BMS Neuroanatomy Lecture 1 PDF

BMS Neuroanatomy Lecture 1 Introduction to the Nervous System Presented By: Dr. K. Lumsden; [email protected] (Toronto Campus) Dr. M. Doroudi; [email protected] Boucher Campus)  INTRODUCTION The Nervous System & Endocrine System are in charge of maintaining the Homeostasis. The Nervous System is re...

BMS Neuroanatomy Lecture 1 Introduction to the Nervous System Presented By: Dr. K. Lumsden; [email protected] (Toronto Campus) Dr. M. Doroudi; [email protected] Boucher Campus)  INTRODUCTION The Nervous System & Endocrine System are in charge of maintaining the Homeostasis. The Nervous System is responsible for: –Behaviors –Memories –Movements INTRODUCTION Three basic functions 1- Sensing changes with sensory receptors Internal Environment such as? External Environment such as? 2- Interpreting and remembering those changes 3- Reacting to those changes with effectors Muscular contractions Glandular secretions Nervous System Divisions Nervous System Classifications The nervous system is divided into two subdivisions: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord, located in a bony cavity. The brain is in the cranial cavity, and the spinal cord is in the vertebral canal of the vertebral column. The PNS consists of spinal nerves, cranial nerves, associated ganglia and nerve plexuses. The peripheral nervous system is further subdivided into an afferent (sensory) division and an efferent (motor) division. The afferent or sensory division transmits impulses from peripheral organs to the CNS. It includes the general (somatic) sensory, special sensory and visceral sensory impulses. The efferent or motor division transmits impulses from the CNS to the peripheral organs to cause an effect or action. Finally, the efferent or motor division is again subdivided into the somatic nervous system and the autonomic nervous system (ANS). The somatic nervous system supplies motor impulses to the skeletal muscles. The autonomic nervous system (also called the visceral motor) supplies motor impulses to cardiac muscle, smooth muscle, and glands. It is further subdivided into sympathetic and parasympathetic divisions. The enteric nervous system is one of the main subdivisions of the autonomic nervous system and governs the function of the gastrointestinal tract. The Nervous system Nervous System Divisions Somatic (of the body) Senses: Special Senses: Visceral Senses: Somatic motor: Autonomic Motor: 1) The central nervous system (CNS) includes the brain and spinal cord. The brain consists of the cerebrum, diencephalon, cerebellum, and brainstem. The brainstem, in turn, includes the midbrain, pons and medulla oblongata. The CNS processes the incoming sensory and outgoing motor messages and is involved in higher mental activities such as learning, memory, and reasoning. The components of this system – brain and spinal cord – are enclosed and protected by bony cavities, the cranial cavity and the vertebral canal, respectively. The nervous tissue in the CNS is organized as gray and white matter. The gray matter comprises nerve cell bodies, bundles of unmyelinated nerve fibres, and non-neuronal supportive cells, the glial cells or neuroglia. The white matter mainly consists of bundles of myelinated nerve fibres known as tracts or fasciculi (singular, fasciculus). In the spinal cord, the gray matter forms an H-shaped inner core surrounded by white matter. In the brain, however, a thin outer shell of gray matter, the cortex, covers the core of the white matter. A cluster of nerve cell bodies embedded within the CNS is called a nucleus, whereas aggregation of nerve cell bodies outside the CNS is called a ganglion. 2) The peripheral nervous system (PNS) includes the spinal nerves, cranial nerves, associated ganglia, and nerve plexuses. The Central Nervous System Major divisions: Cerebral cortex Diencephalon Cerebellum Brainstem continues inferiorly as the spinal cord 9 Brief Embryology of the Nervous System Nervous system Subdivision Divisions Telencephalon (cerebrum) Diencephalon (structures surrounding the Forebrain (Prosencephalon) 3rd cerebral ventricle) Central nervous system (CNS) Brain Midbrain (Mesencephalon) Metencephalon (pons and cerebellum) Myelencephalon (medulla oblongata) Hindbrain (Rhombencephalon) Spinal cord Peripheral nervous system (PNS) Cranial nerves: 12 pairs Spinal nerves: 31 pairs - GENERAL TERMINOLOGY ❖ Rostral and caudal ❖ Dorsal and ventral ❖ Horizontal, coronal, and sagittal sections Brain at a glance The