Bio Exam 2 Terms

resting membrane potential (RMP)

the electrical charge difference across the cell membrane when the neuron is not sending a signal

• outside = positive

• inside = negative (-70 mV)

Na⁺/ K⁺ pump potential effect

20%

K⁺ leak channels potential effect

80%

Na⁺/ K⁺ pumps

maintenance workers → more positive ions enter than leave; the inside becomes slightly more positive

• pumps 3 Na+ out

• pumps 2 K+ in

K+ leak channel

channels that are always open/leaking → always wants to leave the cell

• K+ concentration high inside - (150 mM)

• K+ concentration low outside - (5 mMs)

graded potential

small changes in membrane potential → small push towards an action potential

• depolarization → less negative

• hyperpolarization → more negative

fatures: variable size, can add together, travel short distances (weaker with distance)

threshold

the membrane potential that must be reached before an action potential begins → (-55 mV)

• graded potential depolarizes enough to reach threshold (POINT OF NO RETURN)

• 1. voltage gated Na+ channels open (axon hillock - initial segment)

• 2. action potential starts

action potential

a rapid electrical signal that travels down the axon

• characteristics:

• 1. all-or-none

• 2. same size everytime

• 3. does not fade away

• 4. long distance communication

graded potential → knock on action potential → door bursts open

depolarization (phase 1)

voltage-gated Na+ channels open → Na+ rushes INTO the neuron due to high concentration outside + negative inside attracts positive Na+

⭐ Na⁺ enters

peak (phase 2)

maximum positive voltage reached

• Na+ channels begin closing/inactivating

• K+ channels begin to open

repolarization (phase 3)

voltage gated K+ channels open → K+ leaves the cell

• positive charges leaves = making the inside negative again

⭐ K⁺ exits

hyperpolarization (phase 4)

K+ channels remain open for a bit longer (continues to leak out = extra K+ enters)

• membrane becomes more negative than resting potential

• → but will eventually return to resting potential

refractory periods

these prevent action potentials from going backwards

absolute refractory period

• 1. Na+ channels are inactivated

• 2. no matter how strong the stimulus → another AP cannot occur

• (Na+ channels must rest first)

IMPOSSIBLE

relative refractory period

1. some Na+ channels have reset, but K+ channels are still open

2. cell is hyperpolarized

3. another AP is possible (requires a stronger-than-normal stimulus)

POSSIBLE BUT HARDER

propagation of action potentials

how the signal moves down to axon

• the depolarized region causes nearby voltage-gated Na+ channels to open

• → signal regenerates itself continuously

contiguous conduction

occurs in unmyelinated axons

• action potentials must activate every section of membrane (one section at a time - 0 0 0 0)

• → results: slower + more energy required

saltatory conduction

occurs in unmyelinated axons → (node → node)

1. myelin acts like insulation

2. action potentials only occur at Nodes of Ranvier, where voltage-gated channels are concentrated.

3. → results: faster + less energy used + more efficient

SKIP AND JUMP CONDUCTION

multiple sclerosis (MS)

an autoimmune disease that destroys myelin

• without myelin = conduction slows + signals may fail to reach destination

• symptoms:

• vision problems, numbness, muscle weakness, poor coordination, paralysis in severe cases

• MS = MYELIN STRIPPED AWAY

neurotransmitter release

when the action potential reaches the axon terminal

• step 1: action potential arrives

• step 2: voltage-gated Ca2+ channels open

• step 3: Ca2+ enters the terminal

• step 4: Ca2+ causes synaptic vesicles to fuse with the membrane

• step 5: neurotransmitter is released into the synaptic celft

AP → Ca2+ in → neurotransmitter out

SNARE proteins

these proteins help vesicles move and fuse with the membrane (hooks for neurotransmitter vesicles)

• without SNARE proteins:

• vesicles CAN’T fuse + neurotransmitters cannot be released

• toxins affecting SNAREs (interfere with neurotransmitter release):

• botulinum toxin, tetanus toxin, some venoms

EPSP (excitatory postsynaptic potential)

a graded depolarization that makes the neuron more likely to fire an action potential

