Topic 6 - Organisms respond to factors in the external or internal environment Flashcards
What is the general outline for how bodies respond to change?
Stimulus receptor central nervous system (brain or spinal cord) effector (muscle for nervous response, gland for hormonal response) response
What two types of response can our bodies have?
hormonal and nervous
Define stimulus
Detectable change in the internal or external environment
Define receptors
Any structure able to respond to a change
Define co-ordinator (CNS)
The ‘switchboard’ connecting information from the receptor to the appropriate effector
Define effector
Causes a response (muscle or gland)
Define response
The output/change in behaviour
With heat on the hand as the stimulus, what happens in the rest of the system?
Heat on hand nerves on hand detect heat message sent to CNS message sent to muscles in arm move hand
Organisms react to stimuli in their environment in different ways, what are the main diffrences?
- The whole organism or only part of it could move in response
- The movement could be directional or non-directional
What does an organisms reaction to its environment enable it to do?
to be better adapted to its environment
What are the types of response?
Kinesis, taxes, and trophisms
What is kinesis / kinetic response?
- Whole organisms
- Alteration in the rate of movement
- In response to a change in the intensity of a stimulus
- Non-directional (not determined by the stimulus)
What is taxes / Tactic Response?
- Movement of the entire organism or cell
- In response to and directed by the stimulus
- Phototaxis = light, Chemotaxis = chemical
- Positive taxis (towards + ) or negative taxis (away from - )
What is tropisms / trophic response?
- Movement of part of a plant
- Directed by the stimulus
- Geotropism, phototropism, hydrotropism
- Growth response
Which responses affect the whole organsim?
tactic and kinetic
Which responses affect part of an organism?
tropic
Describe the processes involved in the transport of sugars in plant stems (5 marks)
At the source, sucrose is actively transported into the phloem via the companion cells. This lowers the water potential in the phloem and water enters by osmosis. This produces a high hydrostatic pressure, causing a mass flow towards roots. At roots, sugars are removed and used in respiration.
What Plant Responses are there?
- Phototropism: response to light
- Hydrotropism: response to water
- Geotropism: response to gravity
Where is IAA produced?
.IAA produced at the apical meristem, at the top of the plant
.Plants do not have a nervous system therefore they use what?
specific growth factors (auxins)
plant growth factors are more descriptive, why?
- Affect growth
- Are made by cells located throughout the plant (not organs)
- Produced in small quantities
- Affect tissues close by and sometimes tissues they released from
What is the main growth factor in plants?
.The hormone indoleacetic acid (IAA) – growth factor causing cell elongation
What is scientific research?
- Observe and try to explain it using prior knowledge
2. Formulate a hypothesis that can be tested experimentally
Darwin’s Evidence for Tropisms: obersvation, hypothesis, and experiment
- Observation: Grasses grown always tilted towards the window
- Hypothesis: Light (stimuli) is detected by the tip of the shoot, leads to tilting response
- Experiment: 5 plants in different conditions, one normal, one with the tip removed, one with the tip covered by an opaque cap, one with the tip covered by a transparent cap, one with base covered by opaque shield, light faced them all in same direction. Only the normal, tip covered by transparent cap and base covered by opaque shield plants bent towards the light. Also the control plant showed smaller cells on the illuminated side and longer ones on the shaded side. This suggested that light affected the tip, causing it to bend towards the light by growing the shaded cells.
Some scientists went on to hypothesis that the response that darwin found in the plants phototropism was a result of:
a. A chemical produced in the tip
b. A electrical signal in the tip
What did boysen-jensen do?
Used two different materials to suggest whether phototropisms used a chemical or electrical signal
They took three plants, with the first they placed a thin barrier of mica on the illuminated side, with the second they placed a thin barrier of mica on the shaded side, and with the third they removed the tip and put a gelatin lock on top then put the tip on top of that. The first plant bent towards the light, he second didn’t, but the third did. This suggested it was chemicals on the shaded side coming from the tip which allowed the growth towards the light.
WHat is Mica?
an electrical conductor that does not allow chemical to diffuse through it
What is gelatin?
conducts chemicals but not electricity
What was Arpad Paal’s experiment?
The tips of two plants were removed then placed back on, but displaced to the side (one each way). It was found that the shoots bend towards the side where no tip is present.
There are two main divisions of the nervous system, what are they?
Central nervous system and peripheral nervous system
What makes up the CNS?
.Brain
.Spinal cord
What makes up the PNS?
.Pairs of nerves from the CNS travelling to limbs and organs – sensory neuron, motor neuron
How are the CNS and PNS similar?
- Both carry electrical message
WHat is the PNS and what does it do?
.Pairs of nerves from the CNS travelling to limbs and organs
.Relays messages from the CNS to the effector
What are the two main divisions of the PNS?
somatic, autonomic
WHat is somatic?
(voluntary) nervous system, conscious and involves the brain
What is autonomic?
(involuntary) nervous system, subconscious – reflex arc
What are reflexes?
Involuntary responses to a stimuli
The importance of reflexes?
.Safety/protection .Immediate (fast) .Innate (not learnt) .Prevent the brain from being overworked by not involving the conscious part .Automatic (unconscious)
Why are reflexes good?
.The brain can focus on complex behaviours
.Escape predators, gain food or mates
what are Reflex Arcs?
The pathway of neurons involved in a reflex action
Key structures of reflex arc
.Stimuli .Sensory neuron .Motor neuron .Effector .Relay/intermediate neuron .Spinal cord .Receptor
Define the key structures of the reflex arc
Stimuli The external or internal environmental change
Sensory neuron The neuron which carries the signal from the receptor to the intermediate neuron
Motor neuron The neuron which carries the signal from the spinal cord to the effector
Effector The muscle or gland which is stimulated to respond
Relay/intermediate neuron Links the message between the sensory and motor neurons
Spinal cord The part of the CNS
Receptor Receives the stimuli
What is a receptor?
.Any structure able to respond to a change
Key points about receptors
- Receive information and pass it to the CNS
- Are specific in what they detect
- Two main components for receiving information
What are the receptors two main components for receiving information?
o Sensory reception gathers information (sense organs)
o Sensory perception is making sense of this information (function of the brain)
What happens to information after it has been gathered by receptors?
