1. Nervous System and Neurons (Chap 10&11)

Transcription

1 Lecture 05, 05 Sept 2006 Vertebrate Physiology ECOL 437 (MCB/VetSci 437) Univ. of Arizona, Fall 2006 Kevin Bonine & Kevin Oh 1. Nervous System and Neurons (Chap 10&11) (endocrine system later) 52 Randall et al Wanted to give you a heads up for our next Doings on Sept 15th led by Doug Stuart (UofA, Regents' Professor Emeritus of Physiology ). Doug will be giving us an update of the Physiology seminar he gave at the end of last spring. Title: Historical reflections on the term "motor homunculus". Doings meets in 601 GouldSimpson, 4:005:

2 Housekeeping, 05 September 2006 Upcoming Readings today: Textbook, chapter 10 & 11 Wed 06 Sept: Tipsmark et al. 2002, bring problem set to do Thurs 07 Sept: Textbook, chapter 10 &11 Tues 12 Sept: Textbook chapter 11 & 12 Lab oral presentations 06 Sept 9am Nilam Patel 2pm Nick Brown 3 Wed 06 Sept: Tipsmark et al Kevin Oh will help with short glossary Integrative Good example of using multiple tools to address interesting physiological question Filter the useful information from the unnecessary details What other questions does this paper raise? 4 2

3 Nervous System Comprises Neurons/ Nerve Cells Glial Cells (support) Signalling via combination of Electrical and Chemical Integrate information AFFERENT Coordinate Response EFFERENT 5 52 Randall et al Organization of the Nervous System Three main functions: 1. Sensory Reception (converts environmental stimulus to elect/chem) 2. Central Processing 3. Motor Output Divided into CNS and PNS A. CNS = Central Nervous System Brain and Spinal Cord (and eyes and interneurons) B. PNS = Peripheral Nervous System most sensory and motor axons 6 3

4 Hill et al. 2004, Fig Flow of Information Afferent Signal > CNS > Efferent Signal > Response Very Simple e.g., Sensing Effectors Simple Monosynaptic Interneurons Polysynaptic 82 Randall et al

5 Sensing Effectors Sensors with Afferent and Efferent Properties/Homeostasis e.g., osmolarity and antidiuretic hormone (ADH) 82 Randall et al P.279 Randall et al Evolution of Nervous System: Based on the neuron Elaboration of Reflex Arc Group neurons into CNS More neurons in complex organisms New structures added on to old (not replaced) Size of CNS region correlated with importance Topological Maps 10 5

6 CNS Spinal Cord Retains evidence of segmented ancestors 87 Randall et al CNS Spinal Cord Anatomy Dorsal Root Ganglion (PNS) afferent sensory somata White matter = myelin Gray matter = somata and dendrites Cerebrospinal Fluid in spinal canal Dorsal root, horn = ~afferent Ventral root, horn = ~efferent Spinal Reflexes: locomotion / walking chicken w/o head 88 Randall et al

7 CNS Brain Vertebrate bilaterally paired nerve connections to periphery 89 Randall et al cerebrum tectum cerebellum optic olfactory pituitary Sensory Both Motor 13 Hill et al. 2004, Fig

8 CNS Brain Anatomy Medulla oblongata Respiration, autonomic funct, some sensory (hearing, equil.) Cerebellum Coordinate motor output Integrates info. from proprioceptors (stretch and joint) visual, auditory More convoluted ( s.a.) in higher groups Birds with large cerebellum to handle 3D flight Pons (and tectum) Integrate and communicate Visual, tactile, auditory maps ~ body movement coordination in some groups Cerebral Cortex In higher groups takes over function of tectum 15 CNS Brain Anatomy (con t) Thalamus Sensory and motor coordination Often communicates with cerebral cortex Amygdala Processes info. and output related to emotions Hypothalamus Also involved in emotions Body temp, eating, drinking, sex Water and electrolyte balance Olfactory Bulb Key sense in many vertebrate groups Anterior position Cerebrum (covered by cerebral cortex) More evolved in higher groups (size and folds)... Olfaction straight to cerebrum w/o going through thalamus (in mammals) 16 8

9 CNS Brain Note change in size in difft. groups 810 Randall et al CNS Brain Note change in size in difft. groups 810 Randall et al

10 CNS Brain Cerebrum and Cerebral Cortex Folds increase surface area and # neurons Functional Regions 1. Sensory cortex somatosensory, auditory, visual sensory homunculus ( little man ) 2. Motor cortex often similar to sensory cortex map 3. Association cortex memory, future, thought, communication Size of receptive fields? Relative importance of each region changes among vertebrate groups 19 Hill et al. 2004, Fig

11 Plasticity!? More neurons to make precise movements Cortical Maps (Hill et al. Fig 10.11) 1/2 face and hands Teeth, whiskers claws 815 Randall et 21 al Structural and Functional Regions CNS Most neuronal somata incl. motor neurons Interneurons Nuclei = collections of somata w/ similar function Tracts = bundles of axons from nuclei PNS Nervous system outside CNS Nerve usually with both Afferent and Efferent axons Nerves = axon bundles from sensory motor neurons Ganglia = somata of some autonomic neurons and most sensory neurons 22 11

