Chapter 6 Human Physiology

Nervous System (split into, travel, flows, change)

divided anatomically or functionally

• Afferent/efferent

• Somatic/ autonomic

• Neurons are only one way signals

• Information flows from the dendrites to the axon terminals

• It's morphology changes its function.

Processes

Processes- connects neurons to other neurons

- "neural processes"

-the cells body is the main area of the neuron, any stem coming off is considered a process

-different processes have different functions

dendrite (contains, receives)

-process that receives information and travels down to the axon

- contain ribosomes

-regions that receive information from other neurons

axon (forms, begins, transmits, called, you can (2), spilt, coming off)

-process that can develop and form action potentials

-begins at axon hillock and ends at axon terminals

-transmits information to other neurons or effector cells

- "nerve fibers"

- "varicosities" release signals

-can signal to other neurons directly from the axon

-can spilt signals in multiple different directions

-multiple axons coming off = axon collaterals

-increases connectivity

Dendritic spines (increase, when you, if you, not, (3))

- increase the SA of dendrites by bulbous head

-when you connect a dendrite to another neuron it has to signal through the dendrite via a neurotransmitter (a chemical)

-if you are absorbing something that is a message, the more surface area you have, the more efficient it is

-not actually absorbing but are connecting to a receptor

- plastic

-pathways change over time

-changing the amount of spines

-efficiency between connections by the number of spines attached

Myelin

speeds transmission of signals

made of Schwann cells or oligodendrocytes

polar in nuerons

how many processes coming off

multipolar nueron

multiple directions

Bipolar nuerons

two directions

mainly in the eye

Psuedo-unipolar neurons

- in the sensory system

- carry information in the peripheral system

Unipolar neuron

- carry information in the peripheral system

- only travels in one direction

- pain and touch sensor

Direction of message in nuerons

only in one direction

Can a neuron signal to more than one neuron? How?

- multiple axons

-varicosities

- axons can spilt

- terminal ends

Afferent neuron/sensory neurons

-pseudo-unipolar

- PNS --> CNS

-carries information specific to sensory receptor

Interneurons

-CNS

-multipolar

-Function as integrators and signal changers

-Integrate afferent and efferent neurons into reflex circuits

Efferent neuron/ motor neuron

- CNS --> PNS

-Transmit information out of the CNS to effector cells, particularly muscles, glands, neurons

PNS to CNS pathway

PNS --> CNS --> PNS

• looks just like a reflex arc

- different areas get turned on with one stimulus

Glial cells

-cell that is associated with neurons that helps them

Oligodendrocytes (.., make, in, wraps, matter (2) , looks, stem)

- myelin sheath; white matter

- make myelin

- only in the CNS

- cytoplasmic extension that wraps around neurons in many places

- white matter is the myelin sheath and inside

- Gray matter is the cell bodies and outside

A bunch of cell bodies together makes it look grey

-the axons that stem from the cell bodies make the white matter

Oligodendrocytes (concussions)

happens outside of the brain, damaging the cell bodies and neurons

Oligodendrocytes (brain stem)

-has cell bodies outside the spinal cord and axons that travel and send messages into the body

- white and gray matter is reversed because those are the motor neurons you are synapsing (messages from the brain outward)

microglia

-immunity, phagocytic

-considered glial cells bc they are only in the CNS and to protect the CNS

ependymal cells (lines, various, hold, responsible, act, when, lose)

- lines ventricles/channels of the brain

- homeostasis of various variables

-channels hold cerebrospinal fluid

- responsible for transferring material from the cerebrospinal fluid into the brain

- can act as stem cells for the brain

- when the brain needs neurons etc.

- when you lose brain cells they are gone (harder to make than to get rid of them)

Astrocytes

- regulation of environment

- extend to capillaries and neurons

- perivascular feet

- primary responsible for the blood brain barrier

Why do we not have the same cells in the brain as in the rest of the body? Why do the outside cells never get in and why do the inside never get out?

- Blood Brain Barrier

- protection against what floating outside

- inside of the brain is very regulated

- certain cells cannot make it across the barrier some cant

blood-brain barrier

- capillaries have no pores and astrocyte feet

- Regulate substance entry to the brain

regular capillaries

- endothelial cells

- lumen inside

- tissue outside

- tissues don't connect to each other

- they form pores to exchange material

Blood brain barrier capillary (con, seal, cant)

- endothelial cells connect to each other

- tight junctions seal the cells together so there's no leakage from the free space to the tissue

- The brain barrier can't regulate oxygen, CO2, steroids or ANY LIPID

Blood brain barrier and astrocyte feet in capillary (cause, go, regulate, stuff)

- astrocyte feet cause the development

- go all the way around the endothelial cells

- they regulate and determine what can come through the blood through the endothelial cells

- astrocytes transporting the stuff that the endothelial cell is absorbing and sending it to the cell

astrocytes - regulation of environment (7)

1. BBB creation

2. Nourishes neurons using glycogen

3. Signaling (release of neurotransmitters)

4. Re-uptake of neurotransmitters

5. Repair and regenerate neurons

6.Communicates changes in the blood

7. Regulation of potassium in extra cellular brain

Astrocytes - nourishes neurons using glycogen (require, feed, get)

-neurons require a lot of energy (glucose)

- astrocytes feed glucose to the neurons and store glycogen

- get glucose from the blood

Astrocytes - signaling (can be, can (3))

can be part of the synapse

- astrocyte can regulate..

