CNS Anatomy PDF

CENTRAL NERVOUS SYSTEM Theory CNS Introduction to central nervous system Organization of the Nervous The nervous system is divided into: Central nervous system (CNS), includes the brain and spinal cord, Peripheral nervous system (PNS), includes the cranial nerves arising from brain and the spinal ne...

CENTRAL NERVOUS SYSTEM Theory CNS Introduction to central nervous system Organization of the Nervous The nervous system is divided into: Central nervous system (CNS), includes the brain and spinal cord, Peripheral nervous system (PNS), includes the cranial nerves arising from brain and the spinal nerves arising from spinal cord The nervous system is composed of only two principal categories of cells neurons and neuroglia. CNS Neurons Neurons are the basic structural and functional units of the nervous system. All neurons have three principal components: The cell body is the enlarged portion of the neuron contains a nucleus with a prominent nucleolus and the bulk of the cytoplasm. in the CNS, cell bodies clusters called nuclei in the PNS, cell bodies clusters called ganglia Dendrites, branched processes extend from the cytoplasm of cell body, conduct impulses to the cell body. The axon (nerve fiber), long cylindrical cytoplasmic extension from cell body, conducts impulses away from the cell body. CNS Neuroglia Neuroglia, or glial cells, supportive cells aid the function of neurons. There are six categories of neuroglia: 1) Neurolemmocytes (Schwann cells), form myelin layers around axons in the PNS. 2) Oligodendrocytes , form myelin layers around axons in the CNS. 3) Microglia, migrate through the CNS, removing foreign and degenerated material. 4) Astrocytes, help to regulate the passage of molecules from the blood to the brain. 5) Ependymal Cells, line the ventricles of the brain and the central canal of the spinal cord. 6) Ganglionic Gliocytes, (Satellite cells) support cell bodies within the ganglia of PNS. CNS CNS Myelination : Myelination process, in which a neurolemmocyte or oligodendrocyte which contain a white substance called (myelin) surrounds a portion of axon or dendrite to provide support and aid in the conduction of impulses It is responsible for the color of the white matter of the brain & spinal cord and the white coloration of nerves. Myelination in the PNS occurs as neurolemmocytes wrap around one axon or dendrite Myelination in the CNS occurs as oligodendrocytes wrap around several axons or dendrite Neurofibril nodes : gaps of exposed axon between adjacent neurolemmocytes (due to each neurolemmocyte wraps only 1 mm of axon) CNS Myelination CNS Classification of Neurons and Nerves Neurons Classified according to Structure or Function. A. The Functional classification (based on the direction of conducted impulses) : Sensory neurons (afferent) conducted sensory impulses that originate in sensory receptors to the CNS. Motor neurons (efferent) conducted motor impulses that originate in CNS to a muscle or gland Motor neurons may be: somatic (non-visceral) or autonomic (visceral). CNS Classification of Neurons and Nerves Neurons B. The Structural classification (based on the number of processes extend from the cell body of neuron): Bipolar neuron, spindle-shaped has a process at both ends; (in retina of eye). Pseudo-unipolar neuron has a single process that divides into two. (in sensory neurons). Multipolar neurons the most common type characterized by several dendrites and one axon extending from the cell body. (in motor neurons) CNS Nerves It’s a collection of nerve fibers outside the CNS. the endoneurium a connective tissue sheath surround each nerve fiber , the perineurium a connective tissue sheath surround a group of fibers. the epineurium a connective tissue sheath surround and support the entire nerve , contains tiny blood vessels and, adipose cells. Most nerves are mixed nerves composed of both motor & sensory fibers Some of cranial nerves, composed either of sensory nerves or motor nerves CNS Nerves Sensory nerves serve special senses, such as taste, smell, sight, and hearing. Motor nerves conduct impulses to muscles or to glands. According to the area of innervation neurons & fibers within nerves classified into the following: 1. Somatic sensory (afferent) fibers convey impulses to CNS from skin, bones, muscles, joints, eyes and ears 2. Visceral sensory (afferent) fibers convey impulses to CNS from visceral organs & blood vessels 3. Somatic motor (efferent) fibers convey impulses from CNS to the skeletal muscles (contraction) 4. Visceral motor (efferent) fibers convey impulses from CNS to the cardiac muscle, glands, and