12 Structural and Functional Regions 86 Randall et al Efferent NS 1. Somatic/Voluntary skeletal muscle 2. Autonomic smooth muscle cardiac muscle glands housekeeping A. Sympathetic ~ fight or flight B. Parasympathetic ~ rest and digest C. Enteric Sympathetic Parasympathetic 818 Randall et al

13 Autonomic NS (vs Voluntary/Somatic) Antagonistic Groups in Balance: A. Sympathetic (f or f) B. Parasympathetic (r d) Both function via reflex arcs, but often opposite effects Efferent signal with two neurons: 1. Preganglionic (NT released is Acetylcholine [Ach]) 2. Postganglionic (PNS, receptor is nicotinic ACh) Difference between Symp. and Para. is in: 1. CNS origin 2. Location of postganglionic somata 3. Postganglionic NT 4. Receptors on target tissues Muscle reflexes in spinal cord, autonomic to brain 25 Autonomic NS Sympathetic 2Postganglionic somata nearer CNS in chain ganglia 3 Postganglionic NT is Norepinephrine 4Effector receptor is alpha or beta adrenergic Parasympathetic 2Postganglionic somata near effector, or in effector organ 3 Postganglionic NT is ACh 4Effector receptor is muscarinic ACh Difference between Symp. and Para. is in: 1. CNS origin 2. Location of postganglionic somata 3. Postganglionic NT 4. Receptors on target tissues 26 13

14 Hill et al. 2004, Fig Know a couple of examples: Norepinephrine Acetylcholine Hill et al. 2004, 28 Fig

15 Know a couple of examples: Norepinephrine Acetylcholine (chain ganglia) Hill et al. 2004, 29 Fig Hill et al

16 Squid axons are important to physiologists, and to the squid. Hill et al. 2004, p.281 Sir Alan Hodgkin, Nobel Prize Neurons: Hill et al. 2004, Fig

17 4 types of Glial Cells Outnumber neurons 10:1 in mammalian brain 3. Metabolic support 4. Phagocytes/immune 2. CNS 1. PNS Hill et al. 2004, Fig Osmotic Properties of Cells and Relative Ion Concentrations K Ca Ca Na K Na Cl Cl 412 Randall et al

18 Movement Across Membranes Electrochemical Gradient Electrical gradient Concentration gradient K K Electrochemical equilibrium Equilibrium potential (E x in mv) when [X] gradient = electrical gradient Na Na 35 Equilibrium potential (E x in mv) Every ion s goal in life is to make the membrane potential equal its own equilibrium potential (E x in mv) 36 18

19 Membrane Potential To change Vm, A Small Number of Ions Actually Move Relative to the Number Present both Inside and Outside the cell Gradient established by pumps (ATP) The concentration gradients are not abolished When the channels for an ion species open Gradients allow for work to be done, e.g., action potential sends signal along axon 37 Membrane Potential Driven by ions that are permeable to the membrane (and have different [ ] in as compared to [ ] out a.k.a. gradient created with ATP) K for example Equilibrium Potential (E x in mv): ~The equilibrium potentials of all the permeable ions (a function of their established gradients) will determine the membrane potential of a cell emf determines which direction a given ion (X) will move when the membrane potential is known emf x = V m E x 38 19

20 Membrane Potential Resting Membrane Potential driven by K efflux and, to a lesser extent, Na influx Na/K ATPase pump generates gradients that, for these permeable ions, determine membrane potential 39 Osmotic Properties of Cells and Relative Ion Concentrations K Ca Ca Na K Na Cl Cl 412 Randall et al Permeabilities K >> Na ; Cl A (includes proteins, phosphate groups, etc.) 40 20

21 At Rest Membrane Potential (V m in volts or mv) outside is zero by convention K, Na V rest about 60 mv 57 Randall et al Nernst equation: E = RT ln zf C out C in where E = equilibrium membrane potential R = gas constant T = absolute temperature z = valence F = Faraday s constant (Mistake in Hill et al. text bottom of page 291; see if you can fix it) 42 21

22 Equilibrium Potential Calculate for a given type of ion using the simplified Nernst Equation: E x = log [X] out z [X] in E Na = log [Na ] out z [Na ] in E Na = log 120 mm 1 10 mm = 63 mv (0.063 V) remember Equilibrium potential (E x in mv) when [X] gradient = electrical gradient 43 Osmotic Properties of Cells and Relative Ion Concentrations K Ca Ca 412 Randall et al Na K Na Cl Cl Donnan Equilibrium? Goldman Equation? 44 22

23 Membrane Potential Nernst for single ion V m = E x if only one ion driving Goldman equation for multiple ions 514 Randall et al Hill et al. 2004, Fig

24 channels membrane bilayer Hill et al. 2004, Fig 11.5c 47 Membrane Potentials and Electricity conductance = reciprocal of resistance vs. capacitance deltav = IR Change in Voltage = current x resistance 510 Randall et al