Neurophysiology Notes - PDF

Neurophysiology V ER 12 : The Nervous System: 161- 169 Autonomic Nervous System: 239-249, Organs with and without dual innervation: 256 V ER 13 : The Nervous System: 163- 171 Autonomic Nervous System: 243-252 (end at Responses to adrenergic stimulation), Organs with and without dual innervation: 258...

Neurophysiology V ER 12 : The Nervous System: 161- 169 Autonomic Nervous System: 239-249, Organs with and without dual innervation: 256 V ER 13 : The Nervous System: 163- 171 Autonomic Nervous System: 243-252 (end at Responses to adrenergic stimulation), Organs with and without dual innervation: 258-260 V ER 14 : The Nervous System: 163- 171 Autonomic Nervous System: 244-252 (end at Responses to adrenergic stimulation), Organs with and without dual innervation: 258-260  Neurophysiology V ER 15 : The Nervous System: 163- 171 Autonomic Nervous System: 244-252 (end at Responses to adrenergic stimulation), Organs with and without dual innervation: 258-260 V ER 16 : The Nervous System: 160- 170 Autonomic Nervous System: 242-251 (end at Responses to adrenergic stimulation), Organs with and without dual innervation: 258-260 For any version, extra details beyond what we talk about in class are not needed for Tables 9.2-9.3, Figures 9.2-9.4, 9.6 (though what is in class or on the slides provided is fair game!).  L e a r n in g O u t co m e s 1. What is neurophysiology 2. Functional classification of neurons 3. Structural classifications of brain cells 4. Blood brain barrier 5. Organization of the nervous system 6. Critical Thinking  Introduction to Neurophysiology Nervous system structure = Anatomy Nervous system function = Physiology In this course, to understand physiology, we’ll need to know a little neuroanatomy and microanatomy.  Introduction to Neurophysiology Nervous system structure = Anatomy Two main divisions: Brain and spinal cord: Central Nervous System (CNS) Peripheral nerves and ganglia: Peripheral Nervous System (PNS)  Introduction to Neurophysiology Nervous system function = Physiology Minimal functional “unit” of nervous system = Neuron (This is considered the “Neuron Doctrine” - Ramon y Cajal, 1800s) fundamental concept: nervous system is made up of discrete individual cells  Introduction to Neurophysiology Why is physiology so intimately associated with anatomy in the nervous system? Neurons really only do 2 (3) things: 1. Conduct “Electrical” Signals (Action Potentials) 2. Release “Chemical” Signals (Neurotransmitters) Therefore - much of what the nervous system “does” (ie. neurophysiology) depends on where these processes occur (ie. neuroanatomy).  Introduction to Neurophysiology Two functions of the nervous system: 1) Control of movement and some functions = Motor Nerves 2) Detection of external stimuli = Sensory Nerves Motor Sensory  Introduction to Neurophysiology Third function of the nervous system: 3. Integration of neuronal activity and connections (“Circuitry”): Association Neurons These are the neurons within the CNS responsible for behaviour, thought, emotions etc.  Introduction to Neurophysiology Why study neurophysiology? To understand inherited and acquired diseases To understand drug modulation Because it is interesting  Neurons and Synapses Neuron: basic functional unit of the nervous system - Cell body, dendrites, axons Dendrites: receive information from sensory receptors (or from other cells) and send it to the cell body Axons deliver electric signals from the cell body to another neuron or an effector organ (e.g. a muscle) Neurons and Synapses A neuron performs the function of moving “information” rapidly by conducting electrical impulses called Action Potentials from one physical location to another, then converting the electrical impulse to a chemical signal at a Synapse.  Functional Classification of Neurons Functional classification is based on the direction in which they conduct impulses. “SENSORY”, or “AFFERENT” neurons conduct impulses from sensory receptors INTO the CNS…  Functional Classification of Neurons “ASSOCIATION”, or “INTERNEURONS” are located entirely within the CNS and help integrate CNS functions  Functional Classification of Neurons “MOTOR”, or “EFFERENT” neurons conduct impulses from sensory receptors OUT OF the CNS (to effector organs like muscles or glands…  Functional Classification of Neurons Somatic Motor Neurons: reflex & voluntary control of skeletal muscles  Functional Classification of Neurons Autonomic Motor Neurons: INvoluntary control of smooth muscle, cardiac muscle, and glands  Functional Classification of Neurons Autonomic Neurons: Further subdivided as sympathetic & parasympathetic Functional Classification of Neurons  Functional Classification of Neurons: Simple Neural Circuit  Functional Classification of Neurons: Simple Neural Circuit 1) Sensory, Afferent (carry signals to CNS). 2) Motor or Efferent (carry signals from CNS). 3) Interneurons - send signals from one neuron to another Pearson Education Inc  STRUCTURAL Classification of Neurons 4 types of Neurons: - Pseudopolar (unipolar), sensory, 1 process that splits. - Bipolar, retinal and cochlear, 2 processes. - Multipolar, most common, motor & association, many dendrites but one axon. - Anaxonic, some CNS neurons, no obvious axon There are at least as many supporting cells as there are nerve cells in the human brain (1011-1012)….  