.Sensory information must be converted into information that the body understands
.This is done by transducers (converts energy forms)
.Sensory information nerve impulses
.E.g. (a form of energy like heat, light or sound to action or potential)
Examples of receptors
.Pacinian corpuscle (skin)
.Rod and cone cells (eyes)
What does the Pacinian corpuscle respond to?
.Only responds to mechanical pressure
Where is the pacinian corpuscle found?
.Found deep in the skin:
- Soles of feet
- Fingers
- External genitalia
- Ligaments/tendons
As well as a receptor, what does the pacinian corpuscle act as?
a transducer
Describe the pacinian corpuscle
.The sensory neurone leads to a neurone ending
.The neurone ending is surrounded by layers of connective tissue
.This connective tissue contains blood capillaries and viscous gel, and is surrounded by a capsule
Why does the pacinian corpuscle need blood capillaries?
.It needs blood capillaries to supply it with oxygen and glucose so it can respire and produce ATP to survive, and remove CO2
Why does the pacinian corpuscle need a sensory neurone?
.It needs a sensory neurone to transport the signal to the intermediate neurone or CNS
Why does the pacinian corpuscle need a neurone ending?
.It needs a neurone ending to sense when change occurs and so send a signal, it’s in the middle so that even pressure is felt evenly at all angles
Describe how the nerve membrane in the pacinian corpuscle works
.When the nerve membrane is at rest, the stretch mediated sodium channels are very tight and do not allow the passage of molecules – this doesn’t allow the diffusion of Na+ into the cell from the outside
.When pressure is applied the membrane of the nerve ending becomes stretched, this causes the stretch mediated sodium channels to open and so allow the passage of molecules – this allows the diffusion of Na+ into the cell from outside
How does the pacinian corpuscle work?
.Sensory neurone has sodium channel in its plasma membrane called stretch-mediated sodium channel
.Permeability to sodium ions changes when they change shape
.Pressure on skin = pressure on lamellae = pressure on neuron = stretch mediated channels open = sodium influx = generator potential (nerve impulse) occurs
What is the pacinian corpuscle like when no pressure is applied?
.Stretch-mediated sodium channels are narrow
.Sodium ions cannot/few pass through
.A generator potential is not established
Describe how our sight works, how does light turn into an image in our brain?
.Light passes through the cornea which bends it
.Light goes through the pupil and is focused further by the lens
.An image is formed on the light sensitive cells in the retina
.Retina sends an impulses along the sensory neurones in the optic nerve
.The brain converts impulses into pictures
What is the retina?
Innermost part of the eye where light receptors are found
What are the light receptor cells?
The eye has two types of photoreceptors, found primarily at the retina:
- Rod cells
- Cone cells
How are rod and cone cells similar?
Both act as transducers
.Both convert light energy into the electrical energy of a nerve impulse
.Both are specific to different stimuli
How do red and cone cells work?
- Contain a specific pigment
- Pigment is broken down by a specific wavelength of light
- If broken down a message is sent to the brain
What is there more of, rod or cone cells?
rod cells (20:1)
What pigment is present in rod cells?
Rhodopsin
What pigment is present in cone cells?
3 different pigments of iodopsin
Do rod cells see colour or black and white?
Black and white
Do cone cells see colour or black and white?
Colour
Where are rod cells found?
Top and bottom of eye
Where are cone cells found?
Fovea
Which light intensity is required to break down rod cells?
Broken down at low light intensities
Which light intensity is required to break down cone cells?
Broken down at high light intensity
Visual acuity of rod cell
low
Visual acuity of cone cell
high
Neural connections of rod cell
Often share a single sensory neurone (retinal convergence)
Neural connections of cone cell
Own bipolar cell connected to a sensory neurone
To create generator potential the pigment (rhodopsin) inside the rod cells must be broken down, but:
- Threshold value must be exceeded
- Shared neurone ensures an additive effect of each lower light intensity
Describe how blood moves through the heart
Deoxygenated blood vena cava right atrium atrioventricular valve right ventricle pulmonary artery (out the semi-lunar valve) lungs oxygenated pulmonary vein left atrium tricuspid valve left ventricle aorta (and the semi-lunar valve) rest of the body.
Name the parts of the heart (not valves or nodes)
- Right atrium
- Right ventricle
- Left atrium
- Left ventricle
- Pulmonary artery
- Aorta
- Vena Cava
- Pulmonary vein
Two nodes control the heart beat, together they initiate the cardiac cycle, what are they?
.Sinoatrial node (SAN) – the natural pacemaker
.Atrioventricular node (AV)
Describe how the heart is made to beat?
- SAN sends an electrical impulse across the atria, the atria contracts
- The AVN is non-conductive and stops the impulse travelling to the ventricles
- The electrical activity travels to the AVN
- After a pause, the AVN sends an impulse down the bundle of his
- The bundle of his conducts the impulse through the purkinje fibres
- This causes the contraction of the left and right ventricles from the bottom up
Why is the SAN considered the natural pacemaker?
as it sets the electrical output, and so makes the heart pump
Why are the purkinje fibres important?
as they make sure the electrical signal is sent to all the muscle cells so that the heart contracts fully
Where does the ventricle contract from?
The apex
What is the medulla oblongata?
.A cone shaped neuronal mass
.Responsible for involuntary functions
.Contains the cardiac, respiratory and vomiting centres
.Controls breathing, heart rate and blood pressure
What two centres are in the cardiac centre of the medulla oblongata? How are they linked to the SAN?
- Increases HR
o Linked to SAN by the sympathetic nervous system - Decreases HR
o Linked to SAN by the parasympathetic nervous system
What types of receptors are responsible for rate of heart beat?
- Chemical changes in the blood
o (chemoreceptors in the carotid arteries) - Pressure changes in the blood
o (Pressure receptors in the carotid arteries and aorta)
How does the body respond when blood pressure is high?
- Nerve impulse is sent to the centre in the medulla
- The centre sends an impulse via the parasympathetic nervous system to the SAN
- This decreases the rate at which the heart beats
How does the body respond when blood pressure is low?
