Lecture 2 - Structure and Function of the Brain (Recorded) PDF

Structure and function of the brain Lecture GMED3008 – Applied Bioscience for Health Complexity 1 Lecture 2 (recorded) Curtin University is a trademark of Curtin University of Technology CRICOS Provider Code 00301J  WARNING This material has been reproduced and comm...

Structure and function of the brain Lecture GMED3008 – Applied Bioscience for Health Complexity 1 Lecture 2 (recorded) Curtin University is a trademark of Curtin University of Technology CRICOS Provider Code 00301J  WARNING This material has been reproduced and communicated to you by or on behalf of Curtin University in accordance with section 113P of the Copyright Act 1968 (the Act) The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. Do not remove this notice. Content ◼ Anatomy of the brain ◼ Function of the lobes of the brain ◼ Cerebral Spinal Fluid (CSF) ◼ Blood brain barrier ◼ Cerebral blood flow ◼ Neurotransmission ◼ Neural pathways ◼ Investigating the brain The brain A good understanding of the anatomy and functions of the brain will help to learn in the all modules for Applied Bioscience for Health Complexity (GMED3008) ◼ Head injuries ◼ Seizures ◼ Introduction to mental health ◼ Psychotic disorders ◼ Affective disorders ◼ Substance addiction and withdrawal ◼ Psychopharmacology The brain The brain is part of the central nervous system (CNS). ◼ The brain is well protected by the bony cavities of skull and meninges Anatomy of the brain Image: https://easyscienceforkids.com/all-about-your-amazing- brain/ Lobes of the brain Porth, C. Pathophysiology: Concepts of altered health states 2009 ch. 53 pp 1357-1385 Sensory & motor association areas Image source: https://medicalartlibrary.com/cerebral-cortex/ The Limbic system The Limbic system Hippocampus Memory centre. Episodic memories are formed and catalogued to be filed Also help us associate memories with various senses Is also important for spatial orientation and our ability to navigate the world. Amygdala Plays a central role in our emotional responses, including feelings like pleasure, fear, anxiety and anger. Also attaches emotional content to our memories, and so plays an important role in determining how robustly those memories are stored. It also plays a key role in forming new memories specifically related to fear Hypothalamus Located on the floor of the third ventricle and is the “master” control of the autonomic nervous system. A role in controlling behaviours such as hunger, thirst, sleep and sexual response Also regulates body temperature, blood pressure, emotions and secretion of hormones. Thalamus Relay for almost all of the information that comes in and out of the cortex. Plays a role in pain sensation, attention, alertness and memory The Limbic system. Queensland Brain Institute. University of Queensland. https://qbi.uq.edu.au/brain/brain-anatomy/limbic-system Cerebrospinal fluid (CSF) The brain is very well nourished and surrounded by and floats in a protective CSF. Four ventricles within the brain are filled with CSF. Left and Right Lateral ventricles Third ventricle Fourth Ventricle A choroid plexus in each ventricle produces the CSF. Circulation of the CSF Cerebrospinal fluid (CSF) CSF has the following functions: ◼ Buoyancy. ◼ Protection. ◼ Chemical stability ◼ The CSF does not accumulate in the CNS – it is re-absorbed into the venous circulation. ◼ Increases in CSF pressure can cause damage to the brain (hydrocephalus). Blood supply to the brain ▪ The brain has a very good blood supply that provides oxygen and nutrients ▪ 800–1000 mL per minute (50 to 54 millilitres of blood per 100 grams of brain tissue per minute; 15-20% of cardiac output) ▪ The arteries of the brain have a backup system, ensuring the that brain receives nutrients and oxygen ▪ CO2 is the primary regulator for CNS blood flow ▪ Blood brain barrier provides added protection from potentially harmful substances ▪ Internal carotid and vertebral arteries ▪ Arterial circle (circle of Willis) Cerebral Blood Flow Cerebral blood flow is determined by ◼ Viscosity of blood ◼ Dilatation of the blood vessels ◼ Cerebral perfusion pressure - the net pressure of the flow of blood into the brain; determined by the body's blood pressure and intracranial pressure. ◼ Autoregulation - Constriction and dilation of cerebral blood vessels in