14 Response To Stimuli + and 15 nervous coordination and muscles +

Question 1

Why is being able to detect and move away from harmful stimuli important

Answer 1

Organisms that survive have greater chance of raising offspring and passing their alleles to next generation There is always therefore a selection pressure favouring organisms with more appropriate responses

Question 2

Examples of taxis

Answer 2

Moving towards light positive phototaxis Moving towards more highly concentrated region of glucose positive chemotaxis

Question 3

Kinesis in wood lice

Answer 3

When they move from a damp area into a dry one they move more rapidly and change direction more often, increases the chance of moving back into damp area Once in them area they slow down and change direction less, More likely to stay within damp area If after some time spent changing direction rapidly they are still in dry area, behaviour changes, they move rapidly in straight lines to increase chance of moving through dry area and into new damp one

Question 4

Tropism of plant shoot

Answer 4

Shoots grow towards light positive phototropism and away from gravity negative gravitropism

Question 5

Tropism of roots

Answer 5

Roots grow away from light negative phototropism and towards gravity positive gravitropism

Question 6

Example of plant growth factor

Answer 6

Indoleacetic avid (IAA) Which belongs to a group of substances called auxins, controls plant cell elongation

Question 7

Phototropism and gravitropism

Answer 7

SEE TXTBOOK PG 330

Question 8

Two major divisions of nervous system

Answer 8

Central nervous system, made up of brain and spinal cord Peripheral nervous system, made up of pairs of nerves that originate from either the brain or spinal cord

Question 9

Peripheral nervous system is divided into

Answer 9

Sensory neurons which carry nerve impulses from receptors to the CNS Motor neurons which carry nerve impulses away from CNS to effecters

Question 10

Motor nervous system divided into

Answer 10

Voluntary nervous system which carries nerve impulses to body muscles and is under voluntary (conscious) control Autonomic nervous system which carries nerve impulses to glands, smooth-muscle and cardiac muscle and is not under voluntary control

Question 11

What is the spinal cord

Answer 11

Column of nervous tissue that runs along the back and lies inside the vertebral column for protection

SEE TXTBOOK PG 334

Question 12

What is a reflex and what is a reflex arc

Answer 12

Involuntary response to a sensory stimulus Neurons involved in a reflex Reflex arc also known as spinal reflex

Question 13

Main stages of spinal reflex arc

Answer 13

Stimulus receptor sensory neurones coordinator motor neurone Effector response

Question 14

Importance of reflex arcs

Answer 14

Involuntary so do not require decision-making powers of brain, leaving it free to carry out more complex responses, brain is not overloaded They protect the body from harm, are effective from birth and do not have to be learnt They are fast because the neurone pathway is short with very few synapses where neurones communicate with each other, important in withdrawal reflexes Absence of any decision-making processes means action is rapid

Question 15

Pacinian corpuscles are

Answer 15

Specific to a single type of stimulus, responds only to mechanical pressure Corpuscle transduces mechanical energy of stimulus into nervous impulse known as generator potential

Question 16

Where is the single sensory neuron of a Pacinian corpuscle

Answer 16

At the centre of layers of tissue each separated by viscose gel Sensory neuron ending at the centre of the Pacinian corpuscle has a stretch mediated sodium channel in its plasma membrane

Question 17

How does Pacinian corpuscle function

Answer 17

In normal resting state stretch mediated sodium channels of membrane around neuron of Pacinian corpuscle are too narrow to allow Na+ to pass along them. Neurone of Pacinian corpuscle has resting potential When pressure is applied corpuscle is deformed and membrane around neuron becomes stretched Stretching widens Na channels in membrane and Na + diffuse into neurone Influx of Na + changes potential of membrane, it becomes depolarises therefore producing generator potential Generator potential creates an action potential that passes along neurone

