Functional Organisation of Nervous System 2021 PDF

FUNCTIONAL ORGANISATION OF NERVOUS SYSTEM NG SOOK LUAN, PhD Jabatan Diagnostik Kraniofasial & Biosains Fakulti Pergigian UKM 012-9305208 [email protected]  LEARNING OBJECTIVE 1. Describe the overall functions of the nervous s...

FUNCTIONAL ORGANISATION OF NERVOUS SYSTEM NG SOOK LUAN, PhD Jabatan Diagnostik Kraniofasial & Biosains Fakulti Pergigian UKM 012-9305208 [email protected]  LEARNING OBJECTIVE 1. Describe the overall functions of the nervous system. 2. Describe the classes of neurons that make up the nervous system. 3. Describe the brain component and its major function. DIVISIONS OF THE NERVOUS SYSTEM Sherwood (2016); 9th Edition; page 134 FUNCTIONAL CLASSES OF NEURON Afferent neurons Inform CNS about conditions in both external and internal environment Efferent neurons Carry instructions from CNS to effector organs – muscles and glands Interneurons Found entirely within CNS Integrating afferent information & formulating an efferent response Higher mental function associated with the “mind” (thoughts, emotions, memory creativity, intellect, motivation) Sherwood (2016); 9th Edition; page 135  GLIAL CELLS Glial cells Connective tissue of CNS Support the interneurons physically, metabolically & functionally Do not conduct nerve impulses 4 types Astrocytes Formation of blood-brain barrier (BBB) Formation of neural scar tissue Maintain optimal ion conditions for neural excitability Oligodendrocytes Sherwood (2016); 9th Edition; page 136 Forms myelin sheath around axons in the CNS Microglia Phagocytosis – immune defense cells of CNS Release nerve growth factor Ependymal cells Formation of cerebrospinal fluid (CSF) Works as neural stem cell – to form new neurons and glial cells  Cerebrum Forebrain Diencephalon Sherwood (2016); 9th Edition; page 144  CEREBRAL CORTEX Cerebrum Left and right hemispheres – gyri and sulci Corpus callosum connects left and right White matter (myelinated axons) Innermost layer Interconnects Cerebral cortex or Gray matter Outermost layer Organized in functional vertical column (6 layers) Each column is a team with distinct function Differences are a result of different input/output and different layering patterns Sherwood (2016); 9th Edition; page 143 Divided into 4 pairs of lobes: frontal, parietal, temporal and occipital  CEREBRAL CORTEX Frontal lobe Voluntary motor activity, speaking ability and elaboration of thought Stimulation of different areas of its primary motor cortex moves different body regions, again primarily on the opposite side of the body Parietal lobe Somatosensory processing Each region of its cortex receives somesthetic (feel) and proprioceptive (awareness of body position) input from a specific body area, primarily from the opposite body side Temporal lobe Receives sound sensation Occipital lobe Sherwood (2016); 9th Edition; page 147 Initial processing of visual input Sherwood (2016); 9th Edition; page 148  BASAL NUCLEI A.k.a. basal ganglia Masses of gray matter deep inside the white matter Act by modifying ongoing activity in motor pathways Inhibit muscle tone – proper tone – balance of excitatory and inhibitory inputs to motor neurons that innervate muscles Select and maintain purposeful motor activity while suppressing unwanted patterns of movement Monitor and coordinate slow and sustained contractions – especially those related to posture and support Parkinson’s disease Damage to basal ganglia neurons that release dopamine (deficient in dopamine) Caudate Increased muscle tone or rigidity nucleus Involuntary, useless or unwanted movements (e.g. resting tremors – hands rhythmically shaking) Putamen Slowness in initiating and carrying out motor behaviours Globus Pallidus (e.g. slow to stop ongoing activities – remain sitting, get up slowly)  DIENCEPHALON Diencephalon: thalamus & hypothalamus Thalamus A “relay station” or synaptic integrating centre for processing sensory input on its way to the cerebral cortex – directs attention (e.g. when a baby cries, parents wake up) Also integrates information that important for motor control Receives sensory information from different areas of the body Information is processed by specific thalamic nuclei Hypothalamus Homeostatic control: body temperature, thirst and urine production, food intake, anterior pituitary hormone secretion, production of posterior pituitary hormones, uterine contractions and milk ejection Serves as an autonomic nervous system (ANS) coordinating centre Plays a role in emotional and behavioural patterns Participates in sleep-wake cycle  LIMBIC SYSTEM Several forebrain structures that function together Cortex (limbic association cortex) Cingulate gyrus Hippocampus Amygdala Basal nuclei Thalamus Hypothalamus Plays a role in Emotional state and basic behavioural patterns Learning and memory  CEREBELLUM Highly folded, posterior, baseball-sized part of brain Spinocerebellum Important in Balance Planning and executing voluntary movement Activities Cerebrocerebellum Vestibulocerebellum - Maintenance of balance, control of eye movements Spinocerebellum - Regulation of muscle tone (enhancement, opposite of basal nuclei), coordination of Vestibulocerebellum skilled voluntary movement (e.g. synchronized shoulder, elbow and wrist joint to