The Nervous System

1. The Nervous System

2. Functions of the Nervous System • Sensory input – gathering information • To monitor changes occurring inside and outside the body • Changes = stimuli • Integration • To process and interpret sensory input and decide if action is needed

3. Functions of the Nervous System • Motor output • A response to integrated stimuli • The response activates muscles or glands

4. Structural Classification of the Nervous System • Central nervous system (CNS) • Brain • Spinal cord • Peripheral nervous system (PNS) • Cranial nerves • Spinal nerves

5. Functional Classification is concerned only with PNS 1-Sensory (afferent) division • Nerve fibers that carry information to the central nervous system Figure 7.1

6. Functional Classification of the Peripheral Nervous System 2-Motor (efferent) division • Nerve fibers that carry impulses away from the central nervous system ( to Muscles &Glands) Figure 7.1

7. Motor (efferent) division has two subdivisions 1-Somatic nervous system = voluntary, it controls skeletal muscles • N. B. skeletal muscle reflexes are involuntary 2-Autonomic nervous system = involuntary, it controls smooth &cardiac muscles &glands This also is divided into sympathetic & parasympathetiuc

8. Organization of the Nervous System Figure 7.2

9. Despite the complexity of the nervous system, there are only two functional cell types Neurons - excitable nerve cells that transmit electrical signals Neuroglia (glial) cells - supporting cells Histology of Nervous Tissue

10. Neuroglia - 4 types in the Central NS 1-Astrocytes star shaped with many processes connect to neurons; help anchor them to nearby blood capillaries control the chemical environment of the neurons 2-Microglia oval with thorny projections monitor the health of neurons if infection occurs, they change into macrophages (eating viruses, bacteria and damaged cells) Histology of CNS Tissue - Neuroglia

11. Neuroglia - 4 types in the Central NS Astrocytes star shaped with many processes connect to neurons; help anchor them to nearby blood capillaries control the chemical environment of the neurons Microglia oval with thorny projections monitor the health of neurons if infection occurs, they change into macrophages (eating viruses, bacteria and damaged cells) Histology of CNS Tissue - Neuroglia

12. Neuroglia - 4 types in the CNS (continued) Ependymal cells range in shape from squamous to columnar; many are ciliated line the dorsal body cavity housing the brain and spinal cord form a barrier between the neurons and the rest of the body Oligodendrocytes have few processes line up along neurons and wrap themselves around axons form the myelin sheath – an insulating membrane Histology of CNS Tissue - Neuroglia

13. Neuroglia - 2 types in the Peripheral NS Satellite cells surround neuron cell bodies in the periphery maintain the extracellular environment Schwann cells (neurolemmocytes) surround axons/dendrites and form the myelin sheath around larger nerve fibers in the periphery similar to oligodendrocytes in function - insulators Histology of PNS Tissue - Neuroglia

14. Nervous Tissue: Neurons • Neurons = nerve cells • Cells specialized to transmit messages • Major regions of neurons • Cell body – nucleus and metabolic center of the cell • Processes – fibers that extend from the cell body

15. Anatomy of neuron (Nerve cell) Differ structurally but have common features,all have • A Cell body with Nucleus,the usual organelles Except centrioles • One or more processes Figure 7.4a

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

17. Axons and Nerve Impulses • Axons end in axonal terminals • Axonal terminals contain vesicles with neurotransmitters • Axonal terminals are separated from the next neuron(neuroneural junction) by a gap calledSynaptic cleft (Synapse)

18. Nerve Fiber Coverings -Most long nerve fibers are covered with a whitish, fatty material called Myelin with waxy appearance. It insulates the fiber &Increases transmission rate -Axons outside CNS are wrapped by Schwann Cells Figure 7.5

19. Neuron Cell Body Location • Most are found in the central nervous system • Gray matter – cell bodies and unmyelinated 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 • White matter- collection of myelinated fibers (Tracts)

20. Functional Classification of Neurons 1-Sensory (afferent) neurons Carry impulses from the sensory receptors • Cutaneous sense organs • Proprioceptors – detect stretch or tension in muscles and tendons and joints 2-Motor (efferent) neurons Carry impulses from the central nervous system to muscles and glands ,their cell bodies are always in CNS

