Organization of the nervous system

An introductory lecture on the organization of the nervous system and its components.

1. Organization of the Nervous System Csilla Egri, KIN 306 Spring 2012 Gunther Von Hagen’s Body Worlds: The chess player

2. Outline Introduction to the structure/function of central nervous system (CNS) Protection of CNS Introduction to peripheral nervous system (covered in more detail later) Microanatomy: neurons 2

3. Divisions of the Nervous System http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/8679.jpg Enteric nervous system 3

4. Divisions of the Nervous System http://faculty.washington.edu/chudler/nsdivide.html 4

5. CNS: Spinal cord 5 Functions Conducts afferent stimuli from sensory receptors to the brain Conducts efferent stimuli from brain to effectors/muscles Site of reflex integration and houses certain central pattern generators

6. CNS: Spinal cord input/output Figure 4-8, B&L 6 Afferent fibre Efferent fibre * * Part of the peripheral nervous system * * * *

7. CNS: Spinal cord tracts 7 Silverthorn Figure 9-7 Tract : collection of axons that ascend/descend spinal cord with a specific function dorsal columns: ascending tracts that transmits tactile and proprioceptive info spinothalamic tract: ascending tract that transmits info about pain, temp. and itch lateral corticospinal tract: descending tract that carries motor information to skeletal muscle 1 2 3

8. Divisions of the Nervous System http://faculty.washington.edu/chudler/nsdivide.html 8

9. 9 CNS: Brain, three basic units Illustrative guide to the basic units of the brain: Forebrain/midbrain/ hindbrain

10. CNS: Brain, five regions 10 http://www.ruf.rice.edu/~lngbrain/cglidden/middlelabnoline!!yes2use2.jpg Regions grouped and named as they develop in the embryo Figure 10-6, B&B

11. Forebrain part 1: Telencephalon 11 Includes all of the cerebral cortex and the internal nuclei such as the basal ganglia , hippocampus , the olfactory bulb and the amygdala http://www.3icreative.com/wp-content/uploads/2011/03/telencephalon-limbic-system-300x251.jpg

12. Telencephalon : Cerebral Cortex 12 Outermost layer of the cerebrum Composed of 2-4mm of gray matter Up to 6 horizontal layers with unique neuronal projections and functions Figure 17-6 Kandel Layers I-III intracortical connections Layer IV recieves connections from the thalamus Layer V and VI project to subcortical regions

13. Telencephalon : Cerebral Cortex Silverthorn Figure 9-15 13 Central Sulcus Organized into functional lobes:

14. Cerebral Cortex: Broadman’s Areas Organization based on physiological function Important areas we will visit later: Area 4 = primary motor cortex Area 3,1,2 = primary somatosensory cortex Area 17 = primary visual cortex Area 41, 42 = primary auditory cortex 14

15. Telencephalon : Basal Ganglia 15 Functions Motor control; connections with motor cortex and thalamus Regulate initiation and termination of movements Some role in attention, memory and planning

16. Telencephalon : Amygdala & Hippocampus 16 Amygdala functions Part of the limbic system Associated with pleasure, fear, addiction Important in forming and storing memories of emotional events Hippocampus functions Part of the limbic system Important in formation of memories, including spatial and navigation memories Damage to hippocampus can result in anterograde amnesia

17. includes the thalamus and hypothalamus Telencephalon + diencephalon = forebrain Forebrain part 2: Diencephalon 17 Thalamus functions Main integrating centre for sensory information Receives input from basal ganglia and cerebellum Hypothalamus functions Main control centre for the autonomic nervous system Close association with pituitary gland, important functions in the endocrine system (hormone release) Contains nuclei important in regulation of circadian clock, hunger, thirst, heart rate, and temperature regulation

18. Two divisions: a) tectum superior colliculi contain nuclei for visual reflexes inferior colliculi contain nuclei for auditory reflexes b) tegmentum substantia nigra Release dopamine to basal ganglia red nucleus Connections with cerebellum for coordination of movement Midbrain : Mesencephalon 18

