Cell/Neuro Exam 1 Review

five components in the homeostatic reflex loop

- stimulus- receptor- control center- effector- response


something produces change


protein site on cell membrane that detects the change

control center

central nervous system


response organs


parameter returns toward the "set point

how does the body maintain homeostatic condition?

homeostatic reflex loop

what are the two main control centers?

- nervous regulation- hormonal regulation

characteristics of nervous regulation

- response fast- last for a short time- act exactly or locally- neurotransmitters

characteristics of hormonal regulation

- response slow- last for a longer duration- act extensively- hormone

most of homeostatic control are via _______.

- negative feedback

examples given of negative feedback

- control of body temperature- regulation of blood glucose concentration - regulation of water balance

glucose regulated by


water content regulated by

- antidiuretic hormone- vasopressin

negative feedback body temperature control sequence

- too hot- blood vessel dilating, sweating- blood temperature decreases- inhibitory action on the brain

examples given of positive feedback

- contraction of the uterus during childbirth (oxytocin triggers uterine contraction)- blood clotting (platelets stop bleeding)

positive feedback childbirth sequence

- stimulus from cervix- oxytocin secretion- increase uterine contraction- increase more oxytocin secretion until baby is born

% TBW of male


% TBW of female


% TBW of infant


TBW vs body fat

TBW as % of body weight correlates inversely with body fat

TBW is a greater % of body weight when body fat is (higher/lower).

- lower

Typically, females have higher % of adipose tissue (fat) = _______ TBW

- less

Body Fluid Compartments as fractions

TBW = 100%Intracellular fluid = 2/3Extracellular fluid = 1/3 - Interstitial fluid = 3/4 of ECF - Plasma = 1/4 of ECF

body fluid volume equation

V = Q/CwhereV = body fluid volumeQ = solute quantityC = solute concentration

the ways of measuring the volume of total body fluid, extracellular fluid and plasma are by

injection of some substances

injection of radio labeled water (deuterium)

freely distribute across all membranes into all compartments, measure total body fluid volume

injection of Na (22Na)

distribute in the extracellular fluid, measure extracellular fluid volume

injection of albumin (125I-albumin)

distribute in the plasma, measure plasma volume

requirements for the injection substance

- what you inject is nontoxic- substance does not cause shifts in fluid distribution within the compartment measured- substance is not metabolized quickly

total body volume = _______ + _______


ICF = _______

total body fluid volume - ECF

Interstitial fluid volume = _______

ECF- plasma volume

major ions in ECF and ICF

- Na+- K+- Ca2+- Cl-- HCO3-

ECF/ICF are measured in units of


ECF and ICF pH at rest are


Osmolarity of ECF and ICF at rest are


at equilibrium, Na+ is more concentrated in the (ECF/ICF)


at equilibrium, K+ is more concentrated in the (ECF/ICF)


cell membranes spontaneously form

lipid bilayers

describe phospholipid component of cell membranes

- polar hydrophilic phosphorylated glycerol head facing outward- non polar hydrophobic fatty acid chain tail facing inward

simple diffusion occurs as a result of

the random thermal motion of molecules

does simple diffusion need a carrier?


when does simple diffusion occur?

- whenever there is a concentration difference across the membrane- the membrane is permeable to the diffusing substance

net movement (flux/flow) of simple diffusion

is from area of high concentration to low concentration

simple diffusion: over time,

concentration will be equal

fick's law measures

diffusion rate

ficks law equation

J = PA(Ca-Cb)whereJ = diffusion rateP = permeabilityA = surface areaCa = concentration ACb = concentration B

diffusion rate is dependent upon

- permeability of the membrane - lipid solubility - membrane thickness- surface are of the membrane - microvilli increase surface area- the magnitude of concentration gradient - driving force of diffusion- temperature - higher temperature, faster diffusion rate

what types of molecules are transported by facilitated diffusion via carrier?


facilitated diffusion via carrier: concept

diffusion down their concentration gradients, carried out by carrier protein (transporter)

facilitated diffusion via carrier: substance

- glucose- amino acid

facilitated diffusion via carrier: mechanism

a "ferry" or "shuttle" process

facilitated diffusion via carrier: energy source


example of facilitated diffusion via carrier

glucose transporter-GLT

characteristics of carrier mediated facilitated diffusion

- down concentration gradient- saturation - Tmax (transport maximum): carrier sites have become saturated- chemical specificity (stereospecificity): carrier interact with specific molecule only- competitive inhibition: molecules with similar chemical structures compete for carrier site

