Aston University BE1HAP Lecture 5 The Nervous system PDF

Biomedical Engineering – BE1HAP Human Anatomy and Physiology for Engineers The Nervous System Prof. Igor Meglinski Office: MB154Q E-mail: [email protected] Module Plan Week Topic Instructor Thursday 9:00-11:00 Friday 9:00-11:00 Monda...

Biomedical Engineering – BE1HAP Human Anatomy and Physiology for Engineers The Nervous System Prof. Igor Meglinski Office: MB154Q E-mail: [email protected] Module Plan Week Topic Instructor Thursday 9:00-11:00 Friday 9:00-11:00 Monday 9:00-11:00 Commencing W1 | 23/09 Introduction to HAP Igor Meglinski Lecture | MB158 W2 | 30/09 Human Skin Igor Meglinski Lecture | MB158 W3 | 07/10 Cardiovascular System & Lab Igor Meglinski Lecture | MB158 Laboratory | MB370/372 W4 | 14/10 Cardiovascular System Cont’d Igor Meglinski Lecture | MB158 W5 | 21/10 The Nervous system Igor Meglinski Lecture | MB158 W6 | 28/10 TBC Igor Meglinski Lecture | MB158 Laboratory | MB370/372 W7 | 04/11 *** Reading week *** W8 | 11/11 TBC Igor Meglinski Lecture | MB158 Presentations | MB229 Presentations | MB704 W9 | 18/11 TBC Igor Meglinski Lecture | MB158 Presentations | MB229 W10 | 25/11 TBC Igor Meglinski Lecture | MB158 W11 | 02/12 Quiz Igor Meglinski Lecture | MB371/373 W10 | 18/11 Presentations Igor Meglinski MB266 2 Last week … Learning questions/outcomes What is the circulation system? What are the functions of heart? What are the principles of gas exchange in the body? How Red Blood Cell Carry Oxygen and Carbon Dioxide? What is the The Heart: conduction and contraction? What are the principles of oxygen transportation? How to measure blood pressure? What are the basics of the circulatory system control? 3 The circulatory system: control Nervous control on HR is achieved by – Cardio-accelerator centres Sympathetic stimulation – Cardio inhibitory centres Parasympathetic stimulation Slight stimulation during rest – Autonomic tone 4 Level of Organization and Organ Systems 5 Learning Objectives Describe the Central Nervous System (CNS) and the Peripheral Nervous System (PNS) Understand the functions of the Autonomic Nervous System (ANS) Describe the sympathetic and parasympathetic branches of the ANS and their anatomical differences Distinguish the physiological functions of both sympathetic and parasympathetic divisions of the ANS 6 The Nervous system 7 Central Nervous System (CNS) The Central Nervous System – Brain – Spinal cord It is protected by bones, neuroglia cells and meninges 8  Anatomy of the CNS White matter is found in the deeper tissues of the brain (subcortical). It contains nerve fibres (axons), which are extensions of nerve cells (neurons). Many of these nerve fibres are surrounded by a type of sheath or covering called myelin. Myelin gives the white matter its color. Gray matter is a type of tissue in your brain and spinal cord (central nervous system) that plays a crucial role in allowing you to function normally day to day. It consists of high concentrations of neuron cells bodies, axon terminals (endings) and dendrites. Gray matter is made up of neuronal cell bodies, while white matter primarily consists of myelinated axons. In the brain, white matter is found closer to the centre of the brain, whereas the outer cortex is mainly grey matter. 9  Anatomy of the CNS Meninges: – Specialized membranes Dura Mater: outermost thick and tough membrane Arachnoid Maintain the Pia Mater cerebrospinal fluid – Provide mechanical protection – Act as barrier to toxins and other substances Three layers of membranes known as meninges protect the brain and spinal cord. The delicate inner layer is the pia mater. The middle layer is the arachnoid, a web-like structure filled with fluid that cushions the brain. The tough 10 outer layer is called the dura mater. Brain: Exterior The cerebellum sits at the back of your head, under the cerebrum. It controls coordination and balance. The brain stem sits beneath your cerebrum in front of your cerebellum. It connects the brain to the spinal cord and controls automatic functions such as breathing, digestion, heart rate and blood pressure. The brain stem is the smallest and is located under the cerebellum, extending downward and back toward the neck. The cerebral cortex is the outside portion of the cerebrum, also called the “gray matter”. It generates the most complex intellectual thoughts and controls body movement. 