Skeletal Muscle Contraction Essay

I. Types of Muscles
a. Skeletal
i. Striated ii. Uses intracellular calcium to contact iii. Big cylindrical cells iv. Multi-nucleated
v. Voluntary vi. Location: attached to the bone vii. Used for locomotion
b. Cardiac
i. Involuntary ii. Uni-nucleated iii. Striated iv. Location: walls of heart
v. Used to propel blood vi. Uses extracellular calcium
c. Smooth
i. Involuntary ii. Location: Walls of hallow organs iii. Non-striated iv. Uses extracellular calcium
v. Spindle shaped cells vi. Uni-nucleated vii. Used to propel things through internal passageways

II. Types of Muscles
a. Locomotion- Moving your body in space
i. Skeletal muscle
b. Move substances within body; food and water
i. Smooth Muscle
c. Stability- hold
bones in position around joint
i. Skeletal Muscle d Regulate Organ Volume- food storage, blood vessels
i. Smooth Muscle
e. Heat Production- 85% of body heat is bi-product of muscle contraction; shivering
i. Skeletal muscle f Maintain Posture- hold body up-right
i. Skeletal Muscle

III. Characteristics of Muscles
a. Excitability
i. Can receive and respond to stimuli ii. Chemical stimulus: food iii. Electrical stimulus: nerve
b. Contractibility

i. Muscle can shorten and thicken
c. Extensibility
i. Muscle can lengthen and stretch ii. Smooth has the most
d. Elasticity
i. Can recoil to original shape

IV. Skeletal Muscle Structure
A. Background
CT Components
a. Fascia: Sheet of broad band of fibrous CT beneath skin or around muscle b. Superficial Fascia: Right under skin (hypodermis)
c. Deep Fascia: made of dense irregular- surrounds skeletal muscle cartilage B. Layers of CT in Skeletal Muscle
a. Epimysium: dense irregular- surrounds entire outer surface of muscle- where blood vessels come in- protection
i. Fascicle: bundles of cells
b. Perimysium: surrounds each fascicle (bundle)
c. Endomysium: surrounds each individual cell (fibers)

*All three layers extend to form tendon
*All layers help reinforce muscle
*All contribute to elasticity
*All provide entry/exit pathogens for blood vessels and nerves

V. Blood and Nervous Supply
a. Blood supply
a. Very good
b. Needs 0xygen and glucose for ATP
c. Needed for waste removal
d. Each muscle has an artery- blood to; vein- blood away
e. Capillaries in endomysium- where things are exchanged between blood & tissue
f. Each skeletal muscle cell in control with 1 or 2 capillary help feed muscle cell
b. Nervous Supply
a. Branches through muscle layers
b. Somatic nervous system controls muscles
c. Skeletal muscle- needs electrical stimulation
d. Action Potential- signal sent to skeletal muscle
e. Motor Neuron- control skeletal muscle (carry Action
Potentials)

VI. Microanatomy of Skeletal Muscle cell (fiber)
a. Background
1. Very large 10x the size of average cell
2. Up to 30cm in length cell goes whole length of muscle
i. Sarcolemma: cell membrane ii. Sarcomere: cytoplasm iii. Sarcoplasmic Reticulum: ER (Smooth ER) used to store and release
Ca+ for muscle contraction iv. Myofibril: rod like structures run in parallel length of cell used for contraction v.Syncytium: joining together 100’s of embryonic cells fuse together to make a muscle cell vi. Glycosome: vesicles of glycogen (storage polysaccharides) vii. Myoglobin: protein/pigment bind to and stores oxygen for ATP production *Skeletal muscle has lots of mitochondria (ATP)

b. Myofibrils
i. Cylindrical rod shaped, tightly packed ii. 100’s to 1000’s in a single cell iii. ≈ 80% of cell volumes iv. Contractile element – used for shortening
v.Contain 3 types of myofilaments
1. Thick myofilaments
2. Thin myofilaments
3. Elastic myofilaments
c. Sarcomere
i. Anatomy
1. Smallest unit of contraction
2. Functional unit
3. Where start and end Z disc
4. A-band: dark area makes most of sarcomere (middle)

