Chapter 13- Neuronal communication

Question 1

Describe the key structure of a neurone

Answer 1

Cell body
Dendrons- carry signals towards the cell body
Axons- carry signals away from the cell body

Question 2

Describe the structure of a sensory and motor neurone respectively

Answer 2

Sensory- cell body separated from the axon
Motor neurones- cell body with many dendrites and one long axon

Question 3

What kind of cell produces myelin sheath?

Answer 3

Schwann cells

Question 4

What are the gaps in myelin sheath called?

Answer 4

node of Ranvier

Question 5

List the four types of sensory receptors

Answer 5

Mechanoreceptor
Chemoreceptor
Photoreceptor
Thermoreceptor

Question 6

Describe how a Pacinian corpuscle transduces mechanical energy to electrical energy

Answer 6

1. In a normal state, the stretch-mediated sodium ion channels are too narrow to allow sodium ions to pass through
2. Pressure is applied, corpuscle changes shape
3. Stretch mediated sodium channels widen and sodium ions diffuse into the membrane, which changes the potential and depolarises the membrane
4. This creates a generator potential which transforms into an action potential

Question 7

What are the two ions involved in nerve transmission across an axon?

Answer 7

Sodium and Potassium

Question 8

What is the resting potential of an average membrane?

Answer 8

-70mV

Question 9

Describe the events creating a resting potential

Answer 9

1. Sodium ions are actively transported out the axon whereas potassium ions are transported into the axon by the sodium-potassium pump
2. Sodium channels are closed but potassium gates are opened allowing potassium ions to diffuse back out the axon.
3. This leads to an imbalance of positive ions and means the membrane has a negative potential

Question 10

What is the threshold charge for a potential to be generated?

Answer 10

-35mV

Question 11

Define depolarisation

Answer 11

The rapid change in potential difference from negative to positive

Question 12

How does depolarisation occur?

Answer 12

The change in potential opens voltage gated sodium channels and allows sodium ions to diffuse down the concentration gradient
Positive feedback opens more sodium ion channels :)

Question 13

How does repolarisation occur?

Answer 13

Once the potential difference of +40mV is reached, sodium channels close and and potassium channels open, reducing the charge across the membrane

Question 14

What occurs during hyperpolarisation?

Answer 14

When more potassium ions diffuse out of the axon than normal, resulting in the inside of the axon becoming more negative than at its resting state.

Question 15

How are action potentials transmitted across axons?

Answer 15

Depolarisation of the first section of axon membrane acts as a stimulus for the next region of membrane. Once sodium ions enter the cell they are attracted by the negative region ahead

Question 16

What is the refractory period?

Answer 16

The period after depolarisation where the membrane can’t be excited again as the voltage gated sodium channels remain closed

Question 17

What is saltatory conduction?

Answer 17

The ‘jumping’of an action potential between nodes of Ranvier, speeding up action potential transmission

Question 18

Describe the all or nothing principle

Answer 18

Nerve impulses need a threshold principle to be triggered. All action potentials reach the same potentials, and a more powerful stimulus only triggers more frequent action potentials, not more powerful ones

Question 19

Describe the structure of a synapse

Answer 19

Presynaptic and postsynaptic neurones separated by a synaptic cleft. Presynaptic neurone forms the synaptic knob and postsynaptic knob has external receptors for neurotransmitters

Question 20

Name the two types of neurotransmitters

Answer 20

Excitatory- result in the depolarisation of the post synaptic neurone (eg acetylcholine)
Inhibitory- result in the hyper polarisation of the postsynaptic membrane, preventing an action potential (GABA)

Question 21

What happens after the depolarisation of the presynaptic membrane?

Answer 21

Calcium ion channels open and calcium ions diffuse into the synaptic knob.
Synaptic vesicles containing neurotransmitters fuse to the presynaptic membrane, releasing its contents into the synaptic cleft

Question 22

Define a cholinergic synapse

Answer 22

Use the transmitter acetylcholine- common at vertebrates and neuromuscular junctions

Question 23

What happens to acetylcholine after it has triggered an action potential?

Answer 23

Hydrolysed by the enzyme acetylcholinsterase into choline and ethanoic acid, which are transported back to the presynaptic membrane and used to reform acetylcholine

Question 24

Describe the two types of summation

Answer 24

Spatial- when a number of presynaptic neurone connect to one postsynaptic neurone, each releasing neurotransmitters that build up enough to trigger an action potential
Temporal- a single presynaptic membrane builds up neurotransmitters in the synaptic cleft over several action potentials until it’s enough to activate one action potential in the postsynaptic membrane

Question 25

How is the nervous system structurally organised?

