Detail note on nervous system

2. Overview of Nervous System

3. Learning Objectives • At the end of this session, will be able to understand the following: • Describe the functional components of nervous system. • Describe the major levels of Central Nervous System. • Describe the integrative function of Nervous System. • Classification of nerve fibers. • Synaptic transmission.

4. Nervous System • Functions • Sensory input – monitoring stimuli occurring inside & outside the body • Integration – interpretation of sensory input • Motor output – response to stimuli by activating effector organs Figure 11.1

5. Nerve Tissue • The two principal cell types of the nervous system are: • Neurons – excitable cells that transmit electrical signals • Neuroglia - supporting cells

6. Neuron Classification • Functional: • Sensory (afferent) — transmit impulses toward the CNS • Motor (efferent) — carry impulses away from the CNS • Interneurons (association neurons) — shuttle signals through CNS pathways

8. Nerve Fiber Types in Mammalian Nerve

9. Neuroglia Figure 12.6

10. Support and Protection of the Brain • The brain is protected and isolated by multiple structures: • Bony cranium • Meninges • Cerebrospinal fluid (CSF) • Blood-brain barrier

11. Meningeal Layers • Meningeal layer of the brain cushion and protect delicate neural tissue Figure 9-4b

12. Blood Brain Barrier • It has extensive capillaries & sinuses • It has tight junctions promoted by astrocyte • It limits permeability for most molecules except • O2, CO2, alcohol, steroids, water Figure 9-6: The blood-brain barrier

14. Blood Brain Barrier • Protects brain: hormones & circulating chemicals • Protects CNS from chemical fluctuations • Prevents entry of harmful substances • Prevents entry of molecules that could act as neurotransmitters

15. Organization of the Nervous System • Central nervous system (CNS) • Brain and spinal cord • Integration and command center • Peripheral nervous system (PNS) • Paired spinal and cranial nerves • Carries messages to and from the spinal cord and brain

17. Central Nervous System: • Brain • Spinal cord

18. A common brain division

19. Cerebral Cortex • Three specializations • Sensory areas - sensory input translated into perception • Motor areas - direct skeletal muscle movement • Association areas - integrate information from sensory and motor areas, can direct voluntary behaviors

21. Primary Somatosensory Cortex • Located in the postcentralgyrus, this area: • Receives information from the skin and skeletal muscles • Exhibits spatial discrimination • Somatosensory homunculus – caricature of relative amounts of cortical tissue devoted to each sensory function

23. Primary Motor Cortex • Located in the precentralgyrus • Composed of pyramidal cells whose axons make up the corticospinal tracts • Allows conscious control of precise, skilled, voluntary movements • Motor homunculus – caricature of relative amounts of cortical tissue devoted to each motor function

26. Spinal Cord Regions • Cervical • Thoracic • Lumbar • Sacral Figure 9-4a: ANATOMY SUMMARY: The Central Nervous System

27. Spinal Cord Organization • Gray matter: mostly in cell bodies that have • Dendrites & terminals • These are spinal reflex integrating center • White matter, mostly in • Bundles of myelinated axons • Ascending tracts – sensory • Descending tracts – motor • Dorsal roots • Ventral roots

28. Spinal Cord Organization Figure 9-7: Specialization in the spinal cord

29. Spinal Cord: Integrating Center Figure 9-8

30. Peripheral Nervous System: Afferent Division • Afferent (sensory) division – transmits impulses from receptors to the CNS. • Somatic afferent fibers – carry impulses from skin, skeletal muscles, and joints • Visceral afferent fibers – transmit impulses from visceral organs

31. Peripheral Nervous System: Efferent Division • Motor (efferent) division – transmits impulses from the CNS to effector organs. Two subdivisions: • Somatic nervous system – provides conscious control of skeletal muscles • Autonomic nervous system – regulates smooth muscle, cardiac muscle, and glands

33. Sensory system • General somatic senses – receptors are widely spread • Touch • Pain • Vibration • Pressure • Temperature • Proprioceptive senses – detect stretch in tendons and muscle • Body sense – position and movement of body in space

34. Motor system • General somatic motor – signals contraction of skeletal muscles • Under our voluntary control • Often called “voluntary nervous system” • Visceral motor • Regulates the contraction of smooth and cardiac muscle • Makes up autonomic nervous system • Controls function of visceral organs • Often called “involuntary nervous system” • Autonomic nervous system

35. Cranial Nerves • Total number of cranial nerves = 12 • Sensory cranial nerves = 3 • Motor cranial nerves = 5 • Mixed cranial nerves = 4

36. Cranial Nerves Table 9-1: The Cranial Nerves

38. Neural Reflexes: Overview Stimulus Sensory receptor Sensory (afferent) neuron CNS integration

39. Efferent (motor) neuron Effector (target tissue) Response (movement) Feedback to CNS

41. Synapses • Site where a nerve communicates with a nerve or a muscle • Transmission through synapses is called synaptic transmission

43. Properties of synaptic transmission • Excitation • Inhibition • Spatial summation • Temporal summation • Facilitation • Fatigue • Synaptic delay

44. References • Guyton Medical physiology.11th edition. • Human physiology .Lauralee Sherwood 7th edition. • Ganong. Review of Medical Physiology.23rd Edition • Text book of physiology by Jaypee • Google images