The Nervous System

1. The Nervous System Anatomy & Physiology Chapters 7 & 8

2. Topics • Central Nervous System • Peripheral Nervous System • Special Senses

3. Central Nervous System Anatomy • Brain • Spinal cord • Nerves Physiology • Coordinate and integrate body activities. • The brain is the seat of intellect and reasoning.

4. General Organization of the nervous system

5. Neurons • Structural and functional unit of the nervous system.

6. Neurons • Dendrites – carry messages to the cell body • Axon – carries messages away from the cell body • Schwann cells – generate myelin (PNS) • Neuroglia (Glial cells) – insulate, protect, and support neurons

7. Neurons • Nuclei – clusters of cell bodies within the white matter of the central nervous system. • Ganglia – collections of cell bodies outside of the central nervous system. • Tract – connects one part of the nervous system with another; usually consists of bundles of myelinated neurons (white matter). (Bundles of nerve fibers)

8. Types of Neurons • Sensory (afferent) neurons • Carry impulses to the spinal cord and brain • Motor (efferent) neurons • Carry impulses away from the spinal cord and brain to the muscles and glands • Association neurons • Carry impulses from one neuron to another

9. Neuroglia (glial cells) • CNS neuroglia: • astrocytes • oligodendrocytes • microglia • ependymal cells • PNS neuroglia: • Schwann cells (neurolemmocytes) • satellite cells

10. Astrocytes • create supportive framework for neurons • create “blood-brain barrier” • secrete chemicals for embryological neuron formation • stimulate the formation of scar tissue secondary to CNS injury

11. Oligodendrocytes • create myelin sheath around axons of neurons in the CNS. • Microglia • “brain macrophages” • phagocytize cellular wastes & pathogens

12. Ependymal cells • line ventricles of brain & central canal of spinal cord • produce, monitor & help circulate CSF (cerebrospinal fluid)

13. Action Potential • Normal resting potential • Negative inside the cell, positive outside the cell • Depolarization • Positive inside the cell, negative outside the cell • Repolarization • Negative inside, positive outside • Action Potential • Action Potential and Epilepsy

14. Synapse • A message or impulse going from the axon of one cell to the dendrite of the next cell. • The space between is referred to as the synaptic cleft. • Axon releases a neurotransmitter and the message “jumps” across the synaptic cleft from one cell to the next.

16. The Brain • Located in the cranial cavity and is protected by the skull and meninges. • Divided into white and gray matter. • Meninges – three membranous coverings of the brain and spinal cord. • Dura mater – outer covering • Arachnoid – middle layer • Pia mater – inner covering • Cerebrospinal fluid – acts as a shock absorber and a source of nutrients for the brain.

17. The Brain • Cerebrum • Largest and highest part of the brain • Layer of gray matter that covers the upper and lower surfaces and is divided into two hemispheres • Each hemisphere is divided into four lobes • Frontal – motor area (controls voluntary muscles); speech area in left hemisphere • Parietal – sensory area • Occipital – visual area • Temporal – Auditory and olfactory areas

18. Figure 14.1d

19. Figure 14.1 The Adult Brain Figure 14.1b

21. Structures of the Brain • Thalamus – relay station from incoming and outgoing nerve impulses. • Hypothalamus – the “brain” of the brain; stimulates the pituitary gland to produce hormones. • Cerebellum – coordinates skeletal muscle activity.

23. Figure 14.2

26. Ventricles of the brain • Central passageway of the brain enlarges to form ventricles • Contain cerebrospinal fluid (CSF)

27. Ventricles of the Brain Figure 14.3a, b

28. The cranial meninges • Continuous with the three layers of the spinal cord • Folds of dura mater help stabilize the position of the brain • Falxcerebri • Tentorium cerebelli • Falxcerebelli

29. The Relationship among the Brain, Cranium, and Meninges Figure 14.4a, b

30. Cerebrospinal fluid (CSF) • CSF cushions delicate neural structures • Supports the brain • Transports nutrients, chemical messengers, and waste products • Pathway of CSF • Produced at the Choroid plexus, • Travels through the lateral and medial apertures to the subarachnoid space, • Diffuses across the arachnoid granulations into the superior sagittal sinus

31. Figure 14.5 The Circulation of Cerebrospinal Fluid Figure 14.5a, b

32. Blood supply to the brain • Blood brain barrier isolates neural tissue from general circulation • Incomplete barrier in areas • Parts of the hypothalamus • Pituitary gland • Pineal gland • Choroid plexus

34. Structures of the Brain • Brainstem • Pons – center for respiratory control; two-way conductive path for nerve impulses between the cerebrum, cerebellum, and other areas • Midbrain – reflex center; vision and hearing • Medulla oblongata – vital functions such as heart rate and breathing rate; swallowing and vomiting; vasoconstrictor for blood pressure

35. Structures of the CNS • Spinal cord • Begins at foramen magnum (hole in the base of the skull) and continues to the second lumbar vertebra. • Reflex center and conductive pathway to and from the brain. • 31 segments, each giving rise to a pair of spinal nerves.

36. Effects of Aging on the CNS • There is a general slowing of nerve conduction due to a decrease in the number of functioning neurons along with the degeneration of existing nerves.

37. Meningitis Encephalitis Epilepsy Cerebral palsy Poliomyelitis Hydrocephalus Parkinson’s disease Multiple sclerosis Essential tremors West Nile Virus Alzheimer’s disease Brain tumors Hematoma Spinal cord injury Traumatic brain injury Concussion Cerebrovascular accidents Transient ischemic attacks Homeostatic Imbalances

38. Peripheral and Autonomic Nervous Systems • Peripheral Nervous System - All the nerves of the body (cranial and spinal) • Controlling the involuntary activities of the body • Reflex center of the body • Autonomic Nervous System • Sympathetic nervous system – Exercise, Excitement, Emergency, Embarrassment • Parasympathetic nervous system – Digestion, Defecation, and Diuresis (urination)

40. Cranial and Spinal Nerves • Cranial nerves • Begin in the brain • Concerned mainly with the action of the head and neck • 12 pairs • Spinal nerves • Originate at the spinal cord • Carry messages to and from all parts of the body • 31 pairs