Mark Louie D. LopezCollege of SciencePolytechnic University of the Philippines

NERVE PHYSIOLOGY

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FUNCTIONS OF NERVOUS SYSTEM

Sensory input or detection

Integration processing

transmission of information

perception of sensory information

learning and memory

thought processes and conscious awareness

planning and implementation of motor commands

Expression of behavior - responses to environment

ANIMAL PHYSIOLOGY

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CELLS OF NERVOUS SYSTEM

ANIMAL PHYSIOLOGY

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NEURON VS GLIAL CELLS

ANIMAL PHYSIOLOGY

NE

UR

ON

SN

EU

RO

GL

IA

• electrically excitable cell th

at processes and transmits

information through

electrical and chemical

signals.

• To surround neurons and

hold them in place,

• Supply nutrients and oxyg

en to neurons,

• To insulate one neuron

from another,

• To destroy pathogens and

remove dead neurons.

NERVOUS SYSTEM

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TYPES OF GLIAL CELLS

ANIMAL PHYSIOLOGY

Microglia act as the first and main form of active immune defense in

the central nervous system

Oligodendrocytes provide support and to insulate the axons in

the central nervous system

Astroglia perform many functions, including biochemical support

of endothelial cells that form the blood–brain barrier, provision of

nutrients to the nervous tissue, maintenance of extracellular ion

balance, and a role in the repair and scarring process of the brain and

spinal cord following traumatic injuries

Ependymal cells are a type of Glial cell and are also CSF producing

cells.

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ANIMAL PHYSIOLOGY

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FUNCTIONAL ORGANIZATION OF NEURONS

Receptive segment: Dendrites

Initial segment: Action Potential

Conductive segment: Axon

Transmissive segment: Axon Terminals

Integration segment: Soma

ANIMAL PHYSIOLOGY

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NEURONS ACCORDING TO FUNCTION

ANIMAL PHYSIOLOGY

Afferent/Sensory Neuron – receives and

transmits impulses to the CNS for

processing

Efferent/Motor Neuron – originates in the

CNS and transmits impulses to effector

organs throughout the body

Interneuron – only in CNS; integrators

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NEURONS ACCORDING TO FUNCTION

ANIMAL PHYSIOLOGY

Afferent Neuron

Efferent Neuron

Inte

rneuro

ns

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NEURONS ACCORDING TO MORPHOLOGY

ANIMAL PHYSIOLOGY

Unipolar – one process from cell body

Bipolar – 2 processes from the cell body and

the presence of axon hillock opposite the

body

Multipolar - 1 axon, several dendrites;

presence of axon hillock continuous to the

initial segment

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NEURONS ACCORDING TO MORPHOLOGY

ANIMAL PHYSIOLOGY

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NEURONS ACCORDING TO MORPHOLOGY

ANIMAL PHYSIOLOGY

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POTENTIAL DIFFERENCE

ANIMAL PHYSIOLOGY

Separated electric charges of opposite sign have the

potential of doing work if they are allowed to come

together. This potential is called an electric potential

or, because it is determined by the difference in the

amount of charge between two points, a potential

difference

Negatively Charged

Positively Charged

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RESTING MEMBRANE POTENTIAL

ANIMAL PHYSIOLOGY

All cells under resting

conditions have a potential

difference across their

plasma membranes oriented

with the inside of the cell

negatively charged with

respect to the outside. This

potential is the resting

membrane potential.

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Concentration gradient

Membrane permeability K+ > Na +

Negatively charged protein A-

ANIMAL PHYSIOLOGY

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Non-gated ion channels

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IONS INVOLVED IN MEMBRANE POTENTIAL

ANIMAL PHYSIOLOGY

• Potassium (K+) Located inside the membrane

Diffuses outside and at a faster rate since the

membrane is more permeable to K+ than to Na+

the diffusion of K+ out makes the membrane

negative, resulting to RMP (-70mV) o

• Sodium (Na+) Located outside the membrane and

moves inwards . Na-K Pump: restores the balance

of ions and maintains the -70mV RMP

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IONS INVOLVED IN MEMBRANE POTENTIAL

ANIMAL PHYSIOLOGY

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CHANGES IN MEMBRANE POTENTIAL

ANIMAL PHYSIOLOGY

Graded potential

Action potential

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ACTION POTENTIAL

ANIMAL PHYSIOLOGY

Transient changes in the membrane potential from its

resting level produce electric signals. Such changes

are the most important way that nerve cells process

and transmit information.

