5.1.3 Animal responses

Question 1

What are the 2 subsystems of the nervous system?

Answer 1

-CNS= consists of the brain and spinal cord
-PNS= consists of all the neurones that connect the CNS to the rest of the body.

Question 2

What are the 2 functional systems on the PNS?

Answer 2

-somatic nervous system= controls conscious activities i.e running
-autonomic nervous system= controls unconscious activities i.e the heart beating–} divides into the sympathetic nervous system(‘fight or flight’ response that increases activity) and the parasympathetic nervous system(‘rest and digest’ system that calms the body, releases Ach)

Question 3

Describe the gross structure of the brain

Answer 3

-protected by the skull + surrounded by protective membranes(meninges)
-5 main brain structures: cerebrum, cerebellum, medulla oblongata, hypothalamus, pituitary gland

Question 4

Structure + function of the cerebrum

Answer 4

-largest part of the brain
-divided into 2 halves called the cerebral hemispheres
-each hemisphere controls one half of the body
-has a thin outer layer called the cerebral cortex–} highly convoluted to increase SA
-most sophisticated processes i.e reasoning + decision-making occur in the frontal and prefrontal lobe of the cerebral cortex
-cerebrum receives sensory info and interprets it with info previously stored to produce an appropriate response
-controls voluntary actions i.e learning, memory, personality and conscious thought

Question 5

Function of the cerebellum

Answer 5

-underneath the cerebellum and also has a folded cortex
-controls unconscious functions such as posture, balance + muscle coordination–} coordinates movement but doesn’t initiate it
-sends info to the areas of the cerebral cortex that are involved in motor control

Question 6

Function of the medulla oblongata

Answer 6

-at the base of the brain + top of the spinal cord
-used in autonomic control to control reflex activities i.e controls heart rate and breathing rate

Question 7

Function of the hypothalamus

Answer 7

-found just beneath the middle of the brain
-main controlling region for the autonomic nervous system
-centres for parasympathetic AND sympathetic nervous system
-no. of functions i.e controlling complex patterns of behaviour such as sleeping, monitoring the composition of blood plasma, producing hormones etc

Question 8

Function of the pituitary gland

Answer 8

-found beneath the hypothalamus
-stores + releases hormones that regulate many body functions
- divided into 2 sections:
-anterior pituitary= produces 6 hormones including FSH(involved in reproduction)
-posterior pituitary= stores + releases hormones produced by the hypothalamus, such as ADH(involved in urine production)

Question 9

What is a reflex action?

Answer 9

-where the body responds to a stimulus without conscious thought–} causes a faster response, preventing or minimising damage to the body

Question 10

What is the reflex arc?

Answer 10

-the pathway of neurons involved in a reflex action
-receptor(detects stimulus + creates an action potential in the sensory neurone)–} sensory neurone(carries impulse to spinal cord)–} relay neurone(connects sensory neurone to the motor neurone within the spinal cord/brain)–} motor neurone(carries impulse to the effector to carry out the appropriate response)

Question 11

Spinal cord

Answer 11

-column of nervous tissues running up the back
-surrounded by the spine for protection
-at intervals along the spinal cord, pairs of neurones emerge

Question 12

Knee-jerk reflex

Answer 12

-spinal reflex–} CNS would be the spine
- stimulus: quadricep muscle is stretched
- receptors: stretch receptors in the quadricep muscle detect the muscle is being stretched. Nerve impulse is passed along the sensory neurone
- CNS: the sensory neurone communicates directly with a motor neurone in the spinal cord
- effectors: motor neurone carries nerve impulse to the quadriceps muscle
- response: quadriceps muscle contracts so the lower leg moves forward quickly
-this reflex is used by the body to help maintain posture + balance

Question 13

Blinking reflex

Answer 13

-involuntary blinking of the eyelids that occurs when the cornea is stimulated to protect it from foreign objects i.e dust
-cranial reflex–} occurs in the brain
- stimulus: cornea is irritated by a foreign object
- receptors: sensory nerve endings in the cornea detect the stimulus. A nerve impulse is sent along the sensory neurone to a relay neurone in the CNS
- CNS: the impulse is then passed from the relay neurone to motor neurones
- effectors: the motor neurones send impulses to close the eyelids
- response: muscles contract causing your eyelids to close quickly + prevent your eye from being damaged

Question 14

Why are reflexes important?

