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via electrical and chemical signals

• Sensory Input
• Integration
• Motor output

Information gathered by sensory receptors about internal and external changes

Processing and interpretation of sensory input

Activation of effector organs (muscles and glands) produces a response

• Brain and spinal cord of dorsal body cavity
• Integration and control center (interprets sensory input and dictates motor output)

• The portion of the nervous system outside CNS
• Consists mainly of nerves that extend form brain and spinal cord (spinal nerves and cranial nerves)

Nerves to and from spinal cord

To and from brain

Sensory (afferent division) and motor (efferent) division

• Somatic sensory fibers: convey impulses form skin, skeletal muscles, and joints to CNS
• Visceral sensory fibers: convey impulses from visceral organs to CNS

• Transmits impulses from CNS to effector organs (muscles & glands)
• Two divisions: somatic nervous system & autonomic nervous system

• Somatic motor nerve fibers
• Conducts impulses from CNS to skeletal muscle
• Voluntary nervous system (conscious control of skeletal muscles)

• Visceral motor nerve fibers
• Regulates smooth muscle, cardiac muscle, and glands
• Involuntary nervous system
• Two functional subdivisions: Sympathetic & Parasympathetic (work in opposition to each other)

Yes

Neuroglia & neurons

small cells that surround and wrap delicate neurons

excitable cells that transmit electrical signals

• Astrocytes (CNS)
• Microglial cells (CNS)
• Ependymal cells (CNS)
• Oligodendrocytes (CNS)
• Satellite cells (PNS)
• Schwann cells (PNS)

• Most abundant, versatile and highly branched glial cell
• Cling to neurons, synaptic endings, and capillaries

• Functions:
• -Support and brace neurons
• -Play role in exchanges between capillaries and neurons
• -Guide migration of young neurons
• -Control chemical environment around neurons
• -Respond to nerve impulses and neurotransmitters
• -Influence neuronal functioning

• Small, ovoid cells with thorny processes that touch and monitor neurons
• Migrate toward injured neurons
• Can transform to phagocytize microorganisms and neuronal debris

• Range in shape from squamous to columnar
• May be ciliated
• Line the central cavities of the brain and spinal column
• Form permeable barrier between cerebrospinal fluid in cavities and tissue fluid bathing CNS cells

• Branched cells
• Processes wrap CNS nerve fibers, forming insulating myelin sheaths thicker nerve fibers

• Surround neuron cell bodies in PNS
• Function similar to astrocytes of CNS

• Surround all peripheral nerve fibers and form myelin sheaths in thicker nerve fibers (similar function to oligodendrocytes)
• Vital to regeneration of damaged peripheral nerve fibers

Schwann cells

• Structural units of nervou system
• Large, highly specialized cells that conduct impulses
• Extreme longevity (100+ years)
• Amitotic (few exceptions)
• High  metabolic rate (requires continuous supply of oxygen and glucose)
• All have cell body and one or more processes

• Biosynthetic center of neuron (synthesizes proteins, membranes, etc. best rough ER in the body)
• Spherical nucleus with nucleolus
• Some contain pigments
• In most, plasma membrane part of receptive region
• Most neuron cell bodies in CNS
• Ganglia lie along nerves in PNS

Clusters of neuron cell bodies in CNS

Bundles of neuron processes in CNS

Bundles of neuron processes in PNS

Dendrites and axons

• In motor neurons (100s of short, tapering, diffusely branched processes; same organelles as in body)
• Receptive (input) region of neuron
• Convey incoming messages toward cell body as graded potentials 
• In many brain area fine dendrites specialized
• Collect information with dendritic spines (appendages with bulbous or spiky ends)

Short distance signals

• One axon per cell arising from axon hillock
• In some axon short or absent
• In others most of length of cell ( some 1 m long)
• Occasional branches
• Branches profusely at end
• Can be 10,000 terminal branches

Axon terminals or Terminal boutons

Nerve fibers

• Conducting region of neuron
• Generates nerve impulses
• Transmits them along axolemma to axon terminal
• Carries on many conversations with different neurons at same time
• Lacks rough ER and golgi apparatus

Neuron cell membrane

Either excite or inhibit neurons with which axons in close contact

• Relies on cell body to renew proteins and membranes
• Efficient transport mechanisms
• Quickly decay if cut or damaged

By motor proteins and cytoskeletal elements

• Away from the cell body
• Ex. mitochondria, cytoskeletal elements, membrane components, enzymes

