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Question 1

How fast are action potentials

Answer 1

Action potentials can travel at up to 120 m/s triggering at the nerve terminal, the release of neurotransmitters

Question 2

What is the function of neurotransmitters?

Answer 2

Neurotransmitters carry the signal across the synaptic cleft. From the pre-synaptic neuron to the post-synaptic effector cell

Question 3

What are the 5 steps of neurotransmitter release?

Answer 3

1. Synthesis of Transmitter
2. Storage in vesicles
3. Release
4. Activation of Post-Synaptic Receptors
5. Inactivation

Question 4

What happens in the release state of neurotransmitter release?

Answer 4

Action potential comes down to nerve terminal, where they are densely expressed voltage gated calcium channels. Depolarisation caused by action potential opens the calcium channels, calcium funnels into the nerve terminal, which is essential in causing the coordinated release or exocytosis of transmitter from the vesicles

Question 5

How can drugs enhance synaptic transmission directly?

Answer 5

Direct stimulation of post synaptic receptors by
1. the natural transmitter
2. analogues - compounds that interact/activate the receptor

Question 6

How can drugs enhance synaptic transmission indirectly?

Answer 6

Indirect action via
1. increased transmitter release
2. inhibition of transmitter removal

Question 7

How can drugs inhibit synaptic transmission?

Answer 7

1. Blocking synthesis, storage or release from the pre synaptic neurone
2. Blocking postsynaptic receptors

Question 8

What are agonists?

Answer 8

drugs, hormones, or transmitters which bind to specific receptors and initiate a conformational change in the receptor resulting in a biological response

Question 9

What does affinity mean?

Answer 9

The ability to bind to receptors

Question 10

What does efficacy mean?

Answer 10

the ability of an agonist, once bound to a receptor, to initiate a biological response

Question 11

How do agonists work and what do they possess?

Answer 11

Agonists bind to receptors and activate them
Agonists possess both affinity and efficacy

Question 12

How do antagonists work and what do they possess?

Answer 12

Antagonists bind to receptors but do not activate them
Antagonists possess affinity but lack efficacy
Antagonists block receptor activation by agonists

Question 13

How do competitive antagonists work?

Answer 13

Competitive antagonists competes with the agonist for the “agonist binding site” on the receptor
Block is reversed by increasing agonist concentration

Question 14

What are the 2 classes of cholinoceptor?

Answer 14

Nicotinic cholinoceptors - activated by ACh or the tobacco alkaloid nicotine but not by muscarine
Muscarinic cholinoceptors - activated by ACh or the fungal alkaloid muscarine but not by nicotine

Question 15

How do you calculate Quantal Content?

Answer 15

mean EPP amplitude / mean MEPP amplitude

Question 16

How does tetrodotoxin work?

Answer 16

Blocks Na+ channels (no action potential - no release, no EPP)

Question 17

How does Conotoxins work?

Answer 17

Voltage gated Ca2+ cannels blocked (decrease Ca2+ influx - decreased release)
The EPP amplitude decreases; no change in the MEPP amplitude. A decreased quantal content

Question 18

How does Dendrotoxin?

Answer 18

Dendrotoxin blocks voltage gated K+ channels - prolonged action potential
Increased Ca2+ influx - increased release
Increased epp amplitude; mepp amplitude - no change. Quantal content Increased

Question 19

How does botulinum toxin work?

Answer 19

Blocks vesicle fusion by cleaving a vesicular protein for exocytosis - decreased release
EPP amplitude decreases, MEPP no change. Quantal content decreases

Question 20

What is tubocurarine and what does it do?

Answer 20

Competitive non-depolarising neuromuscular agent
Muscle block reserved by anticholinesterases e.g. Neostigmine

Question 21

What is alpha-bungarotoxin and what does it do?

Answer 21

Component of the venom of the Taiwan banded krait
Binds irreversibly to the agonist recognition site on the nicotinic receptor of the skeletal neuromuscular junction
Decreases the amplitude of both the epp and the mepp, with no effect on quantal content
irreversible and not reversed by neostigmine

Question 22

What are the two functional parts of the Skeletal System?

Answer 22

Axial skeleton - Head, neck and trunk
Appendicular skeleton - Limbs and girdles

Question 23

What are the types of bones?

Answer 23

Flat bones - protective
Long bones - tubular
Sesamoid bones - develop in tendons
Irregular bones - complex shape
Short bones - Cuboidal

Question 24

What is the structure of bone?

Answer 24

Periosteum and Endosteum - Fibrous connective tissue coverings of bone
Perichondrium - Fibrous connective tissue covering articular cartilage
Cortical bone - rigid outer shell
Trabecular bone - interconnected struts (trabeculae)
Medullary Cavity - hollow part of bone containing bone marrow

Question 25

Fibrous Joints Classification

Answer 25

Bones united by fibrous tissue Provides stability Sutures, Syndesmosis and Gomphosis

Question 26

Cartilaginous joints Classification

Answer 26

Primary - Synchondroses - temporary or permanent unions - covered by hyaline cartilage Secondary - Symphyses - permanent unions by fibrocartilage

Question 27

Synovial Joints Classification

Answer 27

Joint capsule spans and encloses joint Lined by synovial membrane and articulacartilage Filled with lubricating synovial fluid - mobility Several different types

Question 28

What are the different types of Synovial joints?

Answer 28

Pivot joints - rotation around axis Hinge joints - permit flexion and extension Saddle joints - permit flexion, extension, abduction and adduction Ball and socket joints- movement in multiple axes and planes Condyloid joints - permit flexion, extension, abduction and adduction Plane joints - sliding movements

Question 29

What are ligaments?

