five components in the homeostatic reflex loop
- stimulus- receptor- control center- effector- response
stimulus
something produces change
receptor
protein site on cell membrane that detects the change
control center
central nervous system
effector
response organs
response
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
insulin
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
60%
% TBW of female
50%
% TBW of infant
65-75%
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 + ECF
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
mEq/L
ECF and ICF pH at rest are
equal
Osmolarity of ECF and ICF at rest are
equal
at equilibrium, Na+ is more concentrated in the (ECF/ICF)
- ECF
at equilibrium, K+ is more concentrated in the (ECF/ICF)
- 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?
no
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?
non-electrolytes
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
none
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
conductance
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?
no
is facilitated diffusion carrier mediated?
yes
is primary active transport carrier mediated?
yes
is secondary active transport carrier mediated?
yes
does simple diffusion use metabolic energy?
no
does facilitated diffusion use metabolic energy?
no
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?
no
does facilitated diffusion depend on Na+ gradient?
no
does primary active transport depend on Na+ gradient?
no
does secondary active transport depend on Na+ gradient?
yes; solutes move as Na+ crosses cell membrane
osmosis
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
isotonic
when two solutions have the same effective osmotic pressure; no net water flow between them
hypertonic
when two solutions have different effective osmotic pressures, the solution with the higher effective osmotic pressure
hypotonic
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)
lidocaine
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
sarcomere
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
actin
backbone, two strands of polymerized globular actin. each actin has thick filament (myosin) binding site
troponin
a complex of three globular proteins (T, I and C). binds Ca2+ to regulated muscle contraction
tropomyosin
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
0
overall organization of central nervous system image
0
neurotransmitters are synthesized by
neurons
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