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Nervous System Cheat Sheet by

Cheat Sheet of NPB 101 Nervous System

TERMS

Autonomic Ganglia - clusters of neuron cell bodies that relay sensory signals from the body's periphery to the central nervous system (CNS) integr­ation centers
Diffusion - the process of movement of molecules under a concen­tration gradient
Neurons - pecialized nerve cells designed to transmit electrical signals over long distances
Membrane Potential - a separation of opposite charges across the plasma membrane
Leak Channels - permit ions to flow down concen­tration gradients
Concen­tration Gradient - Na+/K+ ATPase establ­ishes the unequal distri­bution of Na+ and K+ ions inside and outside of the cell
Depola­riz­ation - change in membrane polari­zation to more positive values than resting membrane potential
Hyperp­ola­riz­ation - change in membrane polari­zation to more negative values than resting membrane potential
Action Potential - a rapid, all-or­-no­thing reversal in membrane potential (spike), lasting about 1 millis­econd, hat is brought about by rapid changes in membrane permea­bility to Na+ and K+ ions
Repola­riz­ation - return to resting membrane potential after depola­riz­ation
Propag­ation occurs when an AP spreads as the locally generated depola­rizing current moves to adjacent regions of the membrane causing it to depolarize
Myelin - multil­ayered sheath made of plasma membrane, produced by specia­lized glial cells, that wraps around axonal fibers. It serves as an insulator, facili­tating the efficient flow of electrical signals
Graded Potentials - ocal changes in membrane potential that decrease in strength as they travel over short distances. The magnitude of a graded potential typically correlates with the size of the stimulus.
Synapse - junction between two neurons, or between a neuron and a muscle or gland that enables one cell to electr­ically and/or bioche­mically influence another cell
Conver­gence - the synaptic input of many neurons onto one neuron
Divergence - the synaptic output of one neuron onto many neurons
Synaptic transm­ission - the primary means of rapid inter- neuronal commun­ication in the brain
Thalamus - sensory relay station and is important in motor control
Hypoth­alamus - regulates many homeos­tatic functions (Circadian rhythms, thermo­reg­ula­tion)
Brain Stem - vital link between the spinal cord and higher brain regions
Sensory System - 6 major sensory systems in the mammalian brain, each is organized according to a common anatomical plan.
Receptors - stimuli are transduced by receptors grouped together to form a sensory surface
Transd­uction - the conversion of stimulus energy to a neuronal signal
Auditory Receptors - hair cells located in cochlea
Somato­sensory Receptors - specific receptors for different modali­tie­s/s­ens­ations
Lateral Inhibition - inhibition of adjacent neurons in a map; facili­tates locali­zation of stimul­i/s­harpen contrast
Spinal Cord - each segment contains motor neurons that project to specific skeletal muscles on the same (ipsil­ateral) side of the body, via ventral roots
Neurom­uscular Junction - motor neurons and skeletal muscle fibers are chemically linked at
Spinal Reflexes - simple neurom­uscular circuits that mediate reflex responses to sensory stimuli
Central Motor System - system of neural structures that carry out specific controls of the skeletal muscul­ature
Limbic System - roup of cortical and subcor­tical structures that form an imprecise ring around the thalamus, playing a key role in emotion, motiva­tion, learning, and memory.
Amygdala - cluster of nuclei at the front of the hippoc­ampus; receives input and output to various subcor­tical and cortical struct­ures. It plays a crucial role in regulating emotional responses, especially fear
Hippoc­ampus - an elongated cortical structure located within the temporal lobe. It is anatom­ically linked to other parts of the limbic system and the cerebral cortex. It plays a key role in memory formation, spatial naviga­tion, and can also be involved in epileptic activity

Organi­zation of the Nervous System

Protection of CNS from injury: Cranium and vertebral column, Meninges, Cerebr­ospinal Fluid, Blood-­Brain Barrier
Brain depends on constant delivery of oxygen + glucose by the blood
Central Nervous System (CNS) --> Subcon­sci­ously regulate homeos­tatic responses; Experience emotions; Volunt­arily control movements; Be aware of body and surrou­ndings; Engage in other higher cognitive processes
Components of the Brai = Forebrain (Cereburm (Cerebral Cortex + Basal Nuclei­/Ga­nglia) ; Dience­phalon (Hypot­halamus + Thalam­us)), Cerebe­llum, and Brain Stem
Cerebral Cortex: Organized into layer and functional columns
Frontal Lobe --> Primary Motor Cortex ; Parietal Lobe --> Somato­sensory Cortex ; Occipital Lobe --> Primary Visual Cortex ; Temporal Lobe --> Primary Auditory Cortex
Thalamus = "­Relay statio­n" for prelim­inary processing of sensory input
Hypoth­alamus = collection of specific nuclei + associated fibers that lie beneath thalamus; integr­ating center importnat for homeos­tatic functions
Circadian Clock (24hr Rhythms) --> Suprac­hia­smatic Nucleus (SCN); Body Temper­ature, Sleep-­Wake, Blood Pressure, Hormone Levels
Brain Stem --> consist of midbrain, pons, and medulla.; MOST cranial nerves arise; regulate equili­brium and postural reflexes; cortical alertness; centers that govern sleep

