Cell and Electrical Signalling, including immune system and muscles (4) + (5)

Question 1

what is the autonomic nervous system

Answer 1

the part of the peripheral nervous system associated with involuntary responses and involuntary muscle movement

Question 2

give two examples of auto-immune disease

Answer 2

DIABETES TYPE 1

MULTIPLE SCLEROSIS

Question 3

give a description of the structure: motor neurone

Answer 3

a nerve cell that carries impulses away from the CNS to an effector eg. muscle or gland

Question 4

give a description of the structure: Schwann cell

Answer 4

glial cells in the peripheral nervous system that produce the myelin sheath around neuronal axons

Question 5

what is a synapse (1 mark)

Answer 5

a junction between two nerve cells, consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter

Question 6

what is the nervous system

Answer 6

a system for coordination and control in animals, along with the endocrine system

Question 7

which specialised cells make up the nervous system + how does this process occur (2 marks)

Answer 7

stimuli are received from the internal/external environment by modified nerve cells called receptors in the sense organs or internal receptors

receptors convert the energy of the stimuli into electrical energy, a process called transduction

the electrical energy is transmitted as electrical impulses along a sequence of neurones/nerve cells- SENSORY NEURONE → INTER/RELAY NEURONE (CNS) → MOTOR NEURONE

motor neurones connect to effectors that carry out a response

Question 8

outline the NS pathway

Answer 8

STIMULUS ⇒ RECEPTOR → SENSORY NEURONE- dendrites, dendron, soma, axon, axon terminals ⇒ INTERNEURONE (CNS) using relay neurone⇒ MOTOR NEURONE- dendrites*, axon, axon terminals → EFFECTOR (MUSCLE OR GLAND) → RESPONSE

*containing soma; motor neurone have soma in CNS, sensory neurones have it near CNS

Question 9

what does the functioning of the NS require

Answer 9

an electrical potential difference across the plasma membrane; a membrane potential

Question 10

how do the characteristics of a SENSORY neurone, INTERNEURONE and MOTOR neurone differ

Answer 10

Sensory neurone: from the effector a dendrite leads to the cell body and away via an axon

Interneurone: very short dendrites lead to the cell body and away via a very short axon, non-myelinated

Motor neurone: cell body with little dendrites branching off, a myelinated axon takes the electrical impulse to the effector

Question 11

how is a membrane potential set up (4 marks)

Answer 11

1. SODIUM/POTASSIUM PUMP: a transmembrane protein pump requiring ATP. It pumps 3 Na⁺ out of the cell for every 2 K⁺ pumped into the cell. Therefore there is more Na⁺ outside and K⁺ inside, polarising the cell to a membrane potential of -70mV.
2. SODIUM CHANNELS ARE CLOSED (2^nd pump)
3. POTASSIUM CHANNELS ARE LEAKING (3^rd pump) K⁺ does not all diffuse out of the cell because it is attracted to the negative region inside the cell.

Question 12

what is a dendrite (2 marks)

Answer 12

(same as dendron) a short branched extension of a nerve cell, along which impulses received from other nerve cells at synapses are transmitted to the cell body

Question 13

what are glial cells

Answer 13

non-neuronal cells that maintain homeostasis, form myelin and provide support and protection for neurones in the CNS and PNS eg. SCHWANN CELLS

Question 14

what do reflex actions involve (1 mark)

+ what is their purpose (3 marks)

Answer 14

They are responses that do not involve conscious thought; involve involuntary movement and a reflex arc.