5. I-band: Part that looks light (each side) cut in ½ by z-disc
6. Myosin {Thick} filament: located in A Band [darker/blocks more light] 7. Thin {Actin} filament: starts at z-disc runs through thick filament
8. Elastic {titin} filament: starts at z disc runs through thick filament 9. H-zone: space between thin filaments
10.M-line: ring of proteins – where elastic filaments anchor
a. A-band: Thick, Thin, Elastic
b. I-band: Thin, Elastic [NO THICK]
c. H-zone: Thick, Elastic

d. Thick filament
i. Found in A-band ii. Made of myosin (protein) iii. ≈200 myosin proteins make a thick filament iv. Myosin head has ATP binding site ATPase
v.Actin binding site = where heads bind to thin filaments vi. When heads grab thin filament = cross bridge = likes thick/thin vii. Myosin heads generate tension viii. No heads in H-zone

e. Thin Filament
i. Z-disc, I-band, Some of A Band ii. 3 different proteins
1. Actin- globular protein
2. Tropomysin- spirals around the actin- reinforces it; blocks active sites (muscle relax)
3. Troponin- made of 3 different polypeptides
a. TnC: troponin calcium- binds calcium
b. TnT: troponin tropomysin- binds to tropomysis and positions in on actin [controls covering/uncovering of active site]
c. TnI: troponin inhibitory- binds to actin
f. Elastic Filament
i. From z disc to M-line ii. Made of protein titin iii. Holds thick filament in place iv. Part in I band; can stretch and recoil
v.Helps to rest excessive stretching and could rip sarcomere

g. Sarcoplasmic Reticulum
i. Smooth ER ii. Stores/Releases Ca+ for muscle contraction iii. Intracellular

iv.

Neuromuscular Junction
i. Where neuron meets muscle cell
a. Background
i. Has to have electrical signal to contract ii. Somatic nervous system (voluntary) controls skeletal muscle iii. Motor neurons go to skeletal muscle iv. Branchy, Branchy then dead in into axon terminal
v.Axon terminal- communicate with muscle cell; don’t actually touch the muscle cell vi. Skeletal muscle neurons located in brain/spinal cord [cell bodies]
1. Synaptic vesicles- contains chemical (neurotransmitter)
Acetylcholine
2. Ca+ Ion Channels
3. Synaptic cleft- space – filled with glycoproteins- help with diffusion vii. Motor end plate- where the sarcolemma is highly folded, right under axon terminal- more surface area for receptors for Acetylcholine viii. Receptor- attached to NA+/K+ ion channels [ACH receptors]

VII.

Terminal Cisterna- Stores Ca++

b. Psychology of the Neuromuscular Junction
i. Start with AP from brain/spinal cord traveling through motor neuron ii. AP hits axon terminal causing Calcium channels to open iii. Calcium goes into terminal and triggers exocytosis of synaptic vesicles iv. Release ACH into synaptic cleft
v.ACH diffuses across cleft and binds to receptor on motor end plate cause
NA+/K+ cross the sarcolemma vi. Some stuff happens and 2nd AP is generated
1. FROM ELECTIRCAL TO CHEMICAL TO ELECTRICAL SIGNAL
a. 1st AP
ACH
2nd AP th of a second
b. ACH only last 1/500
c. Enzymes that break down ACH [Acetylcholinesterase]
d. As long as ACH is present there can be a contraction

VIII.