response to blood pressure or different chemical concentrations (e.g. arterioles dilate in response to higher levels of carbon dioxide in the blood) Cerebral Blood Flow Cerebral blood flow is tightly regulated to meet the brain's metabolic demands. ◼ Too much blood (a condition known as hyperaemia) can raise intracranial pressure (ICP), which can compress and damage delicate brain tissue. ◼ Too little blood flow (ischemia) results if blood flow to the brain is below 18 to 20 ml per 100 g per minute, and tissue death occurs if flow dips below 8 to 10 ml per 100 g per minute. Blood supply to brain ◼ Blood is supplied to the brain through two pairs of large arteries: ◼ Internal carotid arteries, which carry blood from the heart along the front of the neck ◼ Vertebral arteries, which carry blood from the heart along the back of the neck ◼ In the skull, the vertebral arteries unite to form the basilar artery (at the back of the head). The internal carotid arteries and the basilar artery divide into several branches, including the cerebral arteries. ◼ Circle of Willis connects the vertebral and internal carotid arteries. Other arteries branch off from the circle of Willis and carry blood to all parts of the brain. Arteries of the Brain Large veins of the head Blood Brain Barrier The blood brain barrier is both a physical barrier and a system of cellular transport mechanisms. It maintains homeostasis by restricting the entrances of potentially harmful chemicals from the blood, and by allowing the entrance of essential nutrients. Images: https://commons.wikimedia.org/wiki/File:Blood- brain_barrier_02.png Blood Brain Barrier ◼ Lipid soluble molecules, such as ethanol and caffeine are able to enter through the barrier relatively easily via the lipid membranes of the cells. ◼ However, water soluble molecules such as sodium and potassium ions are unable to transverse the barrier without the use of specialized carrier- mediated transport mechanisms. ◼ Some areas of the brain do not have a blood- brain barrier (for example the posterior pituitary) Images: https://commons.wikimedia.org/wiki/File:Blood- brain_barrier_02.png Nervous tissue ◼ The brain itself is made up from nervous tissue ◼ Grey matter (cell bodies) ◼ White matter (axons) Nervous tissue ◼ Nervous tissue comprises neurons (conduct electricity) and glial cells (supporting cells) Neuroglia  Nerve glue’  Support the neurons of the CNS Astrocytes Oligodendrocytes Microglia Ependymal General structure of a neuron Neurotransmission ◼ A neuron imparts electrical movement by discharging chemicals at the junction of the two cells. ◼ Know as neurotransmission ◼ Chemical transmission is the major way nerves communicate with each other in the nervous system Nerve impulse ◼ Neurons generate and conduct electrical and chemical impulses ◼ Achieved by movement of electrolytes across the cell membrane ◼ Movement of charged ions in and out of neurons creates electrical activity in the brain that can be measured. ◼ Speed of transmission is determined by myelin sheath Synapses ▪ The region between adjacent neurons is called a synapse ▪ Impulses are transmitted across the synapse by chemical and electrical conduction ▪ Presynaptic neurons and postsynaptic neurons ▪ Synaptic cleft ▪ Neurotransmitters Neurotransmitters Neurotransmitters are chemicals that move in and out of, or between neurons. ◼ Endogenous chemicals (synthesized from within the CNS) which relay, amplify, and modulate signals between a neuron and another cell. ◼ Chemicals that either change the electrical charge of a neuron’s membrane when the attach to a receptor or cause ion channels to open and close allowing positively or negatively charged ions to cross the membrane. Image: http://www.neurevolution.net/category/history/page/2/ Mechanism of Neurotransmission 1. A nerve impulse or an action potential reaches a presynaptic terminal 2. Voltage-sensitive calcium channels opened - influx of calcium ions leading to a series of chemical changes. 3. Synaptic vesicles pour the neurotransmitters stored in them into the synaptic - releasing the neurotransmitter into the gap between the presynaptic surface and the postsynaptic surface. 