smooth muscle of visceral organs CNS Nerves The entire delicate CNS is protected by : A fixed bony cranium (brain) and a flexible vertebral column (spinal cord). The meninges form a protective membrane between the bone and the soft tissue of CNS. The CNS is bathed in cerebrospinal fluid that circulates within the hollow ventricles of the brain, the central canal of the spinal cord, and the subarachnoid space surrounding the entire CNS CNS The CNS is composed of : Gray matter Consists of nerve cell bodies Forms the outer convoluted cortex layer of cerebrum and cerebellum. White matter Consists of myelinated axons Forms the tracts within the CNS. The brain of an adult weighs nearly 1.5 kg and is composed of 100 billion neurons Cerebrum Cerebrum Consisting of five paired lobes within two convoluted hemispheres, is concerned with higher brain functions, including : Storage of memory Thought processes, Reasoning ability Perception of sensory impulses and the instigation of voluntary movement Emotional functions. Cerebrum Structure of the Cerebrum The cerebrum is the largest and most obvious portion of brain. The right & left hemispheres, incompletely separated by a longitudinal cerebral fissure, and connected internally by the corpus callosum ( a large tract of white matter ). Each hemisphere contains a central cavity (the lateral ventricle) filled with cerebrospinal fluid. The cerebrum consists of two layers: The surface layer (cerebral cortex) is composed of gray matter that is 2-4 mm thick. The second layer is the thick white matter beneath the cerebral cortex. Cerebrum Cerebrum layers : Cerebrum Corpus Callosum : Cerebrum The cerebral cortex: six layers of nerve cells characterized by numerous folds and grooves called convolutions. The elevated folds are the cerebral gyri Functions including: The depressed grooves are the cerebral sulci Determining intelligence and personality Motor function Planning and organization Touch sensation Processing sensory information Language processing Cerebrum Contains: 1. Sensory areas: receive input from thalamus and process information related to the senses. include : the visual cortex of occipital lobe, the auditory cortex of temporal lobe, the gustatory cortex & the somatosensory cortex of parietal lobe. 2. Motor areas: regulate voluntary movement, include : the motor cortex the premotor cortex, Cerebrum Lobes of the Cerebrum Four of these lobes appear on the surface of the cerebrum Frontal Lobe Forms the anterior portion of each hemisphere. The Central Sulcus, deep furrow separates the frontal lobe from parietal lobe extends at right angles from the longitudinal fissure to the lateral sulcus. The Lateral Sulcus, separate the frontal and temporal lobes extends laterally of the cerebrum The precentral gyrus (important motor area) positioned immediately in front of the central sulcus. responsible for motor movement Cerebrum Cerebrum Frontal Lobe Functions include : Initiating voluntary motor impulses for the movement of skeletal muscles, Mediate responses related to memory, emotions, judgment, planning, and verbal communication. Cerebrum Parietal Lobe : Lies posterior to the central sulcus. The postcentral gyrus (important sensory area) positioned immediately behind the central sulcus, responds to sensory stimuli from cutaneous (such as touch ,pain and temperature) Functions include : 1. Understanding speech ,thoughts and emotions. 2. Interprets the textures & shapes of objects as they are handled. Cerebrum Temporal Lobe located below the parietal lobe and the posterior portion of frontal lobe. Separated from both by the lateral sulcus. Functions include : Contains auditory centers that receive sensory fibers from cochlea of ear. Contains olfactory cortex (part of olfactory system) that concern with conscious and smell. Interprets and stores memories of both auditory and visual experiences. Cerebrum Occipital Lobe Forms the posterior portion of cerebrum , not distinctly separated from temporal and parietal lobes Lies superior to the cerebellum and is separated from it by an infolding of the meningeal layer (dura mater) called the tentorium cerebelli The principal function : Contains the visual area that concern with vision Cerebrum Insula is a deep lobe of cerebrum that cannot be viewed on the surface lies deep to the lateral sulcus and covered by portions of frontal, parietal, and temporal lobes. The Function : Little is known about its function except It is thought to have some function in memory. The Brain Stem Connects the cerebrum with the spinal cord through the foramen magnum in the base of the skull The upper