The Brain - Parts of the Brain PDF

Mrs. Sichela Recap on formation of Neural tube  The brain forms from the cranial (superior) part of the neural tube  By the late fourth week of development, three primary brain vesicles form, which eventually give rise to all the different regions of the adult brain.  The names of these vesi...

Mrs. Sichela Recap on formation of Neural tube  The brain forms from the cranial (superior) part of the neural tube  By the late fourth week of development, three primary brain vesicles form, which eventually give rise to all the different regions of the adult brain.  The names of these vesicles describe their relative positions in the developing head:  The forebrain is called the prosencephalon  The midbrain is called the mesencephalon  The hindbrain is called the rhombencephalon  By the fifth week of development, the three primary vesicles further develop into a total of five secondary brain vesicles Prosencephalon  Develops into 1. The telencephalon (cerebrum), which becomes the large cerebral hemispheres 2. The diencephalon, which is hidden from view in the adult brain by the cerebral hemispheres, consists of the epithalamus, thalamus, hypothalamus, and other related structures The mesencephalon  Is the only primary vesicle that does not form a new secondary vesicle  Develops into the midbrain, which surrounds cerebral aqueduct  Gives rise to superior and inferior colliculi and cerebral peduncles The Rhombencephalon  Develops into 1. The metencephalon, which gives rise to the cerebellum and the pons 2. The myelencephalon (medulla oblongata), the caudal most part of the brainstem, which ends at the foramen magnum  The adult brain consists of four major parts:  The cerebrum  The diencephalon  The brainstem  The cerebellum  The brain stem is continuous with the spinal cord and consists of the o medulla oblongata o Pons o midbrain.  Posterior to the brain stem is the cerebellum  Superior to the brain stem is the diencephalon  Supported on the diencephalon and brain stem is the cerebrum the largest part of the brain.  Two distinct tissue areas are recognized within the brain and spinal cord: gray matter and white matter.  The gray matter houses motor neuron and interneuron cell bodies, dendrites, telodendria, and unmyelinated axons.  The white matter derives its color from the myelin in the myelinated axons.  The white matter lies deep to the gray matter of the cortex.  Within the masses of white matter, are discrete internal clusters of gray matter called cerebral nuclei, which are oval, spherical, or sometimes irregularly shaped clusters of neuron cell bodies.  The brain, as well as the spinal cord, is surrounded by three layers of membranes (the meninges  These include  The dura mater: a tough, outer layer  The arachnoid mater: a delicate, middle layer  The pia mater: an inner layer firmly attached to the surface of the brain  The cranial meninges are continuous with, and similar to, the spinal meninges through the foramen magnum, with one important distinction-the cranial dura mater consists of two layers, and only one of these is continuous through the foramen magnum  Separate the soft tissue of the brain from the bones of the cranium  Enclose and protect blood vessels that supply the brain  Contain and circulate cerebrospinal fluid.  Some parts of the cranial meninges form some of the veins that drain blood from the brain.  The cranial dura mater is the thickest, toughest, outermost covering of the brain. It consists of: 1. The outer or periosteal layer  Also called endosteal-Is the endocranium of the cranial bones.  It is continuous with the pericranium at the foramina in the cranial bones.  At the foramen magnum, it is continuous with the pericranium covering the occipital bone.  The branches of middle meningeal artery and accompanying veins ascend on the external surface of the endosteal layer in the extradural space  The cranial dura mater is a thick, tough, outer covering of the brain. It consists of: 2. The inner meningeal layer  Is in close contact with the arachnoid mater  At the foramen magnum, it is continuous with the spinal dura mater.  The two layers of the dura mater are adherent to each other except in places, where o They enclose dural venous sinuses are present o the inner layer forms dural partitions or folds.  The dura mater folds on itself to form partitions  Project inward and incompletely separate parts of the brain They include the  Falx cerebri: passes between the two cerebral hemispheres  Tentorium cerebelli: covers and separates the cerebellum from the occipital lobe of cerebrum and forms the roof of the posterior cranial fossa  Falx cerebelli: partially separates the two cerebellar hemispheres  The diaphragma sellae: forms the hypophysial fossa in the sella turcica of the sphenoid bone. There is an opening in the center of the diaphragma sellae through which passes the infundibulum, connecting the pituitary gland with the base of the brain, and any accompanying blood vessels.  The arachnoid mater is very thin, avascular and transparent membrane.  It lines, but is not adherent to, the inner surface of the dura mater  From its inner surface thin processes or trabeculae extend downward, cross the subarachnoid space, and become continuous with the pia mater.  Unlike the pia, the arachnoid does not enter the grooves or fissures of the brain, except for the longitudinal fissure between the two cerebral hemispheres.  