The Nervous System

1. Central Nervous System (CNS) Peripheral Nervous System (PNS) The Nervous System

2. Functions • Sensory input: monitors internal and external environments • Integration: processes & interprets sensory information • Motor Output: Coordinates voluntary and involuntary responses of effector organs • 2 subdivisions: • CNS – brain and spinal cord (dorsal body cavity) • Integration, Intelligence, memory, emotion • PNS – all other neural tissue • Cranial nerves and Spinal nerves • sensory, motor

3. Give an example Include: • sensory input • integration • motor output

4. Receptors and Effectors • Receptors – receive sensory info • Afferent division – carries info from receptors to the CNS (somatic & visceral) • Efferent division – carries info from CNS to PNS effectors (muscles, glands, adipose) • Somatic Nervous System (SNS) • Controls skeletal muscles (voluntary) • Autonomic Nervous System (ANS) • Controls involuntary actions • Sympathetic Division (increase heart rate) • Parasympathetic Division (decreases heart rate)

6. The sensory part of the PNS is... • Somatic division • Sympathetic division • Afferent division • Efferent division

7. The fight or flight response is the... • Somatic division • Sympathetic division • Afferent division • Efferent division

8. Neurons • Communicate w/other neurons • Large Complex Cells: • Soma -cell body • Dendrites-receive info • Axon -sends signal to synaptic terminals as nerve impulse • Synapse – site of neural communication (gap) • Special characteristics: • Extreme longevity (100 years +) • Amitotic – lose ability to divide (G0) • High metabolic rate – O2 & glucose

9. Cell Body AKA Soma • Biosynthetic center • Outgrowth of neuron processes during embryonic development • Lacks centrioles • Nissil bodies – Rough ER stains darkly • Nuclei - Clusters of cell bodies in CNS • Ganglia - Clusters of cell bodies in PNS

10. Processes • Armlikeprocesses - extend from cell body • Tracts - Bundles of neuron processes in CNS • Nerves - Bundles of neuron processes in CNS • Dendrites • Convey graded potentials towards cell body • Short and branching receptive regions • Dendriticspines -bulbous ends that form synapses • Axon (single) • Generates and transmits nerve impulse away from cell body • Axon hillock – cone shaped area where axon extends from soma • Nerve fiber – long axon (as long as 4 feet!) • Axon collaterals – occasional 900 branch • 1,000 - 10,000+ Terminal branches w/ Axon terminals (synaptic knobs) • Myelin Sheath • Protein-lipid electrical insulation on axons • Increases speed of transmission • Neurilemma – exposed plasma membrane of Schwann cell • Nodes of Ranvier – gaps in the myelin sheath (widely spaced in CNS)

11. Structural Classification of Neurons • Multipolar • multiple dendrites & single axon • motor neurons • most common in humans • Bipolar • 2 processes: one dendrite and one axon • cell body between them • Rare: special senses (retina & olfactory) • Unipolar • 1 continuous dendrites & axon • cell body lies to side • sensory neurons (ganglia of PNS)

12. Functional Classification of Neurons • Sensory– afferent division • info about surrounding environment • position/movement skeletal muscles • digestive, resp, cardiovasc, urinary, reprod, taste, and pain • Mostly unipolar (some bipolar in special senses) • Motor – efferent division (response) • skeletal muscles • cardiac and smooth muscle, glands, adipose tissue • Mostly multipolar • Interneurons • Integration • Brain and spinal cord - memory, planning, and learning • Mostly multipolar

13. Neuroglia of PNS • Regulate environment around neurons, smaller & outnumber neurons • 2 Types in PNS: • Satellite Cells • Surround neuron cell bodies of NS • Function unknown • Schwann Cells • Surround nerve fibers of PNS • Secrete myelin sheath

14. Neuroglia AKA Glial cells • 4 types inCNS: • Astrocytes(most common in CNS) • Radiating processes connect to capillaries • Control chemical environment • Microglia • Ovoid shape w thorny processes • Moniternueron health • Can turn into macrophages • Ependymal • Range shape from squamour to columnar, usually ciliated • Circulate CSF • Oligodendrocytes • Wrap around nueron fibers & produce myelin

