Bio Unit 3

What is a twitch? What are the 3 phases of a twitch?

Single stimulus-contraction-relaxation sequence in a muscle fiber

Fast twitch, white fibers
-Large in diameter
-When contracting ATP made anaerobically,
increased glycogen reserves
few mitochondria
quick to fatigue
-They contract hard and fast, and reaches peak tension quickly (intensity fibers ex sprinting)

Slow twitch, red fibbers
-Small in diameter compared to whiter fibers
-Make ATP aerobically
-Many mitochondria
-Will have myoglobin (Red protein that binds oxygen)
-Slow to fatigue (endurance fibers example walking)
-Won’t reach as high as tension as white fibers

Three phases
1. Latent phase
AP moves through sarcolemma, causing Ca2+ release from SR
2. Contraction phase
Ca2+ binds, cross-bridge formation, power-stroke, tension builds to peak
3. Relaxation phase
Calcium is pumped back into the SR, causing calcium levels to drop, active sites to close, and the muscle to relax.

Describe: treppe, wave summation, incomplete tetanus and complete tetanus.
How do these graphs demonstrate summation?
How is the skeletal fiber stimulated to produce treppe, wave
summation, incomplete tetanus and complete tetanus?
As tension increases with increased frequency as stimulation, what is happening within the cell to allow for this increased tension (aka Force of contraction)

Treppe
-A muscle is stimulated right after it relaxes, the next contraction is slightly stronger because calcium builds up in the cell faster than it can be removed.

Wave summation
-A second stimulus comes before the muscle fully relaxes (late in the relaxation phase), causing a stronger contraction as the twitches add together.

Incomplete tetanus
-The muscle is stimulated repeatedly without fully relaxing (early in the relaxation phase), so tension keeps rising and gets close to its peak.

Complete tetanus
-Occurs when rapid, repeated stimuli prevent muscle relaxation, causing calcium to build up in the cell and produce a continuous contraction.
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Graphs demonstrate summation
Treppe
-All subsequent stimulations occur just after the previous one returns to zero tension

Wave summation
-All subsequent stimulations late in the relaxation phase (pops tension back up)

Incomplete tension
-All subsequent stimulations occur early in the relaxation phase

Complete tetanus
-Stimulates before it ever starts relaxing
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Skeletal fibers stimulation

Treppe
-Apply single stimuli at regular intervals after the muscle fully relaxes each time

Wave summation
-Apply a second stimulus before the first twitch ends

Incomplete Tetanus
-Apply rapid, repeated stimuli where the muscle has only partial time to relax between twitches

Complete tetanus
-Apply very high-frequency stimuli with no time to relax at all.
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What is happening within the cell
-When stimulation gets faster, calcium builds up inside the muscle, letting more cross-bridges form and making the muscle contract stronger without fully relaxing.

Complete tetanus gives you the maximum tension a muscle cell can produce

What is a motor unit?
What is the difference between a small vs a large motor unit? What type of muscles would have small vs large motor units? What functional difference is observed in muscles containing mostly small motor units vs muscles containing a high number of large motor units?

Motor Unit
-One neuron plus its muscle’s fibers

Small vs Big
-Small precise muscles have 1 or few muscle fibers per motor unit (eye muscles)
-Large muscles have up to 1000 muscle fibers per motor unit (thigh muscle)

Muscle Functions of Big and small
Small; eye muscles
Big; thigh muscles

Different functions of big and small motor units
Small: precise movement
Big; strong powerful movement

Define recruitment. How is recruitment of motor units used to
increase tension

Recruitment
-Turning on more motor units so more muscle fibers contract, producing greater force.

How it increased tension
-Increase motor units, more fibers stimulated to contract, greater the force of contraction

Explain how increasing tension is achieved through motor unit recruitment and motor unit summation to get the maximum tension a muscle could produce.
Can this type of tension/intensity be sustained for very long periods of time? Why or why not?