• Toward the cell body
• Ex. organelles to be degraded, signal molecules, viruses, bacterial toxins

• Composed of myelin 
• Segmented sheath around most long or large diameter axons (myelinated fibers)

whitish protein-lipid substance

• Protects and electrically insulates axon
• Increases speed or nerve impulse transmission

Yes

• Formed by schwann cells (wrap around axon in jelly roll fashion, one cell forms one segment of myelin sheath)
• Myelin sheath (concentric layers of schwann cell plasma membrane around axon)
• Outer collar of perinuclear cytoplasm (peripheral bulge of schwann cell containing nucleus and most of cytoplasm)
• Plasma membranes of myelinating have cells less protein (no channels or carriers, good electrical insulators, interlocking proteins bind adjavent myelin membranes)
• Nodes of rangier (myelin sheath gaps between adjacent schwann cells, sites where axon collaterals can emerge)
• Nonmyelinated fibers (thin fibers not wrapped in myeline, surrounded by schwann cells but no coiling, one cell may surround 15 different fibers)

• Formed by multiple flat processes of oligodendrocytes, not whole cells
• Can wrap up to 60 axons at once
• Nodes of ranvier present
• No outer collar of perinuclear cytoplasm
• Thinnest fibers are unmyelinated (covered by long extensions of adjacent neuroglia)
• White matter & Gray matter

Regions of brain and spinal cord with dense collections of myelinated fibers, usually fiber tracts (tract=PNS)

mostly neuron cell bodies and nonmyelinated fibers

• Grouped by number of processes; 3 types
• Multipolar, Bipolar & Unipolar

• 3 or more processes
• 1 axon, others dendrites
• most common; major neuron in CNS

• 2 processes
• 1 axon and 1 dendrite
• rare e.g. retina and olfactory mucosa

• 1 short process
• Divides T-like with both branches now considered axons (distal (peripheral) process is associated with sensory receptor and proximal (central) process enters CNS

• Grouped by direction in which nerve impulse travels relative to CNS; 3 types
• Sensory (afferent), Motor (Efferent), Interneurons

• Transmit impulses from sensory receptors toward CNS
• Almost all are unipolar
• Cell bodies in ganglia in PNS

• Carry impulses from CNS to effectors
• Multipolar
• Most cell bodies in CNS (except some autonomic neurons)

• Lie between motor and sensory neurons
• Shuttle signals through CNS pathways; most are entirely within CNS
• 99% of body's neurons
• Most confined in CNS

by generating an action potential

a nerve impulse

yes; regardless of stimulus

potential energy

a measure of potential energy generated by separated charge

flow of electrical charge (ions) between two points

is a hindrance to charge flow; an be an insulator or conductor

substance with high electrical resistance

substance with low electrical resistance

• current (I)=voltage (V)/resistance (R)
• *current is directly proportional to voltage
• *no net current flow between points with same potential
• *current inversely related to resistance

large proteins serve as selective membrane ion channels; there are two types; leakage (nongated) or gated

nongated channels that are always open

part of protein changes shape to open/close channel

• chemically gated
• voltage-gated
• mechanically gated

open with binding of a specific neurotransmitter

open and close in response to changes in membrane potential

open and close in response to physical deformation of receptors, as in sensory receptors

• -ions diffuse quickly across membrane along electrochemical gradients
• -ion flow creates an electrical current and voltage changes across membrane

• -potential difference across membrane of resting cell (-70)
• -membrane is polarized
• -generated by differences in ionic makeup of ICF and ECF/differential permeability of the plasma membrane

extracellular fluid

intracellular fluid

ECF

ICF

K+

• -slightly permeable to Na+ through leakage channels
• -25 times more permeable to K+ than sodium (more leakage channels)
• -Very permeable to Cl-

it becomes hyperpolarized

True; cell more negative inside and establishes resting membrane potential

Yes; it stabilizes resting membrane potential, maintains concentration gradients for Na+ and K+

-for every 3 Na+ pumped out of cell 2 K+ pumped in

• -when concentrations of ions across membrane change
• -membrane permeability to ions change

graded potentials and action potentials

incoming signals operating over short distances

long-distance signals of axons

signals to receive, integrate, and send information

• -decrease in membrane potential (toward zero and above)
• -inside of membrane becomes less negative than resting membrane potential
• -increases probability of producing a nerve impulse

it is negative because of protein

-55; -55 and above is called action potential & -54 and below is graded potential