- how responsive the post synaptic neuron is

- how active the presynaptic neuron is

- how active the post synaptic cell is by regulating how many neurotransmitters are in the synapse

tripartite synapse

- presynaptic neuron

- post synaptic neuron

- astrocyte or other glial cell

Astrocytes - re-uptake of neurotransmitters (take, only, spit, need to, is)

- the presynaptic neuron taking back some of the stuff it released through exocytosis

- PNS only wants a certain amount out

- you spit out bulk transport = not specific regulation of the neurotransmitter concentration

-excess outside= need to regulate concentration through reuptake

- re-uptake is receptor-mediated endocytosis

- receptor mediated endocytosis importance in medicine (reuptake SSRI)

(decrease, type, blocks, causes, (2))

- decrease in level of a neurotransmitter

- depression (SSRI) - competitive inhibitor/ antagonist

- blocks re-uptake = more neurotransmitters in synapse

- serotonin causes depolarization in some cases this influences your mood

- light (SAD)

- movement and exercise

What happens when you have to much serotonin

seizures

What happen if you continue to take SSRIs? (2, affects, come, expresses, low)

- up-regulation

- higher dose of SSRI

- When you use SSRI you affect serotonin overall in all pathways

- Hard to come off them

- cell expresses reuptake

- initial state was low serotonin = dramatic rise in depression

Astrocytes - Repair and regenerate neurons

- can't build new neurons but can repair

-ex: concussion

Astrocytes - communicates changes in the blood (link, two things, tells, one more)

- link between the blood stream and the brain

- oxygen and carbon dioxide

-tells your respiratory system how much you should respirate based on the concentration

-regulation of sugar

Astrocytes - regulation of potassium in extracellular brain

- membrane potential connected to ions outside the cell

- Sodium/ Potassium Pump

- astrocytes can take potassium into their cell and move it into brain

- potassium is moved inside so potassium level should be low

- when potassium is moved outside and its level increases, the membrane potential isn't right

- astrocytes make sure potassium concentration is balanced

- if they didn't = seizures and epilepsy because neurons fire when they aren't supposed to

How do neurons send messsages?

Electricity

How is this electricity generated

Ions

Main players in potentials

Na+, K+, Cl-

How electricity generates "work"

ELECTRICAL POTENTIAL through opposing electrical forces

Potential difference, potential , voltage

-degree of difference

-how much "work" you can do

Charges in the body (+-, has, is so that, carry)

positive outside, negative inside membrane due to Na+/K+ pump

-cell has negative proteins that act as a magnet on the cell mem.

membrane is non polar and a insulator so charges cant go through it where the charges can't go but can hold a different charge right next to it

-capacitance

• polar = carries charge

Resting potential of cells (what the, every, in order to do, to, maintain)

-the characterization of what the cell is doing before it acts

-every cell has a membrane potential

-(-5mv - -100mv depending on cell)

-neurons = -70mV

How does a voltmeter work?

measures the change by sticking one node in the intracellular and one in the extracellular

In order to do work what has to happen?

ions have to move

-diffusion to harvest energy

-maintain ion difference on either side and once you let them through, you get work

Ion movement across membrane is influenced by

1) Concentration gradients

-the steeper the conc. gradient the more it goes from high to low

2) Ion channels

3) Equilibrium potential

-the amount of charge it takes to oppose an ions concentration gradient

-net flow is 0

-every ion has its own equilibrium potential

-charge property influences its movement (against or with the concentration gradient)

Nernst equation (X, R, T, F , Z)

-X = The extracellular and intracellular concentration of that ion

-R = The ideal gas constant

-T = temerature

-F = Faraday's constant

-Z = the ion's valence

Ion movement across membrane pathway

1. Potassium channels open and the concentration gradient takes over = HIGH to LOW

2) doors open, K+ builds up on one side = more positive charges that are going to repel K+ from coming over. PROBLEM= Electrical force pushing

3) End up with net flow equaling zero bc the conc. gradient moves in the opposite direction

-potassium equilibrium potential bc its determined by the conc. gradient of the ion and its charged properties

Why -70mV resting membrane potential?

multiple ions= Equilibrium potential is rarely ever reached

Goldman-Hodgkin-Katz equation

61•log (Pk[K+]out + PNa[Na+]out + PCl[Cl-]in)/(Pk[K+]in + PNa[Na+]in + PCl[Cl-]out)

How do we maintain the resting potential? (nerve function)

1) Na+/K+ pump - begins the gradient

2) K+ leak channels

- if you only used the pump, you couldn't maintain a certain number

-K+ leak channels move potassium out of the cell

Nerve function

utilizes membrane potential

If you increase the permeability of the membrane for a certain ion what would the membrane potential look like?

