-brain: 100 billion neurons (each synapse with 1,000-10,000 other neurons)

-spinal cord

-cranial nerves (12 pairs) emerge from brain

-spinal nerves (31) pairs emerge from spinal cord

-ganglia:masses of neuron cell bodies outside of CNS

-enteric plexuses: network of neurons in GI tract

-sensory receptors: structure that monitors inter/exter environment

-somatic

-autonomic

-controls skeletal muscle

-voluntary

-sympathetic division (responds to short term stress)

-parasympathetic division(returns body to normal functions following stress)

-controls smooth muscle, cardiac muscle and glands

-involuntary

-controls smooth muscle and glands of the digestive system

-involuntary

A. Efferent

B. Afferent

C. CNS

D. PNS

-clustered into ganglia in PNS

-clustered into nuclei in brain

-clustered into horns in spinal cord

-contains nucleus

-contain nissl bodies-rough er-site of protein synthesis

part of cytoskeleton, bundles of intermediate filament that provide shape and support

-conduct action potentials toward axon terminal 

-distal end of axons swell into synaptic end bulb that contain neurotransmitters in synaptic vessicles

-bundles of neuron axons in cns:tracts(axons bundled with neuroglia)

-bundles of neuron axons in pns:nerves(axons bundled with endoneurium, perineurium, epineurium)

-frequently myelated in both cns and pns

one process from cell body

-sensory/afferent in function

-begins as a bipolar neuron in embryo but fuses into single extension

2 extensions from cell body

-1 main dendrite 1 axon

-ex: rods and cones (shape of dendrite) of retina, olfactory nuerons, inner ear neurons

many extensions from cell body

-most of CNS (internueurons) and all motor neurons

strictly PNS-transmit impulses toward CNS from receptors

-include both unipolar (mostly) and bipolar neurons

-in unipolar neurons, cell bodies are just outside the spinal cord in a structure called posterior dorsal root ganglia

support, connect, protect the neurons in both cns and pns

-cancer of NS-(gliomas) involves neuroglia and not neurons bc neuroglia have retained mitotic aility but neround have not retained mitotic ability beyond infancy

-neruoglia outnumber neurons by 5-50x

star shaped

-twine around neurons to form supporting network

-attach neurons to blood vessels

-create blood-brain barrier

-produce "scar tissue" if there is damage to cns

derived from monocytes

-become phagotic and remove injured brain or cord tissue

epithelial cells that line ventricles of brain and central canal of cord

-ciliated to assist in circulation of CSF

similar to astrocytes but have fewer extensions

-produce myelin sheath in CNS

CAMEO: Cns, Astrocyte, Microglia, Ependymal, Oligodendrocyte

produced around an axon by the following two neuroglia cells:

oligodendrocyes and schwann cells

-cns

-can myelinate up to 15 different neurons (axons)

-pns

-can have up to 500 schwann cells along the longest neurons (mylenate only one axon)

gaps in myelinated neuron where myelin is absent.

-produced by both schwann cells as well as oligondendrocytes, so nodes of ranvier are present in both CNS and PNS

cell processes (axons) with myelin

-nerve fiber: general term for any process projecting from the cell body of a neuron 

parts of neuron, especially cell bodies and dendrites, that lack myelin.

-always located in protected areas of CNS

-ganglia would also be gray bc cell bodies are NOT myelinated.

an electric signal that propagates along the membrane of a neuron or mucle fiber and allow for communication over long distances.

found in action potentials.

-ability to respond to a stimulus and convert it into an action potential

-stimulus: any condition capable of altering the cell's membrane potential enough to cause an AP

-nerve conduction of action potentials involves an electrochemical mechanism

-proteins in the cell membrane

-don't require ATP-movement of ions is by channel-mediated facilitative diffusion

-nongated

-leakage channels: randomly open

--cell membranes of muscle/neurons have more K+ leakage channels than Na+ leakage channels

open and close in response to some stimulus (chemical, electrical, mechanical)

-chemical (ligand) gated: open adn close in response to chemical like neurotransmitters, hormones, (dendrites and cell bodies).