STRUCTURAL Classification of Neurons Supporting Cells: PNS - Schwann Cells – form myelin sheaths around PNS neuron axons - Satellite cells – support neuron cell bodies within ganglia of the PNS  STRUCTURAL Classification of Neurons Supporting Cells: CNS - Oligodendrocytes – form myelin sheaths around CNS neuron axons (like Schwann cells in PNS) - Microglia – migrate through CNS & phagocytose debris - Astrocytes – help regulate external environment of neurons in CNS - Ependymal cells – line the ventricles (cavities) of the brain and spinal cord.  STRUCTURAL Classification of Neurons Supporting Cells: CNS  STRUCTURAL Classification of Neurons Supporting Cells: PNS CN S Successive wrapping of One oligodendrocyte forms Schwann cell membrane around myelin sheaths around several one axon, cytoplasm on outside. axons.  Neurons or Nerve cells h ttp s :/ / w w w.y o u tu b e.c o m / w a tc h ? v = c U G u W h 2 U e M k  STRUCTURAL Classification of Neurons Supporting Cells: CNS - Oligodendrocytes – form myelin sheaths around CNS neuron axons (like Schwann cells in PNS) - Microglia – migrate through CNS & phagocytose debris - Astrocytes – help regulate external environment of neurons in CNS - Ependymal cells – line the ventricles (cavities) of the brain and spinal cord.  STRUCTURAL Classification of Neurons Supporting Cells: CNS  STRUCTURAL Classification of Neurons Supporting Cells: PNS CN S Successive wrapping of One oligodendrocyte forms Schwann cell membrane around myelin sheaths around several one axon, cytoplasm on outside. axons.  STRUCTURAL Classification of Neurons Supporting Cells: CNS Astrocytes – most abundant glial cell in the CNS, constituting up to 90% of the nervous tissue in some areas of the brain. Processes terminate in “end feet” at capillaries, others on neurons (axon, cell body, or dendrite) thus they can influence interactions between neurons and blood.  STRUCTURAL Classification of Neurons Supporting Cells: CNS 1. Take up K+ from ECF (diffuses from neurons during nerve impulses), may help maintain proper ionic environment for neurons.  STRUCTURAL Classification of Neurons Supporting Cells: CNS 2. Can take up neurotransmitter glutamate and transform it to glutamine, which can be released back into neurons, which can use it to reform the neurotransmitter glutamate.  STRUCTURAL Classification of Neurons Supporting Cells: CNS 3. The “end-feet” surrounding blood capillaries take up glucose from blood, metabolize it to lactate, then release it for use as an energy source by neurons, which metabolize it aerobically into CO2 & H2O for production of ATP.  STRUCTURAL Classification of Neurons Supporting Cells: CNS 4. Astrocytes are needed for the formation of synapses in the CNS.  STRUCTURAL Classification of Neurons Supporting Cells: CNS 5. Astrocytes regulate neurogenesis in the adult brain (needed for stem cells to differentiate into both glial cells and neurons). 6. Help with the formation of the blood-brain barrier. 7. Release neurotransmitters (glutamate, ATP, adenosine, D-serine, others) that can stimulate or inhibit activity of neurons.  Blood Brain Barrier If you inject a green dye into the bloodstream, all the tissues in the body will turn green except for the brain. Capillaries in the brain, UNLIKE those of most other organs, do not have pores between adjacent endothelial cells (the cells that make up the walls of the capillaries). Instead, the endothelial cells of the capillaries are joined by tight junctions.  Blood Brain Barrier Nonpolar O2 and CO2 can move through, and organic molecules including alcohol and barbiturates can pass through the phospholipid components of the plasma membrane. Other molecules have to go through specific processes (e.g. active transport, endocytosis).  Blood Brain Barrier Astrocytes influence the structure and function of the blood brain barrier.  Blood Brain Barrier Nicotine binds acetylcholine receptors. Other components in tobacco smoke decrease MAO activity So why do people still smoke?  Blood Brain Barrier CNS depressant, directly affects brain cells. Affects areas involved in inhibiting behaviours (animated, talkative, social). Also altered speech, slowed reaction time, foggy memory. Reactions depend to some part on dose, size, weight, gender, genetics, etc.  Blood Brain Barrier Inhibition of NO through a variety of neurotransmitter receptors including N-methyl-D- aspartate and substance P.  Blood Brain Barrier Rabies – deadly viral infection – bit by an infected animal.  Blood Brain Barrier Virus infects the brain. Immune cells and antibodies can’t enter the brain. There is no treatment after symptoms appear, but before, rapid treatment with anti-rabies antibodies can help attenuate the infection. Blood Brain Barrier Drug treatments and BBB – especially neurological disorders. Brain Cancer Parkinson's Alzheimer's Dementia Review Blood Brain Barrier Astrocytes influence the structure and function of the blood brain barrier. M e d s ca p e M e d ica l N e w s > N e u r o lo g y B lo o d - B r a in B a r r ie r S a fe ly B r e a ch e d N ove m b e r 8 , 2 0 15 Doctors at Sunnybrook Health Sciences Centre in Toronto, Ontario, Canada, have noninvasively penetrated the blood-brain barrier to deliver a chemotherapeutic agent directly into ONE patient’s malignant brain tumor. This is the first time that the blood-brain