biol 3151: principles of animal physiology

BIOL 3151: Principles of Animal

Physiology

ANIMAL PHYSIOLOGY

Dr. Tyler EvansEmail: [email protected]: 510-885-3475Office Hours: M 8:30-11:30 or appointmentWebsite: http://evanslabcsueb.weebly.com/

mailto:[email protected]

PREVIOUS LECTUREMEMBRANE PHYSIOLOGY

• many cellular processes, including the formation of chemical or electrical gradients, are dependent on the ability to move molecules across membranes.

• transport of molecules across membranes can occur in two ways:1. WITHOUT the assistance of membrane proteins• PASSIVE DIFFUSION

2. WITH the assistance of membrane proteins• FACILITATED DIFFUSION• ACTIVE TRANSPORT

PREVIOUS LECTUREPASSIVE DIFFUSION• WATER is another molecule able to pass across cell membranes via passive

diffusion (most other ions cannot cross)• the passive diffusion of water across cell membranes is called OSMOSIS• controlling the movement of water via osmosis is essential for cells to operate

properly• here’s why: ions and other molecules in cells must be in specific concentrations

(i.e. dissolved in the correct amount of water) both inside and outside of cells if animals are to function normally

• virtually every cell, in every animal has a total intracellular and extracellular concentration of 300 mOsm.

PREVIOUS LECTUREWhy is the passive diffusion of water a

problem for physiology?

• movement of water in and out of cells causes changes in CELL VOLUME

• changes in cell volume are problematic for physiological function

• swollen cells can disrupt tissue structure or occlude blood vessels and with too much swelling cells can burst

• shrinking cells can deform the plasma membrane and cytoskeleton

textbook Fig 2.9 pg 31

PREVIOUS LECTUREPASSIVE DIFFUSION• the effect of the passive diffusion of water on cell volume is easily tested using

isolated red blood cells.• and you will get to do it in lab!

SWELL(IF BURSTS CALLED

HEMOLYSIS)

CRENATE(SHRINK)

NO VOLUME CHANGE

PREVIOUS LECTURE

ions

water

OH H

K+Na+

Ions

water

K+Na+

OH H

• Ions will enter cells• Water will exit cells

• Water will enter cells• Ions will exit cells

FRESHWATER FISH LIVE IN HYPOOSMOTIC WORLD

MARINE FISH LIVE IN HYPEROSMOTIC WORLD

Fish are excellent osmoregulators!

TODAY’S LECTUREINTRO TO NEUROPHYSIOLOGY

• chemical gradients are crucial for the function of animals nervous systems• recall that cells of the nervous system called NEURONS communicate via

electrical signals called ACTION POTENTIALS• action potentials are made when the membrane becomes permeable to

certain ions, causing ions to move down concentration gradient and generate an electrical signal

• ensuring that more negatively charged molecules are present inside cells than outside creates a chemical gradient or stored electrical energy

• this electrical energy can be released to create electric signals that drive physiological processes


TODAY’S LECTURENEURON STRUCTURE AND FUNCTION

(CHAPTER 4)

FRANKENSTEIN?• pioneering experiments in nervous system physiology were the inspiration

for Mary Shelley, the author of Frankenstein• influenced by the work of Luigi Galvani who showed that the muscles of a

dead frog would twitch when an electrical current was applied• experiments led the way to modern neurophysiology

INTRO TO NEUROPHYSIOLOGY• animals have a variety of cell types that can either send or receive electrical

signals, but the best known excitable cells are NEURONS• animals use neurons to send electrical signals to either other neurons (like in the

brain) or to stimulate glands and muscles


• neurons vary in their structure and function, but all neurons have the same basic design that allows them to send and receive electrical signals

NEUROPHYSIOLOGY• each neuron has specialized regions that perform specific tasks:

• these tasks are: reception, integration, conduction or transmission• e.g. VERTEBRATE MOTOR NEURON (Fig 4.2 pg. 145)

Zone 1RECEPTION:

Dendrites and Soma

Zone 2INTEGRATION:

Axon hillock

Zone 3CONDUCTION: Myelin sheath

Zone 4TRANSMISSION:

Axon terminal

Direction of incoming signal

NEUROPHYSIOLOGYZone 1 RECEPTION (includes DENDRITES and SOMA)• DENDRITES are fine branching extensions of the SOMA or cell body

• dendrites sense incoming signals and convert the signal into electrical signals

• the soma contains all of the organelles and performs all of the routine metabolic functions

SOMA

DENDRITES


NEUROPHYSIOLOGYZone 2 INTEGRATION: • incoming signals from the dendrites are integrated in the AXON HILLICK,

located at the junction of the soma and AXON.• here important parts of the incoming signal are processed.