The pia mater is the innermost of the cranial meninges.  It is a thin layer of delicate areolar connective tissue that is highly vascularized and tightly adheres to the brain, following every contour of the surface.  There is a unique arrangement of meninges, coupled with real and potential spaces within the cranial cavity  A potential space is related to the dura mater, while a real space exists between the arachnoid mater and the pia mater. Extradural space  Is a potential space between the dura mater and the adjacent bone.  This space becomes apparent when extradural bleeding takes place due to rupture of meningeal vessels results in an extradural hematoma  Bleeding due to the tearing of a vein as it enters a dural venous sinus can result in a subdural hematoma. Subdural space  Is present between the dura mater and the arachnoid mater.  The superior cerebral veins pass through it.  Their rupture is the cause of subdural hemorrhage. Subarachnoid space  The subarachnoid space surrounds the brain and spinal cord and in certain locations it enlarges into expanded areas (subarachnoid cisterns).  It contains cerebrospinal fluid (CSF) and blood vessels  A pooling of blood outside of a vessel is referred to as a hematoma  An epidural hematoma is a pool of blood that forms in the epidural space of the brain.  Most epidural hematomas are caused by a severe blow to the side of the head, usually at the pterion, resulting in hemorrhage of the middle meningeal artery  A subdural hematoma is a hemorrhage that occurs in the subdural space between the dura mater and the arachnoid mater.  These hematomas typically result when veins are ruptured due to fast or violent rotational motion of the head  Largest part of the brain  Is composed of two halves, called the left and right cerebral hemispheres  The paired cerebral hemispheres are separated by a deep longitudinal fissure that is occupied by the falx cerebri  The hemispheres are connected internally by the corpus callosum at the floor of the longitudinal fissure  Three surfaces o Superolateral o Medial o Inferior surface (orbital and tentorial surface)  Three borders o Superomedial o Inferolateral o Inferomedial  Three poles o Frontal o Occipital o Temporal (at the anterior end of the temporal pole)  The outer surface of the cerebral hemisphere is has gray mater and is called cerebral cortex  It is highly folded due to the presence of sulci (depressions) and gyri (elevations).  The core of the hemisphere consists of white matter containing a group of nuclei called basal ganglia.  The cavity inside each hemisphere is called the lateral ventricle.  The longitudinal fissure of cerebrum intervenes between the medial surfaces of the right and left hemispheres.  At the bottom of the fissure lies the corpus callosum, which connects the cerebral hemispheres  It is abroad band of white matter containing axons that extend between the hemispheres  Each cerebral hemisphere can be further subdivided into several lobes.  The lobes are named after the bones that cover them: o Frontal o Parietal o Temporal o Occipital  The central sulcus separates the frontal lobe from the parietal lobe  Pre central gyrus: located anterior to the central sulcus. This is were the primary motor cortex is located. Responsible for controlling voluntary motor movement on the opposite side of the body  Post central gyrus: located posterior to the central sulcus. This contains the primary sensory area which receives sensory input from the opposite half of the body  The lateral cerebral sulcus separates the frontal lobe from the temporal lobe.  The parieto-occipital sulcus separates the parietal lobe from the occipital lobe.  Limbic Lobe Frontal Lobe Parietal Lobe Occipital Lobe Temporal Lobe The frontal lobe is the area of the brain responsible for higher cognitive functions. These include:  Problem-solving  Spontaneity  Memory  Speech: speaking and writing (Broca’s area- responsible for expressive motor speech)  Motivation  Judgment  Impulse control  Social and sexual behavior.  The temporal lobe plays a role in hearing, memory, emotions, processing visual information  The temporal lobe also contains the language area of the brain.  Understanding language (Wernicke’s area)  Injury to language areas of the cerebral cortex results in aphasia an inability to use or comprehend words. Damage to Broca’s speech area  Results in nonfluent aphasia, an inability to properly form words.  People with nonfluent aphasia know what they wish to say but cannot properly speak the words. Damage to Wernicke’s area  Results in fluent aphasia, characterized by faulty understanding of spoken or written words.  A person experiencing this type of aphasia may produce strings of words that have no meaning (“word salad”).  For example, someone with fluent aphasia might say, “I rang car porch dinner light river pencil”.  The parietal lobe plays a role in our sensations of touch, smell, and taste.  It also processes sensory and spatial awareness, and is a key component in eye-hand co- ordination and arm movement.  The occipital lobe is at the rear of the brain and controls vision and recognition.  The word insula means hidden.  The insula is a small lobe deep to the lateral sulcus.  It forms the floor of the lateral sulcus  The surface of the insula is marked by a number of sulci and gyri.  The middle cerebral blood vessels lie on its surface.  