Nervous System 3 - Synapse, Neural Circuits and Spinal Nerves

Question 1

What is a Synapse?

Answer 1

Anatomically specialised junction between two or more neurons, or neuron & effector organ (muscle, gland, etc.)

Question 2

What is an electrical synapse?

Answer 2

Action potentials conduct between adjacent cells
Achieved via gap junctions – Connexons provide direct connection between cells
Faster communication -Direct connection allows for faster transmission
Synchronisation - Actions potentials in several neurons at one time |
Coordinated contraction of muscle (e.g heart)

Question 3

What is a chemical synapse?

Answer 3

Synapse communicates with other synapse via neurotransmitters (indirect)
Pre-synaptic neuron communicates with post-synaptic neuron across the synaptic cleft – 20-50 nm
Postsynaptic neuron receives post-synaptic potentials (PSP’s) –
Excitatory or inhibitory
Transmission is slower than electrical synapse

Question 4

Neurotransmitters are excitatory or inhibitory. True or False?

Answer 4

True

Question 5

What are Excitatory neurotransmitters?

Answer 5

Acetylcholine
Adrenaline
Dopamine
Glutamate

Question 6

What are Inhibitory neurotransmitters?

Answer 6

γ-aminobutyric acid (GABA)
Endorphins
Glycine

Question 7

What can neurotransmitters be classified as?

Answer 7

Ionotropic receptor
Metabotropic receptor

Question 8

What is an Ionotropic receptor?

Answer 8

A neurotransmitter receptor that has a binding site & ion channel – Components of same protein
Binding of neurotransmitter opens channel & generates an excitatory/inhibitory post-synaptic potential
Acetylcholine receptor generates an excitatory postsynaptic potential – Sodium & calcium influx |Potassium efflux
GABA receptor generates an inhibitory postsynaptic potential – Chloride influx

Question 9

What is a metabotropic receptor?

Answer 9

A neurotransmitter receptor that has a binding site but lacks an ion channel – Separate components
Metabotropic receptor coupled to a separate ion channel via G-protein
G protein can open channel directly or indirectly via second messenger
Metabotropic acetylcholine receptor generates an inhibitory postsynaptic potential – Potassium efflux

Question 10

What is spatial summation?

Answer 10

Synaptic potentials occur in different locations at the same time

Question 11

What is temporal summation?

Answer 11

Synaptic potentials occur in same location at different times

Question 12

What is the neuromuscular junction?

Answer 12

A synapse between a somatic motor neuron & muscle fibre

Question 13

What is a neural circuit?

Answer 13

Functional neuron groups that process specific information

Question 14

What types of neural circuits are there?

Answer 14

Diverging circuit
Converging circuit
Reverberating circuit
Parallel after-discharge circuit

Question 15

What is a diverging circuit?

Answer 15

Single presynaptic neuron stimulates increasing numbers of cells in the circuit

Question 16

What is a converging circuit?

Answer 16

Several presynaptic neurons stimulate a single postsynaptic neuron

Question 17

What is a reverberating circuit?

Answer 17

Presynaptic neuron causes postsynaptic neuron to transmit a series of nerve impulses

Question 18

What is a Parallel after-discharge circuit?

Answer 18

Single presynaptic cell stimulates a group of neurons that synapse a single
postsynaptic cell

Question 19

What is the diameter of the spinal cord?

Answer 19

Approx 2cm

Question 20

What nerves arise from the cervical enlargement?

Answer 20

Nerves to & from upper limbs

Question 21

What nerves arise from the lumbar enlargement?

Answer 21

Nerves to & from lower limbs

Question 22

How many pairs of spinal nerves are there?

Answer 22

33

Question 23

Spinal nerves & the nerves that branch from them are part of the peripheral nervous system (PNS). True or False?

Answer 23

True

Question 24

True or False? Spinal nerves are paths of communication between
spinal cord & specific regions of the body

Answer 24

True

Question 25

What are the steps of processing sensory input and motor output?

Answer 25

1 - Sensory receptors detect stimulus
2 - Sensory neurons convey sensory input along the axon into the posterior root
3 – Axons of sensory neurons extend into white matter of spinal cord & ascend to
brain (sensory tract)
4 – Axons of the sensory neurons enter posterior grey horn & synapse with interneurons that ascend to brain
5 – Axons of sensory neurons may enter the posterior grey horn & synapse with
interneurons that innervate somatic motor neurons involved with spinal reflex
6 – Motor output from spinal cord to skeletal muscles
7 – Activation of somatic motor neuron
8 – Motor output from spinal cord to cardiac muscle, smooth muscle or glands involve
autonomic motor neurons
9 – Autonomic motor neurons from spinal cord synapse with another group of
autonomic motor neurons in the PNS