nervous conditions and muscles Flashcards
What is the cell body
Contains all the usual organelles
Large amounts of RER for protein synthesis and neurotransmitter production
What is a dendron
Divides into branches
Carries nerve impulses to cell body
What is an axon
Carry nerve impulses away from the body
What is a schwan cell
Surrounds the axon providing electrical insulation
Carry out phagocytosis
Nerve regeneration
What is the myelin sheath
Covering an axon made up of the membrane of a schwan cell
Rich in the lipid myelin
What is the node of ranveir
Between schwan cells where there is no myelin sheath
What is the direction of flow along a neurone
From dendrite to axon
Why does the cell body of a neurone have lots of RER Golgi body and mitrochondria
ATP for moving neurone transmitter vesicle down to synaptic knob
What’s the difference between a sensory neurone and motor neurone
Sensory - cell body above axon
Motor - cell body in between axon
Differences between nervous and endocrine system
Nervous
Uses impulses
Very rapid
Travels to spesific parts of the body
Localised
Short lived
Endocrine
Hormones
Transmissions in the blood plasma
Slow
Travels around the body but targets cells
Wide spread
Long lasting
Slow
Describe the resting potential
3 NA+ are actively pumped out of axon and 2 K+ into axon by sodium potassium pump so more NA+ in the tissue fluid and more K+ in the cytoplasm creating an electrochemical gradient
Due to the gradient NA+ diffuses in and K+ out
Most of the voltage gated sodium channels are closed but potassium ones are open so K+ diffuses out faster than sodium moving in
Tissue fluid becomes possitively polarised and cytoplasm becomes negatively polarised causing some k+ diffuses back into cytoplasm
Equilibrium is reached
Electrochemical gradient is balanced and resting potential is established
Describe the action potential
NA+ channels are open and sodium moves in by facilitated diffusion
If enough NA+ enters the threshold is reached and more gated channels open
Depolarisation
Action potential - at 40mv NA+ shut and K+ open
Proton motive force makes K+ leave
Hyperpolarisation - all channels close but too many potassium leave so cell overshoots resting potential
Sodium potassium pump moves NA+ out and K+ in reestablishing resting potential
Describe action potential passage in the myelinated neurones
A stimuli to threshold causes sodium channels to open. Sodium ions diffuse down the concentration gradient to enter the axon. Action potential reached. The axon membrane is depolarised.
The first action potential causes the opening of the sodium voltage gated channel further along the axon. This is positive feedback. It causes a new action potential and depolarisation.
Behind this region the sodium voltage gates closed and potassium opened
Action potential is regenerated for the 3rd time and the 1st area is returning to its resting potential
What is saltatory conduction
Jumping of action potentials between nodes along the axon
What is the refractory period
Minimum intervals between action potential and therefore between impulses
What is depolarisation
Temporary reversal of charges across the cell membrane of a neurone that occurs what a nerve impulse is transmitted
Structure of a myelinated neurone
Axon is wrapped in a lipid rich layer fatty sheath called myelin
Myelin is made from schwan cells
No action potential is generated in the myelin so it only happens at the node of ranveir
What is the all or nothing principle
What a nerve is stimulated at the synapse Some NA+ ion channels open - NA+ ions diffuse in
If it is below threshold - no action potential
If it is above threshold - rapid opening of NA+ channels so action potential made
How does temperature change speed of propagation
Higher temp gives ions more kinetic energy so they diffuse quicker
How does myelination effect speed of propagation
Action potential travels faster in myelin because it only occurs at the node of ranveir so they jump myelinated area
How does size effect speed of propagation
Width of the axon - larger diameter leads to quicker transmission
What is the refractory period
Once an action potential has been created there is a period is afterwards when further inward movement of sodium ions us prevented because sodium voltage gated channels are closed
No action potential can be generated
What is the purpose of the refractory period