Its function is not fully known but is apparently involved in memory and the interpretation of taste.  Three categories of functional areas are recognized:  Motor areas that control voluntary motor functions  Sensory areas that provide conscious awareness of sensation  Association areas that primarily integrate and store information. They deal with more complex integrative functions such as memory, motions, reasoning, will, judgment, personality traits, and intelligence.  The cortical areas that control motor functions are housed within the frontal lobes.  The primary motor cortex, also called the somatic motor area, is located within the precentral gyrus of the frontal lobe  Neurons there control voluntary skeletal muscle activity.  The axons of these neurons project contralaterally (to the opposite side) to the brainstem and spinal cord.  Thus, the left primary motor cortex controls the right-side voluntary muscles, and vice versa.  The innervation of the primary motor cortex to various body parts can be diagrammed as a motor homunculus on the precentral gyrus  These reflect the amount of cortex dedicated to the motor activity of each body part.  The motor speech area, previously called the Broca’s area, is located in most individuals within the inferolateral portion of the left frontal lobe  This region is responsible for controlling the muscular movements necessary for vocalization.  The frontal eye field is on the superior surface of the middle frontal gyrus, which is immediately anterior to the premotor cortex  These cortical areas control and regulate the eye movements needed for reading and coordinating binocular vision  The cortical areas within the parietal, temporal, and occipital lobes typically are involved with conscious awareness of sensation.  Each of the major senses has a distinct cortical area.  The primary somatosensory cortex is housed within the postcentral gyrus of the parietal lobes.  Neurons in this cortex receive general somatic sensory information from touch, pressure, vibration, itch, tickle, temperature (coldness and warmth), pain, and proprioception (joint and muscle position) and is involved in the perception of these somatic sensations  A sensory homunculus may be traced on the postcentral gyrus surface, similar to the motor homunculus  The surface area of somatosensory cortex devoted to a body region indicates the amount of sensory information collected within that region.  Sensory information for sight, sound, taste, and smell arrives at other cortical regions  The primary visual cortex, located in the occipital lobe, receives and processes incoming visual information.  The primary auditory cortex, located in the temporal lobe, receives and processes auditory information.  The primary gustatory cortex is in the insula and is involved in processing taste information  The primary olfactory cortex, located in the temporal lobe, provides conscious awareness of smells.  The primary motor and sensory cortical regions are connected to adjacent association areas that either process and interpret incoming data or coordinate a motor response.  Association areas integrate new sensory inputs with memories of past experiences.  The following are the main association areas The premotor cortex  Also called the somatic motor association area, is located in the frontal lobe, immediately anterior to the precentral gyrus.  It permits us to process motor information and is primarily responsible for coordinating learned, skilled motor activities, such as moving the eyes in a coordinated fashion when reading a book  The prefrontal cortex  Also known as frontal association area  Is an extensive area in the anterior portion of the frontal lobe  Has numerous connections with other areas of the cerebral cortex, thalamus, hypothalamus, limbic system, and cerebellum.  The prefrontal cortex is concerned with the makeup of a person’s personality, intellect, complex learning abilities, recall of information, initiative, judgment, foresight, reasoning, conscience, intuition, mood, planning for the future, and development of abstract ideas The somatosensory association area  Is located in the parietal lobe and lies immediately posterior to the primary somatosensory cortex.  It interprets sensory information and is responsible for integrating and interpreting sensations to determine the texture, temperature, pressure, and shape of objects. The auditory association area  Is located within the temporal lobe, posteroinferior to the primary auditory cortex.  Within this area, the cortical neurons interpret the characteristics of sound and store memories of sounds heard in the past. Wernicke’s (posterior language) area  A broad region in the left temporal and parietal lobes  The Wernicke area is involved in recognizing, understanding, and comprehending spoken or written language. The visual association area  Is located in the occipital lobe and surrounds the primary visual area.  It enables us to process visual information by analyzing color, movement, and form, and to use this information to identify the things we see.  Receives sensory impulses from the primary visual area and the thalamus. The gnostic area (or common integrative area)  Is composed of regions of the parietal, occipital, and temporal lobes.  This region integrates all sensory, visual, and auditory information being processed by the association areas within these lobes.  