Excitation Contraction Coupling
i. 2nd AP traveling down sarcolemma and goes into t-tubule ii. Causes Ca++ channels to open [in terminal cisterna] iii. Ca++ goes out into sarcoplasm from terminal cisterna iv. Binds to the subunit of troponin
v.Causes troponin to change shape and moves tropomyosin from active sites 1. Only last 30 milliseconds
a. Take Ca++ and put it back into terminal cisterna using a pump [low to high]

IX. Cross Bridge Cycle
a. Active sites uncovered – heads not yet attached
b. Where you actually shorten/contract muscle
i. Cross Bridge Formation
1. Myosin heads energized
2. ADP/Phosphate group attach
3. Myosin heads attach to active sites on actin ii. Power stroke
1. Myosin head loses phosphate group; goes from high to low NRG; pulls thin filament towards Hzone
2. Releases ADP iii. Cross Bridge Detachment
1. New ATP molecule comes in and binds to myosin head, causes myosin head to release thin filament iv. Cocking of Myosin Head
1. ATP undergoes hydrolysis
2. NRG is released
3. Myosin head goes back to upright cocked position
a. During contraction ≈ ½ of myosin heads are in contact with actin b. Muscle will shorten 30%-35% of its resting length
c. Each time you go through cross bridge cycle it shortens
1%- must go through cycle 65-70X
4. H Zone disappears at end of contraction
5. Z disc get closer together
6. I band gets smaller
7. A band stays the same

X. Contraction of the Whole Muscle
a. Definition
i. Muscle tension- force exerted on an object by a muscle ii. Load- force exerted on a muscle by the weight of the object to be moved iii. Isometric Contraction- muscle develops tension by the load is not moved iv. Isotonic- muscle develops tension by shortening or lengthening
1. “Concentric”- muscle shortens to do work- triceps brachia
2. “Eccentric” muscle lengthens to do work- bicep brachia

b. Motor Unit
i. Motor neuron and all of the muscle fibers (cells) it incarcerates ii. Electrically isolated every cell must get electrical signal to contract
(skeletal muscles only) iii. # Of cells per motor unit will vary iv. Depends on the level of fine motor skills- fingers, face, eyes
v.Less cells per motor unit for fine control

vi. If you contract a single signal the whole muscle will contract because cells of a motor unit are spread through a muscle
c. All or None Principal
i. Threshold stimulus- weakest stimulus that causes muscle contraction
1. “If a threshold stimulus or greater is applied to the cells of a motor unit then those cells will contract to the fullest extent” ii. Myogram- shows tension generated over time (milliseconds)
a. Twitch- 1 AP to 1 Motor unit
1. Latent period= short 5-8 milliseconds, after stimulus but before contraction (neuromuscular junction/ excitation contraction coupling) 2. Period of Contraction= 10-100 milliseconds long 0 to peak (cross bridge formation)
3. Period of Relaxation= 10-100 milliseconds long peak to 0 (Ca++ goes back to the terminal cisterna, active sites covered)

d. Graded Muscle Responses
i. Different strengths/ levels ii. Two ways to get muscle response levels
a. Changing frequency of stimulation
i. Sending more AP’s per second
b. Changing strength of stimulus iii. Muscle Response to Frequency
a. Wave Summation: two identical stimuli are delivered to a muscle in rapid succession
i. Tension goes up relaxes a little then goes up ii. Partial relation
b. Un-fused/Incomplete Tetanus
i. 20-30 stimuli per second to a muscle ii. Quivering state
c. Fused/Complete Tetanus
i. 80-100 stimuli per second ii. No relaxation between AP until the end iii. Tension plateaus off
*Our muscles work anywhere between fused and un-fused tension

*Used to get a smooth non-jerky muscle contraction iv. Muscle Response to strong Stimuli
a. Controls forces of power of contraction
b. Have to activate more & more motor units

