and its origins G. E. Schneider 2009 Part 1: Introduction MIT 9.14 Class 1 Brain talk, and

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1 A sketch of the central nervous system and its origins G. E. Schneider 2009 Part 1: Introduction MIT 9.14 Class 1 Brain talk, and the ancient activities of brain cells

2 1. Introduction a) b) The plan for this class 1) The goal: Learn an outline of vertebrate, especially mammalian, neuroanatomy. 2) Reaching the goal will be facilitated by studies of origins, using material from studies of development, comparative anatomy and evolution. 3) Since adaptive function is the driver of evolution, we will pay close attention to functions. Initial topics 1) Some terminology 2) Neurons: their evolution and how we study them

3 Talking about the CNS: terminology Directions (illustrated) Rostral vs. caudal; cf. anterior vs. posterior Dorsal vs. ventral; cf. superior vs. inferior Medial vs. lateral Planes of section (illustrated) Sagittal (mid-sagittal, parasagittal) Coronal (frontal; transverse; cross-section) Horizontal Oblique Major parts of the CNS: You will soon know these! About the terms we use: Multiple synonyms or near-synonyms English, Latin or Greek Pronunciation problems

4 From Butler & Hodos, 1996: Directions PLANES OF SECTION Brain Spinal Cord Brain Spinal Cord Dorsal Posterior (Caudal) Dorsal Posterior (Caudal) Anterior (Rostral, Oral) Anterior (Rostral, Oral) Ventral Ventral Figure by MIT OpenCourseWare.

5 Figure by MIT OpenCourseWare.

6 Man and Bird Figure by MIT OpenCourseWare.

7 Talking about the CNS: terminology Directions (illustrated) Rostralvs. caudal; cf. anterior vs. posterior Dorsalvs. ventral; cf. superior vs. inferior Medialvs. lateral Planes of section (illustrated) Sagittal (mid-sagittal, parasagittal) Coronal (frontal; transverse; cross-section) Horizontal Oblique Major parts of the CNS: You will soon know these! About the terms we use: Multiple synonyms or near-synonyms English, Latin or Greek Pronunciation problems

8 Sections TRANSVERSE (Frontal) HORIZONTAL MIDSAGITTAL PARASAGITTAL (Sagittal) OBLIQUE Figure by MIT OpenCourseWare.

9 Standard planes of section, brain of small rodent Side view Frontal sections Horizontal section Front view Fig 1-2b Parasagittal sections

10 Talking about the CNS: terminology Directions (illustrated) Rostral vs. caudal; cf. anterior vs. posterior Dorsal vs. ventral; cf. superior vs. inferior Medial vs. lateral Planes of section (illustrated) Sagittal (mid-sagittal, parasagittal) Coronal (frontal; transverse; cross-section) Horizontal Oblique Major parts of the CNS: These will be discussed repeatedly, from various points of view. Soon you will remember them! [Illustration] The terms we use: Multiple synonyms or near-synonyms English vs. Latin or Greek Pronunciation problems

11 Preview: Fig 1-3 a. Spinal cord a. Spinal a. cord Spinal cord b. Hindbrain b. Hindbrain (rhombencephalon) b. Hindbrain (rhombencephalon (rhombencephalon c. Midbrain c. Midbrain (mesencephalon) c. Midbrain (mesencephalon) (mesencephalon) d. Tweenbrain d. Tweenbrain (diencephalon) d. Tweenbrain (diencephalon) (diencephalon) e. Endbrain e. Endbrain (telencephalon) e. Endbrain (telencephalon) (telencephalon) The thickening embryonic neural tube Forebrain (prosencephalon)

12 What is the nature of the CNS? One of the difficulties in understanding the brain is that it is like nothing so much as a lump of porridge. -- R.L. Gregory, 1966 [an experimental psychologist] CNS as a tissue: What kind of tissue? What kind of cells? How can we see them? Levels of observation; techniques. CNS as a system: Communication system: information flow/handling Secretory organ What is its functional architecture? [In class 3 we will illustrate this in a basic way, considerably simplified; later we will see more details.] Basic elements of CNS [This week we nerve cells and their properties.] will have a look at First: a look at the gross anatomy of the nervous system some

13 The gross anatomy: A young human from N. Gluhbegovic and T.H. Williams, 1980 (Harper & Row) Positions of vertebrane Note: dura mater; Spinal nerves vs CNS Fig 1-4 Figure by MIT OpenCourseWare.

14 Hamster Brain (similar to rat) Figures removed due to copyright restrictions. Fig.1-5

15 Primitive cellular mechanisms present in one-celled organisms and retained in the evolution of neurons Irritability and conduction Specializations of membrane for irritability Movement Secretion Parallel channels of information flow; integrative activity Endogenous activity

16 Why do organisms need neurons? Protozoa do these things! Limitations of being a single cell are many, especially limits due to small size. Hence, the evolution of multicellular organisms had to occur eventually.

17 Specializations for irritability, seen in modern survivors of primitive species Protozoa: responses to stimulation Sponges and other metazoans: specialized cells responsive to contact or chemicals Coelenterates (Parker s studies): primary sensory neurons plus neurons responsive to other neurons Worms with forward locomotion, with evolution of head receptors and their consequences (We will return to these topics later.)

18 Irritability and conduction: Examples of two neurons Fig.1-6 What are the three major functionally distinct parts of a neuron?

