M5, C13 Neuronal Communication

Question 1

what are the 2 main branches of the nervous system

Answer 1

CNS - brain and spinal cord

PNS (peripheral nervous system) - neurones that carry impulses to and from the CNS

Question 2

what 2 parts is the peripheral nervous system divided into

Answer 2

Somatic - motor neurones carry impulses from CNS to skeletal muscles under CONSCIOUS control

Autonomic - motor neurones carry impulses from CNS to cardiac muscle, smooth gut muscle and glands under UNCONSCIOUS control

Question 3

what 2 systems is the autonomic peripheral nervous system divided into
what are the neurotransmitters involved

Answer 3

Sympathetic - gets body ready for action “fight or flight”. the neurones secreted is noradrenalin

Parasympathetic - calms body down “rest and digest”. neurones secreted are acetylcholine

Question 4

for involuntary muscles, describe the cell structure, speed of contraction & fatigue, nervous system that controls it, examples and appearance under microscope

Answer 4

structure: non-striated, smooth, spindle cell shaped, one nucleus per cell
slow speed of contraction and slow to fatigue
autonomic nervous system
examples: organ walls, blood vessels, iris, uterus
appearance: unstriped, uninucleated

Question 5

for skeletal/voluntary muscles, describe the cell structure, speed of contraction & fatigue, nervous system that controls it, examples and appearance under microscope

Answer 5

structure: lots of nuclei, long, striated
speed of contraction: rapid and quick to fatigue
nervous system: somatic
examples: bulk of body muscle tissue
appearance: stripy, multinucleated

Question 6

for cardiac muscle, describe the cell structure, speed of contraction & fatigue, nervous system that controls it, examples and appearance under microscope

Answer 6

structure: branched, uninucleated, discs between cells, some striations
speed of contraction and fatigue: intermediate speed and never fatigues
nervous system: autonomic
examples: found only in the heart
appearance: some striations, uninucleated

Question 7

name the features of a cell in skeletal muscle

Answer 7

sarcolemma (cell-surface membrane)
sarcoplasm (cytoplasm)
mitochondria
myofibrils (cause contraction)
nucleus (many nuclei per cell)
sarcoplasmic reticulum (endoplasmic reticulum)
T tubules (a fold of the sarcolemma)

Question 8

describe the structure and function of muscle fibres in skeletal muscles

Answer 8

Muscle fibres are enclosed in a plasma membrane called sarcolemma
They contain a number of nuclei and are much longer than normal cells
They make the muscle stronger
Have lots of mitochondria to provide ATP for muscle contraction
Has a modified version of ER called sarcoplasmic reticulum which extends the muscle fibre and contains calcium ions

Question 9

what are myofibrils

what proteins are they made of

Answer 9

myofibrils are long, cylindrical organelles made of protein and specialised for contraction. they are lined up in parallel in the skeletal muscle

actin - thinner filament, 2 strands twisted around each other

myosin - thicker filament, consists of long, rod-shaped fibres

Question 10

in myofibrils, describe the different bands that can be seen

Answer 10

Because of the way the myofilaments are arranged, the myofibril appears to have dark and light bands, giving the muscles a striated appearance.
The dark bands consist of thick filaments (myosin) and some thin filaments (actin).
At the centre of the dark band is the H-zone, where only thick filaments are present.
The light bands, are the regions containing thin filaments only (actin), and are found between the dark bands.
There is a Z-line found at the centre of each light band where the sarcomere distance between each adjacent Z-line

Question 11

what is the sliding filament model

Answer 11

where myosin and actin filaments slide over one another to make the sarcomeres contract
the myofilaments themselves don’t contract

the simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract

Question 12

In the sliding filament model, what happens to each of the bands of the myofibrils during contraction

Answer 12

The light bands become narrower
The Z lines move closer together, shortening the sarcomere
The H zone becomes narrower
Dark band remains same width

Question 13

What is the structure of myosin (thick bands)

Answer 13

They have globular heads that are hinged which allows them to move back and forwards

On the head is a binding site for each of actin and ATP

The tails are aligned together to form the myosin filament

Question 14

What is the structure of actin filaments (thin bands)

Answer 14

2 strands of actin wrapped around each other
a long strand of tropomyosin wrapped around the actin
attached to the tropomyosin are heads called troponin

Question 15

When a muscle is in resting state what has happened to the actin-myosin sites

Answer 15

They are blocked by tropomyosin
This means the myosin heads can’t bind to the actin
So the filaments can’t slide past each other
The muscle can’t contract

Question 16

describe what is happening when a muscle is stimulated to contract
(from the neuromuscular junction to muscle contraction)

Answer 16

1) An action potential arrives at a motor neurone
2) A neurotransmitter diffuses across the cleft and binds to the receptors on the sarcolemma
3) A wave of depolarisation spreads around the sarcolemma down the T-tubules to the sarcoplasmic reticulum
4) Causes sarcoplasmic reticulum to released stored calcium ions into the sarcoplasm
5) The influx of calcium ions triggers muslce contraction. They diffuse into the myofibril
6) Calcium ions bind to the troponin causing it to change shape
7) This pulls the attached tropomyosin out of the actin-myosin binding site on the actin filament
8) This allows the myosin to bind to the binding site
9) An actin-myosin cross-bridge is formed
10) With the addition of ATP, the myosin head which is attached to the actin moves to the side in a rowing action

Question 17

What happens when a muscle stops being stimulated to contract

Answer 17

1) Calcium ions leave their binding sites on the troponin
2) the ions are moved by active transport back into the sarcoplasmic reticulum
3) Troponin molecules return to its original shape so the tropomyosin block the actin-myosin binding site again
4) Actin filaments slide back to their relaxed position which lengthens the sarcomere

Question 18

How is ATP used in muscle contraction

Answer 18

ATP is broken down by ATPase into ADP which releases energy.
This energy is used to move the myosin head which is moved along the actin filament to cause muscle contraction.
The energy is also used to remove the myosin head and position it in another place on the actin.

Question 19

what are the differences between a synapse and a neuromuscular junction (NJ)

Answer 19

-synapse is from a neurone to a neurone
NJ is from motor neurone to muscle

-synapse creates new action potential
NJ makes muscle contraction

-the neurone before the junction on the synapse is round and is called the synaptic knob
the neurone before the junction on the NJ is flat called the motor-end plate

Question 20

what are the similarities between a synapse and a neuromuscular junction (NJ)

Answer 20

• both involve neurotransmitters that have been released by exocytosis
• both have complementary receptors for that neurotransmitters

Question 21

where does the ATP supply come from for the neuromuscular junction

Answer 21

• aerobic respiration
• anaerobic respiration
• creatine phosphate (the phosphate from this can be added to ADP to make an ATP molecule)