Nervous System

1. Patrick Yerkes Nervous System

2. Introduction • The nervous system carries information from one part of the body to another • The nervous system transmit information by nerve impulses to communicate with other parts of the body • Main parts of the nervous system are the: Brain, Spinal Cord, and Nerves • Regulate homeostasis and responds to disease

3. Organs and Divisions of the Nervous System • Central Nervous System (CNS) • Occupies the midline or central part of the body • Peripheral Nervous System (PNS) • Nerves extend to the outlying or peripheral part of the body • Autonomic Nervous System (ANS) • Regulate the body’s involuntary functions

4. Cells of the Nervous System Two types of cell: Neurons Nerve cells Conduct nerve impulses Gila Specialized connective tissue cells Support neurons

5. Neurons • Neurons consist of three parts • Cell body- main part of the neuron • Dendrites- branching projections of the neuron • Processes that transmits impulses to the cell bodies • Axon- elongated projection • Transmits impulses away from the cell body

6. Transmitted Impulses • 3 main types of neurons • Sensory- Transmits impulses to the spinal cord and brain from all parts of the body. Also called Afferent. • Motor- Transmits impulses away from the brain or spinal cord. Only conduct impulses to two kinds of tissues (muscle and glandular epithelial). Also call Efferent. • Interneuron- conduct impulses from the sensory neurons to motor neurons. Also call Central or Connective Neurons

7. Neurons continued • Myelin is a white fatty substance formed by a Schwann Cells that wrap the axons around the CNS • The fibers are called Myelinated Fibers • Nodes of Ranvier are indentations between nearby Schwann Cells • The outer cell membrane is the Neurilemma • Axons in the brain and spinal cord do not have Neurilemma and decreases healing or regeneration

8. Gila • Also called- Neuroglia • Do not specialize in transmitting nerve impulses • Are support cells • Greek word Gila means “glue” • Holds the functions neurons together and protect them • Regulates nerve function • Common brain tumor is called Glioma

9. Gila continued • Gila can be different in size • Large cells that look somewhat like star from their thread like extensions are called- Astrocytes • Microglia- are the smaller cells, they remain stationary • When inflamed or degenerating brain tissue they will enlarge and act as micro scavengers • Eat other micros

10. Gila continued • Oligodenrocytes- hold nerve fibers together and serve a more important function which is to produce fatty myelin sheath that envelops nerve fibers located in the brain or spinal cord

11. Nerves • Nerve- is a group of peripheral nerve fibers bundles together • Peripheral nerve fibers usually have myelin sheath • Often look white • Bundles of axons in the CNS are called tracts • The axons could be myelinated and forming white matter • Unmyelinated axons and dendrites are called grey matter for being grey

12. Nerves End • Each axon in a nerve is surrounded by thin wrapping fibrous connective tissue called ‘endoneurium’ • Groups of endoneurium are called ‘fascicles’ • Each fascicle is surrounded by a thin fibrous ‘perineurium’ • A tough fibrous sheath is called a ‘epineurium’ which covers the whole nerve

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14. Reflex Arcs • Some nerve impulses are called ‘Action Potentials’ • Can travel over trillions of routes • Neurons create the paths • Routes named Neuron Pathways • Reflex Arcs are one way streets, the impulse can only go one way

15. Reflex Neurons • A specialized type of neuron pathway is called the ‘reflex arc’ • The simplest kind of reflex arc is a two- neuron arc • Consist on only 2 types of neurons: Sensory and Motor neurons • Three- neuron arc is the next simplest arc • Consist of all 3 neurons: Interneurons, Motor, and Sensory

16. Reflex Arc: Receptors • Are the beginnings of dendrites of sensory neurons • Often away from the spinal cord mostly located in; (in tendons, skin, or mucous membranes) • Sensory receptors are located in the quadriceps and the patellar tendon • Reflex response for the patellar tendon which is the rubber hammer and creates a knee- jerk • Example of a two- neuron arc

17. Reflex Arc: Ganglion • A group of nerve- cell bodies located in t he PNS • Near the Spinal cord • Each spinal ganglion contains no sensory neuron • The axon of the sensory neuron travels from the cell body in the dorsal root ganglion • Ends in the dendrites of another neuron in the grey matter

18. Reflex Arc: Continued • A microscopic space that separates the axon ending with one neuron from the dendrites to another • This is called a Synapse • Nerve impulse stops at the synapse • The neuron axon forms a synapse called the ‘effectors’ • Organs put the nerve signals to effect

