Module 5 Angel

Question 1

describe a reflex arc

Answer 1

stimulus detected by receptor
sensory neurone passes impulse to CNS
relay neurone passes information across CNS
motor neurone sends impulse to effector
effector brings about a response

Question 2

what is each of these in the knee-jerk and blinking reflex?
stimulus
receptor
location of relay neurone
effector
importance

Answer 2

tap below knee cap - touch on cornea (+light/sound)
stretch receptor in muscle - touch receptor in cornea
spinal cord - lower brain stem
quadricep - muscles in eyelid
balance - protecting eyesight

Question 3

list three importances of reflexes

Answer 3

don’t have to be learnt and therefore provide protection for babies
extremely fast as only has one or two synapses
are involuntary, so the brain is not overloaded and can focus on more important things

Question 4

what are the three types of muscle?

Answer 4

skeletal
cardiac
involuntary

Question 5

describe the organisation of muscle

Answer 5

A muscle is an organ made of muscle tissue, made of muscle fibres (cell). Each muscle fibre is packed with organelles called myofibrils. A myofibril is composed of two muscle filaments called actin and myosin. Myofibrils are divided into functional units, each called a sarcomere.

Question 6

describe the structure of muscle fibres

Answer 6

They are multinucleated, and much longer than normal cells. This is because they are a result of many embryonic muscle cells fusing together, making the muscle stronger as the junction between cells would be a point of weakness. The shared cytoplasm between fibres is called a sarcoplasm. They have lots of mitochondria

Question 7

describe the structure of actin and myosin

Answer 7

actin- thinner filament, consists of two strands twisted around each other.
myosin- thicker filament, consists of long- rod shaped fibres with bulbous heads that project to one side

Question 8

what does a myofibril look like ?

Answer 8

alternating dark and light bands, resulting in a striped appearance

Question 9

what is a light band?

Answer 9

lighter areas as they are the regions where actin and myosin do not overlap

Question 10

what is a dark band?

Answer 10

darker areas because of the presence of thick myosin filaments. The edges are particular dark as myosin is overlapped with actin

Question 11

what is a Z line?

Answer 11

The line at the centre of each light band. The distance between each Z line is a sarcomere

Question 12

what is a H zone?

Answer 12

The lighter region at the middle of each dark band. Only myosin filaments are present at this point. When the muscle contracts, the H zone gets smaller.

Question 13

what happens when muscles contracts in terms of the sarcomere?

Answer 13

myosin pulls actin towards the middle of the sarcomere, making the sarcomere shorter.
light band becomes narrower
H zone becomes narrower

Question 14

describe the structure of myosin

Answer 14

have globular heads that can move forwards and backwards. There are binding sites for actin and ATP

Question 15

describe the structure of actin

Answer 15

have binding sites for myosin heads, but these are often blocked by tropomyosin, which is held in place by troponin

Question 16

how does a neuromuscular junction work?

Answer 16

impulses arrive at neuromuscular junction and cause vesicles to fuse with membrane and release acetylcholine which binds to receptors on the sarcolemma, causing depolarization. The depolarisation travels down the tubules, and causes the sarcoplasmic reticulum to release calcium ions. This causes contraction. Acetylcholinesterase then breaks down acetylcholine so contraction only occurs when impulses continuously arrive

Question 17

describe the sliding filament model of muscle contraction

Answer 17

Tropomyosin prevents myosin head attaching to actin
Ca2+ released from sarcoplasmic reticulum cause tropomyosin to pull away from binding sites
Myosin head attaches to binding site on actin
Head of myosin changes angle, moving the actin filament along. ADP molecule is released
ATP fixes to myosin head, causing it to detach from the actin filament
ATP is hydrolysed to ADP, causing myosin to return to its normal position where the cycle can be repeated

Question 18

What are the energy sources of muscle contraction?

Answer 18

Aerobic respiration/oxidative phosphorylation
Anaerobic respiration
Creatine phosphate- acts as a reserve supply of phosphates that can regenerate ATP