Lecture 1 - Organization of the Nervous System PDF

Welcome to Human Physiology 2 PHYG 13383D  Human Systems Physiology Schedule and Evaluation Lectures: Mondays and Wednesdays 12-2pm Evaluation Plan: Assignment 10% Quizzes (6) 15% Midterm exam 1 25% Midterm exam 2 25% Final exa...

Welcome to Human Physiology 2 PHYG 13383D  Human Systems Physiology Schedule and Evaluation Lectures: Mondays and Wednesdays 12-2pm Evaluation Plan: Assignment 10% Quizzes (6) 15% Midterm exam 1 25% Midterm exam 2 25% Final exam 25% Total 100% 2  Lecture 1: Organization of the Nervous System Sherwood & Ward 5th Edition, Chapters , 3, 4, 5 Objectives Knowledge The levels of organization of the nervous system Distinguish both structurally and functionally between neurons and neuroglia Mechanisms involved in the maintenance of brain homeostasis Gross anatomical divisions of the brain (review BIOL 19201) Application Describe how brain homeostasis can be altered Correlate pathophysiological changes in the brain tissue with the obstruction in cerebral blood flow 4 Objectives Today’s focus Major structures within the brain Organization of the nervous system Maintenance of CNS homeostasis 5 Major Structures Within the Brain  The Brain General anatomy 1) Cerebrum 2) Diencephalon 3) Brain stem 4) Cerebellum Diencephalon (Deep to cerebral hemispheres) 7  4 lobes 1) Cerebrum -Superior part of brain containing 83% of its mass -Divides brain into two halves called cerebral hemispheres -Hemispheres divided by longitudinal fissure -Each hemisphere has 4 lobes (more information on slides 17-19) -Surface areas defined by the existence of Gyri Sulci Fissures (deep sulcus) Each cerebral hemisphere has three basic regions: i. Cerebral cortex ii. Cerebral white matter 8 i. Cerebral cortex Superficial gray matter; accounts for 40% mass of brain Enables sensory perception, communication, memory, understanding, and voluntary movements Each hemisphere acts contralaterally Hemispheres are not equal in function Lateralization of cortical functioning No functional area acts alone; conscious behavior involves entire cortex 9 ii. Cerebral white matter Communication between cerebral areas and cerebral cortex Areas are classified according to direction they run: Commissures: connect areas between the 2 hemispheres, enabling them to function as a whole Association fibers: connect different parts of the same hemisphere Projection fibers: connect the cortex to the iii. Basal ganglia/basal nuclei rest of the nervous system Several masses of gray matter located deep within cerebral white matter – Hub of complex interconnection with cerebrum and diencephalon Control of movement through inhibition of muscle tone Suppression of useless muscle tone 10 2) Diencephalon Consists of two distinct regions deep within brain: Thalamu s i. Thalamus Relay station for all sensory input on its way to the cortex – Screens out insignificant signals and directs important signals to proper areas within brain Sensation and consciousness Role in motor control ii. Hypothalamus Collection of specific nuclei located inferior to thalamus Integrating center for homeostatic function – Temperature control, thirst, urine control, hunger Role in sleep-wake cycle 11 3) Brain Stem Adjoining structure continuous with Thalamu spinal cord s Consists of – Pons – Medulla oblongata – Midbrain Main function is integration of motor output and sensory perception 4) Cerebellum Located posterior to brain stem Monitors and enhances information from major motor system of brain Opposite compared to basal ganglia, which inhibits information from major motor systems 12  Cerebrum Diencephalon 13 Summary Functional areas of the cerebral cortex  Three types of functional areas are: 1) Motor areas – Movement and change of muscle tone 2) Sensory areas – conscious awareness of sensation 3) Association areas – Integrate different areas together 14 1) Motor areas (frontal lobe) 1. Primary motor cortex Controls voluntary movement 1 3 2 2. Premotor cortex Controls learned, repetitious, or patterned motor skills Coordination of complex movements Sends signal to primary motor cortex 4 3. Frontal eye field Controls voluntary eye movement 5 4. Prefrontal cortex Decision making, higher