Control And Coordination Flashcards
What are the 5 things which make up the structure of neurons
A) cell body
B)Cytoplasmic processes
C)Axon terminal/presynaptic knob
D)Myelin sheath
E)Nodes of Ranvier
Describe the structure of the cell body in neurons
The cell body has a nucleus and a cytoplasm.
The cytoplasm has many mitochondria, ribosomes, RER and Golgi
Describe the structure of cytoplasmic processes in neurones
Thin, cytoplasmic extension of cell body
1) Dendrites
* Carry impulses towards the cell body
2)Axons
*Carry impulses away from the cell body
Describe the structure of the axon terminal/presynaptic knob in neurones
Has many mitochondria, synaptic vesicles containing voltage gates Ca2+ channels
Part of a synapse= junction between neurones/muscles
A synapse also includes:
*Synaptic cleft=gap
→has enzymes to break down neurotransmitters
*postsynaptic membrane
→has receptor proteins for neurotransmitters
What is the function of the myelin sheath?
Insulates axons of many neurones and speeds up conduction of nerve impulses.
What is the myelin sheath made of?
Made of Schwann cells.
Schwann cells have a nucleus and consist of layers of cytoplasm and plasma membrane spiraling around the axon.
What are the Nodes of Ranvier?
Gaps between Schwann cells where there is no myelin.
What are the three types of neurones?
- Sensory neurone (afferent)
- Motor neurone (efferent)
- Intermediate / relay neurone
Characteristics of sensory neurones?
Longer sensory axon / dendron and shorter axon.
Characteristics of motor neurones?
Shorter dendrites and much longer axon.
What is the role of intermediate / relay neurones?
They connect sensory and motor neurones.
What is a common feature of all neurones?
They have a cell body, dendrites, and an axon.
What is the Reflex Arc?
Pathway where impulses are carried along during a reflex action.
E.g. knee jerk reflex, sneezing.
What are the advantages of the Reflex Arc?
Fast,
automatic, involuntary, without conscious thought,
innate/instinctive, response is always the same
and protects from harm.
What are impulses?
Brief changes to the distribution of electrical charge across membrane (aka membrane potential)
What is the resting potential of a nerve cell?
At rest: more negatively charged on inside than outside
Resting potential = -70mV
What happens when impulses are formed?
More positive on inside than outside
What is the action potential or depolarization value?
Action potential is a brief change in the potential difference from -70mV to +30mV across the cell surface membranes of neurones and muscle cells caused by the inward movement of sodium ions
What is the role of sensory receptor cells?
- Detect stimuli
- Act as transducers
How do sensory receptor cells respond to stimuli?
Receptors are specific to one type of stimulus, such as chemical, light, heat, sound, or pressure.
What is the function of transducers in sensory receptors?
They convert stimulus energy to electrical energy and produce generator/receptor potential.
What happens after a generator potential is produced?
The impulse is passed along the sensory neuron.
What are taste chemoreceptor cells?
Sensory receptors that respond to chemical stimuli.
Different chemoreceptors are specific for different chemicals=diff tastes
How do taste chemoreceptor cells function?
e.g. NaCl
1. Na+ ions diffuse into cell via microvilli
→Increase in positive charge inside cell
2. Membrane depolarised
→receptor/generator potential generated
- Voltage gated Ca2+ channels open
→Ca2+ enter cell
- Trigger movement of vesicles containing neurotransmitters
→ exocytosis occurs
→ neurotransmitter released
- Neurotransmitter stimulate action potential/impulse in sensory neuron
→ send impulse to taste Centre in brain
What occurs after the membrane of a taste receptor cell is depolarized?
A receptor/generator potential is generated.
Describe the transmission of action potential
- Resting potential-70mV
- Depolarisation-70mV->+30mV
- Repolarisation +30mV->-70mV
- Hyperpolarisation/Refractory period less than-70mV
Describe what resting potential is and how it is maintained
At rest=no stimuli, no impulses formed and transmitted
Inside of axon more negatively charged than outside
Neurone is polarised and maintained at -70mV
How is a resting potential maintained?
1. Na+/K+ pump
2. More K= channels open than Na_ channels
Describe how the Na+/K+ pump helps to maintain a resting potential gradient?
3 Na+ pumped out, 2K+ pumped in
ATP needed
Axon phospholipid bilayer impermeable to K+/Na+
Electrochemical gradient is set up=difference in both charge and chemical ions across membrane
-> so K+ diffuse out, Na+ diffuse in
->via channel proteins
Describe how more K+ channels open than Na+ channels helps maintain resting potential
Membrane more permeable to K+ than Na+
More K+ leaves than Na+ enter
Leaking K+ is responsible for resting potential
Inside becomes relatively more negative than outside Neurone
P/S: these channel proteins are open all the time. But voltage gated K+ and Na+ channels are closed.