Question 18

Where are light receptors of eye found

Answer 18

Innermost layer: the retina

Question 19

What is retinal convergence

Answer 19

A number of rod cells connected to a single bipolar cell

Question 20

Pigment in rod cells vs pigment in cone cells

Answer 20

Rhodopsin Iodopsin

Question 21

Why do rods give low visual acuity

Answer 21

Many rods linking to single bipolar cell Light received by rod cells sharing same neuron will only generate a single impulse brain cannot distinguish between the separate sources of light that stimulated them Two dots close together cannot be resolved and appear as a single dot

Question 22

How many different types of cone cell

Answer 22

Three different types of cone cell each containing specific type of iodopsin As a result each cone cells is sensitive to a different specific range of wavelengths

Question 23

Distribution of Rod and cone cells

Answer 23

Uneven Light focused by the lens on the part of the retina opposite the pupil, the fovea The fovea receives the highest intensity of light therefore cone cells are found here Concentration of cone cells diminishes further away from the fovea At peripheries of retina where light intensity is at its lowest only rod cells are found

Question 24

Muscle of heart

Answer 24

Cardiac muscle Myogenic, contraction is initiated from within the muscle itself

Question 25

Where and what is Sino atrial node

Answer 25

Within the wall of the right atrium A distinct group of cells it is from here that the initial stimulus for contraction originates The SAN has a basic rhythm of stimulation that determines the beat of the heart

Question 26

Two centres of the medulla oblongata

Answer 26

Centre that increases heart rate, links to the SAN by the sympathetic nervous system Centre that increases heart rate, linked to the SAN by the parasympathetic nervous system

Question 27

Summary of control of heart rate

Answer 27

SEE TXTBOOK pg 341

Question 28

Chemo receptors

Answer 28

Found in the wall of carotid arteries, arteries that serve the brain Sensitive to changes in the pH of blood that result from changes in CO2 conc In solution CO2 forms an acid and therefore lowers pH

Question 29

Two main forms of coordination

Answer 29

Nervous system, uses nerve cells to pass electrical impulses, stimulate their target cells by secreting neurotransmitters, directly onto them Results in rapid communication between specific parts of an organism, responses short lived and localised Hormonal system, produces hormones that are transported in the blood plasma to their target cells, Target cells have specific receptors on the cell surface membrane change in concentration of hormone stimulates them, Response is long-lasting and widespread

Question 30

types of neurons

Answer 30

SEE TXTBOOK PG 348

Question 31

At resting potential potassium voltage gated channels are

Answer 31

Open, but Na voltage gated channels are closed

Question 32

What is hyper polarisation

Answer 32

Inside of axon being more negative than usual

Question 33

Difference between action potential and resting potential

Answer 33

Movement of sodium ions inwards during action potential is purely due to diffusion, passive process Resting potential is maintained by active transport, active process

Question 34

Passage of an action potential

Answer 34

At resting potential the conc of Na outside axon is high relative to inside whereas K is high inside relative to outside. Overall conc of +ve ions is greater outside, axon membrane is polarised A stimulus causes a sudden influx of Na and hence a reversal of charge on the axon. This is the action potential, axon membrane is depolarised Localised electrical currents established by influx of Na cause opening of sodium voltage gated channels further along axon, causes depolarisation, Na voltage gated channels close and K open. K begin to leave axon along the electrochemical gradient, depolarisation moves along membrane AP propagated in the same way further along axon, outward movement of K continued to extent that axon membrane behind AP returned to its original charged state, repolarised Repolarisation of axon allows Na to be actively transported out, returning axon to its resting potential

Question 35

Passage of action potential along myelinated axons

Answer 35

Fatty sheath around axon acts as electrical insulator, preventing AP forming At intervals there are breaks called nodes of ranvier AP can occur at these points Saltatory conduction AP Passes along faster because events of depolarisation do not have to take place all the way along an axon