Ensuring action potential is only propagated in 1 direction ( they can only move forward)
Ensuring that action potentials are discrete impulses (gaps)
Limits the number of action potentials in a given time so there can be gaps so stimuli is detected
What is a synapse
The place where the axon of one neurone connects with the dendrite of another or with an effector
Describe how information crosses a synapse
Impulses cause calcium ion channels to open and they diffuse into the synaptic knob
Vesicles move towards and fuse with the presynaptic membrane
Acetylcholine diffuses across synaptic cleft
It binds with receptor on sodium ion channels in the post synaptic membrane
Sodium ion channels open and they diffuse into the postsynaptic neurone
Depolarisation of postsynaptic membrane
If it is above threshold an action potential is produced
How doe a synaptic knob reset
Calcium ions are removed from the synaptic knob by active transport which uses atp produced in the mitochondria. This makes sure the conc of calcium is always higher outside the membrane
Acetylcholine is removed from receptors by acetylcholineterase which hydrolyses acetylcholine which diffuses back into the synaptic knob
Acetyl and choline are synthesised to make acetylcholine to be used in the vesicles again
What is summation
Rapid build up of neurotransmitters in the synapse by either:
Temporal summation - single presynaptic neurone releases neurotransmitters many times
Spatial summation - simultaneous stimulation by several presynaptic neurones
Why summation
Prevents overstimulation
Synapses act as a barrier
Magnifying lots of small stimuli together
Describe inhibition
Presynaptic neurone releases a neurotransmitter that causes opening of potassium channels, this means potassium diffuses out of the cell body so sodium ions diffusing in aren’t enough to reach threshold
Presynaptic neurone realise neurotransmitter which binds to chloride ions opening the channels so chloride diffuses into the cell body making the inside more negative so sodium ions are not enough to reach threshold
Name the parts of the muscle
Tendon
Muscle
Bundle of muscle fibre
Connective tissue
Sheath muscle fibre
Myofibril
Parts of a skeletal muscle fibre cell
Myofibrils, mitrochondria , sarcolemma , sarcoplasmic , nucleus , sarcoplasm
What are the advantages of muscle fibres being multinucleated
Muscle mainly made of protein
Protein synthesis all the way along
Produces MRNA
Describe the myofibril structure
Actin thin filament - tropamin , tropmyosin
Myosin thick filament
Parts of a single myofibril and how they act on contraction
I band - shrinks
A band - stays the same
Z line
H zone - shrinks
Why is it good that there are lots of neuromuscular junctions
Fibres can contract simultaneously and movement is fatser
Structure and role of myosin
Heads protrude
Tail wraps around to form a filament
Does the power stroke and contains atp hydrolase
Structure and role of actin
Long chains of globular proteins which are coiled into a helix
Tropinin is where calcium binds
Tropomiosin - threat wound around an actin
Allows myosin to bind
What is the role of calcium ions
Changes tropomyosin position and uncovers myosin binding site
Activates myosin atp hydrolase
What is the role of atp
Release of myosin head from actin binding site - breaking cross bridges
What is the role of phosphocreatine
Phosphorylase’s atp from adp
Describe muscle stimulation
Action potential arrives at neuromuscular junction and calcium channels open
Calcium diffuses into the synaptic knob
Vesicles move towards the presynaptic membrane
Acetylcholine is released into the neuromuscular cleft
Acetylcholine diffuses across cleft and binds with receptors in the sarcolema
Sodium channels open and sodium diffuses in
Sarcolema becomes depolarised
If threshold is reached action potentials spread to T tubules which are in contact with the sarcoplasmic reticulum
Calcium ions are released
Calcium binds to troponin causing tropomyosin to move exposing myosin bind site
Myosin head binds to actin forming cross bridges
Power stroke occurs ( myosin head swivels pulling actin over myosin)
ATP binds to myosin head and breaks the cross bridge
ATP hydrolase hydrolyses atp to adp + pi causing myosin head to recock
Myosin head binds to actin
Another power stroke
If calcium is present the process carries on