Mechanically gated ion channels

nonconducting neuron has a rmp of -70mV

-small amounts of K+ move to the outside through leakage (nongated) channels with anions following (cannot diffuse through the membrane and get stuck at the membrane)

-the inside of the cell has a more negative charge thane the outside which is positive; overall the inside of the membrane is -70mV

-the inside of the membrane has non-diffusible anions (-) phosphate and protein anions

-K- ions are more numerus on the inside than on the outside

-Na+ and Cl- ions are more numerous outside

-neuron transmits action potentials according to all or none principle

-if the stimulus is strong enough to generate an action potential, the impulse is conducted down the neuron at a constant and maximum strength for the existing conditions

-stimulus must raise membrane potential to less negative than -55mV (threshold position)

-affected at site of stimulation and effect decreases with distance

-spreads passively

-the stronger the stimulus, the greater the change in potential and the larger area affected

-the potential change could be positive or negative

increases Na+ into cell making membrane hypopolarized

-partially depolarizes and makes membrane less negative

-causes depolarization (but not to -55mV)

-single excitatory stimulus usually does not initiate nerve impulse but membrane is closer to the threshold and more likely to reach threshold with next excitatory stimulus

increases K+ outward or increases Cl- inward

-makes membrane more negative

-makes the membrane hyperpolarized (as low as -90mV)

-generation of action potential is now more difficult

rapid change in membrane potential (polarity) that can spread down the length of the axon

-the membrane will depolarize and then repolarize

-only muscle and neurons can produce AP

-in neurons, an AP lasts about 1ms or less

-propagation of APs down axons=nerve impulses

First step in generating an action potential

-depolarization: when a stimulus is applied, if the sum of stimuli is excitatory(mechanical gated of chemical gated ion channels open and cause a net flow of Na- into the cell) and depolarization occurs to threshold potential (threshold=-55mV)

-at -55mV, voltage gated Na+ channels open and Na+ rushes in (na+inflow) making the inside of the cell positive

repolarization: membrane potential returns to a negative value

-it is due to K+ ions flowing outward through voltage gated K+ channels

-channels open in response to positive membrane and remain open until membrane potential returns to a negative value

-ion distribution is reverse of that at resting

-inside= (-)

refractory period: period of time during which an excitable cell cannot generate another action potential

-because of ion distribution has not returned to resting, sufficient potential has not built up on either side of the membrane to generate a new action potential

-refractory period begins at depolarization and continues until the resting membrane ion distribution is restored.

allow ions to flow into and out of the cell

-Na+K+ pump also operates in restoring the resting ion distribution by pumping Na+ out of the cell and K+ into the cell

-each action potential acts as a stimulus for development of another action potential in an adjacent segment of membrane

-Na+ inflow during the depolarization phase of an action potential diffuses to an adjacent membrane segment

-increase in Na+ concentration raises the membrane potential of that membrane segment to the threshold potential, generating a new action potential

-action potentials do not travel but are regenerated

in sequence along an axon like tipping dominoes

-refractory period prevents action potential from going backwards

-action potentials continue to be regenerated in sequence until the potential reaches the end of an axon

action potentials are only generated at the nodes of ranvier

-ap will skip from node to node 

-ionic movement is inhibited beneath myelin sheath

-conserves energy because Na-K pump is not needed as extensively because only nodes of ranvier are depolarized and repolarized

-conducts up to 50x faster than unmyelinated neuron

-presence of myelin sheath: the further the nodes are apart, the faster the transition

-diameter of fiber: the greater the diameter the greater density of voltage gated Na+ channels. the greater the diameter, the faster the transmission

temperature: the greater the temperature the faster the transmission

-localized cooling can block impulse conduction; therefore pain can be reduced by application of ice

-A fibers: myelinated and large diameter; fastest conduction; in areas where split second responses can mean survival, speeds up to 280mph

