Human Physiology Exam 1

2 types of electrical signals

graded and action potentials

graded potentials

short distance signals

>local flow between active area and inactive areas

>passive flow

>decremental

>occur in cell body and dendrites

>magnitude and duration varies

action potentials

long distance signals: how neurons communicate

> Occur along the axon

what leads to an Action potential

graded potentials, if magnitude is great enough

cell body

contains the nucleus and organelles

dendrites (input zone)

numerous extensions from cell body

axon hillock (trigger zone)

first portion of axon, initiates action potentials, lowest threshold potentials

Axon (conducting zone)

single elongated tubular extension

> conducts action potentials away from cell body

axon terminals (output zone)

releases neurotransmitters that influence other neurons

what are triggering events

1) a stimulus

2) interaction of a chemical messenger with surface receptor

3) change in membrane potential caused by an imbalanced leak-pump cycle

how does the potential change in graded potentials

-70 to -60

what is resting membrane potentials

-70

can graded potentials summate??

yes

Where is an axon potential generated?

axon hillock

How does the membrane potential change in a triggering event (threshold potential)

-70 to -50 (depolarization)

what is the mV for after hyperpolarization

-80

the membrane of axons contain what type of channels

voltage gated Na and K channels

at rest, some ____ are open, but much fewer ___ are open..

k+, Na+

K+ equilibrium potential

Ek+= -90

explain the positive feed back loop in the action potential mechanism

Na+ concentration and electrical gradients are INTO cell, so Na+ begins to move into cell. This causes further depolarization, which opens more voltage-gated Na+ channels and a positive feedback loop is established as more voltage-gated Na+ channels rapidly open

what is threshold mV

-50

what happens at threshold

membrane becomes more permeable to Na+ than K+ bc all VG Na channels are open

as Na+ flows into the cell, the potential of the cell becomes

30

Na+ equilibrium potential

-60

voltage gated Na+ channels become inactive by ball and chain at ___ mV

30

what repolarizes the membrane?

K+ leaving.

remember at this time there is a positive membrane potential, meaning the inside of the membrane is more positive compared to the outside

what would happen without ATPase pumps?

repeated action potentials would eventually erode separation of Na+ and K+

how does conduction of action potential occur

local current flow down axon along every patch of membrane

What happens when the first action potential is generated in a neuron?

It triggers another action potential in the adjacent area, creating a self-perpetuating (self-regenerating) cycle down the neuron.

what is myelin

thick layer composed mostly of lipids that surround a portion of axon and acts like a rubber insulation

Myelin forming cells in CNS

oligodendrocytes

myelin forming cells in PNS

schwann cells

gaps between myelin

nodes of ranvier

saltatory conduction

impulse jumps from node to node along a myelinated axon

what does myelin do

increase the speed of the conduction of action potentials

do we want action potentials to move in both directions along an axon?

NO!

refractory period is required to keep an action potential from bouncing back and forth

absolute refractory period

Na+ gates are closed and inactivated; no action potential can occur.

relative refractory period

an action potential can occur, but the stimulus must be much larger than normal to get one started. Occurs after the action potential is complete. K+ gates are slow to close and are still open during this time. In addition, not all of the Na+ channels have been reset.

what do refractory periods ensure

unidirectional movement of action potentials and sets and upper limit to the frequency of occurrence of action potentials

physiology

study of how the body functions

chemical level

all matter, living or nonliving is composed of atoms. O,H,N,C make up 96% body chemistry

Cellular level

cells are the least complex organization capable of performing the tasks of life

Tissue level

made up of similar types of cells

muscle tissue

specialized cells for contracting

nervous tissue

specialized cells for initiating and transmitting electrical impulses

epithelial tissue

tissues with many cells arranged close together with little extracellular matrix and specialized barrier

connective tissue

few cells arranged in extensive extracellular matrix to support the body

Organ level

two or more primary tissues

body systems

MURDERS LINC

Muscle

urinary

respiratory

digestive

epithelial

reproductive

skeletal

lymphatic

immune

nervous

connective

homeostasis

dynamic steady state in the internal environment

> cells require homeostasis for survival

ECF made up of

interstitial fluid & plasma

plasma membrane composed of what 4 things

phospholipid bilayer, carbohydrates, cholesterol and proteins

what are the 3 subdivisions of the cells

plasma membrane, nucleus and cytoplasm

Rough ER vs Smooth ER

RER- ribosomes for protein synthesis and contain enzymes for protein synthesis

SER- packages proteins in transport vesicles to move new synthesized proteins to the golgi complex. Lipid metabolism

Golgi complex

packages secretory vesicles for release by exocytosis. Sorting and segregating products by function and final destination

> adds docking markers(address)

lysosomes

intracellular digestion- removes aged or damaged cells

peroxisomes

produces and decomposes H2O2 into water and oxygen by an enzyme called catalase

mitochondria

power plants

generates ATP needed by the cell.

vaults

cellular transport from nucleus out of the cell

Centrosomes and Centrioles

cells main microtubule organizing center.

