PBL(1L) Physiology

Physiology - Chapter 25

What is balanced during steady-state conditions?Fluid intake and output

Primary means of up-regulating output?Renal excretion

Aside from fluid, what else does the kidney alter to match input/output?Electrolytes (Na+, Cl-, K+)

Total amount of body water in a 70 kg adult?42 L

Two main compartments of the extracellular fluid?Plamsa (1/4) and Interstitial Fluid (3/4)

Non-cellular portion of the blood that mixes continuously with the interstitial fluid through capillary membrane pores?Plasma

Excessive production of RBC's?Polycythemia

Normal hematocrit for men and women?0.42 and 0.38, respectively

Plasma and interstitial are seperated by what, so their ionic compositions are very similar?Highly permeable membrane

Which one has a higher protein concentration, intersitial or plasma?Plasma

What has low permeability to proteins and therefore leak only small amounts of protein?Capillaries

Intracellular is seperated from the ECF by what?A highly selective membrane

What is the highly selective membrane permeable to?Water

What is it not permeable to?Electrolytes found in the body

Osmolarity and concentration of water are approximately equal in the what?ICF and ECF

What is different in the ICF and ECF?Concentrations of various solutes

Can the volume of the ECF and ICF be measuered directly?No, they are calculated from other compartments

ICF and ECF distribution is mainly determined by what, which acts across the cell membrane?Osmotic Effect of Electrolytes

Can Na+ and Cl- pass through the cell membrane?No, but water can. Therefore, the concentrations of these solutes determine osmotic gradient

Concentration expressed as osmoles per kilogram of water?Osmolality

Concentration expressed as osmoles per liter of solution?Osmolarity

Amount of water pressure required to prevent osmosis of water through a semipermeable membrane?Osmotic pressure

What is directly proportional to the concentration of osmotically active particles in a solution?Osmotic pressure

Small differences in the solute concentration across a cell membrane can result in?Rapid osmosis of water

Solution in which NO osmotic force develops across a cell membrane when a normal cell is placed in solution?

Example of isotonic solutions?0.9% sodium chloride and 5% glucose solution

Solution that contains a higher concentration of osmotic substances than does the cell?Hypertonic

What happens to a cell placed in hypertonic solution?Shrinks

Solution that contains a lower concentration of osmotic substances than does the cell?Hypotonic

What happens to a cell placed in hypotonic solution?Swells

Do osmolarities of the ICF and ECF stay different for very long?No, water moves rapidly across the cell membrane.

Cell membranes are impermeable to solutes, therefore - what stays relatively constant?number of osmoles, unless solutes are added to or lost from the ECF

Increased ECF osmolarity?Hypertonic

Decreased ECF osmolarity?Hypotonic

Net osmosis of water OUT of the intracellular fluid -> extracellular fluidHypertonic

Increase osmolarity of both compartments?Hypertonic

Net osmosis of water INTO the intracellular fluid from the extracellular fluid?Hypotonic

Increase in fluid volume of both compartments (Intracellular slightly more than ECF)Hypotonic

Three conditions that are likely to cause INTRACELLULAR edema?1. Hyponatremia

2. Depression of the metabolic systems of the tissues

3. Lack of adequate nutrition to the cells

Sodium ions usually leak from where to where?Extracellular to Intracellular

What happens when they dont get enough nutrition or the metabolic systems are depressed?Na+ cant be pumped effectively out of the cell

What does the excess sodium cause?osmosis of water into the cells

Has a direct effect on permeability of the membrane, allowing sodium to diffuse into the interior of the cells?Inflammation

What type of edema will this result in?Intracellular Edema

Increased intracellular ions will result in what?osmosis of water into the cells

Two general causes of ECF edema?1. abnormal leakage of fluid from the plasma to the interstital spaces around the capillaries

2. failure of the lymphatics to return fluid from the interstitium of the blood = lymphedema

Increased capillary filtration coefficient allows what?Increased leakage of fluids and plasma proteins through capillary membranes

When does this occur?Allergic reactions, bacterial infections, and toxic substances that injure the capillary membranes and increase permeability

Obstruction of veins, excessive blood flow from arteries to capillaries or failure of the heart to pump results in?Increased capillary hydrostatic pressure

