Chapter 12 Nervous Tissue - Part B

Resting Membrane Potential

Electrical difference between the inside of the neuron and the outside.

The inside is -70 mV, a negative charge.

The outside is 0 mV, a relatively positive charge.

Ion concentrations relative to the cell membrane:

• There is more k+ inside.

• There is more OA- inside.

• There is more Na+ outside.

• There is more Ca+ outside.

• There is more Cl- outside.

Electrical force

Ions will always travel to the area of opposite charge. Electrical force has less influence compared to chemical force.

Chemical force

Ions travel from an area of low concentration to an area of high concentration. Chemical force has more influence compared to electrical force.

K+ Forces

Electrically K+ wants to go in.

Chemically K+ wants to go out.

OA- Forces

Electrically OA- wants to go out.

Chemically OA- wants to go out.

Na+ Forces

Electrically Na+ wants to go in.

Chemically Na+ wants to go in.

Cl- Forces

Electrically Cl- wants to go out.

Chemically Cl- wants to go in.

Ca+ Forces

Electrically Ca+ wants to go in.

Chemically Ca+ wants to go in.

Resting Membrane Potential Mechanism

Who up charging they membrane??????

The method by which a neuron retains a -70mV charge inside, and a +0 charge outside.

Steps of the Resting Membrane Potential Mechanism

(All of these technically happen at once).

1. The rough ER in the cell body produces negatively charged organic proteins. These proteins are too big to flow down their concentration gradient, so the inside of the cell gains a -5 mV charge.

2. The sodium potassium pump pumps 3 Na+ out of the cell and 2 K+ into the cell. Since the pump removes 3 positive species and takes in only 2 positive species, the charge of the inside of the cell jumps to -10mV. (Note that this pump does not effect extracellular fluid cause it big and spacious)

3. K+ exits the cell via leakage channels, further decreasing the membrane potential to -70 mV. Once at -70mV, the electrical force and chemical force acting on potassium balance out.

4. Cl- is removed via K+/Cl- symports.

5. Ca2+ is removed via Na/Ca+2 exchangers (antiports).

Graded Potential

A small, localized change in a cells membrane potential, usually hovering around the resting membrane potential of -70 mV.

Depolarization

An positive increase in charge of the membrane potential.

Hyperpolarization

A decrease in charge away from -70 mV of the membrane potential.

Repolarization

A decrease in charge back towards -70 mV of the membrane potential.

Potential threshold

-55 mV. Once the trigger zone (axon hillock) reaches a charge of -55 mV the action potential will spread through the axon and the neuron will fire an action potential.

Excitatory Action

A different axon sending neurotransmitters to the neuron, causing the charge to increase.

Inhibitory Action

A different axon sending neurotransmitters to the neuron, causing the charge to decrease.

Action strength

A neuron can send:

• A short burst of charged particles.

• A large burst of charged particles

• A sustained burst of charged particles.

Ligand Gated Channel

A specific kind of channel that requires a particular neurotransmitter to open, like fitting a key into a lock. Once the key is inserted, a specific kind of ion will either enter or exit the cell, leading to depolarization/repolarization/hyperpolarization.

How do charges dissipate after entering?

Some exit through pumps, like Na+.

Others simply diffuse through the cell, becoming so spread out that their addition has a negligable effect on the charge.

Remember, the charge must be -55 mV AND reach the axon hillock (Trigger zone) to fire an action potential.

Action Potential Description

As positive ions enter the neuron, they’ll eventually travel towards the axon hillock (trigger zone); if enough make it to the zone then the action potential fires, bring the charge of the cell up from -55 mV to +30 mV. This action potential is expedited by the myelin sheath (saltatory conduction).

How does an Action Potential mechanism work?

• Positively charged Na+ enters the cell via ligand gated channels around the dendrites and the cell body.

• After enough Na+ enters, the trigger zone (axon hillock) depolarizes to a charge of -55 mV.

• This charge causes Na+ voltage gated channels to open, flooding the cell with positive charge and leads to a cascade effect, depolarizing the cell all the way up to 30 mV.

