page 320-329 Flashcards
Lesion on one side causes
Ipsilateral motor loss (corticospinal).
■ Ipsilateral touch/sensory loss.
■ Contralateral pain and temperature loss (spinothalamic).
https://drive.google.com/open?id=0B8uJUY-tie8GU1RKaGFxb05MTzQ
https://drive.google.com/open?id=0B8uJUY-tie8GRENDaFRSdWZnakk
——– set up across the resting nerve membrane.
■ Due to separation of charged particles (ions and proteins) between
extracellular and intracellular fluids.
Charge differential or voltage set up across the resting nerve membrane.
■ Due to separation of charged particles (ions and proteins) between
extracellular and intracellular fluids.
Polarized membrane■ ).
More positive ions (cations) outside (extracellular).
■ More negative ions (anions) inside (intracellular
Charge separation occurs because:
xxx leak (resting K+ conductance)
yyyyy charges leave cell down electrochemical gradient.
■zzzz zzzz determinant of RMP.
Charge separation occurs because:
■ K+ leak (resting K+ conductance)
■ + charges leave cell down electrochemical gradient.
■ Most important determinant of RMP.
Na+/K+ pump
■ Using ATP, establishes the x and y gradient; creates gradient to
allow zz leak to occur.
■ Pump is electrogenic: a K+ in for every b Na+ pumped out = net loss
of c charges from the cell.
Na+/K+ pump
■ Using ATP, establishes the Na+ and K+ gradient; creates gradient to
allow K+ leak to occur.
■ Pump is electrogenic: 2 K+ in for every 3 Na+ pumped out = net loss
of + charges from the cell.
RMP: ranges between a and b
■ RMP in humans (most cells) is xxxx (close to K), skeletal muscle
yyyyy, cardiac muscle zzzz
■ Threshold for depolarization: ~ tttt
RMP: ranges between –40 and –85 mV.
■ RMP in humans (most cells) is ~ –70 mV (close to K), skeletal muscle
–90 mV, cardiac muscle –90 mV
■ Threshold for depolarization: ~ –50 mV
Initiated by depolarizing stimulus (depolarization).
AP
RMP becomes more positive (less negative).
■ Ion channels open.
■ Positive ions move from outside to in.
■ As positive ions go intracellularly, RMP becomes positive.
Na+ (sodium)
■ Na+ entry initially causes more Na+ channels to open.
■ Membrane potential approaches that of sodium equilibrium potential.
■ Once threshold reached, the action potential (AP) will fire.
■ Threshold = 20 mV+.
All or none phenomenon.
■ If don’t reach threshold, don’t get AP.
■ AP is same with supra threshold and threshold stimuli
REFRACTORY PERIOD
■ Period of time after an AP that the membrane cannot again be stimulated,
ie, another AP cannot be initiated
ABSOLUTE REFRACTORY PERIOD
■ No stimulus, no matter how large, will stimulate an AP (corresponds to
close of voltage-sensitive Na+ channel).
RELATIVE REFRACTORY PERIOD■
A larger than usual stimulus will stimulate an AP, ie, the threshold is
increased (due to increased permeability to K+ channel).
Repolarization (Figure 10–5)
■ Membrane potential returns to normal following an AP.
■ ↓ Na+ permeability (rapid).
■ Block Na+ entry.
■ ↑ K+ permeability (in to out)(slower).
■ K+ leaks out of the cell.
https://drive.google.com/open?id=0B8uJUY-tie8GaXBwV21SRWRNTEU
https://drive.google.com/open?id=0B8uJUY-tie8GaG55MVVkcWJXUjg
Hyperpolarization
■ During repolarization there is an overshoot in the more negative direction.
■ Membrane potential briefly becomes more negative than RMP before
returning to RMP.
■ This is because of ↑ K+ conductance.
This is because of ↑ K+ conductance.
■ K+ channels stay open.
■ K+ efflux is greater than in resting.
hyperpol.
Note: Hyperpolarization is responsible
for the relative refractory period (cell
remains hypoexcitable). Influx of Cl– will also hyperpolarize and make AP
more difficult to generate.
Block sodium channels (↓ Na+ permeability).
■ Bind to inactivation gates of fast, voltage-gated Na+ channels,
■ keeping them closed and
■ prolonging absolute refractory period.
↓ Membrane excitability → cannot generate AP → no nerve impulse
conduction.
■ Reversible.
■ K, Cl, Ca conductances are unchanged
LA
Affect small myelinated fibers first (size rule).
Unmyelinated C-fibers (slow, dull, long lasting) (smallest)
↓
Small myelinated nerve fibers (pain, temp)
↓
Larger A-fibers (touch proprioception, Golgi tendon)
Depolarize (more positive) the postsynaptic membrane potential.
■ Brings it closer to threshold.
■ ↑ probability of AP in postsynaptic neuron
excitability
Creates an excitatory postsynaptic potential (EPSP).
■ Glutamate is the major excitatory neurotransmitter.
excitability
Inhibitory
■ Hyperpolarize (more negative) the postsynaptic membrane potential.