Recruitment and summation maximize muscle tension
-Activating more motor units and facilitating faster stimulation of existing units. This leads to a greater number of muscle fibers contracting simultaneously

Sustainment
-This cannot be sustained for long due to fatigue and depletion of energy sources.

What is muscle tone?

Continuous contraction that are always active even at rest to maintain stable conditions

What is ATP?

Adenosine Triphosphate
-Activation energy

How is energy obtained from ATP?

–Aerobic metabolism:  in mitochondria
–Anaerobic metabolism/ glycolysis:  in cytoplasm

What is the mitochondria’s role in ATP production? Is oxygen
required?

Mitochondria make most of the cell’s ATP by using oxygen to turn food into energy.
Oxygen is required

Describe aerobic metabolism and glycolysis/anerobic metabolism.
What is required for each mechanism?
How much ATP is produced?
What are the pros and cons of each?

Aerobic metabolism = slow but efficient, uses oxygen, produces lots of ATP
Anaerobic metabolism (glycolysis) = fast but limited, no oxygen, produces little ATP and lactic acid

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Requirements
-Aerobic Metabolism
Oxygen (O₂)
Glucose, fatty acids, or amino acids (as fuel)
Mitochondria

-Anaerobic Metabolism / Glycolysis
Glucose (only fuel source)
Cytoplasm (takes place outside mitochondria)
-O2 is not required
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Aerobic metabolism produces 36-38 ATP
Anaerobic metabolism produces 2 ATP
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-Aerobic
Pros; Efficient, waste products, H2O+Co2 is easy to diffuse, variety of starting nutrients
Cons: Slow (biggest con), needs O2, mitochondria

-Anaerobic
Pros: Fast, don’t need O2 or mitochondria
Cons: 1 glucose molecule= 2ATPs (lactic acid), waste products= Latic acid low in pH=pain
-Inefficient
-glucose comes from stored glycogen

Describe how the pattern of energy production and use changes as the level of muscular activity changes. (ex. start at rest, then do low intensity endurance activities – like walking, then moderate activity – like jogging, then high intensity activities – like sprinting

1. At rest:

• Use mostly oxygen to make energy from fat and sugar.

• Energy use is low.

2. Walking (low activity):

• Still use oxygen to burn fat and sugar for energy.

• Energy use goes up a bit.

3. Jogging (moderate activity):

• Use more sugar and oxygen for energy.

• Body starts to use some quick energy without oxygen.

4. Sprinting (high activity):

• Use mostly sugar without oxygen to make quick energy.

• This makes less energy and produces lactic acid, causing fatigue.

What occurs during muscle fatigue?

Muscle fatigue is when the muscle cell can no longer
function because its using ATP faster than it can be made.

If ATP can’t be made, myosin heads that formed cross-
bridges can’t get re-energized to continue the contraction, nor can the myosin head break from actin. The myosin heads get stuck in a cross-bridge. Muscle cell can’t lengthen and relax nor can it continue contracting.

Fast twitch fibers are prone to fatigue, while slow twitch
fibers are not prone to fatigue.

Describe the different divisions of the nervous system

The nervous system is divided into two major parts: the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system (PNS), which connects the CNS to the rest of the body, encompassing sensory and motor nerves.

What is the CNS

The CNS stands for the central nervous system

It includes both spinal cord and brain

It takes information(sensory) in and tells the body how to respond (Motor)

Sensory= Information
Motor=control

What is the PNS

PSN stand for Peripheral Nervous system

Includes all of neural tissue outside of the CNS

Carriers your senses toward the CNS
(Sensory afferent division)

Moves AP down a motor neuron for the organ to move always away from CNS
(Motor efferent Division)

Can divide motor into

Somatic motor -control skeletal muscle voluntary control

Visceral motor- ANS is going to control cardiac muscle, smooth muscle and glands, involuntary

Describe a typical neuron. What do the different parts of a neuron do?
Discuss: dendrites, cell body (soma), axon hillock, axon, initial segment of axon, telodendria, axon terminals (presynaptic terminal)