Lobes of Cerebral Cortex

Thalamus + Hypoth­alamus

 

Diffusion + Membrane Potential

Diffusion Through Membrane --> Net movement due to random collisions between molecules ; Diffusion down a concen­tration Gradient
Rate of Diffusion Depends On: (1) Magnit­ude:↑ concen­tration gradient, ↑ rate of diffusion (2) Permea­bility: ↑perme­abi­lity, ↑rate of diffusion (3) Surface Area: ↑surface area, ↑ rate of diffusion (4) Molecular Weight: ↑ molecular weight, ↓ rate of diffusion (5) Distance: ↑ distance , ↓ rate of diffusion
Nonpolor Molecules (O2, CO2, fatty acids) = Chemical Gradient Small Ions (Na+, K+, Ca2+, Cl-) = Chemical Gradient + Electrical Gradient = electr­och­emical Gradient
Plasma membranes of ALL living cells have a membrane potential (Vm)/polarized electr­ically
Across Membrane, most fluid is electr­ically neutral; separated charges forming a layer along plasma membrane
GREATER the separation of charges across membrane --> LARGER the potential
Equili­brium Potential for K+ --> (1) K+ tends to move out of the cell (2) Outside of the cell becomes more positive (3) Electrical gradient tends to move K+ into the cell (4) Electrical gradient counte­rba­lances concen­tration gradient (5) No further net movement of K+ occurs (6) EK+ = -90mV
Equili­brium Potential for Na+ --> (1) Na+ tends to move into the cell (2) Inside of the cell becomes more positive (3) Electrical gradient tends to move Na+ out of the cell (4) Electrical gradient counte­rba­lances concen­tration gradient (5) No further net movement of Na+ occurs (6) ENa+ = +60mV
Resting Membrane Potential (-70mV): Membrane more permeable to K+ than Na+; Large; Large net diffusion of K+ and Small net diffusion of Na+
Na/K ATPase --> Establ­ishes and maintains concen­tration gradient ; Pumps 3 Na+ OUT of the cell for every 2 K+ pumped INTO the cell = Na+ is higher outside the cell and K+ is higher inside of the cell
Na+ = LOW intrac­ellular concen­tration K+ = HIGH intrac­ellular concen­tration
Resting Potential neither K+ nor Na+ is at equili­brium potentials and remain constant at resting state.

Vision

Sensory Motor Transf­orm­ation (cycle): Brain --> Motor Outputs --> Body --> Sensory Inputs --> Brain
Organi­zation: Receptor --> Relay Nuclei --> Thalamus --> Primary Cerebral Cortex --> Secondary Cerebral Cortex
Retina: photor­ece­ptors, bipolar cells, ganglion cells, horizontal cells, amacrine cells; light passes theough retina before contract with photor­ece­ptors in the back of the eye
Blind Spot = Optic Disc
Macula = Location of Fovea; bipolar and ganglion cell layers are pulled aside so light strikes photor­ece­ptors directly
Photot­ran­sdu­ction --> (1) Light activates rhodop­sin­Rho­dopsin activation causes the cGMP phosph­odi­est­erase activation (3) Rhodopsin activation decreases cGMP, closes cGMP-gated Na+ channel (4) Membrane hyperp­ola­rizes
Photor­ece­ptors: Rods--> sensitive to very low light, LOW acuity + peripheral vision, and do not distin­guish between different wavele­ngths of light; Cones--> sensitive to bright light; HIGH acuity in central field vision (fovea); distin­guish between different wavele­ngths of light
Color Perception --> Blue, Green, and Red Cone
Optics of Eye - lens inverts and focuses the visual stimulus onto the surface of the retina
Thermo­sen­sat­ion­/No­cic­eption --> Prevents us from being burned; influence decisions about enviro­nment and clothing