mental functions Personality traits Planning for voluntary activity *Wernicke’s area* 5. Broca’s area Also present in left Present in the left hemisphere hemisphere Motor speech area that directs muscles of tongue Ability to understand speech 15 2+3) Sensory and association areas 1. Visual and auditory areas Visual: Receives visual info from the eyes 3 Auditory: Ears 2 2. Somatosensory association cortex 1 Integrates sensory information 3. Primary somatosensory cortex Receives information from skin and skeletal muscles 4 4. Olfactory, gustatory, and vestibular cortices Olfactory: Smell (nose) Gustatory: Taste (tongue) Vestibular: Positional information (inner ear) 16 Quiz 1. The brain and spinal cord are part of the ______nervous system. 2. Name 4 brain lobes. 3. Name an area of the brain that is involved in motor control. 4. Name one structure of the diencephalon. 5. Name one structure of the brain stem. 6. Sensory neurons enter the spinal cord through the ______ horn. 7. In which direction does an afferent neuron carry information: 17 toward the brain or away from the brain? Cells of the Nervous System Cells of the nervous system Neurons Supporting Cells Afferent, efferent and (Glial) interneurons Do not participate Have synapses directly in synaptic Target other neurons, interactions Some glial cells do have muscles, glands synapses, though these are supportive in nature Supportive role More numerous than neurons (form ~90% of nervous tissue), but occupy ½ the volume within brain because branching much less 19 Neurons Highly specialized to transmit nerve impulses All neurons have a cell body (contains the nucleus) and one or more processes (fibers) 2 types of processes Dendrites—carry impulses toward the cell body Axons—conduct impulses away from the cell body 20 Neurons One neuron will form hundreds to thousands of axon terminals Terminals contain neurotransmitters NO physical continuity Gap called the synapse Most large fibers are myelinated Myelin protects and insulates nerve fibers Increases the transmission rate of nerve impulses Example of a synapse, which separates the axon terminal of one neuron from the dendrite of a distal neuron 21 Neuron Structural Classifications  Neuron Resting Membrane Potential What determines the resting membrane potential? Resting Membrane Potential: The relative concentration of ions inside and outside of a semipermeable membrane and the electrochemical forces surrounding them when voltage gated channels are closed.  31 Keyboard Polarization 90 80 70 60 50 40 Polarized = separation of charge, 30 20 VOLTAGE 1 mV 10 inside of the cell is sitting at a 0 -10 -20 negative potential -30 -40 -37.49 Depolarized = removal of the -50 -60 31 Keyboard 340.5 341.0 341.5 342.0 342.5 343.0 343.5 344.0 344.5 345.0 345.5 346.0 346.5 90 s polarized state, cell is moving 80 70 60 toward a 0mV potential 50 40 Repolarized = cell is returning to 30 20 VOLTAGE 1 mV 10 0 the polarized state -10 -20 Hyperpolarized = cell has moved -30 -37.49 -40 -50 -60 beyond the polarized state, a 342.10 342.12 342.14 342.16 342.18 342.20 342.22 342.24 342.26 342.28 s 342.30 greater negative charge than normal Voltage Gated Ion Channels Voltage gated ion channels are sensitive to membrane potential and will open or close in response to changing potentials Opening and closing can happen at varying speeds https://www.youtube.com/watch?v=KTTeD2AMiPA Voltage Gated Ion Channels The Na channels usually open very rapidly and then become inactivated very rapidly They stay inactive until a depolarized potential is re- established and then they return to a closed state  Sodium-Potassium Pump 6 K+ is released and Na+ Extracellular 1 Binding of cytoplasmic Na+ sites are ready to bind fluid to the pump protein Na+ again; the cycle stimulates phosphorylation repeats. by ATP. Cytoplasm Phosphorylation causes the 2 protein to change its shape. Concentration gradients of K+ and Na+ 5 Loss of phosphate 3 The shape change restores the original expels Na+ to the conformation of the outside, and pump protein. 