Neuronal Communication Flashcards
What is a stimulus
A change in the environment
It can be internal (drop in body temp or blood sugar) or external (seasonal temperature change)
What is the stimulus - response loop
Stimulus > receptor > communication system > Effector > response
What makes a good communication system
-rapid response
-specific response
-covers whole body
-enables cells to communicate with each other
Give the differences between a neuronal and hormonal response
Hormonal
-endocrine
-hormones
-long term
-glands
-ADH
Neuronal
-neurones
-short term
-electrical impulse
-synapses
-short term
What is homeostasis
The maintenance of the constant internal environment
What is the negative feedback loop
Automatic response
-body at optimum condition
-changes away from optimum
-receptor detects change
-communication system informs effector
-effector reacts to reverse change
-body returns to optimum conditions
What is the positive feedback loop
It accelerates response
-at optimum condition
-receptor detects change
-communication system informs effector
-effector reacts to INCREASE change
What is one harmful positive feedback mechanism
-Breathing pure O2 under pressure raises respiratory rate in tissue
- this produces more CO2 raising heart and breathe rate
-this sends more O2 which further raises respiratory rate producing more CO2 leading to hyperventilation
What is one beneficial positive feedback mechanism
During childbirth
-dilation of cervix stimulates anterior pituitary gland to secrete hormone oxytocin
-this stimulates increased uterine contractions which stretches cervix more
-triggers more release of oxytocin
Why control body temperature
-all metabolic reactions are enzyme catalysed
-at low temperatures molecules have less Ke and so collisions are less frequent and reaction rate falls
-at high temperatures lots of collisions so enzymes lose tertiary structure and become denatured
-so it’s to keep the body temperature constant to function at their optimum rate
What is core temperature
The internal temperature of an organism (36-37.5’ in mammals)
Why is core temperature important
Because it is where most vital organs operate
Significant changes in core temperature is dangerous
What is peripheral temperature
Body’s surface temperature that can be allowed to vary in extreme conditions
How do animals control their body temperature
By balancing heat gain against heat loss
What is an ectotherm
Source of gained heat is the environment
They generate little inside their bodies
How does an ectotherm gain heat (behavioural responses)
-By basking in the sun - this is radiation
-By pressing against hot surfaces- conduction
-Contracts muscles or wings
-Turns towards sun
How does an ectotherm gain heat (physiological response)
-dark colours- absorbs sunlight
-alters heart rate- make it beat faster to increase temperature
How does an ectotherm cool down?
-seeks shade
-by convection standing away from ground lose heat currents from air
-wallowing in mud - loses heat by evaporation of water from surface of skin
Give advantages of ectotherm
-Less of their food used in respiration
-More used in growth
-Can survive long periods without food
-Do not use up energy to keep warm
Give disadvantages of an ectotherm
-less active in cooler temperatures
-cannot take advantage of food if available
-More risk of predators as can’t move in cold
What is an endotherm
main source of heat is internal -their own metabolism
How is temperature controlled in mammals
By the thermoregulatory centre in the hypothalamus
What does the skin do if an endotherm is too hot
-Sweat gland secretes fluid on surface of skin which cools them down
-hairs lie flat to reduce insulation and increase heat loss
-Vasodilation of arterioles as they’re close to surface of skin so increased heat loss
What does the gas exchange system do if it’s too hot
-some animals pant increasing evaporation of water from surface of lungs and airways
What does liver do when it’s too hot for an endotherm
Less respiration takes place so less heat released
What does the skeletal muscles do if it’s too hot in an endotherm
Fewer contractions
What does the skin do if it’s too cold for an endotherm
-Less sweat secreted
-Hairs and feathers erect to trapair
-Vasoconstriction - blood directed away from skin surface
What does the gas exchange system do if it’s too cold for an endotherm
Less panting so less evaporation of heat
What does the liver do if it’s too cold for an endotherm
-increased respiration
More energy from food turned into heat
What does the skeletal muscles do if it’s too cold for an endotherm
-more contractions releasing heat
Give advantages of an endotherm
-Constant body temperature regardless of external environment
-activation possible in cooler temperature
-able to inhabit cooler parts of the world
Disadvantages of endotherm
-more food required
-less energy from food can be used for growth
-significant part of energy used to maintain body temperature
What are sensory receptors
Specialised cells that detects change in our surroundings
What is an transducer
Convert energy into electrical energy
What is pacinian corpuscle
A pressure receptor
- found in dermis of skin
-Largest skin receptor
How does the pacinian corpuscle carry out its function
-consists of concentric rings surrounding a nerve ending
-pressure causes the rings to apply pressure on the sensory nerve fibre
-nerve fibre detectsbchange in pressure