barrier has been safely breached in a human, the researchers say. The Toronto doctors hope that the technique they used, focused ultrasound, will continue to be successful in safely penetrating what has been a persistent obstacle to treating not only brain tumors but also other diseases, such as Alzheimer's disease and Parkinson's disease. Two main divisions: Central Nervous System (CNS): Brain and spinal cord: Peripheral Nervous System (PNS): Peripheral nerves and ganglia: Organization of the Nervous System NERVOUS SYSTEM Peripheral NS CNS Spinal Afferent Efferent Brain cord Somatic Autonomic SNS PSNS  Somatic Nervous System Somatic = have cell bodies in the CNS & send axons to skeletal muscles (usually those under voluntary control). e.g. conduct impulses along a SINGLE axon from the spinal cord to the neuromuscular junction.  Autonomic Nervous System Autonomic = involves TWO neurons in the efferent pathway. 1st - cell body in the CNS gray matter (brain or spinal cord). This axon does not directly innervate the effector organ, but instead synapses with a 2nd neuron in this pathway, called a postganglionic neuron, that has an axon that extends from the autonomic ganglion to an effector organ, where it synapses with the target tissue. Text Table 9.1  Divisions in the Autonomic Nervous System Autonomic Nervous system helps regulate the activities of glands, smooth muscles, and cardiac muscle. Integral aspect of the physiology of most body systems. ANS further subdivides into: 1. Parasympathetic Division 2. Sympathetic Division  Divisions in the Autonomic Nervous Parasympathetic Nervous System (PSNS) System “Rest & digest”  Divisions in the Autonomic Nervous Sympathetic Nervous System (SNS) System “Fight or flight” - Reuters  Divisions in the Autonomic Nervous System Most organs receive input from both systems In general, PSNS and SNS mediate opposing responses in effector organ - MJ Mycek Sympathetic= RED Parasympathetic= BLUE Text Fig. 9.5  Divisions in the Autonomic Nervous System Organs without dual innervation: - Adrenal medulla - Arrector pili muscles in the skin (muscle associated with hair that makes your hair “stand on end”) - Sweat glands in the skin - Most blood vessels In these cases, regulation is achieved by increases or decreases in the tone (firing rate) of the sympathetic fibers. Pr o o f o f e v o lu tio n th a t yo u c a n fin d o n yo u r o w n b o d y  Neurotransmitters in the Autonomic Nervous System Autonomic nerves classified based on primary neurotransmitter released across the synapses Acetylcholine (ACh) Norepinephrine (NE) Cholinergic neurons = release ACh Adrenergic neurons = release NE (or E) ACh and NE bind different receptors to mediate target organ response  AUTONOMIC OUTFLOW TRACTS Parasympathetic Outflow CNS Ganglion Preganglionic Axon Postganglionic Axon Effector ACh ACh Cell (Cholinergic) (Cholinergic) Neuroeffector Junction Sympathetic Outflow CNS Ganglion Preganglionic Axon Postganglionic Axon ACh NE Effector Cell (Cholinergic) (Adrenergic) Neuroeffector Junction Notes to previous slide: 1. ACh is the neurotransmitter for all PREganglionic fibers (both sympathetic & parasympathetic). Since they use Ach, transmission is said to be cholinergic. 2. ACh is also the transmitter released by most parasympathetic postganglionic fibers at their synapses with effector cells. Transmission at these synapses is thus said to be cholinergic. 3. The neurotransmiter relased by most sympathetic nerve fibers is NE. Transmission at these synapses is said to be adrenergic.  ANS Dysfunction ANS controls a number of functions in the body, such as HR, BP, digestive tract peristalsis, sweating, etc. Dysfunction of the ANS can involve any of these functions. “Lyme Disease” Dysautonomia may also be caused by brain injury, diabetes, genetics, etc….  ANS Dysfunction Deer ticks carrying Borrelia burgdorferi ANS Dysfunction  ANS Dysfunction Bit by infected tick, substances in tick saliva disrupt the local immune response. Spirochetes multiply in the skin. Immune response causes the characteristic circular lesion, but neutrophils which are necessary to eliminate the infection fail to appear. Bacteria spread via the bloodstream to joints, heart, nervous system, and distant skin sites. HR , B P  SUMMARY: Organization of the Nervous System NERVOUS SYSTEM Peripheral NS CNS Spinal Afferent Efferent Brain cord Somatic Autonomic SNS PSNS A co m m o n fo r m o f s yn e s th e s ia ( g r a p h e m e , o r co lo r s yn e s th e s ia , o r co lo r - g r a p h e m ic s yn e s th e s ia ) le tte r s o r n u m b e r s a r e p e r ce iv e d a s in h e r e n tly co lo r e d “Some musicians have chromothesia - a form of synesthesia where they hear music as colors. Mozart … - D Major had a warm "orangey" sound - B flat minor was blackish. - A major was a rainbow of colors. Synaesthesia: When coloured sounds taste sweet N a tu r e 4 3 4 , 3 8 ( 2 0 0 5 ). B e e li, E s s le n , J ä n cke “H e r e w e d e s c r ib e th e c a s e o f a m u s ic ia n w h o e x p e r ie n c e s different tastes in response to hearing different musical tone in te r v a ls ….” T a b le 1 T a s te s tr ig g e r e d b y to n e in te r v a ls T o n e in te r v a l T a s te e x p e r ie n ce d M in o r s e co n d S o ur M a j o r s e c o n d B itte r M in o r th ir d S a lty M a j o r th ir d S w e e t F o u r th ( M o