Question 36

Passage of action potential diagram

Answer 36

SEE TEXTBOOK PG 356

Question 37

Importance of refractory period

Answer 37

AP can only pass from active region to resting region, Because cannot be propagated in the region that is refractory, Prevents AP spreading out in both directions Due to refractory period new AP cannot be formed immediately behind the first one, ensures AP are separated from one another As AP are separated from one another, limits number of AP that can pass alone axon in a given time, thus limits strength of stimulus that can be detected

Question 38

Structure of synapse

Answer 38

SEE TXTBOOK PG 360

Question 39

Spatial summation diagram

Answer 39

SEE TXTBOOK PG 361

Question 40

Temporal summation diagram

Answer 40

SEE TXTBOOK PG 362

Question 41

Synapse allows…

Answer 41

Single impulse to initiate a new impulses in a number of different neurons at a synapse, allows single stimulus to create a number of simultaneous responses (temporal) A number of impulses to be combined at a synapse, allows nerve impulses from receptors reacting to different stimuli to contribute to a single response (spatial)

Question 42

How do drugs act on synapses

Answer 42

Stimulate nervous system by creating more AP in postsynaptic neuron, mimic neurotransmitter, stimulating release of more neurotransmitter or inhibiting the enzyme that breaks down neurotransmitter Inhibit the nervous system by creating fewer AP in postsynaptic neuron, inhibit release of neurotransmitter or block receptors on sodium potassium ion channels on postsynaptic neurone

Question 43

diagram of cholinergique synapse

Answer 43

See TXTBOOK pg 366

Question 44

What are muscles

Answer 44

Effector organs that respond to nervous stimulation by contracting and so bring about movement

Question 45

How are muscles structured

Answer 45

Individual muscles are made up of tiny muscle fibres called myofibrils Myofibrils are arranged parallel in order to give maximum force Muscle fibres share nuclei and cytoplasm called sarcoplasm Sarcoplasm contains large concentration of mitochondria and endoplasmic reticulum

Question 46

Structure of acting and myosin molecules diagram

Answer 46

SEE TXTBOOK PG 368

Question 47

Myofibrils appearance and structure

Answer 47

Appear striped due to alternating light coloured, I, and dark coloured, A bands. I bands appear lighter because thick and thin filaments do not overlap in this region Are you bands appear darker because thick and thin filaments overlap At centre of each a band is lighter coloured region called H zone At centre of each I band is line called Z line, distance between adjacent Z lines is called the sarcomere When muscle contracts sarcomere shortens and pattern of light and dark bands change Another important protein found in muscle is tropomyosin which forms fibrous strand around actin filament

Question 48

Fast twitch fibres adapted to role by having

Answer 48

High conc of enz involved in anaerobic respiration which provides ATP rapidly Store of phosphocreatine, molecule that can rapidly generate ATP from ADP in anaerobic conditions and so provide energy for muscle contraction

Question 49

What is the neuromuscular junction

Answer 49

Point where a motor neurone meets a skeletal muscle fibre As rapid and coordinated muscle contraction is essential for survival there are many neuromuscular junction is spread throughout the muscle, ensures contraction of the muscle is rapid and powerful when it is simultaneously stimulated by AP All muscle fibres supplied by a single motor neuron act together as a single functional unit and are known as a motor unit Arrangement gives control over the force that the muscle exerts

Question 50

When a nerve impulse is received at the neuromuscular junction….

Answer 50

Synaptic vesicles fuse with the presynaptic membrane and release their ACh ACh defuses to the postsynaptic membrane altering its permeability to Na, Which enter, rapidly depolarising the membrane ACh is broken down by ACh esterase to ensure muscle is not overstimulated Resulting choline and ethanolic acid diffuse back into the neurone

Question 51

Similarities of neuromuscular junction and cholinergic synapse

Answer 51

Have neurotransmitters that are transported by diffusion Have receptors that on binding with the neurotransmitter cause an influx of Na Use a sodium potassium pump to repolarise axon Use enzymes to break down the neurotransmitter