• response to danger
• to avoid damage to the body
• to maintain balance

Question 15

what is the pathway for a reflex arc

Answer 15

RECEPTOR ⇒ SENSORY NEURONE ⇒ RELAY NEURONE in spinal cord or unconscious part of brain ⇒ MOTOR NEURONE ⇒ EFFECTOR

in a monosynaptic reflex, the sensory neurone connects directly to a motor neurone eg. the knee jerk reflex

Question 16

give an example of a reflex arc and its purpose (3 marks)

Answer 16

KNEE JERK REFLEX

used by body to maintain balance and posture, allowing the person to stand with little effort or conscious thought

used by doctors to detect nervous problems eg. cerebellar disease

Question 17

INTERNEURONES: compare structure and position in NS

Answer 17

• same structural components as motor and sensory neurones- dendrites, soma, axon, synaptic endings NO MYELIN SHEATH- no need for accelerated speed of conduction along axon/dendron bc they do not extend across long distances*
• found entirely in CNS and tf do not need extended axons or dendrons*

Question 18

what is an action potential

Answer 18

a momentary change in the membrane potential caused by a transient change in the membrane’s permeability to sodium and potassium ions

can be observed with an oscilloscope that monitors the electrical potential or voltage, recorded by a microelectrode

Question 19

what is a membrane potential (3 marks)

Answer 19

In the neurone it is a resting potential, which is an electrical potential difference across the plasma membrane, typically between -60mV and -80mV. The inside is negative relative to the outside, the membrane is polarised

Question 20

what causes an action potential (3 marks)

Answer 20

1. It is initiated when a neurone or muscle cell (an excitable cell) is depolarised to threshold value (approx. -50mV)
2. Initiated by a change in permeability of the membrane to Na⁺ and K⁺ ions; Na⁺ ions flow into the cell.

Question 21

what happens after depolarisation (4 marks)

Answer 21

1. During the AP, the inside of the cell becomes positively charged relative to the outside.
2. Repolarisation/downstroke is caused by a change in the membrane permeability to Na⁺ and K⁺ ions; potassium ions flow out of the cell.
3. The cell becomes negatively charged inside relative to the outside again.

Question 22

what occurs at the end of an action potential (2 marks)

Answer 22

The membrane becomes more negative on the inside than at a resting potential; HYPERPOLARISATION. It is a necessary refractory period.

Question 23

what is a voltage-gated ion channel?

Answer 23

Nerve axons contain two types of channels: Na+ specific and K+ specific, that are opened and closed by voltage dependent gates.

These enable neurones to produce action potentials because these are contained in their membranes.

Question 24

what is a Node of Ranvier (1 mark)

Answer 24

a gap in the myelin sheath of a nerve, between adjacent Schwann cells

Question 25

what is an axon (1 mark)

Answer 25

a projection of the neurone that **conducts electrical impulses away** **from** the neurone's **cell body**/soma

Question 26

what is a _dendron_ (1 mark)

Answer 26

a projection of the neurone which **conducts nerve impulses from a synapse to the cell body** (*synonymous with dendrites*)

Question 27

what is a *synaptic knob* (1 mark)

Answer 27

a **swelling** at the very **end of the axon** which **communicates with a dendrite or cell body of another neurone** across a **synapse**

Question 28

what is a _sensory neurone_ (1 mark)

Answer 28

a **nerve cell** that **transmits impulses** from **receptors** to the **CNS**

Question 29

what are the _structural differences_ between SENSORY and **motor** neurones (*6 marks*)

Answer 29

1. CELL BODY IN PNS **cell body in CNS** 2. CELL BODY IN THE MIDDLE OF THE NEURONE **cell body at the start of the neurone** 3. SHORTER AXON **longer axon** 4. DENDRON PRESENT **dendron absent** 5. STARTS AT/ CONNECTS TO SENSORY NEURONE **ends at neuromuscular junction/ motor-end plate/ effector** 6. DENDRITES AT THE END OF DENDRON (DO NOT CONNECT DIRECTLY TO CELL BODY) **dendrites connect directly to cell body**

Question 30

give one main difference between sensory and motor neurones

Answer 30

**Sensory** neurones **transmit** impulses **received from a receptor** and transmit them to the **CNS**. Motor neurones: **from CNS to effector**.

Question 31

how is an electrical impulse created in a sensory receptor (*4 marks*)

Answer 31

_DEPOLARISATION:_ **Stimuli received** by **sensory receptors** eg. Pacinian corpuscle- pressure receptors, **reverse the polarisation in the membrane** of the receptor cells. This causes depolarisation in the **sensory neurone**. _ENERGY TRANSDUCTION:_ **Stimulus energy** is converted to **electrical energy** in the **receptor cells** of **sense organs**, triggering an electrical impulse/action potential in the sensory neurone.