4 K+ binding triggers extracellular K+ binds. release of the phosphate group. https://www.youtube.com/watch?v=ZKE8qK9UCrU Figure 3.10  The Electrochemical Gradient K+ K+ Na+ _ Cl- Na+ Cl - https://www.youtube.com/watch?v=ZKE8qK9UCrU The Nernst Equation Calculates Membrane Potentials. For any ion there is a membrane potential (Em) at which there will be no net movement of that ion across a membrane Em = -RT log [ion]in = -61 log [ion]in zF [ion]out z [ion]out Calculate the Nernst potentials for the following ions: Ion [In](mM) [Out](mM) Z Em Na 15 150 +1 K 150 5 +1 Cl 10 120 -1 The Goldman Equation The Goldman Equation states that membrane potential is the sum of the Nernst potentials for the existing ion channels multiplied by the relative permeability of the membrane to each of these ions : Em = -61 log CNai*PNa + CKi*PK + CCli*PCl CNao*PNa + CKo*PK + CClo *PCl Em = ENa*PNa + EK*PK + ECl*PCl What is the membrane potential? Ion Em Perm Em x P Na 60mV 0.2 K -90mV.7 Cl -60mV.1 Total The Neuron Action Potential Na+ The action potential is the result of ion channels suddenly opening and closing, changing the membrane permeability for an ion The action potential is a propagated electrical current K+ that is used to do chemical work Changing permeabilities during the action potential. Some real data… PK2 (20nM) Membrane potential (Em) changes 70 60 50 40 30 during PK2 application 20 10 VOLTAGE 0 -10 mV 1 -20 -30 -40 -50 -60 -70 -80 -80mV -90 10mV -100 340 360 380 400 420 440 460 480 500 520 540 560 580 600 620 640 660 680 700 60s s A Real Action Potential 31 Keyboard 90 80 70 60 50 40 30 20 VOLTAGE 1 mV 10 0 -10 -20 -30 -37.49 -40 -50 -60 31 Keyboard 340.5 341.0 341.5 342.0 342.5 343.0 343.5 344.0 344.5 345.0 345.5 346.0 346.5 90 s 80 70 60 50 40 30 20 VOLTAGE 1 mV 10 0 -10 -20 -30 -37.49 -40 -50 -60 342.10 342.12 342.14 342.16 342.18 342.20 342.22 342.24 342.26 342.28 342.30 s What triggers the AP? Graded potentials EPSP IPSP What triggers graded potentials? Synaptic neurotransmitter release  How does a synapse trigger a graded potential? https://www.youtube.com/watch?v=LT3VKAr4roo How does a synapse trigger a graded potential? What triggers the AP? Integrated spatial and temporal summation of EPSP and IPSP Once an action potential is triggered in the cell body, it will propagate down the axon to trigger neurotransmitter release in the axon terminal. What is the sequence of events that result in an action potential, starting at the presynaptic neuron? 43 Neurotransmitters Inhibitory Excitatory Norepinephrine Acetylcholine Serotonin Norepinephrine Dopamine GABA Glutamate Glycine ATP Peptides Neurotransmitters: Classification by Function Neuromodulators Neuromodulator: chemical messenger released by neuron that does not directly cause EPSPs or IPSPs but instead affects the strength of synaptic transmission May influence synthesis, release, degradation, or reuptake of neurotransmitter May alter sensitivity of the postsynaptic membrane to neurotransmitter. May be released as a paracrine Effect is only local Examples 1. SSRI’s: Selective serotonin reuptake inhibitors Increases duration of serotonin release by inhibiting reuptake Assists with mood stabilization Can also assist with sleep because serotonin is a precursor to melatonin 2. MAOI’s: Monoamine oxidase inhibitors Monoamine oxidase breaks down norepinephrine, dopamine and serotonin Limits their duration of effect of Monoamine oxidase inhibitors prevent the action of MAO’s Application: You’re designing a pre-workout and want to include a (legal) derivative of phenylethylamine to promote dopamine release. Using your knowledge of neurophysiology, specifically that MAO’s will degrade your ingredient in ~5 minutes, what class of substance can you add to increase the duration of effect of your product? Glial cells 5 Copyright © 2022 by Cengage Canada 48 Figure 4-3, p. 100 Glial cells in the CNS 1) Astrocytes Most abundant, star-shaped Protect neurons from harmful substances in the blood Help maintain chemical environment in the brain 2) Microglia Spider-like projections Immune cells of CNS Can move to area of infection within CNS 49 Glial cells in the CNS 3) Ependymal Line central cavities of the brain and spinal cord (e.g. choroid plexus) Cilia helps circulate the CSF Form a protective cushion 4) Oligodendrocytes Coil around nerve fibers, producing fatty insulating coverings called myelin