> moving vesicles throughout the cytosol and function in formation of cilia, flagella and mitotic spindles

cytosol

intermediary metabolism, ribosomal protein synthesis and nutrient storage

Cytoskeleton

integral whole and links other parts of the cell together

microtubules

help maintain shape and complex cell movements

microfilaments

contractile systems and mechanical stiffeners

intermediate filaments

important in cell regions subject to mechanical stress

integral proteins

proteins embedded in in lipid bilayer

peripheral proteins

outer layer of lipid bilayer

membrane proteins

found on outer layer that function to recognize self cells. Types include- channels, receptors, carriers/transporters, docking marker acceptors, membrane bound enzymes, CAMs and glycoproteins

what are CAMs

specialized proteins protude from both of the adjacent membranes and form hooks and loops that hold adj cells together- cadherins and integrins

what is the extracellular matrix composed of

elastin, collagen and fibronectin

Desmosomes

act like velcro that anchors tow adjacent non touching cells.

> plaques and strong filaments containing cadheriams

Tight junction

bind touching adjacent cells firmly together to seal off passageway

> epithelial cells

Gap junctions

gap linked by small connecting tunnels formed by connexons

> connexon formed by 6 proteins called connexins

what can directly pass through the plasma membrane

lipid soluble and small water soluble substances

passive transport

the movement of substances across a cell membrane (H->L)without the use of energy by the cell

Simple diffusion

uniform spreading out of molecules die to random movements along the chemical gradients directly through the plasma membrane (lipophilic) or through channels (hydrophilic)

Ficks Law of diffusion

rate of diffusion

osmosis

net diffusion of water down its concentration gradient.

Movement of water across a permeable membrane is driven by

by net osmotic pressure (pulling pressure)

Osmotic pressure is the result of

unequal distribution of non penetrating and penetrating solutes across the membrane

What type of solution will promote the movement of water into the solution?

high osmotic pressure (hyperosmotic)

Active transport

Energy-requiring process that moves material across a cell membrane against a concentration difference

Facilitated diffusion

passive transport of ions from hight to low using a carrier

Primary active transport

directly uses ATPase to physically change shape of pumps

Secondary Active transport

driven by ion concentration gradient (Na+) and requires a carrier

>symport and antiport

endocytosis

transport of materials into the cell

exocytosis

transport of materials out of a cell

membrane potential

separation of opposite charges or the difference in relative number of cations and anions across the plasma membrane (mV)

what is membrane potential due to

differences in concentration and permeability of key ions

Nernst equation

equilibrium potential for specific ion.

> The equilibrium potential is the membrane potential that would need to exist for a single ion,such as Na+, to balance across the membrane so that no net movement of that ion would occur.

Goldman-Hodgkin-Katz equation

calculate resting membrane potential resulting from the relative distributions and membrane permeabilities of ALL permeable ions (Na, K and cl)

what are excitable tissues

nerve and muscle

at RMP is there a separation of charge?

yes, this results in polarization of the membrane

chemically gated channels

change shae in response to specific chemicals binding to surface receptors

voltage gated ion channels

open or close in response to changes in membrane potential

mechanically gated channels

respond to stretching or other deformations in the channel

thermally gated channels

respond to local changes in temperature

synapses

junctions between presynaptic and postsynaptic neurons.

> can be electrical where 2 neurons are connected by gap junctions which allow ions to flow directly between cells however most are chemical

chemical synapses

neurotransmitters are released from the presynaptic cell into synaptic cleft and diffuse across the synapse to the postsynaptic cell where NTs may bind to promote EPSP or IPSP

explain the process for events at a synapse

1) AP travels down axon terminals and opens VG Ca2+ channcels

2) Calcium enters presynaptic knob which induces binding of the synaptic vesicle to the presynaptic membrane

3) synaptic vessicles fuse with the membrane and nts are released unto cleft

4) nts diffuse across cleft and bind to chemically gated channels or receptors on post synaptic membrane

5) either EPSP or IPSP produced