11 Brain: Exterior Cerebrum – The largest part of the brain – Processing centre for thought, memory, language, sensory information Cerebellum – Coordinates muscle movements and controls balance Brain stem – At the base of the brain – Regulate the reflexes and body’s basic involuntary actions (heart rate, blood pressure, sleeping) 12  Brain: Exterior – Hemispheres The cerebrum is divided into the left and right hemispheres by a deep longitudinal fissure; the two hemispheres remain in contact and communication with one another by the corpus callosum. Left Controls most of the function of the right side of your body Mathematical, analytical, language information processing Right Controls most of the function of the left side of your body Creative, artistic and spontaneous thoughts 13 Brain: Exterior – Cerebral lobes Each hemisphere further subdivides into a frontal, parietal, occipital, and temporal lobe. Frontal Complex mental activities (speech) Parietal Pain, touch, temperature Temporal Sounds, some memory function Occipital Processing vision images 14  Brain: Interior Corpus callosum – Communication between left and right hemispheres – Sight, hearing and body movements information delivery Interbrain (Diencephalon) – Thalamus Sensory gatekeeper Axons from the peripheral sensory organs synapse in the thalamus, Thalamic neurons project directly to the cerebrum – Hypothalamus The executive region in charge of the autonomic nervous system and the endocrine system 15  Brain: Interior Pons – Relay station – Sleep Medulla oblongata – Some involuntary activity HR, blood pressure Midbrain (Mesencephalon) – Sight, hearing and body movements information delivery The pons is a part of the metencephalon and forms the middle portion of the brainstem. It is located beneath the midbrain and above the medulla oblongata in the posterior cranial fossa. Like the other structures of the brainstem, the pons contains a multitude of nuclei and is the site of passage and relay of numerous neural tracts. The pons regulates respiration, sleep, equilibrium and other vital functions of the body. 16 Brain: Exterior The ventricles are an interlinked network of cavities in the brain. They are filled with cerebrospinal fluid. The cerebrospinal fluid supplies the brain and the spinal cord with glucose and other nutrients and removes waste products. Moreover, the cerebrospinal fluid (CSF) protects the brain and spinal cord (discussed below) through shock-absorption. Together there are four ventricles of the brain: two lateral ventricles, the third, and the fourth ventricle. 17  Brain: Interior – Ventricles of the Brain The ventricles of the brain are a communicating network of cavities filled with cerebrospinal fluid (CSF) and located within the brain parenchyma. 4 ventricles (hollow chambers) Two larger lateral ventricles located in each cerebral hemisphere Third ventricle located in diencephalon Fourth ventricle located within brain stem and is continuous with spinal canal Choroid plexuses -ependymal cells -cerebrospinal fluid The fluid inside the ventricular system and subarachnoid space is called cerebrospinal fluid (CSF). CSF is produced by specialized ependymal cells of the choroid plexus within the ventricular system. After circulating through the ventricular system, they return t the circulation through the arachnoid granulations. 18  Brain: Interior – CSF The functions of CSF: (1) buoyancy of the brain, spinal cord, and nerves; (2) volume adjustment in the cranial cavity; (3) nutrient transport; (4) protein or peptide transport; (5) brain volume regulation through osmoregulation; (6) buffering effect against external forces; (7) signal transduction; CSF is the clear, colourless fluid that protects and cushions your brain and spine. CSF flows through the ventricles and bathes the brain and spinal cord before being reabsorbed into the bloodstream. The body typically produces enough CSF each day and absorbs the same amount. 