Question 32

what is the difference between a resting potential and action potential

Answer 32

Resting potential: when the membrane is **polarised** Action potential: when the membrane is **depolarised**

Question 33

name a type of sensory receptor and where it is found, the nature of its stimulus and the type of stimulus energy that is transduced (x2)

Answer 33

EYE- **rods and cones of the retina**- photoreceptor- LIGHT- *electromagnetic spectrum/light* SKIN- **Pacinian corpuscle/mechanoreceptor**- PRESSURE- *mechanical*

Question 34

*how* do *stimuli* trigger an action potential in sensory receptors (5 marks)

Answer 34

*Stimulus energy* is *transduced/converted* to *electrical energy* in the receptors, triggering an electrical impulse/action potential in the sensory neurone. 1. **Stimulus energy** causes **sodium channels to open** in the **membrane** of the receptor cell. (*closed at resting potential*) 2. **Concentration of sodium is higher outside** the cell relative to inside. Sodium **diffuses in**. 3. Membrane is **depolarised**. This creates a GENERATOR POTENTIAL.

Question 35

how does the _size/strength of stimulus_ affect generator potential and action potential

Answer 35

The **larger** the **stimulus strength**, the **greater** the **diffusion of Na⁺** into the cell the **greater** the **depolarisation** of the membrane the **larger** the **generator potential** WHEN THE **GENERATOR POTENTIAL** IN THE RECEPTOR REACHES A **THRESHOLD VALUE approx. -50mV**, IT TRIGGERS AN **ACTION POTENTIAL** IN THE **SENSORY NEURONE**

Question 36

what is _myelin sheath_ (2 marks)

Answer 36

a mixture of proteins and phospholipids forming a whitish **insulating** sheath **around many nerve fibres**, **made by Schwann cells**, which **increases** the **speed** at which **impulses are conducted**. It is **impermeable** to Na⁺ and K⁺ **ions**

Question 37

what is the cell body/soma (1 mark)

Answer 37

the portion of a neurone that **contains the nucleus** but does not incorporate the dendrites or axon

Question 38

what is a _neuro-muscular junction_ (1 mark)

Answer 38

the **synapse** formed by the **contact between a motor neurone and a muscle fibre**

Question 39

why is an action potential described as an _all or nothing response_

Answer 39

* an action potential is not produced unless a stimulus depolarises the cell membrane to threshold value: -60mV to -50mV usually. * all action potentials along the neurone have the same amplitude and duration

Question 40

Stage: **RESTING** describe: 1. INSIDE THE MEMBRANE 2. OUTSIDE THE MEMBRANE 3. POTENTIAL 4. NA/K PUMP WORKING 5. V-G SODIUM CHANNELS 6. V-G POTASSIUM CHANNELS

Answer 40

1. HIGH K⁺ LOW Na⁺ 2. LOW K⁺ HIGH Na⁺ 3. -70mV 4. yes 5. closed 6. closed but leaking

Question 41

Stage: **DEPOLARISATION** describe: 1. INSIDE THE MEMBRANE 2. OUTSIDE THE MEMBRANE 3. POTENTIAL 4. NA/K PUMP WORKING 5. V-G SODIUM CHANNELS 6. V-G POTASSIUM CHANNELS

Answer 41

1. HIGH K⁺ HIGH Na⁺ 2. LOW K⁺ Decreasing Na⁺ 3. Rises from -70mV to +35mV 4. yes 5. open 6. closed but leaking

Question 42

Stage: **REPOLARISATION** describe: 1. INSIDE THE MEMBRANE 2. OUTSIDE THE MEMBRANE 3. POTENTIAL 4. NA/K PUMP WORKING 5. V-G SODIUM CHANNELS 6. V-G POTASSIUM CHANNELS

Answer 42

1. Decreasing K⁺ HIGH Na⁺ 2. Increasing K⁺ relatively low Na⁺ 3. decreases from +35mV to -70mV 4. yes 5. closing or closed 6. open

