NERVOUS SYSTEM SEPT 2024 (PART 2)-BRAIN 2 PDF

RNB10603 BASIC ANATOMY AND PHYSIOLOGY 1 TOPIC 6 NERVOUS SYSTEM (PART 2) Y.S. PEK  LEARNING OBJECTIVES At the end of the topic, students should be able to” 1. describe the structures of the meninges; 2. describe the flow of cerebrospinal fluid in the brain and funct...

RNB10603 BASIC ANATOMY AND PHYSIOLOGY 1 TOPIC 6 NERVOUS SYSTEM (PART 2) Y.S. PEK  LEARNING OBJECTIVES At the end of the topic, students should be able to” 1. describe the structures of the meninges; 2. describe the flow of cerebrospinal fluid in the brain and functions of CSF; 3. name the lobes and principal sulci of the brain; 4. state the functions of the cerebrum; 5. describe the position and functions of the thalamus and hypothalamus; 6. describe the position and functions of the midbrain, pons, medulla oblongata and reticular activating system. 7. describe the structure and functions of the cerebellum. 2 RECAP … 3 Recap…. 4  CENTRAL NERVOUS SYSTEM (CNS) Consists of: ‒Brain ‒Spinal cord The brain lies within the cranial cavity. Brain is one of the largest organs of the body. Brain connected to the spinal cord at the foramen magnum. 5  THE BRAIN The brain consists of 4 major parts: I. Cerebrum II. Diencephalon III. Brain stem Midbrain Pons Medulla oblongata IV. Cerebellum Parts of the central nervous system 6 Brain: Major Parts 7 Brain: Major Parts 8  PROTECTION OF THE BRAIN The brain is protected by the cranium and cranial meninges. Blood-brain barrier (BBB) protects brain cells from harmful substances and pathogens. Cerebrospinal fluid (CSF) further protects the brain from chemical and physical injury. Meninges 9  MENINGES Three enveloping connective tissue layers that enclose the brain Dura mater (outermost) Arachnoid mater (middle) Pia mater (innermost) Meninges of the brain 10 Cranial Meninges 11  CEREBROSPINAL FLUID (CSF) Circulates in the subarachnoid space and cushions the brain all around. CSF is a clear, colourless liquid that: Carry oxygen, glucose and other chemicals from the blood to neurons and neuroglia Removes wastes and toxic substances produced by brain and spinal cord cells Sites of CSF production = choroid plexuses in cerebral ventricles. Ependymal cells cover the choroid plexus capillaries = form CSF from blood plasma by filtration & secretion CSF pressure is 120–180 mmH2O The cranial cavity contains 80-150 ml of CSF 12  CEREBROSPINAL FLUID (CSF) CSF circulates through the subarachnoid space, around the brain and spinal cord, and cavities in the brain known as ventricles. There are 4 ventricles: ‒two lateral ventricles ‒one third ventricle ‒one fourth ventricle Pathway ‒From the fourth ventricle → central canal of the spinal cord and within subarachnoid space →reabsorbed through arachnoid villi into the blood in the superior sagittal sinus Cushions brain and provides nutrients. 13 THE VENTRICLE OF THE BRAIN 14 Flow of CSF in The Brain Pair of lateral ventricles Interventricular foramen Third ventricle Cerebral aqueduct Fourth ventricle 15  FUNCTIONS OF THE CSF Protection to CNS by acting as a 'shock absorber' as it absorbs shock in the event of blows to the head. Removal of waste products of brain metabolism. Regulates the extracellular environment of the CNS neurons. Transports hormones and hormone-releasing factors. 16 17  Clinical Application Lumbar Puncture (Spinal Tap)  A lumbar puncture is a common medical test that involves taking a small sample of cerebrospinal fluid (CSF) for examination  A spinal needle is inserted between the lumbar vertebrae L3 and L4 or L4 and L5 18  BLOOD SUPPLY & BLOOD-BRAIN BARRIER Requires 20% of the body’s O2 supply ‒4 min lack of O2 → permanent damage Requires continuous glucose supply Protected by blood-brain barrier (BBB) ‒Allows passage of lipid-soluble materials: O2, CO2, alcohol, anaesthetic agents ‒But controls entry of most harmful materials Created by tight capillaries and astrocytes. 19 BRAIN  Forebrain ‒ cerebrum  Hindbrain ‒cerebellum  Brain Stem ‒ Midbrain ‒ Pons ‒ Medulla oblongata  Diencephalon ‒ Thalamus ‒ hypothalamus 20 CEREBRUM Largest portion of brain Divisions: ✓Right hemisphere ✓Left hemisphere - separated by longitudinal fissure Lobes: frontal, parietal,occipital, temporal 21 CEREBRUM 22  CEREBRUM The cerebrum consists of the: ‒cerebral cortex (outer rim of grey matter) ‒Internal region of cerebral white matter ‒Grey matter nuclei deep within the white matter The cerebrum provides us with the ability to read, write, speak, memorize, remember, plan & create Gyri = folds on cerebral cortex Fissures = the deep grooves between folds Sulci = shallow grooves Longitudinal fissure separates the cerebrum into right and left cerebral hemispheres - connected internally by the corpus callosum 23  Cerebrum 4 lobes: 