Dendrites= Antenna to pick up messages from neurons (cell body)
Cell body is where nucleus and most organelles are

Axon Hillock=Decides to generate AP or not
Initial segment= first part of the axon and electrical segments start (AP)

Axon=carry electrical signals away from the cell body to other cells (muscles cells)

Telodendria=the tiny branches at the end of an axon that lead to axon terminals
Axon terminal=End of neuron that sends out is message to other parts of the cell
(presynaptic terminal)

What are the different classification of neurons based on structure(anatomy)?
What are the different classification of neurons based on function?
Where do you find these types of neurons?

Based on Structure
Bipolar Neuron
-Cell body in between 2 distinct processes
-Rare, important in special sense organs (sight, smell, hearing) (sensory)

Unipolar neurons
–2 processes are continuous; cell body lies off to side,
-Most sensory neurons in PNS,
-Can be 1meter+, tips of toes to SC, carries general sensory- touch, temp, pain, vibration, proprioception

Multipolar neurons
–2+ dendrites and single axon
–Most common in CNS
–Motor neurons innervating skeletal muscles
–As long as unipolar neurons

What are the different classification of neurons based on function?
Where do you find these types of neurons?

Based on Function

Sensory (afferent) neurons
Processes of specialized sensory neurons or cells monitored by sensory neurons
Carries sensory information to the CNS

Motor Neurons
Carry instructions from CNS to peripheral effectors (muscle and glands)
Cell body Located in CNS, axon goes into PNS into muscles
Axons=Efferent fibers
Somatic motor neurons= Sending nerves to skeletal muscles
Visceral motor neurons (involuntary)=Use two connected neurons to send signals that control involuntary organs.

Interneurons= Association Neurons
Location is brain and spinal cord
-Distribute sensory info and coordinate motor activity
-Synapse with sensory and motor neurons
-More complex the response, more interneurons are involved
-Also involved in all higher functions: memory, planning, learning

Microglia
-Gila cells that are phagocytic
-Wander around brain & spinal cord
-Look for things that are there

What are the different neuroglia? What do they do? Are they found in the PNS or CNS?

PNS
-Satellite cell (General support cells for neurons in PNS)
Maintain local levels
-Schwan Cells
Axon that is myelinated

CNS
-Astrocytes(=Schwan Cells)
1. Act like general support for cells for neurons in CNS
2. Form Blood brain barrier
(chemicals released from the astrocytes that make capillaries)
-Ependymal Cells
Line all the ventricles of your brain
(ventricles=hollow place in brain)
Hollow place in sc =central canal
Help flow CSF through ventricles

How are neurons and glia different? (big picture)

Neurons
-amitotic (does not divide)
-Consist of cell body, dendrites, send AP along the axon

Gila
-Always dividing

What is myelin? Why is it important? What cells are responsible for myelin in the CNS?, PNS?

-Myelin is fatty layer/ sheath that surrounds some axons of neurons, providing insulation.
-It is important for increasing the speed of electrical signals (AP) along the axon.
-In PNS, Schwann cells are responsible for myelin formation.
-In CNS oligodendrocyte form myelin

Describe gray vs white matter. Are the following (nerves, ganglion -ganglia is plural form of ganglion, tracts/pathways, nuclei and cortex) gray matter or white matter and are these found in the PNS or CNS?

Gray matter is areas that consist of cell bodies, dendrites and synapsing cell bodies and dendrites
White matter is bundles of axons that can be myelinates or not

Gray matter
PNS
-Ganglion

CNS
-Cell bodies synapsing
-Nuclei and cortex
-Gray matter at the surface of the brain is the cortex
-Gray matter in the spinal cord and in the brain (not in the surface) is nuclei

White matter
PNS
-Nerves

CNS
-Tracks=Pathways Are white matter in the CNS

What is the RMP? Is it positive or negative? What are the units? What is a depolarization vs repolarization vs hyperpolarization?

