chapter 13 - neuronal communication Flashcards
What are three characteristics of nervous communication?
- fast
- short lived
- localised
What does the nervous system(NS) breakdown into?
Hint - think about the tree diagram
- NS breaks down into the peripheral NS and central NS
- The peripheral NS breaks down into the somatic NS and autonomic NS
- The autonomic NS breaks down into the parasympathetic NS and sympathetic NS
What is the difference between the peripheral NS and the central NS
- central NS consists of the brain and spinal cord
- peripheral NS consists of all other neurones
What is the difference between the autonomic NS and the somatic NS?
- Autonomic NS controls unconscious control(heart rate)
- Somatic NS controls conscious control (bicep curl)
What is the difference between the parasympathetic NS and the sympathetic NS?
- parasympathetic NS slows things down using a neurotransmitter called acetylcholine (slows heart rate down)
- sympathetic NS speeds things up using a neurotransmitter called noradrenaline (increasing heart rate)
What pathway does a nervous impulse follow?
- receptor
- sensory neurone
- relay neurone
- motor neurone
- effector
What does the sensory neurone consist of?
- A single long dendron
- A single long axon
What does the relay neurone consist of and where is it located?
- many short dendrites
- many short axons
- located in the CNS
What does the motor neurone consist of?
- many short dendrite
- single long axon
- ends with a neuromuscular junction
What is meant by resting potential ?
- There are more positive ions outside the membrane then inside
What is happening at the membrane during resting potential?
- At the sodium potassium pump , 3 Na ions are pumped out and 2 K ions in
- At the voltage gated sodium ion channels, they are closed and membrane is not permeable to Na
- At the potassium ion channel, its open and some K diffuses out down the electrochemical gradient, but does not reach equilibrium because of the positive charge outside
What are the stages of an action potential?
1 - resting potential
2 - generator potential
3 - threshold
4 - depolarisation
5 - repolarisation
6 - hyperpolarisation
What is happening at the membrane during generator potential stage of an action potential?
- weak stimulus
- some voltage gated Na channels open and some Na ions diffuse in
- does not reach threshold
- Na and K pump restores resting potential
What is happens when threshold is reached?
- Many voltage gated Na channels open and sodium diffuses into the axon
- This is a positive feedback
what happens at the membrane during depolarisation stage of an action potential?
- voltage gated Na channels are open and so Na diffuses in
What happens at the membrane during the repolarisation stage of an action potential?
- Voltage gated K channels open and K diffuses out
- voltage gated Na channels close
What happens during the hyperpolarisation stage of an action potential?
- the membrane potential is more negative than the resting potential as the K channels are slow to close
What is the refractory period and why are they useful?
- its the period between repolarisation and hyperpolarisation
- during this period an action potential cannot be started
- ensures action potentials are discrete(do not overlap) and unidirectional
What is depolarisation?
- a process during an action potential where the membrane potential of a neurone becomes more positive than its resting state
- this change in membrane potential occurs as the voltage gated Na channels open allowing an influx of Na ions
What is behind and ahead of the depolarisation phase of an action potential?
- behind is the refractory period
- ahead is the resting potential
what does the propagation of a nerve impulse involve ?
- sodium ions enter a neurone and depolarise it
- the sodium ions diffuse further along the neurone
- the increased positive charge caused by the diffusion of sodium ions open more voltage gated sodium ion channels
- the action potential passes along the neurone
what factors increase the speed of a nerve impulse?
- a greater axon diameter
- a higher temperature
- the presence of myelin sheath
What is salatory conduction and what is the purpose of it?
- its where an action potential jumps between the nodes of ranvier
- it speeds up the transmission of nerve impulses
What produces myelin?
- schwann cells
Along a neurone, where can depolarisation only occur?
- at the nodes of ranvier
What is the pacinian corpuscle?
- receptors that detect pressure, touch and vibrations in the skin
What happens when the pacinian corpuscle is stimulated?
- pressure causes the lamellae to stretch and deform
- stretch mediated Na ion channels open allowing Na to diffuse into the membrane
- The greater the stimulus the more Na ion channels open
What is synaptic divergence and what is the purpose of it?