Answer 14

-increases your chances of survival and avoid harm by:
-being involuntary responses–} prevents brain being overloaded and allows it to deal with complex responses
-not having to be learnt–} immediate protection
-extremely fast

Question 15

Fight or flight response

Answer 15

-instinct that is triggered when an organism is threatened–} responds by preparing the body for action
-nerve impulses from sensory neurones arrive at the hypothalamus, activating both the hormonal system and the sympathetic nervous system
-the sympathetic NS sends our impulses to glands + smooth muscles and instructs adrenal medulla to release adrenaline & noradrenaline into the bloodstream
-the pituitary gland is stimulated to secrete ACTH–} travels to the adrenal cortex, where it activates the release of steroid hormones which help to respond to stress

Question 16

What are the effects of adrenaline?

Answer 16

-heart rate is increased
-intercostal muscles and the diaphragm contract faster + increase the rate of breathing
-muscles around the bronchioles relax, causing the airway to widen, so breathing is deeper
-erector pilli muscles in the skin contract
-glycogen converted into glucose via glycogenolysis
-muscles in the arterioles in the skeletal muscles, heart + lungs dilate to increase blood flow to skeletal muscles, ready for action

Question 17

The action of hormones in cell signalling

Answer 17

-adenylyl cyclase triggers the conversion of ATP into cAMP on the inner surface of the cell membrane in the cytoplasm
-the increase in cAMP levels activates enzymes called protein kinases which phosphorylate + activate other enzymes
-hormone is the first messenger + cAMP is the second messenger

Question 18

Controlling heart rate

Answer 18

-SAN generates electrical impulses that cause the cardiac muscles to contract
-heart rate is involuntary + controlled by the ANS
-the medulla oblongata in the brain is responsible for controlling heart rate–} has 2 centres linked to the SAN that regulate heart rate depending on the info received by receptors in blood vessels

Question 19

What are the 2 types of receptors that detect stimuli that affect heart rate?

Answer 19

-baroreceptors(pressure receptors)= detect changes in blood pressure, present in the vena cava, aorta + carotid arteries
-chemoreceptors= detect changes in the level of particular chemicals in the blood i.e O2 and CO2, present in the aorta, carotid artery and the medulla

Question 20

How do chemoreceptors respond to low pH levels in the blood?

Answer 20

-if CO2 levels in the blood increase, then pH decreases–} chemoreceptors detect decrease in pH and send impulses along sensory neurones to the centre in the medulla oblongata, which sends impulses along sympathetic neurones that secrete noradrenaline= bind to receptors on SAN and increase heart rate
-increased blood flow removes CO2 faster and brings pH levels back to normal

Question 21

How do chemoreceptors respond to high pH levels in the blood?

Answer 21

-if CO2 levels in the blood decrease, then pH increases–}
-rise in pH is detected by chemoreceptors, which send impulses along sensory neurones to the medulla oblongata–} sends impulses along parasympathetic neurones which secrete Ach= binds to receptors on the SAN and causes heart rate to decrease and pH levels to go back to normal

Question 22

How do baroreceptors detect high blood pressure?

Answer 22

-impulses are sent along the sensory neurone to the medulla oblongata–} sends impulses along parasympathetic neurones which secrete Ach that bind to receptors on the SAN
-decrease heart rate which reduces blood pressure back to normal

Question 23

How do baroreceptors detect low blood pressure?

Answer 23

-send impulses along sensory neurones to the medulla oblongata–} sends impulses along sympathetic neurones to secrete noradrenaline, which binds to the SAN which increases the heart rate to speed up in order to increase blood pressure to normal

Question 24

How does the hormonal system help control heart rate?

Answer 24

-when an organism is threatened, the adrenal glands secrete adrenaline–} binds to specific receptors in the heart
-this speeds up heart rate by increasing the frequency of impulses produced by the SAN

Question 25

Investigating heart rate

Answer 25

-measure your heart rate at rest(use your wrist pulse) and record it in a table
-do some gentle exercise + immediately afterwards, measure your heart rate again
-return to a resting position–} measure your heart rate every minute until it returns to resting state. Record how long it takes to get back to normal

Question 26

Heart rate monitors

Answer 26

-electronic heart rate monitors are likely to consist of a chest strap and a wrist monitor
-chest strap contains electrodes which detect the electrical activity of the heart as it beats
-data is picked up by the electrodes + then transmitted wirelessly to the wrist monitor, which displays the data as bpm
:) -monitor can measure your heart rate as you are exercising + keep a continual record of how it changes rather than measuring at intervals

Question 27

What are the 3 types of muscle in the body?

