phys EXAM 1

negative feedback loop

change in a regulated variable in one direction results in actions that causes change in the variable in the opposite direction (ex: body temp)

positive feedback loop

effectors activity increases in response to a stimulus, reinforcing the initial stimulus (ex: blood clotting)

gradient

present any time more of something is in one area than in another and the two areas are connected

diffusion

movement of solute molecules from area of higher solute concentration to area of lower solute concentration

concentration gradient

difference in concentrations

simple diffusion

nonpolar molecules through phospholipid bilayer

facilitated diffusion

ions through a channel; polar and ionic compounds using a carrier

osmosis

reversible movement of solvent across a selectively permeable membrane from a solution with a lower solute concentration to a solution with a higher solute concentration

osmotic pressure

pressure that must be applied to a solution to stop osmosis; depends on the number of molecules

hydrostatic pressure

force that water exerts on the walls of its container

tonicity

comparison between ability of two solutions separated by a selectively permeable membrane to cause water movement by osmosis —> way to compare solute concentrations

hypotonic

more solute, less solvent inside

hypertonic

more solvent, less solute inside

isotonic

equal amount of solvent and solute inside and outside of the cell

primary active transport

pump binds solute and transports it against concentration gradient using ATP

Na+/K+ pump

2 K+ released into cytosol —> 3 Na+ bound from cytosol —> ATP is hydrolyzed and the phosphate binds to the pump and changes its shape —> 3 Na+ released into the ECF and 2 K+ bound —> phosphate detaches and pump goes back to its original shape —>

secondary active transport

uses ATP indirectly to create a concentration gradient by pumping one substance across the plasma membrane; many rely on NA+/K+ pump to transport sugar, amino acids, Cl-, etc.

electrical potential

the unequal concentration off ions between cytosol and ECF results in separation of charges across plasma membrane

membrane potential

electrical potential present in cell membranes

endocytosis

substances taken into the cell via invagination of plasma membrane into a vesicle; ex: phagocytosis, pinocytosis, and receptor mediated endocytosis

exocytosis

substances released from cell via fusion of a vesicle with plasma membrane

transcytosis

substance taken into one side of the cell by endocytosis and released from the other side by exocytosis

central nervous system

brain & spinal cord

peripheral nervous system

cranial nerves & spinal nerves; carry signals to and from CNS

functional divisions of the nervous system

sensory, motor, and integrative

sensory (PNS)

sensory stimuli detected by sensory receptors in PNS (neurons in skin, muscle stretch, receptors, etc.); somatic and visceral sensory

somatic sensory

neurons carry signals from skeletal muscle, bones, joints, skin (pain, temp, touch); special senses

visceral sensory

neurons transmit signals from organs (ex: heart, stomach, GI tract, kidneys, and urinary bladder)

integrative (CNS)

neurons of CNS integrate different types of sensory input to form a more complete picture and can elicit response if necessary

motor (PNS)

consists of motor neurons that carry out motor functions of nervous system; somatic motor division & autonomic nervous system

somatic motor division

neurons that transmit signals to skeletal muscle

autonomic nervous system

neurons that carry signals primarily to thoracic and abdominal organs

neuron

excitable cell resonsible for sending and receiving signals in the form of action potentials

neuroglia

smaller than neurons but more prevalent; do not transmit electrical signals but serve supportive functions

dendrites

short, highly forked processes; receive input from other neurons (transmit as electric impulses to soma); most neurons have 1+ dendrites

axon

“nerve fiber”— generate and conduct action potentials

axon collateral

branches of some axons that arise at right angles to axon

telodendria

axon and its collaterals split near ends to produce multiple fine branches

functional regions of neurons

receptive region, conducting region, and secretory region

receptive region

dendrites receive signals from other neurons or by monitoring environment; signals are collected in soma

conducting region

where information is transmitted

secretory region

where chemical messengers are released once signal reaches axon terminal

neuroglia in CNS

astrocyte, oligodendrocyte, microglial cell, & ependymal cell

astrocyte

anchor neurons & blood vessels, regulate the extracellular environment, facilitate the formation of the blood brain barrier and repair damaged tissue

oligodendrocyte

myelinate certain axons in CNS

microglial cell

act as phagocytes

ependymal cell

line cavities, cilia circulate fluid around brain and spinal cord, some secrete this fluid

schwann cells

cells that insulate axons of the PNS; also important for the repair of damaged axons

satellite cells

flat cells that surround cell bodies of PNS neurons —> have intertwined processes that link them with other parts of the neuron, other satellite cells, and some schwann cells

myelin sheath

key for electrophysiology, high lipid content insulates axon and prevents ion leakage

