response to internal and external environments

What are animals’ (invertebrates) behavioural response?

Innate behaviour, which is inherited and controlled by their genetic makeup

What are the two types of response movement made by animals?

Taxis - directional movement towards (positive) or away (negative) from a directional stimuli

Kinesis - non directional (random) movement in response to a intensity stimuli

How is turning affected in a more unfavourable environment?

Less turning at an increased speed

How is turning affected in a more favourable environment?

More turning at a slower speed

what are two different types of kinesis?

• orthokinesis - change in the speed of movement

• Klinokinesis - change in the rate of turning

What are the three main stimuli that plants are sensitive too?

Light , moisture and gravity

What are tropisms?

Growth responses to stimuli

What hormone causes these tropisms?

Auxin (IAA)

How do tropisms work?

• auxin made in tip and passes down to tip of root

• This depends on the distribution of exposure to the stimuli

• e.g IAA speeds up cell growth in shots but slows cell growth down in roots

• This results in a negative / positive tropism

what is phototropism?

Growth movement in response to light

What is hydrotropism?

Growth movement in response to water

What is geotropism?

Growth movement in response to gravity

How is phototropism measured in plants?

In a clinostat - where plant slowly turns to be exposed to light at all sides

What are the 5 growth factors in plants?

• auxin (IAA) → promotes shoot growth due to phototropisms

• Ethane → gas released from ripening fruits, stems, ageing leaves and flowers

• Gibberellins → regulate growth and influence various development processes e.g germination and flowering

• Cytokinins → chemicals that promote cell division

• ABA → growth inhibitor

What is a stimulus ?

Change in the internal or external environment

What does a receptor do?

Detect change e.g the chemoreceptors eyes and ears

What does a co ordinator do?

Controls responses e.g brain

What does an effector do?

Brings about the response e.g muscles and glands

What is a response?

The reaction to a stimulus

What are the steps of responding to a stimulus in the central nervous system?

1. Stimulus

2. Receptor (sensory neurone)

3. Relay neurone (co ordinator)

4. Effector (motor neurone)

5. Response

What is the structure of a neurone?

What is the role of the sensory neurone?

Carries electrical impulses from receptor to CNS

What do motor neurones do?

Carry electrical impulses from CNS to effector organ

What do relay neurones do?

Carry electrical impulses between sensory and motor neurons

What do human receptor cells do?

• act as transducers converting energy of stimulus into electrical energy, generating a nerve impulse from the sensory neurone to CNS

• E.g chemoreceptors , photoreceptors

What are the three different reflex actions?

• automatic - without thought

• Involuntary - uncontrollable

• Stereotyped - protect from harm

What is a hormone?

Steroids or proteins that are chemical messengers

what’s the difference between non steroid and steroid hormones?

• non steroid - specific protein receptors on surface of target cells

• Steroid - specific protein receptors in the targets cytoplasm and are lipid soluble

What are the differences in nervous and endocrine systems and local chemical mediators?

Nervous

• communication by electrical impulses

• Response is fast and short lived

Endocrine

• communication by chemical messengers (hormones)

• Responses are slower and often long lasting

Mediators

• communication by chemicals

• Resonse quicker than hormones and lasts as long as the chemical is secreted

how does the skin respond to mechanical, thermal and chemical stimuli?

Sensory receptors transform mechanical, thermal and chemical energy into impulses that travel to the brain

What receptor responds to mechanical stimuli in the skin?

Pacinian corpsucles

How are each Pacinian corpsucles structured?

• Myelin sheath connects to a nerve fibre which is surrounded by concentric layers of lamellae

• the lamellae is separated by gel

How do Pacinian corpsucles respond to stimuli e.g pressure?

• sodium channels open allowing Na+ to diffuse in by facilitated diffusion

• This creates a nerve impulse

• these charged ions moving into the channels creates a generator potential (inside of nerve becomes less negative than the outside)

What is the role of the sclera, fovea, retina, iris, and chloroid in the eye?