sheaths Each oligodendrocyte has several projections 50 Glial cells in the PNS Satellite Cells Act as protective, cushioning cells Protect neuron cell bodies Schwann Cells Form the myelin sheaths around nerve fibers in the PNS (*not CNS*) 51 Maintenance of CNS Homeostasis  Maintenance of CNS homeostasis 1. Meninges Three protective, nourishing membranes surrounding CNS 2. Blood Brain Barrier (BBB) Highly selective endothelium/basement membrane 3. Cerebrospinal Fluid Protects and feeds neurons and support cells 4. Blood Supply Constant to provide adequate nutrients 53 1) Meninges: 3 layers a) Dura mater: Tough outer layer Attached firmly to inside of skull Dural partitions extend into some fissures Dural sinuses carry venous b) Arachnoid blood mater: Thinner middle layer Follows contour of dura c) Pia mater: Very thin inner layer Follows contour of surface of CNS 54 1) Meninges: 3 layers and 3 Dural sinus (carries venous blood) spaces Scalp Arachnoid villi Skull Epidural Dura space mater Arachnoid Subdural mater space Subarachnoid space (contains CSF) Pia mater 55 1) Meninges: Anatomical location along spinal cord Spinal cord Epidural space Spinal nerves Lots of nerve fibres and blood Dura mater vessels Pia mater Arachnoid mater Dura mater Spinal vertebrae © John Wiley & Son Inc 56 Clinical case: Epidural hemorrhage Blow to the head causes brain to ‘jerk’ in the cranial cavity Blood collects in the epidural space Results in brain tissue being compressed due to meninges being forced “inward” by increased pressure Symptoms: Brief loss of consciousness and possible coma due to compression of the brain as blood mass increases 57 2) Blood brain barrier 1) Non-fenestrated (no openings) capillary endothelial cells 2) Thick basement membrane 3) Astrocytes Permit minimal transport CO2, O2 freely; glucose active transport (3) Blood (2) (1 ) 58 3) Cerebrospinal fluid Clear, colourless liquid Ventricles Fills the ventricles and subarachnoid space Functions: Mechanical protection of brain and spinal cord Cushioning through buoyancy Brain nourishment/waste elimination Provides a stable chemical Ventricles: four hollow chambers within the brain, environment filled with cerebrospinal fluid 59 3) Ventricles and brain areas A B B A C C D D E E 60  3) CSF circulation circulation has 3 major steps. We will break down these steps in the following sli 1. CSF is secreted from the blood by choroid plexuses (capillaries) 2. Circulates through the ventricles, sub- arachnoid space, and central canal of the spinal cord 3. Returns to blood via arachnoid villi 61 3) CSF Lateral ventricles circulation Interventricular foramen Secreted from Third ventricle choroid plexuses (red things in Cerebral aqueduct this picture; one within Fourth ventricle each lateral ventricle) Lateral aperture Central canal Median aperture Subarachnoid space © John Wiley & Son Inc 3) CSF “dysfunction” Hydrocephalus (ventriculomegaly) CSF accumulates and exerts pressure on the brain if not allowed to drain Possible to occur without damage in an infant because the skull has not yet fully fused In adults, this situation results in brain damage 63 4) Brain blood supply 64 4) Brain blood supply 1. Common carotid arteries (L & R) External (face, scalp) Internal (anterior 3/5 of cerebrum) 2. Vertebrobasilar Circle of arteries Posterior 2/5 of cerebrum Willis At the base of the brain, the carotid and vertebrobasilar arteries form a circle of communicating arteries Significance: If there is reduction of blood flow from one artery, flow through other arteries can compensate 65 https://www.youtube.com/watch? How does spinal manipulation result in a stroke? 66 Conclusions The nervous system is organized into central and peripheral systems, with the peripheral nervous system including the sensory and motor divisions, and the motor divisions including autonomic and somatic divisions. Electrical excitability of cells is determined by the concentration of ions on the inside and outside of cells and the permeability of those ions across the membrane 90% of the nervous tissue is represented by the support system cells termed the neuroglia Brain continuity is maintained by a meningeal layer, cerebrospinal fluid and a constant blood supply 67