XI.
Muscle Metabolism
a. Background
i. Needs ATP in order to contract
1. Energize myosin head
2. Causes head to release ii. Stored ATP gives 4-6 seconds worth of contraction iii. Three ways to make ATP
b. Direct Phosphorylation of ADP by Creatine phosphate
i. Creatine phosphate = HIGH NRG molecule found in muscle ii. Enzyme Creatine kinase performs direct phosphorylation iii. Takes a phosphate group + NRG from Creatine phosphate and gives it to ADP iv. ≈15 seconds worth of muscle contraction
v. Stored ATP and Creatine phosphate first ≈20 seconds then anaerobic or aerobic c. Anaerobic Cellular Respiration
i. Does not need Oxygen
Glucose
ii. Occurs in sarcoplasm iii. Uses Glycolysis
Glycolysis
1. Start with glucose in blood stream in cystole or breaking down glycogen
Pyruvic
2. Glucose enters glycolysis
2 ATP
Acid
3. Pyruvic Acid gets converted into lactic acid
4. Lactic acid causes muscle fatigue
Lactic Acid
5. Once in blood Lactic acid is removed by heart, kidneys, liver, and
(released to converted back to glucose blood) iv. 2 ½ times faster then aerobic
v.Net only 2 ATP per glucose/lactic acid build up
Oxygen
vi. Only use continuously for ≈60 seconds
d. Aerobic Cellular Respiration
i. Requires Oxygen
Carbon

2 ½ x longer – More Net ATP
3 different phases
1. Glycolysis: starts in sarcoplasm
a. Pyruvic acids do not turn
Glucose
into lactic acids because of oxygen
Pyrvic
2. Krebs Cycle:
Acid
a. Pyruvic acids enter into mitochondria Aerobic
Respiration in
b. Oxidation/ reduction occurs – removing electrons/protons
Mitochondria
c. Enzymes gives electrons to electron carriers
Amino
Fatty
d. Carbons Get released as CO2
Acids [IN] Acids [IN]
e. Makes 2 ATP
3. Electron Transport System
CO2
H20
a. In mitochondria
[OUT]
[OUT]
b. In inner membrane
c. Series of proteins
i. Makes about 28-30 ATP per glucose ii. Used for hours iii. Can use fatty Acids/Amino Acids for ATP
e. Muscle Fatigue
i. Physiological inability to contract due to a relative deficit of ATP ii. Get a contracture: state of continuous contraction “muscle cramp/
Charlie horse”, dead- rigger mortise iii. Lactic acid disrupts anaerobic muscle respiration iv. Ionic imbalance Na+/K+- wont get a second AP
XII.
Smooth Muscle
a. Arrangement and Structure
i. Spindle shaped ii. Uni-nucleated iii. Smaller then skeletal muscle cell iv. Non-striated
v. No sarcomeres vi. Only has endomeysum (surrounds each cell) vii. Has gap junctions (allows AP’s to travel from cell to cell)
viii.
Contracts in sheets ix. Found in walls of hallow organs
x. Most organs have 2 layers of smooth muscle
1. Longitudinal layer: runs up and down (contraction: shortens/ dilates) 2. Circular layer: runs around (contraction: constricts/lengthens) xi. Alternates contracting and releasing xii. Peristalsis mixing and moving
1. Controlled by Autonomic Nervous System
a. Involuntary

ii. iii. b. Controlled by autonomic neuron
2. Vericosities: swollen area; similar to axon terminal does not dead end a. Has synaptic vesicles which could contain ACH or
Norepinephrine
b. Neurotransmitter can be excitatory (cause contraction) or inhibitory (cause it to relax)
*BE ABLE TO COMPARE SKELETAL AND SMOOTH MUSCLE!!
b. Contraction of Smooth Muscle
a. Background
i. Slow synchronized contractions ii. Whole sheet contracts as a unit iii. Takes 30X longer to contract then skeletal iv. More of a sustained contraction
v. Fatigue resistant; because it only uses 1% of the NRG that skeletal uses vi. Most organs have smooth muscle contraction all of the time = smooth muscle tone vii. Some organs (stomach, small intestine) have pace maker cells
[have set rhythm of contraction] viii. Pace maker cells are self excitatory can generate AP
without external stimuli ix. Mechanical stimuli/nerve stimuli
x. Local Factors- Chemicals that affect smooth muscle
1. Only affects muscle in that specific are
a. Hormones & histamine
c. Regulation of Contraction
a. Diffuse Junction- Neural Regulation
i. AP traveling down autonomic neuron and hits vericosities ii. Ca++ channels open and comes into vericosities iii. Triggers exocytosis of the synaptic vesicles iv. Can release ACH or norepinephrine into the wide cleft
v.Neurotransmitter diffuses across cleft vi. Binds to receptors on smooth muscle vii. Opens Na+/ K+ channels and crosses sarcolemma viii. Some stuff happens ix. May or May not get a 2nd AP depends on receptors
b. Excitation-Contraction Coupling
i. Start with 2nd AP traveling down sarcolemma ii. Hits the caveolae and SR causes Ca++ channels to open iii. Goes into cell iv. Ca+ binds to Calmodulin
v.Calmodulin is activated and activates enzyme myosin light chain kinase vi. Enzyme states to perform phosphorylation for cocking of the myosin head