Answer 27

-skeletal muscle= make up the bulk of body muscle tissue, responsible for movement i.e the biceps + triceps, postural support and heat production
-cardiac muscle= found in the heart, these muscle cells are myogenic(contract without the need for a nervous stimulus) which allows the heart to beat in a regular rhythm
-smooth/involuntary muscle= line the walls of hollow organs i.e stomach and found in the walls of blood vessels and the gut. fibres contract slowly + regularly(do not fatigue) and it is controlled by the ANS

Question 28

Explain the structure of cardiac muscle

Answer 28

-uninucleated
-long fibres which branch to form cross-bridges, resulting in simultaneous contractions
-does show striations but they are much fainter than those in skeletal muscle
-muscle fibres have intercalated discs between cells(low resistance so nerve impulses can pass between cells)
0.1 mm long
-involuntary contractions, which are intermediate in speed and length

Question 29

Explain the structure of smooth muscle

Answer 29

-uninucleated
-muscle fibres are spindle shaped
-no striations
-0.2 mm long
-involuntary contractions that are slow and can last for a relatively long time

Question 30

Explain the basic skeletal muscle structure

Answer 30

-multinucleated
-muscle fibres are long tubular cylinders(made up of lots of cells fused together)
-have cross striations
-can be many cms in length
-contractions are regularly arranged so muscle contracts in one direction
-contractions are rapid and short lasting

Question 31

Skeletal muscle structure: muscle fibres

Answer 31

-skeletal muscles are made up of bundles of muscle fibres–} enclosed within a plasma membrane called the sarcolemma
-muscle fibres contain a no. of nuclei + are much longer than normal cells(formed as a result of many individual embryonic muscle cells fusing together, which makes the muscle stronger)
-parts of the sarcolemma fold inwards and stick to the sarcoplasm(like the cytoplasm in muscle cells) to form T tubules–} help spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre(all fibres receive impulses simultaneously)
-have a modified version of the endoplasmic reticulum called the sarcoplasmic reticulum–} stores + releases calcium ions needed for muscle contraction
-muscle fibres have a lot of mitochondria to provide the ATP needed for muscle contraction and contain many myofibrils

Question 32

Skeletal muscle structure: myofibrils

Answer 32

-long, cylindrical organelles made up of protein and specialised for contraction
-lined up in parallel to provide max force when they all contract together
-made up of 2 types of protein filaments:
- actin: thin myofilament, consist of 2 strands twisted around each other(including troponin and tropomyosin)–} makes up the light band and bits are found in the dark band
- myosin: thick myofilament, consists of long rod-shaped fibres with bulbous/globular heads that project to one side(makes up most of the dark band)

Question 33

Explain what a sarcomere is and describe its function

Answer 33

-a sarcomere is the functional until of a myofibril + each end is marked with a z line–} the distance between adjacent z lines is a sarcomere
made up of:
-Z line(line at the centre of each light band/end of each sarcomere)
-M line(middle of the myosin filament)
-I band(aka light band, appear light because they are the region where actin and myosin don’t overlap, only has thin filaments)
-A band(aka dark band due to the presence of thick myosin filaments along with thin filaments)
-H zone(lighter coloured region near the M line, contains only myosin/thick filaments)

Question 34

Histology of a skeletal muscle

Answer 34

-under a stained section of skeletal muscle under a microscope, you should be able to see:
-individual muscle fibres- long, thin and multinucleated and crossed with striations
-highly structured arrangement of sarcomeres, which appear as A bands and I bands
-streaks of connective + adipose tissue
-capillaries running in between the fibres

Question 35

Explain the sliding filament model

Answer 35

-when the myosin and actin filaments slide over one another to make the sarcomere contract
-results in:
- I band becoming narrower/less visible
- Z lines get closer together, shortening the sarcomere
- H zone becomes narrower/less visible
-the A band stays the same length, as the myosin filaments themselves don’t contract, but now overlap the actin by a greater amount

Question 36

How does the sliding filament model allow muscles to contract?

Answer 36

-the simultaneous contraction of lots of sarcomeres means that the myofibrils and muscle fibres contract
-results in enough force to pull on a bone and cause movement
-sarcomere returns to original length as the muscle relaxes

Question 37

Structure of myosin

Answer 37

-myosin filaments have globular heads that are hinged–} allows them to move back and forth
-each myosin head has a binding site for actin and ATP

Question 38

Structure of actin

Answer 38

-actin filaments have binding sites for myosin heads called actin-myosin binding sites
-two other proteins called troponin and tropomyosin are found between actin filaments(troponin holds tropomyosin in place)–} help myofilaments move past each other when the muscle is stimulated

Question 39

How exactly do troponin and tropomyosin work?