neurons can send signals to…

other neurons, glands, muscles

local potentials

travel only short distances, generated by ligand gated channels, generated in soma & dendrites, have reversible effect

action potential

a series of rapid depolarization and repolarization — travel the entire length of an axon, “all or nothing” principle, generated in the trigger zone/axon hillock, generated by voltage gated channels

polarized

negative, normal, resting membrane potential state

depolarization

occurs with influx of cations

hyper-polarization

occurs with efflux of cations and influx of anions

repolarization

occurs when a cell returns to resting membrane potential

events of an action potential

depolarization, repolarization, and hyper-polarization

step 1 of action potential

a local potential depolarizes the axolemma of the trigger zone to threshold

step 2 of action potential

voltage gated Na+ channels activate — NA+ enters and axon section depolarizes

step 3 of action potential

Na+ channels deactivate and K+ channels activate, repolarization begins

step 4 of action potential

Na+ channels return to resting state and repolarization continues

step 5 of action potential

axolemma may hyper-polarize before K+ channels return to resting state — after, axolemma returns to resting membrane potential

refractory period of action potential

membrane of neuron is unable to fire second action potential for brief time after first action potential; absolute vs relative

absolute refractory period

no additional stimulus can produce action potential because Na+ channels cannot be activated until they return to resting states

relative refractory period

only a very strong stimulus will produce an action potential — K+ is still flowing out rapidly

conduction speed of an action potential is influenced by…

axon diameter and myelin sheath presence

saltatory conduction

on myelinated axon, nodes of ranvier are only segments that must be depolarized to threshold — generates current that flows efficiently with little loss of charge through next internode

continuous conduction

in absence of myelin sheath, each section of axolemma must be polarized to threshold — action potentials mist be generated in continuous sequence along entire axolemma

synapse

where neuron meets its target cell; can be electrical or chemical; generally occur between an axon and another part of a different neuron

electrical synapses

occur between cells that are electrically coupled via gap junctions

gap junction

contain aligned channels that form pores — bidirectional & nearly instantaneous

chemical synapse

involves conversion of electrical signal into chemical signal by presynaptic neuron — chemical signal then reconverted into electrical signal in post synaptic neuron

chemical synapse

an AP in the presynaptic neuron triggers Ca2+ channels in the axon terminal to open

step 1 of chemical synapses AP

an action potential in the presynaptic neuron triggers Ca2+ channels in the axon terminal to open

step 2 of chemical synapses AP

influx of Ca2+ causes synaptic vesicles to release neurotransmitters into the synaptic cleft

step 3 of chemical synapses AP

neurotransmitters bind to receptors on the postsynaptic neuron

step 4 of chemical synapses AP

ion channels open, leading to a local potential and possibly an action potential

EPSP

excitatory postsynaptic potential; local depolarization moves membrane potential closer to threshold

IPSP

inhibitory postsynaptic potential; local hyper-polarization moves membrane potential farther from threshold

summation

result of neuron receiving input from multiple presynaptic neurons each of which causes and EPSP or IPSP; cumulative effect is neural integration

iontropic

ligand-gated channels that directly control the movement of ions

metabotropic

connected to separate ion channel; require signaling cascade to regulate ligand-gated ion channel

neuromodulators

neurotransmitters that bind to metabotropic receptors to tune release of other neurotransmitters

termination of synaptic transmission methods

diffusion & absorption, degradation, or reuptake

muscle tissue consists of…

myocytes and endomysium

properties of muscle cells

contractility, excitability, conductivity, distensibility, elasticity

transverse tubules

dive into muscle fiber and surround each myofibril; terminal cisternae flank each side

myofibrils

100s to 1000s of myofilaments; contractile, regulatory, and structural

contractile myofibril

myosin in thick filaments, actin in thin filaments

regulatory myofibril

tropomyosin and troponin in thin filaments

structural myofibrils

titin in elastic filaments

sarcomere

section of a myofibril that extends from one z-disc to next z-disc

sliding-filament mechanism

mechanism of muscle cell contraction in which thick and thin filaments slide past one another while generating tension

axon terminal

releases neurotransmitters acetylcholine (Ach) into synaptic cleft

synaptic cleft

narrow space between axon terminal and muscle fiber

motor end plate

specialized region of sarcolemma whose folded surface contains many Ach receptors

resting stage at sarcolemma

both voltage gated Na+ and K+ channels are closed; sarcolemma is at resting membrane potential

depolarization stage at sarcolemma

in response to stimulus, Na+ channels open and Na+ enters the cell

repolarization stage at sarcolemma

Na+ channels close; voltage gated K+ channels open and K+ leaves the cell