M5, C13 Neuronal Communication Flashcards
what are the 2 main branches of the nervous system
CNS - brain and spinal cord
PNS (peripheral nervous system) - neurones that carry impulses to and from the CNS
what 2 parts is the peripheral nervous system divided into
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
what 2 systems is the autonomic peripheral nervous system divided into
what are the neurotransmitters involved
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
for involuntary muscles, describe the cell structure, speed of contraction & fatigue, nervous system that controls it, examples and appearance under microscope
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
for skeletal/voluntary muscles, describe the cell structure, speed of contraction & fatigue, nervous system that controls it, examples and appearance under microscope
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
for cardiac muscle, describe the cell structure, speed of contraction & fatigue, nervous system that controls it, examples and appearance under microscope
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
name the features of a cell in skeletal muscle
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)
describe the structure and function of muscle fibres in skeletal muscles
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
what are myofibrils
what proteins are they made of
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
in myofibrils, describe the different bands that can be seen
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
what is the sliding filament model
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
In the sliding filament model, what happens to each of the bands of the myofibrils during contraction
The light bands become narrower
The Z lines move closer together, shortening the sarcomere
The H zone becomes narrower
Dark band remains same width
What is the structure of myosin (thick bands)
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
What is the structure of actin filaments (thin bands)
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
When a muscle is in resting state what has happened to the actin-myosin sites
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
describe what is happening when a muscle is stimulated to contract
(from the neuromuscular junction to muscle contraction)
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
What happens when a muscle stops being stimulated to contract
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
How is ATP used in muscle contraction
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.
what are the differences between a synapse and a neuromuscular junction (NJ)
-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
what are the similarities between a synapse and a neuromuscular junction (NJ)
- both involve neurotransmitters that have been released by exocytosis
- both have complementary receptors for that neurotransmitters
where does the ATP supply come from for the neuromuscular junction
- aerobic respiration
- anaerobic respiration
- creatine phosphate (the phosphate from this can be added to ADP to make an ATP molecule)
