Nervous coordination Flashcards
Describe the structure of a myelinated motor neurone
Dendrite, axon, cell body, myelin sheath, node of ranvier
Describe resting potential - define
When the inside of an axon has a negative charge and the outside is more positive compared to inside
Explain how a resting potential is established across the axon membrane in a neurone
Pump actively transports sodium out of the axon and K into the axon
This creates an electrochemical gradient - higher K conc inside and higher Na conc outside
This means the neurone is more permeable to K and less permeable to Na
Explain how changes in membrane permeability lead to depolarisation and the generation of an action potential
Stimulus: Sodium channels open and sodium diffuse into the axon down an electrochemical gradient causing depolarisation
Dpolarisation: If threshold reached, action potential is generated. More Na channels open so more Na diffuses
Repolsarisation: Na channels clos and K channels open. K diffuses out of the axon
Hyperpolarisation: K channels slow to close so too many diffuse out
Resting potential: Restored by Na/k pump
Describe the all or nothing principle
For an action potential to be produced, depolarisation must exceed threshold potential
Action potentials produced are always same size at same potential
Bigger stimuli instead increase frequency of action potentials
Explain the passage of an action potential along a non myelinated axon
Action potential passes as a wave of depolarisation
Influx of sodium increases permeability by causing sodium channels to open
Explain the passage of action potential across a myelinated axon
Myelination provides electrical insulation
Depolarisation of axon at nodes of Ranvier
Causes salatory conduction
No need for depolarisation across whole axon
How can damage to the myelin sheath cause slow responses
Less salutary conduction so there is a delay in muscle contraction
Ions leak to other neurones causing wrong muscle fibres to contract
What is the refractory period
Time taken to restore axon to resting potential when no further action potential can be generated
As Na+ channels are closed
What is the importance of refractory period
Action potentials don’t overlap
Limits frequency of impulse transmission
Ensures action potentials have one direction
Factors that affect speed of conductance
Myelination - salatory conduction so impulse doesn’t travel the whole length of the axon
Axon diameter - Bigger diameter means less resistance to flow of ion s
Temp- Increased rate of diffusion of Na and K but proteins could denature if too high
Structure of synapse
Describe transmission across a cholinergic reponse at pre synaptic neurone
Depolarisation of pre synaptic membrane causes calcium channels to open and diffuse into the pre synaptic neurone
This causes vesicles with ACH to fuse with pre synaptic membrane and releases ACH into synaptic cleft
Describe transmission across a cholinergic reponse at post synaptic neurone
ACH diffuses across synaptic cleft to bind to receptors on post synaptic membrane
Na channels open and diffuse into post synaptic non causing depolarisation
Explain what happens to acetylcholine after synaptic transmission
It is hydrolysed by acetylcholinesterase
Products are reabsorbed by the presynaptic neurone
To stop overstimulation - if not removed it would keep binding to receptors, causing depolarisation
Explain how synapses result in unidirectional nerve impulses
Neurotransmitter only released from pre synaptic neurone
Receorots only on post synaptic ]
Explain summation
Addition of a number of impulses
Causing rapid buildup of neurotransmitter (NT)
So threshold more likely to be reached to generate an action potential
Describe spatial summation
Many pre synaptic neurones share one synaptic cleft
Collectively release sufficient neurotransmitter to reach threshold to trigger an action potential
Describe temporal summation
One pre synaptic neurone release neurotransmitter many times over a short time
Sufficient neurotransmitter to reach threshold to trigger an action
Describe inhibition by inhibitory synapses
Inhibitory neurotransmitters hyperpolarise postsynaptic membrane as
Cl channels open, K channels open
This means inside of axon has a more negative charge relative to outside
So more Na required to enter depolarisation
Reduces likelihood of threshold being met
Structure of neuromuscular junction
Similar to synapse except:
Receptors are on muscle fibre sarcolemma instead of postsynaptic membrane and there are more
Muscle fibre forms clefts to store enzyme
Compare transmission across choligernic synapses and neuromuscular junctions
In both - transmission is unidirectional
Choligernic synapse:
- Neurone to Neurone
- Neurotransmitters can be excitatory or inhibitory
- Action potential may be initiated in postsynaptic neurone
Neuromuscular junction
-neurone to muscle
- Always excitatory
-Action potential propagates along sarcolemma down T tubules
Use examples to explain the effect of drugs on a synapse
Some drugs stimulate the nervous system leading to more action potential ie
Similar shape to neurotransmitter
Stimulate release of more neurotransmitter
Inhibit enzyme that breaks down neurotransmitter
Some drugs inhibit the nervous system, leading to fewer action potentials:
Inhibit release of neurotransmitter eg. prevent opening of calcium ion channels
Block receptors by mimicking shape of neurotransmitter
Describe how muscles work
Work in antagonistic pairs → pull in opposite directions
One muscle contracts, One muscle relaxes
Skeleton is incompressible so muscle can transmit force to bone
Describe the gross and microscopic structure of skeletal muscle
Made of many bundles of muscle fibres (cells) packaged together
Attached to bones by tendons
Muscle fibres contain:
Sarcolemma
Sacroplasm
Nuclei
Myofibrils
Sacroplasmic reticulum
Mitochondria
Describe the ultrastructure of a myofibril
Made from 2 types of protein filaments:
Myosin - thick
Actin - thin
Arranged in sacromeres
- Ends - Z line
- Middle - M line
- H - Zone - contains only myosin
Explain the banding pattern to be seen in myofibrils
I-bands - light bands containing only thin actin filaments
A-bands - dark bands containing thick myosin filaments
H zone contains only myosin
Darkest region contains overlapping actin and
myosin
Give an overview of muscle contraction
- Myosin heads slide actin along myosin causing the sarcomere to contract
● Simultaneous contraction of many sarcomeres causes myofibrils and muscle fibres to contract
● When sarcomeres contract
○ H zones get shorter
○ I band get shorter
○ A band stays the same
○ Z lines get closer
Describe the roles of actin, myosin, calcium ions, tropomyosin and ATP in myofibril contraction
- Depolarisation spreads down sarcolemma via T tubules causing Ca2+ release from sarcoplasmic reticulum, which diffuse to myofibrils
- Calcium ions bind to tropomyosin, causing it to move → exposing binding sites on actin
- Allowing myosin head, with ADP attached, to bind to binding sites on actin → forming an actinomyosin crossbridge
- Myosin heads change angle, pulling actin along myosin, (ADP released), using energy from ATP hydrolysis
- New ATP binds to myosin head causing it to detach from binding site
- Hydrolysis of ATP by ATP(hydrol)ase (activated by Ca2+) releases energy for myosin heads to return to original position
- Hydrolysis of ATP by ATP(hydrol)ase (activated by Ca2+) releases energy for myosin heads to return to original position
What happens during muscle relaxation
Ca2+ actively transported back into the endoplasmic reticulum using energy from ATP
Tropomyosin moves back to block myosin binding site on actin again → no actinomyosin cross bridges
Compare the structure, location and general properties of slow and fast skeletal muscle fibres