Describe what happens during depolarisation (-70mV->+30mV)
- Voltage-gated K+ channels remain closed
- Voltage gated Na+ channels open
→Channels change shape when membrane potential changes when action potential arrives from previous section
*Na+ enter cell
*Membrane becomes less negative/depolarised →+30mV
→Action potential is generated
*size of action potential is fixed at +30mV
*the higher the strength/intensity of the stimulus, the higher the frequency of action potentials
*also-the more neurones are depolarised
Describe what happens during repolarisation (+30mV->-70mV)
- Voltage gated Na+ channels close
- Voltage gated K+ channels open
*K+ move out of cell
*inside becomes more negative/repolarised->-70mV
What is a voltage-gated channel protein:
A channel protein through a cell membrane that opens or closes in response to-changes in electrical potential across the membrane
Describe what happens during hyper-polarisation/refractory period (less than -70mV)
- Voltage-gated Na+ channels remain closed
- Voltage-gated K+ channels close
*but slight delay so excess K+ ions have moved out of axon
When membrane is hyperpolarized=refractory period
*Membrane is insensitive to any depolarisation
*No action potential can be generated
→Function=ensure one way transmission
*due to the refractory period, action potentials are discrete events/do not merge into one another
→Function:Length of refractory period limits maximum frequency of action potentials
E.g. longer refractory period=lower maximum frequency
Describe the return to resting potential (-70mV) after hyperpolarisation/refractory period
*Na+/K+ pump acts again
→Membrane can be depolarised again
→Action potential can be generated again
Describe how action potentials are transmitted along a non-myelinated axon?
- depolarisation spreads to next region due to movement of positive ions to negative regions
→A “local circuit” is set up
→This causes voltage -gated Na+ channels to open in the next region
→Causing next action potential
How are action potentials are transmitted along a myelinated axon?
With the myelin sheath, there is an increased speed of conduction.
Myelin insulates axon
→does not allow movement of ions
→Lengthens local circuits
*Passage of ions only at nodes of Ranvier
→Action potential/depolarization only at nodes of ranvier
→Local circuit is set up between nodes
→Action potential “jumps” from node to node
→This is called saltatory conduction
Explain saltatory conduction
Saltatory conduction is the faster transmission because myelin sheath insulates axons
Local circuit is set up between nodes
Action potential jumps from node to node
What is threshold potential (-50mV)
*minimum potential needed for action potential to be generated
→only depolarisation that reaches threshold produces an action potential
*If depolarisation <-50mV, action potential is not generated
→only local depolarisation occurs
*Only if depolarisation >=-50mV action potential is generated
→Size of action potential is fixed at +30mV
→All or nothing law
What are the roles of synapses
- Ensure one way transmission.
- Allow interconnection of nerve pathways.
- Involved in memory and learning.
- Filter out low level stimuli.
Describe how the synapses ensure one way transmission
Synapse ensures one way transmission as the receptors and neurotransmitter vesicles are only on pre-synaptic neuron.
Describe how the synapses allow interconnection of nerve pathways
The synapse allow the interconnection of nerve pathways because nerve impulses can diverge/integrate and allow wider range of behaviour/action in response to a stimulus.
Describe how the synapses are involved in memory and learning
Synapses are involved in memory and learning due to new synapses being formed
Describe how synapses filter out low level stimuli
Weaker stimulus cause release of low quantities of neurotransmitters
No impulse generated in post synaptic neuron ➡️brain
Prevent brain from being overloaded with sensory information
In normal conditions where is the concentration of K+ and Na+ in the axon higher?
Na+ concentration higher outside of axon and lower inside of axon
K+ concentration lower outside axon and higher inside axon.
Describe the cholinergic synapse
Neurotransmitter = acetylcholine (ACh)
1. Action potential reaches presynaptic membrane
2. Voltage-gated Ca2+ channels open
→Presynaptic membrane becomes more permeable to Ca2+
→Ca2+ ions enter pre-synaptic neuron
3. Vesicles containing ACh move towards and fuse with presynaptic membrane
→Exocytosis occurs
→ACh released into synaptic cleft
4. ACh diffuse across synaptic cleft
5.ACh binds with receptor proteins on post synaptic membrane
6. Receptor proteins change shape and Na+ channels open
→Na+ enter post synaptic neuron
* Postsynaptic neurone depolarized
* Action potential is generated
*As long as ACh binds with receptors, Na+ channels will stay open
→Continuous transmission of action potential
→Can cause synaptic fatigue/paralysis
7. ACh breakdown by acetylcholinesterase at synaptic cleft
ACh →acetate and choline
ACh is recycled (ATP needed)
*Depolarisation stops in post synaptic membrane
→Stop continuous action potential
Describe the striated muscles
Striated=striped under microscope
Attached to bones by tendons
Many Long, cylindrical muscle fibres
→Multinucleated
→Each muscle fibre is made up of myofibrils
Muscle fibre
Muscle fibres have=
*Plasma membrane = sarcolemma
→Sarcolemma infoldings= transverse system tubules ( T-tubules)
→ Can conduct action potentials
*Cytoplasm=sarcoplasm
→ Many parallel myofibrils
→ Fibres are Multinucleated
→ Many mitochondria
*Specialised ER=sarcoplasmic reticulum
→ have protein pumps
→ have lots of Ca2+
What are the two type of myofilaments:
*Thick filaments = made of myosin
→Fibrous protein with globular protein head
→ Attached to M line
*Thin filaments=made of actin
→Chain of globular protein molecules
→Has binding sites for myosin
→ Troponin and tropomysin is attached to actin
→ Attached to Z line
What is a sarcomere
Sacromere is the repeating unit of myofibril
It is the interdigitation of thick and thin filaments and gives striated appearance.
