Animal Physiology 2

Question 1

Explain neurons? What is the origin of nerve impulses?

Answer 1

Neurons are specialized cells that function to transmit electrical impulses within the nervous system.

The nervous system converts sensory information into nerve impulses (electrical signals) in order to rapidly detect/respond to stimuli.

Question 2

What are the three basic components that most neurons share, and what are their functions? (Suck A Dick)

Answer 2

Soma: a cell body containing the nucleus and organelles – where essential metabolic processes occur to maintain cell survival

Axon: elongated nerve fibre that transmits electrical signals to terminal regions for communication with other neurons/effectors

Dendrites: short-branched nerve fibres that convert chemical information from other neurons / receptor cells into electrical signals

Question 3

Explain the myelin sheath.

Answer 3

• An insulating layer on some nerve fibres
• Consists of many layers of phospholipid bilayer
• Deposited by Schwann cells that grow around the nerve fibre
• Improves conduction speed of electrical impulses along the axon

Question 4

What is the node of Ranvier?

Answer 4

A gap in the myeline between adjacent Schwann cells.

Question 5

How does saltatory conduction work?

Answer 5

In myelinated nerve fibres, the nerve signal is forced to jump from one node of Ranvier to the next, creating a faster speed of impulse transmission.

Question 6

Define the resting potential of neurons.

Answer 6

The potential difference/voltage across the membrane of a non-transmitting neuron.

It’s created due to an imbalance of positive/negative charges across the membrane.

Question 7

Explain how resting potential in neurons works.

Answer 7

• Sodium-potassium pumps transfer sodium (Na+) and potassium (K+) ions across the membrane
• Na+ ions are pumped out, K+ ions are pumped in.

Question 8

What creates the concentration gradient and imbalance with regards to resting potential? What is the typical resting membrane potential of a neuron?

Answer 8

• 3 Na+ pumped out for every 2 K+ pumped in, unequal; creates concentration gradients for both ions.
• Membrane is more permeable to K+, so it leaks back across the membrane faster; Na+ concentration gradient is steeper, creating charge imbalance.
• Organic anions inside the nerve fibre are negatively charged, increasing charge imbalance.
• Resting membrane potential is approx -70 mV.

Question 9

What is an action potential?

Answer 9

• Action potential: a rapid change in membrane polarization, consisting of depolarization (negative to positive) and repolarization (positive back to negative)

Question 10

How does depolarization work in neurons?

Answer 10

• Due to the opening of sodium channels, allowing Na+ to diffuse into neuron down concentration gradient
• Entry of ions reverses charge imbalance; inside is positive relative to outside
• membrane potential of +30 mV

Question 11

How does repolarization work in neurons?

Answer 11

• Occurs rapidly after depolarization
• Sodium channels close, potassium channels open
• K+ diffuses out of neuron down concentration gradient, restoring relative negativity of cell
• Channels remain open until membrane falls to -70mV potential
• Once concentration gradients are re-established, neuron can transmit another nerve impulse

Question 12

What is a nerve impulse and how do they work?

Answer 12

Nerve impulse: action potential beginning at one neuron end, propagated along the axon the the other end

• Propagation occurs because depolarizing ion movements trigger depolarization in neighbouring parts
• Impulses can only be initiated at one terminal, must be passed on to other neurons / different cells at another terminal
• Refractive period after depolarization prevents backwards propagation

Question 13

What are local currents, and how do they work?

Answer 13

Local currents: movements that reduce the concentration gradient in the polarized part of the neuron

Inside the axon
- Higher Na+ concentration in depolarized part of axon, ions diffuse along axon to polarized part

Outside the axon
- Higher Na+ concentration in polarized part, ions diffuse along axon to depolarized part

• Membrane potential rises from -70mV to -50mv;
• Threshold potential of voltage gated sodium channels is reached, allowing depolarization (then repolarization)

Question 14

How can membrane potentials in neurons be measured/analyzed?

Answer 14

• By placing electrodes on each side of the membrane, potentials can be displayed using an oscilloscope.
• Time on x-axis, membrane potential on y-axis
• Rising and falling signifies depolarization and repolarization
• May show potential rising before threshold potential is reached

Question 15

Explain synapses, where they exist, and how they’re used.

Answer 15

Synapses: junctions between neurons; between neurons and receptor/effector cells

Sense organs
- Synapses between sensory receptor cells and neurons
Brain / Spinal cord
- Immense number of synapses between neurons
Muscles + glands
- Synapses between neurons and muscle fibres / secretory cells

Chemicals called neurotransmitters send signals across synapses; system used at all synapses where presynaptic and postsynaptic cells are separated by the synaptic cleft (fluid-filled gap) that electrical impulses cannot cross

Question 16

How does synaptic transmission work?

