Bio 207 Exam 2

dendrites

receives signals and sends them to the axon hillock

axon hillock

the action potential begins here (if there is one)

myelin sheath

increases conduction speeds of electrical impulses & prevents ion loss

nodes of ranvier

gaps in the myelin sheath that allows for jumping of the action potential (saltatory conduction)

axon terminals (electrical vs chemical)

the end of the neuron that sends electrical or chemical signals at the synapse

electrical: directly between cells, ex: retina

chemical: communicates using chemical messengers, most common

Sensory Neurons AFFERENT

transmits action potentials in

TO spinal cord or brain

PERIPHERAL NERVOUS SYSTEM

-taste, smell, balance, etc.

Motor Neurons EFFERENT

transmits action potentials out

FROM spinal cord or brain

TO muscles, glands, visceral organs (heart, liver, intestines, etc.)

PERIPHERAL NERVOUS SYSTEM

-only the cell body is in the spinal cord

-motor nerves drive to different locations

SOMATIC & AUTONOMIC motor neurons

Interneuron

short cable that connects 2 different points

CENTRAL NERVOUS SYSTEM (spinal cord or brain)

Somatic Motor Neuron

can be controlled, VOLUNTARY

-drives skeletal muscles

Autonomic Motor Neuron

is on autopilot, INVOLUNTARY

-reflex

-drives smooth muscle, digestion, glands, cardiac muscle

2 neurons

Schwann Cells

cells responsible for producing myeline sheaths in the PERIPHERAL NERVOUS SYSTEM

Oligodendrocytes

cells responsible for producing myeline sheaths around neurons in the CENTRAL NERVOUS SYSTEM

Microglia

immune defense cells of CNS, may contribute to dementias

Central Nervous System

• oligodendrocytes

• microglia

• astrocytes

Peripheral Nervous System

• schwann cells

• autonomic and somatic

Astrocytes

holds neurons in place

Ependymal Cells

line cavity, contributes to cerebral spinal fluid

Protection of Central Nervous System Tissue

Bony Structures, Meninges, Cerebrospinal Fluid, Blood-brain barrier

Bony Structures (CNS tissue Protection)

• the cranium protects and encases the brain

• vertebral column surrounds spinal cord

Meninges (CNS tissue protection)

• membranes between bones and CNS tissue

• mater tissues (3 layers of tissue)

Cerebrospinal Fluid (CNS tissue protection)

• cushion against impact

Blood-brain Barrier (CNS tissue protection)

• highly selective

• limits access of blood-borne materials into brain tissues

• separates blood from brain tissue

Diencephalon (in the brain)

• Glands

• Thalamus

• Hypothalamus 

Forebrain (in the brain)

• cerebral hemispheres

• right and left lobes

Brain Stem Components

Midbrain, PONS, Medulla Oblongata

Midbrain

• higher level reflexes

• startle reflexes

• visual reflexes

PONS

• bridge between midbrain and medulla oblongata

• conduction tissue

Medulla Oblongata (brain stem)

• blends into spinal cord

• homeostatic mechanisms

• respiratory and cardiovascular systems

• vomiting, swallowing, coughing, sneezing

Cerebellum

• located at the back of the brain, near brainstem

• autopilot, subconscious

• coordinates

  • motor signals

  • visual stimulu

  • equilibrium

• produces smooth voluntary movements?

Resting Membrane Potential

1: Sodium Potassium ATPase ^{3:2 OUT:IN}

^{*on all the time}

^{*creates a gradient of high sodium (and Cl) outside and high potassium inside}

^{*20% of the effect of creating RPM}

2: Sodium Leak Channel

^{*RMP is far from what sodium wanted (+30)}

3: Potassium Leak Channel

^{*there’s more potassium leak channels than sodium leak channels}

^{*80% of the effect of creating RPM}

^{*potassium gets its way because theres WAY more}

^{*RPM is close to what potassium wanted (-90)}

Phases of an Action Potential

1: Depolarization

2: Peak

3: Repolarization

4: Hyperpolarization

Depolarization

membrane potential is NOT ZERO

• membrane potential is becoming more positive

• membrane potential is LESS POLARIZED than the rest

• polarized = -70mv

• membrane potential becomes +30mv

• VG Na+ is open

• VG K+ not open yet

*if you go towards ZERO, this is depolarization

Peak

Repolarization

membrane potential returns to RESTING potential

• VG K+ channels open

• K+ diffuses out of the axon

• membrane potential goes beyond resting state NEGATIVE

• goes beyond -70mv (example: -74mv)

Hyperpolarization

membrane is MORE POLARIZED than the rest

• VG K+ channels remain open

• by the end of this phase ions leave through leak channels only

• membrane potential returns to resting state of -70mV

*below threshold

Graded Potentials

variety gives you GRADATION hence the name GRADED POTENTIALS

• short distance signals

• can exist without action potentials

• localized in a part of the nerve (like little sparks in a specific area)

• its like a chatter that may or may not speak to an AP

• come in different sizes

• can go up or down (depolarization or hyperpolarization)