■ Moves it away from threshold.
■ ↓ probability of AP in postsynaptic neuron.
Creates an inhibitory postsynaptic potential (IPSP).
■ Result of ↑ membrane permeability to either Cl– or K+.
inh
glycine
GABA.
■ Both bind receptors and open Cl– channels (↑ Cl– permeability
inh
Spatial Summation
■ Two excitatory inputs arrive at a postsynaptic neuron simultaneously.
■ Converging circuit.
■ Arrival of impulses from multiple presynaptic fibers at same time.
Temporal Summation
■ Two excitatory inputs arrive at a postsynaptic neuron in rapid succession.
■ ↑ frequency of nerve impulses from a single presynaptic fiber.
Nerve impulse =
action potential spreads along plasma membrane.
Occurs in myelinated fibers (remember: Schwann cells (periphery) and
oligodendrocytes (CNS)).
■ ↑ velocity of nerve transmission along myelinated fibers.
Salt conduction
salt conduction
Conserves energy because:
■ Only the Ranvier node depolarizes.
■ Less energy for Na+/K+ ATPase to reestablish resting ion gradients.
■ Na+/K+ pumps reestablish concentration gradient only at Ranvier
nodes.
■ Allow repolarization to occur with less transfer of ions.
Electrochemical basis behind saltatory conduction is xx membrane
capacitance (yyyy distance between charges; zzz charges necessary).
Electrochemical basis behind saltatory conduction is ↓ membrane
capacitance (increase distance between charges; less charges necessary).
MYELIN■
Prevents movement of Na+ and K+ through the membrane.
■ Na+, K+ conductance only at Ranvier nodes.
■ ↓ membrane capacitance.
■ ↑ membrane resistance.
NODES OF RANVIER
■ Exposed nerve membrane where depolarization occurs.
■ Continue fueling spread of AP during nerve transmission.
nodes of ranvier
■ Located every 0.2–2 mm along the myelin sheath.
■ APs could not be produced if the myelin sheath were continuous.
■ APs travel down axon and “jump” from node to node.
CONTINUOUS CONDUCTION
■ Occurs in unmyelinated fibers.
■ Nerve transmission (AP) travels along entire membrane surface.
■ Relatively slow conduction (1.0 m/sec).
WALLERIAN DEGENERATION
■ Axon is cut.
■ The axon remnant distal to the cut (away from the cell body) degenerates
because axonal transport is interrupted.
wallerian degen.
■ Regeneration of axons possible if endoneurial sheath is intact (neurolemma).
■ Occurs at a rate of 2–4 mm/day.
■ If cell body is irreversibly injured, the entire neuron degenerates.
NEUROPRAXIA
■ Transient block (bruise).
■ Incomplete paralysis or loss of sensation.
■ Rapid recovery.
AXONOTMESIS
■ Axon damaged, but connective sheath remains intact.
■ Wallerian degeneration occurs distally but then regeneration can occur.
NEUROTMESIS
■ Complete transaction of nerve trunk.
■ Results in:
■ Motor
■ Flaccid paralysis.
■ Atrophy of end-organ.
Sensory
■ Total loss of cutaneous sensation.
NEUROTMESIS
synapse
Functional connection, anatomical junction between
■ Nerve axon (presynaptic axon) and
■ Target cell
■ Nerve (postsynaptic neuron)
■ Muscle (NMJ)
■ Gland
Synapse controls direction of nerve impulse
PRESYNAPTIC NEURONS
■ Transmit information toward a synapse.
SYNAPTIC CLEFT
■ Space between presynaptic terminal and postsynaptic cell.
POSTSYNAPTIC NEURONS
■ Transmit away from a synapse (dendrite → axon).
NERVE IMPULSES
■ Travel in only one direction because synapses are polarized.
Neuronal Excitability
■ Nerves are excited (APs generated) electrically or chemically.
■ Ligand-gated (NT binding) (most common).
■ Voltage-gated channels.
■ Mechanically gated (stretching).
Types of Synapse
■ Chemical synapse (most common).
■ Ligand-gated: Use NTs.
■ Electrical synapse.
CHEMICAL SYNAPSE.
■ Most common type.
■ Consists of:
■ Presynaptic membrane.
■ Synaptic vesicles within this terminal contain a NT.
■ Synaptic cleft.
■ Space between the presynaptic and postsynaptic membranes.
■ Postsynaptic membrane.
■ Membrane of postsynaptic neuron that contains specific receptors
for the NT
SYNAPTIC TRANSMISSION
■ Release of NTs.
■ NTs are stored in synaptic vesicles within the presynaptic axon terminal.
■ AP depolarizes the presynaptic membrane, causing:
■ Voltage-gated Ca2+ channels opened (on the presynaptic membrane).
■ ↑ Ca2+ influx.
synaptic transmission
■ Ca2+ causes the synaptic vesicles to fuse with membrane.
■ NTs are released by exocytosis into synaptic cleft.