Auditory

External Ear - pinna, external auditory meatus, tympanic membrane
Middle Ear - tympanic membrane, ossicles, oval window
Inner Ear - oval window, cochlea, vestibular apparatus, round window
Mechan­ograph is a stretch receptor that respond to mechanical pressure or distor­tion; Stretc­h/Open = Depolarize AND Loosen­/Close = Hyperp­olarize
Sound Transd­uction: Sound Waves --> Vibration of Tympanic Membrane --> Vibration of Middle Ear Bones --> Vibration of Oval Window --> Fluid Movement within the Cochlea --> Vibration of Basilar Membrane --> Bending of Hair Cells --> Graded Receptor Potential --> Action Potentials Generated in Auditory Nerve --> Propag­ation to Auditory Cortex
Auditory Discri­min­ation: Pitch discri­min­ation depends on the region of the basilar membrane that vibrates (where) ; Loudness discri­min­ation depends on the amplitude of vibration of the basilar membrane (how much)
Somato­sensory Receptors --> Touch (Mecha­nor­ece­ptors), Pain (Nocic­ept­ors), Temper­ature (Therm­ore­cep­tors), and Propri­oce­ption (Mecha­nor­ece­ptors)
Touch - Tonic Receptor = don't adapt/­adapt slowly and sustain pressure and stretch of the skin ; Phasic Receptor = adapt rapidly, off response, and signal changes in pressure on the skin surface
Receptive Field - each sensory neurons respond to stimulus inform­ation only within a restri­cti­ve/­spe­cific area
Acuity (discr­imi­native ability) INFLUENCED by (1) Density of receptors (2) Receptive Field Size (3) Lateral Inhibition

Higher Brain Functions

Language Areas areas of the cerebral cortex, predom­inantly located in the left hemisphere in about 97% of people, respon­sible for language processing and production
Wernicke's Area located ventrally and poster­iorly to the auditory cortex, it integrates input from the auditory, visual, and somato­sensory cortices; damage to this area leads to impaired language compre­hen­sion.
Broca's Area is located in the ventral and posterior part of the left frontal lobe, it sends signals to motor regions of the cortex; damage to this area causes diffic­ulties with speech production
PERSON­ALITY --> Prefrontal Associ­ation Areas are in the frontal lobe, in front of the premotor regions, receiving input and sending output to various regions of the cerebral cortex; Damage to this area can lead to impair­ments in planning, person­ality, and social behavior
Phineas Gage had a tamping iron through his head and most of the front part of his left side of his brain was destroyed. Deficits: (1) socially unacce­ptable behavior (2) Unfocused (3) Lack of planning
Walter Freeman --> "­Ice­-pick loboto­my"; He used a transo­rbital approach to the prefontal cortex using an ice pick and a hammer. Performed under local anesth­esia. The ice pick would perforate skin, subcut­aneous tissue, bone and meninges in a single plunge; and then Freeman would swing it to severe the prefrontal lobe. (later seen as inhumane)
Patient HM - removal of hippoc­ampus to treat intrac­table epilepsy --> RESULT: Total Antero­grade Amnesia= couldn't form new long-term memories; slight display of retrograde amnesia= old memories until the age of the accident
 

Action Potentials

Action Potential (cont'd)

