Animal & Plant Responses - Muscles

Question 1

What is the cardioregulatory centre ? Structure/location?

Answer 1

The medulla - base of brain near top of spinal chord

medulla made up of 2 distinct parts:
- acceleratory centre- causes the heart to speed up
- inhibitory centre - causes the heart to slow down
- both centres connected to SAN by nerves that make up AUTONOMIC NERVOUS SYSTEM

Question 2

How is heart rate increased in acceleratory centre?

Answer 2

• acceleratory centre activated
• impulses sent along the sympathetic neurones to the SAN
  Noradrenaline secreted at the synapse with the SAN
  Noradrenaline causes SAN to increase the frequency of the electrical waves it produces
• increased heart rate

Question 3

How does inhibitory centre reduce heart rate?

Answer 3

Inhibitory centre activated
- impulses sent along PARASYMPATHETIC neurones to SAN
- ACETYLCHOLINE secreted at synapse with SAN
This causes SAN to reduce the frequency of electrical waves it produces
REDUCE ELEVATED HR to resting rate

Question 4

How is heart rate controlled by cardiovascular centre?

Answer 4

Exercise cause internal conditions to change - create internal stimuli :
CO2 conc in blood increases - react with water to form carbonic acid - REDUCE pH
Internal stimuli (low pH) detected by CHEMORECEPTORS
- Receptors release nerve impulses sent to cardiovascular centre*
Higher frequency impulses - activate acceleratory
After excercising, conc off blood CO2 falls—> reduce activity of accelerator pathway —> HEART RATE DECLINES

Increase in BP during excerise, DETECTED by stretch/pressure receptors aorta/carotid artery
- if pressure is too high, stretch receptor send low frequency impulses to cardio centre (activate inhibitory centre)—> REDUCE HR

Question 5

What is a gland?

Answer 5

Group of cells that produces/releases one or more substances - secretion
NORADERENALINE/ADRENALINE - made in adrenal gland - increase HR
THYROXINE - made in thyroid gland - increase HR

Question 6

3 types of muscles?

Answer 6

Skeletal (striated/voluntary) - move skeleton
Smooth (involuntary)
Cardiac

Question 7

Skeletal muscles structure ?

Answer 7

Made up of muscle fibres - highly specialised cell-like unit:
- muscle fibres contain contractile proteins in cytoplasm /surrounded by cell surface membrane
- muscle fibres contain many nuclei

Cell surface membrane = sarcolemma
Cytoplasm = sarcoplasm
Endoplasmic reticulum = sarcoplasmic reticulum (SR)

Question 8

Structure of sarcolemma?

Answer 8

Deep tube-like projections that fold in from its outer surface - T-Tubules
- they run close to SR

Question 9

Structure of sarcoplasm?

Answer 9

Contains mitochondria
- aerobic respiration to generate ATP for muscle contraction
Contain myofibrils - bundles of actin/myosin filaments , which slide past each other during muscle contraction

Thick filaments- myosin
Thin filaments- actin

Question 10

What does the membrane of SR contain?

Answer 10

Protein pumps that transport Ca2+ ions into lumen of SR

Question 11

Myofibril structure?

Answer 11

H BAND : only thick myosin filaments present
I BAND : only thin actin filaments present
A BAND : contain areas where only myosin filaments present and where myosin/actin filaments overlap
M LINE : attachment for myosin filaments
Z LINE : attachment for actin filaments
SARCOMERE : section of myofibril between 2 Z lines

Question 12

Structure of involuntary (smooth) muscle?

Answer 12

Contain both ACTIN AND MYOSIN FILAMENTS - no banding/striation
- consists of small elongated cells/spindle shaped fibres* with 1 nucleus

Question 13

Cardiac muscle properties?

Answer 13

Myogenic - contract without external stimulation via nerves/hormones
Doesn’t tire/fatigue so can CONTRACT CONTINUOUSLY through life
Cardiac muscle fibres form NETWORK that spread through walls of atria/ventricles
Cardiac muscle fibres connected to each other via intercalated discs
Large no. Mitochondria - generate ATP for contraction

Question 14

How are impulses trasmitted across neuromuscular junction?