-B fibers: myelinated and smaller diamter; speeds up to 32mph

-C fibers: unmyelinated and smaller diameter; speeds up to 4mph

---note: B and C fibers are going to and from viscera

neurotransmitter is secreted from one cell and a second cell responds to it

-flow of information is one direction

--Structure of chemical synapse

-synaptic end bubld of first neuron (presynaptic neuron)=presynaptic membrane

-presynaptic electrical signal is converted to chemical signal

-presynaptic neuron releases neurotransmitter

20-50 nm gap between neuron and next structure

-impulse cannot jump cleft, therefore, will need chemical transmission in form of neurotransmitter

cell membrane of second neuron (postsynaptic neuron)=postsynaptic membrane

-postsynaptic neuron has receptors for neurotransmitter

-postsynaptic neuron receives chemical signal (neurotransmitter) and in turn may generate an electrical signal (action potential)

-when nerve impulse (action potential) arrives at synaptic end bulb, the depolarization phase opens voltage cated Ca2+ channels

-extracellular Ca2+ flows inward

-Increase in Ca2+ inside the neuron, triggers exocytosis of synaptic vessicles

-neurotransmitter enters synaptic cleft

interact with receptor sites of chemically gated ion channels on the postsynaptic membrane to produce EPSP: excitatory postynaptic potential: a type of graded potential

--typically results from the opening of chemically gated Na+ channels

inhibitory postysnaptic potential-a type of graded potential

--typically results from the opening of chemically gated K+ channels of Cl- channels

inhibition or excitation

-spatial (multiple synapse stimulation)

main neurotransmitter of PNS (not common in CNS)

-excitatory for skeletal muscle

-inhibitory for cardiac muscle

-important in hippocampus for memory consolidation (destroyed in Alzheimers)

excitatory in pns and cns

-caffeine accts as a competitive inhibitor at adenosine receptors in the brain

-secreted in the limbic system, cerebral cortex, basal ganglia, hypothalamus (brain)

-excitatory for emotional response but inhibitory in basal ganglia

-responsible for pleasurable expiriences

-low levels are associated with parkinsons

-excess is associated with schitzophrenia

-seems to be the neurotransmitter involves in addiction to heroin, meth, cocaine, marijuana, aocohol, nicotine, and caffeins.

-cocaine prevents DA reuptake

-found in the brain and secreted by sympathetic nervous system

-affects mood

-low levels are associated with depression

-methamphetamines (speed)-prevents NE reuptake

epinephrine=adrenaline

-secreted by the adrenal gland

-enhances sympathetic nervous system response

-produced from amino acid, tryptophan

-high amounts in milk and turkey

-secreted in limbic system, hypothalumus, cerebellum, spinal cord.

--affects mood, sleep, memory

-common inhibitory neurotransmitter in spinal cord (1/2) of inhibitory synapses in cord use glycine)

-tetanus toxin inhibits clycine, causing "lockjaw"

-strychnine blocks glycine receptors, causing the disphragm to continously contract which leads to suffocation

-1/2 of inhibitory synapses in spinal cord use gaba

-common inhibitory neurotransmitter in brain (as many as 1/3 of brain isynapses use gaba)

-prevents chaos in nervous system

-gaba reduces anxiety

-valium, xanax, alcohol and barbituates enhance the action of gaba

-treatment for epilepsy is a drug that increases gaba

-common in excitatory in cns

-increase in glutamate after stroke may lead to death of neurons bc of oxygen deprivation to glutamate transporters that wrk by active transport (requires oxygen for atop synthesis)

aspartate (aspartic acid)

endogenous morphine like substances

-both are structurally similar to morphine and bind to morphine receptors

-typical neuron recieves input from 1000 to 10000 synapses

-each presyn. neuron may branch and synapse with up to 25,000 or more different postsynaptic neurons

-convergence-single postsynaptic neuron controlled by converging signals coming from 2 of more presynaptic neurons