4. The postsynaptic surface becomes depolarized (under the influence of the neurotransmitter) resulting in a nerve impulse in the postsynaptic neuron, and the neurotransmitter reaches and binds onto the receptor Neurotransmitters ◼ The action of a neurotransmitter can be “Excitatory” or “Inhibitory” ◼ The terms “Excitatory “or “Inhibitory” refers to the effect the neurotransmitter has on the postsynaptic cell Excitatory Inhibitory Act to increase the probability that the Act to reduce the membrane potential of target cell will fire an action potential. the effected cells, thus “calm” and create balance. Membrane potential is therefore Easily depleted when excitatory increased in the target cell, resulting in neurotransmitters are over active. E.g. depolarisation. e.g. Noradrenaline GABA Image: https://psychology.stackexchange.com/questions/17179/is-it-true-that-stimulants-make-neurons-fire- more-often-and-depressants-make-th Neurotransmitters In addition to function, neurotransmitters can be broadly categorized into three groups according to their chemical structure (Porth, 2014. 1. Monoamines (Serotonin, dopamine, noradrenaline & adrenaline) 2. Amino acids (glutamine, glycine, and GABA) 3. Peptides (somatostatin, substance P, and opioid peptides such as endorphins and enkephalins) Neural Pathways Neural pathway consist of interconnected neurons which allow communication between different brain regions. Brain region 2 Brain region 3 Brain region 1 Some neural pathways are activated by specific neurotransmitters Some neurotransmitter pathways are localised and relatively specific in their targeting of brain regions (e.g. Dopamine and Noradrenaline), while other transmitters are widely distributed throughout the brain (e.g. Glutamate) Dopamine Pathway Dopamine interacts with several subtypes of dopamine receptors - D1, D2, D3, D4 & D5 (these all have different functions and are names according to size and function). 4 major dopamine pathways Noradrenergic Pathway ◼ The Noradrenaline pathway projects from the brainstem to cerebellum, forebrain and spinal cord & hypothalamus. Serotonin Pathway ◼ Serotonin (5- HT) originates in the brainstem (Raphe nuclei) to the cerebellum, forebrain and limbic system. Cholinergic Pathway ◼ Cholinergic pathways originate at the brain stem to cortex (basal forebrain nuclei to frontal cortex). Amino Acids GABA and Glutamate regulate action potentials GABA is an ‘inhibitory’ neurotransmitter stops action potentials Glutamate is an ‘excitatory’ neurotransmitter, starts action potentials and keeps them going. Work together to control many processes in the brain, including the brain’s overall level of excitation. Many substances change the balance of glutamate and GABA Amino Acids Glutamate GABA ◼ Important for learning and ◼ Is implicated in memory, and perception. emotional control & arousal. ◼ Controls the release of other neurotransmitters, ◼ Inhibits the release of toxic to cells if in high other neurotransmitters concentration. especially noradrenaline, dopamine and serotonin. GABA and Glutamate ◼ Substances decrease or increase one or the other, changing the balance of glutamate and GABA. Substance Effect on glutamate and GABA Sedative or depressant Tends to shift the balance toward GABA, decreasing brain drugs activity. Stimulant drugs Shift the balance toward glutamate, causing an energized, wakeful state in the user. Alcohol Decreases glutamate activity. Alcohol Increases GABA activity. PCP, or "angel dust," Increases glutamate activity Caffeine Increases glutamate activity and inhibits GABA release. Tranquilizers Increase GABA activity. Nicotine Chronic nicotine exposure facilitates excitatory glutamate neurotransmission. Repeated nicotine exposure attenuates inhibitory GABA neurotransmission (D’Souza & Markou, (2013). Neuropeptides ◼ Are made up of three or more amino acids and are larger than the small molecule transmitters. ◼ Many different types. ◼ Common ones include: ◼ Endorphins and enkephalines which inhibit pain ◼ Substance P which carries pain signals ◼ Neuropeptide Y which stimulates eating and may act to prevent seizures Common neurotransmitters and function Neurotransmitter Function Acetylcholine Alertness, attention learning and memory. Adrenaline Regulates mood & attention, mental focus, speed of information processing, arousal and cognition Reponses to pain, stress, fear, or excitement. Dopamine Motor systems, pleasure/reward, emotional arousal GABA Emotional control, arousal, Inhibits the release of other neurotransmitters