Neuron Structure and Function

Neuron Structure and Function

• Neurons are fundamental units of the Central Nervous System (CNS) and Peripheral Nervous System (PNC).
• Nerves are bundles of thousands of neurons that facilitate communication from sensory organs to the brain, and from the brain to muscles or glands.
• CNS includes the brain and spinal cord.
• PNC includes ganglia in the periphery.

Types of Neurons

• Unipolar neurons transmit body sensations and are involved in reflexes, primarily in the PNC.
• Bipolar neurons are present in sensory systems processing specific information like vision and hearing.
• Multipolar neurons receive and process a high volume of information, forming advanced connections typically in the CNS as interneurons, and are the most common in the CNS.
• Somatic Sensory Neurons/Afferent Neurons send information from senses to the brain.
• Interneurons/Intermediate Neurons are located in the CNS, between neurons involved in receiving sensory info, decision making, and sending motor signal..
• Motor neurons are from the brain to muscles, conveying commands to muscles.
• Neuron types vary by function (sensory, motor, interneuron), polarity (unipolar, bipolar, multipolar), size, shape, sensitivity to stimuli, and biochemical characteristics.

Neuron Structure

• Dendrites receive information from other neurons.
• The Soma (cell body) contains the nucleus, nucleolus, and chromosomes, and creates and maintains information.
• An Axon Hillock is the junction between the cell body and axon.
• The Axon propagates action potentials.
• The Myelin Sheath is a layer of fat covering portions of the axon, aiding faster conduction.
• Terminal Buttons connect with the next neuron at the synapse by releasing neurotransmitters.
• Synapse connect two neurons, facilitating chemical communication, referring to gap between terminal button of one neuron & dendrite of the next.

Internal Structures - Includes organelles and nucleus surrounded by the membrane

• Membranes define the boundary of the cell, separating intracellular from extracellular environments; is the fatty sheath of each cell.
• The hydrophobic side is water impermeable, while the hydrophilic side is water permeable.
• Consist of a double layer of lipid molecules with embedded proteins, and exhibits selective permeability via channels, receptors, and pumps allowing only lipid-soluble or smaller substances to pass through.
• Mitochondria are organelles for cellular respiration where ATP is produced.
• The Cytoplasm is the fluid inside the cell contains organelles.
• The Nucleus contains the nucleolus and genetic information (DNA) arranged in chromosomes.
• The Nuclear Membrane has pores for substance exchange.

Axoplasmic Transport

• Anterograde transport moves materials from the cell body to terminal buttons via kinesin and microtubules.
• Retrograde transport moves materials from terminal buttons back to the cell body via dynein.
• Cytoskeleton maintains the position of organelles.

Additional Organelles

• Microtubules are hollow tubes of the cytoskeleton aiding in intracellular transport.
• Endoplasmic Reticulum includes RER with ribosomes for protein synthesis and SER for lipid synthesis and detoxification.
• Golgi apparatus processes, sorts,and packages proteins.
• Lysosomes contain digestive enzymes.

Protein Synthesis

• Protein synthesis involves transcription of a specific gene to create messenger RNA (mRNA) in the nucleus.
• Ribosomes translate mRNA into proteins in the cytoplasm and rough endoplasmic reticulum

Glial Cells

• Glial cells are support cells that do not generate action potentials or synapses; communicate chemically; do not have axons/dendrites and are far more numerous than neurons.
• They provide structural support, maintain chemical environment, provide insulation (myelin), and clear debris, important in cases of trauma/injury and protect blood-brain barrier, acting as astrocytes.

Glial Cells in CNS

• Astrocytes provide physical support to neurons and control the chemical environment by supplying and removing substances.
• Oligodendrocytes form the myelin sheath by insulating axons for faster and energy-efficient conduction.
• Microglia are immune cells of the brain that protect against invaders.
• Multiple sclerosis impairs myelin due to an autoimmune reaction.

Glial cells in the PNS

• Schwann cells form myelin surrounding one axon, aid in digestion of damaged axons, and facilitate growth of new neurons.
• Involved in regeneration of nerves.