Fail of liver to produce p. proteins, loss of large amounts of proteins, or severe burns results in?Decreased plasma colloid pressure ( -> increase capillary filtration rate)

Lymphatic blockage, which prevents return of protein from interstitial to the blood results in?Increased interstitial fluid colloid osmotic pressure ( -> draws fluid out of the plasma into the tissues)

Plasma proteins leak into the intersitium but can't returnto the plasma via lymphatics in what disease condition?Lymphatic blockage

What will rise due to the increased interstitum plasma proteins?Intersitial collloid osmotic pressure

Increased intersitial colloid osmotic pressure will result in what?Fluid drawn out of the capilliaries -> EC Edema

Infection with what can result in lymphatic edema?Filarial Nematodes

Three major safety factors that prevent edema?1. Low compliance of tissues as long as interstitial fluid hydrostatic pressure is in the negative range

2. Lymph flow can increase 10 - 50 fold

3. "Wash down" of interstitial fluid protein as lymph flow increases

Low compliance means?That small increases in interstitial fluid volume are assoicated with large increases in IFHP.

When Interstitial fluid volume increases, IFHP increases and opposes what?Further exessive capillary filtration

What is the safety factor (mmHg) for Low compliance?3 mmHg

What is the safety factor (mmHg) for Lymph flow increases?7 mmHg

With increased fluid volume, what happens to protein concentration?It is decreased, as it is washed away before it can be filtered

What does the decrease in protein concentration cause?lowers the net filtration force across the capillaries and tends to prevent further fluid accumulation

Safety factor for protein "wash down"?7 mmHg

Combind safety factor in mmHg?17 mmHg

Capillary pressure could theoretically rise 17 mmHg without what occuring?Significant Interstital Edema occurance


Homeostatic functions of the Kidney?Excretion of wastes and chemicals

Regulate water and electrolytes

Regulate body fluid osmolarity

Regulate arterial pressure via water, AII, Renin, etc.

Regulate acid/base balance via excretion of acids and buffers

Regulation of D3


Fundamental unti of operation for the NSNeuron

Much of NS activity arises from mechanisms that activate what?Sensory receptors

Sensory input can be stored in form of what?Memory

The brain compares new sensory information with stored memory information to develop what?Successful strategies to form motor output

At a termination site, axons give off many small branches that end in what? Synaptic terminals

Synaptic Terminal is apposed to but seperated from an adjacent what?Post synaptic structure (either soma or dendrite)

The narrow space between is called the what?The synaptic cleft

Synaptic Boutons contain an abundance of what organelle?Mitochondria

They also contain many synatpic vesicles which contain what?NTs

What happens when the NT binds to receptors on the postsynaptic membrane?Alters membrane permeability to ions

Overwhelming majority of synapses in the brain are what type of synapses?Chemical

Transmission of signals at chemical synapses is described as what?One Way

Least common type of synapse in mammals is what?The electrical synapse

Electrical synapses consist of what?Gap junctions

Why are these important?They form low resistance channels between the pre and post synaptic membranes

Why are these type of electrical synapses important?Ions can move freely and this allows rapid transfer of signals that can spread through large pools of neurons

What happens after an action potential hits the presynaptic element?Ca2+ channels open

After the Ca2+ channels open, where does the calcium go?It moves into the axon terminal

What does the ca2+ influx cause?Synaptic vesicles to move/fuse with the membrane and be released

The amount of vesicle release is proportional to the amount of what?Ca2+ influxR

Receptors are complex proteins that contain two things?1. Binding Domain

2. Ionophore (extends through the membrane, into the interior of the post synaptic structure)

Ionophores can be what?Ion specific channel or second messanger activator

Most, if not all, receptors are linked to what?Ligand-gated ion channels

These ligand-gated channels can be?Cationic or Anionic

Post synaptic cationic channels that allow sodium to enter are usually?Excitatory

Post synaptic anionic channels that allow chloride to enter are usually?Inhibitory

Second messanger activators are typically G-proteins attached to what?A portion of receptor that protrudes into the postsynaptic element

When the receptor is activated, a portion of it is released and moves within what?The cytoplasm

What does it do in the cytoplasm? (1 of 4 possible things)1. Opens membrane channel specific for an ion species (Na or K) and keeps it open