-it becomes closer to that ions equilibrium potential

Why is potassium leaving outside and not inside

Concentration gradient

If you stopped the pump but the leak channels where still there what would happen?

The CG wouldn't equalize

If you wanted to make the difference between the membrane less (-70mV) what could you do?

-if you added more positive ions inside the membrane the difference will be smaller

-add more positive ions by opening a sodium channel

-DEPOLARIZATION

Depolarization (excitatory)

-turning it on, increase in activity

-add + inside (Na+)

- sodium is used because it is already high outside

Hyperpolarization (inhibitory)

-turn off, decrease in activity

-add + outside (K+)

-potassium is used because it is already high inside

Action potential mechanism (starts, open, getting, voltage, was enough, open, less, starts, out flow, stops, abruptly, is, begin to, one more)

1. Starts at -70mV

2. opening of Na+ channels

3. # is getting smaller (depolarization) adding positive numbers inside

4. threshold potential= voltage that opens up more sodium channels (-50mV)

5. Threshold stimuli= stimuli was enough to open the channels

6. Na+ channels open = sharp depolarization

7. Slope is less at top because you are reaching equilibrium potential

8. 30mV = K+ channels starts opening more but respond slower than Na+ gates to voltage change

9. out flow of positive ions begins repolarization

10. Depolarization stops at +30mV

11. Na+ channels stop abruptly= inactivation gates

12. Repolarization is steep

13. Na+ and K+ gates begin to close; K+ is still sluggish

12. Hyperpolarization (-80mV) (under sheet)

Refractory period (a, what, how, before, hit, after, always)

-a neuron fires repeatedly

- what action potential looks like over time

-how many positive charges happen to be at a certain time

- the ones before it dont activate the Na+ channels to open

-when you finally hit the threshold you get a full action potential

-after that no matter how big the initial charges are the action potential always looks the same

- proteins always respond the same way

action potentials "all or none"

can't use degree of action potential to determine strength of stimulus

So how does your sensory system do refractory periods?

- regulation of the number of action potentials which determines how much information you are sending and sensing

absolute refractory period (cannot, get, at a time, no matter)

-absolutely cannot get another action potential at this time

-get depolarization which must stop at a certain point

-one action potential at a time due to depolarization (Na+ channels get block by the. activation gate)

- no matter how much you stimulate the channels, nothing will happen

relative refractory period (dependent, How, how, closer)

-whether or not you get another action potential is dependent upon

-how much you are stimulating

- how close or far you are to the end of the absolute refractory period

- The closer you are to absolute the more stimulus you need and vice versa

One-way Action Potential

-once you fire an action potential in one part of the neuron that part of the mem. shuts off

-only ones you can do is further away or in front

Absolute refractory period defines maximum

-fire as much as the activation gates allow you

-need to pause in between (determined by inactivation gates)

Relative refractory period is determined by (how, if you, the further, fully out, antime, dont)

how long you have be in relative

-if you wanted to fire immediately again, you need a really big stimulus

-The further you go in relative, the less stimulus you need for the membrane to respond

-fully out of undershoot, you only need threshold stimulus

-anytime you fire during the relative refractory period, the action potentials are also of a lesser magnitude

-Na+ channels don't respond as well so depolarization isn't as strong

Na channels are opened by different causes

Graded potentials

Action potentials

Action potential propagation steps

• 1) Starts at resting

• 2) Positive charges go inside and activate/open up Na+ channels

• 3) Na+ channels open and go down conc. Gradient= depolarization

• 4) K+ channels open = repolarization and Na ions are still inside (concentration gradient of sodium= very little inside)

-ions will diffuse back and forth bc channels are closes

• 5) As they diffuse we get a slight depolarization

• 6) If enough diffuse you activate another Na+ channel and process starts again =PROPAGATION

• 7) Diffusion in seconds channel goes both ways

• Whole body responds to a change in the environment

• How well these channels are doing this is determined by what the whole environment looks like

• when there is a pathology that changes the charges your propagation of your signal isn't going to function

• If I start the action potential in the middle it shoots in both directions because you haven't activated the absolute refractory period of any channels

Myelin purpose (better, makes, allows)