• At 30 mV the Na+ voltage gated channels shut, and K+ voltage gated channels open.

• K+ rushes out of the cell via voltage gated channels and leakage channels, repolarizing the cell back down to -70 mV.

• K+ voltage gated channels begin to close slowly at -70 mV. Potassium continues to enter for a bit and hyperpolarizes the cell.

• The cell will finally reach its resting membrane potential as leak channels for Na+ slowly let sodium back in. -70 mV

Whats the point bruz. Why we even action potential???

• You need 30+ mV to activate Ca+2 voltage gated channels.

• Ca+2 helps vessicles filled with neurotransmitters attach to synaptobrevin, which allows the neurotransmitters to leave the axon.

Absolute Refractory Period

From -70 mV to -55 mV, at this point the neuron CANNOT fire another action potential.

Relative Refractory Period

From -55mV onwards, can get to another action potential if enough sodium enters.

Sumation

Combining gated potentials to reach the trigger zone.

Temporal Sumation

Keep on sending neurotransmitters consistently until -55 mV is reached.

Spatial Sumation

Have multiple axons work together in a single location to combine their neurotransmitters to get a large gated potential for -55 mV.

Excitatory Post Synaptic Potential (EPSP)

Adds positive charge to the inside of the neuron by allowing Na+ in.

Inhibitory Post Synaptic Potential

Decreases charge in the neuron by either allowing Cl- in or taking K+ out.

Saltatory Conduction

Where there is no myelin sheathe, the positive charges have to fight through collected negative charges to move, afterall, at resting potential the opposites attract. However, the myeline sheathes put distance between the positive and negative charges at rest; therefore, when a myelin sheathe is present, the positive charge doesnt have to fight through a bunch of negative charge.

Action potential speed in narrow vs wide axons.

Axons have protiens, in narrow channels Na+ gonna bonk into them, not in wide channels

Lidocaine

Local anethstetics, blocks the inner part of sodium, no sodium, no signal, no signal no pain.

Tetrodotoxin

Pufferfish, blocks sodium and kills you

Multiple Sclerosis

Removes myelin sheath, slow signals

Brain

The braon in the head

Cerebrum

The big part on the top.

Made of four lobes, makes up 80% of the brain, and is the center for all intelligence, reasoning, memory, and voluntary processes.

Cerebral Hemisphere

One half of the cerebrum

Each contains four lobes.

Frontal Lobe

Lobe in da front

Responsible for our personality and decision making.

Precentral gyrus (Primary Motor Cortex)

Divides front and back kinda

Responsible for voluntary movement.

Parietal Lobe

Back upper lobe

Responsible for physical sensations like touch from the skin and for joint proprioception.

Contains the post central gyrus

Postcentral gyrus (Primary somatosentory cortex)

Kinda behind the motor cortex 

Main sensory receptive area for touch.

Occipital Lobe

is occipital

Responsible for processing and storing visual information

Temporal Lobe

Da one on the side sliiide to the left

Responsible for our ability to smell and hear.

Brainstem

its a stem, that comes out of the brain

Midbrain

Pons

Medulla

Responsible for not dying. Makes us breathe and makes our heart beat.

Cerebellum

brain under the brain brain part 2 brain

Responsible for fine motor control, coordination of skeletal muscle, and equilibrium.

Arbor vitae

Tree thing in the cerebellum

Made of white fat.

Vermis

Down the middle of the cerebellum.

Seperates the 2 halves of the cerebellum.

Means worm.

Fissures / sulci

1. Central sulcus

2. Lateral sulcus

3. Longitudinal fissure

4. Transverse fissure

5. Parieto-occipital sulcus

Central sulcus

Central

Divides the frontal and parietal lobes.

Lateral sulcus

Kinda middle bottom cleft

Seperates the temporal lobe from the frontal and parietal lobes.

Longitudinal fissure

Right down mid

Seperates left and right cerebrum

Transverse fissure

Between brain and brain pt 2.

Seperates the cerebrum and the cerebellum.

Parieto-occipital sulcus

Between the parietal and occipital lobes

Separates the the parietal and occipital lobes