w n g r a s s ) T r ito n e ( D is g u s t) F ifth Pu r e w a te r M in o r s ix th C r e a m M a j o r s ix th L o w - f a t c r e a m M in o r s e v e n th B itte r M a j o r s e v e n th S o u r O cta v e N o ta s te T a s te s e x p e r ie n ce d b y s yn a e s th e te E.S. in r e s p o n s e to d iffe r e n t m u s ica l S yn a e s th e s ia : T h e a v e r a g e p e r s o n ca n h o ld a b o u t 7 d ig its in w o r kin g m e m o r y a t a n y g iv e n tim e. 555-1212 π is a mathematical number - It is the ratio of a circle's circumference to its diameter. - 3.14159 A Japanese mathematician and a U.S. grad student smashed the world record for calculating the value of Pi. After a manic 371 days of computing, Shigeru Kondo and Alexander Yee reached 10 trillion decimal places, doubling the previous record. To give you a sense of how big that is: It would take an average person 158,000 years to recite every last digit. New York-based interdisciplinary designers TWO-N, Inc. wanted to pay homage to the mathematicians’ remarkable discovery, so they decided to visualize a subset of Pi as pixel art. They took Pi’s first 4 million decimals and assigned each digit a different color.”  h ig h - fu n ctio n in g a u tis m , s a v a n t s yn d r o m e , n u m e r ica l s yn e s th e s ia T h e M a n W h o M e m o r iz e d P i ( A p r. 2 0 0 5 ) N E W Y O R K - - W h e n D a n ie l T a m m e t s e t th e E u r o p e a n r e co r d fo r p i m e m o r i z a t i o n l a s t y e a r , m e m o r i z i n g 2 2 ,5 1 4 d i g i t s i n j u s t o v e r 5 h o u r s , h e a ttr ib u te d th e fe a t to h is a b ility to s e e n u m b e r s a s c o m p le x , 3 - d im e n s io n a l la n d s c a p e s , c o m p le te w ith c o lo r , te x tu r e , a n d s o m e tim e s e v e n s o u n d.  L e a r n in g O u t co m e s 1. What is neurophysiology 2. Functional classification of neurons - sensory, afferent, associating, interneurons, motor, efferent 3. Structural classifications of brain cells - Central vs. peripheral types of cells 4. Blood brain barrier 5. Organization of the nervous system 6. Critical Thinking Electrical Activity in Axons E LE CT R I CA L A CT I V I T Y : Ver 12: Pages 53 (fluid mosaic model); Pages 170 - 182 (nervous system) Ver 13: Pages 53 (fluid mosaic model); Pages 172 - 185 (nervous system) Ver 14: Pages 53 (fluid mosaic model); Pages 172 – 185 (nervous system) Ver 15: Pages 53 (fluid mosaic model); Pages 172 – 185 (nervous system) Ver 16: Pages 51-52 (fluid mosaic model); Pages 170 – 182 (nervous system) L e a r n in g O u t co m e s 1. Cell Membranes 2. Electrical Activity in Axons 3. Action Potentials 4. Synapses 5. Critical Thinking T h e Cell M em b r a n e Cell membrane is just 2 molecules thick. 2 phospholipid molecules thick.  T h e Cell M em b r a n e – Ph o s p h o li p i d B i la ye r Outside (EXTRACELLULAR) Inside (INTRACELLULAR)  T h e Cell M em b r a n e – F lu i d M o s a i c M o d el E x tr a c e llu la r G lyco lip id G lyco p r o te in Ph o s p h o lip id H eads & ta ils C h o le s te r o l Pr o te in s I n tr a c e llu la r  T h e Ce ll M e m b r a n e – F lu id M o s a ic M o d e l http://www.youtube.com/watch?v=Qqsf_UJcfBc  T h e Cell M em b r a n e Molecules can not get across the cell membrane very easily- it is a barrier. But some still have to cross. How? A. By SIMPLE DIFFUSION – a process that does not consume energy  T h e Cell M em b r a n e Simple diffusion (passive) Small uncharged molecules (relatively lipid soluble) can diffuse through the lipid bilayer (e.g. steroid hormones) OUT IN  T h e Cell M em b r a n e Simple diffusion (passive) Small charged molecules (ions) can diffuse through water-filled pores OUT IN  T h e Cell M em b r a n e Simple diffusion (passive) Ion Channels – some are “leaky”, ions flow in or out as needed. OUT IN  T h e Cell M em b r a n e Simple diffusion (passive) Ion Channels – others are VOLTAGE GATED – can only be opened or closed by gates. OUT IN ACTIVE transport T h e Cell M em b r a n e S o , th e r e a r e o th e r m e c h a n is m s to m o v e s u b s ta n c e s in a n d o u t o f c e lls , a g a in s t g r a d ie n ts , a c tiv e tr a n s p o r t n e e d s m e ta b o lic e n e r g y ( u s u a lly A T P). - e.g. Na+/K+ ATPase - Moves Na+ ( ) out of cell - Moves K+ ( ) into cell OUT IN Primary active transport (Direct consumption of ATP) ATP ADP  T h e Cell M em b r a n e Endocytosis, exocytosis, phagocytosis…. and so on  T h e Cell M em b r a n e S um m ar y Cell membranes act as barriers to chemical movement Integral membrane proteins can act as transporters Movement of substances across the membrane can be passive (diffusion) or active (consumes energy) Active transport of Na+/K+ is important in establishing the electrochemical gradient. Ion channels are especially important in the nervous system because they help produce electrical impulses that transmit information rapidly.  