Central Nervous System The Cerebral Cortex: Each hemisphere is made up of white and gray matter “Matter” is made up of different parts of CNS cells called neurons: CORONAL VIEW Gra y ma tter 14 Nervous Connective Tissue Two cells of nervous tissue Neuroglia Support cells of the nervous system Nourish and clean up after neurons Neurons Functional unit of nervous system How signals travel to and from PNS to CNS and within CNS The Central Nervous System Grey matter Cell bodies (soma), dendrites, axon terminals of neurons Where synapsing occurs between cells Information processing / passing of signals Where can we find grey matter? Cerebral cortex Cortical nuclei/diencephalon (ex: Thalamus) Grey horns of spinal cord White matter Bundles of axons forming white matter pathways in the central nervous system Where signals travel from one location to another within the CNS Where can we find white matter? Cerebral tracts (Corpus callosum) White columns of spinal cord Spinal pathways (coming next week!) Peripheral Nerves 16 Gray and White Matter Where is the cortex in this image? Nucleus Vs Ganglion Tract(s) and/or Fasciculus Cerebrum The cerebrum consists of an outer cerebral cortex, an internal region of cerebral white matter, and some nuclei deep within the white matter. It comprises left and right cerebral hemispheres within the anterior and middle cranial fossae. In a superior view, the longitudinal fissure separates the two hemispheres. Each cerebral hemisphere is a highly convoluted structure that can be divided into four main lobes; frontal, parietal, occipital, temporal, and a small hidden portion deep to the lateral sulcus, the insula (insular lobe, insular cortex). Each lobe is responsible for different aspects of brain functions; however, the primary role of these lobes is to initiate motor impulses (frontal lobe), to receive general sensory stimuli (parietal lobe), auditory impulses (temporal lobe), visual impulses (occipital lobe), and taste impulses (insula). The outer surface of the cerebral hemispheres represents folds, gyri, separated by furrows, sulci. There are three main sulci in each cerebral hemisphere. 1. Central sulcus separates the frontal lobe from the parietal lobe. 2. Lateral sulcus is the superior boundary of the temporal lobe and separates it from the frontal and parietal lobes. 3. Parieto-occipital sulcus separates the parietal lobe from the occipital lobe. SUPERIOR VIEW The Central Nervous System The Cerebral Cortex: Outermost layer of the brain Associated with higher level processing and functioning Divided into right and left hemispheres Folded to increase surface area for information processing S G Gyri – bumps/folds of cortex Sulci – grooves/indentations Fissure – deep sulcus Longitudinal fissure divides hemispheres 19 LATERAL VIEW The Central Nervous System The Cerebral Cortex: Each hemisphere is divided functionally into four lobes: Frontal = cognition, control of voluntary movement, motor production of speech (expressive language) Special Sensation: Smell Parietal = processes sensory information General sensations: pain, pressure, temperature, touch, tickle, and vibration Special Sensations: taste Temporal = processes memories Special Sensation: auditory information Occipital = primarily responsible for processing visual sensation (special sensation) 20 LATERAL VIEW The Central Nervous System The Cerebral Cortex: Central sulcus The central sulcus is a prominent landmark of the brain, separating the parietal lobe from the frontal lobe Separates the Frontal and Parietal lobes from the Temporal lobe. 21 Parieto-occipital sulcus Cerebrum Gyri & Sulci Cerebral Cortex Cerebral Hemisphere (Gyri, Sulci, and Lobes) Cerebrum (Continued) The gray matter forms the cerebral cortex, and clusters of nuclei within the white matter are collectively known as basal ganglia (nuclei). The main components of the basal ganglia include the caudate and lenticular (putamen and globus pallidus) nuclei. These nuclei are involved in the coordination of motor function. The white matter is located deep in the cortex and is formed by myelinated nerve bundles. These nerve bundles can be classified into three groups based on the CNS's parts that connect. 1. Association fibres join the different parts of the same cerebral hemisphere. 2. Commissural fibres connect different gyri of one hemisphere to the corresponding gyri of the other hemisphere. The corpus callosum is the most extensive commissural fibre bundle located at the bottom of the longitudinal fissure. 