• sclera → outer layer of eye that maintains shape

• Fovea → has great density of photoreceptors

• Iris → controls the amount of light entering the eye by contracting to prevent light from entering and damaging cells in the eye

• Chloroid → contains blood vessels that supply the retina, and black pigments to prevent reflection

What wavelengths of light is the human eye sensitive to?

360-780nm is the visible spectrum

What are the two types of human photoreceptors?

Rods and cones

How are rods and cones different?

• Rods have a rod shape end section containing rhodopsin pigment

• Cones have cone shaped end section containing iodospin pigment

How do photoreceptors work?

• light enters eye and hits the photoreceptors

• Light absorbed by the pigments, causing them to become bleached

• This leads to a chemical change, altering the permeability of the cell membrane to sodium ions

• This creates a generator potential, leading to nerve impulses being send along a bipolar neurone if the threshold potential is reached

• This neurone connects the photoreceptors to the optical nerve, which takes impulses to the brain

What is visual acuity?

(Resolution) the ability to tell apart points that are very close together

What is visual acuity like in rods and cones?

• Rods → low visual acuity as there are many rods joined to the same bipolar neurone → produced black and white image with fuzzy edge in little light

• Cones → high visual acuity because only one cone joins to one bipolar neurone → produces coloured and sharp images in bright light

What is the trichromatic theory of colour vision?

• each of the three types of cone (red, green and blue) have different sensitivities to light, but the ranges of sensitivities overlap, meaning wavelengths stimulate at least 2 types of cones

• If all three are stimulated, impulses are interpreted as white light

What is the structure of a neurone?

What is the term for the gap between two neurones?

The synapse

What is meant by a myelinated neurone?

• neurones that have an insulating cover from the myelin sheath

• The myelin sheath is made up of Schwann cell phospholipid membranes

• This prevents the movement of water soluble charged ions from entering by facilitated diffusion

What is meant by resting potential?

The difference in charge across a resting neurone membrane (when there is a net positive charge on the outside (high cons of sodium ions) compared to the inside (high conc of potassium ions))

What two mechanisms maintain the potential difference?

• sodium-potassium pumps by active transport

• Differential permeability by facilitated diffusion

How does the sodium potassium pump work?

• Using ATP every turn

• The pump moves 3 sodium ions out and 2 potassium ions in via active transport for every turn

• This caused the inside of the membrane to become negatively charged compared to the outside

How does differential permeability work?

• sodium and potassium ions move by facilitated diffusion through axon membrane using their own specific channel proteins

• Axons membranes contain more potassium than sodium channels, meaning more potassium ions move out than sodium ions in

• Therefore the inside of the membrane becomes negatively charged in comparison to the inside

What is the generator potential?

• detected stimulus causes the excitement of the cell membrane, making it become more permeable

• So, more ions move in and out

• This changed the potential difference

What is meant by the all or nothing nature of the action potential?

• If the generator potential is large enough, it will trigger an action potential if the generator potential reaches the threshold level

What is depolarisation?

• impulse passing along an axon causes the resting potential to be momentarily reversed

• Causing a sudden change in the inside becoming positive compared the outside (depolarisation of the membrane)

• This happens because sodium channels open, allowing sodium to enter the axon

What is repolarisation?

• depolarisation leaves the action potential to be 40mV

• This caused the sodium channels open to close and potassium channels to open, causing potassium to diffuse out

• When the inside returns to resting potential of -70mV, potassium channels close

In summary, what is the 7 stages of the transmission of impulses?

1. Resting potential of -70mV

2. Depolarisation → neurone stimulated, causing sodium channels to open, allowing sodium to diffuse in to axon

3. Depolarisation → inside of membrane becomes more positive than the outside and localised electrical current created which moved the impulse along the axon

4. Repolarisation → action potential reaches 40mV, causing potassium channels to open

5. Repolarisation → potassium leaves axon and inside of membrane becomes less negative than outside

6. Refraction period → potassium channels close, but slower than the sodium channels once the impulse has passed

7. Axon membrane returns to resting potential of -70mV from the action of sodium potassium pump and differential permeability

What is summation?

• Post synaptic neurones receive impulses from pre synaptic cells

• the neurones response depends on the sum of all the potentials it recieves

What is spatial summation?

