The Nervous System

1. The Nervous System Introduction • Nervous control vs. endocrine control of the body • What does the nervous system do? • Receive, process, store sensory information • Integrate and interpret • Stimulation of skeletal muscle • Stimulation/inhibition of smooth and cardiac muscle • Stimulation/inhibition of glands • cognition

2. The Nervous System Introduction • 3. Why is the nervous system of prime importance to understanding aging effects on the body? • It controls virtually all body functions • Neurons are postmitotic – why is this important?

3. The Nervous System B. Cells of the nervous system • Neurons • Basic structure • Cell body • Dendrites • Axon • Fiber vs. nerve • What is myelin?

4. The Nervous System B. Cells of the nervous system • Neurons • d. Types of neurons • Motor • Sensory • Association (interneuron) • What is a center? • What is a ganglion?

5. The Nervous System B. Cells of the nervous system • 2. Neuroglia (glial cells) • Support cells of the nervous system • Greatly outnumber neurons • Types of cells • Astrocytes (CNS) • Oligodendrocytes (CNS) • Microglial cells (CNS) • Ependymal cells (CNS) • Neurolemmocytes (Schwann cells) (PNS)

6. The Nervous System C. Membrane potentials • What is a polarized membrane? • How is it formed? • What are voltage-gated channels? • Resting potential vs. action potential • Continuous conduction • Saltatory conduction

7. The Nervous System D. The synapse • Presynaptic neuron • Synaptic cleft • Postsynaptic neuron • Excitatory neurotransmitters • Acetylcholine • Norepinephrine • c. Dopamine • d. Serotonin • 5. Inhibitory neurotransmitters • Gamma aminobutyric acid (GABA) • Glutamate

8. The Nervous System E. Organization of the nervous system • Sensory • peripheral nervous system • Motor • peripheral nervous system • Central nervous system • Brain • Spinal cord • Somatic motor neurons (voluntary) to skeletal muscles • Somatic receptors • Visceral receptors • Special sensory receptors • Sympathetic and parasympathetic nervous systems • Autonomic motor neurons (involuntary) to smooth muscle, cardiac muscle, and glands • Sensory receptors and neurons in the gut • Enteric motor neurons (involuntary) in gut to smooth muscle and glands

9. The Nervous System F. Central nervous system • Brain and spinal cord • Meninges • Dura mater • Arachnoid membrane • Pia mater

10. The Nervous System F. Central nervous system • 3. Cerebrospinal fluid • Subarachnoid space • Ventricles and central canal • Flow pattern

11. The Nervous System F. Central nervous system • 4. Cerebrum (white and gray matter) • Hemispheres and lobes • Gyrus – sulcus – fissure • Cerebral cortex • Functional areas • Primary sensory areas • Primary motor areas • Association areas • f. Basal ganglia (cerebral nuclei)

12. The Nervous System F. Central nervous system • Cerebellum (white and gray matter) • Diencephalon (gray matter) • Thalamus • Hypothalamus • Epithalamus • 7. Brainstem (white and gray matter) • Midbrain • Pons • Medulla oblongata

13. The Nervous System F. Central nervous system • 8. Spinal cord (white and gray matter) • Regions • Cervical • Thoracic • Lumbar • Sacral • Coccygeal

14. The Nervous System F. Central nervous system • 8. Spinal cord • b. Cross-sectional anatomy • Horns • Dorsal = sensory nuclei • Ventral = motor nuclei • ii. Roots • Dorsal = sensory axons • Ventral = motor axons • iii. Tracts • Ascending • Descending

15. The Nervous System F. Central nervous system • 8. Spinal cord • c. What is a reflex? • Inborn • Unconscious • Unlearned • d. Reflex arc components • receptor  sensory neuron  • integration center  • motor neuron  effector

16. The Nervous System G. Peripheral nervous system • Cranial nerves (12 pairs) • Spinal nerves (31 pairs)

17. The Nervous System G. Peripheral nervous system • 3. subdivisions • Afferent • Somatic sensory from skin, joints, skeletal muscles • Visceral sensory from organs • b. Efferent • Somatic (voluntary) motor to skeletal muscles • Autonomic (involuntary) motor to cardiac muscle, smooth muscle, glands • Sympathetic nervous system • Parasympathetic nervous system

18. The Nervous System G. Peripheral nervous system • 4. Autonomic nervous system sympathetic parasympathetic • Dual innervation • Antagonistic • Sympathetics • Thoracolumbar • Fight-or-flight • d. Parasympathetic • Craniosacral • Feed- and-breed

19. The Nervous System H. Age-related changes • Nerve cells die with aging (~10,000 per day) • Neurons do not undergo mitosis • Therefore, lost neurons are not replaced • Nervous tissue is gradually reduced • 2. Other neuronal changes • Axons swell • Myelin diminishes • Cytoskeleton decreases in abundance

20. The Nervous System H. Age-related changes • Why does routine loss of neurons not affect function until very late in life? • Loss of neurons + loss of myelin = decreased brain mass • Decrease isn’t uniform throughout brain • 25% loss of cerebellum; other areas lose nothing • Decline is size begins slowly at age 30, much faster at age 60; 10% gone by age 90 • Ventricles enlarge, gyri become smaller, sulci widen

21. The Nervous System H. Age-related changes • 5. Loss of brain mass = loss of learning new skills • What functions tend to have greater decline? • Response times in reflexes • Integration of things observed • Alertness (brain reactivity time) • b. What functions do not decline as quickly? • Verbal ability • Memory

22. The Nervous System H. Age-related changes • 6. Some neurons sprout new axons and establish new synapses • New synapses = net increase in connections • Learning requires development of new synapses • 7. However, there is age-related decline in IQ test scores • Thought to be associated with neuronal loss • Elderly may have as much as 25% loss in verbal ability • Wide range of individual variability

23. The Nervous System H. Age-related changes • 8. Memory is affected by age • Long-term memory least affected • Higher intellects retain better memory • Active brains retain memory longer • Decreased rate of nerve impulse conduction • Increased synaptic delay • Decreased neurotransmitter released • Decreased postsynaptic receptors

24. The Nervous System H. Age-related changes • Reduced dendrites and dendritic spines • Intracellular neuronal changes • Decreased Nissl substance (ribosomes) • In the hippocampus, particularly: • Neurofibrillary tangles • Neuritic plaques • 13. Glial cell changes

25. The Nervous System H. Age-related changes • 14. Changes in sympathetic nervous system activity • Increased norepinephrine secretion + • Decreased removal of norepinephrine at the synapse + • Decreased norepinephrine receptor sensitivity • 15. Changes in parasympathetic nervous system activity

26. The Nervous System I. Age-related dysfunctions • Decreased somatic reflex responses • Declining autonomic reflex responses • Body temperature control • Blood pressure control • Urethral and anal internal sphincter control • 3. Insomnia • REM vs. non-REM sleep • Difficulty falling asleep + frequent awakenings • Reticular activating system dysfunction

27. The Nervous System I. Age-related dysfunctions • 4. Dementia (organic brain syndrome) • What is it? • Reversible vs. irreversible • Categories • Alzheimer’s disease • Non-Alzheimer’s disease • Multi-infarctional dementia • Parkinson’s disease • Cerebrovascular accident (stroke)

28. The Nervous System J. Take home messages • What are the divisions of the nervous system and how are they communicated together? • What is the basic structure and function of the neuron? • Neurons die with aging and aren’t replaced • Conduction velocities decrease with aging • Synaptic delay increases with aging • Reflex times increase with aging • Many intracellular changes with aging • What are dementias? end