Answer 16

1. Propagated nerve impulse reaches pre-synaptic membrane
2. Depolarization causes Ca2+ to diffuse through membrane channels into neuron
3. Calcium influx causes vesicles containing neurotransmitter to fuse with presynaptic membrane
4. Neurotransmitter released into synaptic cleft by exocytosis
5. Neurotransmitter diffuses across synaptic cleft, binds to postsynaptic membrane receptors
6. Binding causes adjacent sodium channels to open
7. Sodium ions diffuse into postsynaptic neuron, which reaches threshold potential
8. Action potential triggered and propagated

Question 17

Explain what acetylcholine is and how it works.

Answer 17

• Acetylcholine is a neurotransmitter in many synapses
• Produced in presynaptic neuron by combining choline (from diet) with an acetyl group (from aerobic respiration)
• Loaded into vesicles and released into synaptic cleft during transmission
• Binds to receptors on postsynaptic membranes
• Remains bound for one action potential initiation – acetylcholinesterase in synaptic cleft breaks it down
• Choline reabsorbed into presynaptic neuron, converted back into an active neurotransmitter with new acetyl group

Question 18

What are neonicotinoids, and how do they work? Explain their advantages and disadvantages.

Answer 18

• Synthetic compounds – bind to the acetylcholine receptor in cholinergic synapses in CNS of insects
• Irreversible binding blocks receptors and prevents transmission – acetylcholinesterase does not break down neonicotinoids
• Causes paralysis and death in insects

Advantages – less toxic!
- More CNS synapses in insects are cholinergic than humans/mammals
- Neonicotinoids bind less strongly to mammal receptors

Disadvantages
- May impact honeybees and other beneficial insects

Question 19

What happens at a synapse if the amount of neurotransmitter secreted is not sufficient?

Answer 19

• Threshold potential will not be reached
• Postsynaptic membrane does not depolarize
• Newly entered sodium ions are pumped out by sodium potassium pumps
• Postsynaptic membrane returns to resting potential

Question 20

How do nerve impulses display positive feedback?

Answer 20

Opening of some sodium channels and inward diffusion of sodium ions increases membrane potential, causing more sodium channels to open.

Question 21

How do bones and exoskeletons support muscles?

Answer 21

1. They provide an anchorage
2. They act as levers.

Question 22

Explain levers and different classes of levers.

Answer 22

Levers change the size/direction of forces with three parts – the effort force, the fulcrum (pivot point), the resultant force. The relative positions of the three determine the lever’s class.

First class lever (e.g. spine when nodding head)
- Effort force
- Fulcrum
- Resultant force

Second class lever (rising onto balls of feet)
- Fulcrum
- Resultant force
- Effort force

Third class lever (grasshopper leg)
- Fulcrum
- Effort force
- Resultant force

Question 23

How do pairs of skeletal muscles work?

Answer 23

• Skeletal muscles work in antagonistic pairs to faciliate movement.
• When one muscle contracts, the other relaxes
• Opposite movements are produced at a joint

Example: in the elbow, the triceps extend the forearm and the biceps flex the forearm

Question 24

Explain the mechanism of antagonistic muscles in a grasshopper.

Answer 24

The hindlimb of a grasshopper is specialized for jumping – jointed appendage with three main parts.

• Below the joint is the tibia; at the tibia’s base is another joint, the tarsus
• Above the joint is the femur, with extensor and flexor muscles

1. (Flexion) When the grasshopper prepares to jump, the flexor muscles contract and the extensor muscles relax. This brings the tibia and tarsus into a Z-like position, and brings the femur and tibia closer together.
2. (Extension) Extensor muscles contract, extending the tibia and producing a powerful propelling force.

Question 25

Name and explain the three major aspects of a synovial joint.

Answer 25

Cartilage - tough, smooth tissue that covers the regions of bone in the joint. Prevents bone-to-bone contact, preventing friction; absorbs shocks that could fracture bones.

Synovial fluid - fills a cavity in the joint between cartilages on bone ends. Lubricates the joint, preventing friction between cartilages.

Joint capsule - tough ligamentous covering to joint. Seals joint + holds in synovial fluid, helps to prevent dislocation.

Question 26

Name and outline the eight parts of the human elbow to annotate.

Answer 26

Humerus - bone to which biceps/triceps are attached
Triceps - extends joint
Biceps - flexes joint
Joint-capsule - seals joint, helps prevent dislocation
Synovial fluid - lubricates joint, prevents friction
Ulna - bone to which triceps is attached
Radius - bone to which biceps is attached
Cartilage - covers bones, prevents friction

Question 27

Wild carrrrrd! Go label the human elbow, everyone’s favorite synovial joint!