portion of brain stem is the Midbrain. Below it , are the Pons and the Medulla Oblongata that visible from the under view of brain The Brain Stem Function include: The respiratory center control the muscle of respiration The cardiac center regulates the rate and force of the heartbeat. The vasomotor center regulates the contraction of smooth muscle of blood vessel thus determine blood pressure. Diencephalon Is a major autonomic region of brain is the second subdivision of forebrain and is completely surrounded by the cerebral hemispheres. The most important structures of the diencephalon are the thalamus, Hypothalamus, epithalamus (pineal gland), and pituitary gland. The third ventricle is a narrow cavity within the diencephalon. Pons The pons can be observed as a rounded bulge on the inferior surface of the brain, between the midbrain and the medulla oblongata. It consists of white fiber tracts that course in two principal directions:The surface fibers extend transversely to connect with the cerebellum through the middle cerebellar Peduncles. The deeper longitudinal fibers connect the medulla oblongata with the tracts of the midbrain. Medulla Oblongata Is a bulbous structure , 3 cm long, the most inferior structure of the brain stem. It is continuous with the pons anteriorly and spinal cord posteriorly at the level of the foramen magnum Externally, resembles the spinal cord, except for: Two triangular elevations called pyramids on the inferior side An oval enlargement called the olive on each lateral surface. Internally, medulla oblongata composed of :white matter. Gray matter The fourth ventricle, space within the medulla oblongata. Cerebellum Is the 2nd largest structure of brain occupies the inferior and posterior aspect of cranial cavity separated from the cerebrum by a transverse fissure. Consists of two hemisphere and a central constricted area called vermis Like the cerebrum, has a thin outer layer of gray matter (cerebellar cortex) and a thick deeper layer of white matter. Cerebellum Cerebellar peduncles, three paired bundles of nerve fibers support and communicate the cerebellum with the rest of brain : Superior peduncles Connect the cerebellum with the midbrain. Middle peduncles Connect the cerebellum to the pons and cerebrum. Inferior peduncles Connect the cerebellum with the medulla oblongata and spinal cord. Cerebellum The Principal Function is : Coordinating skeletal muscle voluntary contractions Constantly initiates impulses for maintaining posture balance and muscle tone. Ventricles of the Brain Connected to one another and to the central canal of the spinal cord First & Second ventricles, Two lateral ventricles Each located in one hemispheres of cerebrum, Inferior to the corpus callosum and Connected to the third ventricle by A narrow, oval opening called the inter-ventricular foramen Ventricles of the Brain Third ventricle Located in the diencephalon, Between the thalami and Connected to the fourth ventricle by cerebral aqueduct Fourth ventricle Located in the medulla oblongata, Between the pons and cerebellum , Connected posteriorly with the central canal of the spinal cord. Meninges The CNS covered by three membranous connective tissue called the meninges , from outside in :- A. Dura Mater contact with the bone : 1. The cranial dura mater is a double-layered structure : The outer periosteal layer adheres to the cranium constitutes the periosteum The inner meningeal layer, is thinner, follows the general contour of the brain. 2. The spinal dura mater is not double layered. similar to the inner meningeal layer Meninges B.Arachnoid is the middle of the three meninges. Net-like membrane spreads over the CNS but does not extend into the sulci or fissures of the brain. The subarachnoid space, located between the arachnoid mater and deepest pia mater, contains cerebrospinal fluid. C.Pia Mater Its thin tightly bound to the convolutions of the brain and irregular contours of the spinal cord. It is highly vascular and supports the vessels that nourish the underlying cells of brain & spinal cord. Cerebrospinal Fluid (CSF) is a clear, lymph-like fluid that produced each day by:1. Filtration of blood plasma 2. Secretions of ependymal cells. CSF circulates through the ventricles of brain, the central canal of spinal cord, and the subarachnoid space then returns to the circulatory system by draining through the walls of arachnoid villi (which are venous capillaries) Cerebrospinal Fluid (CSF) CSF functions: Acts as neutral buoyancy for brain (the brain weighs 1,500 grams, but suspended in CSF its buoyed weight is about 50 grams) Reduces the damaging