Thus it provides comprehensive understanding of a current activity  The cerebral white matter consists primarily of myelinated axons in three types of tracts : 1. Association tracts: contain axons that conduct nerve impulses between gyri in the same hemisphere. 2. Commissural tracts: contain axons that conduct nerve impulses from gyri in one cerebral hemisphere to corresponding gyri in the other cerebral hemisphere.  Three important groups of commissural tracts are the o corpus callosum o anterior commissure o Posterior commissure. 3. Projection tracts: contain axons that conduct nerve impulses from the cerebrum to lower parts of the CNS (thalamus, brain stem, or spinal cord) or from lower parts of the CNS to the cerebrum.  An example is the internal capsule, a thick band of white matter that contains both ascending and descending axons  The basal ganglia or the basal nuclei are the collections of gray matter situated inside the cerebral hemisphere.  The basal ganglia belong to the extrapyramidal system and their lesion results in movement disorders in the body. Component Nuclei  Broadly, the basal ganglia consist of four nuclei:  Caudate nucleus  Lentiform nucleus  Claustrum  Amygdaloid nucleus: has complex chemical connections with the limbic system and hence functionally, it belongs to the limbic system.  The lentiform nucleus consists of the lateral part called putamen and the medial part called the globus pallidus  The structure and functions of the putamen and globus pallidus are different.  Corpus Striatum includes the caudate nucleus and the lentiform nucleus.  Striatum: the caudate nucleus and the putamen of the lentiform nucleus are similar in structure and connections. Therefore together, they are called the striatum.  Pallidum: the globus pallidus is known as the pallidum  The caudate nucleus has a large “head” connected to a smaller “tail” by a long comma-shaped “body  Receive input from the cerebral cortex and provide output to motor parts of the cortex via the thalamus  A major function of the basal nuclei is to help regulate initiation and termination of movements.  Also control subconscious contractions of skeletal muscles. Examples include automatic arm swings while walking  They help initiate and terminate some cognitive processes, such as attention, memory, and planning, and may act with the limbic system to regulate emotional behaviors.  The cerebellum, the second-largest part of the brain  The cerebellum is located posterior to the medulla oblongata and pons and inferior to the occipital lobes of cerebrum in the posterior cranial fossa  A deep groove between the cerebrum and cerebellum known as the transverse fissure is occupied by the tentorium cerebelli  The central constricted area is the vermis and on each side are the cerebellar hemispheres.  Each hemisphere consists of two lobes, the anterior lobe and the posterior lobe, which are separated by the primary fissure.  On the anterior and inferior to each cerebellar hemisphere are the slender flocculonodular lobes  The cerebellum is partitioned internally into three regions:  An outer gray matter layer of cortex, an internal region of white matter  The deepest gray matter layer, which is composed of cerebellar nuclei.  The white matter of the cerebellum is called the arbor vitae because its distribution pattern resembles the branches of a tree.  Cerebellum  Its function is to coordinate voluntary muscle movements and to maintain posture and balance.  The cerebellum is connected to the rest of the nervous system by three pairs of peduncles  The cerebellar peduncles anchor the cerebellum to the brainstem.  All afferent and efferent fibers of the cerebellum pass through the three peduncles and the pons to the other levels of the nervous system.  Three thick tracts, called peduncles, link the cerebellum with the brainstem  The superior cerebellar peduncles connect the cerebellum to the mesencephalon (midbrain)  The middle cerebellar peduncles connect the pons to the cerebellum.  The inferior cerebellar peduncles connect the cerebellum to the medulla oblongata.  It is these extensive communications that enable the cerebellum to “fine- tune” skeletal muscle movements and interpret all body proprioceptive movement.  The diencephalon lies at the top of the brain stem, under and between the cerebral hemispheres  It is divided into two symmetrical halves by the cavity of the third ventricle.  Includes the  Thalamus  Hypothalamus  Epithalamus  Each part of the thalamus is a gray matter mass composed of about a dozen major thalamic nuclei that are organized into groups; axons from these nuclei project to particular regions of the cerebral cortex Functions  The thalamus is a relay station for nearly all sensory information to the cortex, including vision, taste, touch and balance, but excludes olfactory information  It maintains the state of wakefulness and alertness  In addition, the thalamus contributes to motor functions by transmitting information from the cerebellum and basal nuclei to the primary motor area of the cerebral cortex.  Is the anteroinferior region of the diencephalon  A thin, stalk like infundibulum extends inferiorly from the hypothalamus to attach to the pituitary gland  Although the hypothalamus is small, it controls many critical bodily functions:  Controls autonomic nervous system  Center for emotional response and behavior  Regulates body temperature The hypothalamus is shaded blue.  