Question 43

Stage: **HYPERPOLARISATION** describe: 1. INSIDE THE MEMBRANE 2. OUTSIDE THE MEMBRANE 3. POTENTIAL 4. NA/K PUMP WORKING 5. V-G SODIUM CHANNELS 6. V-G POTASSIUM CHANNELS

Answer 43

1. Decreasing K⁺ Na⁺ starting to decrease 2. LOW K⁺ Na⁺ increasing 3. -70mV to 80mV 4. yes 5. closed 6. closing

Question 44

what is the difference between passive and active immunity, giving examples of each

Answer 44

_active_ immunity = we have produced antibodies **by our own B cells** eg. due to a vaccination, chicken pox _passive_ immunity = we are **given antibodies** but do not produce them ourselves eg. from a mother's breastmilk

Question 45

which factors affect the speed of conduction of an action potential

Answer 45

1. DIAMETER OF AXON 2. MYELINATION- SALTATORY CONDUCTION

Question 46

how does DIAMETER affect *speed of conduction* of an action potential (2 marks)

Answer 46

the *wider the diameter* of the axon, the *faster the speed* of conduction. The *resistance to flow* of an electrical current is *inversely proportional to the cross-sectional area of conductor* eg. a wire or axon

Question 47

how does _myelination affect speed of conduction_ of an action potential (5 marks)

Answer 47

*Myelination is lipid-based myelin sheath produced by schwann cells that prevents electrical conduction i.e. of electrical impulses/action potentials. Gaps where the axon membrane is exposed are nodes of Ranvier*. ACTION POTENTIALS are only generated at the NODES OF RANVIER. The current of Na⁺ ions during depolarisation of the action potential at one node of Ranvier diffuses along the interior of the axon to the next node. Sodium channels will only open at nodes. Therefore conduction is faster because fewer channels are opened and each region does not need to be depolarised, repolarised and hyperpolarised. This is saltatory conduction.

Question 48

what is _myelination_ (4 marks)

Answer 48

*myelinated neurones contain myelin sheaths along their axons formed by schwann cells - myelin is closer to the axon, nucleus+cytoplasm on outside. It is mostly made of **lipid**, a **poor conductor** of electrical currents, providing **electrical insulation** of the axon.*

Question 49

why is electrical conduction _slower_ in non-myelinated axons

Answer 49

Action potentials occur on each continuous patch of membrane- it takes time for each part to depolarise, repolarise, hyperpolarise and channels to open/close.

Question 50

what is _multiple sclerosis_ (3 marks)

Answer 50

* a progressive auto-immune disease * the myelin sheath gradually breaks down * the speed of nervous transmission along the axon is reduced * impulses may be stopped completely if V-G channels only occur at nodes

Question 51

how are electrical impulses conducted between neurones (5 marks)

Answer 51

_SYNAPTIC TRANSMISSION_ * Junctions between neurones or neurone/muscle cell are chemical synapses. * Presynaptic neurones synthesise and package the NT into synaptic vesicles, stored in the synaptic terminals (knobs). * release of neurotransmitters by the presynaptic neurone, * An action potential reaches the synaptic knob, releasing neurotransmitters into the synaptic cleft. NT bind to receptor sites on the post-synaptic neurone. * If enough NT are released, an action potential is initiated in the postsynaptic neurone.

Question 52

what is the mechanism for synaptic transmission (6 marks)

Answer 52

1. An **action potential** **depolarises** the pre-synaptic membrane of the **synaptic terminal**, opening **V-G Ca²⁺ channels** in the **pre-synaptic neurone.** 2. **Ca²⁺ ions diffuse** into the **synaptic cleft**. The high concentration of Ca²⁺ causes synaptic vesicles to fuse with the pre-synaptic membrane, releasing the neurotransmitters by exocytosis into the cleft. 3. Neurotransmitter diffuses across the synaptic cleft and bind to the receptor on ligand-gated Na⁺ channels in the post-synaptic membrane, opening channels through which sodium diffuse into the post-synaptic neurone across the membrane. 4. A post-synaptic generator potential is generated. If enough NT is released to bind and open sodium channels, enough generator potentials combine and create an action potential in the post-synaptic neurone. 5. The neurotransmitter is released from the receptors and synaptic transmission ends.