-the greater the pressure the greater the frequency of nerve impulse along the neurone
What is the basic structure of neurones
-long - can transmit impulse over long distances
-cell surface has gated ion channels
-cell body that contains nucleus, mitochondria and ribosomes
Describe the sensory neurone
-Long dendron
-Short axon
-AP from sensory receptor to CNS
(direction of impulse is towards cell body)
Describe the relay neurone
-connects sensory and motor neurone
-many short dendrites
-short axon
-within CNS
describe the motor neurone
-long axon
-carries AP from CNS to effectors
-cell body within CNS
(Direction of impulse away from cell)
What is Myelinated neurones
Layer of myelin sheath on neutron
Gaps in the sheath are Rhodes of ranvier the AP jumps from one node to the next
What is non myelinated neurones
They don’t have myelinated
Still associated with Schwann cells
Several neurones wrapped in one loose Schwann cell
AP moves along in a wave
What is an advantage of myelinated neurones
-transmit AP more quickly
-carries signals over long distances
-enables rapid response to stimulus
what is the process of your body detecting pain when touching a pin
-When you touch a pin it exerts a mechanical pressure on your skin
-Pacinian corpuscle detects the pressure changes
-Sodium ion channel widens and sodium ions diffuse in membrane
-Membrane is depolarised
-AP is created
-AP is transmitted along neurones to CNS
why do you see bright light when you rub your eyes
-sensory receptors only detects one type of stimulus
-Rubbing the eyes stimulates the cells in the eys
- Brain doesn’t recognise the stimulus is different
-So perceives the pressure as light
What is the resting potential
-the negative internal electrical potential
(-60mv is the typical)
How is the resting potential achieved
Polarised- negatively charged inside than outside so have a higher concentration of NA+ ions outside the cell so there is a steep concentration gradient across the cell membrane
how is the resting potential maintained
-3 Na+ ions out and 2 K+ ions in
How is a nerve impulse generated
-sodium ion channels open
-sodium diffuses into the cell
-membrane depolarises (less negative thsn outside)
-positive feedback causes nearby sodium ion channels to open and sodium diffuses in
-potential difference reaches x+40
-sodium ions channel close and potassium channels open
-potassium diffuses out making inside of cell more negative (repolarisation)
-The potential difference overshoots as excess of K+ leaves making I drop below 70 resting level (hyperpolarisation)
-the original potential is restored
what is the refractory period and what does it do
-after an AP soodium and potassium ionsare in the wrong place
-So potassium-sodium pumps must restore the ions in the right place
an action potential cannot happen during this
What is the all or nothing law
-AP only occurs if the stimulus causes enough sodium ions to meter the cell to reach the threshold level
Why does the AP only happen at the nodes of ranvier
Because ions cannot diffuse through the myelinated neurones- only the gaps (nodes of ranvier )
What is a synapse
- a junction between 2 neurones
-the gap between 2 neurones is called the synaptic cleft
how does an AP cross the synapse
by the diffusion of a chemical called neurotransmitter
what is the synapses called that use acetylcholine
Cholinergic synapse
How is transmission across the synapse done
-an action potential arrives at the synaptic bulb
-voltage gated calcium channels open
-calcium diffuses into synaptic bulb
-they cause the synaptic vesicles to fuse with the pre synaptic membrane
-acetylcholine is released by exocytosis
-it diffuses across the cleft
-it binds to the receptors on the post synaptic membrane
-sodium ion channels open
-the sodium ions diffuse across the post synaptic membrane into the post synaptic neurone
-a generator potential is created
-a new AP is created in the post synaptic neurone
what is acetylcholinesterase
-the enzyme that breaks down acetylcholine into Ethanoic acid and choline
-it recombines suing ATP
Why do we need synapses
-they act as a one way valve
-one side has vesicles amd the other can only respond to the transmitter
-therefore impulses travel only one way across a synapse
What is summation
Where several neurones meet and their effects can be added up to decide whether impulses are triggered or not
What is excitatory post synaptic potential
Not enough to cause an action potential
What is temporal summation
Series of AP’s from one pre synaptic neurone
What is spatial summation
AP’s from different pre synaptic neurones that contribute to AP in post synaptic neurone
What is inhibitory post synaptic potential
Reduces the effect of summation and prevents AP
Synapses can filter out..
Unwanted lows level signals
what happens after repeated stimulation
-synapse runs out of vesicles contain in the neurotransmitter
-synapse is fatigued and the organism has become habituated
(Habituated = getting used to a smell or noise in the background)
How does nicotine affect synaptic transmission
-it mimics the effect of acetylcholine at some cholinergic synapses
-it binds to the receptors on the postsynaptic membrane of nicotinic cholinergic synapses, causing sodium channels to remain open
-small does of nicotine acts as a stimulant
-prolonged exposure blocks the effect of acetylcholine
-nicotine also stimulates adrenaline and endorphin release