Blood Brain Barrier (BBB)

• BBB is the barrier between blood capillaries everywhere in the body and capillaries in the brain.
• Selectively permeable to control the extracellular fluid in the brain and prevent toxins from entering.
• Composed of tight junctions between endothelial cells and astrocyte endfeet, transporting substances.
• Psychoactive drugs cross the BBB due to their fat solubility.

Communication

• Electrical transmission within a neuron is based on changes in voltages to the terminal buttons
• Chemical transmission at a synapse involves neurotransmitter release into the synapse between two neurons.
• Sensory neurons can trigger a motor neuron in the spinal cord for reflexes.

Membrane Potential

• The difference in electrical charge between the inside and outside of the cell, with each neuron having a threshold for nerve impulse reception.
• Ions (charged molecules) carry electrical charges.
• Membrane permeability to ions depends on the type and status of ion channels.
• Membrane potential results from the equilibrium between the diffusion force and electrostatic pressure.

Resting Potential

• During resting potential there is no nerve transmission, most channels are closed, there is no ion transmission in the polarized state.
• In a resting state the concentration of ions: A- (organic anions - large molecules that can't get out, reside in the cells), CI- (chlorine - force diffuses inside, electrostatic force wants to pull out of the cell both forces are balanced, mostly outside of cell - no channels in axon), +Na (sodium - diffusion force pushes inside and electrostatic pressure force pushes inside - sodium potassium pumps force them outside - most outside cell), and +K is inside cell because diffusion force is too strong

Action Potential

• Sodium-potassium pumps preserve ion concentration gradients at the expense of energy (ATP).

Communication Within the Neuron

• Communication in the neuron takes place by electrical transmission within the neuron and chemical transmission at between two neurons
• Neuron will be on the move because of the change inside of a voltage for the cell
• Voltage that comes outside is the sodium and calcium (NA, CA) ion charges
• The voltage is charged based on the cell

Neuron Response

• Resting - no excitement - is -70mv, and stays at that zone until something stimulates it
• Threshold - needs outside stimulus to become excited - is about -55mv - must be activated to change zones
• Action – moves and spreads quick for synapse to change something
• Synapse - needs message to move, needs Dendrites so that Electrical messages can move through the neuron, and can stimulate changes

Nerve Stimulation and Frequencies

• Nerve has a certain frequency and must stick to it - never changes - but when it does, there are consequences
• Never half excites nerve - will do nothing - never turns half off during use
• Needs to move forward - never goes backwards - will do nothing, and will not reach target
• Always need full nerve action to move nerve signals

Ion Transmission

• A +NA charge moves in - the nerve will rise voltage and change and begin polarizing as well
• A +K charge means moves out - voltage will lower and polarize
• Will drop a little over before stopping
• When voltage overcharge - will reset through channels to correct point
• Over a refract - another nerve signal will start

Refract - to be unresponsive to neuron stimuli for a period of time,

Relative - can function, but only with higher stimulation rate to activate Absolute - no voltage can change it until it resets

Transmissions

• Action - for active transfers, they need to move until target is reached
• Passive - the action lessens quick until the point of nothing

Chemical Transfers

• Chemical - when something causes pain, needs sensory neuron the message to reach spinal cord, which is close to other nerves
• Between two nerves messages that are needed passes on action of action for the message to continue

Progress Transmissions

Progress Transmission Transmissions has no speed It can change positions quick in each point

• More fatty material helps make the action go quick in the neuron area If fatty cover exists, the channel has no need for anything to do because it covered

Neuron Contacts

• Contact is made from Pre side neurons

• The side channels come together and synapse to come together Needs the chemical effect to move action forward with signals to change direction Types of channels in this system

• Dendrite-axonal end for the postsynaptic area to stay the same, and the soma does not need to move to the surface

• Soma-Axonal sides do not make many changes in this area, like the dendrite side

Nerve Action Side and parts

The sides dont need to move, they change due the position that each take There always need something special so that a neuron can take action If all is good, then you will notice you dont need the sodium and potassium sides The sides start due the need for +NA charges and their need for action.

Neurotransmitters

• Nerves start because neurotransmitter are produced at the start This all starts at the end point with channels and how there used

• Ion gated channel is one channel that all travel (NA,K) but is gated to only travel in channel

Molecules in the area stay out The channels need change so that nothing else gets by

A. - the transmitters move due their channel If the voltage changes, then the charge will take over the channels.