RMP= Resting membrane potential
RMP is negative; -70 mV
RMP units are negative are milli Volts

Always reference to the inside

Depolarization; membrane potential becoming more positive
Repolarization; membrane potential going back at rest
Hyperpolarization: membrane potential is more negative

Explain how the resting potential is created and maintained.
a. Passive and active forces involved with Na+ and K+

b. Chemical and Electrical gradients for each ion and their combined Electrochemical gradients. These passive gradients cause Na+ and K+ ions to move in or out of the cell

c. Equilibrium potential for each ion. What does the equilibrium
potential mean? Is the equilibrium potential for Na+ and K+
depolarized or hyperpolarized from a RMP?

A. Passive forces (leak channels) (require no energy) let K+ out and Na+ in
Active forces (Na+ and K+ pump) push 3 Na⁺ out, 2 K⁺ in

B. Chemical gradients; move from high to low concentration
Electrical gradient: Opposite charges attract
Electrochemical gradient (both forces combined): It decides which way an ion moves and how fast/strongly it moves across the membrane

C. Equilibrium potential means is voltage inside the cell where the ion is balanced — it doesn’t want to go in or out anymore
The equilibrium potential for Na+ is 66mV
The equilibrium potential for K+ is -90mV

List the different types of channels. How are they regulated? What are the 3 states of channels?

Chemically gated channels: Open or close due to binding of specific chemicals
Voltage gated channels: Open or close due to binding of specific chemicals
Mechanical gated channels: Open or close due to physical distortions of membrane surface

Describe a graded potential (GP) – characteristics. Where do they occur on a neuron? How do they occur? How is it different from an AP?

Characteristics
-Only affect small areas of the neuron and its signal fades away as it spreads, this is because ions spread out and no voltage-gated channel to boost the signal
-Graded potentials happen because gated channels open
-Stronger signal causes a bigger and wider change in the neuron’s electrical charge

Location
-Cell
-Bodies

How they occur
-Stimulus → gated channels open → ions move → graded potential

Difference from AP
-They can vary in their size or magnitude

-can either be depolarizing or hyperpolarizaing

Example; Na+ entering cell is a depolarization

Example; potassium leaving or chloride entering is a hyperpolarization

Describe an AP. Where do you find APs? What are their characteristics?
Where do they begin on the neuron? How do they start – why occurs when a threshold voltage is reached?

Description
-A large change in the electrical charge across a neuron's membrane. It is how neurons send signals over long distances

Location of AP
-Axon
-Axon hillock
-Axon terminals

-plasma membrane of muscle cells (sarcolemma)

Characteristics
- All-or-nothing response, meaning if the threshold potential is reached, an action potential will occur
-Can propagate along the axon without diminishing, maintaining strength over distance
-Involves depolarization followed by repolarization of the membrane

Beginning
-Axon hillock

How do they start
They start when they reach thresh hold,
Then when voltage gated sodium channels open,
And then when lots of sodium ions rush in

Graph an AP (time vs TMP). What are the different phases of an AP?
What ion is diffusing across the PM during each phase? How long does an AP take (roughly)?

Lable
A-Depolarization phase
B-Repolarization phase
C-Absolute Refractory period
D- Relative Refractory period
E-voltage gated sodium channels closes and becomes inactive, and voltage gated potassium channels open
F- Resting period

Ion that diffuses across the PM

• Sodium ions during depolarization phase

• Potassium ions during repolarization phase

An action potential takes roughly 1-2 milliseconds to complete.

Explain the absolute vs relative refractory periods. What is the
significance of the absolute refractory period?

Absolute Refractory period
-Voltage-gated Na+ channels either open or inactivated

Relative Refractory period
-Voltage-gated Na+ channels regain resting state, but TMP not stabilized, is slightly hyperpolarized

Significancy of Absolute Refractory period
-makes sure signals only go one way
-stops the neuron from firing too fast
-gives the neuron time to reset before sending the next signal

Describe the events involved in generation and propagation of an AP on a myelinated vs unmyelinated AP.