• for example, is it a strong or weak signal


NEUROPHYSIOLOGYZone 3 CONDUCTION: • the AXON forms the third functional zone and is specialized for conduction

(sending signal from place to place)• the axon can be short or long depending on specific function, but each neuron

has only a single axon.


Zone 4 TRANSMISSION: • the AXON TERMINAL makes up the fourth region, which is specialized for

transferring electrical signals to target cells• in motor neurons the end of the axon branches to several axon terminals• each axon terminal is enlarged at the end to form a SYNAPSE• electrical signal is converted to a chemical signal (i.e. NEUROTRANSMITTER) at

the synapse, which then binds to receptors on target cell to trigger response


NEUROPHYSIOLOGYELECTRICAL SIGNALS IN NEURONS

• We now know the path that signals take in neurons, but how are they generated?

• neurons constantly maintain chemical gradients across their cell membrane that can be used to generate electrical signals

• this gradient makes the inside of cell more negative than the outside of cells

• this baseline charge is called RESTING MEMBRANE POTENTIAL

• the resting membrane potential is usually -70mV, meaning when not sending signals the inside of the cell membrane is more negatively charged than the outside


NEUROPHYSIOLOGY

• three factors contribute to establishing membrane potential:1. distribution of ions across the membrane2. the relative permeability of the membrane to these ions3. the charges of these ions

• the GOLDMAN EQUATION describes resting membrane potential

textbook pg 147

membranepotential temp

Faraday’s constant• measure of electrical charge

gas constant ion concentrations

ion permeabilities

ELECTRICAL SIGNALS IN NEURONS


• electrical signals are created by altering the permeability of the membrane to ions, or in simpler terms, opening or closing ions channels

• ions to flow down concentration gradient and create electrical signals• last lecture we described that some ion channels are voltage gated and open

or close to change resting membrane potential

e.g. potassium (K+) channel in muscles and neurons

• this channel opens when the net charge across the membrane changes

• these type of channels are involved in forming action potential

e.g. IP3-sensitive calcium channel

• this channel induces the release of calcium stores when inositol triphosphate (IP3) is present



• ion channels can be opened or closed by certain molecules or LIGANDS• ligand gated ion channels are also involved in neuronal signaling• for example, neurotransmitters are used to open ion channels and cause

muscle contraction

NEUROPHYSIOLOGYWHAT TYPES OF ELECTRICAL SIGNALS ARE SENT BY NEURONS?

1. GRADED POTENTIALS: weak signals that occur in the soma and decrease in strength they get further away from the opened channel

e.g. Graded potential created by ligand gated sodium channel

Several properties of the neuron influence why a graded potential decreases as it travels:

• leakage of ions across membrane• electrical resistance of cytoplasm• electrical properties of

membrane


NEUROPHYSIOLOGY

• more sodium outside of cells than inside.

• when ligand-gated Na channels open, sodium enters cells and intracellular regions become more positively charged.

• at +60mV there is no longer a gradient driving sodium inward.


1. GRADED POTENTIALS: weak signals that occur in the soma and decrease in strength they get further away from the opened channel

e.g. Graded potential created by ligand gated sodium channel


2. ACTION POTENTIALS: are stronger signals used to transmit information over longer distances without degrading

• action potentials typically occur in three phases:i. DEPOLARIZATION: occurs when membrane potential at the axon hillock

reaches threshold (i.e. trigger point). Once this threshold is crossed the membrane quickly moves from a net negative to a net positive charge.

ii. REPOLARIZATION: during which membrane potential rapidly returns to the resting membrane potential.

iii. AFTER-HYPERPOLARIZATION: membrane becomes even more negative than the resting membrane potential. This period is very brief and membrane returns to resting potential very quickly (milliseconds)


2. ACTION POTENTIALS: are stronger signals used to transmit information over longer distances without degrading


NEUROPHYSIOLOGY

• the three phases of an action potential are driven by the opening and closing of ion channels (with some variation between groups of animals)

• Na+ channels open during depolarization and Na+ enters cell

• K+ channels open during repolarization and K+ exits cells, making interior more negatively charged than exterior

• K+ channels close slowly which causes the hyperpolarization response

• membrane returns to resting potential.


