5.1.3 Neuronal communication

Question 1

Peripheral nervous system (2)

Answer 1

• Nerves that branch off the CNS and attach to muscles and tissues
• Branches out into sensory division and motor division- autonomic and somatic

Question 2

Central nervous system

Answer 2

• The brain and the spinal cord, mainly responsible for processing information

Question 3

Somatic NS (4)

Answer 3

• Part of the motor division that allows voluntary movements especially in muscle contracts
• contain heavily myelinated axons for fast impulses
• contains single neurones from CNS to effector organs

Eg lifting a weight

Question 4

Autonomic motor system (5)

Answer 4

• actions that are involuntary: reflexes
• divided into sympathetic and parasympathetic systems
• neurotransmitter involved: acetylcholine
• axons are lightly myelinated
• impulses are carried to glands and smooth muscle cells in organs

Eg responsible for the heart beating and the digestion of food (peristalsis)

Question 5

Sympathetic motor system

Answer 5

• part of the autonomic system
• actions that occur to increase activity
• controls urgent situations like an increase in heart rate
• neurotransmitter: noradrenaline

Question 6

Sympathetic actions for the following:

• Salivary glands
• lungs
• kidneys
• stomach
• small intestine

Answer 6

Sympathetic:

salivary glands: saliva reduced 
lung: bronchi relaxed
Kidney: less urine secreted 
Stomach: peristalsis reduced 
Small intestine: peristalsis reduced

Question 7

Stimulus

Answer 7

Changes in the internal/ external environment

Question 8

Describe the structure of a neurone

Answer 8

• Cell body: contains main organelles for the cell: nucleus, RER, mitochondria, ribosome which produce neurotransmitters
• Dendron: extend and divide into dendrites and carry impulses towards the cell body
• Axon: single extension that carries impulses away from cell body

Question 9

Sensory neurones

Answer 9

• carry impulses from sensory receptor cells to a relay neurone, motor neurone or the brain.
• Contains one dendron that carries impulses towards the cell body and an axon to carry the impulse away from the cell body.

Question 10

Relay neurone

Answer 10

• Transmits impulses between neurones

- have multiple short axons and neurones

Question 11

Motor neurones

Answer 11

• Carry impulses from a sensory or relay neurone to an effector cell- eg muscle
• contain many dendrites: multipolar

Question 12

Schwann cells

Answer 12

• Peripheral glial cell that produces myelin sheath that wraps around axons for insulation
• this allows quicker transmission of impulses

Question 13

How does the myelin sheath contribute to the speed of impulses (3)

Answer 13

• In peripheral nerves they have ‘nodes of Ranvier’ around the axon which are gaps between myelin sheath
• the sheath acts as an electrical insulator which quickens impulses
• the nodes allow a jump (saltatory conductivity) for the impulses which is quicker than a continuous transmission in non-myelinated axons

Question 14

Sensory receptor (6)

Answer 14

• Convert stimulus into a nerve impulse which is picked up by sensory neurones (transducer)
• They are specific to a single type of stimulus
• mechano: pressure and movement
• chemo: chemicals
• thermo: temperature
• photo: light

Question 15

Pacinian corpuscle

Answer 15

• Sensory receptors that detect mechanical pressure in the skin
• most prominent in finger tips and toes as well as joints
• contain stretch mediated sodium channels

Question 16

How does the pacinian corpuscle convert mechanical pressure into an impulse? (4)

Answer 16

• Pacinian corpuscle detects pressure in the skin and changes shape
• this also changes the shape surrounding membrane of neurones and stretch sodium pumps
• this allows sodium ion channels to open so that Na can diffuse up to the point where the cell is depolarised
• this causes an action potential which is created by the generator potential and sends impulse to the CNS

Question 17

Olfactory receptor

Answer 17

• Chemoreceptor that detects smell in the nose

Question 18

End bulbs of Krause

Answer 18

Thermoreceptor that detects heat in the tongue

Question 19

Cone cells

Answer 19

Photoreceptor that detects light wavelengths in the eyes

Question 20

Resting potential

Answer 20

• When a neurone is not transmitting any impulses and the outside of the membrane is more positively charged than the inside
• The polarised membrane usually has a voltage of -70 mV