• happens between synapses

  • nerves to nerves

  • nerves to muscle

• short distance but can add up with SUMMATION

• strong where it happens and decays in strength as you go away

• no refractory period (they can pile up)

• occurs with touch, hearing, smell, or any other STIMULI

• happens at CELL BODY

  • the RECEIVING part of the cell

Action Potentials

• gets the signal, takes it, and runs

• makes it all the way to the end of an axon

• doesn’t matter if its very far

• the cell is trying to talk to something EXTERNALLY

• taking a message somewhere

• ALL or NOTHING

• starts life at threshold (which is the trigger)

• you go from resting to trigger by GRADED POTENTIALS

• very fast

• stereotype size / identical

• can stack up behind each other if you need them to

• will not die out from when you start

• same strength all the way

• VG channels must be present (they open and close)

• self-regeneratory - one turns on the next like a domino

• yes refractory period (absolute and relative)

• only one the entire time

• always depolarization to peak to repolarization

• happens at the AXON hillock

Refractoriness

• prevents AP from going back to where it came from

• keeps a little bit of air space between AP so ots quantifiable

  • you can count it

  • may give extra info from an AP

Absolute Refractory Period

• you can’t get an AP because you’re in the middle of one

• due to inactivated Na+ channels

  • open

  • closed

  • closed and locked

Relative Refractory Period

• after AP theres a dip

• K+ channels take longer than usual to close and clean up

• theres a possibility to have another AP

  • BUT you have to jump a bigger jump due to continued outward diffusion of K+

Synapses

Electrical: membranes are very close together

• special channels allow current to flow

Chemical: narrow space, synaptic cleft

• prevents flow of electricity

• must be bridged by transmitters

theres up to 100,000 synapses for CNS

Presynaptic Cell and Postsynaptic Cells

pre: releases NT

post: receives NT

Synaptic Vesicles

membrane-bound spheres with neurotransmitters

Motor Proteins (Axonal Transport)

Kinesin: anterograde

Dynein: retrograde

• they are responsible for physically walking vesicles full of material to one end and back for recycling

• they move down microtubules

ACh Receptor

• predominantly Na+ Channel

• when you open it it allows Na+ to come in

• requires ACh to bind to it to open

• Acetylcholinesterase gets rid of it and it closes pretty quickly

• ACh keeps it open

• Acetylcholinesterase closes it

SNARE Proteins

• physically takes vesicles and moves them to the membrane (docking)

• it fuses them

• releases NT into the synapse by exocytosis

• snare proteins are well known because they are easily poisoned

  • toxins target snare proteins

Famous Synaptic Toxins

Tetanus: in the soil and can get into your bloodstream through a cut

• Its target is to destroy snare proteins▶no vesicles▶no NT

• Symptom is muscle locking up and becoming contracted

  • The toxin targets the inhibitory nerve (which relaxes muscle)

Botulism: another bacterial toxin that targets snare proteins

• Blocks NT of activating nerves

• Now you cant turn on the muscle

• Muscle is tense and contracted

• Think of BOTOX, no movement of face

Spider Venom: interferes with SNARE proteins

• Its possible to have too much NT 

• Explosive paralysis because you overwhelm the synapse

Epinephrine and Norepinephrine (MONOAMINE)

alpha adrenergic: a1, a2

beta-adrenergic: b1, b2, b3

Dopamine (MONOAMINE)

Schizophrenia: excess of dopamine, can be treated with blockers

Parkinsons: deficiency of dopamine, can be treated with L-dopa

Serotonin (MONOAMINE)

affects mood, food intake, reproductive behavior

• tryptophan derived

• serotonin uptake blockers treats depression, lowers appetite

Glutamate (Amino Acid NT)

• most common excitatory amino acid in CNS

• cooperate in long-term potentiation (LEARNING!)

• brain

GABA

• major inhibitory NT in brain

• receptors cause influx of Cl, hyperpolarizes cell

  • Xanax & Valium also bind to receptors

• Reduces anxiety

• Anti-seizure

• induces sleep

Endogenous Opioids (Neuropeptides and Gases)

• “good feeling”

• morphine and codeine

• receptors bind to opiates

• b-Endorphin

• possibility to stop breathing

• enkephalins

Nitric Oxide (Neuropeptides and Gases)

• learning and development

• arousal (viagra)

• dilation of blood vessels

Glycine

• major inhibitory NT in spinal cord and brainstem

• allows Cl in

  • stabilizes / hyperpolarizes membrane

• especially MUSCLE

Sarcomere

• Smallest structural unit of muscle contraction

• Most basic unit that makes up a muscle

• Items between Z discs

• Myosin makes up thick filament of the sarcomere

• Within each muscle fiber

• Densely packed subunits

• Extend in parallel rows from one end of the cell to the other

  • Leaving no room between for other organelles

M line

• The center of the sarcomere

• Attached site for thick filaments

Z disk

• Anchoring point of thick filaments

• Anchor the thin filaments into the cytoskeleton of the cell

• Marks the edge of the sarcomere

• The dark lines that can be seen in the middle of the I bands

• Anchors the thin filaments into the cell

• Provides the boundary of the sarcomere units

H zone

• Zone of thick filaments where sarcomere shortens

A band

• Area where thick and thin filaments overlap

• Actin and myosin make it up

• DARK bands

i band

• Zone of thin filaments

• LIGHT bands in skeletal muscle

• Actin makes it up

Titin

• Protein that stabilizes thick filament to prevent overstretching and elasticity

