neuronal communication

Question 1

What are sensory receptors described as?

Answer 1

Transducers

They convert one form of energy into another form of energy (e.g., mechanical to electrical) into another form of energy

Question 2

What happens to the plasma membrane at the tip of the pacinian corpuscle during deformation?

Answer 2

The membrane becomes more permeable to Na+

Increased pressure causes sodium ion channels to open as temporary gaps appear between the phospholipids

Question 3

Why are action potentials not generated constantly when a person is wearing clothes?

Answer 3

Sodium ion channels remain open, so resting potential is not re-established

Ions are in the wrong place for correct ion movement across the membrane

Question 4

Where is the cell body of motor neurones located?

Answer 4

In the CNS, at the end of the neurone

Motor neurones carry impulses from the CNS to the effector (muscle or gland)

Question 5

What is the structure of sensory neurones?

Answer 5

Cell body in the PNS, dendrites at the end of their dendron, and a short axon

They connect to sensory receptors

Question 6

How do myelinated fibres compare to unmyelinated neurones in terms of conduction speed?

Answer 6

• Myelinated fibres conduct more quickly
• The myelin sheath acts as an electrical insulator, allowing saltatory conduction
  -lack of na+ +k+ vg in myleinated region

Question 7

What is the function of the myelin sheath?

Answer 7

Acts as an electrical insulator

Prevents movement of ions out of the neurone in myelinated regions

Question 8

What is saltatory conduction?

Answer 8

Action potential jumps from one node to another

Occurs at nodes of Ranvier in myelinated neurones

Question 9

What effect does temperature have on the speed of conduction?

Answer 9

• Increases speed due to increased kinetic energy
• Faster diffusion of ions (faster depolarisaion) and movement of neurotransmitter vesicles
• so faster exocytosis of the neurotransmitter
• neurotransmitter difffuses more quickly across the synaptic cleft
• broken down by enzyme acetylcholinesterase more quickly

Question 10

What happens to conduction of impulses at high temperatures?

Answer 10

• Ceases due to denaturation of ion channels/pumps
• The membrane fluidity increases so membrane is distrupted and synaptic enzymes are denatured

Question 11

What occurs when an action potential reaches the synaptic knob?

Answer 11

Calcium channels open –> Ca diffuse in –> causing acetylcholine vesicles to move towards the postsynaptic membrane –> release by exocytosis –> Acetylcholine diffuses across the synaptic cleft–> at postsynaptic neurone the neurotransmitter attaches to receptors

Question 12

What is the role of acetylcholine in the postsynaptic neurone?

Answer 12

Attaches to receptors causing sodium ion channels to open

This generates an action potential in the postsynaptic neurone

Question 13

Why are junctions/synapses between neurones important?

Answer 13

Allow communication, ensure one-way transmission, and enable convergence(many to one)/divergence( one to many) of impulses

Also filter out low-level stimuli and permit memory and learning

Question 14

True or False: Synapses allow transmission in both directions.

Answer 14

False

• Transmission is unidirectional due to the specific distribution of receptors and calcium channels
• only presynaptic neurone contains acetylcholine + ca channels
• only postsynaptic membran has ACh receptors + broken down there

Question 15

What is the all-or-nothing law in relation to action potentials?

Answer 15

Only stimuli greater than -65mV produce an action potential

• AP is the same size
• A strong stimulus produces many action potentials in rapid succession

Question 16

What effect do protease toxins have on SNARE/VAMP proteins?

Answer 16

Hydrolyze peptide bonds, destroying them so that VAMP proteins cannot bind to SNARE complex

• so microtubles broken down , so vesicles cannot move towrads membrane
• Prevents vesicles from fusing with the cell membrane, so ACh not secreted

Question 17

What common structures do both sensory and motor neurones have?

Answer 17

Dendrites, an axon, a cell body with a nucleus, and are myelinated by Schwann cells

Both have nodes of Ranvier and voltage-gated channels

Question 18

What does TTX do to voltage-gated sodium ion channels?

Answer 18

Binds to them, keeping them closed

• na+ cannot enter
• Prevents depolarization and action potential generation
• so impulse is not conducted along the axon , so no release of neurotransmitter

Question 19

What maintains the resting potential in neurones?

Answer 19

Sodium-potassium pump

Uses ATP to move 3 sodium ions out and 2 potassium ions in

Question 20

Fill in the blank: The synaptic cleft is the _______ between two neurones at a junction.

Answer 20

gap