- when one neurone joins many neurones
- its purpose is to spread the action potential to multiple parts of the body
What is synaptic convergence and what is the purpose of it ?
- its where multiple neurones join one neurone
- the purpose is to amplify the signal
What is the difference between spatial and temporal summation?
- temporal : where the action potentials from a single presynaptic neurone add up overtime
- spatial : the action potentials are added together from multiple presynaptic neurones
What is a synapse and what happens here?
- its a junction between neurones
- a chemical transmission by neurotransmitters
How is an action potential passed along the cholinergic synapse?
- action potential arrives at the presynaptic neurone
- voltage gated Ca ion channels open and Ca ions diffuse in
- vesicles containing acetylcholine(Ach - neurotransmitter)fuse with the presyanptic membrane
- Ach diffuses across the synaptic cleft
- Ach binds with the receptors on the post synaptic membrane
- some Na channels open and Na diffuses in
- voltage gated Na channels open
- an action potential is triggered in the post synaptic membrane
- acetylcholinesterase(enzyme) breaks down Ach and stops the response
- the product of this breakdown is reabsorbed back into the presynaptic knob and recycled
What are the advantages of a reflexes?
- helps organism avoid damage
- very fast
- does not need to be learned(protects infants)
explain how the nerve impulse travels in the knee jerk reflex?
- stretch receptors detect a stretch
- nerve impulse moves along the sensory neurone
- then along the motor neurone
- and then to the effector producing a response
what are the different parts of the brain and what are their functions?
- cerebrum: coordinates voluntary responses
- hypothalamus: autonomic functions(thermoregulation)
- medulla oblongata: autonomic functions (heart and breathing rates)
- pituitary gland: releases hormones and stimulates other glands
- cerebellum: controls balance and posture and also controls muscle contraction
explain the structure of the voluntary (skeletal) muscle
- is striated(bands of actin and myosin)
- long cylindrical cells
- multinucleate
- lots of mitochondria
what are the functions of the skeletal muscle ?
- fast twitch(bicep curl) and slow twitch (posture)
Explain the structure of the involuntary muscle
- thin cells
- uninucleate
- slow twitch
What are the functions of the involuntary muscle?
- control diameter of blood vessels(vasodilation and vasoconstriction)
- control of pupil size
- peristalsis(digestive muscles contract and relax)
Explain the structure of the cardiac muscle
- branched muscle fibres
- uninucleate
- muscle fibres connected by intercelated discs
- some striations
What are the functions of the cardiac muscle?
- pumps blood
- myogenic, meaning it contracts on its own and does not require a nerve impulse
What are muscle fibres made of?
- muscle fibres are made up of myofibrils
- myofibrils contain myofilaments (actin and myosin)
what does the microscopic structure of a skeletal muscle consist of ?
- H zone
- dark bank (A)(consists of myosin)
- light band(I) (consists of actin)
- sarcomere
- m line
- z line
What happens to the structure of the skeletal muscle during a contraction?
- sarcomere gets shorter
- H zone gets shorter
- light band gets shorter
- dark band stays the same
What is a neuromuscular junction?
- its a synapse between a neurone and a muscle fibre
why is a neuromuscular junction different to a cholinergic synapse?
- Acetylcholinesterase is found in pits on the post synaptic membrane
- There is more receptors on the post synaptic membrane meaning an action potential is always generated in the post synaptic membrane
Explain the sliding filament model
- The sarcolemma is depolarised which spreads through the t-tubules and into the sarcoplasmic reticulum
- Sarcoplasmic reticulum releases Ca ions
- Ca binds to troponin changing its shape causing tropomyosin to move away from the binding site
- Myosin heads bind to the binding sites on the actin forming cross bridges
- Myosin heads tilt, thereby moving the actin (power stroke)
- ATP binds to myosin, causing it to detach from the actin
- ATP is hydrolysed to ADP causing the myosin head to resume its original position (head is free to attach further down)
What is ATP used for in the contraction of muscles?
- Changing the shape of the myosin head
- detaches the myosin head
- returns the myosin head to its resting position
- reabsorb Ca ions into sarcoplasmic reticulum by active transport