2. Activates cAMP or cGMP -> specific metabolic machinery

3. Activates enzymes -> biochemical reactions

4. Activated gene transcription -> protein synthesis -> long-term changes

Small-molecule, rapidly acting transmitters can be synthesized and packed into what?Synaptic Vesicles

SmNT have _______ action and usually act open or close an ion channel.rapid

Aside from this action, they can activate enzymes to alter what?Metabolism in the postsynaptic element

Where are smNT recycled?Axon Terminal

Acetyl CoA and Choline yeild what?ACH

What is the enzyme necessary to synthesize ACH?Choline Acetyltransferase

Where is ChAT synthesized?Soma and delivered to the bouton via axonal transport

What breaks down ACH?AChE

Where is AChE present?Cleft

Choline is transported back to where for reuse?Synaptic Bouton

Transmitter agents that are typically synthesized in the Soma as integral parts of large proteins?Neuropeptides

Are larger or small amounts of neuroactive peptide released, as compared to smNT?Smaller amounts

Are vesicles for neuroactive peptides recycledNo

An important feature of neuropeptides is what?Prolonged duration of action

What can neuropeptides do?Alter ion channel function and modify cell metabolism or gene expression

Neuronal resting membrane potential?-65 mV

Move to a MORE POSITIVE value is also called what?Depolarization

Move to a MORE NEGATIVE value is also called what?Hyperpolarization

Depolarization makes the cell more/less excitable?More

At rest, excellular sodium is higher/lower than intracellular?Higher

At rest, excellular potassium is higher/lower than intracellular?Lower

The electrical potential that opposes movement of that ion down its concentration gradient?Nerst Potential

Nerst potenital for sodium+61 mV

Would you expect sodium to move in or out with a resting membrane potential of -65 mV?In, but it can't because the channels aren't open

Some does leak in however, and potassium leaks out - what corrects this?Na/K pump

Neuronal membrane is maintained at -65 mV b/c it is much more permeable to ?K

Thus, the interior of the cell is negatively charged and outside it become what?Positively charged

The interior of the soma consits of what that allows changes in potential to spread throughout the neuron?hightly conductive fluid

Ligand-gated channel open, Na+ out of cell -> potential in terminal moves closer to +61 mV, called?EPSP (excitatory post synaptic potential)

Action potential initated at?Initial segment

Why would it be initiated there?Region contains approx. seven times the number of voltage gated channels

Simulaneous discharge of many axon terminals is required to bring post synaptic element to threshold, called?Summation

Basis of production for an inhibitory postsynaptic potential (IPSP)NTs that open Cl- gated channels

Nernst Potential for chloride?-70mV

This is more negative than resting potential so chloride would be expected to do what?move into the cell

Occurs when a second postsynaptic potential arrives before the membrane has returned to resting potential?Temporal Summation

Occurs when a number axon terminals over the surface of a neuron are active simultaneously?Spatial Summation

At any given time, the neuron is combining all the IPSPs and EPSPs

Dendrites contain a relatively small number of voltage gated channels and therefore are not able to what?Propogate action potentials

However, they can do what?Support the spread of electrical current via electrotonic conduction

This mode of tranmission is subject to what?Decay over time

Therefore synapses on proximal dendrites have more what than distal?Influence over action potentials

Firing rate of a neuron is directly related to ?the degree by which the threshold is exceeded (the farther above, the greater the firing rate)

Rapid, repetitive stimulation of a synapse will lead to whatFatigue

Fatigue will cause what to happen?decreased responsiveness

The decrease in responsiveness is the direct result of what?increased build up of ca2+ in the bouton and inabilty to replenish the NT

Repetitive stimulation + excitatory neuron after brief rest period = requires less current and produces more responsePost-tetanic Facilitation

More acid EC synaptic environments will cause what to happen to excitability (decrease pH)?Decreased Excitability

Decrease in the supply of oxygen will cause what?Decreased Synaptic Activity

Increases the excitability of many neurons?Caffeine

Indirectly increases the activity of neurons by inhibiting certain populations of inhibitory neurons?Strychnine

Amount of time to cross the synapse that varies in different pools of neurons?Synaptic Delay