3. Projectional fibres include the ascending (sensory) and descending (motor) fibres connecting the cortex to the lower centers of the CNS. An example of the projectional fibres is the internal capsule, a thick band of white matter between caudate nucleus and putamen (two of the nuclei of the basal ganglia) anteriorly, thalamus and globus pallidus (one of the basal ganglia) posteriorly. Cerebral Tracts: Association Basal Ganglia Cerebral Fibers Functional Areas of the Cerebral Cortex There are three major areas in each cerebral hemisphere: ❖ Primary sensory areas ❖ Primary motor area ❖ Association areas (Sensory and Motor) General idea about the primary sensory areas: The human body is equipped with different types of receptors. They exhibit a characteristic receptor selectivity, which means that only a specific type of stimulus can stimulate the receptor to produce its receptor potential. From the receptor, we follow a course of peripheral nerve (either cranial or spinal), which will convey the impulse into the appropriate pathway (tract). Pathways generally tend to make synapses on one of the thalamic nuclei. The thalamus only gets a crude perception of the signal received. It can’t determine the exact location or shape; therefore, the thalamus must forward the incoming signals toward the appropriate cortical area of the cerebrum. Final analysis and interpretation happen at the cerebral cortex, where visual pathway signals are perceived as images, auditory signals are perceived as sounds or words, or any tactile sensation would be interpreted fully (exact location, shape, weight, texture, etc.) Functional Areas of the Cerebral Cortex There are three major areas in each cerebral hemisphere: ❖Primary sensory areas ❖Primary motor area ❖Association areas (Sensory and Motor) Functional Areas of the Cerebral Cortex General idea about the primary sensory areas: ❖Only a specific type of stimulus can stimulate the receptor to produce its receptor potential. ❖From the receptor A course of peripheral nerve (either cranial or spinal), A pathway (Tract) Thalamus (crude sensation) Appropriate cortical area for the perception of the sense Primary Sensory Areas Primary somatosensory area (cortex); is located in the postcentral gyrus. It is a long gyrus, which represents itself over the lateral surface of the cerebral hemisphere, as well as on the medial surface (within the longitudinal fissure). “Cortical mapping” – Homunculus - This human-like creature illustrates different parts of the human body having different spatial presentations on the cortex. Primary visual area (cortex); is located in the occipital lobe. Primary auditory area (cortex); is located in the upper portion of the temporal lobe. Primary gustatory area (cortex); is located in insula (insular lobe) Primary olfactory area (cortex); is located on the medial aspect of the temporal lobe 32 33 Primary Taste Area (Cortex) 34 Motor Cortex Generally speaking, there are only two motor areas, both located on the frontal lobe. Primary motor area (cortex) This portion controls (creates impulses) that travel along the corticospinal tract (pathway) and feed spinal nerves, or the corticobulbar tract (pathway), providing stimuli to the nuclei of cranial nerves. These pathways start from the pyramidal cells in the precentral gyrus located in the frontal lobe (the corticospinal tract is also called the pyramidal tract because of its origin form the pyramidal cells). On the surface of this gyrus, one should also imagine the homunculus (small man), as the area is disproportionally divided. The largest area generates motor signals for the muscles of hands, muscles of facial expression and muscles that functionally belong to the vocal apparatus (the areas that initiate fine movements). Injury to this area leads to motor paralysis of the contralateral side of the body. The precentral gyrus extends itself over the medial and lateral cerebral surfaces. That part of the gyrus, which extends to the medial surface, produces motor signals for muscles of the leg and foot (area that is supplied by branches of the anterior cerebral artery, so that an isolated cerebrovascular accident of this area only causes motor weakness of the leg and foot muscles). The rest of the precentral gyrus is located on the lateral surface of the cerebral hemisphere and produces motor signals for the rest of the body. Motor Cortex Primary Motor Area (cortex) Precentral gyrus Involved in conscious control of precise, skilled, voluntary