19 The Spinal Cord The spinal cord (right figure) is part of the CNS and consists of a tightly packed column of nerve tissue that extends downwards from the brainstem through the central column of the spine. It is a relatively small bundle of tissue (weighing 35 g and just about 1 cm in diameter) but is crucial in facilitating our daily activities. 20 The Spinal Cord It is divided in segments (31) – Each of them is identified by a letter, which relates with the vertebral segment 8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal – a number, which represents the individual segment Its diameter generally decreases – Top to bottom 21 The Spinal Cord 22 Dorsal root ganglion (DRG) Spinal cord segments connects to a pair of ganglia Each segment contains – a posterior root (dorsal) through which sensory information arrives – a anterior (ventral) root through which information is sent out Dorsal and ventral roots unite into a single spinal nerve Spinal cord extends only to L1 or L2. After this, nerves extend inferiorly without spinal cord protection 23 Peripheral nervous system (PNS) PNS connects neurons in CNS and rest of the body: it is vital as a pathway between brain and body PNS consists of: Nerves coming to or from the CNS Ganglia: groups of neuron cell bodies in the periphery Afferent (sensory) Efferent (somatic, autonomic) 24 Peripheral nervous system (PNS) 25  Afferent sensory receptors A huge amount of stimuli comes from the environment Different form of energies (mechanical, thermal, electromagnetic) Specific sensors (e.g. taste) Bitter/sweet Transduction of the energy Action Potential These sensory afferents whose cell bodies reside within the dorsal root ganglia (DRG) or trigeminal ganglia are a heterogeneous population of cells able to convey information relating to distinct sensations such as touch, temperature, itch and pain. 26  An example: skin receptors Receptors of the skin are classified as thermo-receptors, mechanoreceptors, and nociceptors — the last being sensitive to stimulation that is noxious, or likely to damage the tissues of the body. 27  Sensory receptors Coding Stimulus frequency (impulses/s = Hz) Adaptation Sensory coding is one of the several information processing occurrences in the nervous system. This process involves four different but highly related events, which include 28 reception, transduction, coding, and awareness. Sense Receptor Information Coding and Transfer https://youtu.be/WeUAr33sWp8 29 Somatic nervous system (SNS) The somatic nervous system (SNS) is also known as the voluntary nervous system. It contains both afferent nerves (which send information to the brain and spinal cord), made of sensory neurons that inform the central nervous system about our five senses; and efferent nerves (which send information from the brain), which contain motor neurons responsible for voluntary movements, such as walking or lifting an object. The nerves in the somatic nervous system are classified based on their location, either in the head regions or in the spine region. There are 12 pairs of cranial nerves, which send information to the brain stem (base of the brain where the spinal cord connects) or from the brain stem to the periphery. These nerves are required for the five senses and for the movement of head, neck and tongue. The spinal nerves are 31 pairs of nerves that send sensory information from the periphery to the spinal cord and muscle commands from the spinal cord to the skeletal muscles. 30  The Reflex Arc There are five components of a reflex arc which, together, form a reflex loop: Sensory receptor. Sensory neuron. Integration center. Motor neuron. Effector target. In addition to regulating the voluntary movements of the body, the somatic nervous system is also responsible for a specific type of involuntary muscle responses known as reflexes, controlled by a neural 31 pathway known as the reflex arc. The Reflex Arc: CNS-PNS Integrated Functions Certain actions need to be made without or before entering cerebral cortex and conscious awareness Automatic motor responses – Arise from specific trigger In – Muscle spindles Transmission – Sensory neuron Out – Motor neuron 32  The Autonomic Nervous System (ANS) The ANS is a component of the peripheral nervous system that regulates involuntary