Question 21

Sodium- potassium pump

Answer 21

• Helps maintain resting potential by actively transporting 2 potassium ions into the cell and 3 sodium ions out
• This creates an electrochemical gradient where sodium diffuses into the axon and potassium diffuse out
• Potassium ion gates are mainly opened which enables potential

Question 22

Action potential (5)

Answer 22

When the charges of the axon are reversed from -70 mV to +40 mV- neurones are depolarised

Change in voltage of the membrane above around -55 cause sodium ion channels to open and cause them to diffuse into the axon

When the voltage reaches +40, voltage gates sodium pumps close which allow more K to diffuse into the now more permeable membrane

This causes a more negative axon where it goes into hyperpolarisation

Once Na ions move out of the cell via the sodium/ potassium pump, the resting potential is reached

Question 23

Repolarisation

Answer 23

This happens after the voltage- gated sodium ion channel closes

Voltage gated Potassium ion channels open which causes potassium to diffuse out of the axon, down its electrochemical gradient.

Causes the inside of the axon to be more negative than outside

Question 24

Hyperpolarisation (4)

Answer 24

When the axon is repolarising, initially a lot of Potassium ions diffuse out of the axon.

This makes the inside of the axon more negative than its usual resting potential.

This causes the voltage- gates potassium ion channels to close which prevents the inside of the axon to be too negative.

Now the sodium-potassium pump controls the K+ and Na+ ions until resting potential is achieved

Question 25

Explain what saltatory conduction is and evaluate its effectiveness.

Answer 25

This is the method in which electrical impulses travel across the axon at the ‘Node of Ranvier’ in myelinated axons.

Here, sodium ions can only pass through the membrane proteins in the nodes. This creates a ‘localised’ circuit between nodes, which the action potential jumps between.

This is much quicker than a wave depolarisation down an axon, as there are less places for sodium to transport.

This is also more energy efficient as less ATP is needed for reploarisation when using the sodium ion channels.

Question 26

Describe how the first neurone communicates with the second neurone across the gap. (6)

Answer 26

An action potential travels along the presynaptic neurone which causes Ca2+ channels to open and allow calcium to diffuse in the knob.

This pushes vesicles containing neurotransmitters towards the membrane.

Vesicles fuse with meme range and releases neurotransmitters from vesicles via exocytosis.

The neurotransmitters diffuse across the synaptic cleft and binds to receptors in the post synaptic neurone.

This cusses Na+ channels to open and causes diffusion of Na+ into post-synaptic knob. This causes a depolarisation.

Enzymes are released (such as acetylcholinesterase) to break down neurotransmitters.

Question 27

How are neurones adapted to cell signalling

Answer 27

The pre-synaptic knob allows storage of vesicles filled with neurotransmitters.

The PS knob also provides a larger surface area to release more neurotransmitters.

Specialised proteins in the post synaptic membrane such as ligand gated sodium channels- specified response to molecules.

Question 28

Importance of synapses.

Answer 28

Allows the transmission of impulse in one direction as neurotransmitters can only be released from the Pre-S knob.

Allows acclimatisation: prevents continuous response to unimportant stimuli.

Allows summation: never impulses from more than one neurone combine to create the same response.

Inhibitory synapse prevent the formation of an action potential in postsynaptic neurone.

Question 29

The use of ATP at a cholinergic synapse.

Answer 29

Formation of acetylcholine: combines choline and ethanoic acid.

Exocytosis: release of acetylcholine from the pre-synaptic neurone.

Formation and movement of vesicles which store acetylcholine.

Question 30

Compare the structure of the sensory and motor neurone.

Answer 30

• Motor neurone has a longer axon.
• The cell body in the motor neurone is terminal whereas it’s in the middle for the sensory neurone.
• Motor neurone contains no dendrons whereas sensory neurone contains long dendrons.