Question 52

Differences between a neuromuscular junction and cholinergic synapse

Answer 52

SEE TXTBOOK PG 370

Question 53

How can parts of the skeleton be moved relative to one another

Answer 53

If muscle exerts a force via tendons, the bones move rather than muscle changing shape, different parts of the skeleton can be moved relative to another around a series of points called joints Contraction of skeletal muscle move a part of the skeleton in One Direction but the same muscle cannot move it in the opposite direction To move the limb in the opposite direction requires a second muscle that works antagonistically Skeletal muscles therefore occur and act in antagonistic pairs

Question 54

Comparison of two sarcomere is in a relaxed and contracted muscle diagram

Answer 54

SEE TXTBOOK PG 371

Question 55

When a muscle contracts the changes that occur to a sarcomere include

Answer 55

I band becomes narrower Z lines move closer together, sarcomere shortens H zone becomes narrower A band remains the same width, as the width of this band is determined by the length of the myosin filaments and they have not become shorter

Question 56

Three main proteins involved in the sliding filament mechanism

Answer 56

Myosin, made up of two types of protein: A fibrous protein arranged into a filament made up of lots of molecules(tail) A globular protein formed into two bulbous structures at one end (head) Actin, a globular protein whose molecules are arranged into long chains that are twisted around one another to form a helical strand Tropomyosin, forms long thin threads that are wound around actin filaments

Question 57

Sliding filament mechanism of muscle contraction divided into…

Answer 57

Stimulation, contraction, relaxation

Question 58

What occurs in muscle stimulation

Answer 58

AP reaches many neuromuscular junction simultaneously causing Ca Protein channels to open and Ca to diffuse into the synaptic knob Ca causes the synaptic vesicles to fuse with the presynaptic membrane and release ACh into the synaptic cleft ACh defuses across the synaptic cleft and binds with receptors on the muscle surface membrane causing it to depolarise

Question 59

Muscle contraction continuation after calcium ions

Answer 59

ATP molecules attached to the myosin heads Mean they are in a state to bind to the actin filament and form a cross bridge Once attached to the actin filament the myosin heads change the angle pulling the actin filament along as they do so and releasing a molecule of ADP An ATP molecule attaches to each myosin head causing it to become detached from the actin filament Ca then activate the enzyme ATPase which hydrolyses ATP to ADP, providing energy for myosin head to return to its original position Myosin head once more with an attached ADP molecule then re-attaches itself further along the actin filament and cycle is repeated as long as the conc of Ca ions in the myofibril remains high As myosin molecules are joined to tail to tail in oppositely facing sets, movement of one set of myosin heads is an opposite direction to other set, this means that actin filaments to which they are attached also move in opposite directions The movement of actin filaments in opposite directions pulls them towards each other shortening the distance between the two adjacent Z lines

Question 60

Sliding filament mechanism of muscle contraction diagram

Answer 60

SEE TXTBOOK PG 374

Question 61

Muscle relaxation

Answer 61

When nervous simulation ceases Ca are actively transported back into the ER using energy from the hydrolysis of ATP This reabsorption of Ca allows tropomyosin to block the actin filament again Myosin heads are now unable to bind to actin filaments and contraction ceases, muscle relaxes In this state force from antagonistic muscles can pull actin filaments out from between myosin

Question 62

Energy from hydrolysis of ATP to ADP is needed for what in muscle contraction?

Answer 62

Movement of the myosin heads Reabsorption of Ca into the ER by active transport

Question 63

What is the importance of phosphocreatine

Answer 63

In a very active muscle the demand for ATP and therefore oxygen is greater than the rate at which the blood can supply O A means of rapidly generating ATP anaerobically is required Partly due to using chemical called phosphocreatine and partly by more glycolysis Phosphocreatine cannot supply energy directly to the muscle so instead regenerates ATP, which can Phospho stored in muscles and acts as a reserve supply of Phosphate which is available immediately to combine with ADP and reform ATP Phospho store is replenished using P from ATP when muscle is relaxed