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

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?

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

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?

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)

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

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

The Nervous System E. Organization of the nervous system Sensory peripheral nervous system Motor peripheral nervous system Central nervous system Brain Spinal cord Somatic receptors Somatic motor neurons (voluntary) to skeletal muscles 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

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

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

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)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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)

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