Electrical Activity in Axons All cells in the body have a potential difference – or voltage – across the membrane. This is called the resting membrane potential. The inside of the cell is negatively charged compared to the outside. + + + + + + + + + In neurons, it is -70mV. - - - - - - - - - - -  Electrical Activity in Axons Voltage gated ion channels are important for electrical activity in axons because when the channels open they can change the membrane potential of the cell. This is what we need to happen to conduct an electrical signal in neurons. + + + + + + + + + - - - - - - - - - - -  Electrical Activity in Axons So the channels are initially closed, they open, this allows the ions (whatever they are – Na+, K+, Ca2+ etc) to move across the membrane. Na+ starts outside, K+ inside At start of action + + + + + + + + + potentials - - - - - - - - - - - A c t i o n Po t en t i a ls Action potentials are signals that go along the nerves, taking the signal from one place to another place. N e r v o u s S ys te m p r e s e r v e d u s in g D r v o n H a g e n s ' co n tr o v e r s ia l " p la s tin a tio n " te c h n iq u e. — a t O 2 A r e a n a L o n d o n.  A c t i o n Po t en t i a ls A primary function of nerve cells is to receive, conduct, and transmit signals. Neurons propagate signals in the form of action potentials.  Action Potentials l Action potentials are momentary discharges (depolarizations) of the resting membrane potential caused by a rapid influx of Na+ caused by the opening of sodium ion channels l Once initiated they move along the axon membrane toward the synapse  Action Potentials l Signals have to go a long way without weakening l So the signals have to be continuously reamplified along the way. l To do this, they use voltage- gated ion channels  Ion Gating in Axons This can happen as the ions Na+ and K+ move across the plasma membrane. They move through gated channels.  I o n Gat ing in A xo ns A B A. Channel closed at resting membrane potential. B. Gated channel C opens in response to depolarization C. Gated channel closes (ball & chain).  Ion Gating in Axons If appropriate stimulation causes positive charges to flow into the cell, so the cell becomes more POSITIVE then the resting potential, this change is called depolarization (or HYPOpolarization).  A c t i o n Po t en t i a ls Na+ channels open Na+ (remember, Na+ starts outside) -------++------------------------------------- +++++--++++++++++++++++++++++++++++++++++ Na+ Na+ channels open ----------------++----------------------------- ++++++++++++++--+++++++++++++++++++++++++++ Na+ Na+ channels open -------------------------++------------------ + + + + + + + + + + + + + + + + + + + + + + ++ - - + + + + + + + + + + + + + + + + +  A c t i o n Po t en t i a ls lThe explosive increase in Na+ permeability results in a rapid reversal of membrane potential in that region, from -70 mV to +30 mV. The axon is depolarizing. lAt that point, the Na+ channels close. There is a rapid decrease in Na+ permeability.  A c t i o n Po t en t i a ls lTo help compensate, the cell needs to repolarize. lTo do this, K+ which is also positively charged will diffuse out of the cell, making the inside of the cell less positive (or more negative) again, restoring the original resting membrane potential.  A c t i o n Po t en t i a ls The Na+ and K+ pumps are constantly working in the plasma membrane. They pump out the Na+ that entered the axon during an action potential and pump in the K+ that had left.  A c t i o n Po t en t i a ls Because opening the gated Na+ and K+ channels is stimulated by depolarization, these ion channels in the axon membrane are said to be voltage-regulated channels, or voltage-gated channels. V o lta g e G a te d Ch a n n e ls https://www.youtube.com/watch?v=mKalkv9c 2iU  H o w A c t i o n P o t e n t i a ls a r e Pr o p a g a t e d h ttp s :/ / w w w.y o u tu b e.c o m / w a tc h ? v = S a 1 w M 7 5 0 R v s A c t i o n Po t en t i a ls M e m b r a n e p o te n tia l d o e s n o t n o r m a lly b e com e m ore p o s itiv e th a n 3 0 m V b e ca u s e th e N a + c h a n n e ls q u ic kly c lo s e a n d th e K + c h a n n e ls o p e n. T h e a m p litu d e ( s iz e ) o f a ctio n s p o te n tia ls is th e r e fo r e A L L o r NONE. If d e p o la r iz a tio n r e a c h e s th e th r e s h o ld , th e m a x im u m p o te n tia l ch a n g e is r e a ch e d. A c t i o n Po t en t i a ls APs are sometimes called “Spike” potentials.  Action Potentials – Non-myelinated vs. S a lt a t o r y c o n d u c t i o n In non-myelinated axons, the action potential passes smoothly along the axon, and all parts of the membrane are depolarized. Na+ -------++------------------------------------- +++++--++++++++++++++++++++++++++++++++++  Action Potentials – Non-myelinated vs. S a lt a t o r y c o n d u c t i o n In myelinated axons, the action potential jumps between the non-insulated nodes [of Ranvier] by saltatory conduction. Allows more rapid movement of the action potentials, and needs less energy to restore the membrane after the action potential has been transmitted. A c t i o n Po t en t i a ls – S a lt a t o r y c o n d u c t i o n R e fr a cto r y p e r io d ( h e r e o r in u n m ye lin a te d n e u r o n ) h e lp s e n s u r e th e A P o n ly g o e s in o n e d ir e c tio n d o w n th e a x o n to it’s e n d  T h e S yn a p s e Axons end close to or contacting another cell. Postsynaptic neuron Presynaptic neuron  T h e S yn a p s e Once action potentials reach the end of the axon, they stimulate the next cell.  T h e S yn a p s e In the CNS, the 2nd cell is also a neuron. In the PNS, it may be a neuron, or an effector cells within a muscle or gland. N e uron : n e uron N e u r o m u s cu la r j u n ctio n  T h e S yn a p s e Directional: PREsynaptic – to – POSTsynaptic.  