Answer 39

-when a muscle is relaxed, the actin-myosin sites are blocked by tropomyosin–} myosin heads cannot bind to actin + the filaments cannot slide past each other
-when a muscle is stimulated to contract, the myosin heads form bonds with actin filaments known as actin-myosin cross bridges–} allows myosin and actin filaments to slide past each other

Question 40

Muscle contraction: Action potential

Answer 40

-when an action potential arrives at a neuromuscular junction(point between a motor neurone and muscle cell), it stimulates calcium ion channels to open
-calcium ions diffuse from the synapse into the synaptic knob, where they cause synaptic vesicles to fuse with presynaptic membrane
-Ach is released into synaptic cleft via exocytosis and diffuses across the synapse
-Ach binds to receptors on the sarcolemma called nicotinic cholinergic receptors(post synaptic membrane), opening sodium channels + resulting in depolarisation
-Ach is broken down by acetylcholinesterase( stored in clefts in the postsynaptic membrane) into choline + ethanoic acid(prevents muscle being overstimulated)–} reabsorbed into the neurone

Question 41

Muscle contraction: Sarcoplasm

Answer 41

-depolarisation of the sarcolemma spreads down the T-tubules to the sarcoplasmic reticulum
-releases its stored calcium ions into the sarcoplasm as calcium ion channels open
-calcium ions bind to troponin, causing it to change shape
-this pulls on the tropomyosin, moving it away from the actin-myosin binding sites on the actin filament
-binding site is now exposed, which allows myosin heads to bind, forming actin-myosin cross bridges

Question 42

Muscle contraction: Movement of the actin filament

Answer 42

-calcium ions also activate the enzyme ATPase, which hydrolyses ATP into ADP and phosphate–} provides the energy needed for muscle contraction
-energy released from ATP is used to move the myosin head to the side, which pulls the actin filament along in a kind of rowing action
-action releases the molecule of ADP bound to the myosin head and a new ATP molecule can form(restart)

Question 43

Muscle contraction: breaking of the cross bridges

Answer 43

-ATP also provides the energy to break the actin-myosin cross bridge, so the myosin head detaches from the actin filament after its moved
-myosin head then returns to its starting position + reattaches to a different binding site further along the actin filament–} a new actin-myosin cross bridge is formed
-the cycle continues as long as the muscle remains stimulated + the pulling of the actin filament along shortens the sarcomere, causing the muscle to contract

Question 44

Muscle contraction: Returns to resting state

Answer 44

-when the muscle stops being stimulated, calcium ions leave their binding sites on the troponin molecules + are moved by active transport back into the sarcoplasmic reticulum(requires ATP)
-troponin molecules return to their original shape, pulling the attached tropomyosin molecules with them–} tropomyosin molecules block the actin-myosin binding sites again
-muscles aren’t contracted as no myosin heads are attached to actin filaments, so actin filaments slide back to their relaxed position, which lengthens the sarcomere

Question 45

How is ATP provided by aerobic respiration?

Answer 45

-most of the ATP used by muscle cells is regenerated from ADP during oxidative phosphorylation
-reaction takes place in the mitochondria(muscle has lots)
-can only occur in the presence of oxygen, so is used for long periods of low-intensity excercise

Question 46

How is ATP provided by anaerobic respiration?

Answer 46

-ATP is made rapidly by glycolysis–} end product is pyruvate, which is converted to lactate by lactate fermentation
-can build up in the muscles resulting in muscle fatigue
-used for short periods of high intensity exercise–} oxygen is used up more quickly than blood supply can replace it in a very active muscle

Question 47

How is ATP provided by creatine phosphate?

Answer 47

-ATP is made by phosphorylating ADP–} CP acts as a reserve supply of phosphate, which is available immediately to combine with ADP and reform ATP
-generates ATP rapidly, but the store of phosphate is used up quickly–} used for short bursts of vigorous exercise

Question 48

How may chemicals affect neurotransmitters?

Answer 48

-may block the release of a neurotransmitter or affect the way it binds to the receptors on the postsynaptic membrane–} may prevent action potential from being passed on to the muscle (no contraction)
-can be fatal if they affect the muscles involved in breathing i.e diaphragm/intercostal muscles–} ventilation + respiration cannot take place

Question 49

Detecting electrical activity

Answer 49

-attach 2 electrodes to places on the muscle being tested and a third electrode on an inactive point to act as control i.e bony wrist area
-switch off any other electrical equipment that may interfere with the electrical signal
-connect electrodes to an amplifier(increases the strength of the electrical signals from the muscle) + a computer
-when muscle is relaxed, a straight line should show up on the EMG
-contracting the muscle by bending an arm should show spikes in the graph as motor units are activated to contract
-the more motor units activated, the higher the amplitude of the trace i.e lifting weights
-when muscle begins to fatigue, an increase in amplitude will show on the trace as your brain is trying to activate more motor units to generate the force needed to hold the weight up