Generation and propagation of an action potential (AP) on a myelinated axon

-saltatory propagation
where the impulse jumps between nodes of Ranvier, allowing for faster transmission. In contrast, unmyelinated axons propagate APs continuously along the entire length of the membrane, resulting in slower signal transmission.

Discuss the factors that affect the speed with which APs are propagated.

Axon diameter, myelination

What are the 3 types of fibers (aka. Axons)? Describe their characteristics in regard to amount of myelin and their diameters.
Relative to one another, which one has the fastest and slowest conduction speeds of APs? Why aren’t all axons Type A fibers?

The three types of axons are Type A, Type B, and Type C fibers.

Type A fibers
-A large diameter and are heavily myelinated, resulting in the fastest conduction speeds.
Type B fibers
-Have a moderate diameter and myelination, leading to intermediate speeds.
Type C fibers
Small in diameter and unmyelinated, causing the slowest conduction speeds.

Not all axons are Type A fibers
-Distance of synapse
- Not pain sensory
-Can be as big a telephone pole

Discuss the difference between continuous and saltatory propagation.

Continuous propagation
Occurs along unmyelinated axons, where the action potential is generated along the entire membrane,

Saltatory propagation
Takes place in myelinated axons, where the impulse jumps between nodes of Ranvier, significantly increasing transmission speed.

What is a synapse?
What is the difference between an electrical synapse vs a chemical synapse?

connection where a neuron passes a signal to another neuron or a muscle cell using chemicals (neurotransmitters) or electrical signals.

Electrical synapse
-Involve direct contact between cells through gap junctions, allowing action potentials to pass quickly between them as if they shared one membrane, though this is rare in the nervous system.

Chemical synapse
-Most common type, where cells aren't directly connected; the presynaptic neuron releases neurotransmitters that may or may not trigger an action potential in the postsynaptic cell, and communication only goes one way.

What is the structure of a chemical synapse?
What is found in the presynaptic terminal vs synaptic cleft vs postsynaptic terminal

A chemical synapse consists of a presynaptic terminal, synaptic cleft, and postsynaptic terminal.

The presynaptic terminal
-neurotransmitter vesicles and release machinery,

Synaptic cleft is the gap between the two neurons where neurotransmitters are released, and the postsynaptic terminal has receptors for these neurotransmitters, allowing signal transmission.

Describe events at a Cholinergic Synapse.
Where are cholinergic synapses found?

1. AP arrives and depolarizes synaptic knob

2. Calcium (Ca²⁺) enters the synaptic knob and triggers the release of ACh (about 3,000 molecules per packet), but this release stops quickly as calcium is rapidly removed by active transport.

3. ACh binds to its receptors (AChR), causing a graded depolarization of the postsynaptic membrane; the more ACh released, the greater the depolarization—if it reaches threshold, an action potential is triggered.

4. ACh is quickly broken down by AChE in the synaptic cleft—about half is destroyed before reaching receptors, and the rest within 20 ms after binding; choline is reused to make more ACh, while acetate is absorbed and processed by nearby cells.
   
   Cholinergic Synapses found
   -Nicotinic Cholinergic receptors
   

What is the synaptic delay?
How long is a synaptic delay and what events occur during a synaptic delay?
How does it affect transmission of information?

Synaptic Delay
is the time it takes for neurotransmitter release, diffusion across the synaptic cleft, and binding to receptors

Takes 0.2-0.5 msec

Affection of information
Fewer synapses involved, shorter the
cumulative synaptic delays, faster the
response

List some NTs (specifically Ach, GABA, NE/Epi).
What types of effects occur at the postsynaptic membrane when these NTs bind to their receptors?