• neurotransmitter is released, diffusing into the synapse and binding to receptors on the postsynaptic neurone

• Caused sodium channels to open, creating an action potential

What is temporal summation?

• One impulse arrives when there is only a small amount of neurotransmitter in the synaptic cleft

• Causes post synaptic knob to depolarise, but threshold value is not reached so no action potential is sent along postsynaptic neurone

What factors affect the speed of nervous transmission?

• mylenation

• Axon diameter

• Temperature

What is myelination?

• myelin sheath provides insulated on neurones due to it being made up of Shawn cells, which are phospholipid membranes

• This speeds up nervous transmission

How does myelination speed up nervous transmission?

• there are nodes of ranvier inbetween Schwann cells, where sodium ion channels are concentrated

• Depolarisation happens at the nodes, where the neuron conducts electrical charge to depolarise the next node

• Allows the impulse to jump from node to node (saltatory conducition)

How does the diameter of the axon determine speed?

• greater the diameter, the faster the speed

• Myelinated axons conducts faster than non myelinated

How does the temperature of the axon determine speed?

• higher the temp, the more kinetic energy, the faster the conductions

• Too high temperature causes enzymes to denature so no impulses are conducted

How do inhibitory drugs impact nervous transmission?

• they block the receptor site on the postsynaptic membrane, or blocking the release of neurotransmitters

• This prevents depolarisation

• E.g atropine competing with acetylcholine

How do excitatory drugs impact nervous transmission?

• bind to receptor site to mimic the transmitter

• Caused more frequent depolarisation

• E.g nicotine mimics acetylcholine, increasing the effect of dopamine

How is heart beats controlled?

1. Impulses produced by sino-atrial node (SAN) conducted through atria, stimulating atria to contract (atrial systole)

2. Impulses stimulate AV node at base of atria

3. Impulses from AV node pass down the bundle of His, which are fibres that seperate into the left and right ventricles

4. These fibres spread through the walls at the base of the ventricles

5. Purkinje fibres carry impulses up through the walls of the ventricles

6. Impulses from purkinje fibres cause beneficial muscles to contract from base upwards (ventricular systole)

What is the role of baroreceptors and chemoreceptors?

• baroreceptors detect change in blood pressure

• Chemoreceptors detect chemical changes in the blood

How do blood pressure stimuli detected by baroreceptors cause increased or decreased heart rate?

• baroreceptors detect high pressure → impulses sent to medulla → impulses sent along parasympathetic neurone → acetylcholine secreted, which binds to SAN receptors → heart rate slows down to reduce blood pressure

• Baroreceptors detect low blood pressure → impulses sent to medulla → impulses sent along sympathetic neurone → noradrenaline secreted, which binds to SAN receptors → heart rate speeds up to incredible blood pressure

How do blood o2, co2, or pH levels stimuli detected by chemoreceptors cause increased or decreased heart rate?

• high blood o2, low co2, high pH detected by chemoreceptors → impulses sent to medulla → impulses sent along parasympathetic neurone → acetylcholine secreted, which binds to SAN receptors → heart rate decreased to return levels to normal

• Low blood o2, high co2, low pH detected by chemoreceptors→ impulses sent to medulla → impulses sent along sympathetic neurones → noradrenaline secreted, which binds to SAN receptors → heart rate increased to return levels back to normal

What are the three types of muscles?

• smooth muscle → contracts without conscious control → found in walls of internal organs

• Cardiac muscle → contracts without conscious control → found in heart

• Skeletal muscle → is a voluntary muscle → e.g biceps and triceps to move lower arm

What can muscles do and can’t do?

Can pull, cannot push

How do you straighten the arm?

• tricep contracts

• Bicep relaxes

What is the structure of a skeletal muscle?

• skeletal muscle made up of muscle fibres, which contain many nuclei and have many organelles called myofibrils

• Each muscle fibre enclosed in sarcolemma

• Sarcolemma folds inwards into the sarcoplasm, forming T tubules which help spread electrical impulses through the sarcoplasm

• Internal membranes called sarcoplasmic reticulum, which stores and releases calcium ions needed for contraction

• Are many mitochondria in muscle fibres to provide ATP

What makes up myofibrils?