19. Reflex Arc: Effectors • Effectors are the muscles and glands • Muscles contract • The glands secretion • Only kind of reflexes by these effectors • A response to impulse conduction on the reflex arc is called a reflex

20. Reflex Arc: Interneuron • Some neurons need 3 neurons • More complex involves one more sensory and motor neuron • In the 3 neuron reflex • End of the sensory neurons’ axon synapses first with a interneuron • Before chemical signals are sent to a second synapse • Ending up with a conduction motor neuron

21. Reflex Arc: Example • Applying an irritating stimulus to the skin of the thigh • It creates a 3- neuron reflex response • Causes contractions of the muscles to pull away from the leg away from the irritant • 3 neuron contraction is also called a - withdrawal reflex

22. Reflex Arc: Interneurons Continued • All interneuron's’ lie entirely within gray matter of the brain or spinal cord • Grey matter forms the ‘H’ shaped inner core of the spinal cord • 3 neuron reflex has 2 synapses • 2 neuron reflexes has 1 synapses between a sensory neuron and the motor neuron

23. Reflex Arc: Identify ID motor neuron Look at its dendrites and cell body Located in spinal cord Dies in the muscles

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25. Nerve impulse: Introduction • A nerve impulse is a self- propagation wave of electrical disturbance that travels along the surface of a neuron’s plasma membrane. • Example • A Spark going to fuse

26. Nerve Impulse: Neuron • First they have to be stimulated ( a change in the neuron’s environment) • Temperature, Pressure, and chemical changes are used as stimuli • Membrane of a resting neuron has a slight positive charge on the outside and a negative charge on the inside • This occurs from excessive amounts of sodium ions (NA+) on the outside of the membrane

27. Nerve Impulses: Neuron continued • When the section of the neuron is stimulated and the channels open • The sodium ions (NA+) flood inside • Causing the membrane to become positive temporarily and then becomes negative • The neuron immediately recovers the electrical disturbance stimuli (Na+) • If a impulse is traveling interacts with a section of a membrane insulating myelin • ‘jumps’ around the myelin called ‘saltatory conduction’ • Saltatory Conduction can travel much faster then the nonmyelinated sections

28. Saltatory Conduction

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30. Synapse: Introduction • By definition a synapse is a place where impulses are transmitted from one neuron called presynaptic neuron to another postsynaptic neuron. • The presynaptic and postsynaptic neuron makes up the synapse

31. Synapse: Structures • Three structures of the synapse is: a synaptic knob, a synaptic cleft, and the plasma membrane of a postsynaptic

32. Synapse: Synaptic Knob • Is a tiny bulge at the end of the terminal branch of a presynaptic neuron’s axon • Each synaptic knob has many small sacs or vessels • Each vessel contains a very some quantity of a chemical compound called a neurotransmitter • After the nerve impulse arrives at the synaptic knob neurotransmitters molecules are released from the vesicles into the synaptic cleft

33. Synapse: Synaptic Cleft • Is the space between the plasma membrane (of the postsynaptic neuron) and the synaptic knob • About 2 millionths of a centimeters in width • Has protein molecules embedded in opposite synaptic knobs • The receptors and neurotransmitters bind • The binding can cause an impulse in the postsynaptic neuron by opening the ion channels in the postsynaptic membrane

34. Synapse: Neurotransmitter • Neurotransmitters -Chemicals help neurons communicate • Around 30 different compounds have been identified as neurotransmitters • Neurotransmitters are did sent randomly • They are localized in certain types of neuron groups and released in specific pathways

35. Synapse: Neurotransmitter Sub Groups Acetylcholine catecholamine Includes Norepinephrine Dopamine Serotonin All three of these transmitters play a role for Sleep Motor function Mood Pleasure recognition • Released in certain areas in the Spinal Cord • Also in the neuromuscular junctions • Also called nerve- muscle

36. Synapse: Sub Groups

37. Synapse: Pain Killer (Neurotransmitters) • 2 ‘morphine’ like N.transmitters are called endorphins and enkephalins • Released in multiple areas in the spine and brainin the pain conduction pathways • Are natural pain killers • Endorphins are released mainly in intense exercise • Pain is normally used as a warning sign that draws our attention to injuries • Hold back against severe pain because it can stop us from continuing an activity that is needed for survival

38. Activities to help relieve pain

39. Synapse: Nitric Oxide • Unlike other transmitters Nitric Oxide diffuses directly across the plasma membrane • Rather then being released in the vesicles • Nitric Oxide is important for the male sexual response to create a penile erection • Drugs like Viagra (sildenafil) treats MED or Male Erectile Dysfunction by promoting the Nitric Oxide response

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