especially norepinephrine, dopamine and serotonin. Glutamate Learning and memory, and perception. Controls the release of other neurotransmitters. Noradrenaline Regulates mood, attention, mental focus, speed of information processing, arousal and cognition Serotonin Regulates sleep, mood, emesis, libido, appetite, pain perception, body temperature, blood pressure and hormonal activity Endorphins Release is associated with feelings of euphoria and a reduction in pain (body’s natural 'pain killers’). Released during exercise, excitement and sex. Neurotransmitters A visual reminder Image: http://ib.bioninja.com.au/options/option-a-neurobiology- and/a5-neuropharmacology/types-of-neurotransmitters.html Neurotransmission & disorders ◼ Disorders or substances that alter the production, release, reception, breakdown, or reuptake of neurotransmitters or that change the number and affinity of receptors can cause neurologic or psychiatric symptoms and cause disease. ◼ E.g., ◼ Alzheimer's disease ◼ Parkinson's’ disease ◼ Depression ◼ Anxiety ◼ Depression ◼ Brain Injury ◼ Mania ◼ Psychosis ◼ Drugs that modify neurotransmission can alleviate many of these disorders (e.g., Parkinson disease, depression). Investigating the brain Curtin University is a trademark of Curtin University of Technology CRICOS Provider Code 00301J Investigating the brain The brain can be studies in many ways ◼ Effects of brain damage ◼ Effects of electrical and chemical stimulation ◼ Measurement of electrical and chemical activity ◼ Computer-based brain scans Effects of brain damage ◼ Damage to different areas of the brain produces different behavioural and psychological effects. ◼ E.g. ◼ Damage to the frontal lobe of the brain effects the ability to make decisions and to inhibit socially inappropriate behaviours. ◼ Damage to the occipital lobe may disturb vision ◼ A neurologic examination helps to localize and lateralize lesions due to traumatic injury. Neurological assessment ◼ Neurological assessment focuses on identifying and assessing vital portions of the CNS ◼ The neurological exam includes assessing mental state, a sensory exam, a motor exam and reflexes. ◼ The Glasgow coma scale may be used for grading the severity of brain injury following a traumatic injury and supplements the neurological assessment in the trauma setting. Neurological assessment ◼ Assesses sensory neurons ◼ Cranial nerves can also be and motor responses to assessed as part of a neurological determine whether the exam nervous system is impaired https://anatomy-library.com/img/anatomy-and-physiology-coloring- workbook-cranial-nerves-27.html Mental state assessment Glasgow coma scale Used to evaluate the following: ◼ Assesses how the brain functions as ◼ Attention a whole. ◼ Orientation to time, place, & person ◼ Memory The scale assesses three major brain ◼ Various abilities, such as thinking functions: abstractly, following commands, using language, and solving math ◼ Eye opening problems ◼ Mood ◼ Motor response ◼ Thoughts of self harm/ suicide ◼ Verbal response The mental status evaluation consists of a series of questions and tasks, such as naming objects, recalling short lists, writing sentences, and ◼ A “normal” score = 15 copying shapes. Measuring electrical activity ◼ Electroencephalograms (EEG) ◼ Event-related potentials (ERP) ◼ Magnetoencephalograms (MEG) X-Ray Imaging ◼ X-Ray imaging techniques ◼ Conventional Radiology ◼ Angiography Computer Brain Imaging ◼ Magnetic resonance imaging (MRI) ◼ Functional magnetic resonance imaging (fMRI) Computer Brain Imaging ◼ CT scanning (multiple images) CT Versus MRI Image source: https://www.regencymedicalcentre.com/ct- scan-vs-mri/ Computer Brain Imaging ◼ Positron Emission Tomography (PET scan) ◼ Single Photon Emission Computed Tomography (SPECT) Testing CSF ◼ Lumbar Puncture Other biological investigations ◼ Brain stimulation ◼ Transcranial magnetic stimulation (TMS) ◼ Usually used therapeutically but also used to investigate brain functioning https://psychscenehub.com/psychinsights/transcranial-magnetic-stimulation-for- depression/ Activity 1 ◼ Watch the following video and complete the worksheets provided on Blackboard (BB) Neurons Neurotransmission Lobes of the brain Parts of the brain Brain anatomy The brain Activity 2 Complete the worksheet provided on Blackboard (BB) ◼ Neurotransmitters and functions