reach a pencil) Cerebrocerebellum - Planning and initiation of voluntary activity by providing input to the cortical motor area, stores procedural memories Cerebellar disease Intention tremor – present only during voluntary activity Sherwood (2016); 9th Edition; page 166  BRAIN STEM Critical connecting link between rest of brain and spinal cord Functions: Most of cranial nerves arise from brain stem Neuronal clusters within brain stem control heart and blood vessel function, respiration and digestive functions Regulating muscle reflexes involved in equilibrium and posture Reticular formation within brain stem receives and integrates all incoming sensory synaptic input – modulating sensitivity of spinal reflexes and regulating transmission of sensory info (especially pain) into ascending pathways Centres that govern sleep are in the brain stem (evidence suggests centre promoting slow-wave sleep lies in hypothalamus)  BRAIN STEM Consists of midbrain, pons and medulla Midbrain Nerve pathway of cerebral hemispheres Auditory and visual reflex centres Cranial nerves III, IV Pons Respiratory centre Cranial nerves V-VIII Medulla Crossing of motor tracts Cardiac centre Respiratory centre Vasomotor centre (nerves having muscular control of the blood vessel walls) Centres for cough, gag, swallow and vomit Cranial nerves IX-XII  SPINAL CORD Extends from brain stem through vertebral canal Below L2 turns into a bundle of nerves (Cauda equina, spinal tabs are below this point) 2 vital functions: Neuronal link between brain and peripheral nervous system (PNS) Integrating centre for spinal reflexes 31 pairs of spinal nerves emerge from spinal cord through spaces formed between arches of adjacent vertebrae: 8 pairs cervical (neck) nerves: C1-C8 12 pairs thoracic (chest) nerves: T1-T12 5 pairs lumbar (abdominal) nerves: L1-L5 5 pairs sacral (pelvic) nerves: S1-S5 1 pair coccygeal (tailbone) nerve  SPINAL CORD Fairly uniform cross-section Gray matter in the core: Cell bodies Each horn houses different types of neurons White matter in the outer segment: Axons organized into bundles Bundles organized into tracts  LEARNING OBJECTIVE 4. Describe the functions of cerebrospinal fluid (CSF). 5. Explain formation and absorption of CSF and factors affecting them. 6. Describe blood brain barrier and its function.  CEREBROSPINAL FLUID (CSF) Protection of the CNS from injury Enclosed by hard bony structures (cranium encases the brain & vertebral column surrounds the spinal cord) Three membranes (the meninges) protect and nourish it The brain floats in the cushioning fluid - CSF. The blood-brain barrier (highly selective) limits access to harmful blood-borne substances Meningeal membranes 1. Dura mater Two layers mostly attached Dural and venous sinuses return venous blood & CSF 2. Arachnoid mater Richly vascularized layer Arachnoid villi (CSF reabsorbed into venous circulation here) 3. Pia mater Layer closer to the brain & ependymal cells Sherwood (2016); 9th Edition; page 140  CEREBROSPINAL FLUID (CSF) Characteristics Same density as brain – brain floats in and is cushioned by the CSF CSF and interstitial fluid of the brain cells are free to exchange materials Formed by choroid plexuses in the ventricles Richly vascular cauliflower-like masses Selective and regulated transport Differ from plasma (e.g. lower K+ and higher Na+, almost no proteins) 125 – 150 ml is replaced > 3 times per day Flow Flows through the four ventricles and spinal cord’s narrow central canal Throughout the ventricles → 4th ventricle → out to subarachnoid space → over the entire brain → top of the brain → subarachnoid villi → reabsorbed into the dural sinuses Facilitated by ciliary beating along with circulatory and postural factors Pressure 10 mmHg. Even small reduction (e.g. dural spinal tabs for lab analysis) can lead to severe headaches Excess CSF: malformation or tumour → obstruction of CSF pathways; hydrocephalus (water on the brain) → brain damage if untreated  BLOOD-BRAIN BARRIER (BBB) Blood-brain barrier Tight junctions between endothelial cells of brain capillaries (anatomical restriction) Few materials allowed to freely diffuse Lipid soluble substances (O2, CO2, alcohol, steroid hormones) – lipid plasma membrane Water - aquaporins Careful and controlled exchange between blood and CSF Advantage: Brain shielded from changes in the ECF and harmful blood borne materials Disadvantage: Limited types of drugs (brain or spinal cord treatment) can pass through BBB Formation & maintenance of BBB Astrocytes Surround the brain capillaries Signal the brain capillaries to ‘get tight” Promote the production of specific carrier proteins & ion channels Participate in the cross-cellular transport of some substances, e.g. K+  BRAIN NOURISHMENT Brain can only use glucose but does not store glucose Brain can only metabolize aerobically (O2 present) to produce ATP Highly dependent on blood supply (15% blood supplied by heart)– high demand for ATP – resting conditions: brain uses 20% O2 and 50% glucose During starvation, the brain can resort to use ketone bodies produced by the liver via passive diffusion. Ketone bodies → acetyl-CoA → citric acid cycle → oxidized in the mitochondria for energy. Brain damage if O2 deprived for > 4-5 min, glucose cut off for > 10-15 min