CBNS lecture 2

What is the CNS?

brain and spinal cord

What is the PNS?

Somatic and autonomic nervous system

Somatic system

controls voluntary muscle movements

Autonomic system

Involuntary moments, and has sympathetic and parasympathetic systems

Sympathetic nervous system

fight or flight

Parasympathetic system

rest and digest

Flow of signals

Stimulus (ex: knee hitting a table) —> sensory neurons —> CNS (brain and spinal cord) —> motor neurons —> response

Neurons

nerve cells; transmit chemical and electrical signals around body to brain and other way around (use neurotransmitters)

glia

support and maintain neurons

Soma

cell body (contains mitochondria, nucleus and cytoplasm)

dendrites

recieve neurotransmitters/signals from other neurons

axon

relays neurotransmitters through the neuron to the axon buttons

synaptic terminals

where neurotransmitters leave to another neuron

astrocytes

• regulate blood flow

• provide structure

• maintain chemical balance

oligodendrocytes

build myelin sheath

shwaan cells

build myelin sheath

microglia

immune cells

membrane potential

difference in overall charge outside and inside of the neuron

why is there a membrane potential?

more Na+ outside than inside, more K+ inside than outside, lipid bilayer is impermeable (doesn’t let ions in), the Na+/K+ pump

electrochemical gradient

influences movement of ions in and out of cell

chemical forces

conc. differences (high to low movement)

electrical forces

voltage differences (negative to positive movement)

Does Na+ want to move in or out?

inside because chemical- the conc is lower inside than outside, and electrical- more negative inside, which attracts positive Na

Neuron at rest, is the conc of K+ larger inside or outside?

inside

In a neuron at rest, potassium ions (𝐾+) are more concentrated inside the cell than outside and the cell interior is negatively charged; based on electrochemical gradients, which statement correctly describes the direction of 𝐾+ ion movement?

Both chemical and electrical want it out. Chemical because K+ conc is higher inside, so it wants to go from high to low. Electrical because even though it is negative inside, K+ wants to go outside to make the inside more negative to polarize the cell. The concentration gradient is stronger than the electrical

If a cell has a higher concentration of sodium ions (𝑁𝑎+) outside than inside and also maintains a negative voltage inside, what will be the combined effect of the chemical and electrical forces on sodium ion movement?

both forces drive Na+ inside the cell

Na+/K+ pump and why its important

pumps Na+ out, K+ in. maintains ion gradients

K+ leak channels and why its important

K+ leak passively out of cell. Helps stabilize and make RMP negative

Passive transport

move ions (nonpolar, small) high to low conc. using NO ATP

Diffusion through channel

tunnels that are open that let specific particles through (ex: water or ion channels)

Examples of diffusion through channel

aquaporin (water), K+ channel, Na+ channel

Facilitated diffusion

molecule binds to protein, then changes to it’s shape and carries the molecule through (ex: glucose transport)

is facilitated diffusion passive?

yes, it follows concentration gradient

active transport

going against the gradient, low conc to high conc (high effort)

active pump

Uses ATP to force molecules across the membrane and shoves molecules in and out

A cell needs to move glucose, a large polar molecule, from a high concentration outside to a low concentration inside. Which transport mechanism would be most effective for this process?

facilitated diffusion

Na+/K+ pump steps in cycle

1. intracellular Na+ binds to protein

2. protein undergoes phosphorylation from ATP (phosphate is added)

3. conformational change ejects NA+ to outside the cell

4. extracellular K+ binds

5. phosphate removed

6. protein returns to regular shape, and the K+ is released inside

when K+ diffuses out, what happens inside the cell?

Becomes more negative

If potassium leak channels in a cell are blocked, what would be the immediate effect on the cell's resting membrane potential?

It would become less negative due to accumulation of potassium ions inside the cell

Nernst equation

calculates the eq potential of an ion across a cell membrane

Resting membrane potential (RMP)

voltage difference inside vs outside when there are no signals firing

If a neuron's potassium leak channels were suddenly blocked while the sodium-potassium pump continued to function normally, what would happen to its resting membrane potential?

less negative since there are lots of K+ being pumped in, not enough passively leaving

If a neuron's sodium-potassium pump stops working properly, what would be the most immediate effect on the resting membrane potential?

The cell would become less negative (more positive)

The Peripheral Nervous System (PNS) consists of nerves outside the brain and spinal cord.

True

CNS glia

Astrocyte, oligodendrocyte

PNS glia

satellite, schwann

ependymal cell

creates CSF

Zone of integration

AP initiated, and has voltage gated ion channels

Zone of input

where neurotransmitters are taken in. ligand gated ion channels

Zone of conduction

AP conduction, moves neurotransmitters, has voltage-gated ion channels

Zone of output

neurotransmitter release, voltage gates ion channels (Na+ and Ca++)

anterograde transport (what direction, what protein, what is in the vesicle)

• soma to axon terminal buttons

• kinesin

• usually enzymes, neurotransmitters, or nutrients

retrograde transport (what direction, what protein, what is in the vesicle)

• axon terminal buttons to soma

• dynein

• usually growth factors

How can pathogens get into the nervous system?

through retrograde traveling of the highway (ex: polio)

Where is myosin?

In the actin in peripheral structures, like the dendrites

How do these proteins move along the ___?

Move along the microtubule through ATP hydrolysis

neurofibrillary tangles

when tau protein fills up and clumps together and tangles

tau proteins

hold microtubules together