• positive ions enter: Na+, Ca2+, sometimes Mg2+

• result → cell becomes less negative

(excites the neuron → moves toward threshold)

IPSP (inhibitory postsynaptic potential)

a graded hyperpolarization that makes the neuron less likely to fire an action potential

• Cl- enters OR K+ leaves

• result → cell becomes more positive

(inhibits the neuron → moves away from threshold)

the Nernst equation

tells you the electrical voltage needed to perfectly balance the concentration gradients of one ion

(if one side has a higher concentration, it would want to go to the other side → charge resistance)

• Ion + nernest potential:

• 1. K+ ~ -90 mV

• 2. Na+ ~ +60 mV

• 3. Cl- ~ -70 mV

cerebral hemispheres

responsible for thinking, learning, memory, language, and conscious decisions (“thinking brain”)

• Everything that makes you, YOU

cerebellum

coordinate movements without thinking about them (“autopilot”)

• help with balance, coordination (motor signals, visual stimuli, and equilibrium), smooth voluntary movement, posture (ex: walking and texting)

medulla oblongata

controls vital functions (“life support center”)

• heart rate, blood pressure, breathing

• coughing, sneezing, swallowing, vomiting

stops working = survival threatened

brain stem

connects the brain to the spinal cord (“connection highway”) + carries signals between the brain and body

reflex center:

• visual reflexes

• startle reflexes

spinal cord

links transmission of information to and from the brain and integrates many reflexes ('“telephone line”)

functions:

• send signals between the brain and body

• control reflexes

• contains autonomic nervous system pathways

glial cells

keep everything running as neurons do the talking (“support cell”)

• 90% of cells in the CNS are neuroglia → 10% actual neurons

Astrocytes

the nurses and janitors of the CNS (“caretakers”)

functions:

• hold neurons in place

• help form blood-brain barrier

• clean up neurotransmitters

• form scar tissue after injury

Oligodendrocytes

wrap neurons like electrical tape (“insulators”)

function

• form myelin around CNS axons → myelin allows signals to travel faster

microglia

the brain’s security guards (“immune cells”)

function:

• defend the nervous system

• remove debris and damaged tissue

ependymal cells

help make the brain’s cushion fluid (“CSF makers”)

function:

• line cavities in the brain

• help produce cerebrospinal fluid (CSF)

concussion

temporary brain injury → usually not permanent neurological damage (shaken brain)

symptoms:

• confusion

• dizziness

• headaches

stroke (CVA)

a blood vessel becomes blocked → no blood = no O2 = dead neurons

result:

• brain tissue loses oxygen

• brain cells die

common outcome:

• paralysis

• sensory deficits

alzheimer’s disease

progressive degeneration of the brain → brain slowly loses memory

symptoms:

• memory loss

• personality changes

• dementia

• cognitive decline

Association:

• acetylcholine (ACh) deficiency

• plaque accumulation

parkinson’s disease

casued by loss of dopomine-producing neurons

symptoms:

• tremors

• rigid movements

• reduced facial expressions

w/o dopmine:

• movement control worsens

edema

swelling caused by fluid accumulation in brain tissue → compressed brain

danger:

• increased pressure inside the skull

chronic traumatic encephalopathy (CTE)

occurs after repeated head trauma → can cause long term neurological damage

symptoms:

• memory loss

• depression

• aggression

• dementia

• brain atrophy

(common in boxers + football players)

cholinergic system

uses Acetylcholine (ACh) → neurotransmitter

nicotinic receptors (preganglionic)

found on ALL autonomic postganglionic neurons (1st synapse)

→ both sympathetic and parasympathetic preganglionic neurons release ACh onto nicotinic receptors

muscarinic receptors

found on parasympathetic target organs (ex: heart, smooth muscle, glands)

parasympathetic postganglionic neurons release ACh onto (MR)

parasympathetic end organ = M

adrenergic system

uses norepinephrine (NE) + epinephrine (Epi) → usually associated with sympathetic responses

alpha receptors (α)

usually excitatory + cause contraction (ex: blood vessel constriction)

excitatory = Epi + Ne

A = squeeze

beta- 1 receptors (β₁)

mainly found in the heart → “Be my #1 Lover”

excitatory = Epi + Ne

effects:

• increased heart rate

• increased force of concentration

B1 = 1 heart

beta-2 receptors (β₂)

usually inhibitory to smooth muscle → causes relaxation = MORE Epi

ex:

• blood vessels (relaxation → vasodilation = more blood flow)

• airways (relaxation → bronchodilation = more airflow)

→ opens tubes

dual control

most organs receive BOTH sympathetic and parasympathetic input → usually with opposite effects

ex: heart

• sympathetic → speeds heart rate (fight or flight) = gas pedal

• parasympathetic → slows heart rate = break pedal

sweat glands

only sympathetic → only uses ACh

blood vessels

most blood vessels only receive sympathetic innervation

salivary glands

recieve both sympathetic and parasympathetic input

→ both increase saliva, but they produce different types of saliva

adrenal medualla

instead of sending nerve signals, it releases hormones that reinforce sympathetic effects

→ it is a modified part of the sympathetic nervous system and releases:

• 80% epinephrine

• 20% norepinephrine

into the blood stream

CNS (central nervous system)

consists of the brain and the spinal cord

responsibilities:

• processing information,

• making decisions

• learning and memory

• creating responses

brain region = cerebral hemisphere (largest part of the brain)

function:

• conscious thought

• learning

• memory

• language

• voluntary movement

neurons included:

• astrocytes, oligodendrocytes, microglia, ependymal cells

PNS (peripheral nervous system)

consists of cranial nerves, spinal nerves, ganglia → everything outside of the brain + spinal cord

→ job is to carry information between the body and the CNS

components:

• sensory neurons (afferent) + motor neurons (efferent)

• motor = somatic NS + autonomic NS

sensory neuron (afferent)

carries INFO from body → CNS

ex:

• touch

• pain

• temperature

• vision

• hearing

afferent = arrives at CNS

motor neuron (efferent)

carries COMMANDS CNS → body

ex:

• move muscle

• stimulate galnds

efferent = exit CNS

somatic nervous system (motor)

controls the skeletal muscle → conscious control

voluntary actions:

• walking

• writing

• talking

autonomic nervous system

controls the cardiac/spinal muscle + glands → automatic control

involuntary actions:

• heart rate

• digestion

• blood pressure

• sweating

neurotransmitters:

• acetylcholine(ACh)

• Norepinephrine (NE)

sympathetic nervous system (autonomic)

fight or flight response → gas pedal

activated:

• stress

• fear

• exercise

effects:

• increase heart rate

• pupil dilation

• decreased digestion

• increase blood flow to muscles

parasympathetic nervous system (autonomic)

rest and digest → break pedal

activated:

• relaxation

effects:

• decrease heart rate

• increase digestion

• increase saliva

• promotes waste elimination

has nicotinic/muscarinic receptors

acetylcholine → degraded by the enzyme cholinesterase

major excitatory NT that helps learn

glutamate, most common excitatory NT

affects mood, food intake, reproductive behaviors

serotonin → tryptophan derived

excess of this NT leads to schizophrenia

dopamine → deficiency leads to parkinson’s

an anti-seizure NT

GABA → xanax and valium also bind to receptors, reduce anxiety, and induce sleep

hyperpolarizes membrane in muscle (espically)

glycine → major inhibitory NT in spinal cord/brain stem

has alpha and beta receptors

epinephrine/norepinephrine → includes a1, a2, b1, b2, and b3

muscle fiber

one muscle

• very large cell

• has many nuclei

• filled with myofibrils

myofibril

long tubes inside the muscle fiber → made of repeating units called saromeres

sacromere

the functional unit of contraction

→ sarcomere = smallest part that actually shortens (physically)

thick filament

also known as myosin → which is the motor protein that pulls on the actin

contains:

• head

• tail

• ATPase site

• actin-binding site

(the mover)

thin filament

contains 3 proteins:

• actin

• tropomyosin

• troponin

actin

the “rope” that myosin grabs

tropomyosin

blocks the binding sites on actin → acts as a cover

troponin

binds the Ca2+ → calcium sensor

binded:

• tropomyosin moves away

• myosin can attach

A band

• dark band

• contains thick filament

A = All myosin

I band

• light band

• contains thin filaments

I = Thin

Z line

end of a sarcomere (sarcomere to sarcomere)

M line

middle of sarcomere

H zones

center region containing only myosin → gets smaller during contraction

sliding filament theory

muscle shortens due to:

• thin filaments sliding

• thick filaments pulling

→ NONE of the filaments themselves get shortened

during contraction:

• Z lines move closer together

• I band decreases

• H zone decreases

• A band stays the same

neuromuscular junction (NMJ)

this is where a motor neuron meets a muscle fiber

1. action potential travels down to α-motor neuron

2. voltage-gated Ca2+ channels open

3. Ca2+ enter nerve terminal

4. ACh released

5. ACh binds ACh receptors on muscle

6. Na+ enters muscle

7. muscle action potential begins

(skeletal muscle = 1 motor neuron)

(smooth/cardica muscle = 2 motor neuron)

excitation-contraction coupling

this explains how an electrical signal becomes a contraction

sequence:

1. motor neuron AP

2. ACh released

3. muscle AP produced

4. AP spreads across sarcolemma

5. AP enters T-tubles

6. Ca2+ released from SR

7. cross-bridge cycling

8. contraction

T-tubules

carry action potential deep into the muscle → electrical tunnels

sarcoplasmic reticulum (SR)

stores calcium

DHP + Ryanodine receptors

DHP = voltage-sensitive cork

sequence:

• action potential enters T-tubles

• DHP receptors senses voltage

• ryanodine receptors opens

• Ca2+ released from SR

(electricity in → calcium out)

SERCA pumps

after contraction → Ca2+ must be removed

SERCA pumps:

• uses ATP

• pump Ca2+ back into sarcoplasmic reticulum (SR)

results:

• troponin loses Ca2+

• tropomyosin covers actin again

• muscle relaxes

cross-brige cycle

Needs: ATP + Ca2+ (without either = contraction stops)

sequence:

1. Ca2+ exposes binding site

2. myosin binds actin

3. power stroke occurs

4. ATP binds myosin

5. ATP splits → re-cock myosin head

(repeats as long as ATP + Ca2+ are present)

motor unit

1 motor neuron + all muscle fibers it controls

→ more force = turn on MORE motor units

• ex: lift pencil → few motor units

• lift heavy backpack → many motor units

load-recruitment relationship

more motor unit recruitment

(heavier weight = more nerves activated)

length-tension relationship

maximum force occurs when actin and myosin overlap optimally

• too short → filaments overlap too much

• top stretched → filaments barely touch

both reduce force

(best force occurs in the middle range)

force-velocity relationship

• no load = fastest contraction

• heavy load = slower contraction

• maximum load = no movement

• greater than maximal load = muscle lengthens while active

(eccentrics contractions)

isometric

1. force generated

2. NO length change

• ex: holding a dumbbell still

• MIDDLE GROUND → NEUTRAL

concentric

1. muscle shorten

• ex: lifting a bicep curl

• lifting UP

eccentric

1. muscle lengthens while producing force

2. most damaging type of contraction

• ex: lowering a dumbbell + walking down stairs

• lifting DOWN

muscle fiber types

type I, type 2a, type 2x, type 2b

type I

red fibers → slow oxdiative

characteristics:

• lots of mitochondria

• lots of myoglobin

• uses oxygen

• fatigue resistant

ex: marathon runners + posture muscles

type 2a

red fibers → fast oxidative

characteristics:

• faster than type I

• fairly resistant to fatigue

ex: balance of speed + endurance

type 2x

white fibers → fast glycolytic

characteristics:

• very powerful

• uses glycogen

• fatigues quickly

ex: sprinting + jumping

type 2b

white fiber → glycolytic

characteristic:

• fastest

• rapid fatigue

ex: ONLY FOUND IN ANIMALS