WHAT TYPES OF ELECTRICAL SIGNALS ARE SENT BY NEURONS?

NEUROPHYSIOLOGYWhat types of electrochemical signals are sent via neurons?1. ACTION POTENTIALS: are used to transmit information over longer distances

without degrading

• The ability of an axon to generate a new action potential varies during these phases:

i. ABSOLUTE REFRACTORY PERIOD: during which axon is incapable of generating a new action potential. Need to wait for membrane potential to be re-established.

ii. RELATIVE REFRACTORY PERIOD: enough membrane potential has been re-established to allow another action potential to be triggered, but only triggered by very large stimuli.

NEUROPHYSIOLOGYWhat types of electrochemical signals are sent via neurons?

textbook pg 154

NEUROPHYSIOLOGYHow do action potentials travel long distances?• axons of vertebrates are wrapped in an insulating layer of MYELIN• myelin is formed by SCHWANN CELLS wrapping in a spiral pattern around

the axon

• all other things equal, conduction along a myelinated axon is faster than conduction along a non-myelinated axon and signal can travel farther with less degradation


NEUROPHYSIOLOGYTRANSMISSION ACROSS THE SYNAPSE

• once the action potential reaches the AXON TERMINAL, the neuron must transmit the signal across the SYNPASE to the target cell

• the cell that transmits the signal is called the PRE-SYNAPTIC CELL and the cell that receives the signal is referred to as the POST-SYNAPTIC CELL

• The space between the pre-synaptic and post-synaptic cell is the SYNAPTIC CLEFT.

• Collectively, these three components make up the SYNPASE

NEUROPHYSIOLOGYTRANSMISSION ACROSS THE SYNAPSE:

THE NEUROMUSCULAR JUNCTION

http://www.rci.rutgers.edu/~uzwiak/AnatPhys/APFallLect13.html

TRANSMISSION AT THE NEUROMUSCULAR JUNCTION• when an action potential reaches the axon terminal of the neuromuscular

junction it triggers calcium (Ca+2) channels to open• the concentration of Ca+2 inside the neuron is much lower than outside, so

Ca+2 moves into the neuron along its concentration gradient• this increase in internal Ca+2 concentration triggers the release of SYNAPTIC

VESICLES, synaptic vesicles contain neurotransmitters, which are then released across the synapse

Textbook Fig 4.16pg 162

TRANSMISSION AT THE NEUROMUSCULAR JUNCTION• the main neurotransmitter released at vertebrate neuromuscular junctions is

ACETYLCHOLINE • acetylcholine is released from synaptic vesicles and binds to specific cell

surface receptors in the membranes of post-synaptic cells• acetylcholine binds to receptors to induce muscle contraction• the enzyme ACETYLCHOLINESTERASE removes acetylcholine from its receptor

to terminate the signal.

Textbook Fig 4.17pg 163

TRANSMISSION AT THE NEUROMUSCULAR JUNCTION• strength of contraction is determined by two factors:

1. amount of neurotransmitter released2. number of receptors on target cells

• if the amount of neurotransmitter or density of receptors is high a large response will result. Conversely, a low response will result when amount of neurotransmitter or density of receptors is low

• disease called MYASTHENIA GRAVIS occurs when muscles contain a reduced number of acetylcholine receptors• experience muscle weakness and muscle fatigue

NEUROPHYSIOLOGY

Weakened eye muscles can cause a drooping eyelid or PTOSIS, a common symptom

LECTURE SUMMARY• neurons vary in the structure and properties, but use the same basic mechanisms

to send signals: reception, integration, conduction and transmission

• reception occurs in the dendrites, integration in the axon hillock, conduction in the axon and transmission at the axon terminal or synapse

• the Goldman equation describes resting membrane potential

• electrical signals can be weak graded potentials or strong action potentials-but both are electrical signals caused by opening and closing ions channels

• action potential are used for long distance signals and occur in three stages: depolarization, repolarization and hyperpolarization of the cell membrane

• acetylcholine is the main neurotransmitter used in muscle contraction

NEXT LECTUREDIVERSITY OF NEURAL SIGNALING

(Chapter 4 165-191)

biol 3151: principles of animal physiology

Documents

cell membranes

swelling cells

shrinking cells

cell volume changes

electrical gradients

electrical signals

movement of water

electrical energy