Central Nervous System (CNS) Peripheral Nervous System (PNS)

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

Include: sensory input integration motor output

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)

1. Somatic division 2. Sympathetic division 3. Afferent division 4. Efferent division

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 (G 0 ) High metabolic rate O 2 & glucose

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

Armlike processes - 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 Dendritic spines -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 90 0 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)

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)

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

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

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

1. multipolar 2. bipolar 3. unipolar

1. Dendrites 2. soma 3. axon 4. Myelin sheath

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

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

-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

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 HCO 3 - ), then causing the neighboring membrane to depolarize The plasma membrane is leaky and charge is quickly lost and dissipates quickly

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)

Resting State all voltage gated Na+ and K+ gated channels closed Depolarizing phase Na+ channels open (increasing + chargeopening 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 1,000s of Na+/K+ pumps in axon membrane

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

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)

1. Increases electrical impulse 2. Causes the release of more neurotransmitters 3. Is released in a synaptic cleft 4. All of the above

1. 0mV 2. 30mV 3. -60mV 4. -70mV

1. depolarization 2. repolarization 3. hyperpolarization

1. More Na+ rushing into the cell 2. K+ leaving the cell 3. Neurotransmitters binding to dendrite 4. Vesicles release neurotransmitters

1. 0mV 2. 30mV 3. -60mV 4. -70mV

1. The resting potential is restored 2. K+ diffuse out of cell 3. The cell membrane becomes negatively charged again 4. All of the above

1. Na+ ions 2. Neurotransmitters 3. K+ ions 4. All of the above

1. more 2. less 3. No effect at all

1. Increase electrical stimulus 2. Decrease electrical stimulus 3. Increase neurotransmitters released 4. decreased neurotransmitters released 5. 1&3 6. 2&4 0 of 25

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 bugs 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 persons ability to control their skeletal muscles?

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

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

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

1. Ca 2+ channels open in presynaptic axon terminal When nerve impulse reaches axon terminal Ca 2+ gated channels also open w/Na+ channels, Ca 2+ rushes in causing 2. Neurotransmitters are released Synaptic vesicles fuse w/membrane Ca 2+pumped out, or taken in by mitochondria 3. Neurotransmitter binds to postsynaptic receptor 4. Ion channels open in the postsynaptic membrane Receptor changes shape, causing ion channels to open generating graded potential 5. 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

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 2 0 messenger

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

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

Documents

Central Nervous System (CNS) Peripheral Nervous System (PNS)