effect of an impact to the head by spreading the force over a larger area. Carries nutrients to the cells, and remove metabolic wastes. Practical Cerebrum Consisting of five paired lobes within two hemispheres, The right & left hemispheres : Incompletely separated by a longitudinal cerebral fissure, Internally connected by the corpus callosum Each contains a central cavity (the lateral ventricle) The cerebrum consists of two layers: The surface layer (cerebral cortex) gray matter The second layer thick white matter. The cerebral cortex : Characterized by convolutions :The elevated folds are the cerebral gyri The depressed grooves are the cerebral sulci Cerebrum Cerebrum Frontal Lobe Anterior portion of each hemisphere. The Central Sulcus, deep furrow separates the frontal lobe from parietal lobe extends at right angles from the longitudinal fissure to the lateral sulcus. The Lateral Sulcus, separate the frontal and temporal lobes extends laterally of the cerebrum The precentral gyrus (motor area) immediately in front of the central sulcus. Parietal Lobe Posterior to the central sulcus. The postcentral gyrus (sensory area) immediately behind the central sulcus, Cerebrum Temporal lobe Below the parietal lobe and the posterior portion of frontal lobe. Separated from both by the lateral sulcus Occipital lobe Posterior portion of cerebrum , Superior to the cerebellum Not distinctly separated from temporal & parietal lobes Separated from cerebellum by an infolding of dura mater called the tentorium cerebelli Cerebrum Insula Is a deep lobe of cerebrum that cannot be viewed on the surface Deep to the lateral sulcus and Covered by portions of frontal, parietal, and temporal lobes. The Brain Stem Connects the cerebrum with the spinal cord through the foramen magnum of the skull The upper portion of brain stem is the Midbrain. Below it , the Pons & Medulla Oblongata , visible from the under view of brain Diencephalon Completely surrounded by the cerebral hemispheres. Include: thalamus, hypothalamus, epithalamus (pineal gland), and pituitary gland. The third ventricle within the diencephalon. Diencephalon Pons Rounded bulge on the inferior surface of the brain, between midbrain & medulla oblongata. It consists of:The surface transverse fibers : to connect with the cerebellum The deeper longitudinal fibers: connect medulla oblongata with midbrain. Medulla Oblongata Bulbous structure , 3 cm long, the most inferior structure of brain stem. Continues with pons anteriorly and spinal cord posteriorly at the level of the foramen magnum Externally, have: Two triangular elevations called pyramids on the inferior side An oval enlargement called the olive on each lateral surface. The fourth ventricle, space within the medulla oblongata, Medulla Oblongata Cerebellum Is the 2nd largest structure of brain Occupies the inferior and posterior aspect of cranial cavity. Separated from the cerebrum by a transverse fissure. Consists of two hemispheres and a central constricted area called vermis Has a thin outer layer of gray matter (cerebellar cortex) and a thick deeper layer of white matter. Cerebellar peduncles, three paired bundles of nerve fibers : 1. Superior peduncles connect the cerebellum with midbrain. 2. Middle peduncles connect the cerebellum to pons & cerebrum. 3. Inferior peduncles connect the cerebellum with medulla oblongata & spinal cord. Cerebellum Ventricles of the Brain Connected to one another and to the central canal of the spinal cord First & second ventricles (lateral ventricles) located in hemispheres of cerebrum, inferior to the corpus callosum Connected to the third ventricle by interventricular foramen - Third ventricle located in diencephalon, between the thalami Connected to the fourth ventricle by cerebral aqueduct Fourth ventricle located in medulla oblongata, between the pons and cerebellum , Connected posteriorly with central canal of spinal cord. Ventricles of the Brain Meninges The CNS covered by three membranous connective tissue called the meninges , from outside in :Dura Mater Contact with the bone : The cranial dura mater ,double-layered : The outer periosteal layer adheres to the cranium The inner meningeal layer, is thinner, follows the general contour of brain. The spinal dura mater, single layer. similar to the inner meningeal layer Arachnoid The middle layer. Net-like membrane spreads over the CNS but does not extend into the sulci or fissures of the brain. The subarachnoid space, located between the arachnoid mater and pia mater, Meninges Pia Mater thin tightly bound to the convolutions of the brain and irregular contours of the spinal cord.