Ach
-ACh can excite or inhibit the postsynaptic cell, depending on the receptor type it binds to

Gaba
-Generally, has inhibitory effect
– Appears to reduce anxiety

Ne/Epi
-bind to adrenergic receptors, causing either excitation or inhibition of the postsynaptic cell, depending on the receptor subtype

What is an EPSP?
How could an EPSP form?

EPSP
-Excitable depolarization post-synaptic potential

Formation
-neurotransmitters open ion channels that let positive ions in, depolarizing the postsynaptic cell

What is an IPSP?
How could an IPSP form?

IPSP
-Inhibitory post synaptic potential

Formation
-Neurotransmitters open ion channels that let negative ions in or positive ions out, hyperpolarizing the postsynaptic cell

Explain summation of graded potentials.
Where do EPSPs and IPSPs get integrated or summated?
What is the difference between spatial and temporal summation?
What must occur at the axon hillock for an AP to first form at the initial segment?

Summation of graded potentials
-graded potentials combine over space or time to increase or decrease the chance of an action potential

EPSPs and IPSPs are integrated (summated) at the axon hillock of the postsynaptic neuron

Difference between spatial and temporal
Summary of difference: Spatial summation involves multiple inputs
from different neurons arriving simultaneously, whereas temporal
summation focuses on rapid, repeated signals from a single
source

Must occur
-At the axon hillock, enough positive signals must add up to reach a certain level (threshold) to open special channels and start an action potential.

How is information encoded?
How does the brain tell the difference between a light touch and a deep pressure?

Information is encoded through the frequency and pattern of action potentials. The brain differentiates between light touch and deep pressure by the rate at which receptors fire and the specific pathways activated.

How fast treppe, wave summation, incomplete tenanus, and complete tetanus is stimulating?

Treppe
-All subsequent stimulation as soon as the previous ones got back to 0 tension stimulation

Wave summation
-All subsequent stimulation late in the relaxation phase

Incomplete tenanus
-All subsequent stimulation early in the relaxation phase

Complete tenanus
-stimulate before it ever start relaxing

Do all muscles in a body have, small, medium and large ones?

No

Which division is controlling cardiac muscles, smooth muscle, glands?

Visceral Motor=Efferent (ANS)
Motor info going away from CNS and going towards muscle, cardiac, smooth muscle, and glands

Which neurons based on structure stimulates muscle

Multipolar neurons

Is neuroglia in the CNS or PNS? Name a function for each

Neuroglia are found in both CNS and PNS.

CNS

PNS

Two functions include supporting and protecting neurons, and maintaining homeostasis in the neural environment.

If auditory nerve begins to demyelinate, this is most likely due to damage of what which gila cell?

Schwan cells

All sensory information on the right side of the brain is being processed on which hemisphere of the brain?

The left hemisphere

Touch is traveling in these kinds of neurons to the periphery to the central nervous sysyem

Unipolar Neuron

Motor neuron, such as neurons synapsing on skeletal muscles will have what type of structure?

Multipolar structure

Is a neuron is talking to another cell what structure if that cell?

Muscle cell, dendrite or cell body of a neuron

What do you need for action potential

excitable membrane on an axon that hits thresh hold (V-G Na+ Ch open)

What is a refractory period?

The time after an action potential during which a neuron cannot fire another action potential, allowing recovery of ion channels.

Why cant you get another action potential during absolute refractory period vs relative

During the absolute refractory period, voltage-gated sodium channels are inactivated and cannot be reopened, whereas during the relative refractory period, some sodium channels are closed but capable of reopening, allowing for a potential action if the stimulus is strong enough.

What is the primary ion at the depolarization phase?

Sodium (Na⁺) ions

Where is sodium diffusing during the depolarization phase?

In the cell

When do these channels open in the depolarization phase?

Opens at thresh hold voltage

Voltage gated Na+ ch of that peak voltage close (inactive), when do voltage gated ch become inactive?

At peak voltage

What is the primary ion at the repolarization phase?

Potassium (K+)

When do action potentials become inactive?

During the refractory period

Remember