YES

depolarization

• -an increase in membrane potential (away from zero)
• -inside of cell more negative than resting membrane potential
• -reduces probability of producing a nerve impulse

• -short-lived, localized change sin membrane potential (magnitude varies with stimulus strength; stronger stimulus=father current flow)
• -either depolarization of hyperpolarization
• -triggered by stimulus that opens gated ion channels
• -current flows but dissipates quickly and decays (graded potentials are signals only over short distances)

-70 resting membrane potential --> +30 =100

action potentials

action potentials

action potentials

No they don't; graded potentials do though

activation gates and inactivation gates

*they shut out unnecessary stimuli

closed at rest; open with depolarization allowing Na+ to enter the cell

open at rest; block channel once it is open to prevent more Na+ from entering cell

• -each K+ channel has one voltage-senstive gate
• -closed at rest
• -opens slowly with depolarization

• -all gated Na+ K+ channels are closed
• -Only leakage channels for Na+ and K+ are open; which maintains the resting membrane potential

• depolarizing local currents opens voltage-gated Na+ channels
• Na+ influx causes more depolarization which then opens more channels making ICF less negative
• at threshold, positive feedback causes opening of ALL Na+ channels; creates a spike of action potential

• Na+ channel slow inactivation gates close
• membrane permeability to Na+ declines (AP spike stops rising)
• slow voltage-gated K+ channels open and K+ exits the cell so internal negativity is restored

• some k+ channels remain open, allowing excessive K+ efflux (membrane becomes more negative than -70)
• this causes hyperpolarization of the membrane
• Na+ channels begin to reset

• repolarization resets electrical conditions no ionic conditions
• after depolarization Na+/K+ pumps restore ionic conditions

• -55
• not all depolarization events produce APs
• for the axon to "fire" signals, depolarization must reach threshold

• @ threshold:
• membrane has been depolarized by 15-20 mV
• Na+ permeability increases
• Na+ influx exceeds K+ efflux
• the positive feedback cycle begins

an AP either happens completely or not at all

• propagation allow AP to serve as a signaling device
• Na+ influx causes local currents, which causes depolarization of adjacent cells in the direction AWAY from the AP origin
• Na+ channels closer to AP origin are inactivated so no new AP is generated there
• once initiated, AP is self-propagating

each successive segment of membrane depolarizes and then repolarizes

• all APs are alike, regardless of stimulus intensity
• CNS differentiates between weak and strong stimuli by frequency of impulses sent per second.
• more impulses per second=stronger stimulus

• when voltage-gated Na+ channels open neuron cannot respond to another stimulus
• time from opening of Na+ channels until resetting of the channels
• ensures that each AP is an all-or-none event
• enforces one-way transmission of nerve impulses

• -follows absolute refractory period
• -Most Na+ channels have returned to their resting state
• -some K+ channels still open
• -repolarization is occuring

• -threshold for AP generation is elevated
• -inside of the membrane is more negative than resting state

-only exceptionally strong stimulus could stimulate an AP

• varies widely
• rate of AP propagation depends on the axon diameter and degree of myelination
• axon diameter: larger diameter fibers have less resistance to current flow so a fast impulse conduction
• degree of myelination: continuous conduction in unmyelinated axons is slower than saltatory conduction in myelinated axons

• faster than continuous conduction
• happens in myelinated axons
• 30x faster
• myelin sheaths insulate and prevent leakage of charge

• slower than saltatory conduction
• happens in unmyelinated axons

• diameter
• degree of myelination
• speed of conduction

group A, group B, group C

• large diameter
• myelinated somatic sensory and motor fibers of skin, skeletal muscles, joints
• transmit at 150 m/s

• intermediate diameter
• lightly myelinated
• transmit at 15 m/s

• smallest diameter
• unmyelinated ANS fibers
• transmit at 1 m/s

• body: nuclei
• process: tract

• body: ganglia
• process: nerve

• through synapses
• they mediate information transfer from neuron to neuron or neuron to effector cell

• axodendritic: between axon terminals of one neuron and dendrites of others
• axosamatic: between axon terminals of one neuron and soma of others

• neuron conducting impulses towards the synapse
• sender of the information

most cells function as both post & pre synaptic neurons

• neuron transmitting electrical signals away from the synapse
• receives the information

most cells function as both post & pre synaptic neurons

• less common than chemical synapses
• neurons electrically coupled
• communication very rapid
• may be unidirectional or bidirectional
• synchronize activity
• more abundant in nervous tissue
• nerve impulse remains electrical