Answer 25

The Central Nervous system and the Peripheral Nervous system

Question 26

How is the Nervous system functionally organised?

Answer 26

Somatic nervous system- under conscious control Autonomic nervous system- under subconscious control

Question 27

What is the difference between the parasympathetic and sympathetic nervous system

Answer 27

Both under the autonomic nervous system, but sympathetic increases activity and the parasympathetic system decreases activity

Question 28

Name the 5 main areas of the brain

Answer 28

Cerebrum- conscious thought, learning, memory Cerebellum- unconcious posture, balance and non voluntary movement Medulla- Heart rate and breathing rate Hypothalamus- Regulatory centre for temperature and water content Pituitary gland- stores and secretes hormones

Question 29

Name a hormone produced by the anterior and posterior pituitary gland

Answer 29

Anterior- FSH Posterior- ADH (storage)

Question 30

What happens to impulses in the brain?

Answer 30

Impulses from each side of the body cross (impulses in the right are received in the left side of the brain, ect)

Question 31

Where is the cerebral cortex located?

Answer 31

The outer 2-4 mm of the cerebral hemispheres

Question 32

When might an impulse not pass through a coordination centre?

Answer 32

When it’s involved in a reflex arc- Runs through relay neurones in the spinal cord

Question 33

What initiates the knee jerk reflex?

Answer 33

The tap just below the patella stretches the patellar tendon contracting the extensor muscle on the top of the thigh and relaxing the flexor muscle

Question 34

What are the ways the blinking reflex can be stimulated?

Answer 34

Something touching the cornea or loud noises triggers an impulse along the fifth cranial nerve which is returned along the seventh, initiating the motor response of closing the eyelids

Question 35

Name and describe the three types of muscle

Answer 35

Skeletel- voluntarily controlled, striated, regularly arranged so that muscle contracts in one direction Cardiac- only found in the heart, specially striated and branch and interconnect for simultaneous contraction. Myogenic Involuntary (smooth) - non striated, no regular arrangement, can contract in many different directions. Often found in organ walls

Question 36

Describe the structure of skeletal muscle

Answer 36

Made up of bundles of muscle fibres enclosed in a plasma membrane called the sarcolemma Muscle fibres are made of a number of embryonic cells fused together. The shared cytoplasm is called the sarcoplasm Parts of the sarcoplasm folds inwards called T tubules which spread electrical impulses through sarcoplasm so the entire fibre contracts at once

Question 37

Describe the structure of myofibrils

Answer 37

Long cylindrical organelles made of protein and specialised for contraction lined up in parallel.

Question 38

Describe the two filaments that make up myofibrils

Answer 38

Actin- the thinner filament, consisting of two thinner strands twisted around eachother Myosin- the thicker filament- consists of long rod shaped fibres with bulbous heads projecting to one side

Question 39

What causes the striped appearance of myofibrils?

Answer 39

Alternating light and dark bands Light bands (I bands) the region where actin and myosin filaments don’t overlap Dark bands (A bands)- presence of already thick myosin overlapped with actin Z lines- Found at the centre of each I bands. H-zone- lighter region found in the centre of A bands where only myosin filaments are present

Question 40

Define the sarcomere

Answer 40

The distance between the Z lines

Question 41

Describe the structure of myofibrils in a resting state

Answer 41

Myosin heads are bent Binding sites on actin filaments are blocked by tropomyosin molecules held in place by troponin

Question 42

What happens to myofibrils when a muscle is stimulated to contract?

Answer 42

Myosin heads form myosin-actin cross bridges and they flex in union, pulling actin along the myosin filament, myosin detaches and they return to their original angle using ATP

Question 43

Define a motor unit

Answer 43

All the muscle fibres stimulated to contract by a singular neurone

Question 44

What has to occur to allow actin-myosin bridges to form?

Answer 44

Calcium ions have to bind to troponin stimulated by action potentials reaching the sarcoplasmic reticulum. This causes the troponin shape and pulls the tropomyosin away from the actin binding site

Question 45

Name the three ways that ATP are generated for muscle contraction

Answer 45

Aerobic respiration Anaerobic respiration Creatine Phosphate

Question 46

How does creatine phosphate help to generate ATP for muscle contraction?

Answer 46

Creatine phosphate can be used as a reserve supply of phosphate to phosphorylate ADP