Chapter 12

1. Chapter 12 Nervous System

2. Outline • Nervous Tissue • The Nerve Impulse • Action Potential • Central Nervous System • The Spinal Cord • The Brain • Peripheral Nervous System • Nerves and Ganglia • Drug Abuse • Degenerative Nervous System Diseases

3. Nervous Tissue • Nervous Tissue contains two types of cells. • Neurons transmit nerve impulses between parts of the nervous system. • Neuroglia support and nourish neurons.

4. Neuron Structure • Neurons are classified according to function. • Sensory neurons take impulses from a sensory receptor to the CNS. • Interneurons receive input from sensory neurons, and other neurons, and then communicate with motor neurons. • Motor neurons take nerve impulse away from the CNS to an effector that carries out responses to environmental change.

5. Neuron Structure • Neurons contain three basic parts. • Cell body contains nucleus and other organelles. • Dendrites receive signals from sensory receptors or other neurons. • Axon conducts nerve impulses.

6. Types of Neurons

7. Myelin Sheath • Some axons are covered by a protective myelin sheath. • Formed by Schwann cells containing myelin in plasma membranes. • Nodes of Ranvier are gaps on the axon with no myelin sheath.

8. Myelin Sheath

9. The Nerve Impulse • The nervous system uses the nerve impulse to convey information. • Resting potential is the voltage level when an axon is not conducting an impulse. • Sodium-potassium pump causes greater concentration of Na+ outside the axon, and greater concentration of K+ inside the axon. • Unequal ion distribution causes inside of axon to be negative relative to the outside.

10. Action Potential • An action potential is a rapid change in polarity across an axomembrane as the nerve impulse occurs. • All-or-none once threshold is reached. • Sodium gates open, allowing Na+ to move inside the axon. • Potassium gates open, allowing K+ to move outside the axon.

11. Transmission across a Synapse • Transmission across a synaptic cleft is carried out by neurotransmitters stored in synaptic vesicles. • Depending on the neurotransmitter and the receptor, the response of the postsynaptic neuron can be towards excitation or inhibition. • Integration is the summing of signals received by a postsynaptic neuron.

12. Integration

13. The Central Nervous System • The central nervous system (CNS) is made up of the spinal cord and the brain. • Both are wrapped in protective membranes, meninges, with spaces between meninges filled with cerebrospinal fluid. • CNS is composed of two types of nervous tissue. • Gray matter – Short, nonmyelinated fibers. • White matter - Myelinated axons.

15. The Spinal Cord • The spinal cord extends from the base of the brain through the foramen magnum into the vertebral canal.

17. Functions of the Spinal Cord • The spinal cord provides a means of communication between the brain and the peripheral nerves that leave the cord, and is a center for reflex actions.

18. The Brain • The Cerebrum. • The cerebrum, telencephalon, is the largest portion of the human brain. • Communicates with, and coordinates activities of, other parts of the brain. • Divided into left and right cerebral hemispheres. • Divided by longitudinal fissure.

19. The Human Brain

20. The Brain • Gray matter of cerebrum consists of cerebral cortex and basal nuclei. • Cerebral cortex is a highly convoluted outer layer that covers the cerebral hemispheres. • Basal nuclei are masses located deep within white matter. • White matter consists of long myelinated axons organized into tracts.

21. Lobes of Cerebral Hemisphere

22. The Brain • Diencephalon is made up of hypothalamus and thalamus, and circles the third ventricle. • Cerebellum is separated from the brain stem by the fourth ventricle. • The brain stem contains the midbrain, pons, and medulla oblongata. • Reticular formation is a complex network of nuclei and fibers extending the length of the brain stem.

23. Reticular Activating System

24. The Limbic System • Limbic system is a complex network of tracts and nuclei. • Blends primitive emotions and higher mental functions into a united whole. • Composed of hippocampus and amygdala.

25. Limbic System

26. Higher Mental Functions • Memory is the ability to hold a thought in mind or to recall events from the past. • Short-term versus long-term. • Skill memory. • Learning takes place when we retain and utilize past memories. • Language and speech depends on motor centers in the occipital and temporal lobes.

27. Language and Speech

28. Language and Speech • Left and right brain have different functions. • Left Hemisphere: • Verbal, Logical, Analytical, Rational. • Right Hemisphere: • Nonverbal, Intuitive, Creative.

29. Peripheral Nervous System • Composed of nerves and ganglia. • Cranial nerves take impulses to and from the brain. • Spinal nerves take impulses to and from the spinal cord.

30. Cranial and Spinal Nerves

31. Somatic System • Somatic system includes nerves that take sensory information from external sensory receptors to the CNS and motor commands away from the CNS to the skeletal muscles. • Reflexes are automatic responses to a stimulus.

32. Reflex Arc

33. Autonomic System • Autonomic system regulates the activity of cardiac and smooth muscles and glands. • Sympathetic division brings about fight or flight responses. • Parasympathetic division brings about relaxed responses.

34. Drug Abuse • Drugs that affect the nervous system have two general effects. • Impact limbic system. • Promote or decrease action of a particular neurotransmitter. • Drug abuse is apparent when a person takes a drug at a dose level and under circumstances that increase the potential for a harmful effect.

35. Drug Actions at a Synapse

36. Drug Abuse • Alcohol. • Nicotine. • Causes neurons to release dopamine. • Excess dopamine has reinforcing effect that leads to dependence. • Cocaine. • Prevents synaptic uptake of dopamine. • Continued use causes body to produce less dopamine.

37. Drug Abuse • Heroin. • Binds to receptors meant for endorphins. • Continued use causes body to produce fewer endorphins. • Marijuana. • Binds to receptor for anandamide. • Brain impairment?

38. Homeostasis • Governance of internal organs and the regulation of blood and tissue fluid usually takes place below the level of consciousness. • Heart Rate. • Breathing Rate.

39. Degenerative Nervous System Diseases • Alzheimer disease. • Presence of abnormal neurons. • Plaques. • Neurofibrillary tangles. • Parkinson disease. • Overactive basal nuclei due to the degeneration of dopamine-releasing neurons in the brain.

40. Review • Nervous Tissue • The Nerve Impulse • Action Potential • Central Nervous System • The Spinal Cord • The Brain • Peripheral Nervous System • Nerves and Ganglia • Drug Abuse • Degenerative Nervous System Diseases