-makes propagation better by wrapping the axon and speeds up action potential

-makes it faster by creating a bigger distance for Na+ to diffuse

-ALLOWS NEURONS TO BE FAST AND GET AROUND TISSUE

Diameters and the speed of propagation (myelin)

-bigger axon = travels faster bc they have less resistance (inhibition of the current)

the membrane is an insulator (myelin)

-take the membrane and squeeze it closer, it is harder to move, vice versa

Oligodendrocytes vs. Schwann cells (where are they, combination, use same, affects (2)

-Oligodendrocytes = CNS

-Schwann cells = PNS

-myelin is a combination of proteins and lipids (Protein= 3% Lipid =70%)

-Schwann cells use the same lipids but different proteins than oligodendrocytes

-lipid disorder affects CNS and PNS

-protein disorder affects just CNS or PNS

effective distance (myelin) (stops, how far, occur)

- Insulate to stop leakage of ions; causes longer effective distance of ions to activate next Na+ channels

-Effective distance: how far it can go but still activate a Na+ channel

-Na+ channels occur as Node's of Ranvier

Action potentials appear to

"Jump" from Node to Node

• If you put a voltage meter at every point along the axon only the ones at the nodes would show the action potentials

• Only can get action potentials at Na+ channels

• Myelin is decrease how much leakage is happening

• BENEFITS

-Nervous system can use small neurons that propagate as fast as large diameter one

-Fewer ions to deal with- more efficiently approach resting and thresholds

•

Graded potentials steps

• 1) Stimulus opens channel

-can be mechanic (ligand) or chemo

• 2) Na+ channel opens, Na+ comes in and causes depolarization

• 3) Doesn't have to be depolarization/ Na+ channels

-can be caused by hyperpolarization

-let out K+ ions

-bring in Cl- ions

• 4) UNIQUE to graded potentials: how ever long the channels are open determines how much depolarization you will get

-1. Degree

-2. Direction

-3. Leaky membrane

• 5) ISSUE: the membranes of the dendrites are very leaky

-causes diffusion of ions out

-depolarization can't travel far

-every membrane is different and

has different amounts of leak

• 6) Leakyness will affect the distance

- you goal is to bring this to threshold

• 7) All dendrites differ in their sensitivity

to create an action potential

- nervous system regulates how much it can be stimulated by

-the only way to get the ions to

the axon is to repeatedly stimulate the dendrite and make the depolarization big enough so it can make it to the voltage gate

Types of stimulus

-synaptic vs. receptor vs. pacemaker

-process is similar no matter where

-sodium comes in different ways

synaptic stimuli

activated by neurotransmitter

receptor stimuli

anything in your sensory system where the environment is causing activation/depolarization

-photoreceptors in eye

-touching the desk

pacemaker stimuli

potentials that cause themselves to happen (spontaneous)

-depolarize spontaneously

length constant

Effective distance for dendrites

• Measured when the charge dissipates

• Rm= resistance of the membrane

-greater= length constant is bigger

• Ri= resistance of axon (axial resistance)

-greater= length constant is smaller

• Ro= resistance outside membrane

-constant unless there's a pathology

• Length constant for neurons is the length it takes voltage to be 37% of it's original value.

- depolarization and leakage occurs

- affected by resistances

-changes from dendrite to dendrite

and from neuron to neuron

• The time constant for neurons is the time it takes for this to happen

Why does the length constant matter?

- goal is bring axon hillock to threshold

-these characteristics illustrate the ability to do that

-ability of a neuron to continually send communication based on the stimulus its receiving

-if it can't= it ends and dies and you don't receive the information or stimulate the effector

Graded potential characteristics

• Variable types

• Variable sizes

• Short distances

-greater potential = shorter distance

• Can be only means of communication

for some neurons

Summation

need multiple to reach threshold

• regulates whether or not a neuron fires has to do with how often you are stimulating a receptor and how many different ones you are able to stimulate

• Through spatial and temporal the axon hillock will reach threshold and action potential oc

Temporal summation

-stimulated closer in time

-depolarization is greater

spatial summation

-multiple simultaneous inputs

-depolarization is greater

Neuropathy

signal isn't conducting

-idiopathic - can't find the cause

-inability to myelin = leaky= brain doesn't receive information

neuropathy symptoms

initial symp: tinging/ "Pins and Needles"

-vitamin deficiency (can't absorbs in the gut)

B1

Thiamine

B2

Riboflavin

B3

Niacin (ATP synthesis)

B6

Pyridoxine

B7

Biotin (atP synthesis)

B12

Cobalamin (makes myelin)

Folic acid

Developing and maintaining nervous system

multiple sclerosis

Loses myelin

-Symptoms. depends on where the myelin is disappearing

-Usually motor

-mainly CNS myelin

-autoimmune disease (attack protein in the CNS)