Actin

THIN filaments

Myosin

THICK filaments

Muscle Types

Cardiac, Skeletal, Smooth

Cardiac Muscle

• Involuntary control

• Only muscle found in the heart

• Used for heart coordinated contractions

Skeletal Muscle

• Voluntary control

• Attached to muscles

• Used for contraction, protection, support, homeostasis

Smooth Muscle

• Involuntary control

• Contracts slowly and automatically

• Found in hollow organs like the intestines and stomach

Myoglobin

makes meat RED

RED vs WHITE

red = slow

white = fast

Muscle Fiber Types

• Type I

• Type II a

• Type II x

• Type II b

Type I Muscle Fiber

• SLOW

• oxidative (must have oxygen)

• RED

• little fatigue

• long distance running

• maintaining posture / standing

Type II a Muscle Fiber

• FAST

• oxidative (no oxygen)

• PINK

• a little of myoglobin

• medium fatigue

• middle distance running

• moderate intense

• running

Type II x Muscle Fiber

• FASTER

• glycolytic (no oxygen)

• WHITE

• more fatigue

• sprinting

Type II b Muscle Fiber

• FASTEST

• glycolytic (no oxygen)

• WHITE

• rapid fatigue

• not in people

Muscle Fatigue factors

Conduction Failure:

Results from excess K+ in t-tubules ▶ which will inactivate Na+ Channels because the charges are off

Lactic Acid Buildup:

Affects Ca2+ pumps and myosin

Inhibition of Cross Bridge Cycling

Because of lack of ATP

Central Command Fatigue

the brain can’t send signals properly in the CNS

What do Muscle Cells require energy for?

1: Crossbridge cycle contracting filament

2: SERCA Protein (pumping Calcium back into the SR)

3: Fiber Membrane Potential (Na+ / K+ ATPase)

Energy Sources for Muscle Contraction

1: Glycogen (60 seconds)

2: ATP (1-2 seconds)

3: Phosphocreatine (5-8 seconds)

4: Oxidative Metabolism (95% of energy)

Hypertrophy

existing muscle cells increasing in diameter (size) as a result of exercise

• In adults that are fully grown

Hyperplasia

new muscle cells produced (via cell division) as a developing child

Atrophy

muscle disappears or degenerates because of disuse

Sensory Receptors in muscle

Muscle Spindle Organ: length detector

Golgi Tendon Organ: tension detector

Muscle Spindle Organ

Length Detector

• Composed of intrafusal fibers

• Negative Feedback prevents overstretching

Golgi Tendon Organ

Tension Detector

• Kill switch based on too much pressure in tendons

• Located at tendons

• Negative Feedback prevents over-contraction

  • which is too much force that the muscle isn’t capable of producing

Twitch

Twitch - single short contraction due to a single pulse of stimulation 

• At or above threshold

the amount of force generated by a muscle receiving a single electrical stimulation

Tetanus

Tetanus - smooth, sustained, muscle contraction

• At threshold

• frequency increases ▶summation occurs until tetanus is reached

• Summation: A second twitch that builds from the first due to a second pulse of stimulation right after

smooth muscle contraction which occurs when sequential summation leads to sustained muscle contraction

Summation

a second twitch that builds from the first due to a second pulse of stimulation right after

Concussion

no permanent neurological damage

Contusion

tissue destruction

Hemmorrhage

bleeding into spaces which increases pressure, may not show symptoms at first

Cerebral Edema

swelling due to fluid formation, administer anti-inflammatory

CTE

• deformed and brittle brain

• brain functions begin to decline

• mood swings

• dementia

• severe depression

• aggression

• suicidal thoughts

What are CVAs caused by?

• blood clots / blocked artery

• death in initial attack

Stroke

• Cerebral Vascular Accident (CVA)

• blood to the brain is blocked

  • Causes tissue to die from lack of oxygen

Ischemia

• Cerebral Vascular Accident (CVA)

• deprivation of blood or nutrients from any tissue

  • blood thinners may remedy it

Alzheimers Progressive Nervous System Disorder

brain cells waste away and die leading to loss of important brain functions

Causes:

• result of AcetylCholine DEFICIT

• leads to plaque BUILDUP with brain neurons

Symptoms:

• memory loss

• confusion

Parkinsons Progressive Nervous System Disorder

disrupts movement

Cause:

• DOPAMINE deficiency leading to lack of motor function

Symptoms:

• persistent tremors

• lack of facial expression

Spinal Cord

• extends through vertebral canal

• link for transmission of info to & from brain

• connected to spinal nerves

  • nerves carrying sensory info to brain

  • nerves carrying motor info to muscles

  • nerves carrying autonomic nerve impulses

• responsible for integration of many basic reflexes

  • basic unlearned

  • acquired or conditioned (music, sports)