries messages to and from the brain and the rest of the body.

The pineal gland is located deep in the brain and attached by a stalk to the top of the third ventricle. The pineal gland responds to light and dark and secretes melatonin, which regulates circadian rhythms and the sleep-wake cycle.

The ventricles manufacture cerebrospinal fluid, or CSF, a watery fluid that circulates in and around the ventricles and the spinal cord, and between the meninges. CSF surrounds and cushions the spinal cord and brain, washes out waste and impurities, and delivers nutrients.

The external carotid arteries extend up the sides of your neck, and are where you can feel your pulse when you touch the area with your fingertips. The internal carotid arteries branch into the skull and circulate blood to the front part of the brain.

The vertebral arteries follow the spinal column into the skull, where they join together at the brainstem and form the basilar artery, which supplies blood to the rear portions of the brain.

The circle of Willis, a loop of blood vessels near the bottom of the brain that connects major arteries, circulates blood from the front of the brain to the back and helps the arterial systems communicate with one another.

processing.... Drugs & Diseases > Anatomy Brain Anatomy Updated: Aug 24, 2015 Author: Anand I Rughani, MD; Chief Editor: Thomas R Gest, PhD more... Share Print Feedback Close Facebook Twitter LinkedIn WhatsApp Email webmd.ads2.defineAd({id: 'ads-pos-421-sfp',pos: 421}); Sections Brain Anatomy Sections Brain Anatomy Overview Gross Anatomy: Cerebrum Gross Anatomy: Cortex Gross Anatomy: Brainstem and Cranial Nerves Gross Anatomy: Cerebellum Gross Anatomy: Meninges Gross Anatomy: Ventricles and Cerebrospinal Fluid Gross Anatomy: Blood Vessels Microscopic Anatomy Functional Neuroanatomy Show All Media Gallery References Overview Overview The central nervous system consists of the brain and the spinal cord. The peripheral nervous system consists of the extensions of neural structures beyond the central nervous system and includes somatic and autonomic divisions.

The brain is composed of 3 main structural divisions: the cerebrum, the brainstem, and the cerebellum (see the images below). At the base of the brain is the brainstem, which extends from the upper cervical spinal cord to the diencephalon of the cerebrum. The brainstem is divided into the medulla, pons, and midbrain. Posterior to the brainstem lies the cerebellum.

The outermost layer of the cerebrum is the cortex, which has a slightly gray appearance--hence the term "gray matter." The cortex has a folded structure; each fold is termed a gyrus, while each groove between the folds is termed a sulcus. Cortical anatomy is discussed in greater detail below.

Below the cortex are axons, which are long fibers that emanate from and connect neurons. Axons are insulated by myelin, which increases the speed of conduction. Myelin is what gives the white appearance to these fibers of the brain--hence the term "white matter."

The limbic system is a grouping of cortical and subcortical structures involved in memory formation and emotional responses. The limbic system allows for complex interactions between the cortex, the thalamus, the hypothalamus, and the brainstem. The limbic system is not defined by strict anatomic boundaries but incorporates several important structures. The limbic structures conventionally include the amygdala, the hippocampus, the fornix, the mammillary bodies, the cingulate gyrus, and the parahippocampal gyrus.

The amygdala is a collection of nuclei that lies within the uncus. It receives multiple modes of sensory information as inputs. The outputs from the amygdala travel through the stria terminalis and the ventral amygdalofugal pathway. Output structures include the hypothalamus, as well as the thalamus, hippocampus, brainstem, and cortex. The amygdala appears to be involved in mediating the emotional aspects of memory, especially the subjective aspects of fear responses.

Positioned between the brainstem and the telencephalon, the diencephalon is composed of the thalamus, the epithalamus, the subthalamus, and the hypothalamus. The thalamus serves as a relay station for ascending input to the cortex and receives information from each of the cardinal senses (except smell). It is hypothesized that the thalamus serves a gating function in filtering information. The thalamus consists of multiple nuclei that are briefly described here (see the image below).

Other thalamic structures not included in the anatomic divisions above include the medial and lateral geniculate bodies, which process auditory and visual information, respectively. The pulvinar connects reciprocally with the parietal and occipital association cortex. Intralaminar nuclei within the internal medullary lamina obtain input from the brainstem, cerebellum, and other thalamic nuclei and project to basal nuclei structures and other thalamic nuclei. Amongst the intralaminar nuclei, the centromedian nucleus is a part of the reticular activating system, which plays a role in maintaining cortical arousal.

Located between the midbrain and the thalamus, the subthalamus contains the subthalamic nucleus, the red nucleus, and the substantia nigra. Subthalamic structures are closely integrated with the basal nuclei and play a role in modulation of movement.

The neocortex is the most phylogenetically developed structure of the human brain as compared with the brains of other species. The complex pattern of folding allows an increased cortical surface to occupy a smaller cranial volume. The pattern of folding that forms the sulcal and gyral patterns remains highly preserved across individuals. This enables a nomenclature for the cortical anatomy.

Similarly, the temporal lobe is divided into the superior, middle, and inferior temporal gyri, which are separated by the superior and inferior temporal sulci. On the inferior surface of the temporal lobe just lateral to the midbrain the parahippocampal gyrus can be identified, with the collateral sulcus lying lateral. Between the parahippocampal gyrus and the inferior temporal gyrus lies the occipitotemporal gyrus, also known as the fusiform gyrus.

Evolutionarily, the brainstem is the most ancient part of the brain. Structurally, it can be divided into the medulla oblongata, pons, and midbrain. These three structures are briefly described below. Cross-sectional anatomy of the brainstem is rather complex, given the multiple traversing pathways and cranial nerve nuclei (see the image below). [1, 2, 3]

The medulla oblongata, or simply medulla, is continuous with and superior to the cervical spinal cord. There are several external anatomic features of the medulla that can be visible grossly. Ventrally, the pyramids and pyramidal decussation is visualized just below the pons. These are the descending corticospinal tracts. Just lateral to the pyramids, the rootlets of the hypoglossal nerve can be seen as they exit the brainstem. Lateral to the rootlets of the hypoglossal nerve is the inferior olive. Dorsolateral to the inferior olive, the rootlets of the 9th and 10th cranial nerves (glossopharyngeal and vagus) exit.

On either side of the midline, there are bulges that are produced by the descending corticospinal tracts. At the pontomedullary junction, the 6th cranial nerve (abducens) can be seen exiting the brainstem. Laterally, but anterior to the middle cerebellar peduncle, the fifth cranial nerve (trigeminal) is seen exiting the brainstem. Below the middle cerebellar peduncle, the seventh and eighth cranial nerves (facial and vestibulocochlear) can be seen exiting. Dorsally, the pons forms the floor of the fourth ventricle.

The midbrain, also termed the mesencephalon, is the superiormost aspect of the brainstem. Ventrally, the midbrain appears as 2 bundles that diverge rostrally as the cerebral peduncles. Between the cerebral peduncles, the third cranial nerve (oculomotor) can be seen exiting. The fourth cranial nerve (trochlear) exits dorsally and is unique in this regard. It then courses anteriorly against the cerebral peduncles. 006ab0faaa