Answer 29

Connect bone to bone Fibrous bands of dense regular connective tissue Stabilise articulating bones and reinforce joints In musculoskeletal system classified into - capsular ligaments, intracapsular ligaments and extracapsular ligaments

Question 30

What does skeletal muscles attach to?

Answer 30

Most skeletal muscles are attached directly or indirectly to bones, cartilage, ligaments or fascia, or to a combination of structures Some attach to organs (eyeball), skin (facial muscles), mucous membranes (tongue muscles) Organs of locomotion Provide support and form, and heat

Question 31

What is skeletal muscle?

Answer 31

Individual cells cylindrical with multiple elongated nuclei located peripherally Cytoplasm has alternating dark and light bands (striations) - overlapping bands of contractile tissue (actin and myosin) Muscle cells = muscle fibres Tens or hundred of muscle fibres bundled together = fascicle

Question 32

Skeletal muscle classification

Answer 32

Pennate - fascicles attach obliquely - unipennate, bipennate or multipennate Convergent - arise from a broad area and converge to form a single attachment Circular or sphincter - surround opening - constrict when contracted Fusiform - spindle shaped with thick round bellies and tapered ends Flat - parallel fibers

Question 33

What are tendons?

Answer 33

Connect muscle to bone Dense regular connective tissue Transmits mechanical forces

Question 34

What are the three types of contraction?

Answer 34

Reflexive - automatic e.g. diaphragm Tonic - muscle tone - posture Phasic

Question 35

What are the two main types of phasic contraction?

Answer 35

Isotonic contractions - muscle changes length - two types - concentric (shortening) and eccentric (lengthening) Isometric contractions - muscle length remains the same

Question 36

What is the primary function of muscle?

Answer 36

Generate force or movement in response to a physiological stimulus - all muscles transduce a chemical or electrical signal into a mechanical response

Question 37

Skeletal muscle contracts in response to neuromuscular synaptic transmission

Answer 37

A skeletal muscle fibre has a single NMJ where ACh receptors are concentrated ACh released from the presynaptic nerve terminal binds to the nicotinic ACh receptors at the NMJ - receptors are non selective cation channels that open in response to ACh binding, resulting in a depolarization of Em known as an end plate potential - if the epp exceeds threshold for activating V-gated Na+ channels, an AP is generated Generation of an AP initiates the sequence of events leading to contraction - ACh is rapidly inactivated by ACh-esterase

Question 38

Levels of organisation in a skeletal muscle

Answer 38

Whole skeletal muscle (organ) - muscle fibre (a single cell) - myofibril (a specialised intracellular structure) - thick and thin filaments (cytoskeletal elements) - myosin and actin (protein molecules)

Question 39

Skeletal muscle fibres are striated by a highly organised internal arrangement

Answer 39

A single, skeletal muscle cell (muscle fibre) is relatively large, elongated and cylinder shaped - 10-100 micrometers in diameter and up to ~75 cm in length Myofibrils - specialised contractile elements that extend the entire length of the muscle fibre - muscle fibre can contain 100s to 1000s of myofibils Each myofibril consists of a regular arrangement of cytoskeletal elements - the thick and thin filaments - Thick (special assemblies of the protein myosin) - Thin (made up primarily of the protein actin)

Question 40

Troponin

Answer 40

Heterotrimer - Troponin T binds to a singe molecule of tropomyosin - Troponin C bind Ca2+ - Troponin I binds to actin and inhibits contraction Each heterotrimer of troponin interacts with a single molecule of tropomyosin, which in turn interacts directly with 7 actin monomers

Question 41

What do thick filaments consist of?

Answer 41

Composed of multiple myosin-II molecules Each myosin-II molecule is a double trimer composed of - 2x intertwined chains - 2x regulatory chains - 2x alkali (or essential) light chains

Question 42

What are the two heavy chains made up of in relation to thick filaments?

Answer 42

3 regions - tail, hinge and a head Tail regions are alpha helices that intertwine Hinge region the molecule opens to form 2 globular heads Head regions (aka S1 fragments) are the cross-bridges between the thick and thin filaments of the sarcomere

Question 43

What do the heads of heavy chain possess in relation to thick filaments?

Answer 43

Possess a binding site for actin and a site for binding and hydrolysing ATP

Question 44

What complex is formed with the head portions of each myosin in relation to thick filaments?

Answer 44

Forms a complex with 2 light chains, 1 alkali and 1 regulatory The alkali light chain stabilises the myosin head region The regulatory light chain regulates the ATPase activity of myosin. The activity of this chain is regulated via phosphorylation by kinases

Question 45

Muscle contraction

Answer 45

Muscle contraction is a cycle in which myosin-II heads bind to actin, these cross-bridges become distorted, and finally the myosin heads detach from actin Energy for this cycling comes from the hydrolysis of ATP In all 3 muscle types, an increase in intracellular Ca2+ concentration triggers contraction by removing the inhibition of cross bridge cycing Upon stimulation the intracellular Ca2+ concentration ma rise from its resting level of less than 10^-7 M to greater than 10^-5 M The subsequent decrease in intracellular Ca2+ concentration is the signal to cease cross-bridge cycling and relax

Question 46

Role of Ca2+

Answer 46

Ca2+ modulates contraction via regulatory proteins rather than interacting directly with the contractile proteins In the absence of Ca2+, these regulatory proteins act together to inhibit actin-myosin interactions, thus inhibiting the contractile processes When Ca2+ bind to one or more of these proteins, a conformational change takes place in regulatory complex that releases the inhibition of the contraction