vii. Myosin head can attach to actin on thin filament
d. Smooth Muscle Response to Stretch
a. If you stretch any type of muscle it will contract with more force
b. In smooth muscle the increase in tension the contraction only last briefly then it adapts to the new length then it relaxes [Stress Relaxation
Response]
c. Hallow organs can slowly fill up without expelling everything out
e. Nervous System
a. Background
i. Basic Characteristics
1. Nervous System: Master controlling and communication system a. Uses electrical signals (rapid communication)
b. Signals are specific
c. Usually causes an immediate response
b. Three Main Functions of Nervous System
i. Nervous system uses millions of receptors to monitor changes inside/outside (stimulus) ii. Nervous system has to process and interpret the sensory input determines the set point and response (integration) iii. Nervous system triggers a response by sending signals called motor output to effectors, muscles, or glands
1. Carry out the response
XIII. Organization of Nervous System
a. Central Nervous System [CNS]
i. Brain/Spinal Cord
1. Integration: Process information
2. Located in dorsal cavity
b. Peripheral Nervous System [PNS]
i. Receptors, Nerves, Nerve Endings etc. ii. Cranial nerves: to from brain iii. Spinal nerves: to from spine
c. Connects Body to CNS
d. Sensory [Afferent]
i. Input from receptors to PNS ii. Somatic Afferent- from receptors in skin, skeletal muscle joints to CNS iii. Visceral Afferent- from receptors in visceral organs, stomach, blonder, intestine to CNS
e. Efferent [Motor]
i. From CNS to effectors ii. Somatic Efferent: from CNS to skeletal muscle
(voluntary)
iii.
Autonomic Nervous System: CNS to cardiac muscle, smooth muscle, glands [involuntary]
1. Parasympathetic: Normal daily functions

a. “Rest and digest”- increases digestion, regular heart rate, increases urination [stores NRG]
2. Sympathetic: “fight or flight”
a. Emergency or excitatory situations
b. Shuts down digestion, urination
c. Increases heart rate and respirations
d. Directs blood to skeletal muscle
e. Releases NRG

Central Nervous System

Peripheral Nervous system

Efferent

(CNS to effectors)

Afferent

(Receptor To CNS0

Somatic (from CNS to Skeletal)

Autonomic Nervous System (From CNS to cardiac/smooth)

Somatic (receptors in skin & skeletal to CNS)

Parasympathetic

"rest and digest"

Visceral (receptors in bladder& stomach to CNS)

increase digestion, regulate heart rate

Sympathetic

"fight or flight"

increased heart rate, shut down digestion/urination XIV.

Nervous System
a. Mainly maid up of nervous tissue
b. Cells tightly packed, highly cellular
i. Neurons ii. Supportive cells

A. Supporting Cells
a. 6 Types: 4 in Central 2 in Peripheral
b. Supporting Cells in Central Nervous System
i. Do not carry electrical signals ii. Have processes that stick out