Facilitated diffusion via channels transports

electrolytes (ions)

types of facilitated diffusion channels

- non-gated (leak channel)- voltage-gated (controlled by charge)- ligand-gated (controlled by chemicals)

facilitated diffusion via channels direction of movement

Ions (Na+, K+, Cl-, Ca2+) diffuse across membranes down their concentration gradients.

if the ion channel is open it is said to have a


primary active transport

- substance is moved from an area of low concentration to an area of high concentration, needs carrier (active transport pump)- uphill movement of molecules, needs energy from ATP (bind to carriers)

Primary active transport carrier examples

- Na+-K+ ATPas (Na+-K+ pump) in all cell membrane- Ca2+ ATPase (Ca2+ pump) in sarcoplasmic reticulum of muscle cells- H+-K+ ATPase (H+-K+ pump) in gastric parietal cells

Na+-K+ ATPase (Na+-K+ Pump)

- Na+-K+ pump is present in the membranes of all cells- it uses about 40% of the body energy- it pumps Na+ from ICF to ECF and K+ from ECF to ICF. each ion moves against its concentration gradient.- ATP (hydrolysis to ADP and phosphate ion) provides energy.- it is responsible for maintaining concentration gradients for Na+ and K+ across cell membranes.

secondary active transport

- substance transports against concentration gradient, coupled with Na+ transport- needs transporter energy

secondary active transport given example

- Na+-glucose co-transporter (SGLT) transport Na+ and glucose together- the downhill movement of Na+ provides energy for the uphill movement of glucose- energy indirectly provided by Na+ gradient across membrane which is established by Na+-K+ pump

list carrier mediated transports

- facilitated diffusion- primary active transport- secondary active transport

simple diffusion: active or passive?

passive; downhill

facilitated diffusion: active or passive?

passive; downhill

primary active transport: active or passive?

active; uphill

secondary active transport: active or passive?

active; uphill

is simple diffusion carrier-mediated?


is facilitated diffusion carrier mediated?


is primary active transport carrier mediated?


is secondary active transport carrier mediated?


does simple diffusion use metabolic energy?


does facilitated diffusion use metabolic energy?


does primary active transport use metabolic energy?

yes; direct

does secondary active transport use metabolic energy?

yes; indirect

does simple diffusion depend on Na+ gradient?


does facilitated diffusion depend on Na+ gradient?


does primary active transport depend on Na+ gradient?


does secondary active transport depend on Na+ gradient?

yes; solutes move as Na+ crosses cell membrane


the flow of water across a semipermeable membrane from lower solute concentration to higher solute concentration (due to concentration gradient)

driving force for osmotic water flow

the osmotic pressure difference

osmotic pressure

the minimum pressure which needs to be applied to a solution to prevent the net flow of water (osmosis), expressed as mmHg or atm

osmotic pressure of a solution (expressed as pi) depends on two factors:

- the concentration of osmotically active particle- whether the solute remains in the solution


when two solutions have the same effective osmotic pressure; no net water flow between them


when two solutions have different effective osmotic pressures, the solution with the higher effective osmotic pressure


when two solutions have different effective osmotic pressures, the solution with the lower effective osmotic pressure

water will flow from (hypertonic/hypotonic) solution in the the (hypertonic/hypotonic) solution

hypotonic solution into the hypertonic solution

how does tonicity affect cells? cell in isotonic solution

does not cause swelling or shrinking of cells

osmolarity of isotonic solution

osmolarity is close to 290 mOsm/L

how does tonicity affect cells? cell in hypertonic solution

cause cells to shrink

osmolarity of hypertonic solution

osmolarity > 290 mOsm/L

how does tonicity affect cells? cell in a hypotonic solution

causes cells to swell

osmolarity of hypotonic solution

osmolarity < 290 mOsm/L

nernst equation

equilibrium potential (Ex) for an ion at a given concentration difference across a membrane- takes a concentration difference for ion and converts it t a voltage

how is the resting membrane potential established?