- Nerve impulse is sent to the centre in the medulla
- The centre sends an impulse via the sympathetic nervous system to the SAN
- This increases the rate at which the heart beats
Describe what chemoreceptors are and where they are?
.Found in the walls of the carotid arteries (serve the brain)
.Detect pH changes in the blood
What are changes in the pH of blood caused by?
- Carbon dioxide in the blood
How does the Medulla Oblongata control blood pH? (6 marks)
.High respiratory rate
.Releasing a lot of carbon dioxide into the blood
.Carbon dioxide in blood decreases the pH
.The change in pH is picked up by the chemoreceptors in the walls of the carotid arties
.A nerve impulse is sent to the cardiac centre in the medulla oblongata
.The centre sends an impulse via the sympathetic nervous system to the SAN
.This increases the rate at which the heart beats
.This means more blood is being pumped round the body, to pick up the extra CO2 and resultantly increase the pH of the blood back to normal levels
What are nerve cells (also called neurones)?
- Highly specialised cells
- Adapted to rapidly carry electrochemical changes (nerve impulses)
- Amongst the largest cells in the body (especially in length)
Draw and label a basic nerve cell
check notes or google
Function of cell body
Contains the nucleus and large amount of rough endoplasmic reticulum. Nucleus holds DNA and controls the cell, large amounts of RER to form neurotransmitters
Function of axon
Collect and carry the nerve impulse away from the cell body
Function of myelin sheath
Multiple cells wrapped around the axon; they increase the speed of the impulse, wrapped around to form Myelin layer
Function of nodes of ranvier
Gaps where there is no myelination, increases speed
Function of shwan cells
Individual cells protect the neurone, provide electrical insulation
Function of dendrite
Extensions of the cell body, carry impulses towards the cell body, increase action potential
Function of dendrons
Extensions of the cell body, thickest part of the branches, they subdivide into dendrites
How are motor neurones different? Why?
- Lots of dendrites, to make sure it gathers as much information as possible
- Axons split into 3 at the end, to make sure a response occurs by carrying the impulse to different places
- Cell body at basic position, to pick up neurone and carry it
- Long axon length, to carry the signal far
- Nerve endings at muscle or gland
How are sensory neurones different? Why?
- Nerve endings in tissue, like skin
- Cell body not at end, mid-way
- Dendrites come off the end in different places, so it can send different messages to coordinate a response
How are intermediate neurones different? Why?
- Short axon
- Lots of dendrites
What is a nerve impulse?
- A self-propagating wave of electrical disturbance that travels along the surface of the axon membrane
Specifically, it is a temporary reversal of the electrical potential difference across the axon membrane
NOT in the neurone
NOT an electrical current
What are the two states of a nerve impulse?
- Action potential
- Resting potential
What is resting potential?
- Negative inside
- Positive outside
What is action potential?
- A nerve impulse occurs when there is a temporary reversal of these charges
- The reversal is then propagated along the axon
- Neurones send messages ________
electrochemically
- Chemicals in the body are _____ charged
electrically
The important ions in the nervous system are:
- Sodium (1+ charge)
- Potassium (1+ charge)
What controls nervous system ions movement?
- Phospholipid bilayer
- Intrinsic proteins
- Gated channels
How is ion movement controlled?
- Phospholipid bilayer
o Non-polar fatty acid tails repel charged molecules - Intrinsic proteins
o Ion channels allow specific ions to pass - Gated channels
o Na+ and K+ gated channels control amount of movement
Value of resting potential
= -65mV
describe the Formation of a Resting Potential
- Na+ are actively pumped out of the axon by sodium-potassium pumps
- K+ are actively pumped into the axon by sodium-potassium pumps
- For every 3Na+ pumped out, 2K+ move in
- There are more Na+ outside (tissue fluid), than there are inside the axon cytoplasm, a chemical gradient is formed
- Due to the gradient, Na+ try to move back in and K+ try to more out, down there concentration gradient
- However, the Na+ gates are shut, and the K+ gates are open
- So only the K+ can move, and so they leave the axon
- At this point the membrane is 100x more permeable to K+
- This causes K+ to diffuse out faster than Na+ can move in, causing the outside of the axon to become positively polarised, and the inside of the axon to become negatively polarised
- But now, due to the massive positive charge outside of the axon (electrical gradient), some K+ are compelled to move back inside, they are attracted to the negative charge and repelled by the positive outside
- Some of the K+ do move back in, but an equilibrium is formed, where there is no more net movement of ions
- The electrical and chemical gradient becomes balanced, and the resting potential is established
• The energy of a stimuli causes ________________________ on the axon membrane
a temporary reversal of the charge
• Resting potential value meaning?
the difference in charge across the membrane
What is the change in charge from resting potential to action potential?
• The temporary reversal causes the charge of -65mV difference in the resting potential to become a +40mV difference
What happens to the membrane when it goes from -60mV to +45mV?
It is depolarised
Where is negative and positive in action potential?
outside negative, inside positive
Voltage-Gated Ion Channels, what are they?
- Channels in the membrane change shape
- Open or close, depending on the voltage across the membrane
At rest, which voltage gated ion channels are open on the axon?
.Some potassium gated channels are open
.Sodium channels are closed
Draw the graph for resting potential to action potential
CHECK NOTES OR GOOGLE
How is an action potential produced and restored along an axon?
- At resting potential (-65mV) the potassium voltage-gated channels are both open and closed, while the sodium voltage-gated channels are closed
- A stimuli causes the sodium voltage-gated channels to open
- The sodium ions move in (facilitated diffusion) down there electrochemical gradient, this causes more sodium voltage-gated channels to open so more sodium ions can move in
- This causes a change in voltage from -65mV resting to +40mV action, depolarisation has occurred
- This new voltage causes the sodium voltage-gated channels to close and the potassium voltage-gated channels to open
- The potassium ions move out (facilitated diffusion), down its electrochemical gradient, this is called repolarisation, this causes more potassium voltage-gated channels to open so more potassium ions can move out
- Too many potassium ions have moved out and the charge has gone past -65mV to -70mV, this is called hyperpolarisation
- As the neurone cannot react to a stimulus when not at resting potential, the sodium-potassium pump pumps 3 sodium ions out and 2 potassium ions in so the charge difference increases from -70mV to the resting potential of -65mV
Describe the passage of action potentials
Passage of an action potential along a non-mylenated neurone
.After initiation of the ‘start’ of an axon, it ‘moves’ rapidly down it
Key Points:
- Nothing physically moves
- The reversal of charge is reproduced
HOw is an impulse passed along an axon in an unmyleinated sheath?
