Nervous System: Resting Membrane Potential, Neurons, and Glial Cells

The central nervous system (CNS) includes…

• The brain

• The spinal cord

The peripheral nervous system (PNS) includes…

• Sensory neurons which transport information or signals from external stimuli to the CNS

• Effector neurons which carry out the response and includes the somatic nervous system and the autonomic nervous system

How does information flow in the nervous system?

1. Receptor perceives a stimulus

2. The sensory neuron carries the signal in the form of an action potential to the CNS

3. CNS makes sense of the information and determines if a response is needed

4. Efferent neuron elicits a response by stimulating muscles/glands

What are the two components of the nervous system and what do they do?

• Neurons handle information

• Glial cells are the supporting cells of the nervous system by holding neurons together and providing neurons with an optimal environment

Cell body includes the…

nucleus and organelles

Dendrites are…

processes that extend from the cell body and are the part that receives information

The axon is…

a long process that carries information

The axon hillock or trigger zone is where…

the action potential is initiated

Synaptic terminals is the…

swelling at the end of the axon and has vesicles with neurotransmitters

The neurotransmitter is a…

chemical signal used for cell-to-cell communication

What is the function of the sensory neuron and where is it located?

• Carries sensory information generated by a stimulus from the body to the CNS

• Located outside the CNS in the periphery region 

What is the function of interneuron and where is it located?

• Facilitates communication between neurons

• Located in CNS

What is the function of motor neurons and where is it located?

• Carries efferent information to an effector 

• Located in the CNS

What are the three kinds of neurons?

Sensory, interneuron, motor neurons

What are the 6 kinds of glial cells?

• Schwann cells (peripheral nervous system)

• Satellite cells (peripheral nervous system)

• Oligodendrocytes (central nervous system)

• Microglia (central nervous system)

• Ependymal cells (CNS)

• Astrocytes (CNS)

Function of schwann cells?

They surround the axons of neurons in the peripheral nervous system and myelinate them

Function of satellite cells?

Mains the environment of neurons (O2, nutrients)

Function of oligodendrocytes?

Myelinate axons in the CNS

Function of microglia?

Removes waste and pathogens

Function of ependymal cells?

Monitor and circulate the cerebral spinal fluid (CSF)

Function of astrocytes?

Maintains blood-brain barrier

How do neurons transmit information?

1. Receives information through dendrites

2. Transmit the electrical signal (action potential) along the axon to the presynaptic terminal

3. Transmit information to other cells through synapses 

Why are cells electrically charged?

Because of the uneven distribution of ions across the cell membrane

What causes the uneven distribution of ions across the cell membrane?

• Phospholipid bilayer prevents the movement of ions expect for when there are channels but potassium has more channels than sodium

• Sodium-potassium ATP pump

What is the resting membrane potential?

The difference between the charge inside and outside the cell

How do channels allow ions to cross the cell membrane?

• Selective for certain ions

• Passive transport so no ATP used

• Ions move down a concentration gradient

• Fast

How do leak channels allow ions to cross the cell membrane?

• Always allow things to move through (always open)

• Potassium and sodium leak channels

How do voltage-gated channels allow ions to cross the cell membrane?

• Have doors which will open when there is a change in the membrane potential

• Voltage-gated sodium channel

• Voltage-gated potassium channel

How do ion pumps allow ions to cross the cell membrane?

• Selective for certain ions

• Active transport, needs ATP

• Slow

• Creates concentration gradients by moving ions against their gradients

Describe Na+/K+ ATP pumps

• Moves 3 Na+ ions out of the cel and 2 K+ ions into cell using ATP

• 2 main purposes are to generate a…

  • concentration gradient

  • electric gradient

How is a concentration gradient/electrical gradient created?

• A concentration gradient is created when there is more sodium is on the outside while more potassium is on the inside

• Generates a small electrical gradient because inside is more negative than outside 

How does potassium affect the resting membrane potential?

• Because of the sodium/potassium pump, there is more K+ inside than outside the cell

• The cell membrane has lots of K+ leak channels so K+ is very permeable

• K+ will move out of cell because the concentration gradient acts as a driving force

• As K+ leaves the cell, it leaves its negative partners behind so the cell becomes more negative than the outside

• Electrical gradient is trying to pull K+ in while concentration gradient wants to push K+ out

How does sodium affect the resting membrane potential?

• Because of the sodium/potassium pump, there is more Na+ outside than inside cell

• The cell membrane has fewer Na+ leak channels so Na+ is less permeable

• Concentration gradient moves Na+ into cell because Na+ is more concentrated outside while the electric gradient also moves Na+ inside because K+ leak channels caused inside cell to be more negative

• As Na+ enters the cell, it makes the cell a bit less negative