Synaptic delay is influenced by?1. Time required to release NT

2. Time need for NT to diffuse across

3. Time needed for binding of NT to receptor

4. Time needed for NT to carry out its action

5. Time required for ions to diffuse into the PostS cell and alter membrane potential


Responsible for tast and smell, O2 and CO2 levels in blood, and osmolarity of tissue fluids?Chemoreceptors

Sensory is convey to the spinal cord using a ______ ____ approach?Labeled Line

They are basically all conveyed the same/differently?Same, action potential from pain is the same as action potential from temperature

What does allow us to differentiate pain from some other sensation, is where it?Terminates in the NS

Action potentials in the spinothalamic tract are perceived as?Pain

Action potentials in the dorsal column-medial lemniscal system are perceived as?Touch or pressure

Local current generated at the receptor when activated by the appropriate simulus is called?Receptor Potential

The maximum receptor potential amplitude of about 100 mV is achieved when membrane Na+ is at its?Maximum

When is a self propogating action potential initiated in the fiber?When the receptor potenital exceeds a set value

Receptor potential is proportional to the?Stimulus intenisty

As stimulus intensity increases, the action potentials will increase in frequency

Sensory receptors can ____ to their stimuli?adapt

Compression anywhere on the pacinian corpuscle will cause what?Indentation, elongation, or defromation of the central fiber

Any type of change in the central fiber leads to what?Increase in membrane permability

The fluid will redistribute within the corpuscle in response to the whatApplied pressure

A process that may involve the gradual inactivation of the sodium channels over time?Accomodation

Continue to transmit signals with little change in frequency so long as the stimulus is still present?Slowly adapting fibers

Another name for slowly adapting fibers?Tonic Receptors

Examples of Tonic Receptors?Golgi Tendon Organs

Pain Receptors

Baroreceptors

Chemoreceptors

Activated only when stimulus intesity changes?Rapidly adapting fibers

Other names for these rapidly adapting fibers?Rate Receptors and Movement Detectors

Example of Rapidly Adapting?Pacinian Corpuscle

Receptors of the Semi Circular Canals

Joint Receptors (proprioceptors)

Typical large and myelinated fibers of the spinal nerves?Type A

Small unmyelinated nerve fibers that conduct impulses at low velocities?Type C

Largest and most rapidly conducting fiber?Type A

Fibers from the golgi tendon organs?Group 1b (Type A)

Weak stimulus excites a small/large receptive field?Small

Any aggregate of neurons can be referred to as what?a neuronal pool

Each neuronal pool has set of several inputs to its _______ _____Receptive field

membrane potential that is slightly depolarized but not enough to reach threshold?Facilitated

Are these fibers more or less excitable and why?More, they require less depolarization to reach threshold

Input signal spreads to an increasing number of neurons as it passes through successive orders of neurons in its path?Amplifying divergence

What pathway utilizes this type of amplifying divergence?Corticospinal Tract

Signal is transmitted in two directions from the pool?Divergence into multiple tracts

Example of diverenge into multiple tracts?Dorsal column -> Cerebellum and Lower Brain

Results when multiple afferent sources reach a single neuron in the pool?Convergence

Can also have convergence on a single neuron from ?Multiple sources

One of the most important ways that the CNS correlates, summates, and sorts different types of information?Convergence

While moving flexors, inhibiting extensors?Reciprocal Inhibition Circuit

Prolonged output discharge is called?Afterdischarge

Positive feedback to re-excite the input of the same circuit is called?reverbatory

Some neuronal pools generate a rhythmical output signal, one example of this would be?Respiratory centers in the reticular formation of the medulla

When the carotid body is stimulated by arterial O2 deficiency?Both the frequency and amplitude of the respiratory rhythmical output signal increase progresively

Two main mechanisms to inhibit seizures or uncontrolled firing of neuronal circuits?Inhibitory circuits and fatigue of synapses

With feedback inhibition, output signals what located in the pool to provide inhibitory feedback to the main output?Inhibitory Interneurons

Exerts inhibtory influences throughout the muscle control system?Basal Ganglia


Includes both tactile and position sensations?Mechanoreception

Detects increases or decreases in temperature?Thermoreception

Detects tissue damage or the release of specific pain-mediating molecules?Nociception