- Sodium outside, potassium inside: polarised (-65mV)
- Influx of sodium ions: reversal of charge (+40mV)
- Acts as a stimuli causing sodium gated channels to open further along: depolarisation
- Behind, sodium gated channels close and potassium open
- Removal of K+ returns membrane to resting potential (-65mV)
The myelin sheath is an electrical insulator, what does this cause?
- Prevents action potentials forming
- Action potentials can only occur at nodes of ranvier
- Results in ‘node hopping’ (saltatory conduction)
Draw the diagram of saltatory conduction
CHECK NOTES OR GOOGLE
Describe and explain saltatory condcution
- Stimuli causes an influx of sodium ions through the open sodium ion gates into the axon (facilitate diffusion)
- Reversal of charges, action potential occurs
- Sodium ions diffuse from a high concentration to a low concentration in the cell
- A build up of positive ions causes the next sodium ion voltage gated channel to open
- Sodium ions diffuse in
- New action potential occurs
- Action potential moves along the axon
Action potential propagation along myelinated axons from what to what?
one node of ranvier to the next node
Key points of saltatory conduction
- Energy is not lost between action potentials
- Each action potential is the same size
What factors effect the speed of an impulse?
Myleination, temperature, diameter of the axon
How does temperature effect the speed of an impulse?
o High temperature increases speed of nervous impulse, particles have more kinetic energy, diffuse quicker, also increased enzyme action, and more energy available for active transport
o Too high, enzymes and proteins denature, doesn’t work
o Low is opposite effect of high
How does diameter effect speed of an impulse?
o Smaller axon causes the ions to leave easily
o Harder to build up ions in the axon
o Harder to establish electrical and chemical gradients
o Membrane potentials are difficult to maintain
What is the refractory period?
The refractory period is the time that it takes for Na+ influx to be possible again.
Where is the refractory period on the graph?
The refractory period is the portion of the graph that leads back to the resting potential.
For an action potential to occur, it needs to reach ________ – if it does not it is called a _______.
a threshold value
failed initiation
Why are refractory periods important?
- Ensures action potentials are in one direction
- Ensures action potentials are discreet (separate)
- Ensures action potentials are limited in number at one time
- The area before the action potential will be in refractory period, so how does this allow the impulse to travel in one direction?
o A new action potential cannot occur
o Axon must be at rest
o Travels in the correct direction (brain or effector)
How is a refractory period discrete? Why is this good?
- Area behind means AP cannot occur
- Refractory period takes time
- Messages sent to the brain are discrete (not muddled)
How can there only be a certain number of action potentials? Why is this good?
- Action potentials are a fixed distance apart
- Cannot occur ‘behind’ one another
- Axon is a fixed length, therefore
o Only a certain number of action potentials will ‘fit’
What is the synapse
The synapse is the point where a neurone communicates with the dendrite of another neurone or with an effector.
Draw and label a diagram of a synapse
check notes
What does the synaptic knob contain? Why are each required?
- Many mitochondria o Release energy for movement of vesicles toward the synaptic cleft o Release energy for protein synthesis - Large amounts of ER o Synthesise chemical messengers (neurotransmitters) - Vesicles containing neurotransmitters o Package up the neurotransmitters o Move neurotransmitters to the membrane
What are neurotransmitters?
Neurotransmitters are:
- Chemical messages
- Specific
- Enable synaptic transmission
The response to the arrival of a neurotransmitter will however depend on what?
- The cell
- The cells location
- The neurone
A synapse that relies on the neurotransmitter acetylcholine, it is made of what?
- Acetyl (ethanoic acid)
2. Choline
Which synapse relies on the neurotransmitter actylcholine?
cholinergic synpase
Describe the sequence of events leading to the release of acetylcholine and its binding to the postsynaptic nerve.
- Action potential in the neurone causes depolarisation of the pre-synaptic neurone which leads to the calcium ion gated channels to open
- This causes an influx of calcium ions into the synaptic knob via facilitated diffusion
- The 2+ charged calcium ions cause a change in the voltage of the synaptic knob and moves the vesicles containing neurotransmitters to the membrane of the synaptic knob
- The vesicles fuse to the membrane
- The neurotransmitters diffuse across the synapse and attach to the neuroreceptors of the post-synaptic membrane
- This changes the tertiary structure of the neuroreceptors, opening them and allowing an influx of tissue fluid – which contains sodium ions – and so causing an impulse if the threshold is met
What are neuroreceptors?
Chemical gated ion channels in the post synaptic neuron membrane
They are:
- Specific, binding site for the neurotransmitter involved
- Usually closed
- When neurotransmitter bind they undergo a conformational change
- Cause the influx of sodium ions
What is acetylcholinesterase?
Acetylcholinesterase is:
- A hydraulic enzyme (hydrolysis)
- Located on the membrane
- Breaks up acetylcholine into acetyl (ethanoic acid) and choline
What happens after hydrolysis of acetylcholine?
- Acetyl and choline diffuse back across the cleft into the presynaptic neurone
- Neurotransmitters are recycled and repackaged
- Generation of a new action potential is prevented
Define neurotransmitter
Chemical messenger released form the pre-synoptic neurone and involved in the communication between adjacent neurones or cells
Define cholinergic synapse
The gap where a neurone that produces acetylcholine sends messages to other neurones, or to muscle cells
Define synapse
A junction between two neurones in which they do not touch but have a narrow gap, across which neurotransmitters cross
Define refractory period
Period during which the membrane of an axon of a neurone cannot be depolarised and no new action potential can be initiated
Define saltatory conduction
The propagation of a never impulse along a mylenated neurone in which the action potential jumps from one node of Ranvier to another
Synapses transmit impulses in ___ direction to a ______ location
one
precise
Synapses prevent ____________
overstimulation
Synapses act as a junction between, allowing what to what?
a. A single impulse to multiple neurones
b. A number of impulses to be combined at a synapse
What is summation?