Question 53

what is a _cholinergic_ synapse and _where_ do they occur

Answer 53

Synapses using the neurotransmitter **acetylcholine (ACh)** When ACh binds to the receptors on the ligand-gated Na⁺ channels on the post-synaptic membrane, it opens and Na⁺ diffuses in, initiating a post-synaptic action potential They occur in the **central** **NS**, **autonomic NS** and at **neuromuscular junctions** (between a motor neurone and skeletal muscle cell)

Question 54

what happens to acetlycholine after synaptic transmission

Answer 54

ACh is *hydrolysed* to *acetic/ethanoic acid* and *choline* in the synaptic *cleft* by enzyme ACETYL CHOLINESTERASE. These molecules are *reabsorbed* into the *pre-synaptic neurone* and recycled to ACh by a *condensation* reaction, and *packaged into vesicles* in the synaptic terminals.

Question 55

what are the two branches of the nervous system

Answer 55

CENTRAL nervous system and PERIPHERAL nervous system

Question 56

what are the two branches of the CENTRAL nervous system and what are their FUNCTIONS

Answer 56

**BRAIN ------- SPINAL CHORD** ## Footnote receives and processes sensory information, initiates responses, memories, thoughts, emotions conducts signals to and from the brain, controls reflex activities

Question 57

what are the two branches of the PERIPHERAL nervous system and what are their FUNCTIONS

Answer 57

**MOTOR neurones &** SENSORY neurones ## Footnote **CNS to muscles and glands** & sensory organs to CNS

Question 58

what are the two branches of the motor neurone branch of the PNS and what are their FUNCTIONS

Answer 58

_SOMATIC_ nervous system vs. *AUTONOMIC* nervous system somatic controls **voluntary/conscious movements** and autonomic **involuntary/unconscious responses**

Question 59

what are the two branches of the AUTONOMIC (involuntary responses) branch of the motor neurones/PNS and what are their FUNCTIONS

Answer 59

SYMPATHETIC division: fight or flight ## Footnote ***PARASYMPATHETIC division: rest or digest***

Question 60

what is the *location* of SKELETAL muscle in the body and what is its *role/what is it controlled by*

Answer 60

*-attached to bones/skeleton* part of the **somatic** nervous system, **voluntary** movement of body and limbs, controlled by the **cerebrum + cerebellum**

Question 61

what is the *location* of CARDIAC muscle in the body and what is its *role/what is it controlled by*

Answer 61

-*only found in the heart. -MYOGENIC* **involuntary continuous rythmic contractions** from formation of heart to end of life, controlled by **medulla oblongata**

Question 62

what is the *location* of SMOOTH muscle in the body and what is its *role/what is it controlled by*

Answer 62

-*in arteries and arterioles, bronchi and bronchioles, alimentary canal, visceral organs* part of the **autonomic** nervous system, **involuntary contractions**

Question 63

describe the _contractions_ of SKELETAL muscle and how their cells are _arranged_

Answer 63

**RAPID & SHORT** **multinucleate cells** lie end to end in *tubular parallel fibres*

Question 64

describe the _contractions_ of CARDIAC muscle and how their cells are _arranged_

Answer 64

*INTERMEDIATE CONTRACTION SPEED & INTERMEDIATE PERIOD OF CONTRACTION* **uninucleate** cells, **high quantity** of mitochondria, respiration remains **aerobic**, no fatigue cells **branch** and **interconnect**

Question 65

describe the _contractions_ of SMOOTH muscle and how their cells are _arranged_

Answer 65

**SLOW & can REMAIN contracted for PROLONGED period of time** **uninucleate** cells that can contract in **different directions**

Question 66

what is the *appearance* and *structure* of the muscle fibres of skeletal muscle

Answer 66

shows CROSS STRIATIONS/stripes cells are PARALLEL to each other and contract in ONE DIRECTION