Sensations that originate from stimulation of body surface structures (skin and sub c tissues, muscle, fasica, tendons)?Exteroceptive

Sensory signals that arise from internal organs (endodermally derived structures)?Visceral Sensations

Touch, pressure, vibration are each detected by what general class of tactile receptors?Mechanoreceptors

Found in varying density in all areas of the skin (as well as cornea of the eye)?Free Nerve Endings

Encapsulated, rapidly adapting receptor found in non-hairy areas of skin (fingertips) - senitive to lighest touch?Meissners' corpuscle

Found in glabrous skin but are also present in moderate numbers in hairy skin surfaces, slow adapting - continuous touch?Merkels' discs

Entwined at base of each hair, rapidly adapting, detect movement of objects over the skin that displaces hair?Hair end-organs

Encapsulated, located at skin and deeper tissues and joint capsules, little adaptation - signal continous touch/movement?Ruffini's end-organs

Present in the skin and deeper tissues, such as fascia - Adapt rapidly, important for vibration and mechanical change?Pacinian corpuscles

Most of these receptors transmit signals over what type of fibers?Large, myelinated fibers that exhibit rapid conduction

Are linked to small myelinated fibers and unmyelinated type C fibers that conduct at slow velocity?Free Nerve Endings

Detect the most rapid change in vibration - linked to large, myelinated fibers?Pacinian corpuscles

Sense of tickle or itch is linked with what type of receptor?Free Nerve Endings

Signals that orgininate in the thermoreceptors and nociceptors are processed along what system?Anterolateral

Signals that originiate in the mechanoreceptors are processed along what system?Dorsal Column-Medial Lemniscal

Somatosensory information for the face is carried mainly along branches of what nerve?Trigeminal

Some of the DC-ML fibers enter the SC and synapse in the?Gray Matter

Most of the DC-ML fibers enter the SC and do not synapse until they travel upward and reach what?Dorsal Column Nuclei

Where is the dorsal column nuclei located?Caudal Medulla

Lower extremity fibers synapse in what part of the dorsal column nuclei?Nucleus Gracilis

Upper extremity fibers synapse in what part of the dorsal column nuclei?Nucleus Cuneatus

Axons of the cuneate and gracilis form what?Medial Lemniscus

Where does the medial lemniscus cross the midline?Caudal Medulla

Where does the bundle travel next?Thalamus

Where do the axons then terminate?VPL (Ventrolateral Posteior Nucleus)

Axons of the VPL neurons then enter the posterior limb of the?Internal capsule

From the internal capsule, where do these axons then project?Primary Somatosensory Cortex (Postcentral Gyrus)

Information for the LE travels in what part of the dorsal column?Medial

Information for the UE travels in what part of the dorsal column?Lateral

LE information terminates in what part of the VPL?Laterally

UE information terminates in what part of the VPL?Medially

LE information then travels to what part of the SI?Medial Part of the SI

UE information then travels to what part of the SI?Arm section of the SI (contralateral to the body)

Tacticle somatosensory information travels from the fact through what nerve?Trigeminal

Where does CN V enter the BS?Midpontine Levels

Where does CN V terminate in the BS?Trigeminal Sensory Nucleus

Axons from CN V cross the midline, course rostrally, and terminate where?VPN (Ventral Posteriomedial Nucleus)

LE projects toward the _______ part of the hemisphere in the SI?Medial

UE projects toward the _______ part of the hemisphere in the SI?Mid-Lateral

Most characteristic of the six horizontally arranged layers of the cortex?Layer IV

Why is the the most characteristic layer?Receives the important projections from VPL and VPM of the ventrolateral thalamus

In the most anterior part of area 3 in the SI, the vertical columnar arrays are concered with what?Muscle Afferents

In the most posterior part of area 3 in the SI, the vertical columnar arrays are concerned with what?Cutaneous Input

In area 1, the verical columnar arrays process what?Additional Cutaneous Input

In area 2, the vertical columnar arrays are concered with what?Pressure and Proprioception

Lesions that involve the primary somatosensory cortex result in:1. Inability to localize cutanous stimuli on the surface of the body (crude localization may remain)

