Nervous System Cheat Sheet by hildana

Autonomic Ganglia - lusters of neuron cell bodies that transmit sensory signals from the periphery to the integr­ation centers in the CNS

Neurons - nerve cells are specia­lized for electrical signaling over long distances

Leak Channels - permit ions to flow down concen­tration gradients

Depola­riz­ation - change in membrane polari­zation to more positive values than resting membrane potential

Action Potential - brief all-or­-no­thing reversal in membrane potential (spike), lasting on the order of 1 millis­econd, hat is brought about by rapid changes in membrane permea­bility to Na+ and K+ ions

Propag­ation - action potentials propagate when locally generated depola­rizing current spreads to adjacent regions of membrane causing it to depola­rize.

Graded Potentials - local changes in membrane potential that decay over short distance; the size of the graded potential often correlates with the size of the stimulus

Conver­gence - the synaptic input of many neurons onto one neuron

Synaptic transm­ission - the primary means of rapid inter- neuronal commun­ication in the brain

Hypoth­alamus - regulates many homeos­tatic functions (Circadian rhythms, thermo­reg­ula­tion)

Sensory System - 6 major sensory systems in the mammalian brain, each is organized according to a common anatomical plan.

Transd­uction - the conversion of stimulus energy to a neuronal signal

Somato­sensory Receptors - specific receptors for different modali­tie­s/s­ens­ations

Spinal Cord - each segment contains motor neurons that project to specific skeletal muscles on the same (ipsil­ateral) side of the body, via ventral roots

Spinal Reflexes - simple neurom­uscular circuits that mediate reflex responses to sensory stimuli

Limbic System - a system of cortical and subcor­tical structures that form a loosely defined ring around the thalamus, involved in emotion, motiva­tion, learning and memory.

Hippoc­ampus - elongated cortical structure located within the temporal lobe. Anatom­ically connected with other parts of the limbic system and cerebral cortex. Is involved in memory formation, spatial guidance of behavior and epileptic activity.

Protection of CNS from injury: Cranium and vertebral column, Meninges, Cerebr­ospinal Fluid, Blood-­Brain Barrier

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

Cerebral Cortex: Organized into layer and functional columns

Thalamus = "­Relay statio­n" for prelim­inary processing of sensory input

Circadian Clock (24hr Rhythms) --> Suprac­hia­smatic Nucleus (SCN); Body Temper­ature, Sleep-­Wake, Blood Pressure, Hormone Levels

Diffusion Through Membrane --> Net movement due to random collisions between molecules ; Diffusion down a concen­tration Gradient

Nonpolor Molecules (O₂, CO₂, fatty acids) = Chemical Gradient Small Ions (Na+, K+, Ca²⁺, Cl^-) = Chemical Gradient + Electrical Gradient = electr­och­emical Gradient

Across Membrane, most fluid is electr­ically neutral; separated charges forming a layer along plasma membrane

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) E_K⁺ = -90mV

Resting Membrane Potential (-70mV): Membrane more permeable to K⁺ than Na⁺; Large; Large net diffusion of K⁺ and Small net diffusion of Na⁺

Na⁺ = LOW intrac­ellular concen­tration K⁺ = HIGH intrac­ellular concen­tration

Sensory Motor Transf­orm­ation (cycle): Brain --> Motor Outputs --> Body --> Sensory Inputs --> Brain

Retina: photor­ece­ptors, bipolar cells, ganglion cells, horizontal cells, amacrine cells; light passes theough retina before contract with photor­ece­ptors in the back of the eye

Macula = Location of Fovea; bipolar and ganglion cell layers are pulled aside so light strikes photor­ece­ptors directly

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

Optics of Eye - lens inverts and focuses the visual stimulus onto the surface of the retina

External Ear - pinna, external auditory meatus, tympanic membrane

Inner Ear - oval window, cochlea, vestibular apparatus, round window

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

Somato­sensory Receptors --> Touch (Mecha­nor­ece­ptors), Pain (Nocic­ept­ors), Temper­ature (Therm­ore­cep­tors), and Propri­oce­ption (Mecha­nor­ece­ptors)

Receptive Field - each sensory neurons respond to stimulus inform­ation only within a restri­cti­ve/­spe­cific area