Question 67

what is the *appearance* and *structure* of the muscle fibres of cardiac muscle

Answer 67

FAINT STRIATIONS INTER-CALATED DISCS BRANCHED fibres resulting in SIMULTANEOUS contractions (squeezing action)

Question 68

what is the *appearance* and *structure* of the muscle fibres of smooth muscle

Answer 68

NON-STRIATED SPINDLE-SHAPED IRREGULARLY arranged, contraction NOT in one direction

Question 69

what is the structure of *voluntary muscle* (*3 marks*)

Answer 69

Voluntary muscle consists of **bundles of striated multinucleaste muscle fibres (muscle cell)** surrounded by **connective tissue** the bundles contain **myofibrils**

Question 70

how do *motor neurones* (somatic and autonomic NSs) connect to *muscle cells*

Answer 70

fibres are innervated by a motor neurone nerve ending; a **motor end plate**

Question 71

what is *sarcolemma* (1 mark)

Answer 71

**muscle cell membrane;** has many folds at the neuromuscular junction (*transverse tubules* = deep invaginations)

Question 72

what is a *myofibril* (*1 mark*)

Answer 72

a *contractile organelle* made up of units of *sarcomeres* (contains repeating dark and light bands, I and A, which are responsible for striated appearance)

Question 73

what is a *motor-end plate* (*1 mark*)

Answer 73

divisions of the axon of the **motor neurone** forming **fine branches** ending in **synaptic knobs**

Question 74

what is a *neuro-muscular junction* (*1 mark*)

Answer 74

the motor-end plate + synaptic gap where a motor neurone connects to a muscle fibre by a chemical synapse, with the diffusion of acetylcholine across the synaptic cleft

Question 75

what is a *sarcomere* (*1 mark*)

Answer 75

**contractile unit** of a **myofibril**, made of **actin** and **myosin filaments**

Question 76

what is *sarcoplasmic reticulum* (*1 mark*)

Answer 76

**specialised membrane** system- **store** of **calcium ions** surrounded by sarcoplasm

Question 77

what are the events that occur at the motor end plate in the excitation of muscle fibres

Answer 77

* action potential reaches synaptic knob of the **motor-end plate**, depolarising the pre-synaptic membrane and opening voltage-gated Ca²⁺ channels * Ca²⁺ diffuses in and vesicles containing ACh bind to the pre-synaptic membrane, where ACh is released into the synaptic cleft by exocytosis * ACh diffuses across the cleft and binds to complementary receptors on the **sarcolemma**, opening Na⁺ ion channels in the post-synaptic membrane/**sarcolemma** * the membrane is depolarised and it it reaches threshold value an **action potential passes along the sarcolemma and into the muscle fibre through the transverse tubules** * **T-tubules connect to the sarcoplasmic reticulum surrounding the myofibrils** * the wave of depolarisation triggers the **release of Ca²⁺ ions from the sarcoplasmic reticulum**. The **ions initiate the sliding of filaments** by allowing **myosin to bind to actin** in the **myofibrils** * ACh in the synaptic cleft is hydrolysed by acetyl cholinesterase, re-enters the pre-synaptic **motor** neurone to **prevent overstimulation of the muscle fibre**, and is recycled

Question 78

where does the trigger for muscle fibre contraction come from

Answer 78

an action potential (wave of depolarisation) is distributed to the sarcoplasmic reticulum by the T-tubule system Ca²⁺ ions released from the sarcoplasmic reticulum trigger muscle fibre contraction by allowing myosin to bind to actin in the myofibrils

Question 79

name the 2 bands, 2 lines, 2 filaments and 1 zone and what they correspond to

Answer 79

**I band =** z line + region of actin only, where myosin does not overlap *light band* **A band =** M line, H zone and region of myosin (with actin) *dark band* **M line =** very centre of myosin, keeps myosin tethered **Z line =** centre of actin filaments *a sarcomere is from Z line to Z line* **actin =** thin filament **myosin =** thick filament **H zone =** myosin only