The additive effect of low frequency action potentials to produce sufficient neurotransmitters to trigger an action potential across the synapse.
What are the two forms of summation?
- Spatial
- Temporal
What is spatial summation?
Different presynaptic neurones come together to trigger one action potential.
What is the number of pre and post synaptic neurones with spatial summation?
o Multiple pre-synaptic neurones at one synapse
How does spatial summation reach the threshold value?
o A single neurone does not release enough neurotransmitter
o Multiple neurones release neurotransmitter
o Threshold is exceeded
What is temporal summation?
Single presynaptic neurone release neurotransmitters many times over a short period to exceed the threshold.
What is the number of presynaptic neurones for temporal summation?
o One neurone per post synaptic neurone
What is the amount of neurotransmitters for temporal summation?
o Low frequency action potentials means they do not release enough neurotransmitter so there is no threshold met
o High frequency action potentials means neurotransmitters are released multiple times over a short period which means the threshold is met
What is an inhibitory synapse?
A synapse in which the nerve impulse in a presynaptic cell results in reduced likelihood of an action potential initiation in the post synaptic cell.
How does an inhibitory synapse inhibit?
- Neurotransmitters diffuse across
- Causes chloride ion channels in the post synaptic membrane to open
- Chloride ions diffuse across the post synaptic membrane
- Membrane becomes more negative than at resting (hyperpolarisation)
How do some drugs create fewer action potentials? with example
o Inhibiting the release of neurotransmitter o Blocking the sodium/potassium channels o For example: Gaba • Inhibits or slows the brain’s function • Promotes sleepiness
How do some drugs stimulate the nervous system?
o They create more action potentials by:
Mimicking the neurotransmitter
Stimulating the release of more neurotransmitter
Inhibiting the break down of neurotransmitter (block the enzyme)
For example:
• Serotonin
o Believed to help regulate mood and social behaviours, digestion, sexual and sleep desire, and function
Define tendon, ligament and cartilage
Tendon – connect bone to muscle
Ligament – connective tissue that connects bone to bone
Cartilage – connective tissue found between bones, a ‘shock absorber’
What are muscles?
- Bundles of fibres
- Different structures
- Different jobs
What is a cardiac muscle?
a. Present in the heart
b. Acts involuntarily
c. Myogenic
d. Strong and continuous contraction
What is a skeletal muscle?
a. Attached to bones
b. Vast majority of muscle
c. Discontinuous contraction
d. Controlled voluntarily
What is a smooth muscle?
a. Involuntary muscle
b. Found in the gut, blood vessel walls, and in the iris of the eye
c. Slow and weak contraction
How do muscles act?
- Receiving a nerve impulse
- Working in antagonistic pairs
o You cannot stimulate the contraction of two antagonistic muscles at the same time - Pulling bones
What is antagonistic?
one muscle (prime mover) contracts and the other (antagonistic) relaxes
What happens in flexion and extension of the arms?
Flexion:
Biceps contracted, triceps relaxed (extended). The prime mover is the biceps.
Extension:
Triceps contracted, biceps relaxed. The prime mover is the triceps.
Structure of skeletal muscle with analogy
Muscles are composed of small units, bundled into progressively larger units. Myofibrils (individual threads) are bundled into individual muscle fibres (string), which are bundled together into a bundle of muscle fibres (thin rope), which are then bundled together to form the whole muscle (thick rope).
What is the structure of skeletal muscles?
- Individual muscle cells are fused together
- Form muscle fibres (myofibrils)
- Lie parallel to each other
- Increases strength
What are the two types of fibres found in muscles?
- Slow twitch fibres
- Fast twitch fibres
How can muscles fibres be grouped?
Group based on two properties:
- Resistance to fatigue
- Speed of contraction
Slow twitch, speed of contraction, power of contraction, type of activity, type of respiration, and example of muscle containing fibre
Slow Low but prolonged Endurance: walking, posture, standing, long distance running Aerobic Calf muscles
Fast twitch, speed of contraction, power of contraction, type of activity, type of respiration, and example of muscle containing fibre
Fast High Intense activity over a short period: weight lifting, sprinting Anaerobic Biceps
Slow twitch fibres adaptations
- Large amount of myoglobin (red molecule that stores oxygen)
- Good supply of glycogen
- Good blood vessel network
- Many mitochondria
- Small diameter (diffusion)
- Tend to be darker in colour
Why is each slow twitch fibre adaptation beneficial?
- Large amount of myoglobin (red molecule that stores oxygen)
o For oxygen for aerobic respiration for energy and ATP - Good supply of glycogen
o For glucose for aerobic respiration for energy and ATP - Good blood vessel network
o For a good supply of oxygen and glucose for aerobic respiration for energy and ATP and removes carbon dioxide from aerobic respiration - Many mitochondria
o For aerobic respiration to take place for energy and ATP - Small diameter (diffusion)
o To allow glucose and oxygen to diffuse in easily, allowing for a good supply of them for aerobic respiration for energy and ATP reduce diffusion pathway - Tend to be darker in colour
o Because of the large amount of myoglobin (a red molecule that store oxygen)
Fast twitch fibre adaptations
- Thicker and more myosin filaments
- High concentration of enzymes involved in anaerobic respiration
- A store of phosphocreatine – provide energy (energy buffer)
Why do fast twitch fibres tire quickly?
- Fewer blood vessels
- Run out of oxygen quicker
- Thicker; larger diffusion distance
Individual myofibrils are fused together into one long cell, what do they share? What is it called?
o Nuclei = multinucleated
o Cytoplasm = sarcoplasm
o Cell membrane = sarcolemma
Why do nucleic need to be dotted all over the sarcoplasm?
- Transcription
- All muscle cells controlled
Which organelle will be in large number in the sarcoplasm and why?