Language Areas are areas of cerebral cortex located in the left hemisphere in approx­imately 97% of the population

Broca's Area is located in the ventral and posterior region of the left frontal lobe and sends output to the motor areas of the cortex. Damage results in a deficit in speech production

Phineas Gage had a tamping iron therough 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

Patient HM - sremoval of hippocamus 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

Rising Phase (Depol­ari­zation) = membrane polari­zation more POSITIVE

Falling Phase (Repol­ari­zation) = return to membrane potential after depola­riz­ation

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 PREVENT "­Bac­kwa­rd" current flow: Action potential cannot be initiated in a region that has just undergone an action potential ; Refractory period ensures one-way propag­ation of action potentials and limits their frequency

Myelin = Axon --> Plasma Membrane --> Myelin Sheath

Schwann Cells (PNS) - myelin­-fo­rming glial cells in the peripheral nervous system

Graded Potentials: occur in varying grades­/de­grees of magnitude; die over short distances; spread by passive current flow

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 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

Excitatory Postsy­naptic Potential (EPSP): most common excitatory neurot­ran­smi­tters are glutamate (Glu) and acetyl­choline (ACh) ; depola­rizing potential that brings V_m towards threshold for generation of an action potential

Transm­itter Removal: Degrad­ation _{enzymatic breakdown}, Transport _{active transport back into the presyn­aptic cell “reuptake}, Diffusion _{the transm­itter simply diffuses away from the synaptic terminal}

Temporal Summation - the additive effect of PSPs occurring close together in time at the same place (PSP)

Cancel­lation Summation - EPSP and IPSP cancel each other

Neurmu­scular Junction: (1) An action potential in a motor neuron is propagated to the terminal (2) This local action potential triggers the opening of voltage- gated Ca2+ channels and the subsequent entry of Ca2+ into the terminal button (3) Ca²⁺ triggers the release of acetyl­choline (ACh) by exocytosis from a portion of the vesicles (4) ACh diffuses across the space separating the nerve and muscle cells and binds with recept­or-­cha­nnels specific for it on the motor end plate of the muscle cell membrane (5) This binding brings about the opening of these nonspe­cific cation channels, leading to a relatively large movement of Na⁺ into the muscle cell compared to a smaller movement of K⁺ outward (6) The result is an end-plate potential. Local current flow occurs between the depola­rized end plate and the adjacent membrane (7) This local current flow opens voltag­e-gated Na+ channels in the adjacent membrane. (8) The resultant Na⁺ entry reduces the potential to threshold, initiating an action potential, which is propagated throughout the muscle fiber (9) ACh is subseq­uently destroyed by acetyl­cho­lin­est­erase, an enzyme located on the motor end-plate membrane, termin­ating the muscle cell’s response

Each muscle cell has only one neurom­uscular junction

Myasthenia Gravis: autoimmune disease where the body generates antibodies that attack nicotinic ACh receptors (involves the neurom­uscular junction); TREATMENT: ACh-es­terase inhibitors (Neost­igm­ine). By reducing the rate of ACh degred­ation, ACh persists in the NMJ longer and has the increased potential to find healthy ACh receptors

Tetanus via a wound which becomes contam­inated with the bacteria Clostr­idium tetani ; Botulism via ingesting the spores from bacteria (Clost­ridium botulinum) allowed to grow in an anaerobic enviro­nment

Primary Motor Cortex - located on the precentral gyrus, and contains a somato­topic map of the skeletal muscul­ature. A subset of the neurons project directly to the spinal cord forming the cortic­ospinal tract

Cerebellum compares the intended movement with the actual movement and makes corrective adjust­ments; large neural lobe located on the lower posterior region of the brain. Involved in numerous functions, and is partic­ularly important in the control of motor coordi­nation. Heavily interc­onn­ected with the cerebrum, partic­ularly the cerebral cortex

Basal Ganglia --> arge nuclei in the center of the brain interc­onn­ected with the cerebral cortex and the thalamus. Involved in motor planning and the initiation of motor sequences (e.g. Parkin­son's Disease)

Multiple Sclerosis: demyel­ination of neurons in cerebellum; difficulty making precise movements; action tremors