The Nervous System

1. The Nervous System

3. The Nervous System • Responsible for linking the body to the external environment while maintaining complex processes • Neurons • With the aid of endocrine system, maintains homeostasis. • Epilepsy, Alzheimer’s Disease, MS, and Stroke are disorders of the nervous system.

5. Subdivisions of Nervous System Two major anatomical subdivisions • Central nervous system (CNS) • brain and spinal cord enclosed in bony coverings • Peripheral nervous system (PNS) • Every Nerve outside of the CNS! • NERVE: a bundle of neurons • GANGLIAN: a cluster of neuron bodies ( resembles a knot)

6. Central Nervous System (CNS) - Consists of brain and spinal cord. Occupies the dorsal body cavity Interprets sensory information Peripheral Nervous system (PNS) Spinal Nerves- carry impulses to and from the spinal cord Cranial Nerves- carry impulses to and from the brain Structural Classification

7. Subdivisions of Nervous System

9. Nervous Tissue • The nervous system consists of nervous tissue…the unit cells being neurons and their supporting cells: • Supporting cells

10. Supporting Cells

11. Support Cells: Glial Cells 10X as many neuroglial cells as neurons!! Collectively referred to as neuroglia. • Oligodendrocytes (CNS)- Primary role is to produce myelin which encases the axons of neurons at points. Schwann cells do this in (PNS). • Astrocytes- a source of nourishment for neurons as they connect to capillaries. Also, regulates extra-cellular cellular space at synapse. • Ependymal cells- provides the lining of the fluid-filled brain ventricular system. (epithelial cells) • Microglia- phagocytes that remove cell debris or degenerating neurons or glia.

12. Myelin: composed from lipids (contains cholesterol) Creates nodes of ranvier This insulation causes saltatory conduction, a more rapid conduction than w/out insulation MS is a disease where myelated sheath is distorted (Multiple Sclerosis) Oligodendrocyte

14. About Neurons… • Neurons do NOT regenerate…( a few exceptions) • They lack centrioles: organelles which for spindles for mitosis. • Neurons of the hippocampus regenerate.

15. Classification of Neurons

17. Extensions outside the cell body • Dendrites – conduct impulses toward the cell body • Axons – conduct impulses away from the cell body Figure 7.4a

18. Neuron Anatomy • Cell body • Nissl substance – specialized rough endoplasmic reticulum • Neurofibrils – intermediate cytoskeleton that maintains cell shape Figure 7.4a

22. Channels

23. SENDING INFORMATION: NERVE IMPULSE Sending Information- The nerve impulse refers to the series of separate action potentials that take place segment by segment as they move down the length of the axon. All-or-None law – If an action potential starts at the beginning of the Axon, the action potential will continue at the same speed segment to segment to the very end of the axon.

24. Sending information (Cont.) Definition of AP: action potential is a tiny electrical current that is generated when the positive sodium ions rush inside the axon What does This DO? the enormous increase of Na ions inside the axon causes the inside to reverse its charge the inside becomes positive & the outside becomes negative

25. Action Potential = Nerve Impulse • Is an “all or nothing” response • Does not die out • Continues to end of axon • Series of depolarizations • Refractory period follows

27. Sodium-Potassium Pump: (Remember Me?)

28. Na-K Pump: How it Works • A type of active transport. • 3 sodium ions move out of cell • 2 potassium ions move into cell. • ATP is needed as each of these ions are moving against their conc. gradient. • Mostly used in cardiac muscle and nervous tissue. Maintains Na+K gradient concentration. • MAINTAINS RESTING POTENTIAL!!! • Huge amount of ATP goes into this NaK pumps!

29. Characteristic of areas of excitable membrane Capable of generating an action potential Open or close in response to changes in transmembrane potential Example: the sodium channel ( seen to the right) At membrane potential of –60mV the channal opens, +30, it closes Voltage-Regulated Channels

30. INSIDE-0UT!!!GO!!!

31. Saltatory Conduction

33. Neuron Cell Body Location • Most are found in the central nervous system • Gray matter – cell bodies and unmylenated fibers • Nuclei – clusters of cell bodies within the white matter of the central nervous system • Ganglia – collections of cell bodies outside the central nervous system

34. Sensory neurons- or Afferent neurons collect information from the external environment. Bring information to the CNS It All Starts at The Sensory Receptor

36. NEUROTRANSMITTERS • Neurotransmitter - A chemical messenger released from the synaptic terminal of a neuron at a chemical synapse that diffuses across the synaptic cleft and binds to and stimulates the post-synaptic membrane. • Examples of neurotransmitters are epinephrine, dopamine, seratonin and acetylcholine. • When in the neuron, neurontransmitters are stored in vessicles.

37. Some NTs Stimulate AP, Some Inhibit AP • Excitatory NTs: acetylcholine, epinephrine, norepinephrine, serotonin, • Inhibitory NTs: Dopamine, GABA and Glycine

38. Afferent Neuron – Moving away from a central organ or pointRelays messages from receptors to the CNS

39. Efferent Neuron :Relays messages from the CNS to the motor neurons and organs

43. Neuron Classification Figure 7.6

44. Somatic Reflex Arch • Autonomic Reflex Arch

45. Neuron Cell Body Location • Most are found in the central nervous system • Gray matter – cell bodies and unmylenated fibers • Nuclei – clusters of cell bodies within the whitematter of the central nervous system • Ganglia – collections of cell bodies outside the central nervous system

47. Simple Reflex Arc Figure 7.11b–c

49. Central Nervous System (CNS) • CNS develops from the embryonic neural tube • The neural tube becomes the brain and spinal cord • The opening of the neural tube becomes the ventricles • Four chambers within the brain • Filled with cerebrospinal fluid

50. Regions of the Brain • Cerebral hemispheres • Diencephalon • Brain stem • Cerebellum Figure 7.12b