movements Receives input from: premotor area & supplementary motor areas sensory cortex, thalamus, basal ganglia, and cerebellum http://defiant.ssc.uwo.ca/Jody_web/fMRI4Dummies/brains/corticalsulci/central_sulci_saggitalview.jpg Primary Motor Area (cortex) Motor control to different parts of the body comes from the appropriate part of this area as outlined by the motor homunculus Size of the body parts is proportional to the degree of fine motor control allotted to those parts Premotor area Located in the frontal lobe in front of precentral gyrus, serves as a space where the patterns of movement are stored. Learned and several times performed movement is stored as an algorithm into this gyrus. Later, when a person wants to repeat that same type of movement that was previously learned and through the exercise mastered, the algorithm is simply imported into the precentral (primary motor) gyrus that just initiates motor signals based on the information received. Premotor Frontal Eye Field (FEF) The FEF is in front of the premotor area of the front lobe. The FEF controls the voluntary, synchronized movement of eyeballs. Left-sided center forces both eyes to move to the right, and the right-sided center moves them to the left. Since both centers are simultaneously active, eyes should not deviate to either side. If one of the two centers is injured, the other side center dominates and forces eyes to “look into the side of injury.” Broca’s Area It is located in the inferior frontal gyrus of the frontal lobe, just anterior to the inferior part of the precentral gyrus. It is almost always (99% of the population) found on the left side of the brain. That area is a center for generating motor signals for the vocal apparatus. Its injury results in Broca or motor aphasia, where the patient understands the speech but cannot speak. Wernicke’s Area The Wernicke area is located around the posterior end of the lateral sulcus (loops around the end of the sulcus) in the left temporoparietal junction. It is critical for the understanding of language. Damage to this area causes receptive/sensory/ Wernicke’s aphasia. A person with this aphasia has empty, fluent speech and a loss of speech comprehension. Speech may be effortless and without hesitancy, but little meaningful information is conveyed. Person speaks jumbled, meaningless words Wernicke’s aphasia Speech and Language Broca’s and Wernicke’s areas are connected by a white matter tract called the arcuate fasciculus Lesion of tract = conduction aphasia Can comprehend and articulate Difficulty repeating heard speech Modified from: http://www.bioon.com/book/biology/whole/image/1/1 -8.tif.jpg Association Areas The association areas are adjacent to the primary areas and are connected to the primary area by the association fibres. It will enable sharing of different signals by an entire cerebral hemisphere to create a comprehensive perception of objects or things that surround us or come into contact with the surface of our bodies. Association Areas ❖ The somatosensory association area is located behind the primary somatosensory area in the parietal lobe. It integrates and interprets general sensations, such as shape, texture, and weight. It compares objects by their shapes and interprets the position of body parts relative to the rest of the body. It stores that information in long-term memory. A lesion in the somatosensory association area results in a condition known as astereognosis (astereognosia) or the inability to recognize an object placed in the hand. ❖ The visual association area surrounds the primary visual area in the occipital lobe. It gives meaning and interpretation to what we see. ❖ The auditory association area is located adjacent to the primary auditory area on the lateral surface of the superior temporal gyrus, which enables us to interpret the sounds we hear and give them meaning. Common Integrative Area The common integrative area ( is located among the sensory, visual, and auditory association areas and integrates signals it receives from primary areas. It redirects those signals into other parts of the brain, where it generally creates thoughts and ideas that we understand and then voluntarily look for the most appropriate responses. Please focus on the notes in the RED boxes! Diencephalon The diencephalon is located between the cerebral hemispheres and the midbrain. It includes the thalami and all other structures surrounding the third ventricle, such as the hypothalamus and epithalamus. The