1. Frontal Parieto-occipital Central sulcus sulcus 2. Parietal 3. Occipital 4. Temporal Parietal Frontal Eachlobe is divided Temporal by fissure: Occipital - Lateral sulcus - Central sulcus - Parieto-occipital Lateral sulcus sulcus 24  CEREBRUM Major gyrus: i. Precentral gyrus ‒ located immediately anterior to the central sulcus ‒ Contains the primary motor area of the cerebral cortex ii. Postcentral gyrus ‒ Located immediately posterior to the central sulcus ‒ Contains the primary somatosensory area of the cerebral cortex The insula ‒the fifth part of the cerebrum ‒Cannot be seen at the surface of the brain ‒Lies within the lateral cerebral sulcus, deep to the parietal, frontal and temporal lobes 25 CEREBRUM 26 CEREBRUM 27 INTERIOR OF THE CEREBRUM 28  LIMBIC SYSTEM Ring of structures on the inner border of the cerebrum and floor of the diencephalon. Called the “emotional brain” ‒Plays a primary role in the range of emotions ‒Example: pain, pleasure, anger, affection and in behavior Control involuntary activity related to survival. Together with parts of the cerebrum, the limbic system is important in memory development. Damage to the limbic system will cause memory impairment. 29 Limbic System 30 FUNCTION OF CEREBRUM There are 3 main types of activities related to cerebral cortex I.Mental activity II.Sensory perception III.Initiate and control contraction of skeletal muscles (voluntary) 31  FUNCTIONAL AREAS OF CEREBRAL CORTEX Specialized areas in specific regions of cerebral cortex I. Sensory areas ‒ Receive sensory input → perception ‒ The conscious awareness of sensation II. Motor areas ‒ Initiate movements III. Association areas ‒ Complex integration: memory, emotion, reasoning, judgment, personality traits, intelligence 32  I. SENSORY AREA ❑ Information relayed from peripheral sensory receptor → sensory input to the cerebral cortex (posterior half of the cerebral hemispheres, mainly the regions behind the central sulci) i. Primary somatosensory area ‒ Posterior to the central sulcus in the poscentral gyrus of the parietal lobe ‒ Receive nerve impulse for touch, proprioception (joint and muscle position), pain, itching & temperature ii. Visual area ‒ Located in the occipital lobe ‒ Receive visual information ‒ Visual perception 33  I. SENSORY AREA iii.Auditory (Hearing )area ‒ Located in the temporal lobe ‒ Receive information for sound ‒ Auditory perception iv. Gustatory (Taste) area ‒ Located at the base of the postcentral gyrus ‒ Receive impulses for tast ‒ Gustatory perception v. Olfactory (Smell) area ‒ Located on the medial aspect of the temporal lobe ‒ Receive impulses for smell ‒ Olfactory perception 34 Functional areas of the cerebrum 35  II. MOTOR AREAS Located anterior to the central sulcus The most important motor areas are: i. Primary motor area ii. Broca’s speech area Primary motor area: precentral gyrus ‒Located in the precentral gyrus ‒Control voluntary contractions of specific muscles Broca’s speech area ‒Interacts with premotor area and primary motor area to regulate breathing and speech muscles Language areas are localised in the left hemisphere in 97% of persons 36 37  III. ASSOCIATION AREAS Consist of large areas of the occipital, parietal, temporal & frontal lobes anterior to the motor areas Adjacent to sensory and motor areas and connected via association tracts Integrate and interpret information Examples ‒Somatosensory association area ▪ Posterior to primary somatosensory area ▪ Integrates & interprets sensation, for example: the exact shape and texture of an object compared with stored memories Wernicke’s area: ▪ left temporal & parietal lobes ▪ Interprets meaning of speech: translate words into thoughts ▪ The right hemisphere adds emotional content, such as anger or joy, to spoken words 38 ASSOCIATION AREAS A: Broca’s area B: Wernicke’s area39  HEMISPHERIC LATERALIZATION The two hemispheres are quite symmetrical; however, there are slight anatomical differences. There are also functionally different in some ways, with each hemisphere specialized in certain functions. This functional asymmetry is termed hemispheric lateralization. Brain controls the opposite side of the body: ‒ The left side of the brain controls the right side of the body ‒ The right side of the brain controls the left side of the body Left hemisphere = important for spoken & written language, numerical & scientific skills and reasoning Right hemisphere = more involved with musical & artistic awareness, spatial & pattern perception, recognition of faces and emotional content of languages. 40  MEMORY Memory is the process by which information is acquired through learning, also storing and retrieving information. Involves structural and functional changes in the brain. Parts of the brain involves in memory: ‒association areas of the frontal, parietal, occipital & temporal lobes ‒parts of the limbic system ‒diencephalon Motor skill memory also involves cerebellum and basal ganglia. 