resting membrane potential is established by various ions moving across the cell membrane - Em takes into account the movement of ALL ions across the membrane- it is NOT the same as the equilibrium potential for each separate ion.

ionic equilibrium potentials vs resting membrane potentials

- Em (-70 mV) is close to the equilibrium potential for K+ and Cl-- Em (-70 mV) is far from the equilibrium potential for Na+ and Ca2+

Ionic equilibrium potential for Na+

ENa+ = +65 mV

ionic equilibrium potential for Ca2+

ECa2+ = +120 mV

ionic equilibrium potential for K+

EK+ = -85 mV

ionic equilibrium potential for Cl-

ECl- = -90 mV

the formation of resting membrane potential depends on

- all ions across the membrane- mainly depends on concentration difference of K+ across the membrane, this causes K+ diffusion from ICF to ECF- Na+-K+ pump established K+ concentration gradient

action potentials sequence: depolarization

voltage-gated Na+ channels open and Na+ rushes into the cell; membrane potential becomes less negative

action potential sequence: repolarization

Na+ channels close, but voltage-gated K+ channels open, causing an outflow of K+; return of the membrane potential towards resting level

ion basis of action potentials (ion conductance)

- at rest, K+ conductance is higher than other ions (K+ leak channels are open; outward movement of K+). Na+ conductance is low- depolarization. stimulus will move the cell membrane potential to threshold (-45 to -60 mV). This initial depolarization will open voltage-gated Na+ channels (Na+ conductance high). Na+ rushes into the cell.- repolarization. Na+ gates inactivate. depolarization opens voltage-gated K+ channels (K+ conductance high). K+ leaves cell at high rate (outward K+ current).- hyper polarization. K+ conductance is higher than at rest, but eventually returns to normal

characteristics of action potential

- size and shape. each cell of a certain type's action potential looks identical. but different types of cells (muscle and nerve cells) have different shapes of action potentials.- threshold, all or none response. an action potential either occurs or it does occur.- refractory period- propagation

absolute refractory period

a period where it is completely impossible for another action potential to be activated, regardless of the size of the stimulus. results from closure of the inactivation gates of Na+ channel

relative refractory period

time after the absolute refractory period when another action potential can be stimulated (some of the Na+ channels have been recovered), but only if a stronger stimulus is applied. membrane is less excitable after the initial action potential.

conduction velocity

the speed at which action potentials are conducted along a nerve or muscle- this property determines the speed at which information can be transmitted in the nervous system

there are two mechanisms that increase conduction velocity:

- increasing nerve diameter: lowers internal resistance and increases conduction velocity- myelinating the nerve fiber

ion channel inhibitor examples

- lidocaine- tetrodotoxin (TTX)


is a medication used to number tissue in a specific area (local anesthetic). it blocks voltage-gated Na+ channels, imparts ability to generate and conduct action potentials. Produces numbing effect.

tetrodotoxin (TTX)

is a potent neurotoxin from the Japanese puffer fish. it blocks Na+ channels. no action potentials. especially critical for inhibition of contraction of respiratory muscle

types of muscle include

- skeletal muscle- cardiac muscle- smooth muscle

skeletal muscle characteristics

- attached to skeleton- striated- voluntary - high power- no gap junctions

cardiac muscle characteristics

- heart- striated- involuntary- high power- gap junctions

smooth muscle characteristics

- hollow organs- non-striated- involuntary- low power- gap junctions

skeletal muscle fibers (muscle cells)

- muscle fibers are enormous compared to other cells- contain hundreds of nuclei; each muscle fiber is surrounded by the cell membrane (sarcolemma)- known as striated muscle due to striations (light band: i band; dark band: a band)- contain numerous thin strands called myofibrils


functional unit of muscle fiber- the basic contractile unit in muscle. sarcomeres join need to end to form myofibrils. each myofibril has thousands of sarcomeres.