iii.
Out number neurons 10 to 1 iv. ½ if the mass of your brain
Astrocytes: star shaped
i. Most common ii. Most abundant iii. Support and brace capillaries iv. Help to exchange materials between capillaries and neurons v.Help guide migration of young neurons vi. Control chemical environment around neurons
1. By absorbing K+ and to capture/recycle neurotransmitters Microglial:
i. Touches neurons and monitors health ii. Detects if neuron is injured or if any micro organisms are present
1. Turn into macrophages if a problem is detected
Ependymal: columnar cuboidal shaped
i. Line spaces in brain and spinal cord ii. Help circulate CFS
Oligodendrocyte:
i. Wrap around axon of cells [myelin sheath] ii. Insulator iii. Prevent Na+/K+ from crossing membrane
Supporting Cells in Peripheral Nervous System
Satellite Cells:
i. Surround cell body ii. Ganglia iii. Function unknown
Schwann Cells:
i. Form myelin sheath ii. Insulator
Neurons
i. Background
1. Carry electrical signals
a. Graded potentials/Action Potentials
2. Have extreme longevity [last whole life]
3. High metabolic rate: Need Co2 and glucose
4. Can only last a few mins without oxygen ii. Anatomy
1. Cell body (Soma)
a. Nucleus, organelles, cytoplasm
b. Rough ER [Nissl bodies]
c. Ribosomes
d. Golgi apparatus
e. Makes neurotransmitters

c.

d.

e.

f.

g.
h.

i.

j.

f. Intermediate filaments; neurofibrils
i. Help maintain shape
g. Most found in CNS in clusters [nucleus]
h. In PNS clusters [ganglia]
2. Process from Neuron
a. Found in bundles
b. CNS- tract
c. PNS- nerves
3. Dendrites
a. Short, tapering, branching, extensions
b. Receptive; receive signals
c. Carry graded potentials; different levels
d. Many dendrites
4. Axon
a. Usually only 1 axon
i. Axon hillock: where axon starts
b. AP starts in the hillock
c. Can be short or long
d. End of axon: it branches forming axon terminals
i. Axon terminal: considered secretory
(releases neurotransmitters)
5. Nodes of Ranvier
a. Breaks in myelin sheath
b. So Na+ K+ cab cross membrane
c.
Areas with lots of myelin sheath [white matter]
d. White matter sends/receives signals
e. Areas with lots of cell bodies & unmyelinated sheath called [gray matter]
f. Gray matter used for processing [integration] iii. Sensory Neurons (Afferent) carries input towards CNS iv. Motor Neurons (efferent) carries inputs towards effectors v.Interneuron (associations) connects sensory to motor
1. Integrates information

XV.Neurophysiology
i. Background
1. Highly irritable – responsive to stimuli
2. Have a separation of charge across membrane
3. Inside (-) outside (+)
4. Difference across membrane is -70milivolts
5. When you separate charges they have potential NG [measured in voltage]
6. Difference in charger between two areas is Potential
Difference
7. Measuring across membrane is Membrane Potential

a. é Potential Difference é Voltage
i. More of difference across the membrane ii. = More voltage
Current: flow of electrical charge from one place to another
a. Use Na+/ K+
Resistance: hindrance to current
a. High electrical resistance: insulator: Myelin sheath,
Cell membrane
b. Low electrical resistance: conductor: ion channel
c. éVoltage éCurrent
i. More potential NRG
d. ê Resistance
éCurrent
i. Less resistance [open channels]
e. éPotential Difference éCurrent
Different types of Channels in Neurons
Passive channels
a. Always open; leaky
Active Channels
a. Gated: open&close
i. Chemically gated [ligand]: neurotransmitters
1. Cause channels to open so Na+/K+ can pass through ii. Voltage gated: open in response to a change in the membrane potential from – to +
1. AP can cause voltage gate channel to open
a. Skeletal
i. Ca+ axon terminal ii. Ca+ terminal cisterna b. Smooth
i. Ca+ vericosities ii. Ca+ caveolae
Once you open a channel ions will follow that electrochemical gradient. Go from high to low concentration or to opposite charges Resting Membrane Potential
-70mV
More K+ inside (negative)
More Na+ outside (positive)
Two ways to maintain resting membrane potential
Differential Permeability of the membrane to Na+/K+
a. Have unequal permeability
b. 75x more permeable to k+
c. 75 K+ out 1 Na+ in more negative
Sodium Potassium Pump [active transport – low to high]

8.

9.

ii.

1.

2.

3.

iii.

