the nervous system
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Central Nervous System (CNS) Peripheral Nervous System (PNS ). The Nervous System. Functions. Sensory input : monitors internal and external environments Integration: processes & interprets sensory information - PowerPoint PPT PresentationTRANSCRIPT
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The Nervous System
Central Nervous System (CNS)Peripheral Nervous System (PNS)
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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
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Give an example
Include: sensory input integration motor output
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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)
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The sensory part of the PNS is...
1 2 3 4
6%
47%
35%
12%
1. Somatic division2. Sympathetic
division3. Afferent division4. Efferent division
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The fight or flight response is the...
1 2 3 4
6%
24%
0%
71%1. Somatic division2. Sympathetic
division3. Afferent division4. Efferent division
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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
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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
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Processes
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 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)
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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)
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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
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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
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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 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
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The most common type of neuron is
1 2 3
100%
0%0%
1. multipolar2. bipolar3. unipolar
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The part of the neuron that has receptor proteins on its surface is
1 2 3 4
94%
0%0%6%
1. Dendrites2. soma3. axon4. Myelin sheath
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Action Potential & WKBK
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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
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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
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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
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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
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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)
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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
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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 subthreshold
depolarizations that do not generate AP AP is an ALL or NONE Phenomenon
Once AP is generated all alike
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Action Potentialmyelinated vs. unmyelinated
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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)
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An excitatory neurotransmitter
1 2 3 4
25% 25%25%25%1. Increases electrical impulse
2. Causes the release of more neurotransmitters
3. Is released in a synaptic cleft
4. All of the above
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The resting membrane potential inside a neuron is
1 2 3 4
25% 25%25%25%1. 0mV2. 30mV3. -60mV4. -70mV
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After stimulus, the rush of sodium ions into the cell is called
1 2 3
33% 33%33%1. depolarization2. repolarization3. hyperpolarizatio
n
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The action potential is propagated by
1 2 3 4
25% 25%25%25%1. More Na+ rushing into the cell
2. K+ leaving the cell
3. Neurotransmitters binding to dendrite
4. Vesicles release neurotransmitters
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The cell’s charge at the peak depolarization is
1 2 3 4
25% 25%25%25%1. 0mV2. 30mV3. -60mV4. -70mV
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During repolarization
1 2 3 4
25% 25%25%25%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
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Once the action potential reaches the axon terminal, the signal will be carried to the next neuron by
1 2 3 4
25% 25%25%25%
1. Na+ ions2. Neurotransmitte
rs3. K+ ions4. All of the above
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If an excitatory neurotransmitter binds to neuron number one, how will that affect the number of neurotransmitter released?
1 2 3
33% 33%33%
1. more2. less3. No effect at all
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If previous neuron releases GABA, an inhibitory neurotransmitter, how will that affect neuron #2
1 2 3 4 5 6
17% 17% 17%17%17%17%
1. Increase electrical stimulus
2. Decrease electrical stimulus
3. Increase neurotransmitters released
4. decreased neurotransmitters released
5. 1&36. 2&4
0 of 25
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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?
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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
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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
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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
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Information transfer across Chemical Synapse
1. Ca2+ channels open in presynaptic axon terminal When nerve impulse reaches axon terminal Ca2+
gated channels also open w/Na+ channels, Ca2+
rushes in causing2. Neurotransmitters are released
Synaptic vesicles fuse w/membrane Ca2+pumped out, or taken in by mitochondria
3. Neurotransmitter binds to postsynaptic receptor4. 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
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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
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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
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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