the sarcomere is delineated by

z disks

each sarcomere contains

an a band (center) and 1/2 i bands X2

a bands

contain the thick filaments - fixed length

i bands

are on either side of a bands and they contain thin filaments and z disks

thin filaments are composed by three proteins

actin, troponin, tropomyosin


backbone, two strands of polymerized globular actin. each actin has thick filament (myosin) binding site


a complex of three globular proteins (T, I and C). binds Ca2+ to regulated muscle contraction


a filamentous protein that runs along the "groove" of actin. blocks actin binding sites to myosin in absence of Ca2+

thick filaments

- thick filaments are comprised of a large molecule weight protein called myosin- each myosin molecule consists of - tail: binds to other myosin molecules - head: have a binding site to actin (thin filament) necessary for cross bridge formation- bends and straightens during contraction

sliding filament theory of muscle contraction

- muscle shortening is due to movement of the thin filament over the thick filament- thin filaments slide toward the center of sarcomere

during contraction: (z line, i band, a band)

- z lines move closer together- i bands narrow- width of a band remains constant)

transverse tubules (t-tubules)

the tubes that extend from surface of muscle fiber deep into sarcoplasm. responsible for transmitting action potential at the surface of muscles to interior. action potentials trigger contraction

sarcoplasmic reticulum (SR)

a tubular network surrounding each myofibril. similar to endoplasmic reticulum- site of storage and release of Ca2+ for excitation-contraction coupling- form chambers (terminal cisternae) that attach to t-tubules- two terminal cisternae plus a t-tubule form a triad, the site to transmit action potential, release Ca2+ from SR.

sequence of events in neuromuscular transmission

1. action potential travels down the motor neuron to the presynaptic terminal2. depolarization of the presynaptic terminal opens Ca2+ channels3. acetylcholine (ACh) is extruded into the synapse cleft4. ACh binds to its receptor on the motor end plate5. ligand-gated Na+ channels are opened in the motor end plate6. depolarization of the motor end plate causes action potential (endplate potential, EPP) to be generated in the muscle tissue7. ACh is degraded by acetylcholinesterase (AChE)

excitation-contraction coupling sequence (inside muscle fiber)

1. action potential travels down t-tubules to triads2. Ca2+ is released from Ca2+ channels on the SR (ryanodine receptor)3. Ca2+ binds to troponin C4. troponin-tropomyosin complex changes position to expose actin active sites on thin filaments, cross-bridge between thin and thick filament forms5. contraction cycle is initiated

cross-bridge formation in muscle contraction

1. begins with the arrival of Ca2+ resulting in the exposure of the active sites on the the thin filament2. the energized myosin heads attach to active sites, forming corss-bridges3. the energy (ADP and Pi) is released as the myosin head pivots toward the M line. the action is called the power stroke4. cross-bridge detachment: when another ATP binds to the myosin head, the link between the myosin head and the active site on the actin molecule is broken5. myosin reactivation occurs when the free myosin head splits ATP into ADP and Pi (repositioned)

what is tetanus (tetanic contraction)

tetanus is a sustained muscle contraction evoked when the motor nerve that innervates a skeletal muscle emits action potentials at a very high rate

explain tetanus process

during repeated stimulation, there is not enough time for Ca2+ reuptake by SR (muscle is not completely relaxed). Ca2+ is continuously bound to troponin. this results in muscle twitch (contraction) summation, eventually a maximal sustained contraction tetanus occurs

smooth muscle contraction sequence

1. action potential occur int eh smooth muscle cell membrane2. opening of Ca2+ channels, Ca2+ enters from ECF3. increase in intracellular Ca2+ concentration 4. Ca2+ binds to calmodulin (CaM) to activate myosin-light-chain (MLC) kinase5. MLC kinase phosphorylates myosin, then bind to actin to form cross-bridge, produce contraction

characteristics of cardiac muscle cells

- small, single nucleus, striated, branched, with t-tubules, SR, a lot of mitochondria- composed of sarcomeres- cardiac muscle cells (cardiomyocytes) are coupled through intercalated discs (gap junctions) to synchronize contractions of atria or ventricles - cardiomyocytes can contract without innervation. auto rhythmic cells (1% cardiac muscle cells) generate action potential (pacemaker activity)- some cardiomyocytes transform int o the cardiac conduction system

why is the action potential of cardiac muscle cells unique

long duration of action potential with prolonged refractory period (200 msec), no tetanus (no fatigue) develops

action potential of cardiac muscle cell steps image


overall organization of central nervous system image


neurotransmitters are synthesized by


where are neurotransmitters stored?