1.
2.
3.

iv.

1.

2.

a. 3 Na+ out 2 K+ in
b. Between the leaking and pumping it makes the membrane -70mV
v.Membrane potentials as Signals
1. Neurons use changes in membrane potential for communication a. Depolarization: reduction in membrane potential [less potential NRG – more positive - Na+ going into neuron; if depol strong enough can cause an AP
b. Hyperpolarization: increase in the membrane potential [more potential NRG] – more negative K+ goes out of neuron; can prevent an AP vi. Graded Potential
1. Located in dendrites/cell bodies
2. Short lived local changes in membrane potential that can be depolarization or hyperpolarization’s
a. Die out
3. Have different strengths
a. Depol GP = Na+ into the membrane more positive inside
i. If strong enough can generate an AP vii. Action Potentials
1. From axon hillock to axon terminals
2. Cell membrane of muscle cells
3. Do not die out!
4. Only have one strength +30mV
5. Cause AP by membrane potential exceeding threshold of -
55mV
6. Has to go past the threshold in axon hillock viii. Generation of an AP
1. Depolarization of Action Potential
a. Depol gp wave travels along hits hillock causing Na+ channels to open
b. NA+ into neuron causing membrane to be positive
c. Past -55mV [self perpetuating]
d. Membrane will go to +30mV causes next Na+ cannel to open etc.
2. Repolarization: from +30mV to -70mV
a. After 1 millisecond Na+ channels close
b. Same time Na+ channels closing K+ channels open
c. Makes membrane -70mV
d. Brings it back to rest
3. Propagation of an Action Potential
a. Continuous Conduction
i. Found in an un-myleinated axon [slow]
b. Saltatory Conduction
i. Found in myleinated axon [fast]

ii.
Opens channels of nodes of Ranvier iii. Myelin keeps the current
4. All or None Principal
a. An action potential is either on or off
b. If you open enough Na+ channels in the hillock to pass the threshold you can get a Action Potential [+30]
c. If you don’t open enough Na+ channels or K+ you wont go pass the threshold; you don’t get an action potential
5. Synapse
a. Where the axon terminal of the neuron meets the dendrites and cell body of the next neuron
b. Depending on where the neuron is located determines its name
i. Pre-synaptic neuron: has action potential [1st neuron] ii.
Post-synaptic neuron: has graded potentials [2nd neuron]
1. Electrical Synapse
a. Use gap junctions to connect neurons b. Mainly found in embryonic tissue
c. Get replaced as we develop
2. Chemical Synapse
a. Use neurotransmitters
b. From electrical to chemical to electrical 3. AP traveling down axon of presynaptic neuron 4. AP hits Axon terminal causing Ca+ channels to open
5. Ca+ enters terminal triggering exocytosis of synaptic vesicles
6. Release neurotransmitter into synaptic cleft 7. Neurotransmitters diffuse across cleft
8. Bind to receptors on post-synaptic neuron dendrites/cell bodies
c. ESPS: Excitatory Post-Synaptic Potential
i. Two neurons communicating with one another
[depol gp] get AP and move towards threshold
d. IPSP: Inhibitory Post-Synaptic Potential
i. Two neurons communicating with one another
[hyperpol gp] No AP.
6. Integration and Modification of Synaptic Events
a. EPSE: not strong enough to go past the threshold

i. Summation: 2 stimuli set off but far apart to generate past threshold ii. Temporal Summation: When one or more pre-synaptic neurons send AP’s in rapid order to get a fast release of neurotransmitters iii. Spatial Summation: When post-synaptic neuron is stimulated by a large number of axon terminals from the same or different neurons at the same time iv. Spatial Summation EPSP/IPSP
1. Na+/K+ going in and out one overriding the other
a. Integration
XVI. Patterns for Neural Processing
a. Serial Processing
i. All or none manner, always get the same response
1. “Reflex” – touching something hot and jerking away
b. Parallel Processing
i. Sensory input is divided into many pathways ii. Will have different responses iii. Depends on what you’ve learned iv. Brain uses parallel processing