Regulates food intake The pituitary gland extends from the  Regulates water balance and thirst hypothalamus.  Controls sleep-wake cycles  Controls endocrine system  The epithalamus partially forms the posterior roof of the diencephalon and covers the third ventricle.  The posterior portion of the epithalamus houses the pineal gland and the habenular nuclei.  The pineal gland (or pineal body) is an endocrine gland. It secretes the hormone melatonin, which appears to help regulate day–night cycles known as the body’s circadian rhythm.  The habenular nuclei help relay signals from the limbic to the mesencephalon and are involved in visceral and emotional responses to odors. The brainstem consists of the  Midbrain  Pons  Medulla Oblongata  The brainstem gives passage to the various ascending and descending tracts besides housing nuclei of third to twelfth cranial nerves.  The functional significance of the brainstem is that it houses the vital centers for the control of respiration, cardiovascular activity and alertness.  Also known as Mesencephalon  The midbrain is the shortest and the uppermost part of the brainstem.  It is connected to the cerebellum by superior cerebellar peduncle  Extending through the mesencephalon is the cerebral aqueduct connecting the third and fourth ventricles Parts of Midbrain  The tectum is the part that lies posterior to the cerebral aqueduct.  It consists of one pair of superior colliculi and one pair of inferior colliculi.  The cerebral peduncles (right and left) are located anterior to the cerebral aqueduct.  Subdivisions of Cerebral Peduncle o Crus cerebri anteriorly o Substantia nigra in the middle o Tegmentum posteriorly.  The crura cerebri and substantia nigra are bilaterally present but the tegmentum is single and is traversed by cerebral aqueduct.  It also acts as a relay station between the lower centers and the higher centers of the brain, but also contains important  Visual reflex centers (superior colliculi)  Auditory reflex centers (inferior colliculi)  Has motor pathways that connect the cerebrum to the cerebellum.  Also houses nuclei of two cranial nerves that control some eye movements are housed in the mesencephalon: o the oculomotor nerve (CN III) o the trochlear nerve (CN IV).  The pons is between the midbrain and the medulla oblongata.  In fact, pons means “bridge” in Latin.  Housed within the pons are sensory and motor tracts that connect to the brain and spinal cord.  Is connected to the cerebellum via the middle cerebellar peduncles  The pons also houses two autonomic respiratory centers: o the pneumotaxic center and o the apneustic center.  These centers regulate the rate and depth of breathing, and both of them influence and modify the activity of the respiratory center in the medulla oblongata.  The pons houses sensory and motor cranial nerve nuclei for the o Trigeminal (CN V) o Abducens (CN VI) o Facial (CN VII)  Some of the nuclei for the vestibulocochlear cranial nerve (CN VIII) are located there  It is the most inferior part of the brainstem and is continuous with the spinal cord inferiorly  All communication between the brain and spinal cord involves tracts that ascend or descend through the medulla oblongata  The anterior surface exhibits two longitudinal ridges called the pyramids, which house the motor projection tracts called the corticospinal (pyramidal) tracts.  In the posterior region of the medulla, most of these axons cross to the opposite side of the brain at a point called the decussation of the pyramids  Paired inferior cerebellar peduncles are tracts that connect the medulla oblongata to the cerebellum  The medulla oblongata merges seamlessly with the spinal cord and creates the base of the brainstem.  Important centers include:  The respiratory center – controls the rate, rhythm, and depth of breathing  The cardiac center – regulates heartbeat  The vasomotor center – controls blood pressure  Reflex centers – reflex arc centers for vomiting, coughing, sneezing, hiccupping and swallowing  The medulla is also the origin of many cranial nerves (3rd-8th)  Sometimes called “emotional brain”  The limbic system is the structural basis of the behavioral and emotional expression of the individual.  The limbic system plays a role in feeling, feeding, fighting and fleeing activities.  It is responsible for emotions necessary for sexual functions.  It integrates the olfactory, visceral and somatic impulses through the hypothalamus.  In addition to the above functions, the limbic system is an integral part of the processes involved in recent memory.  The limbic system affects memory formation by integrating past memories of physical sensations with emotional states.  The term limbus means a ring.  The structures of the limbic system form a ring or border around the diencephalon  Some of the components are;  Hippocampus: It plays important role in learning and recent memory and in the control of emotional behavior  Parahippocampal: also plays a role in memory  The amygdaloid body: is involved in several aspects of emotion, especially fear. It can also help store and code memories based on how a person emotionally perceives them—for example, as related to fear, extreme happiness, or sadness  The olfactory bulbs, olfactory tracts, and olfactory cortex are part of the limbic system as well, since particular odors can provoke certain emotions or be associated with certain memories