lateral walls of the diencephalon form the epithalamus most superiorly, the thalamus centrally, and the subthalamus and hypothalamus inferiorly. The thalamus is an egg-shaped structure consisting of a group of nuclei, most of which are sensory. It plays a crucial role in many brain functions, serving as a processing and distribution centre, relaying and regulating information from the outside world and the internal milieu to the cerebral cortex and sustaining cortico-thalamo-cortical communication. It involves multiple activities, including consciousness, sleep, attention, memory and sensory and motor functions. The thalamus relays all senses (except smell) to certain sensory areas of the cerebral hemisphere. The hypothalamus is inferior and medial to the thalamus and functions as the center of the autonomic nervous system, thus controlling emotion, body temperature, eating, drinking, etc. It also regulates the function of the major components of the endocrine system through the pituitary gland. The epithalamus is a small region posterior and superior to the thalamus, mainly consisting of the pineal gland. The pineal gland regulates the circadian rhythm and distribution of pigment melanin in the skin. Cerebellum The cerebellum is contained within the posterior cranial fossa, underneath the tentorium cerebelli, behind the medulla and pons from which is separated by the fourth ventricle. It consists of two cerebellar hemispheres connected by a worm-like structure, the vermis. It is joined to the brainstem by three bilaterally paired major fibre tracts, the cerebellar peduncles. The superior cerebellar peduncles carry axons that connect the cerebellum to the red nucleus of the midbrain and thalamus. The middle cerebellar peduncles connect the pontine nuclei of the pons to the cerebellum. The inferior cerebellar peduncles carry bundles of axons travelling between the medulla and cerebellum, such as spinocerebellar tracts. The gray matter forms the cerebellar cortex that surrounds the white matter in which deep cerebellar nuclei are located. These nuclei include the fastigial, globose & emboliform (interposed), and dentate. The globose and emboliform together are referred to as interposed nucleus. The cerebellar cortex is thrown into folds that appear as leaf-like ridges, folia, on the surface of the cerebellum. The primary function of the cerebellum includes the coordination of voluntary movements and maintaining posture and balance. Cerebellum Brainstem The brainstem is composed of the medulla oblongata, pons and midbrain from inferior to superior. The major functions of the brainstem include but not limited to: 1. It acts as a passageway for all ascending and descending tracts between the cerebrum and spinal cord. 2. It contains the nuclei of the cranial nerves III to XII. 3. It regulates the automatic behaviours required for survival, such as respiration. Midbrain The midbrain connects to the pons inferiorly and the diencephalon superiorly. The anterior aspect of the midbrain presents two columns, the cerebral peduncles, between which the C.N. III emerges. These columns contain descending tracts such as corticospinal and corticobulbar tracts, collectively known as the crus cerebri. On the posterior aspect of the midbrain, there are four elevations known as superior and inferior colliculi (singular, colliculus). The nuclei deep in these colliculi (named after the colliculi) are a relay center for the visual and auditory reflexes, respectively. Ascending tracts occupy the white matter of the midbrain behind the crus cerebri. Several nuclei are embedded within the white matter, some of which are associated with the cranial nerves III, IV, and V. The other major nuclei include the red nucleus and the substantia nigra. The red nucleus is associated with the rubrospinal tract as part of the extrapyramidal pathways. The substantia nigra is functionally linked to the basal ganglia regulating voluntary movements. In the transverse section of the midbrain, the internal structures can be divided into three main areas (relative to the cerebral aqueduct that connects the 3rd ventricle to the 4th ventricle). The tectum (roof) is located behind the cerebral aqueduct, the tegmentum, from the cerebral aqueduct to the substantia nigra, and the cerebral peduncle. The Periaqueductal Gray Matter (PAG) located around the cerebral aqueduct is a site of production of natural painkillers (endorphins and enkephalins). Tectum, Tegmentum, Base Midbrain, Internal