physiologic processes including heart rate, blood pressure, respiration, digestion, and sexual arousal. It contains three anatomically distinct divisions: sympathetic, parasympathetic, and enteric. Consists of two branches – Sympathetic (fight or flight) – Parasympathetic (rest & digest) Functionally and anatomically distinct Often antagonists Homeostasis The ANS operates independently of the CNS (e.g. - you do not need to consciously tell your heart to beat faster when you run). However, the ANS can be influenced by the brain (e.g. - salivating at the 33 smell of food). Organisation of the ANS 34 The Autonomic Nervous System (ANS) ANS divisions: – fight or flight for the sympathetic system – rest and digest for the parasympathetic system Sympathetic: e.g. increases heart rate, dilates bronchioles, dilates blood vessels in muscle... Parasympathetic: e.g. decreases heart rate, constricts bronchioles, constricts blood vessels in muscle… Sympathetic: Thoraco-lumbar region & Spine vertebrae (T1 to L2) Parasympathetic: Cranio sacral; Cranial nerve components; III (oculomotor); VII (facial); 35 IX (glossopharyngeal); X (vagus); S2 to S4 ANS: Sympathetic vs Parasympathetic https://youtu.be/D96mSg2_h0c 36 ANS An important differentiation of the ANS with respect to the somatic nervous system can be found in the efferent components In the somatic nervous system there is only one single neuron in the efferent component of the somatic nervous system, which extends from the CNS (spinal cord) to the periphery. In the ANS there are two sets of neurons between CNS and PNS. The preganglionic and postganglionicneurons located in ganglia (different from those of the afferent sensory neurons) 37 ANS A preganglionic neuron leaves the CNS via the ventral horn and exits through the ventral root as we have seen in the somatic division However, it does not connect directly with organs or muscles but forms a synapse in another ganglion (a collection of neurons’ bodies that are outside the CNS) This preganglionic neuron synapses onto the postganglionic neuron which then innervates the target organ in example the smooth muscle wall of a blood vessel 38 ANS Parasympathetic and sympathetic preganglionic neurons release acetylcholine Sympathetic division postganglionic neurons are Noradrenergic (i.e. release noradrenaline to the target organs) except those which innervate sweat glands (acetylcholine) Parasympathetic division In the parasympathetic division, the postganglionic neurons release acetylcholine to the target organs (smooth muscle, glands) N.b. Noradrenaline (UK) = norepinephrine (USA) 39 ANS: Neurotransmitters The 2 most common neurotransmitters released by neurons of the ANS are acetylcholine and norepinephrine. Neurotransmitters are synthesized in the axon varicosities and stored in vesicles for subsequent release. 40 How Neurons Communicate https://youtu.be/KLyrTOPLmbM 41 Synaptic transmission https://youtu.be/cZwb8zqAPXc 42 ANS Neurotransmitters and Receptors 43 Summary: The Nervous system 44 Summary Learning questions/outcomes What is the CNS? What is the PNS? What is the ANS? What is the SNS? What are the key elements of the Brain Exterior? What are the key elements of the Brain Interior? What are the CNS-PNS Integrated Functions? What is the CSF? What is the Spinal Cord? 45 What to Expect Next Week… Week Topic Instructor Thursday 9:00-11:00 Friday 9:00-11:00 Monday 9:00-11:00 Commencing W1 | 23/09 Introduction to HAP Igor Meglinski Lecture | MB158 W2 | 30/09 Human Skin Igor Meglinski Lecture | MB158 W3 | 07/10 Cardiovascular System & Lab Igor Meglinski Lecture | MB158 Laboratory | MB370/372 W4 | 14/10 Cardiovascular System Cont’d Igor Meglinski Lecture | MB158 W5 | 21/10 The Nervous system Igor Meglinski Lecture | MB158 W6 | 28/10 Musculoskeletal System Igor Meglinski Lecture | MB158 Laboratory | MB370/372 W7 | 04/11 *** Reading week *** W8 | 11/11 TBC Igor Meglinski Lecture | MB158 Presentations | MB229 Presentations | MB704 W9 | 18/11 TBC Igor Meglinski Lecture | MB158 Presentations | MB229 W10 | 25/11 TBC Igor Meglinski Lecture | MB158 W11 | 02/12 Quiz Igor Meglinski Lecture | MB371/373 Tutorial | MB161(B) W10 | 18/11 Presentations Igor Meglinski MB266 46