Rising Phase (Depol­ari­zation) = membrane polari­zation more POSITIVE
Voltage gated Na+ Channel --> opens quickly (< .5 ms) in response to depola­riz­ation, allowing Na+ to flow down its electr­och­emical gradient into the cell (rising phase of AP)
Falling Phase (Repol­ari­zation) = return to membrane potential after depola­riz­ation
Voltage gated K+ Channel --> opens more slowly in response to depola­riz­ation, allowing K+ ions to flow out of the cell down their electr­och­emical gradient. (falling phase of AP + after hyperp­ola­riz­ation))
AP Propag­ation--> Contiguous Conduc­tion: propag­ation of action potentials in unmyel­inated fibers by spread of locally generated depola­rizing current to adjacent regions of membrane, causing it to depola­rize; The original active area returns to resting potential, and the new activate area induces an action potential in the next adjacent inactive area. The cycle repeats itself down the length of the axon
Refactory Period -- Absolute Refractory Period: a brief period during a spike ; A second spike cannot be generated Relative Refractory Period : A brief period following a spike ; Capable of opening in response to depola­riz­ation
Refactory Period PREVENT "­Bac­kwa­rd" current flow: a region that has just experi­enced an action potential cannot immedi­ately generate another one; this period ensures action potentials travel in only one direction and restricts how frequently they can occur
Contiguous Conduction: unmyel­inated fibers; touching, next to in sequence // Saltatory Conduction: myelinated fibers; jumping; propag­ation of AP in myelinated axons by jumping from node to node
Myelin = Axon --> Plasma Membrane --> Myelin Sheath
Nodes of Raniver - gaps in myelin insulation containing high densities of voltag­e-gated Na+ and K+ channels
Schwann Cells (PNS) - glial cells in the peripheral nervous system respon­sible for producing the myelin sheath around axons
Oligod­end­rocytes (CNS) - glial cells in the central nervous system that generate the myelin sheath around multiple axons
Graded Potentials: occur in varying grades­/de­grees of magnitude; die over short distances; spread by passive current flow
Synapses --> Electrical Synapses: neurons connected directly by gap junctions. Chemical Synapses (most common): chemical messenger transmits inform­ation one way across a space separating the two neurons
Electrical Synapses formed by gap junctions (made up of multiple connexins) permits water-­soluble particles to pass between cells but blocks passage of larger molecules
Chemical Synapses: Presyn­aptic Neurons (Conve­rgence) --> Postsy­naptic Neurons (Diver­gence)
Chemical Synapse --Sequence of Events --> (1) AP propag­ation in presyn­aptic neuron (2) Ca2+ entry into synaptic knob, terminal button (3) Release of neurot­ran­smitter by exocytosis (4) Binding of neurot­ran­smitter to postsy­naptic receptor (5) Opening of specific ion channels in subsyn­aptic membrane
Synaptic Transm­ission = (1) Presyn­aptic axon initiates the signal (2) Neurot­ran­smitter carries the signal across a synapse; binds to postsy­naptic receptors (3) Postsy­naptic (target cell) receives the signal (4) Postsy­naptic targets can be a muscle, gland or another neuron
Excitatory Postsy­naptic Potential (EPSP): Depola­rizing change in membrane potential that moves the neuron closer to the threshold for firing an action potential, commonly triggered by excitatory neurot­ran­smi­tters such as glutamate (Glu) and acetyl­choline (ACh)
Inhibitory Postsy­naptic Potential (IPSP): Hyperp­ola­rizing change in membrane potential that moves the neuron further from the threshold for triggering an AP, typically caused by inhibitory neurot­ran­smi­tters such as gamma-­ami­nob­utyric acid (GABA) and glycine (Gly)
Transm­itter Removal: Degrad­ation (enzymatic breakd­own), Transport (active transport back into the presyn­aptic cell “reupt­ake), Diffusion (the transm­itter simply diffuses away from the synaptic terminal)
Transm­itter Release --> Tetanus Toxin (BLOCK); Transm­itter Uptake --> Cocaine, SSRIs (PROLONG); Transm­itter Removal --> insect­icides (PROLONG); Transm­itter Binding --> Curare (BLOCK)

Synaptic Transm­ission (cont'd)

Temporal Summation - the additive effect of postsy­naptic potentials (PSPs) that occur in rapid succession at the same sy allowing napse, their effects to add together over time
Spatial Summation - the additive effect of multiple postsy­naptic potentials (PSPs) that occur simult­ane­ously at different locations on the same neuron
Cancel­lation Summation - EPSP and IPSP cancel each other
Presyn­aptic inhibition - the inhibition of neurot­ran­smitter release caused by inhibitory input to the presyn­aptic terminal.

Motor System

Neurom­uscular Junction: An action potential travels down a motor neuron to its terminal --> This electrical signal causes voltag­e-gated calcium (Ca²⁺) channels in the terminal button to open, allowing Ca²⁺ to enter --> The influx of Ca²⁺ triggers the exocytosis of acetyl­choline (ACh) from some of the synaptic vesicles --> ACh diffuses across the synaptic cleft and binds to specific receptor channels on the motor end plate of the muscle fiber membrane --> This binding opens nonspe­cific cation channels, resulting in a greater influx of sodium ions (Na⁺) into the muscle cell than potassium ions (K⁺) exiting --> ion movement generates an end-plate potential. Local currents then spread from the depola­rized end plate to adjacent areas of the muscle membrane -> These local currents trigger the opening of voltag­e-gated Na⁺ channels in nearby membrane regions --> Resulting Na⁺ influx brings the membrane potential to threshold, initiating an action potential that spreads along the muscle fiber --> Acetyl­choline is then broken down by the enzyme acetyl­cho­lin­est­erase, located on the motor end plate, thereby ending the muscle’s response
Acetyl­choline (ACh) – neurot­ran­smitter used by motorn­eurons; ACh increases the membrane permea­bility to Na+ leading to an EPSP called the end-pl­ate­-po­tential (EPP) ; Acetyl­cho­lin­est­erase (AChE) – enzyme that degrades ACh
Each muscle cell has only one neurom­uscular junction
 

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