Answer 27

(page 478 / page 486 of file)

https://ebooks.papacambridge.com/directories/IB/IB-ebooks/upload/biology%20-%20course%20companion%20-%20andrew%20allott%20and%20david%20mindorff%20-%20oxford%202014.pdf

Question 28

How does a joint’s structure determine its movements? Explain with regards to the knee and hip joint / shoulder joint.

What are the six types of synovial joints in order of mobility? (Please Help Penis Captain Save Balls)

Answer 28

Synovial joints allow for some movements but not others.

The knee joint can act as a hinge joint, which allows for only flexion and extension. When flexed, it can act as a pivot joint, where it has a greater range of movement.

The hip joint is a ball and socket joint (between the pelvis and femur). It can flex/extend, rotate, and abduct/adduct (move sideways and back).

1. Plane joints
2. Hinge joints
3. Pivot joints
4. Condyloid joints
5. Saddle joints
6. Ball and socket joints

Question 29

Where/how are muscle fibres contained in the body? Why is skeletal muscle called striated?

Answer 29

Skeletal muscle consists of fascicles (tightly packaged muscular bundles) surrounded by perimysium (connective tissue. Fascicles contain muscle fibres.

When examined with a microscope, skeletal muscle has visible stripes.

Question 30

Describe skeletal muscle fibre.

Answer 30

• Muscle fibres are created when embryonic muscle cells fuse together
• They are multinucleate and much longer than typical cells
• They have a large number of mitochondria (contraction requires ATP hydrolysis)
• They have a sarcoplasmic reticulum (specialised ER) that stores calcium

Question 31

What is sarcolemma?

Answer 31

A continuous, single plasma membrane surrounding the muscle fibres – contains invaginations called T tubules.

Question 32

Define myofibrils.

Answer 32

Parallel, tubular structures contained in large amounts inside each muscle fibre, that consist of repeating contractile units called sarcomeres.

Question 33

Define the two protein myofilaments of sarcomeres. What do they induce?

Answer 33

Myosin: thick filament
Actin: thin filament

• Myosin contains small protruding heads that bind to regions of actin.
• Each myosin filament is surrounded by six actin filaments.
• Movement of the two filaments relative to one another causes the lengthening and shortening of the sarcomere.

Question 34

Explain Z-lines.

Answer 34

Each sarcomere is flanked by dense protein disks called Z-lines that hold the myofilaments in place. Actin filaments are attached to a Z-line at one end, helping to anchor the central myosin filaments.

Question 35

Describe the appearance of sarcomeres.

Answer 35

• Recurring sarcomeres produce a striped pattern along the length of muscle fibres – where striated comes from
• The center of the sarcomere (A band) appears darker; due to overlap of actin and myosin filaments
• Peripheries of sarcomere (I band) appear lighter; only actin is present
• A band may contain slightly lighter central region (H zone); only myosin present.

Question 36

Wild carrrrrd! Draw a labelled diagram of a sarcomere!

Answer 36

https://old-ib.bioninja.com.au/higher-level/topic-11-animal-physiology/112-movement/sarcomeres.html

Question 37

How is the contraction of skeletal muscle achieved?

Answer 37

1. Depolarisation / Calcium ion release

• Action potential from motor neuron triggers acetylcholine release into motor end plate
• Acetylcholine initiates depolarisation of sarcolemma; spread through fibre via T tubules
• Depolarisation causes sarcoplasmic reticulum to release stores of calcium ions (Ca2+)

2. Actin-Myosin Cross-Bridge Formation

• Calcium ions binds to protein troponin, which causes tropomyosin (blocks actin binding sites) to move
• Myosin heads form cross-bridges with exposed sites of actin filaments
• Myosin heads swivel towards sarcomere centre, moving actin with them

3. ATP Involvement

• ATP breaks cross-bridges by attaching to myosin heads
• ATP hydrolysis causes myosin heads to swivel outwards away from sarcomere center

4. Movement

• Myosin heads create new cross bridges with adjacent, more peripheral actin filaments
• Myosin heads again swivel towards sarcomere centre, moving actin filaments with them

5. Sarcomere shortening

• The repeated reorientation of myosin heads + resultant movement of actin filaments pulls Z-lines closer together, shortening the sarcomere
• The muscle fibre as a whole contracts as individuals shorten.

Question 38

Explain what relaxed vs contracted sarcomere looks like in an electron micrograph.

Answer 38

In relaxed sarcomere, the Z-lines are further apart, the light bands are wider, the sarcomere is longer. In the centre of the sarcomere, there is another line (M-line). In relaxed sarcomere, there is a more visible light band on either side of the M-line.

Question 39

How is fluorescence used to study contraction?

Answer 39

When muscles are stimulated to contract, strong bioluminescence will coincide with the release of Ca2+ from the sarcoplasmic reticulum.