PNS

Question 1

What are the two main divisions of the nervous system?

Answer 1

• The central nervous system (brain and spinal chord).
• The peripheral nervous system (everything else).

Question 2

What do cranial and spinal nerves have?

Answer 2

Sensory (afferent) motor (efferent) components, ganglia, and sensory receptors.

Question 3

What does the sensory system consist of?

Answer 3

A variety of different receptors as well as sensory neurons.

Question 4

What does the motor system do?

Answer 4

Conducts nerve impulses from the CNS to muscles and glands.

Question 5

What other divisions is the PNS subdivided into?

Answer 5

• Somatic (voluntary),
• Autonomic (involuntary),
• Enteric nervous system

Question 6

What does the somatic nervous system consist of?

Answer 6

• Sensory neurons that conduct impulses from cutaneous and special sense receptors to the CNS
• Motor neurons that conduct impulses from the CNS to skeletal muscle tissue

Question 7

What does the autonomic nervous system contain?

Answer 7

Sensory neurons from visceral organs and motor neurons that convey impulses from the CNS to smooth muscle tissue, cardiac muscle tissue, and glands.

Question 8

How can be signals be passed through the PNS?

Answer 8

1. Nerves - Action potentials signal transduction along nerves and synapses.
2. Muscle – Action potentials and the initiation and propagation of muscle contractions.
3. Endocrine cells - Secretion of hormones.

Question 9

Define the basic reflex arc.

Answer 9

Sensory Receptor -> [pass through a sensory ganglion] -> [enter dorsal horn of spinal cord] -> synapse on motor neurone in ventral grey matter -> [motor neurone leaves via ventral horn] -> innervation of motor organ e.g. muscle.

Question 10

Define the basic properties of a neuron.

Answer 10

• The cell body (contains nucleus).
• Dendrites which spread out from the soma.
• An axon

Question 12

What is the difference between axon and dendrite?

Answer 12

Axons deliver output whereas input is received by dendrites and the cell body.

Question 13

What is a nerve?

Answer 13

Bundle of axons from many neurons (think trunking!)

Question 14

Explain the electrical events that lead to an action potential.

Answer 14

1. opening of voltage-gated Na+ channels
2. Na+ ions will rush into the cell = depolarisation
3. AP generated if threshold potential met

Question 15

Explain the refractory period.

Answer 15

• The interval during which a second action potential absolutely cannot be initiated.
• This is because the all the Na+ channels that originally opened to depolarise the membrane are now inactivated.

Question 16

What are the factors affecting rate of nerve conduction?

Answer 16

• Temperature
• Thickness/diameter of neurone
• Myelin sheath

Question 17

Explain the myelin sheath.

Answer 17

• Produced by Schwann cells
• Electrically insulates the axon
• Has gaps called nodes of Ranvier which enable saltatory conduction

Question 18

What is the relationship between nerve diameter and speed of impulse transmission?

Answer 18

Larger-diameter fibres conduct impulses faster than those with smaller diameters.

Question 19

What codes the intensity of a stimulus and why?

Answer 19

-APs are an all or nothing event so intensity coded in the rate of impulse production i.e. the frequency of APs.

Question 20

What is a synapse?

Answer 20

The junction between two neurons.

Question 21

Explain the difference between an action potential and a graded potential.

Answer 21

• Graded potentials: Small deviation from the resting membrane potential that makes the membrane either more negative (hyperpolarisation) or more positive (depolarisation).
• Graded potentials can vary in amplitude.

Question 22

What is an excitatory neurotransmitter?

Answer 22

One that can depolarise or make less negative the postsynaptic neuron’s membrane, bringing the membrane potential closer to threshold

Question 23

What is an inhibitory neurotransmitter?

Answer 23

Hyperpolarises the membrane of the postsynaptic neuron, making the inside more negative and generation of a nerve impulse more difficult.

Question 24

What are some important neurotransmitters in the PNS?

Answer 24

• Acetylcholine
• Adrenaline

Question 25

How is neurotransmitter removed from the synaptic cleft?

Answer 25

1. Diffusion
2. Enzymatic degradation
3. Uptake into cells

Question 26

What is a neuromuscular junction?

Answer 26

A specialised type of Synapse between a motor neuron and a skeletal muscle cell.

Question 27

Outline the sequence of events at a neuromuscular junction.

Answer 27

1. AN ACTION POTENTIAL IN A MOTOR NEURON IS PROPAGATED TO THE TERMINAL BUTTON.
2. THE PRESENCE OF AN ACTION POTENTIAL IN THE TERMINAL BUTTON TRIGGERS THE OPENING OF VOLTAGE-GATED CA2+ CHANNELS & THE SUBSEQUENT ENTRY OF CA2+ IN TO THE TERMINAL BUTTON.
3. CA2+ TRIGGERS THE RELEASE OF ACETYLCHOLINE BY EXOCYTOSIS FROM A PORTION OF THE VESICLES.
4. ACETYLCHOLINE DIFFUSES ACROSS THE SPACE SEPARATING THE NERVE AND MUSCLE CELLS AND BINDS WITH RECEPTOR SITES SPECIFIC FOR IT ON THE MOTOR END PLATE OF THE MUSCLE CELL MEMBRANE
5. THIS BINDING BRINGS ABOUT THE OPENING OF ION CHANNELS, LEADING TO A RELATIVELY LARGE MOVEMENT OF NA+ INTO THE MUSCLE CELL COMPARED TO A SMALLER MOVEMENT OF K+ OUTWARD.

Question 28

What is a difference between NMJ and synapse (aside from neuron/neuron neutron/muscle)?

Answer 28

A NMJ is always excitatory while a synapse may be either excitatory or inhibitory.

Question 29

Draw a neuromuscular junction.

Answer 29

Look at google.

Question 30

Define synaptic potential.

Answer 30

A change in the voltage difference across the membrane of a postsynaptic cell, produced by the transmission of a nerve impulse across a synapse.

Question 31

What is the difference between synaptic potential and action potential?

Answer 31

Synaptic potentials are small and many are needed to add up to reach the threshold. This means a single EPSP/IPSP is typically not enough to trigger an action potential. The two ways that synaptic potentials can add up to potentially form an action potential are spatial summation and temporal summation.