41 BRAIN STEM 42  BRAIN STEM: MIDBRAIN Connects pons to diencephalon ‒Large tracts: cerebral peduncles Nuclei in the midbrain include: ‒Substantia nigra: related to Parkinson’s disease ‒Red nuclei: help coordinate movements (together with cerebellum) ‒Origin of cranial nerves III and IV (control eye movements) ‒Superior colliculi: nuclei involved in ▪ Scanning eye movements ▪ Responses to visual stimuli ‒Inferior colliculi: responses to auditory input (example: sudden movement of head & body when you hear a loud noise) 43  BRAIN STEM: PONS Serves as a “bridge” ‒Connects medulla to midbrain and above ‒Contains part of ascending (sensory) and descending (motor) tracts ‒Connects left and right sides of cerebellum Contains nuclei ‒Motor (voluntary movement) relays from cerebrum to cerebellum ‒Helps control breathing ‒Cranial nerves V-VIII attached here 44  Brain Stem: Medulla Oblongata Most inferior part of the brainstem. Within the medulla’s white matter are sensory (ascending) & motor (descending) tracts that connect the spinal cord and other parts of the brain. Contains vital nuclei i. Cardiovascular center Regulates heart rate, blood pressure ii. Medullary rhythmicity area Adjusts respiratory rhythm Other nuclei control sensory and reflex motor areas, e.g. swallowing, vomiting, coughing, hiccupping & sneezing. Cranial nerves VIII-XII are attached here. 45 Inferior view of the brain Cerebrum Midbrain Pons Medulla Oblongata Spinal Cord Cerebellum 46  RETICULAR FORMATION The brain stem also consists of small clusters of netlike arrangement of gray and white matter = reticular formation Neurons within the reticular formation contains both ascending (sensory) and descending (motor) tracts Ascending part = reticular activating system (RAS) ‒ Carries sensory pathways to cerebral cortex ‒ Helps to maintain consciousness (wakefulness) ‒ Inactivation of RAS → induce sleep 47  Reticular Formation RAS also functions in selective awareness, which selectively blocks or passes sensory information to the cerebral cortex, e.g.: the slight sound made by a sick child arouses the mother, but the noise of regularly passing trains does not disturb her Descending function = help regulate muscle tone 48  DIENCEPHALONS Located between the brainstem and cerebrum 1. Thalamus 2. Subthalamus 3. Hypothalamus 4. Epithalamus 49 Diencephalon  DIENCEPHALON: THALAMUS The thalamus is the major relay station for most sensory impulses that reach the cerebral cortex from the spinal cord and brain stem. Contributes to motor functions by transmitting information from the cerebellum and basal ganglia to motor areas of the cerebral cortex. Relays nerve impulses between different areas of the cerebrum. Maintenance of consciousness. 51  DIENCEPHALON: HYPOTHALAMUS Hypothalamus lies inferior to thalamus Controls many important body activities and maintain homeostasis Functions: i. Works with ANS regulating contraction of smooth & cardiac muscle and secretion of glands, eg: regulate heart rate, movement of food, contraction of urinary bladder ii. Control of body temperature iii.Control of pituitary and hormone production iv. Involved with feelings and behavior patterns v. Regulation of eating, drinking, fluid levels (thirst center) vi. Regulation of circadian rhythms, eg: pattern of sleep & awakening 52  DIENCEPHALON Corpus callosum Internal capsule Thalamus Hypothalamus 53 CEREBELLUM 54  CEREBELLUM Location: posterior to medulla and pons, inferior to cerebrum ‒Attached to brain stem by cerebellar peduncles Structure: ‒Two cerebellar hemispheres ‒Cerebellar cortex: gray matter ‒Tree-like appearance (seen in sagittal section) of white matter and gray nuclei 55  CEREBELLUM Functions i. Receives wide range of sensory input from muscles, joints, tendons, eyes, inner ears ii. Compares actual movements with intended ones iii. Helps produce smooth, coordinated movements iv. Helps execute skilled motor activities v. Regulates posture and balance 56 CEREBELLUM 57  CLINICAL APPLICATION: AGING Rapid brain growth during first few years of life ‒ Due to increase in size of neurons and proliferation of neuroglia ‒ Increase in development of dendritic branches and synaptic contacts From early adulthood through old age: ‒ Decline in brain mass (by the time one reaches 80, the brain weighs about 7% less) ‒ Fewer synaptic contacts brain function ‒ Some decrease in brain function: processing of information diminishes, conduction velocity decreases, voluntary motor movement slow down 58 SUMMARY - BRAIN 59 SUMMARY - FUNCTIONS OF THE BRAIN 60 SUMMARY - FUNCTIONS OF THE BRAIN 61 62 63