Nervous System

1. Nervous System Hazel Anne L. Tabo

2. Nervous System • Important in transmission of nerve impulses to coordinate the wholistic response coming from the impulse perceived by the body. • Neurotransmitters – chemical messengers that is transmitted between neuronal cells. • In the response: Stimuli  Afferent (sensory) nerve  Center (spinal cord, brain)  Motor (efferent) nerve  Target organ

3. Nervoustissue • Can be organized by anatomical and functional divisions. • Anatomical Divisions: • Central nervous system • Peripheral nervous system • Functional Divisions • Sensory component (impulse towards to CNS) • Motor component (impulse from CNS to effector or target organs) 2.1 – Somatic nervous system 2.2 – Autonomic nervous system (sympathetic and parasympathetic)

4. Anatomical Division • Central nervous system (CNS) • Includes Brain and Spinalcord (SC) • Peripheral nervous system (PNS) • Includes nerves outside CNS and associated ganglia.

6. Cells of Nervous Tissue • Neuron structure a. Neuronal cell body (soma/perikaryon) – contains nucleus, cytoplasmic organelles, inclusions and cytoskeletons. - Nucleus – aggregates of cell bodies in the CNS (do not confuse it with the nucleus organelle!) - Ganglion – cell bodies in the PNS b. Dendrites c. Axons • Neuroglial cells – supporting cells located in the CNS • Schwann cells – neuroglia-equivalent in the PNS

8. The Neuron • Cell Body / Soma / Perikaryon • 1) Nucleus – centrally located in the soma of most neurons; euchromatin and dark nucleolus (“owl-eyed nucleus”) • 2) Cytoplasmic organelles and inclusions: • Nisslbodies – dark clumps in the cytoplasm made of polysomes and rough ER • Cytoskeletons: neurofilaments (regulates neuronal axon diameter); microtubules (in cytoplasm); microfilaments (in plasma membrane) • Dendrites – receive stimuli (signals) from adjacent sensory cells, axons or other neurons and converted into electrical impulse; abundant mitochondria. • Axons – conduct impulses away from the soma and sends it to effector/target organs or adjacent nervous tissue. • Axon hillock – specialized area of soma with high neurofilaments • Axoplasm (axon cytoplasm) – contains sER, rER and long mitochondria • Axolemma – plasma membrane of axon • Axon terminals – ends of axon

11. Electrical Impulse runs through: • Synapse are functional sites where electrical signals are transmitted from 1 neuron to another or to another target cell (myofiber). • Dendriticspines increase surface area for synapse formation with other neurons • Terminal buttons – structure in the ends of axon terminal; form synapse to another cell or dendrite.

12. Example of a neuron: Multipolar neuron http://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab9/lab9.htm#

13. Types of Neuron • Unipolar – one dendrite • Bipolar – two dendrites • Multipolar – multiple dendrites • Pseudounipolar – looks like multipolar but unipolar • Functional types – responds to chemical transmitters (neurotransmitter) • Excitatory neuron • Inhibitory neuron • Neurotransmitters – chemical messengers that may promote or inhibit a certain neural response (impulse). • Ex: Acetylcholine – presents in the myoneural junctions (neuromuscular junctions). Dopamine, Serotonin, GABA

14. Neuroglial cells • Supporting cells of CNS • Small-sized and numerous than neuron; origin: neural crest cells • Support, nourishes and protect neurons • Types: astrocytes, oligodendrocytes, microglia, ependymal cells, Schwann cells

15. Astrocytes – largest neuroglial cell; contain many processes forming pedicels (vascular feet) around a blood capillary forming the “blood-brain barrier”; scavenges ion and debris from neuron metabolism and supplies energy for metabolism; support and protects nervous tissue; forms “scar tissue” after injury to CNS. http://www.kumc.edu/instruction/medicine/anatomy/histoweb/nervous/large/Nerve15.JPG

16. Oligodendrocytes – have small, round, condensed nucleus that lives symbiotically with neurons; necessary for neuron survival; produces myelin in CNS; present in CNS gray and white matter. http://www.microscopy-uk.org.uk/mag/imgapr03/HistPaper03_Fig3a.jpg

17. Microglia – small, phagocytotic neuroglial cell that arised from monocytes in the bone marrow; they become APCs (antigen-presenting cell) in the CNS tissue when activated by trapped foreign bodies.

18. Ependymal cells – epithelial cells that line the neural tube and ventricles of the brain; they have cilia that aids in moving the CSF (cerebrospinal fluid); cells of the choroid plexus (CSF production) http://biology.clc.uc.edu/fankhauser/Labs/Anatomy_&_Physiology/A&P202/CNS_Histology/Spinal_Cord/sp_cd_jpgs/Spinal_Cord_PC271498_lbd.JPG; http://www.lab.anhb.uwa.edu.au/mb140/corepages/nervous/Images/epen100he.jpg

19. Schwann cells – the only neuroglial cell-equivalent in the PNS; function is similar with oligodendrocytes to produce myelin, the myelin sheath consists of several Schwann cell plasmalemma. Myelinated nerve fibers – faster impulse conduction Unmyelinated fibers – slower conduction

20. Schwann cell – triangles • Axon - arrows

21. Peripheral Nervous System • Branches from the spinal cord • Spinal nerves, Ganglion, peripheral nerves • Nerve fiber – individual axons enveloped by myelin sheath • Myelin sheath – insulator of heat, myelinated fibers have higher firing rate, than unmyelinated fibers. It is interrupted by nodes of Ranvier (saltatory conduction) along an axon, these gaps are produced by adjacent Schwann cells. • Nerves – bundles of nerve fibers; appear whitish due to (+) myelin; CT wrappings • Ganglia – encapsulated aggregations of soma or cell bodies

22. Peripheral Nervous System

23. Connective tissue wrappings of Peripheral Nerve • Epineurium – covers the whole nerve bundle that forms external coat of nerves formed by dense CT(fascia). • Perineurium – surrounds each nerve bundle (fascicle); flattened cells are joined by tight junctions (z. occludens) prohibiting passage of macromolecules. • Endoneurium – forms a thin layer of reticular fibers produced by Schwann cells that surrounds individual nerve fibers (neurofiber).

25. Central Nervous System • Brain and Spinal Cord • Matter: Gray Matter and White Matter • Gray Matter (GM) – neuronal cell bodies (nucleus), more neuroglial cells and many unmyelinated fibers • WhiteMatter – mostly myelinated fibers and some neuroglial cells • Brain GM – cortex; WM – medulla • Spinal cord WM – cortex; GM – medulla (H-section)

26. Brain, Frontal section

27. Spinal cord section

28. Meninges • Dura mater – connected to the endosteum of the skull • Arachnoid mater – sublayer between periosteum and brain, contains network (cobweb) of blood vessels. • Pia mater – covers the brain parenchyma

31. Skin Sensory Receptors • Merkel’s disks – free nerve endings (unencapsulated), unmyelinated nerve fibers (skin: stratum basale) • Meissner’s corpuscle – sensitive to light touch (skin dermis) • Pacinian corpuscle – deep pressure or coarse touch (skin dermis) • End bulb of Krause – sensitive to cold (oropharynx lining & eye conjunctiva) • Ruffinian corpuscle – sensitive to heat (soles of feet)

32. Da Lamarcke’s theory of use and disuse can be associated with microcephaly. Such condition may happen if you don’t exercise your brain!

33. THANK YOU FOR LISTENING!