Animal Cells, Neurons, Glia, Blood-brain barrier, Action potential

The Reticular Theory

scientific theory in neurobiology that everything in the nervous system including the brain, is one thing (Golgi)

ANIMAL CELLS

Cell Membrane

• bilayer that surrounds the cell

Separates the inside of the cell from the outside environment

Nucleus

• membrane-bound organelle

Contains the chromosomes / DNA

Endoplasmic Reticulum

Network of thin tubes that transports newly synthesized proteins to their location

Ribosomes

• small, non-membranous organelles

Sites at which the cell synthesizes NEW protein molecules

Mitochondria

• sausage shape

Performs metabolic activities and provides energy that the cells requires

• contains its OWN genes

• inherit it from BIOLOGICAL mother

• decrease in mitochondria links to higher risk depression

NEURONS

Neurons

Receive information and transmit it to other cells

– have variable shapes

Dendrites

Short high branch extensions that pass nerve impulses toward the cell body

• Receives information

• covered in synapses receptors

Cell body: (also called the soma)

The spherical part of the neuron that contains the nucleus, ribosomes, and mitochondria
– Processes and integrates information
information

Axon

Long extenion of the neuron that passes nerve impulses away from the cell body

• Carries information across long distances from one part of the neuron to another

Afferent Axon

(long extension split into two) brings information into a structure (sensory neuron)

Efferent Axon

(long extension split into two) carries information away from a structure (motor neuron)

Presynaptic Terminal

( has Synaptic Vesicles) Transmit information to another neuron (only place in THE neuron that can send signals)

Axon Hillock

The Action Potential starts at the Axon Hillock (Which is where the Axon and Cell body meet) This process only happens when that signal is deemed strong enough ( worth sending through)

Myelin Sheath

Insulating layer that allows electrical impulses to transmit quickly and efficiently along nerve cells

Nodes of Ranvier

Gaps in myelin sheath (not insulated) that facilitates the rapid conduction of nerve impulses

Motor Neuron

• Has its soma in the spinal cord (part of CNS)

• Receives excitation from other neurons

• Conducts impulses along its axon to a muscle/gland

• SENDS SIGNAL

• Cell body is massive

Sensory Neuron

• skin to spinal cord

• Tiny branches lead directly from the receptors to axon

• Cell’s soma is located on a little stalk off the main trunk.

• Is specialized at one end to be highly sensitive to a particular type of stimulation (touch, light, sound, etc.)

If a cell’s dendrites and axon are entirely contained within a single structure, the cell is an…..

interneuron or intrinsic neuron of the structure.

Interneuron/ Intrinsic neuron

neuron whose axons and dendrites are all confined within a given structure

Nerves

• A bundle of axons travelling together

• Nerves can be very long because they often need to transmit information across long distances

GLIA

Astrocytes

Help synchronize the activity of the axon by wrapping around the presynaptic terminal and taking up chemicals released by the axon

– Responsible for dilating blood vessels to bring more nutrients into brain areas with heightened activity

Microglia

Remove waste material, viruses, and fungi from the brain

– Also remove dead, dying, or damaged neurons

Oligodendrocytes and Schwann cells

Build the myelin sheath that surrounds and insulates certain vertebrate axons

– Oligodendrocytes → in the brain and spinal cord

– Schwann cells → in the periphery of the body

Radial Glia

• Neural Progenitor Cells

• Help neurons divide and give rise to different types of brain cells

• Essential for GENERATING NEW NEURONS during brain development

– Guide the migration of neurons and the growth of their axons/ dendrites during embryonic development

BLOOD BRAIN BARRIER

What is the Blood Brain Barrier?

A mechanism that surrounds the brain and blocks most chemicals from entering

Why do we need a Blood- Brain Barrier?

• The immune system destroys damaged or infected cells throughout the body.

• Neurons in the brain usually do NOT regenerate

• important for the blood– brain barrier to block incoming viruses, bacteria…ect from entering.

How does the Blood- Brain Barrier work?

• Outside the brain, endothelial cells (cells that form walls of capillaries) are separated by small gaps

• In the brain, endothelial cells join tightly that they block almost anything from coming in

• the barrier keeps out useful and harmful chemicals

What happens when a VIRUS crosses over the Blood- Brain Barrier?

• Brain’s microglia attack

• Mounts an inflammatory response without killing cell

• Response controls the virus without eliminating it

Viruses than CAN CROSS the Blood Brain- Barrier

• Rabies—> leads to death

• Syphilis—> produces fatal consequences

• Chicken Pox

Neural Signals

Neural Signals

If axons used electrical conduction the strength of the signal would decay as it travelled

• Instead, axons periodically regenerates an impulse

Movement of Ions

• For neural signals… Transmission of signal is dependent on the movement of ions

  – Ions = charged particles

• Presence and movement of ions is important for when a neuron fires or is at rest

• ions are unequally distributed inside/ outside of cell

Ion Channels

Open: the ions can pass through in and out

Closed: the ions cannot pass through the channel

Inactivated: regardless of what happened, these signals are not opening

The cell wants an equal amount of positive and negative charged ions

When cells are closed, doesn't allow for positive ions to go through

What is Resting Potential

the difference in electrical charge between the inside and the outside of a neuron when the cell is in a non-excited state

How to Measure Resting Potential

Connecting electrodes to a voltmeter

−70 (mV)

Electrical Gradient

• RESTING POTENTIAL: When at rest the membrane maintains… electrical gradient:

Concentration Gradient

• Difference in distribution of ions (sodium, potassium..) across the membrane

Electrical Gradient + Concentration Gradient

pull sodium ions into the cell

Sodium Potassium Pump

= protein complex

• Continually pumps out 3 sodium ions and draws in 2 potassium ions

• Helps to maintain electrical gradient

(Potassium keeps the cell at -70)

What is the Action Potential

Electrical charge that runs down the axon from the axon hillock to the terminal buttons.

• conduction of information along an axon

“neuron fires”

How does the Action Potential Work?

Dendrites – receive signals

• Based on signal strength neuron decides whether (or not) to pass information along

• If information is strong enough it is transmitted across the full axon—→Action Potential

Depolarization (threshold of excitation) RISING STAGE

• Some Na+ channels open allowing Na+ ions to enter cell

• Membrane starts to depolarize

• If threshold of excitation is reached, all Na+ channels open

• Resting potential -55

Depolarization PT 2 after THRESHOLD OF EXCITATION—> (peak excitation)

• All Na+ channels are open

• Na+ floods in +30MV =(peak excitation)

Repolarization FALLING STAGE

• At peak action potential, Na+ channels CLOSE, K+ channels OPEN

• K+ leaves cell – membrane becomes hyperpolarized

Hyperpolarization

• means increased polarization.

• neurons membrane becomes more negatively charged in one spot

• When stimulation ends, the charge returns resting level.

  .

Propagation of an Action Potential

• Action potential flows along axon remaining at equal strength

• Behind each sodium entry, potassium ions exit, leads to resting potential

Salatory Conduction

“jumping of action potential from node to node”

Activity within a Neuron

All-or-none Law

Once an action potential is initiated in an axon, it travels along the fiber without losing strength until it reaches the end.

Rate Law

Differences in stimulus intensity or transmitted information along an axon are reflected in changes in the firing rate of the axon (i.e., the number of action potentials).