Describe the structure of the sarcomere
*Myosin attached to the M line
*Actin attached to the Z line
*Sarcomere = between 2 Z lines
*Describe between the Z line decreases during muscle contraction
*I band = light band
*Only thin filaments
*Shortens during muscle contraction
H band = light band at centre of dark band
*Only thick filaments
*Shortens during muscle contraction
A band= dark band
*Overlap of thick and thin filaments
* Stays the same during muscle contraction
What is a neuromuscular Junction?
A synapses between a motor neuron and a muscle
Give an overview of muscle contraction
Muscle contraction begins at neuromuscular junction
→Cholinergic synapse between a motor neuron and a muscle fibre
*Terminal knobs of motor neurone = motor end plate
* Neurotransmitter = acetylcholine (Ach)
What is the name of the four steps that must occur for a muscle contraction
- Cholinergic synapse of neuromuscular junction
- Depolarisation and Ca2+ channels open
- Troponin and tropomyosin
- Sliding Filament model
Describe the role of Cholinergic synapse of neuromuscular junction
*Action arrives at the pre-synaptic membrane
* gated calcium ion channels open
* Calcium ions enter presynaptic knob
- vesicles containing ACh fuse with pre-synaptic membrane
*ACh released by exocytosis into synaptic cleft - ACh diffusers across synaptic left
*ACh bind to receptors on sacrolemma (muscle cell membrane)
*Na+ channels open
*Na+ ions enter sarcoplasm of muscle cell
*Sacrolemma depolarised
Describe the role of depolarisation and calcium ions in muscle contraction
- Depolarisation and Ca2+
*Depolarisation spread via T-tubules →sacroplasmic reticulum (ER)
*Sacroplasmic reticulum depolarised
*Voltage gated Ca2+ channels open
*Ca2+ diffuse out from sacroplasmic reticulum →sarcoplasm
*Ca2+ initiates muscle contraction
Describe the role of troponin and tropomyosin in muscle contraction
When muscle is relaxed:
* Troponin = attached to tropomyosin
* Tropomyosin = blocks myosin-binding sites on actin
When muscle contracts:
*Ca2+ in sarcoplasm bind to Troponin
→Troponin changes shape and moves tropomyosin
→ Exposes myosin-binding site on actin
→ Allows myosin head to attach and form cross-bridge almost with actin
Describe the role of the sliding filament model in muscle contraction
1) Myosin head with ADP and Pi form cross-bridges with actin
→Pi is released
2) Myosin head tilts and pull actin
→ Power stroke moves actin towards M line
→ Myofibril/sacromere shortens
→ ADP released from myosin head
3) ATP binds to myosin head
→ATPase hydrolyses ATP into ADP and Pi
→ Myosin head lets go of actin
→ Myosin moved back to original position
4) Process repeated at site further along actin molecule
Sarcomere shortens during muscle contraction
* H band shortens
* I band shortens
*A band remains the same
What happens when action potential stimulation stops during muscle contraction?
Action potential stimulation stops
Calcium ions is actively pumped into sacroplasmic reticulum
→ calcium ions do not bind troponin on actin filament
→ tropomyosin moves to block myosin-binding sites on actin filament
→Filaments slide back to original position
→ Muscle relaxes
What are the sources of ATP for muscle contraction?
Muscles use a lot of ATP and only a small amount of ATP is present in muscle
More ATP is synthesis by
1. Aerobic respiration in mitochondria.
2.Lactate pathway in sarcoplasm
- Creatine phosphate in sacroplasm
* immediate source of energy once ATP is used up
Creatine phosphate + ADP ⇌ Creatine + ATP
Creatine → blood plasma →ultrafiltration @ kidney → urine
*Reversible when the demand of ATP reduced
*If not, Creatine converted to creatinine and excreted in urine