- Mitochondria: ATP for contraction and protein synthesis
- RER: protein synthesis
Myofibrils consist of two types of protein filaments, what are they?
Actin and myosin
Descibe actin
a. Thinner
b. Made up of two strands coiled around each other
Describe myosin
a. Thicker
b. Consists of rod-shaped fibres with ‘bulbed’ heads which project outwards
What do myofibrils consist of?
- Multiple sarcomeres
- Actin and myosin filaments
Why do myofibrils appear stiped? What are the dots?
Banding pattern
Causes myofibrils to appear striped
Thin dots = actin
Thick dots = myosin
What are the two main components of the sarcomere?
- Dark bands
a. Actin and myosin overlap
b. Anisotropic bands (A-bands)
c. Depends on myosin length - Light bands
a. No overlap
b. Isotropic bands (I-bands)
Label a sarcomere
diagram found in booklet
labelled as follows:
- This area appears light, because only thin, actin filaments are present – I-band
- This area appears dark because there is overlapping of both filaments – A-band
- This area, where there is only myosin is present, is called the H-zone
- Z-line
Where is one sarcomere, in terms of z-lines?
One sarcomere is z-line to z-line
What is a neuromuscular junction?
Where a motor neurone meets skeletal muscle fibres
Often there are multiple neuromuscular junctions connected to different muscle fibres, why?
o Multiple fibres stimulated
o Speeds up the response
o Contraction is quicker and more powerful
o Threshold is met
What is the all or nothing principle?
the strength by which a nerve or muscle fibre responds to a stimulus is independent of the strength of the stimulus
How do neuromuscular junctions affect contraction strength?
- Follow the all or nothing principle BUT
o Multiple neurones = one muscle unit
o Slight force = few fibres stimulated
o Large force = multiple fibres stimulated
o Contraction strength will vary
Neuromuscular junctions are always cholinergic synapses, therefore:
- The neurotransmitter is acetyl choline
- The enzyme that hydrolyses the neurotransmitter is acetyl choline esterase
How do action potentials travel to the muscle fibre?
- Action potentials travel into the muscle fibre through:
o T-tubule
o Branch through the sarcoplasm
o To the sarcoplasmic reticulum
o Releases calcium ions from sarcoplasmic reticulum
As well as actin and myosin, there are two other proteins found in muscle fibres - name and describe them
- Tropomyosin o Long and thin fibrous strands o Wrap around the actin filament - Troponin o Globular protein involved in muscle contraction
What is the sliding filament theory?
- The myosin filament has an ADP attached to it as a myosin head. It needs to attach to the binding site on the actin filament, but there is a tropomyosin molecule blocking the binding site.
- Calcium ions (which have diffused into the myofibrils from the sarcoplasmic reticulum) binds to the troponin, causing the tropomyosin to move out of the way of the binding site
- The ADP (myosin head) binds to the binding site on the actin filament, forming cross-bridges
- The ADP (myosin head) changes angle, which moves the actin filament along
- ATP replaces the ADP in the binding site, and is released from the binding site
- ATPase hydrolyses the ATP into ADP, causing the myosin head to resume the normal position
- This means there is a new point of attachment for the myosin head, and so it can bind to the actin again
What is homeostasis?
The maintenance of a constant internal environment.
What does homeostasis control?
- Water level (osmoregulation)
- Tissue fluid
- Oxygen levels
- Temperature (thermoregulation)
- Composition of blood
- Blood sugar levels
5 main stages of feedback mechanisms
Stimuli (change in the internal or external environment) receptor (detects variation) control unit (co-ordinates the response) effector (returns the body to set point) output (returns body to set point) feedback loop (tells receptor about change) stimuli etc.
WHat is thermoregulation?
The control of internal body temperature
What is the difference between an ectotherm and an andotherm?
Ectotherm – maintains a proportion of their heat from sources outside of their bodies (lizards and snakes)
Endotherm – derive heat from sources metabolic activities inside of their bodies (mammals and birds)
What is the hypothalmus?
- The control unit for most responses
- Link the nervous system and the endocrine system via the pituitary gland
- Responsible for the production of hormones
o Temperature regulation, thirst, hunger, sleep, mood, and the release of other hormones within the body
Finish the stages of the feedback mechanism of an increase in temperature
Stimuli (increase in temperature) receptor (skin senses the increase in temperature and sends a signal to the control unit) control unit (hypothalamus) effector (sweat, vasodilation, pilorelaxation) output (reduced body temperature) stimuli (reduced body temperature) etc.
Finish the stages of the feedback mechanism of a decrease in temperature
Stimuli (decrease in temperature) receptor (skin senses the decrease in temperature and sends a signal to the control unit) control unit (hypothalamus) effector (vasoconstriction, shiver, piloerection) output (increased body temperature) stimuli (increased body temperature) etc.
Why is it good that the body has several different receptors?
- Changes can be detected by several different receptors
- The brain has a better picture of what is being altered
- Allows a more informed response to be made
What are the two forms of feedback?
- Positive feedback
- Negative feedback
- Changes can be detected by several different receptors, meaning that …. menaing that ….
- Meaning that the brain has a better picture of what is being altered
- Meaning that a more informed response is made
What is positive feedback?
A deviation from normal conditions is amplified, leading to a further deviation
This increases any change
Examples of positive feedback
- Blood clotting
- Oxytocin causes more contractions
- Adrenaline levels
What is negative feedback?
Initiating corrective mechanism whenever the internal environment deviates from its normal or acceptable level
Returns conditions to the norm
Reverses any change
Where does glucose in our bodies come from?
diet (carbohydrate break down) and liver (glycogenolysis, glycogenesis, and gluconeogenesis)
What is glycogenolysis?
o Glycogenolysis – the breakdown of glycogen into glucose
What is glycogenesis?
o Glycogenesis – formation of glycogen by converting excess glucose
What is gluconeogenesis?
o Gluconeogenesis – production of glucose from glycerol and amino acids (liver)
Why is the pancreas important?
The pancreas produces: - Digestive enzymes o Protease o Amylase o Lipase - Production of hormones o Insulin Decreases blood sugar levels o Glucagon Increases blood sugar levels
What are hormones?