21. Functional Classification of Neurons 3-Interneurons (association neurons) • Their cell bodies are always found in CNS • Connect sensory and motor neurons in neural pathways

22. Neuron Classification Figure 7.6

23. Structural Classification of Neurons • Multipolar neurons – many extensions from the cell body Figure 7.8a

24. Structural Classification of Neurons • Bipolar neurons – one axon and one dendrite Figure 7.8b

25. Structural Classification of Neurons • Unipolar neurons – have a short single process leaving the cell body which is very short ,divides almost immediatly Figure 7.8c

26. Functional Properties of Neurons • Irritability – ability to respond to stimuli • Conductivity – ability to transmit an impulse • The plasma membrane at rest is polarized • Fewer positive ions are inside the cell than outside the cell

27. Starting a Nerve Impulse • Depolarization – a stimulus depolarizes the neuron’s membrane • A deploarized membrane allows sodium (Na+) to flow inside the membrane • The exchange of ions initiates an action potential in the neuron

28. The Action Potential • If the action potential (nerve impulse) starts, it is propagated over the entire axon • Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane • The sodium-potassium pump restores the original configuration • This action requires ATP

29. Nerve Impulse Propagation • The impulse continues to move toward the cell body • Impulses travel faster when fibers have a myelin sheath Figure 7.9c–e

30. Continuation of the Nerve Impulse between Neurons • Impulses are able to cross the synapse to another nerve • Neurotransmitter is released from a nerve’s axon terminal • The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter • An action potential is started in the dendrite

31. How Neurons Communicate at Synapses Figure 7.10

32. The Reflex Arc • Reflex – rapid, predictable, and involuntary responses to stimuli • Reflex arc – direct route from a sensory neuron, to an interneuron, to an effector • Ref. arch have a minimum 5 elements

33. Simple Reflex Arc Figure 7.11b, c

34. Types of Reflexes and Regulation • Autonomic reflexes eg. • Salivary gland secretion • Heart and blood pressure regulation • Changes in size of the pupil • Digestive system regulation • Somatic reflexes • Activation of skeletal muscles

35. SPINAL CORD, as flexor reflex BRAIN ( for proper evaluation) as response of pupils to light N.B., Exaggerated, Distorted or Absent indicate nervous system disorder. N.B. Reflex changes often occur before the pathological condition become obvious REFEXES MAY USE :

36. Central Nervous System (CNS) • CNS develops from the embryonic neural tube • By the fourth week the anterior end begins to expand and brain formation begins, The rest of the tube becomes the spinal cord • The central canal becomes enlarged in 4 regions of the brain to form ventricles the ventricles: -Four chambers within the brain -Filled with cerebrospinal fluid

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

38. Cerebral Hemispheres (Cerebrum) • Paired (left and right) superior parts of the brain • Include more than half of the brain mass Figure 7.13a

39. Layers of the Cerebrum • Gray matter • Outer layer • Composed mostly of neuron cell bodies Figure 7.13a

40. Layers of the Cerebrum • White matter • Fiber tracts inside the gray matter • Example: corpus callosum connects hemispheres Figure 7.13a

41. Layers of the Cerebrum • Basal nuclei – internal islands of gray matter Figure 7.13a

42. Cerebral Hemispheres (Cerebrum) • The surface is made of ridges (gyri) and grooves (sulci) Figure 7.13a

43. Specialized Area of the Cerebrum • Cerebral areas involved in special senses • Gustatory area (taste) • Visual area • Auditory area • Olfactory area

44. Specialized Area of the Cerebrum • Interpretation areas of the cerebrum • Speech/language region • Language comprehension region • General interpretation area

45. Specialized Area of the Cerebrum Figure 7.13c

46. Diencephalon • Sits on top of the brain stem • Enclosed by the cerebral heispheres • Made of three parts • Thalamus • Hypothalamus • Epithalamus

47. Diencephalon Figure 7.15

48. Thalamus • Surrounds the third ventricle • The relay station for sensory impulses (except olfaction) • Transfers impulses to the correct part of the cortex for localization and interpretation

49. Hypothalamus • Under the thalamus • Important autonomic nervous system center • Helps regulate body temperature • Controls water balance • Regulates metabolism

50. Hypothalamus • An important part of the limbic system (emotions) • The pituitary gland is attached to the hypothalamus