THE NERVOUS SYSTEM

1. THE NERVOUS SYSTEM

2. Neurons React to changes in environment Transmit nerve impulses Dendrites Axons Nerve Synapses Neurotransmitters Neuroglia Fill spaces, surround, support, and nourish neurons General Structure of the Nervous System

3. Functions of the Nervous System • Sensory • Integrative • Motor • Sensory receptors  PNS  CNS  integration  decision  effectors  motor function

4. Divisions of the Nervous System

5. Neuron - Structure • Cell body • Neurofibrils • Nissl bodies • Dendrites • Axon • Axonal hillock • Collateral branches • Synaptic knob • Synaptic cleft

6. Schwann cells form myelin sheath Neurilemma Nodes of Ranvier White matter Schwann cells do not form sheath Gray matter Myelinated vs. Unmyelinated

7. Classification of Neurons

8. Neuroglia • Schwann cells-form myelin sheath in PNS • Astrocytes – blood-brain barrier • Oligodendrocytes-forms myelin in the CNS • Microglia –phagocytes • Ependyma – regulate CSF

9. Neuron Growth and Repair • Neurons can live and function for over 100 years. • Mature neurons generally do not divide. • Neurons develop from neural stem cells. • Injury to the cell body usually kills the neuron – it cannot be replaced. • The axon of a neuron may regenerate. • Growth is extremely slow – 3-4 mm/day.

10. Nerve Impulse Transmission – Membrane Potential • Cell membrane of a neuron is usually polarized – negative charge on the inside. (resting potential) • Charge is maintained by open protein channels and Na+-K+ pumps.

11. Nerve Impulse Transmission – Nerve Impulse Formation • A change in the environment opens gated ion channels. • Na+ rushes into the cell if threshold potential is reached. (action potential) • Voltage-gated K+ channels open to restore resting potential.

12. Nerve Impulse Transmission – Synaptic Transmission • At the synaptic knob, voltage-gated Ca++ channels open  Ca++ enters cell. • Ca++ causes release of neurotransmitters. • Neurotransmitters diffuse across synaptic cleft to receptors on the next neuron’s dendrite or cell body.

13. Neurotransmitters

14. The Central Nervous System (CNS)

15. Meninges • Between bone and CNS tissues • Dura mater • Arachnoid mater • Subarachnoid space • Pia mater

16. Spinal Cord Functions • Center for spinal reflexes • Conduit for nerve impulses to and from the brain

17. Spinal Cord Structure – Gross Anatomy • From foramen magnum to intervertebral disk between L1 and L2 • 31 segments  spinal nerves • Cervical enlargement • Lumbar enlargement • Cauda equina • Conus medullaris • Filium terminale

18. Spinal Cord Structure – Microscopic Cross-Section • Anterior and posterior horns • Gray commissure • Central canal • Funiculi • Ascending and descending tracts

19. Spinal Reflexes • Reflex arc • Sensory neuron  interneuron  motor neuron  effector • Knee-jerk reflex • Wthdrawal reflex

20. Brain Functions • Contains nerve centers associated with sensory functions • Sensations and perceptions • Issues motor commands to skeletal muscle • Memory and reasoning • Coordinates muscular movements • Regulates visceral activities • Personality

21. Brain Development

22. Parts of the Brain • Cerebrum • Diencephalon • Cerebellum • Brain stem

23. Cerebrum - Structure • Cerebral hemispheres • Corpus callosum • Falx cerebri • Convolutions (gyri) • Sulci • Fissures • Lobes – frontal, parietal, temporal, occipital, insula

24. Cerebral Cortex

25. Cerebrum - Functions • Interprets impulses from sense organs • Initiates voluntary muscle movements • Stores information as memory • Retrieves information during reasoning • Seat of intelligence and personality

26. Hemisphere Dominance

27. Basal Nuclei (Ganglia) • Masses of gray matter deep within cerebral hemispheres • Produce most of body’s dopamine • Relay station for motor impulses

28. Ventricles

29. Cerebrospinal Fluid (CSF) • Clear liquid with nutritive and protective functions • Helps maintain stable ion concentration • Pathway to the blood for waste • Absorbs forces to protect CNS • Forms from blood plasma at the choroid plexuses of the pia mater

30. Diencephalon • Mostly gray matter • Between cerebral hemispheres and above brain stem • 7 components

31. Parts of the Diencephalon • Thalamus – relay station for sensory impulses, awareness of pain, touch, and temperature • Hypothalamus – regulates heart rate, arterial blood pressure, body temperature, water and electrolyte balance, control of hunger and body weight, control of stomach and intestines, control of pituitary gland hormone release, sleep and wakefulness

32. Parts of the Diencephalon continued… • Optic chiasma – crossing over of optic nerves • Infundibulum – attaches to pituitary • Posterior pituitary gland • Mammillary bodies • Pineal gland

33. Limbic System • Made of parts of the frontal and temporal lobes, hypothalamus, thalamus, and basal ganglia • Controls emotional experience and expression • Guides behavior to increase chances of survival during upsetting experiences

34. Brain Stem • Midbrain • Reflex centers associated with eye and head movements • Pons • Centers that regulate rate and depth of breathing • Medulla oblongata • Transmits all ascending and descending impulses • Contains vital reflex centers: cardiac, vasomotor, respiratory • Contains centers for other reflexes: coughing, sneezing, swallowing, vomiting

35. Reticular Formation • Complex network of nerve fibers associated with tiny islands of gray matter throughout the brain stem • Wakefulness and sleep • Coma

36. Cerebellum • Inferior to occipital lobes, posterior to pons and medulla oblongata • Coordinates skeletal muscle activity • Maintains posture and equilibrium • Cerebellar cortex • Arbor vitae • Cerebellar peduncles

37. Peripheral Nervous System (PNS)

38. Cranial Nerves • 12 pair of nerves that arise from underside of brain • All except 1st pair originate from brain stem • Pass through foramina of the skull

40. 31 pair that originate from the spinal cord and pass through the intervertebral foramina • Provide communication between spinal cord and parts of the upper and lower limbs, neck, and trunk • Roots • Plexuses

41. Somatic and Special Senses Touch Pain Temperature Smell Taste Hearing Equilibrium Sight

43. Types of Receptors

44. Mechanoreceptors • Touch and pressure sensors • Sensory nerve fibers • Meissner’s corpuscles • Pacinian corpuscles

45. Thermoreceptors • Temperature sensors • Heat receptors – 25-45*C • Cold receptors – 10-20*C

46. Pain • Pain receptors are free nerve endings found everywhere except the brain. • Poorly understood how stimulation occurs. • Most pain fibers terminate in the reticular formation. • Referred pain • Pain fibers adapt poorly.

47. Sense of Smell - Anatomy • Nasal cavity • Olfactory receptors • Olfactory organs • Olfactory receptor cells • Cilia • Olfactory bulbs

48. Physiology of Smell • Chemicals enter nasal cavity as gases and dissolve in fluids that surround cilia. • Receptors detect chemicals and send impulses to olfactory bulbs. • Olfactory bulbs analyze impulses and transmit info along olfactory tracts to the limbic system. • Interpretation occurs within olfactory cortexes. • Receptors adapt quickly.

49. Sense of Taste - Anatomy • Taste buds • Papillae • Taste pore • Taste cells • Taste hairs

50. Physiology of Taste • Chemical stimulus dissolves in saliva. • Receptor cells are stimulated and send impulses along facial, glossopharyngeal, and vagus nerves to the medulla oblongata. • Impulses are sent to the thalamus and then to the gustatory complex.