- Chemical messengers
- Secreted from endocrine glands
What do hormones work on?
- Act on target cells
o Cells that have complementary hormone receptors
The second messenger model of hormone actions is used by what type of hormones?
Non-lipid soluble hormones
Where does the second messenger model of hormone actions initiate a response?
inside of cells
Describe how adrenaline works within its second messenger model
- Adrenaline binds to a transmembrane protein receptor within the cell-surface membrane of a liver cell
- The binding of adrenaline causes the protein to change shape on the inside of the membrane
- The change of protein shape leads to the activation of an enzyme called adenyl cyclase, the activated adenyl cyclase converts ATP to cyclic AMP
- The cAMP acts as a second messenger which binds to protein kinase enzyme, changing its shape and therefore activating it
- The active protein kinas enzyme catalyzes the conversion of glycogen to glucose which moves out of the liver cell by facilitated diffusion and into the blood, through channel proteins
What are the islets of Langerhans?
- Hormone producing cells
o α cells – glucagon (larger)
o β cells – insulin (smaller)
Cyclic AMP activates Kinase which converts what?
glycogen to glucose
Insulin and glucagon work in what way?
Antagonistically
Descibbe the negative feedback for Increase in Blood Glucose Concentration –
- Beta cells detect increase in blood glucose concentration
- Secretes insulin
- Binds to glycoprotein receptors
- Activates enzyme inside cell
- Changes tertiary structure of glucose transport protein channel
- Channels open
- More glucose is absorbed by their liver and muscle cell
- Glucose is converted to glycogen and fat
- Blood sugar concentrations decrease
Describe the negative feedback for decerase in blood glucose concentration
- Alpha cells detect decrease in blood glucose concentration
- Secretes glucagon into blood plasma
- Binds to glucagon receptors
- Only liver cells have glucagon receptors so only they respond
- Glucagon binds to target cells
- Activates kinase enzyme inside cell which convert glycogen to glucose (glycogenolysis)
- Gluconeogenesis also occurs, the synthesis of glucose from glycerol and amino acids
- Glucose is released into the blood sugar
- Blood sugar concentrations increase
`
What is diabetes?
- Diabetes mellitus / sugar diabetes
- Chronic disease
- Cannot metabolise carbohydrates/glucose effectively
What does Chronic disease mean?
o Persistent or long lasting
o Or
o A disease that comes with time
What are the two forms of diabetes?
o Type 1
Insulin dependent
o Type 2
Insulin independent
Describe type 1 diabetes
Insulin dependent
Childhood onset
Treat with insulin injections, biosensor, exercise, and diet
Cannot produce insulin
25% of diabetics are type 1
Can be caused by an autoimmune disease, immune system attacks beta cell
Quick developing
Describe type 2 diabetes
Insulin independent
Develops in adulthood (40+)
Treat with carbohydrate intake and exercise, occasionally insulin prescribed, some drugs also slow down glucose absorption
Mostly developed from obesity and poor diet
Glycoprotein receptors lose their responsiveness to insulin or reduced supply of insulin from pancreas
Slow developing
Can go unnoticed as symptoms less severe
What are the symptoms of diabetes?
Very tired, high blood glucose levels, glucose in urine, thirst and hunger, urinate freuqnlty, weigh loss, blurred vision caused by the lends of you eye changin shape
How does doabetes cause tiredness?
o Less glucose intake, less glucose for respiration, less respiration, less energy
How does doabetes cause high blood glucose levels?
o Less glucose intake, it stays in blood fluid
How does doabetes cause glucose in urine?
o High concentrations of urine, it is removed from the body as waste in urine
How does doabetes cause thirst and hunger?
o High concentrations of glucose in blood causes low water potentials and thirst
o Lots of digested carbohydrates removed from body so hungry
How does doabetes cause frequent urination?
o Lower water potential in blood so water moves in by osmosis and removed in urine
What is osmoregulation?
The homeostatic control of water potential in the blood
Key points of osmoregulation
- The balance of water and mineral ions/salts
- Controlled by the kidneys
T or F, - Your kidneys are located just below your belly button
F
T or F, - Your kidneys clean the blood and control the water levels
T
T or F, - The kidneys work alongside the large intestine
F
T or F, The ureter carries urine from the kidneys to the bladder
T
Draw the diagram of a kidney
check notes
What is the nephron?
The filtering unit of the kidney which performs the job of filtering and fluid balance
Description/function of medulla
Inner region made up of loops of Henle, collecting ducts and blood vessels
Description/function of loop of henle
Long hairpin loop extending from the cortex and into the medulla
Description/function of convoluted tubule
A series of loops surrounded by blood capillaries, walls are made up of epithelial cells with microvilli
Description/function of Renal vein
Returns blood to the heart via the vena cava
Description/function of glomerulus
A many branched knot of capillaries from which fluid is forced out of the blood
Description/function of ureter
A tube that carries urine to the bladder
Description/function of cortex
Outer region made up of renal capsules (Bowman’s capsules), convoluted tubules and blood vessels
Description/function of renal artery
Supplies the kidney with blood from the heart via the aorta
Description/function of bowman’s capsule
A cup shaped structure at the start of the nephron, surrounding a mass of blood capillaries (glomerulus)
Description/function of collecting duct
A tube with several distal convoluted tubules from several nephrons empty, increases in width as it empties into the pelvis from the kidneys
A series of stages occur throughout the nephron in the formation of urine, what are they?
- Ultrafiltration
- Reabsorption
- Maintenance of a gradient of sodium ions
- Reabsorption
What forms in ultrafiltration?
- Formation of the glomerular filtrate
Where does ultrafiltration occur?
- At the glomerulus
What is ultrafiltration the result of?
- Result of hydrostatic pressure
Describe the process of ultrafiltration
- Blood enters artery
- Branches into afferent arteriole
- Enter the Bowman’s capsule
- Divide and forms the glomerulus
- Capillaries merge – efferent artieriole
- Leaves via the renal vein
The diameter of the afferent arteriole is greater than the efferent arteriole, the blood is under higher pressure, so it forces anything that is small enough out, forming the filtrate - Hydrostatic pressure builds up
- Pores allow some substances out
In ultrafiltration, what leaves the blood and what remains in?