Features Pons The pons is related to the cerebellum (posteriorly), medulla oblongata (inferiorly), and midbrain (superiorly). The anterior surface is convex and carries a longitudinal sulcus, the basilar sulcus, occupied by the basilar artery. The cranial nerves VI, VII, and VIII emerge from the ponto-medullary sulcus, whereas cranial nerve V appears at the anterolateral surface of the pons. The white matter of the pons is formed by the ascending and descending tracts. The gray matter is organized as nuclei embedded in the white matter. Some of these nuclei are related to the cranial nerves V, VI, VII, and VIII. The other major nuclei include but are not limited to the pontine nuclei that act as a relay center for motor pathways between the cerebrum and cerebellum to coordinate voluntary movements. Two important nuclei are found within the pons that add more control to the respiration – pneumotaxic and apneustic area. Pons; Internal Features Medulla Oblongata The medulla oblongata or medulla is pyramidal in shape, separated from the pons by a transverse sulcus, the pontomedullary sulcus, superiorly and continuous with the spinal cord inferiorly. Viewing anteriorly, there is an elevation, the pyramid, on either side of the median anterior fissure formed by the pyramidal tracts. Lateral to the pyramid is a second elevation, the olive, that overlies the inferior olivary nucleus. The cranial nerves IX, X, XI, and XII, emerge from the anterolateral surface of the medulla oblongata. At the junction of medulla and spinal cord one can find the decussation of pyramids that deep to that the corticospinal tracts cross each other. Medulla; Internal Features As part of the CNS, the medulla oblongata is composed of gray and white matter, the arrangement of which is the same as the spinal cord in the inferior half of the medulla. However, in the superior half of the medulla, the gray matter is embedded within the white matter as clusters of nuclei. Most of these nuclei are associated with the cranial nerves V, VIII, IX, X, XI, and XII. The other major nuclei include but are not limited to the inferior olivary nucleus - a relay center for proprioceptive information to the cerebellum – and the nucleus gracilis and nucleus cuneatus, both of which are associated with the posterior column- medial lemniscus pathway. The major functional areas in the medulla include but are not limited to the cardiovascular center, respiratory center (medullary rhythmicity area), and centers that control vomiting, coughing, and sneezing. Reticular Formation The reticular formation is not an individual section of the brain but an integral part of the brain stem. It is a collection of nuclei running vertically throughout the brainstem in three columns (the median, medial, and lateral columns). Its functions include, but are limited to, control of skeletal muscle, pain modulation, control of autonomic and endocrine systems, circadian rhythms, and consciousness. The reticular formation receives an enormous number of sensory signals from different parts of the body, inclusive of special senses such as vision or hearing. To prevent sensory overload, one of its tasks is to filter out up to 99% of all incoming sensory signals, preventing them from being consciously perceived. RAS (ARAS) System Although most of the sensory signals are filtered, some will have direct input to the cerebral cortex. Some neurons that fire their impulses into the cerebral cortex create the reticular activating system (RAS) (or ascending reticular activating system (ARAS). It responds to some stimuli, potentially disrupting a relatively constant flow and unchanged level of intensity of incoming signals. (A person will fall asleep with the air conditioner running, and the constant humming sound of the air conditioner will be eliminated by the reticular formation; upon hearing the ring sound of an alarm clock, that person will wake up. A similar scenario can be used to explain the response of RAS to visual or cutaneous stimuli). Additionally, the reticular formation is involved in regulating our circadian rhythm (internal clock) and sleep-wake cycle, plus it makes its input to the spinal cord (reticulospinal pathway). This pathway contributes to muscle tone. - A general anesthetics work to suppress this system ❖ The diagram below represents an overview of inputs to and outputs from the reticular formation: This chart is ONLY to show you the vast connection of the RF with other areas of the brain. Do not memorize it!!