in vesicles in the presynaptic terminal

when a nerve impulse arrives at the presynaptic terminal,

the neurotransmitter is released into the synaptic cleft where they then bind to the specific receptors. receptor activation result in excitatory or inhibitory effects on the postsynaptic neuron.

the neurotransmitter action is terminated by

diffusion into blood, by metabolism or by reuptake into the presynaptic neuron

what are muscle spindles important for

- signaling muscle length (stretch) - signaling the rate of change in muscle length

where are muscle spindles found

most skeletal muscle but seem to be concentrated in muscles responsible for fine motor control (eye and finger movement)

muscle spindles lie _______ to regular muscle fibers

in parallel

muscle spindles and muscle contraction

muscle spindles no not contribute to muscular contraction. but will cause muscle to contract

stretch reflex receiver

muscle spindle senses the muscle length change

golgi tendon reflex receiver

golgi tendon organ senses the muscle contraction

flexor-withdrawal reflex receiver

somatosensory senses painful, noxious stimulus

stretch reflex sensory afferent fiber

group Ia afferent fiber

golgi tendon reflex sensory afferent fiber

group Ib afferent fiber

flexor-withdrawal reflex sensory afferent fiber

group II, III and IV afferent fibers

stretch reflex synapse in the spinal cord

one synapse

golgi tendon reflex synapse in the spinal cord

two synapses

flexor-withdrawal reflex synapse in the spinal cord

multi synapses

stretch reflex motoneuron action

activate alpha motoneuron

golgi tendon reflex motoneuron action

inhibit alpha motoneuron

flexor-withdrawal reflex motoneuron action

activate, inhibit alpha motoneurons

stretch reflex effector

muscle contraction

golgi tendon reflex effector

muscle relaxation

flexor-withdrawal reflex effector

flexor muscle contraction and extensor muscle relaxation (ipsilateral)

overall function of sympathetic nerve system is

to mobilized the body for activity- powerful and widespread responses are 'fight or flight' in nature.

sympathetic nervous system origin of preganglionic neurons

thoracic and lumbar segments of the spinal cord (T1-L3), is referred to as thoracolumbar

sympathetic nervous system postganglionic neurons location

in the sympathetic chain, then postganglionic fibers (long) innervate the target organs, release norepinephrine.

neurotransmitters and receptors of sympathetic nerve system preganglionic neuron

in the brain or spinal cord, release acetylcholine (ACh, cholinergic), interacts with nicotinic (N2) receptors on the postganglionic neuron

neurotransmitters and receptors of sympathetic nerve system postganglionic neuron

release norepinephrine (adrenergic), interacts with adrenergic receptors on the target organs

neurotransmitters and receptors of parasympathetic nervous system preganglionic neuron

release ACh, interacts with nicotinic (N2) receptors on the postganglionic neuron

neurotransmitters and receptors of parasympathetic nervous system postganglionic neuron

release ACh, interacts with muscarinic (M) receptors on the target organs

adrenal medulla

a specialized ganglion in sympathetic division

adrenal medulla preganglionic neurons

located in the spinal cord- preganglionic fibers travel to adrenal medulla, synapse (release ACh) on chromaffin cells

adrenal medulla: chromaffin cells

activated chromaffin cells release epinephrine (80%) and norepinephrine (20%) into the blood, to increase heart rate, blood pressure, increase metabolism, cause blood vessel contraction in the skin, all of which are characteristic of the fight-or-flight response

fight or flight response aka

acute stress response

what is the fight or flight response

a physiological reaction that occurs in response to a perceived harmful event, attack or threat to survival

what does the fight or flight response activate?

coordinated activation of sympathetic nervous system and adrenal medulla

the physiological changes that occur during the fight or flight response are activated in order to

give the body increased strength and speed in anticipation of fighting or running

physiological changes that occur due to fight or flight response

- increased blood pressure- increased heart rate- increased rate and depth of breathing- increased skeletal muscle blood flow- decreased blood flow to kidneys, GI tract, skin- increased metabolic rate- increased blood glucose levels

autonomic control centers in the brain

- hypothalamus- brain stem

autonomic control center hypothalamus is responsible for

- water balance- temperature- food intake- cardiovascular function- sexual behavior

autonomic control center brain stem is responsible for

- breathing - blood pressure- swallowing