Question 80

what happens to the sarcomere when muscle fibres contract

Answer 80

Actin + myosin do not change length. Actin moves towards the centre of the sarcomere (M line) during muscle contraction. The filaments slide over one another/overlap **The widths of the I band and H zone are reduced** **A band is unchanged** **Sarcomere shortens** **After a full contraction, they disappear. Ends of thick filaments touch Z lines. Sarcomere shortens further.**

Question 81

what are the sources of ATP for muscle contraction

Answer 81

*quantity of ATP stored in muscle is low* ATP can be supplied by: aerobic respiration by many mitochondria in muscle cell. Through the respiratory pigment **MYOGLOBIN**, which stores O₂ in the sarcoplasm **phosphocreatine/ creatine phosphate** a store of energy, it can phosphorylate ADP *creatineP + ADP ⇒ creatine + ATP* **anaerobic respiration** when muscle activity is high, produces 2 ATP and lactate, leading to oxygen debt (in order to convert lactate to pyruvate, NAD is required, supplied by etc/oxphos only when O₂ present)

Question 82

what is the *sliding filament model* for muscle contraction

Answer 82

In order for the thick myosin filament to 'slide over' the thin actin, ATP binds to the myosin head and is hydrolysed to ADP and inorganic phosphate. The myosin head straightens and forms a cross-bridge by binding to actin. The head bends towards the centre of the sarcomere by releasing ADP and P: this is the power stroke. Actin moves towards the centre of the sarcomere and ATP binds to the head to release it.

Question 83

what is the *role of calcium* in muscle contraction

Answer 83

1. CALCIUM IONS BIND TO TROPONIN 2. **troponin and tropomyosin move away from myosin-binding sites on actin, allowing the myosin head to bind** _{when excitation finishes, calcium ions are pumped back into the sarcoplasmic reticulum by active transport ; muscle relaxes}

Question 84

what happens to the heart rate in times of danger or exercise (nervous control of heart rate) 4 marks

Answer 84

The heart rate increases (from an average 70bpm approx.) in order to provide extra oxygen required for increased aerobic respiration. The change is controlled by the cardiovascular centre in the medulla oblongata (base of the brain). It uses the autonomic NS to innervate the SA node, therefore influencing the frequency of the waves of excitation/heart rate.

Question 85

what are the two regions of the CARDIOVASCULAR CENTRE

Answer 85

*EXCITATORY CENTRE: increases heart rate by sending impulses to the SA node via the accelerator nerve of the sympathetic branch of the autonomic NS.* **INHIBITORY CENTRE:** decreases heart rate by sending impulses via the vagus nerve of the parasympathetic branch of the autonomic NS.

Question 86

what are the two types of *receptor* in the cardiovascular system for the regulation of heart rate + *where* are they located

Answer 86

**baroreceptors & chemoreceptors** *in the aorta, carotid arteries and vena cava (blood vessels)*

Question 87

what is the function of chemoreceptors (how do they affect heart rate)

Answer 87

*-detect levels of CO₂ and pH in the blood an dsend impulses to the cardiovascular centre* If CO₂ is high (tf pH is low), the accelerator nerve of the sympathetic branch of the autonomic NS in excitatory increases heart rate

Question 88

what is the function of baroreceptors (how do they affect heart rate)

Answer 88

*-they detect changes in blood pressure and send impulses to the cardiovascular centre* If blood pressure is high, the vagus nerve of the parasympathetic branch of the NS decreases heart rate If blood pressure is low, the accelerator nerve of the sympathetic branch of the autonomic NS increases heart rate

Question 89

what is the difference between natural and artificial immunity, giving examples of each

Answer 89

_natural_ = we naturally develop immunity, by being given antibodies or being infected by pathogens and developing an immune response eg. passive- from a mother's breastmilk, active- chicken pox _artificial_ = injected with .... eg. passive- injected with monoclonal antibodies, active- vaccination

Question 90

how is the movement of limbs detected

Answer 90

by **stretch receptors** in the **skeletal muscles** of limbs, which send impulses to the **CV centre** to **increase** heart rate

