The Nervous System

1. The Nervous System Functions, Structures and the Classification of Neurons http://www.alz.org/brain/01.asp

2. FEATURES • Composed of unique tissue which is both responsive and conductive (messages can travel at least 200 mph) • Pinpoint control (targets specific tissues in body) • The most intricately organized matter on Earth (1cm3 Brain = Several million neurons)

3. Organs of the Nervous System • Central Nervous System (CNS) • Brain & Spinal Cord • Peripheral Nervous System (PNS) • Cranial Nerves & Spinal Nerves

4. Nervous System PNS CNS Motor(efferent neurons) *messages from CNS to muscle or glands Sensory (afferent neurons) *incoming messages to CNS *senses external and internal environment Autonomic Somatic Effectors: smooth muscles, cardiac, glands: unconscious control Effectors: skeletal muscles: conscious control Parasympathetic Sympathetic • *fight or flight • Arousal or energy generation • Increase heart &respiratory rate • *NT: norepinephrine *Maintains homeostasis: self-maintenance fxns (calming affect) *NT: AcH

7. Structural Classification • Multipolar • Many processes/extensions but only one is an AXON • Abundant in CNS • Bipolar • ? Extensions; one is still the axon • Abundant in eyes, nose and ears • Unipolar • ? Extension; forms central and peripheral processes

11. General Functions of the Nervous System • Sensory • Integrative • Motor

12. FUNCTIONS • Sensory Input - Conduction of signals from receptors to integration center (eyes) • Integration - Process by which info. from environment is interpreted & associated with appropriate response of the body • Most occurs in CNS (brain & spinal cord) • Motor Output - Conduction of signals from CNS to effector cells (muscles or glands) that actually carry out response to stimulus

13. Integrative Function • CNS • Type of neuron it occurs in: interneuron • Stimulated by: NT-neurtotransmitter • Released by a sensory neuron • Receptive portion: dendrites • Involves interpretation of an incoming sensory impulse • Begins a motor impulse from dendrites down axon into terminal end of the axon

14. Sensory Input Function • PNS • Type of neuron: sensory neuron (afferent) • Sensory Receptors(receptive portion) detect changes occurring in their surroundings at end of dendrites • Stimulated by: light, temp change, etc • Once stimulated, sensory receptors transmits a sensory impulse to the CNS • Sensory impulse is carried on a sensory neuron from dendrites through cell body down axon to synaptic knobs

15. Motor Function • PNS • Type of neuron it occurs in: motor neuron (efferent) • involves the response of a body part • Motor impulses are carried from CNS to responsive body parts called effectors • Stimulated by: NT released by interneurons • Effectors • Muscles (contract) • Glands (secrete a hormone)

16. Cells of the Nervous System • There are 2 main classes of cells: • A. Neurons - conduct messages • Common Features • Cell body (contains nucleus & other organelles…no centrioles???) • Dendrites (conveys signal to cell body) • Axons (conduct messages away from cell body) • Myelin Sheath (insulation layer composed of Schwann Cells) • Synaptic Terminal (relays signals to other cells by releasing neurotransmitters) • Synapse (site of contact between terminal & target cell) • Nodes of Ranvier (gaps in myelin, voltage channels)

17. B. Supporting Cells - protects, insulates, and assists neurons (Outnumber neurons 10-50 times) • Do not conduct impulses, but are essential for the integrity of nervous system • Supporting Cells are called “Glial Cells” (glue) • Several Types • Astrocytes - encircles capillaries in brain, restricts passage of substances into brain • Oligodendrocytes - form insulating myelin sheaths around axons in neurons of CNS 3. Schwann Cells - form insulating myelin sheaths around axons in neurons of Peripheral nervous system • Myelin Sheaths - jelly roll composed of lipid (poor conductor) • Multiple Sclerosis = degenerative disease of myelin sheaths (What symptoms would you expect to see?)

18. Histology of the Neuron 1. Cell Body 2. Dentrites 3. Axon • One per neuron • Long, thin processes with uniform diameter • carry impulses away from cell body • Many fine extensions at end called collaterals • Axon ending= at ends of collaterals contain synaptic knob (comes in contact with receptive surface of another cell)

19. Histology of the Neuron Different types of Axons • Axons in PNS • Large and surrounded by myelin sheath (made of lipids) • Contains Schwann Cells • Myelinated nerve fibers/ produce the myelin • Between each Schwann cell is a space called Nodes of Ranvier • Small axons • Lack myelin sheath • However all axons are associated with Schwann cells

20. Histology of the Neuron • Axons in CNS • Myelin is produced by oligodendrocyte NOT schwann cells • Myelinated nerve bundles are referred to as white matter • Gray matter • Unmyelinated nerve fibers

21. Histology of the Neuron Regeneration of Nerve Fibers • Injury to cell body: dead neuron • Injury to axon: possible regeneration

22. Histology of the Neuron Neuroglial Cells accessory cells of the nervous system form the supporting network for neurons (nerve glue) • PNS= Schwann • CNS= 4 types • Oligodendrocytes • Looks like an eye balls; produces myeline • Astrocytes • Nourishes neurons • Microglia • Looks like spider; phagoctosis • Ependyal cells • Epithelial like layer • Functions to line spaces in CNS

23. Classification of the Neuron • Neurons of classified based on • Function • Structure

24. Functional Classification • Sensory neurons • PNS • Afferent neurons: carry sensory impulses from sensory receptors to CNS • Location: skin and sense organs • Interneurons • CNS • Links other neurons together • “Association” • Motor • PNS • Efferent neurons; carry motor impulses away fron CNS and to effectors • Effectors: muscles and glands (involuntary and voluntary controls)