The Nervous System

1. The Nervous System

2. 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 • All reflex arcs have 5 elements (#ed below) Figure 7.11a

3. Simple Reflex Arc Figure 7.11b–c

4. Types of Reflexes and Regulation • Autonomic reflexes • Smooth muscle regulation • Heart and blood pressure regulation • Regulation of glands • Digestive system regulation • Somatic reflexes • Activation of skeletal muscles

5. 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

6. Regions of the Brain • Cerebral hemispheres • Diencephalon • Brain stem • Cerebellum • Adult brain weighs a little over 3 pounds Figure 7.12b

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

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

9. Lobes of the Cerebrum • Fissures (deep grooves) divide the cerebrum into lobes • Single deep fissure (longitudinal fissure) separates the cerebral hemispheres • Surface lobes of the cerebrum named for the cranial bones that lie over them • Frontal lobe • Parietal lobe • Occipital lobe • Temporal lobe

10. Lobes of the Cerebrum Figure 7.13b

11. Specialized Areas of the Cerebrum Figure 7.13c

12. Specialized Areas of the Cerebrum • Somatic sensory area – receives impulses from the body’s sensory receptors (pain, coldness, light touch) • Located in the parietal lobe posterior to central sulcus • Left side of the sensory cortex receives impulses from the right side of the body

13. Specialized Areas of the Cerebrum • Primary motor area – sends impulses to skeletal muscles • Located in the frontal lobe anterior to the central sulcus • Axons of these motor neurons form the corticospinal or pyramidal tract, which descends to the cord

14. Specialized Areas of the Cerebrum • Broca’s area – involved in our ability to speak • Located at the base of the precentral gyrus • Located in only one hemisphere (usually the left) • Damage to this area causes inability to say words properly – know what you want to say but can’t vocalize

15. Sensory and Motor Areas of the Cerebral Cortex Figure 7.14

16. Specialized Areas of the Cerebrum • Cerebral areas involved in special senses • Gustatory area (taste) • Parietal lobe – corner of the central & lateral sulcus • Visual area • Posterior part of the occipital lobe

17. Specialized Areas of the Cerebrum • Auditory area • In the temporal lobe bordering the lateral sulcus • Olfactory area • Deep inside the temporal lobe

18. Specialized Areas of the Cerebrum • Interpretation areas of the cerebrum • Speech/language region • Junction of the temporal, parietal, & occipital lobes • Allows one to sound out words • Usually in only one cerebral hemisphere

19. Specialized Areas of the Cerebrum • Language comprehension region • Frontal lobes • Word meanings • General interpretation area • Temporal, parietal, & occipital lobes

20. Specialized Areas of the Cerebrum Figure 7.13c

21. Layers of the Cerebrum • Gray matter • Outer layer (cerebral cortex) • Composed mostly of neuron cell bodies • Highly ridged (convoluted) – gives more surface area for neurons Figure 7.13a

22. Layers of the Cerebrum • White matter • Fiber tracts (bundles of nerve fibers) inside the gray matter • Carry impulses to & from cerebral cortex Figure 7.13a

23. Layers of the Cerebrum • Example: corpus callosum connects cerebral hemispheres allowing for communication *Important because some of the critical functional areas are in only one hemisphere

24. Layers of the Cerebrum • Basal nuclei (basal ganglia) – internal islands of gray matter • Help regulate voluntary motor activities by modifying instructions sent to the skeletal muscles by the primary motor cortex Figure 7.13a

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

26. Diencephalon Figure 7.15

27. Thalamus • Surrounds the third ventricle • The relay station for sensory impulses upward to the sensory cortex • Transfers impulses to the correct part of the cortex for localization and interpretation by the neurons

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

29. Hypothalamus • An important part of the limbic system (emotions) • The pituitary gland hangs from the anterior floor of the hypothalamus by a slender stalk • Regulates the pituitary gland • Produces 2 of its own hormones

30. Epithalamus • Forms the roof of the third ventricle • Houses the pineal body (an endocrine gland) • Includes the choroid plexus – forms cerebrospinal fluid

31. Brain Stem (size of a thumb) • Attaches to the spinal cord • Parts of the brain stem • Midbrain • Pons • Medulla oblongata • Provides pathway for ascending & descending tracts • Basal nuclei of brain stem control breathing & blood pressure

32. Brain Stem Figure 7.15a

33. Midbrain • Mostly composed of tracts of nerve fibers • Has two bulging fiber tracts – cerebral peduncles – convey ascending & descending impulses • Has four rounded protrusions – corpora quadrigemina • Reflex centers for vision and hearing

34. Pons (“bridge”) • The bulging center part of the brain stem • Mostly composed of fiber tracts • Includes nuclei involved in the control of breathing

35. Medulla Oblongata • The lowest part of the brain stem • Merges into the spinal cord • Includes important fiber tracts • Contains important control centers • Heart rate control • Blood pressure regulation • Breathing • Swallowing • Vomiting

36. Reticular Formation • Diffuse mass of gray matter along the brain stem • Involved in motor control of visceral organs • Reticular activating system plays a role in awake/sleep cycles and consciousness *Damage to this area can result in permanent unconsciousness (coma)

37. Reticular Formation Figure 7.15b