The Nervous System (Pgs. 184-196)

1. The Nervous System(Pgs. 184-196)

2. The Nervous System • Organs of the nervous system are divided into • Central Nervous System (CNS) • Peripheral Nervous System (PNS)

3. Functions of the Nervous System • Sensory • Integrative • Motor

4. Functions of the Nervous System • Sensory functions detect changes • Sensory receptors at the end of peripheral nerves detect changes inside/outside of the body • External – light, sound touch Internal – pH levels, oxygen/carbon dioxide concentrations • Information gathered is converted to nerve impulses of the PNS which sends the information to the CNS

5. Functions of the Nervous System • Integrative functions bring sensory information together and makes decisions that are acted upon by using motor function

6. Functions of the Nervous System • Motor functions are responses to sensory information • Employ peripheral nerves that carry impulses from CNS to responsive parts called effectors • Effectors are outside the NS and include a. Muscles – contract when stimulated b. Glands – secrete hormones when stimulated (glandular epithelial tissue)

7. Glandular Epithelium

8. Functional Organization

9. Anatomical and Functional Organizaton

10. Nervous Tissue • Neurons (nerve cells) are the functional unit; • Specialized to react to physical & chemical changes in their surroundings and conduct nerve impulses • Neuroglia support the physiological needs of neurons • Fig. 8-2, 8-3, 3-21 pg. 70

11. Anatomy of a Neuron

12. Anatomy of a Neuron • dendrite – provide receptive surfaces to carry impulses toward cell body; relatively short & highly branched • cell body – contains various organelles • axon – a single axon arises from cell body; transmit impulses away from the cell body; some are surrounded by specialized glia cells called Schwann cells that form myelin sheath http://www.viddler.com/explore/annette/videos/7/

13. Functional Differences of Neurons • motor neurons – transmit impulses form brain to an effector (efferent neurons) (multipolar) • sensory neurons – transmit impulses to spinal cord & brain (afferent neurons) (most unipolar, some bipolar) • interneurons – carry impulses from sensor neurons to motor neurons (multipolar)

14. Refex Arc

15. Structural Differences of Neurons • bipoloar – only 2 nerve fibers, one arising from either end; found in specialized parts of the eyes, nose, & ears

16. Structural Differences of Neurons • unipolar/monopolar – single nerve fiber extending from its cell body; found in ganglia outside the brain or spinal cord

17. Structural Differences of Neurons • multipolar – many nerve fibers arising from their cell bodies; most common type of neuron in the brain & spinal cord (ganglia – a mass of neuron cell bodies, usually outside the CNS)

18. Neuroglia Cells • Accessory cells – Schwann cells, astrocytes, microglia, oligodendrocytes, ependymal (We will discuss the functions of each of these types of cell during the lab.) • Fill spaces, support neurons, hold nervous tissue together; play a role in the metabolism of glucose, help regulate K+ concentration, produce myelin, and carry on phagocytosis • Fig. 8-3

19. Types of Neuroglia Cells

20. Regeneration of Nerve Fibers • If a neuron cell body is injured, the neuron is likely to die • If the axon of a peripheral nerve fiber is severed, its distal portion will die, but the proximal portion may regenerate & re-establish its former connections • Significant regeneration is unlikely to take place in the CNS

21. Structure of Peripheral Nerves – consists of bundles of nerve fibers surrounded by connective tissue – Fig. 8-4 • Epineurium – outermost layer; dense and include many collagenous fibers • Fasicicle – a bundle of nerve fibers • Perineurium – less dense connective tissue surrounding fascicle • Endoneurium – small amount of loose connective tissue that surrounds individual nerve fibers

22. Cell Membrane Potential and Nerve Impulses – Fig. 8-6 & 8-7

23. Resting Potential • http://www.dnatube.com/video/5035/Neuron-Resting-Potential

24. A cell membrane is usually electrically charges or polarized so that outside is + and inside is - • Resting Potential (-70 mvolts) • Nerve cell is not conducting impulses • [Na+] is greater on the outside of the cell and [K+] is greater on the inside of the cell • There is a large number of negatively charged ions inside the cell which can’t diffuse out • At rest inside stays negative because K+ can diffuse easily out of the cell through open channels; Na+ can’t diffuse as easily into cells through “their” protein channels • Na+ /K+ pump (active transport) – maintains system so equilibrium is not reached; therefore, Na+ is always being pumped back out and K+ is being pumped back in

25. Local Potential Changes

26. Local Potential Changes • Stimulation of a membrane affects its resting potential in a local region (light, temp., other neurons • Membrane starts to become depolarized (moves toward zero) • Threshold potential is reached which causes an action potential

27. Action Potential • http://www.dnatube.com/video/1105/Understanding-Action-Potential-and-Nerve-Impulses

28. Action Potential 1/1000 sec. or less • At threshold, Na+ channels open and Na+ diffuse inward causing depolarization • About the same time K+ channels open and K+ diffuses outward, causing repolarization • This rapid change in potential is an action potential • Many action potentials can occur before an active transport mechanism re-establishes the original resting potential • The propagation of actions potentials along a nerve fiber is an impulse

29. Refractory Period • Refractory Period • A brief time (10-30 m/sec.) following the passage of a nerve impulse when the membrane is unresponsive to ordinary stimuli • Membrane must return to resting potential before it can be stimulated again • All – or – None Response • If a nerve fiber responds at all, it responds completely • All impulses carried on that fiber will be of the same strength

30. Coding & Interpretation of Messages • Frequency of action potentials – a weak stimulus initiates only a few action potentials/sec., a strong stimulus initiates many (upper limit because of refractory period) • Duration of a burst of action potentials – a weak stimulus may give rise to a short burst of pulses in the neuron, a strong stimulus a longer burst • Number & kinds of neurons firing – The threshold needed to initiate a nerve impulse varies from one neuron to another. Thus a weak stimulus will cause only a few neurons to fire, strong will fire all of these neurons, plus others with higher thresholds.

31. Impulse ConductionMyelinatedvsUnmyelinated

32. Impulse Conduction • Unmyelinated fibers conduct impulses that travel over their entire surface • Myelinated – impulses travel from node to node • Impulse conduction is more rapid on myelinated fibers with large diameters • http://www.youtube.com/watch?v=DJe3_3XsBOg

33. The Synapse – The junction between 2 neurons. A synaptic cleft is the gap between parts of two neurons at a synapse. Fig. 8-7 • Impulses usually travel from a dendrite or cell body, then along the axon to a synapse • Axons have synaptic knobs at their distal ends that secrete neurotransmitters • The neurotransmitter is released when a nerve impulse reaches the end of an axon and the neurotransmitter diffuses across the synaptic cleft. • When the neurotransmitter reaches the nerve fiber on the distal side of the cleft, a nerve impulse is triggered.

34. The Synapse • http://www.dnatube.com/video/261/Neural-Synapse

35. Nerve Pathways – the route followed by an impulse as it travels through the nervous system, Fig. 8-5 • Reflex Arc – simplest nerve pathway • A reflex arc usually includes a sensory neuron, a reflex center composed of interneurons, and a motor neuron • Reflex arc is the behavioral unit of the nervous system • Reflex Behavior • Reflexes are automatic unconscious responses to changes • Help maintain homeostasis • Knee jerk – 2 neurons • Withdrawal reflexes are protective actions

36. Reflex Arc • http://www.youtube.com/watch?v=Y5nj3ZfeYDQ&feature=related