15. The most common type of neuron is • multipolar • bipolar • unipolar

16. The part of the neuron that has receptor proteins on its surface is • Dendrites • soma • axon • Myelin sheath

17. Action Potential & WKBK

18. Neurophysiology • Basic Electrical Principles • Voltage • measure of electrical charge (mV = 1/1000 V) • potential difference measure between two points • Current – flow of electrical charge from one point to the next, used to do work

19. Membrane ion channels review • Membrane proteins that allow specific type of ion(s) to pass • Electrochemical gradient: ions move with concentration gradient and along electrical gradients (towards opposite charge) • Chemically (Ligand) gated channels • Open when appropriate chemical (neurotransmitter) binds • Voltage gated channels • Open and close in response to changes in membrane potential • Mechanically gated channels • Open in response to physical deformation • Non-gated (leakage) channels • Always open

21. Resting Membrane Potential • -70mV (inside of cell is negatively charged in comparison to the outside of the cell) • Is said to be polarized due to difference of ionic concentrations of intracellular and extracellular fluids • Cytosol has low concentrations of Na+, and high conc of K+ • K+ ions diffuse out of leak channels causing the cell to be neg inside (more than Na+ leak in) • Na+/K+ pumps stabilizes the resting membrane potential

22. Graded potentials • Incoming signals over short distance • Decrease in magnitude with distance • Magnitude dependent upon stimulus • Stimulus causes gated channel to open • Receptor potential – heat, light, or other form of energy • Post-synaptic potential – neurotransmitter • Current carried by ions thru fluid in/out of cells • Positive ions move towards neg areas and vice versa • K+ ions move away from depolarized area and accumulate in neighboring membrane areas neutralizing neg ions • Meanwhile positive ions move towards depolarized regions being momentarily replaced by neg ions (Cl- or HCO3-), then causing the neighboring membrane to depolarize • The plasma membrane is “leaky” and charge is quickly lost and dissipates quickly

24. Action potentials AKA nerve impulse • Long distance signals of axons (do not decrease) • Only cells w/excitable membranes (neurons & muscle) • Transition from graded potential to action potential at the axon hillock • Brief reversal of membrane potential (-70mV  +30mV) • Depolarization • reduction in membrane potential (less negative) • Hyperpolarization • Increase in membrane potential (more negative)

25. Generation of Action Potential • Resting State – all voltage gated Na+ and K+ gated channels closed • Depolarizing phase – Na+ channels open (increasing + charge…opening more Na+ channels) • Critical Threshold reached at -60 to -50mV and becomes self-generating (+ feedback) • Until all Na+ channels open and membrane potential reaches +30mV • Repolarizing phase – internal negativity restored • Na+ channels close, Na+ stops entering cell • Potassium channels open, K+ leaves cell w/electrochemical gradient • Hyperpolarization • K+ channels remain open temporarily • Na+ channels reset to their original position • Note: electrical conditions restores not ionic conditions, ionic distribution is restored by 1,000’s of Na+/K+ pumps in axon membrane

27. Propagation of Action Potential • Action potential propagates (is transmitted) away from its point of origin towards the axon terminals • Threshold – unstable equilibrium state • Weak stimuli – generate subthresholddepolarizations that do not generate AP • AP is an ALL or NONE Phenomenon • Once AP is generated all alike

28. Action Potentialmyelinated vs. unmyelinated

29. Refractory period - When neuron membrane is generating AP and Na+ channels are open, neuron can NOT respond to any other stimulus • Conduction velocity – rate of propagation depend on • Axon diameter – the bigger the faster • Degree of myelination (insulation – preventing leakage) • Continues conduction - unmyelinated conduction is relatively slow • Saltatory conduction – AP triggered only at nodes where Na+ channels are located (30x faster!) • Nerve Fiber Classification • Group A – somatic sensory & motor (300mph) • Group B & C – viscera sensory, ANS fibers to viscera, and skin sensory (40mph – 2mph)

30. An excitatory neurotransmitter • Increases electrical impulse • Causes the release of more neurotransmitters • Is released in a synaptic cleft • All of the above

31. The resting membrane potential inside a neuron is • 0mV • 30mV • -60mV • -70mV

32. After stimulus, the rush of sodium ions into the cell is called • depolarization • repolarization • hyperpolarization

33. The action potential is propagated by • More Na+ rushing into the cell • K+ leaving the cell • Neurotransmitters binding to dendrite • Vesicles release neurotransmitters

34. The cell’s charge at the peak depolarization is • 0mV • 30mV • -60mV • -70mV

35. During repolarization • The resting potential is restored • K+ diffuse out of cell • The cell membrane becomes negatively charged again • All of the above