Question 91

what is the function of the _hypothalamus_ in the regulation of heart rate

Answer 91

under 'fight or flight' conditions or stress, the hypothalamus sends signals to the CV centre to increase heart rate. The CV sends impulses via the sympathetic branch of the autonomic NS to the adrenal glands to secrete the hormone _adrenaline._

Question 92

what is the function of the _cerebral cortex_ in the regulation of heart rate

Answer 92

impulses may be sent from the cerebral cortex to the CV centre to affect heart rate eg. meditation, sexual arousal, cognitive factors

Question 93

what is the overall structure of the _autonomic_ NS

Answer 93

* consists only of motor neurones * innervates cardiac and smooth muscle and glands (exocrine, endocrine) * does not involve voluntary/conscious control * controlled by the medulla oblongata and the hypothalamus in the brain * there are two divisions: sympathetic and parasympathetic; each division has two neurones from the CNS to the effectors: PRE-GANGLIONIC + POST-GANGLIONIC

Question 94

what is a _ganglion_ and what is the _pre-ganglionic_ neurone and _post-ganglionic_ neurone

Answer 94

GANGLION- a group of nerve cell bodies outside the CNS (ganglia) PRE: neurone which leaves the CNS in the ventral root and has its synaptic terminals in a ganglion POST: neurone which has its cell body in the ganglion and goes to the effector

Question 95

what is a Schwann cell (*1 mark*)

Answer 95

A glial (non-neuronal) cell in the PSN that produces the myelin sheath around neuronal axons

Question 96

*what is a _leucocyte_*

Answer 96

WHITE BLOOD CELLS, including *lymphocytes, macrophages and other phagocytes.*

Question 97

name two **antibiotic resistant bacteria**

Answer 97

MRSA ## Footnote causes serious wound infections, resistant to several antibiotics, including meticillin *Clostridium difficile* infects the digestive system

Question 98

suggest three ways a doctor can reduce the likelihood of antibiotic resistance developing

Answer 98

- *not prescribing antibiotics for minor infections* ## Footnote * - not prescribing to prevent infections, except patients who are elderly/have HIV* * - advise patients to take _all_ of the antibiotics to make sure the infection is fully killed*

Question 99

what happens in a *fight or flight response*

Answer 99

* **SYMPATHETIC NS** * quickly run out of the way = electrical response from receptors in eyes, brain, muscles * **Hypothalamus** * Neurosecretory cells- adrenal medulla- adrenaline = **non-steroid hormone** i.e. binds to CSM * **Vasodilation** of muscles, **inc. breathing rate** in lungs, **inc. heart rate** in heart, decrease rate of digestion by *vasoconstriction* of intestines, **glycogenolysis** in liver releases **glucose** into bloodstream, **dilation** of pupils

Question 100

name the channels on the *post-synaptic neurone*

Answer 100

**Ligand-gated ion channels**

Question 101

how is the electrical impulse inhibited at a synapse after it has 'diffused across'

Answer 101

*_Acetylcholinesterase_* *enzyme in pre-synaptic cleft hydrolyses acetylcholine to _acetate_ _+ choline_.* - prevents transmission continuing forever - ensures AP is only transmitted in one direction

Question 102

what is *convergence & divergence* in neurones

Answer 102

CONVERGENCE- many neurones releasing neurotransmitters for one post-synaptic neurone DIVERGENCE- one pre-synaptic neurone releases neurotransmitters to many post-synaptic transmitters

Question 103

what is **spacial summation**

Answer 103

*summation = combination of APs* where multiple small action potentials add up to one large action potential that depolarises to threshold in the post-synaptic neurone

Question 104

what is **temporal summation**

Answer 104

*summation = combination of APs* multiple action potentials firing simultaneously (each one becoming larger) depolarise the post-synaptic membrane

Question 105

How does the medulla oblongata of the brain control HR? Which neurotransmitter do they release?

Answer 105

**Accelerator nerve** increases HR by releasing **noradrenaline** at the SAN. eg. during exercise **Vagus nerve** decreases HR by releasing **acetylcholine** at the SAN. - increases delay at the AVN. eg. after exercise These are regulated by the **cardioacceleratory + cardioinhibitory** centres in the brain.