Out: - Water - Glucose - Urea - Mineral ions In: - Red blood cells - Proteins
How is the Bowman’s capsule adapted?
The movement of this filtrate out of the glomerulus is resisted by:
- Capillary epithelial cells
- Connective tissue (lining capillaries)
- Epithelial cells of the renal capsule
- Low hydrostatic pressure
- Low water potential of the blood
How are podocytes and gaps in the epithelial cells good adaptations for the bowman’s capsule?
- Podocytes
a. Specialized epithelial cells, form gaps, shorter diffusion pathway - Gaps in the epithelial cells
a. Shorter diffusion pathways, easy passage of molecules
The kidneys produce urine by filtration of the blood and ____ _____ of useful substances
selective reabsorption
What is selective reabsorption?
Selective reabsorption: The reabsorption of certain molecules back into the blood, this includes glucose, some ions, and water via co-transport
What is reasbosbred into the kidneys and what is left?
Around 85% of the filtrate is reabsorbed back into the blood, this includes useful ions and glucose, while it leaves waste and urea
How does reabsorption occur, steps and location
- Co-transport
a. Proximal convoluted tubule - Counter current mechanism
a. Loop of Henle - Anti-diuretic hormone
a. Collecting duct
How does co-transport occur?
- Sodium ions are actively transported out of the cell
- Lowers Na+ concentration inside the cell
- Na+ diffuses from the lumen into the cell carrier protein (facilitated diffusion)
- Pull with it another molecule such as glucose (co-transport)
- Molecule concentration increases
- Molecule diffuses into the blood alongside some water
What is the loop of henle responsible for?
Responsible for the reabsorption of water from the collecting duct
Key points of loop of henle
- Concentrates the urine
- Determines the concentration of the urine
- Acts as a counter-current multiplier
What are the two regions of the kidney?
Ascending and descending
What is the counter-current multipleier in the loop of henle?
- Allows salts to be transferred from the ascending limb to the descending limb
- This arrangement is called the counter-current multiplier
What is the difference between the ascending and descenidn gparts of the loop of henle?
- Descending o Into the medulla o Narrow o Thing walls o Highly permeable to water - Ascending o Back to the cortex o Wider o Thicker walls o Impermeable to water
In the counter current multiplier, why is it important the two liquids are in opposite flow?
- Two liquids in opposite direction past one another
o Filtrate in collecting duct meets interstitial fluid with an even lower water potential - Increases the efficiency of salt transfer between the ascending and descending limb
- Maintains a water potential gradient
- Exists the length of the collecting duct
- Results in 8% of water entering the fluid and then the blood
Describe the process of the counter current multipler
- Water leaves the filtrate via osmosis and enters the interstitial space and then the blood capillaries in it
- The water potential lowers (more negative) as it moves into the medulla
- At the same time, Na+ ions are actively transported out ascending limb
- Decrease water potential in the medulla between the two limbs, increasing the concentration and the rate of osmosis
- As the filtrate moves up the ascending at the base, Na+ ions diffuse
- Water cannot leave as the ascending wall is impermeable
- Therefore, the filtrate gets a higher water potential
- This maintains a gradient of water potential with the interstitial space
- The collecting duct is permeable to water so water can leave as he filtrate moves through it
- Filtrate has a much lower water potential, leaving concentrated urine to reach the bladder
What happens at the distal convoluted tubule?
- Active transport of salts
- Maintains optimum pH
- Cells lining have microvilli and mitochondria
Define osmoregulation
Control of water potential within and surrounding cells
Explain why our water levels vary (3 marks)
- External temperature
- Exercise
- Fluid intake
- Salt intake
- Diet
- Drug intake
- Medication
How do we control water levels?
- A hormone (ADH)
- Secreted from the posterior pituitary gland
- Acts on the DCT and CD
- Concentrates the urine
Describe the process which ADH is involved in when the body is dehydrated
- Dehydration
- Decreased water potential of blood
- Osmoreceptors cells in hypothalamus detect change (lose water, so shrink)
- Stimulates neurosecretory cells in the hypothalamus
- Increased ADH production which passes to the posterior pituitary gland
- ADH secreted into the blood
- ADH makes collecting duct walls more permeable, more water is absorbed into the blood
Describe the process which ADH is involved in when the body has too much water
- Too much water
- Increased water potential of blood
- Osmoreceptors cells in hypothalamus detect change (gain water, so swell)
- Does not stimulate neurosecretory cells
- Decrease ADH production which passes to the posterior pituitary gland
- No ADH secreted into the blood
- Less ADH makes collecting duct walls less permeable, less water is absorbed into the blood
How does ADH work?
- Binds to receptors on DCT and CD
- Activates enzyme phosphorylase inside
- Moves aquaporin
Describe the effect of ADH’s presence and absence
No ADH – - Not permeable - More water in fluid surrounding collecting duct - Large volume of dilute urine ADH present – - More permeable - Increased water potential gradient - Small volume of concentrated urine
Explain the responses which are brough about by the release of ADH (5 marks)
- Binds to complementary membrane bound receptors on DCT and CD
- ADH binds but cannot pass as it is insoluble
- Activates enzyme phosphorylase inside (through second messenger model)
- Vesicles contain water permeable channels (aquaporin)
- Vesicles fuse due to the fluidity membrane
- Walls more permeable to water and urea
Why is osmoregulation negative feedback?
- Osmoreceptors in the hypothalamus detect rise in water potential
- Fewer impulse to the thirst center of the hypothalamus
- Fewer impulses to the pituitary gland
- Less ADH is released
How is aquaporin removed, and what happens because of this?
- Cell surface membrane folds inwards
- New vesicles remove the aquaporins
- Wall is less permeable
- More water passes out
Why do you need ATP in the synapse?
- Need ATP to move vesicles in synaptic knob, and to join together acetyl and choline then put it in the vesicles
What does a cell lining the kidney have as adaptations?
thin membrane, large surface area, good blood supply, intrinsic proteins, and mitochondria