• specialized for release and reception of chemical neurotransmitters
• composed of two parts: axon terminal of presynaptic neuron and neurotransmitter receptor region of postsynaptic neuron's membrane
• two parts separated by synaptic cleft
• electrical impulse changed to chemical across synapse, then back to electrical

contains synaptic vesicles filled with neurotransmitters

usually on dendrite or cell body

• fluid-filled space
• 30-50 nm wide
• prevents nerve impulses form directly passing from one neuron to the next

• chemical event (not electrical)
• depends on release, diffusion, and receptor binding of neurotransmitters
• ensures unidirectional communication between neurons

• AP arrives at axon terminal of presynatic neuron
• causes voltage gated Ca2+ channels to open (Ca2+ floods into cell)
• synaptotagmin protein binds Ca2+ and promotes fusion of synaptic vesicles with axon membrane
• exocytosis of neurotransmitter into synaptic cleft occurs (the higher the impulse frequency, the more neurotransmitters released)
• neurotransmitter diffuses across synapse
• binds to receptors of postysnaptic neuron (chemically-gated ion channels)
• ion channels are opened
• causes an excitatory or inhibitory event (graded potential)
• neurotransmitter effects terminated

synaptotagmin

• reuptake: by astrocytes or axon terminal
• degradation: by enzymes
• diffusion: away from synaptic cleft

• time needed for neurotransmitter to be released, diffuses across the synapse, and bind to receptors
• is rate-limiting step of neural transmission

neurotransmitter receptors cause graded potentials that vary in strength with the amount of neurotransmitter released and time neurotransmitter stays in area

• excitatory postsynaptic potentials (graded potential)
• shore-distance signaling, depolarization that spreads to axon hillock
• moves membrane potential toward threshold for generating an AP

• inhibitory postsynaptic potentials (graded potentials)
• short-distance signaling
• hyperpolarization that spreads to axon hillock
• moves membrane potential away from threshold for generating an AP

output, efferent, motor

input, afferent, sensory

• neurotransmitter binding opens chemically gated channels and allows simultaenous flow of Na+ and K+ in opposite directions
• Na+ influx greater than K+ efflux --> net polarization called EPSP (not AP)
• EPSP help trigger AP if EPSP is of threshold strength (can spread to axon hillock, trigger opening of voltage-gated channels and cause AP to be generated)

• reduces postsynaptic neuron's ability to produce an action potential (by making membrane more permeable to K+ or Cl-; if K+ channel is open, it moves out of cell, if Cl- channel is open, it moves into cell)
• neurotransmitter hyperpolarizes cell (inner surface of membrane becomes more negative, AP less likely to be generated)

• a single EPSP cannot induce an AP
• EPSPs can summate to influence postsynaptic neuron
• IPSPs can also summate
• most neurons receive both excitatory and inhibitor inputs from thousands of other neurons
• Action potential only happens if EPSPs predominate and bring to threshold

• temporal summation: one or more presynaptic neurons transmit impulses in rapid-fire order
• spatial summation: postsynaptic neuron stimulated simultaneously by large number of terminals at same time

• repeated use of synapse increases ability of presynaptic cell to excite postsynaptic neuron: Ca2+ concentration increases in presynaptic terminala nd postsynaptic neuron
• brief high-frequency stimualtion partially depolarizes postsynaptic neuron: chemically gated channels allow Ca2+ entry, Ca2+ activates kinase enzymes that promote more effective responses to subsequent stimuli

• excitatory neurotransmitter release by one neuron inhibited by another neuron via axoaxonic synapse
• less neurotransmitter released
• smaller EPSPs formed

• language of nervous system
• 50 or more have been identified
• most neurons make 2 or more neurotransmitters
• usually released at different stimulation frequencies
• classified by chemical structure and function

• first identified; best understood
• released at neuromuscular junctions by some ANS neurons, by some CNS neurons
• synthesized from acetic and choline by enzyme choline acetyltransferase
• degraded by enzyme acetylcholinesterase (AChE)

• catecholamines: dopamine, norepinephrine (NE) and epinephrine; synthesized from amino acid tyrosine
• indolamines: serotonin and histamine; serotonin synthesized from amino acid tryptophan, histamine synthesized from amino acid histidine