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ACTION POTENTIAL

ANIMAL PHYSIOLOGY

Action potential - reversal of polarity

normal polarity: negative inside, positive outside

reversed: positive inside, negative outside

Initiated when threshold potential is with explosive opening

of the remaining voltage-gated Na+ channels

Opening voltage-gated ion channels Na+ and K +

successively

Electrical signal that propagate along a long distance

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ACTION POTENTIAL

ANIMAL PHYSIOLOGY

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MEMBRANE ION CHANNELS

ANIMAL PHYSIOLOGY

a. Leak Channels

responsible for the mov’t of ions

non gated ion channels - the resting

potential of the axon is -70mV

b. Gated Ion Channels/Voltage-Gated Channels

sensitive to voltage difference across the

membrane

closed at resting state

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MEMBRANE ION CHANNELS

ANIMAL PHYSIOLOGY

Na Channel – 2 gates

- Activation Gate (M Gate)

– close at rest

- Inactivation Gate (H

Gate) – open at rest

K Channel – (N Gate) -

closing gate

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THRESHOLD POTENTIAL

ANIMAL PHYSIOLOGY

Critical membrane potential o a change of at least 15mV

will elicit an action potential. Otherwise, a local event is

produced. And once the threshold is reached, more

explosive depolarization occurs (reversal of polarity, turned

to positive

70mV to -55mV: caused by the influx of Na+, hence the

membrane potential will lose its positivity resulting to

depolarization

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ACTION POTENTIAL

ANIMAL PHYSIOLOGY

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DEPOLARIZATION

ANIMAL PHYSIOLOGY

Voltage gated Na+ ions open (M, H gates)

Membrane suddenly becomes permeable to sodium ions.

o The rapid influx of Na+ ions causes the membrane

potential to become less negative.

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ACTION POTENTIAL

ANIMAL PHYSIOLOGY

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OVERSHOOT

ANIMAL PHYSIOLOGY

Inactivation gate (H) will close, no entry of

Na+

The rapid influx of Na+ ions causes the

membrane potential to become too positive

o more than 0mV

Reversal of polarity

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ACTION POTENTIAL

ANIMAL PHYSIOLOGY

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REPOLARIZATION

ANIMAL PHYSIOLOGY

The Na+ channels become inactivated,

while voltage-gated K+ channels open.

The efflux of K+ ions gradually restores the

negative membrane potential

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ACTION POTENTIAL

ANIMAL PHYSIOLOGY

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HYPERPOLARIZATION

ANIMAL PHYSIOLOGY

More negative point than the normal RMP

due to the slow closing of K+ channels

and an excess if K+ ions go out of the

cell.

After hyperpolarization, the polarity of the

membrane returns to the resting potential

due to the Na-K electrogenic pump

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ACTION POTENTIAL

ANIMAL PHYSIOLOGY

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ACTION POTENTIAL

ANIMAL PHYSIOLOGY

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CONDUCTION OF IMPULSES

ANIMAL PHYSIOLOGY

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CONDUCTION OF IMPULSES

ANIMAL PHYSIOLOGY

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REFRACTORY PERIODS

ANIMAL PHYSIOLOGY

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REFRACTORY PERIODS

ANIMAL PHYSIOLOGY

Absolute Refractory Period - the period during

which a second action potential cannot be elicited

even with a strong stimulus (because the ion-

gated channels are closed).

no second response no matter how strong the

second stimulus is.

after depolarization, absolute since Na channel is

closed

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REFRACTORY PERIODS

ANIMAL PHYSIOLOGY

Relative Refractory Period - The period wherein

a response may be elicited provided that the

second stimulus is greater than the threshold.

Na+ is slowly returning to resting, from closed H

gate it will open, activation gate will slowly close,

inactivation gate closed –

Technically open Na channel (M closing, H open)

o if the Na gate is open -> returning to resting

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GRADED VS ACTION POTENTIAL

ANIMAL PHYSIOLOGY

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NEUROTOXINSToxin Source Effects

Tetrodotoxin Puffer fish Blocks voltage gated Na+

channels

Saxitoxin Marine dinoflag-gelates, Fresh

water cyanobacterium

Blocks voltage gated Na+

channels

Apamin Honeybee Blocks voltage gated K+

channels

Batrachotoxin Poison arrow frog Keeps Na+ channel from

closing

Calciseptin Black mamba Blocks Ca++ channels

Iberiotoxin Indian red scorpion Blocks K+ channels

Phoneutriatoxin Banana spider Slows closing of Na+ channel

Stichodactylatoxin Sea anemone Blocks voltage gated

K+ channels

ANIMAL PHYSIOLOGY

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3rd review

ANIMAL PHYSIOLOGY

Prepare a powerpoint presentation of the review

Limit your presentation to 10 slides

Must be presentable within 15 minutes given time

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ANIMAL PHYSIOLOGY

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