19 A note from comparative anatomy The position of the cell body of somatosensory neurons: The pseudounipolar shape is recent evolution. (Note the DRG cell in the figure.) Ramon y Cajal s picture: in

20 Primary somatosensory neurons in an animal series Sensory cell of the earthworm Sensory cell of a mollusc Sensory cell of a lower fish Fig.1-7 Sensory cell of amphibian, reptile, bird, or mammal Figure by MIT OpenCourseWare.

21 Santiago Ramon y Cajal, drawing at his microscope Fig.1-8 Courtesy of

22 Names for major parts and activities of neurons Cell body (soma) and its branches (dendrites) Membrane potential The cell s irritability: depolarization when stimulated. This is called excitation. Graded conduction of membrane potential change away from the point of stimulation Axon and its end arborization (telodendria) with synaptic contacts on other neurons or muscle or gland cells The axonal membrane is specialized for conduction of action potentials. Action potentials are conducted in a non-decremental fashion. What membrane component had to evolve to accomplish this? Action potentials are found even in jellyfish axons.

23 A cartoon: Distribution of major ions inside & outside the resting neuronal membrane; recording of electrical potentials Fig.1-9 Sodium-potassium pump

24 Irritability and conduction: Examples of two neurons Fig.1-10a

25 Membrane potentials in neurons; in axons Fig.1-10b

26 Specializations of the membrane for irritability At post synaptic sites: receptors for specific released by other neurons molecules In neurons or associated cells found in, or extending into, skin and other peripheral organs, for detection of specific kinds of energy (chemicals in air or in mouth, light, pressure, stretch, hot or cold, electrical potential changes, sounds) Some of these specializations occur with the evolution of modified cilia, e.g., the olfactory and the visual receptor specializations.

27 Primitive cellular mechanisms present in one-celled organisms and retained in the evolution of neurons Irritability and conduction Specializations of membrane for irritability Movement Secretion Parallel channels of information flow; integrative activity Endogenous activity

28 Movement Contractile proteins: actin and myosin Actin is abundant in growing neurons But neurons are not specialized for moving themselves except early in development. Muscle cells retain property. and specialize in that

29 Primitive cellular mechanisms present in one-celled organisms and retained in the evolution of neurons Irritability and conduction Specializations of membrane for irritability Movement Secretion Parallel channels of information flow; integrative activity Endogenous activity

30 Secretion as an output mechanism: For attacking prey In protozoa In sponges For cell-cell communication in sponges It evolved, or was retained, in neurons.

31 Otto Loewi s discovery: chemical transmission at the synapse The controversy in the early years of the 20 th century: Are synapses electrical or chemical? Loewi s dream: He saw how chemical transmission at the synapse could be demonstrated Innervation of the frog heart: accelerator nerve and decelerator nerve Two frog hearts in saline, in separate petri dishes Evidence for Acceleransstoff and Vagusstoff Electrical synapses are also found, less commonly, in the form of gap junctions. These are found already in sponges

32 Chemical Synapse Figure by MIT OpenCourseWare. Fig. 1-11

33 Recording EPSPs and IPSPs Figure by MIT OpenCourseWare.

34 Synapses: varied structural arrangements: Consider the functional possibilities Axo-somatic Axo-dendritic (to dendritic shaft or dendritic spine) Axo-axonal Presynaptic inhibition and facilitation. (Also: dendro-dendritic, dendro-axonal ) Reciprocal synapses Serial synapses Gating mechanisms Synapses without a postsynaptic site

35 Synapses: varied structural arrangements: Consider the functional possibilities Axo-somatic Axo-dendritic (to dendritic shaft or dendritic spine) Fig 1-13a

36 Synapses: varied structural arrangements: Axo-axonal Presynaptic facilitation (Also: Consider the inhibition and dendro-dendritic, dendro-axonal ) Reciprocal synapses functional possibilities Fig 1-13b

37 Synapses: varied structural arrangements: Consider the functional possibilities Serial synapses Gating mechanisms Synapses without a postsynaptic site (not illustrated) Fig 1-13c

38 Secretion: terms Neurotransmitters Neural hormones Cf. endocrine glands Multiple types of synapses Exocytosis Endocytosis Intracellular transport

39 exocytosis endocytosis Common cellular dynamics with neuronal specializations intracellular transport of organelles and molecules Retrograde Anterograde (involving dynein) (involving kinesin) NEXT CLASS: How such cellular dynamics are used in experimental studies of the CNS

40 Primitive cellular mechanisms present in one-celled organisms and retained in the evolution of neurons Irritability and conduction Specializations of membrane for irritability Movement Secretion Parallel channels of information flow; integrative activity Endogenous activity

41 The need for integrative action in multi cellular organisms How does one end of the animal influence other end? How does one side coordinate with the the other side? With multiple inputs and multiple outputs, how can conflicts be avoided? Hence, the evolution of interconnections among multiple subsystems of the nervous system.

42 How can such connections be studied? The methods of neuroanatomy (neuromorphology) The important roles of neurophysiology, neurochemistry, behavioral studies Neuroanatomical methods will be reviewed in the next class. Thereafter, the last primitive cellular mechanism, endogenous activity, will be explained further.

43 MIT OpenCourseWare Brain Structure and Its Origins Spring 2009 For information about citing these materials or our Terms of Use, visit:

A sketch of the central nervous system and its origins. G. E. Schneider 2014 Part 1: Introduction. MIT 9.14 Class 1

A sketch of the central nervous system and its origins G. E. Schneider 2014 Part 1: Introduction MIT 9.14 Class 1 Brain talk, and the ancient activities of brain cells 1 a) The plan for this class 1. Introduction