T h e S yn a p s e Presynaptic nerve ending releases neurotransmitters that stimulate APs in the postsynaptic cell. Presynaptic neuron ends in a terminal bouton (because of it’s swollen appearance) and it is separated from the postsynaptic cell by a tiny cleft ~10nm in size. c o n ta in n e u r o tr a n s m itte r s T h e S yn a p s e  T h e S yn a p s e On the POSTsynaptic side, the neurotransmitter binds to its receptor on the dendrite. This causes ion channels on the postsynaptic dendrite membrane to open. Note, these gates are chemically regulated (i.e. not voltage-regulated as in the axons). And this stimulates the cell to produce AP...  T h e S yn a p s e h ttp :/ / w w w.g e o r g ia p a in p h y s ic ia n s.c o m / l2 _ e d u _ p h a r m a _ m o d 1 _ s e s h tm T h e S yn a p s e E PS P = e x c ita to r y p o s ts yn a p tic p o te n tia l ( d e p o la r iz a tio n in th e p o s t- s yn a p tic n e uron ) C. Nicolay  M yo t o n i a neuromuscular disorders characterized by delayed relaxation of skeletal muscle after voluntary contraction or electrical stimulation. Can be caused by mutations in muscle Cl- channel (human, dog, etc) à channel gates do not open properly à repolarization delayed, several APs fire instead of just one Myotonic "Fainting" Goats http://www.youtube.com/watch?v=j5kKoBOfPJk  M yo t o n i a Goats: when startled or excited it causes a very temporary stiffening of the muscles. When the muscles relax after a few seconds the animal jumps up and continues on it’s way. “As pets, myotonic goats are poor climbers (easily contained) and have a wonderful disposition. They tame easily when fed and handled regularly and can be very loving pets.” Not supposedly painful in goats. “This myotonic syndrome produces a higher meat-to- bone ratio (3:1 instead of 2:1) and a thicker musculature with a more tender nature that has earned myotonic goats a place on the Slow Food Ark of Taste.” The US Ark of Taste is a catalog of over 1319 delicious foods in danger of extinction S um m a r y: L e a r n in g O u t co m e s 1. Cell Membranes 2. Electrical Activity in Axons 3. Action Potentials 4. Synapses 5. Critical Thinking E v e r yth in g w e p e r c e iv e is in th e p a s t The present that your brain comprehends is around 500 milliseconds behind what is actually “happening,” as your brain scrambles frantically to keep up and maintain coherence. CE N T R A L N E R V O U S S Y S T E M : Ver12: Spinal Nerves p. 232, images p. 234, 235; Brain 204- 208 (exclude Figure 8.7); Cerebral lateralization: 212-214 (up to language); Brain Function, 221-224; Midbrain: 191, 225-226; Hindbrain, Medulla : 226-227 Ver13: Spinal Nerves p. 236, images p. 238, 239; Brain 207- 212 (exclude Figure 8.7, 8.8); Cerebral lateralization: 217-218 (up to language); Brain Function, 224-228; Midbrain: 193, 229-230; Hindbrain, Medulla : 230-231 Ver14: Spinal Nerves p. 236, images p. 236, 238; Brain 207- 212 (exclude Figure 8.7, 8.8); Cerebral lateralization: 216-217 (up to language); Brain Function, 224-228 (Start at Emotion and Memory, end at Midbrain); Midbrain: 193, 229-230; Hindbrain, Medulla : 230-231 CE N T R A L N E R V O U S S Y S T E M : Ver15: Spinal Nerves p. 236, images p. 236, 238; Brain 207- 212 (exclude Figure 8.7, 8.8); Cerebral lateralization: 216-217 (up to language); Brain Function, 224-228 (Start at Emotion and Memory, end at Midbrain); Midbrain: 193, 228-230; Hindbrain, Medulla : 230-231 Ver16: Spinal Nerves p. 234-236; Brain 205- 214 (exclude Figure 8.2, 8.4, 8.7, 8.8); Cerebral lateralization: 214-216 (up to language); Brain Function, 223-227 (Start at Emotion and Memory, end at Midbrain); Midbrain: 191, 227-228; Hindbrain, Medulla : 228-229 L e a r n in g O u t co m e s 1. Protection of the CNS 2. Reflexes 3. Brain Development 4. Major Brain Regions – cerebrum, cerebral cortex, thalamus, epithalamus, hypothalamus, midbrain, hindbrain (cerebellum, medulla). 5. Critical Thinking  The Central Nervous System The CNS is composed of gray matter and white matter. The gray matter, containing neuron cell bodies and dendrites, is found in the cortex (surface layer) of the brain and deeper within the brain in aggregations known as nuclei. White matter consists of axon tracts (myelin sheaths produce white color) that underlie the cortex, and that surround the nuclei. The Central Nervous System Gray matter White matter  Protection of the CNS: Meninges of the Scalp brain Skull Dura mater (“tough mother”) [two layers] Arachnoid mater (think…webby/spidery) Pia mater (innermost membrane, clings to surface of Brain brain/spinal cord, follows every fold. The brain is encased in the skull; it is also protected by several tough layers of connective tissue (the meninges), the dura mater, the arachnoid mater, and the pia mater …. “P”… “A”…. “D”…. “S”….  Protection of the CNS: Meninges of the Spinal Cord Pia mater Arachnoid mater Dura mater The same meningeal layers protect the spinal cord (PADS!!!)  Protection of the CNS: Cerebrospinal fluid Skull Outer Inner fluid fluid cushion cushion Brain In addition to the skull and meninges, the brain is protected by two fluid cushions that give some protection for the brain against head traumas  Protection of the CNS: Cerebrospinal fluid SAS SSS Brain The outer cavity is the superior sagittal sinus (SSS)(sits under dura mater) the inner cavity is the subarachnoid space (SAS) (space between arachnoid and pia mater) The Central Nervous System The cavities (ventricles) of the brain and spinal cord are filled with cerebrospinal fluid (CSF).  