2. Inability to judge degree of pressure or weight of objects

3. Inability to identify objects via touch or texture

Lesions that involve Brodman's Area 5 and 7 (assoication cortex for somatic sensation) result in:1. Inability to recognize objects that have complex shape when palpated with contralateral hand

2. Loss of awareness of the contralateral side of the body (hemineglect) - most acute with lesion of non-dominant parietal lobe

3. Exploring an object, only touch the side that is ipsilateral to the lesion, ignore the contralateral side (amorphosynthesis)

Determined by the combination of primary sensory neurons, dorsal column nuclear neurons, and thalamic neurons?Receptive field for an SI cortical neuron

Used to determine and individuals ability to distinguish two simultaneously applied cutaneous stimuli as separate?Two-point discrimination test

Where can two stimuli be applied close together and still felt as 2 sepearte points with no overlap?Lips and Fingertips

How far apart must two stimuli be to be felt as separate points on the back?30-70 mm

Mechanism used throughout the NS to "sharpen" signal transmission?Lateral Inhibition

Where does lateral inihibition occur in the DC-ML system?At the level of DC nuclei and in the thalamic nuclei

Particularly sensative for detecting rapidly changing repetitive stimuli (basis for vibartory sense)?DC-ML (Pacinian and Meissners)

Awareness of body position or body movement is called what?Proprioception

Combination of what is used by the NS to produce a sense of proprioception?Combination of tactile, muscle, and joint capsule receptors

What type of endings are rapidly acting receptors responsible for detecting the rate of change in movement?Ruffini's end-organs

What accounts for the DC-ML ability to localize stimuli fairly well?Point-to-point organization

What accounts for the less effective localization ability seen in the anterolateral system?Relative diffuseness

Different Characteristics of the Anterolateral System, compared to the DCML?1. Velocity of transmission is approx. 1/2 that of the DCML

2. Degree of localization is poor

3. Gradations in intestity are far less pronounced

4. Ability to transmit rapid repetitive signals is poor

Anterolateral system transmits what type of sensations?Pain, Temperature, tickle, itch, crude touch, and sexual sensations


Protective mechanism for the body?Pain

Not just a sensation but a response to tissue damage?Pain

Felt within 0.1 sec after stimulation?Fast Pain

Begins 1 second or more after the painful stimulus?Slow Pain

Usually associated with tissue damage?Slow Pain

Slow pain can be referred as what?Burning, aching, or chronic pain

All pain receptors are what?Free Nerve Endings

Found in the largest density where?Skin, periosteum, arterial walls, joints, dura, and cranial vault

Activated by mechanical, thermal, or chemical stimuli?Pain receptors

Mechanical and Thermal stimuli tend to elicit what?Fast Pain

Chemical stimuli tend to elicity what?Slow Pain

What two chemical stimuli enchance the sensitivity of pain receptors but do NOT excite them?Substance P and prostaglandins

Items that excite the pain receptors?Bradykinin, serotonin, histamine, potassium, acids, ACH, and proteolytic enzymes

Pain receptors adapt very quickly/slowly/ or sometimes not at all?Slowly

Activation of these receptors can become progressively greater as the pain continues, what is this called?Hyperalgesia

Fast pain trasmitted over what type of fibers?A

Slow, chronic type of pain transmitted over what type of fibers?C

A primiarly excite neurons in lamina ___ of the dorsal horn?I

Wheras, C fibers synapse with neurons in the?Substania Gelatinosa

From the Substania Gelantinosa -> deeper into gray matter -> active neurons in what lamina(s)?Mainly V, but also VI and VII

Neurons that receive A give rise to the?Neospinothalamic Tract

Neurons that receive C give rise to the?Paleospinothalamic Tract

Neospinothalamic Tract axons cross the midline where?Close to their origin

NST ascends what of the SC as part of the anterolateral system?White matter

Where do some of the NST fibers terminate in the BS?Reticular Formation

Where do the majority of the NST fibers terminate?VPL of the thalamus (from here they project to the SI cortex)

Which the phylogenically older of the two pain systems?Paleospinothalamic Tract

Pathway for the PST (after cross midline near origin and anterolateral ascention)?Terminate in BS -> fibers from BS (reticular) -> intralaminar nuclei and posterior nuclei of thalamus and to the hypothalamus

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PBL(1L) Physiology