19. Hinbrain : Myelencephalon Two divisions: a) myelencephalon medulla oblongata Contains ascending and descending sensory and motor tracts connecting the cerebrum to the spinal cord Most spinal cord tracts cross over in the pyramids Contains nuclei that regulate breathing, blood pressure, vomiting 19

20. Hinbrain : Metencephalon b) metencephalon pons Contains pneumotaxic centre which fine tunes breathing rate Relays information between cerebellum and cerebrum cerebellum Feedback center for execution of motor movements Controls posture and balance reticular formation Nuclei diffusely located through the brainstem* Regulates wakefulness and muscle tone 20 *the term “brainstem” refers to the medulla oblongata, pons , and the midbrain

21. Divisions of the Nervous System http://faculty.washington.edu/chudler/nsdivide.html 21

22. CNS Protection Against physical damage Against c hemical damage Both Skull/vertebrae - hard external protection Blood brain barrier - Tight junctions form physical barrier across capillaries Cerebrospinal fluid Shock absorption Stable ionic composition Meninges Pia mater (innermost layer) Arachnoid mater Dura mater 22

23. Protection: Blood Brain Barrier 23 CNS blood vessels prevent paracellular diffusion of macromolecules and ions Capillary endothelial cells in the brain are connected by tight junctions to form a physical barrier, with contribution from astrocytes , pericytes & neurons Specialized transporters required for movement of most molecules Small or lipophilic molecules and gases can diffuse more easily Caffeine, nicotine, heroin, CO 2

24. Protection: Blood Brain Barrier 24 Only a few, small regions of the brain are without a blood brain barrier Creates problems for delivering therapeutic drugs to the brain Methods for drug targeting include: Manufacturing low molecular weight drugs Tagging the drug with ligand to assist in receptor mediated transcellular transport Injecting drug directly into brain matter

25. Protection: Cerebrospinal Fluid 25 Fluid synthesized by the choroid plexuses in each of the four ventricles Fills ventricles and subarachnoid space Less protein than plasma with similar electrolyte composition (but more Cl - , less Ca 2+ and K + ) Acts as a shock absorber during impact Removes waste, regulates pH and maintains ionic homeostasis of neuronal microenvironment

26. Divisions of the Nervous System 26

27. Peripheral Nervous System 27 Autonomic Somatic Parasympathetic Sympathetic Sensory Motor Rest and digest Flight or fight Afferent neurons carrying information from sensory receptors to the CNS Efferent neurons carrying information from the CNS to muscles all parts of nervous system outside the dura mater includes sensory receptors, peripheral portions of spinal and cranial nerves (including those of the ANS), and sensory ganglia sensory ganglia are aggregates of nerve cells located outside the CNS

28. Microanatomy: Neurons and Glial cells 28 Neurons Convey electrical signals within CNS and PNS Glial cells regulate neuron environment & form the myelin sheath around neurons Astrocytes : regulate neuron environment Oligodendrocytes : form myelin sheath in CNS Schwann cells : form myelin sheath in PNS Ependymal cells : line the ventricles, synthesize CSF Microglia : monocytes of the brain

29. Classifications of Neurons 29 neurons can be classified by the following characteristics: B&B Figure 10-3

30. Classifications of Neurons 30 B&B Figure 10-3

31. Classifications of Neurons 31 B&B Figure 10-3

32. Objectives After this lecture you should be able to: List the types of neurons (afferent, efferent, sensory, motor) contained in: dorsal root and ventral root ganglion, ascending and descending tracts of the spinal cord List a major function of: frontal, parietal, temporal and occipital lobes, reticular formation, medulla, pons , midbrain, cerebellum, thalamus, hypothalamus, basal ganglia, limbic system Describe the modes of protection of the CNS List the functions of various neurons and their respective neuroglial cells 32

33. 33 The __________________ is the main control centre for regulating functions of the autonomic nervous system, secretes a variety of hormones, and contains nuclei important for regulation of hunger and temperature regulation. What kind of protection is offered by the cerebrospinal fluid? ____________________ are referred to as the monocytes of the brain and become phagocytic cells when activated in order to removed debris. Test your knowledge