• broadly distributed in the brain
• plays roles in emotional behavior and biological clock
• some ANS motor neurons (esp. NE)
• imbalances associated with mental illness

• gamma aminobutyric acid (amino acid)
• primarily inhibitory 99.9% of time
• amino acid of neurotransmitters

• substance P: mediator of pain signals
• endorphins: beta endorphin, dynorphin and enkaphalins; act as natural opiates and reduce pain perception (e.g. tattoos)

• nitric oxide (NO), carbon monoxide (CO) hydrogen sulfide gases (H2S)
• bind with G protein-coupled receptors in the brain
• lipid soluable
• synthesized on demand
• NO involved in learning and formation of new memories; brain damage in stroke patients, smooth muscle relaxation in intestine
• H2S acts directly on ion channels to alter function

• diverse functions
• effects: excitatory versus inhibitory
• actions: direct versus indirect

• excitatory vs inhibitory
• neurotransmitter effects can be excitatory (depolarizing) and/or inhibitory (hyper polarizing)
• effect determined by receptor to which it binds e.g. GABA usually inhibitory vs glutamate usually excitatory

• direct vs indirect
• direct: neutrotransmitter binds to and opens ion channels, promotes rapid responses by altering membrane potential (ACh and amino acids)
• indirect: neurotransmitter acts through intracellular second messengers usually G protein pathways, broader long-lasting effects similar to hormones (epinephrine and norepinephrine)

• channel-linked: mediate fast synaptic transmission
• g protein-linked: oversee slow synaptic responses

• ligand-gated ion channels
• action is immediate and brief
• excitatory receptors are channels for small cations (Na+ influx contributes most to depolarization)
• inhibitory receptors allows Cl- influx that causes hyper polarization

• responses are indirect, complex, slow and prolonged
• transmembrane protein complexes
• cause widespread metabolic changes
• examples ACh receptors
• neurotransmitters binds to g protein-linked receptor, activates g protein, and activated g protein controls production of second messengers (Ca2+)

• open or close ion channels
• activate kinase enzymes
• phosphorylate channel proteins
• activate genes and induce protein synthesis

• neurons function in groups
• groups contribute to broader neural functions
• there are billions of neurons in CNS, so there must be integration so the individual parts fuse to make a smoothly operating whole

• functional groups of neurons:
• integrate incoming information received from receptors or other neuronal pools
• forward processed information to other destinations

• simple neuronal pool:
• single presynaptic fiber branches and synapses with several neurons in pool
• discharge zone:neurons most closely associated with incoming fiber
• facilitated zone:neurons farther away form incoming fiber

• patterns of synaptic connections in neuronal pools
• four types: 
• diverging: away from
• converging: together
• reverberating: again and again and again
• parallel after discharge: parallel

• input travels along one pathway to a specific destination
• system works in all-or- none manner to produce specific anticipated response
• e.g. spinal reflexes -5 steps (receptor, sensory neuron, CNS integration center, motor neuron, effector)

• input travels along several pathways
• different parts of circuitry deal simultaneously with the information
• important for higher-level mental functioning
• e.g. certain scent may remind one of an odor and associated experiences

• about 2/3 of neurons die before birth
• if they do not make a connection, they die
• also due to apoptosis

• GP:
• location of event: cell body and dendrites
• distance traveled: short (cell body to axon hillock)
• size: various sizes; decays with distance
• stimulus for opening ion channels: chemical or sensory (temp, light)
• positive feedback: absent
• repolarization: voltage independent, occurs when stimulus is no longer present
• summation: stimulus can summate to increase amplitude of graded potential (temporal or spatial)
• function: EPSP or IPSP
• initial effect: opens chemically gated channels that allow NA+ K+ fluxes or opens chemically gated K+ or Cl- channels
• peak membrane potential: depolarizes and hyperpolarizes

• AP:
• location of event: axon hillock and axon
• distance traveled: long, entire length of axon
• size: always the same, all or none
• stimulus for opening ion channels: voltage (depolarization triggered by GP reaching threshold)
• positive feedback: present
• repolarization: voltage regulated; occurs when Na+ channels inactivate and K+ channels open
• summation: does not occur, all or none phenomenon
• function: long distnce signaling; constitutes the nerve impulse
• initial effect of stimulus: opens voltage-gated channels; first Na+ channels then K+ channels
• peak membrane potential: +30 -- +50