Bundles of thick and thin myofilaments, which move past each other to make muscles contract as well of many short units called sacromeres

What are the thick and thin myofilaments made up of??

Thick - protein myosin

Thin - protein actin

How are sacromeres structured?

• ends → marked with Z line

• Middle of myosin filaments → marked with M line

• H zone → contains only myosin filaments

• I bands → are two in each sacromere, composed of actin and shortens during contraction

• A band → full length of the myosin filaments

What is myosin?

Singular → A filamentous tertiary structure protein molecule with a long tail and a specifically shaped head

Many → tails are intertwined with heads sticking up at 360 degrees so they can bind to actin

What is actin?

The sites myosin binds to

What two proteins are between the actin and what do they do?

• troponin (calcium receptor) and tropomyosin

• These help myofilaments move past each other

What is the sliding filament theory?

• explains muscle contraction

1. Myosin binds to actin, allowing the two proteins to move past each other

2. This creates an action potential, which depolarises the sarcolemma

3. The depolarisation travels down the t tubules and to the sarcoplasmic reticulum, releasing calcium ions, which triggers muscle contraction

4. Calcium ions bind to troponin, pulling the tropomyosin out of the actin-myosin binding site, which allows the myosin head to bind to an actin filament called an actin-myosin cross bridge

5. Calcium ions also active ATPase, which hydrolyses ATP into ADP+Pi, providing the energy needed for contraction by moving the myosin head to the side, which pulls the actin filament along

6. ATP hydrolysis also breaks the actin-myosin cross bridge, causing the myosin head to detach from the actin filament, the head then reattaches to a diff binding site on the actin filament

Why is calcium ions so important for the sliding filament theory?

Because without stimulation, the calcium ions moved by active transport back to the sarcoplasmic reticulum and the troponin returns to its original shape and the sacromeres return to their original length

How does neuromuscular junction work?

• ACH binds, causing the gate sodium channels to open and the sarcolemma to become depolarised

• This leads to the action potential travelling along the sarcolemma and into a t tubule

• This carries the action potential into fibre

• The action potential makes sarcoplasmic reticulum release calcium ions, which triggers muscle contraction

What three ways is ATP generated to be used for muscle contraction?

1. Aerobic respiration

2. Anaerobic respiration

3. ATP-PCr - ATP-Phosphocreatine system

How does aerobic respiration generate ATP?

• mitochondria generates the vast majority of the ATP by oxidative phosphorylation

• To work, this needs sufficient oxygen

• The ATP produced by this is good for long periods of low intensity exercise e.g a long walk

How does anaerobic respiration generate ATP?

• ATP made rapidly during glycolysis, which produces pyruvate

• Pyruvate converted into lactic acid, which can quickly build up in muscles causing muscle fatigue (cramps)

• The ATP produced by this is good for short periods of hard exercise e.g a sprint

How does ATP-PCr - ATP-Phosphocreatine system generate ATP?

• ATP made by phosphorylation of ADP when the phosphate group is taken from creatine

• This is catalysed by creatine kinase

• PCr is stored inside cells, which generates ATP quickly

• This production of ATP is good for short bursts of vigorous exercise e.g tennis serve

• Positives → no oxygen needed

• Negatives → affected by metabolic rate (slows with age)

What are the two types of muscle fibres?

Slow twitch and fast twitch

What are slow twitch muscle fibres like?

• contracts half the speed of fast twitch

• Can work for a long time without getting tired

• Contain many more mitochondria and blood vessels than fast twitch

• Produces ATP mainly through aerobic respiration

• Are rich in myoglobin so are red in colour and can store lots of oxygen

• Mainly used whilst jogging, walking and maintaining posture

What are fast twitch muscle fibres like?

• contract very rapidly

• Get tired fast

• Produce ATP very quickly through anaerobic respiration of glycogen using stores of PCR

• have few mitochondria and blood vessels

• Have little myoglobin so cannot store much oxygen and are whitish in colour

• Mainly used for sprinting and jumping