36. Once the action potential reaches the axon terminal, the signal will be carried to the next neuron by • Na+ ions • Neurotransmitters • K+ ions • All of the above

37. If an excitatory neurotransmitter binds to neuron number one, how will that affect the number of neurotransmitter released? • more • less • No effect at all

38. 0 of 25 If previous neuron releases GABA, an inhibitory neurotransmitter, how will that affect neuron #2 • Increase electrical stimulus • Decrease electrical stimulus • Increase neurotransmitters released • decreased neurotransmitters released • 1&3 • 2&4

39. Do Now: • You spray your house with insecticide. Shortly afterwards, you observe roaches lying on the ground with legs and wings twitching uncontrollably. What might the insecticide have done to the bug’s nervous system to cause this reaction? • Multiple Sclerosis is a disease in which the nerve fibers in the CNS lose their myelin. Why would this affect the person’s ability to control their skeletal muscles?

40. Insecticides • Most insecticides affect the nervous system by disrupting the Acetylcholine Esterase enzyme that regulates the neurotransmitter acetylcholine • ACh accumulates in the synapse repetitively stimulating receptors • Organophosphate pesticides were also used in World War II as nerve agents due to similar effects on humans

41. What is Multiple Sclerosis? • Symptoms: visual disturbance, weakness, clumsiness, paralysis, speech disturbance • Autoimmune disease • Myelin sheaths in CNS gradually destroyed leaving lesions (scleroses) • Causes “short circuiting”, AP slows until ceases • Axons not damaged and more Na+ channels can appear

42. Synapses • Synapse – junction that mediates info transfer from neuron to neuron (or effector) • Presynaptic neuron – conducts impulse towards synapse • Postsynaptic neuron-conducts impulse away from synapse • Electrical synapse (uncommon) • Gap junctions between adjacent cells that allow for direct flow of ions and small molecules • Rapid transmission for synchronized activity (eye movements, hippocampus, and embryonic nervous tissue) • Chemical synapse – release/receive neurotransmitters • Axon terminal of presynaptic neuron w/synaptic vesicles filled w/thousands of neurotransmitters • Synaptic cleft – fluid filled space in between • Neurotransmitter receptor on dendrite membrane

44. Information transfer across Chemical Synapse • Ca2+ channels open in presynaptic axon terminal • When nerve impulse reaches axon terminal Ca2+ gated channels also open w/Na+ channels, Ca2+ rushes in causing • Neurotransmitters are released • Synaptic vesicles fuse w/membrane • Ca2+pumped out, or taken in by mitochondria • Neurotransmitter binds to postsynaptic receptor • Ion channels open in the postsynaptic membrane • Receptor changes shape, causing ion channels to open generating graded potential • Neurotransmitter effects are terminated • Degradation by enzymes • Reuptake by astrocytes or presynaptic terminal • Diffusion away from synapse *Note: Synaptic delay – rate determining step b/s slower than AP

45. Neurotransmitters • 50+ have been indentified • Most neurons make 2 or more • Chemical Classifications • Ach • Amines • Purines • Amino Acids • Peptides • Dissolved Gasses • Functional Classifications • Effects • Excitatory – cause depolarization • Inhibitory – cause hyperpolarization • Both – dependent on receptor type • Action Mechanism • Direct - bind to ion channels • Indirect – long lasting • Intracellular 20 messenger

46. Neural Integration • Neurons function in groups • Neuronal pools – integrate incoming info in CNS • Circuits – patterns of neuronal pools • Diverging circuits • Amplify (1 triggers many, which each trigger many more) • Sensory & motor • Converging circuits • Funnel or concentrating effect • Different sensory can have same effect • Oscillating (reverberating) circuits • Chain of neurons w/colateral synapses (+) feedback • Sleep-wake cycle, breathing, arm swing w/walk

48. Reflexes • Reflex – involuntary response to stimulus w/o requiring the brain • Particular stimulus always causes the same response • Reflex arc-receptor  sensory neuron Interneuron motor neuron  effector • Ex. Knee jerk reflex • Babinski reflex (infants only) • Stroke sole of foot  toes fan out • Plantar reflex (adults only) • Stroke sole of foot toes curl • Signals sent to brain by interneurons allow for control • Ex. Toilet training, gag, blink