■ NTs diffuse across cleft.
■ Bind to specific receptors on postsynaptic cell.
■ The time required for this process to occur is called synaptic delay.
Mediate most connections.
■ Small molecule NTs (contained within vesicles):
■ Glutamate, GABA, glycine, ACh, 5HT, NE, Epi, etc.
chemical NT
Neuropeptides (large dense vesicles):
■ Somatostatin, endorphins, enkephalins, opioids, etc.
chemical NT
ELECTRICAL SYNAPSE
■ Gap junctions; minority.
■ Cytoplasm of adjacent cells is connected by gap junctions.
electrical synapse
Allows passage of local electrical currents (ions and small molecules)
(from APs in presynaptic neuron) to pass directly to postsynaptic neuron.
■ Rare in the CNS.
■ Common in cardiac and smooth muscle.
■ Ensure a group of neurons act together; Synchronize groups of
neurons.
■ Important in embryonic development (morphogenic gradients
NM junction
Synapse between lower motor neuron (efferent nerve) and muscle.
■ Presynaptic terminal (lower motor neuron axon)
■ Releases ACh.
■ Postsynaptic membrane (skeletal muscle membrane).
■ Displays nicotinic receptor (NM).
NM junction
Threshold is –65 mV → all or nothing!
■ ~35 ACh required.
https://drive.google.com/open?id=0B8uJUY-tie8GRlZyMlp1OGdyeE0
https://drive.google.com/open?id=0B8uJUY-tie8GSF9nS3IwQkJyNFE
Acetylcholine Metabolism
■ Synthesized in the presynaptic terminal of the motor neuron from which
it is released.
■ Acetyl CoA + choline – (choline acetyltransferase)→ ACh (acetylcholine).
Ach metab.
Stored in synaptic vesicles.
■ Released into synaptic cleft (generates effect).
■ Breakdown:
■ ACh – (acetylcholinesterase [AChE])→ acetate + choline.
ant eyeball
Consists of two chambers (anterior and posterior).
■ Filled with aqueous humor (watery fluid).
pst eyeball
Posterior segment
■ Filled with vitreous humor (thick, gelatinous material
Sclera■
Tough, white outer layer.
■ Maintains size and form of the eyeball.
Cornea
■ Transparent dome on the anterior eye surface.
■ Protective function.
■ Helps focus light on retina at back of eye.
Choroid
■ Lining of the inner aspect of the eyeball beneath the retina; very vascular
Pupil
■ Circular opening (black area) in the middle of the iris.
■ Light enters the eye to reach retina through this opening.
■ Lens is located behind this aperture.
■ Size of the pupil is controlled by muscles in the iris.
Iris
■ Circular colored area of the eye (amount of pigment in the iris determines
the color of the eye).
Miosis:
Constriction of pupil:
■ Sphincter pupillae (iris sphincter) closes iris.
■ Response to:
■ Increased light.
■ Drugs (eg, narcotics).
■ Pathologic conditions.
■ Parasympathetic stimulation.
Mydriasis:
Dilation of the pupil (term often used for prolonged papillary
dilation):
Dilation of the pupil (term often used for prolonged papillary
dilation):
Mydriasis
Dilator pupillae (iris dilator) opens iris.
■ Response to:
■ Decreased light.
■ Sympathetic stimulation (fight or flight).
■ Drug.
■ Disease.
Mydriasis
Lens
■ Directly behind the iris and pupillary opening.
■ Focuses light on the retina.
■ Controlled by ciliary muscle (within the ciliary body).
Ciliary body
■ Functions:
■ Accommodation.
■ Ciliary muscle alters the lens refractory power (to focus light on the
retina).
■ Produces aqueous humor.
■ Holds lens in place
Retina
■ Innermost layer of the eye on the posterior surface.
■ Receives visual stimuli.
■ Communicates via CN II with the brain (visual cortex).
■ Photoreceptors
Rods (higher sensitivity, lower acuity)
■ Contain rhodopsin (photopigment).
■ Perceive different degrees of brightness: Responsible for night
vision (dark adaptation).
■ Relative lack of color discrimination.
■ Located mostly at the periphery of the retina.
Cones (higher acuity (fovea); color)
■ Each contains one of three photopigments.
■ Each being sensitive to a particular wavelength of light.
Three types: Red, green, blue.■
Primarily responsible for color vision.
■ Principal photoreceptors during daylight or in brightly lit areas.
■ Located in the center of the retina, especially in the fovea.
Photopigments
■ Four photopigments:
■ Rhodopsin (rods).
■ Red, green, and blue (cones).
Each photopigment contains:
■ Opsin (protein) bound to
■ Retinal (a chromophore molecule).
■ Together they compose rhodopsin.
Photopigments
The difference among the opsin molecules allows a xxx to
have yyyyy for a particular type or zzzz of light
Photopigments
The difference among the opsin molecules allows a photopigment to
have specificity for a particular type or color of light
https://drive.google.com/open?id=0B8uJUY-tie8GUm5DNlBIQndXbGs
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