Transmembrane Voltages and Neural Communication

2 communication systems in the body

Nervous system

Endocrine system

Is nervous system

Fast or slow

Targeted or widespread

Sustained or short lived

Fast

Targeted

Short lived

Is endocrine system

Fast or slow

Targeted or widespread

Sustained or short lived

Slow

Widespread

Sustained

At the cellular level, animal nervous systems are

Very similar

At higher levels we see

Different organizations and adaptations to animals in different environments

Besides sponges, all animals have

Nervous systems(complexity varies)

Nervous system is a network of specialized cells evolved to do what

Gather info from environment, process info, and produce response

Animals with most complex capacity for behavior have the most complex

Nervous systems

This behavioral complexity comes at a

Metabolic cost

Neurons in Cnidaria

Most primitive polymodal neurons(motor and sensory functions)

Do humans have polymodal neurons

No

In flatworms, what appeared

Longitudinal nerve cord and anterior collection of nerve cells(Cephalization)

Over time, nervous tissue migrated where

Towards midline of the body

Over time, nervous systems have become

More compelx

Centralization

Neurons responsible for integration are centralized rather than dispersed(brain and spinal cord)

Cephalization

Structure responsible for nervous functions are concentrated at one end of the body such as the head

2 types of nervous tissue

Neurons(electrically excitable)

Neuroglial cells(support)

ependymal cells

Create and circulate cerebrospinal fluid

Oligodendrocytes

produce myelin in CNS

Schwann cells

produce myelin in PNS

Microglia

Immune surveillance and phagocytes in CNS

Astrocytes(3 functions)

Maintain extra cellular environment

Create blood brain barrier

Remove excess neurotransmitters

Most abundant glial cell

astrocytes

3 functions of the nervous system

Sensory functions(receive info from sensory receptors)

Integrative functions(analyze and store incoming info)

Response/motor functions(respond to stimuli)

What makes up the lumen(inside) of an axon

Microtubules

anterograde transport

movement of substances down the axon away from soma

retrograde transport

Movement of substances from axon to soma(cell body)

Examples of substances

Organelles, ions, nutrients

White matter

Groups of myelinated nerve fibers(appear white due to myelin)

Function of white matter

Transmission of nerve impulses

Gray matter

Groups of unmyelinated nerve fibers(appear gray due to lack of myelin)

Function of gray matter

Processing of information

Structure/anatomy of neuron allows it to send signals from where to where

Input region to distant output region

Change in voltage generated at cell body travels to

Axon terminal

Change in voltage is called

Action potential

Neuron communication is classified as

Electrochemical

Axons terminals connect with dendrites of another neuron via

Synapse

Goal of action potential

Stimulate release of neurotransmitter housed in axon terminal ends of axon

Dendrites have what type of ion channels

Ligand gated channels

When neurotransmitters bind to dendrite, what happens

Ion channels open or close

At rest, the inside of a cell is

Negative

Membrane potential

Energy stored in membrane keeping oppositely charged particles apart(voltage difference across membrane)

resting membrane potential

-70mV

Electrical potential is due to what 2 things

Differences in concentrations of ions

Selective permeability of ions across plasma membrane

Membrane is more permeable to

Potassium (K+)(low permeability to Na+)

Inside vs outside of neuron

Inside: high K+ and negatively charged proteins, low Na+

Outside: high na+, and low k+ and negatively charged proteins

Action potential is triggered by

Threshold level of depolarization

threshold potential

-55mV(all or nothing response)

Action potential propagates without

Decrements

Absolute refractory period

Period during which a second action potential cannot be initiated

Cause of absolute refractory period

inactivation of voltage-gated sodium channels

Relative refractory period

Period after absolute refractory period where second action potential is possible, but more difficult(stronger stimulus needed)

Inactivation of voltage gated Na+ channels prevents

reverse propagation of an action potential

Which voltage gated channel is faster

Na+(slower K+ is why there is a hyper polarization phase)

Action potential travels down axon via

Saltatory conduction(hopping of action potential from node to node

Alan Hodgkin and Andrew Huxley

Received Nobel prize for uncovering mechanism of action potentials

Hodgkin and Huxley conducted experiments on

Giant squid axons(large size made them easier to experiment on)

The velocity of nerve impulse conduction increases with

Increasing axon diameter

Tetrodotoxin

Neurotoxin that blocks sodium channels and inhibits action potentials

Batrachotoxin

forces Na+ channels to stay open, causing inner membrane to be very positive and unable to fire