Protection of the CNS: Cerebrospinal fluid The fluid that provides the protection also fills the spinal cord - it is called cerebrospinal fluid (CSF) similar in composition to blood plasma  CSF tap - sample of CSF can be examined for signs of disease (bacteria, virus, inflammatory cells, abnormal products of degeneration as in Multiple sclerosis) medscape.com The Spinal Cord There are 31 pairs of spinal nerves. Each nerve is a mixed nerve composed of sensory and motor fibers, packed together. But they separate near the attachment of the nerve to the spinal cord.  The spinal cord and peripheral nervous system (PNS) Spinal cord The spinal cord extends from the brain stem, to the pelvic region, ending before the end of the vertebral column Nerves enter or leave the spinal cord in between the vertebrae Spinal nerves The link between the spinal cord and peripheral nervous system (PNS) The interneurons also communicate with one another along the length of the spinal cord An afferent sensory stimulus can be translated up or down the spinal cord by the interneurons  The link between the spinal cord and peripheral nervous system (PNS): (1) (2 ) Reflexes (3 ) (4 ) For example, the “simple” withdrawal reflex response to a painful stimulus involves the contraction of several muscles, the relaxation of other muscles, and it may also involve responses that are initiated in the brain Critical Thinking  Upper vs. lower motor neuron damage Distinguishing between upper and lower motor neuron damage (UMN vs. LMN damage)  Upper vs. lower motor neuron damage Myotatic (stretch) reflex: e.g. knee-jerk reflex With LMN damage reflex will be: 1) exaggerated 2) normal 3) diminished  Upper vs. lower motor neuron damage Myotatic (stretch) reflex: e.g. knee-jerk reflex With UMN damage reflex will be: 1) exaggerated 2) normal 3) diminished Loss of inhibitory inputs “The study of brain physiology is the process of the brain studying itself.”  The Brain The basic “plan” is established embryonically. By the middle of the 4th week after conception, 3 distinct swellings are evident at the anterior end of the neural tube, which is going to form the brain.  The Brain During the 5th week, these areas become modified to form 5 regions.  The Brain These regions subsequently become greatly modified to form the general regions of the adult brain.  The Brain telencephalon or “cerebrum” diencephalon (thalamus + hypothalamus) The midbrain and hindbrain contain many relay centers for sensory and motor pathways, and are particularly important in the brain’s control of skeletal movements.  The Brain: Cerebrum Cerebrum – consists of left and right hemispheres, connected internally by the corpus callosum. Performs most of what are considered to be the higher functions of the brain. 5 regions.  The Brain: Cerebrum Frontal Lobe: Motor control Occipital Lobe: Vision, & co- ordination of eye movements Parietal Lobe: Perception of somatesthetic sensation – sensation arising from cutaneous, muscle, tendon, and joint receptors. Temporal Lobe: Interpretation and association of auditory and visual information.  The Brain: Cerebrum The Insula is a region buried deep within the lateral sulcus – the division between the frontal and temporal lobes. Implicated in encoding memory, integration of sensory information with visceral responses. Receives olfactory, gustatory, auditory, and somatosensory (mainly pain) information. The Brain: Cerebrum Cerebral Lateralization: Each cerebral hemisphere receives different input, but the two hemispheres communicate with each other via the corpus callosum. Understanding how these hemispheres works comes about to some degree from pathologies relating to damage to the hemispheres or corpus callosum. The Brain: Cerebrum For example. Corpus callosum has been surgically cut in some people with severe epilepsy as a way of alleviating their symptoms. Specially designed experiments then revealed that each hemisphere is good at certain types tasks and poor at others. Leads to the concept of “cerebral dominance” or “cerebral lateralization” or even “handedness”. The Brain: Cerebrum Damage to the right: difficulty with spacial concepts, maps. Damage to the left: severe speech problems, though interestingly may leave the ability to sing unaffected. The Brain: Cerebrum Applicable to ~97% of people. True for all right-handers (who account for 90% of people), and ~70% of left handers. The remaining left handers are divided equally into those who have language- analytic ability in the right hemisphere, and those in whom this ability is present in both hemispheres. Why are there righties and lefties Major Neurotransmitters Neurotransmitters, SSRI’s, Mood disorders Kim Peek - No corpus callosum - “Rain Man” - Remembers every page he reads – over 9000 books Christopher Langan  The Brain: Cerebral cortex Sheet of gray matter tissue that covers the cerebrum (and cerebellum), divided into L, R hemispheres. Especially important in emotion and memory. (Oribitofrontal area of prefrontal cortex shown in yellow). People with damage to the orbitofrontal area of the prefrontal cortex experience severe impulsive behaviour verging