Answer 14

OCCURS IN A SINGLE MUSCLE FIBRE NOT WHOLE MUSCLE
1. Impulse travels along AXON of motor neurone + arrives at presysnaptic membrane
2. AP cause Ca2+ ions to diffuse into neurone
- stimulates vesicles containing (ACh) to fuse with presynaptic membrane
3. ACh released diffuses across neuromuscular junction + bind to receptor proteins on sarcolemma
4. Stimulate ion channels to open in SARCOLEMMA , Na+ DIFFUSES in
5. DEPOLARISES SARCOLEMMA , generating AP that pass down T-tubules towards centre of muscle fibre
- This AP cause VOLTAGE GATED Ca2+ channel proteins in SR to OPEN
6. Ca2+ diffuse OUT SR and INTO sarcoplasm
7. Ca2+ binds to troponin molecules - causes them to change shape
Starts process of muscle contraction

Question 15

How is muscle contraction stopped?

Answer 15

ACETYLCHOLINESTERASE enzyme in synaptic cleft breaks down ACETYLCHOLINE
- Ca2+ pumped back into SR when SARCOLEMMA, T TUBULES,SR are no longer polarised
- movement of Ca2+ ions terminates muscle contraction

Question 16

Is the neuromuscular junction excitatory or inhibitory? What happens if only a few impulses sent via small no. Motor neurones ?

Answer 16

Always EXCITATORY
- the total no. Muscle fibres that contract will be minimal

Question 17

Where is the neuromuscular junction located ?

Answer 17

Between a neurone and muscle cell

Question 18

How does the sliding filament model of muscle contraction occur? Step 1-3

Answer 18

An AP arrives at the neuromuscular junction + all steps follow
1. Ca2+ ions released from SR into sarcoplasm by diffusion
2. Ca2+ ions bind to troponin molecules - they change shape
- causes troponin and tropomyosin proteins to change position on the actin filaments
3. Myosin binding sites are exposed on the actin molecules

Question 19

Structure of thick filament in myofibril ?

Answer 19

• made up of myosin molecules
• Fibrous proteins with globular head
• fibrous part of myosin molecule anchors the molecule into the thick filament
• in filament, many myosin molecules lie next to each other with their globular heads pointing away from the M line

Question 20

Structure of thin filaments in myofibril?

Answer 20

Made up of actin molecules
- globular protein molecules

2 actin chains twist tgt to form 1 thin filament
- fibrous protein - TROPOMYOSIN- twisted around the 2 actin chains
- troponin protein attached to actin chain at regular intervals

Question 21

Role of ATP in muscular contraction?

Answer 21

ATP binds to myosin to detach from ACTIN
ATP hydrolysis allows myosin heads to return to original shape
Also used for active transport - returning Ca2+ ions into SR

Question 22

Role of PHOSPHOCREATINE in muscle contraction?

Answer 22

Molecule stored by muscles that is used for rapid production of ATP

ADP + phosphocreatine —> ATP + creatine
This allows for muscles to continue contracting for short time, until mitochondria can supply ATP

Question 23

What happens when phosphocreatine is used up?

Answer 23

Rate of muscle contraction must = rate of ATP production for both AEROBIC/ANAEROBIC respiration

Question 24

Sliding filament theory step 4-8 ?

Answer 24

4. globular heads of myosin molecules bind to sites- form cross-bridges between actin/myosin
5. myosin heads bend/ pull actin filaments towards the centre of the sarcomere - the muscle contracts a small distance
   movement of the myosin heads - power-stroke
6. When myosin heads bend, releases ADP
7. ATP binds to the myosin head—> can detach from actin
8. myosin head acts as ATPase enzyme —> hydrolyse ATP into ADP and Pi ; energy released allows myosin head to return to its original position

Question 25

Sliding filament theory step 9-10?

Answer 25

9. The myosin head now binds to a new binding site on actin filaments
10. myosin heads move again, pulling the actin filaments even closer to the centre of the sarcomere - sarcomere shortens further
    As long as troponin and tropomyosin not blocking the binding sites/ muscle has a supply of ATP,process repeats until the muscle is fully contracted

Question 26

Role of noradrenaline?

Answer 26

Increase HR/BP
Widen pupils

Question 27

PRACTICAL: Monitor Muscle fatigue

Answer 27

1. Attach 2 electrodes to places on muscle you want to record. 3rd electrde goes on INACTIVE point as a control (bony wrist)
2. Switch off any other electrical equipment not needed, as noises interfere with electrical signal from muscle
3. Connect electrodes to amplifier /computer
4. Keep muscle relaxed - straight line on electromyogram
5. Contract muscle - spikes in graph appear as MOTOR units activated to contract muscle
6. Lifting weights increases amplitude of trace —> more electrical signals as more motor units needs to lift weight
   7 continuing to hold the weight- muscle fatigues . On Electromyogram , amplitude of trace increases further (as brain tries to activate more motor units to generate force needed to hold weight up