on sociopathic. The Brain: Cerebral cortex Phineas Gage (1848) – railway worker involved in an accident and a metal rod 3 ft 7 inches long was driven through his left eye and brain. He recovered, but the damage to his cerebral cortex was said to be associated with striking personality changes. Before – he was responsible, capable, and financially prudent. After – gross profanity, impulsive, friends remarked on how he was no longer “Gage” Moving from the Forebrain Telencephalon to… The Forebrain Diencephalon: Thalamus & Epithalamus Thalamus – relay centre through which all sensory information (except smell) passes on the way to the cerebrum. Promotes alertness Causes arousal from sleep in response to any sufficiently strong sensory stimulus Epithalamus – dorsal segment, contains the pineal gland, which secretes melatonin (“hormone of darkness”, helps regulate circadian rhythms).  The Brain: Thalamus & Epithalamus Thalamus = 4/5ths of the diencephalon. Epithalamus = dorsal segment of diencephalon, also contains the pineal gland which secretes the hormone melatonin to help regulate your circadian rhythms  The Brain: Hypothalamus Hypothalamus – sits above the optic chiasm Hypothalamus = most inferior portion of the diencephalon. Site of master circadian clock - SCN. The Brain: Thalamus & Hypothalamus Hypothalamus – Regulates “DAILY” body processes - hunger, thirst, regulation of body temperature - hormone secretion from the pituitary gland - contributes to the regulation of sleep and wake  The Brain: Midbrain & Hindbrain The midbrain and hindbrain contain many relay centers for sensory and motor pathways, and are particularly important in the brain’s control of skeletal movements.  The Brain: Midbrain Cell bodies of dopaminergic neurons are highly concentrated in the midbrain. The midbrain has 2 systems of dopaminergic (dopamine- releasing) neurons that project to other areas of the brain… The FIRST is the 1) nigrostriatal dopamine system, involved in motor control. - Parkinson’s disease is caused by degeneration of the dopaminergic neurons in the substantia nigra. For example, Michael J Fox…  The Brain: Midbrain The midbrain has 2 systems of dopaminergic (dopamine- releasing) neurons that project to other areas of the brain… The SECOND is the…. 2) mesolimbic dopamine system, involved in emotional reward. - Alcohol, amphetamines, cocaine, marijuana, and morphine promote the activity of these dopaminergic neurons. - May also play a role in addiction (nicotine, other drugs) - Overactivity in this region may contribute to schizophrenia Schizophrenia – late adolescence/early adulthood onset In 40% of men and 23% of women the condition manifested before 19 years of age. … may experience - hallucinations (mostly voices) - delusions (bizarre/persecutory) - disorganized thinking and speech: from loss of train of thought, to sentences only loosely connected in meaning, to incoherence known as word salad in severe cases. - Social withdrawal, poor dress and hygiene - loss of motivation, judgment, emotional difficulty, unresponsiveness. - Impaired social cognition, paranoia, - difficulties in memory, attention, processing The Brain: Hindbrain - Cerebellum  The Brain: Hindbrain - Cerebellum The cerebellum is the 2nd largest structure of the brain. >50 billion neurons, gray and white matter. The cerebellum monitors and refines motor activity initiated elsewhere It receives input from proprioceptors (joint, tendon, muscle receptors) and together with signals from the motor areas of the cerebral cortex, it participates in coordination of movement. The Brain: Hindbrain - Cerebellum  The Brain: Hindbrain – Medulla All ascending & descending fiber tracts providing communication between spinal cord and brain must pass through the medulla. Required for regulation of breathing, CV responses (vital centers). See Fig. 8.22 in text, these are the respiratory centers in the brain stem, and text on Myelencephalon. Critical Thinking  Integrating mental function Attention & Awareness Mental process in which we concentrate on a specific object, issue, or activity and exclude other environmental stimuli. We can’t simultaneously attend to all the information being received through our 5 senses (sight, hearing, taste, smell, and touch) at the same time.  Autism & the Brain Autism Spectrum Disorder: pervasive developmental disorder. Manifests ~ 3 months - 3 years old. Affects speech, motor skill, social interaction. The Courchesne Theory of Overstimulation suggests that autistic children can seem antisocial because they shun external stimulation, since the cerebellum cannot take it. Children get stuck in repetitive behavior because it is "calming" the easily over-stimulated brain. To the extent that they may appear to live in a world of their own.  Autism Spectrum Autism, Asperger Syndrome (AS), Pervasive developmental disorder (PDD) AS: Possibly - hyper focus, mild movement disorder, lack of social cues PDD: some range of the same things  SUMMARY: Organization of the Nervous System NERVOUS SYSTEM Peripheral NS CNS Spinal Afferent Efferent Brain cord Somatic Autonomic SNS PSNS L e a r n in g O u t co m e s 1. Protection of the CNS 2. Reflexes 3. Brain Development 4. Major Brain Regions – cerebrum, cerebral cortex, thalamus, epithalamus, hypothalamus, midbrain, hindbrain (cerebellum, medulla). 5. Critical Thinking