MNSR 15 - Neurophysiology of the synapse, PNS, Autonomic Nervous System

Question 1

What causes hyperpolarization?

Answer 1

Different neurotransmitter may cause the opening of the Cl- ion channels which increase the electronegativity of the postsynaptic membrane, which causes hyperpolarization.

Question 2

How can rapid repolarization occur?

Answer 2

For rapid repolarization to occur, excess neurotransmitter in the synpatic cleft must be removed via enzymes or reuptake by the presynaptic terminal.

Question 3

What two effects may be exhibited in the postsynaptic neuron?

Answer 3

1. Excitatory Postsynaptic Potential (EPSP - initiates depolarization)
2. Inhibitory Postsynaptic Potential (IPSP - causes hyperpolarization and prevents action potential from occurring by allowing the flow of Cl- ions)

Question 4

How many of each vertebra are there?

Answer 4

• 7 cervical
• 12 thoracic
• 5 lumbar
• 5 sacral
• 5 coccygeal

Question 5

What are the two types of nerves that run from the spinal cord?

Answer 5

1. Pre-ganglionic (Spinal cord to the ganglion)
2. Synapse (First nerves synapses with the second nerve)
3. Post-ganglionic (ganglion to the organ)

Question 6

Describe Thoracolumbar outflow for the Sympathetic Nervous System.

Answer 6

1. Short Pre-synaptic ganglion
2. Long Post-synaptic ganglion
3. Both connect to Paravertebral ganglia that run from the base of the skull to the coccyx (2 paravertebral ganglia with 15-16 ganglia per column)

Question 7

Describe how sensory neurons interact with the spinal cord through the vertebrae.

Answer 7

1. Afferent neurons enter via the dorsal root
2. Sympathetic Nervous system efferent neurons leave via the ventral root, pass through the white ramus and then either travel up or down to the ganglion.
3. Synapse occurs in the ganglion or abdominal ganglion

Question 8

Explain neurotransmitters in the Sympathetic Nervous System and list possible effects of it.

Answer 8

1. When the presynaptic ganglion reaches the synapse, it releases ACh.
2. When the postsynaptic ganglion reaches the organ, it releases adrenaline which causes:
   - pupil dilation
   - bronchial relaxation
   - increase in heart rate
   - stimulates glucose release
   - adrenaline release
3. For the Parasympathetic Nervous System, both release ACh.

Question 9

Describe Craniosacral outflow for the Parasympathetic Nervous System.

Answer 9

1. Long pre-synaptic ganglion

2. Short post-synaptic ganglion

Question 10

Explain synaptic transmission.

Answer 10

Acetylcholine is released and reaches the postsynaptic membrane where it is broken down by an enzyme called Acetylcholinesterase. The degraded products are brought to the presynaptic terminal where it is remade into ACh and packaged into vesicles.

Question 11

What are the two main functions of the spinal cord?

Answer 11

1. Transmit nerve impulses to and from the brain
2. Act as a reflex center
   Additionally, the spinal cord is protected by the neural arches of the vertebrae and lies in the vertebral canal.

Question 12

Explain the reflex arc.

Answer 12

The reflex arc is controlled by the Autonomic Nervous System:

1. Stimuli are detected by the receptor cells and travel along the afferent nerves that reach the spinal cord through the dorsal root.
2. In the Grey Matter, it synapses with interneurons
3. Interneurons relay the stimulus to the efferent nerves (depending on the reflex one or more efferent nerves may be stimulated)
4. Efferent nerves leave via the ventral root, travel through the white ramus, and head towards the ganglion and eventually the motor neurons of the effector organ.

Question 13

Explain Monosynaptic reflex vs. Polysynaptic reflex.

Answer 13

A monosynaptic reflex consists of only one sensory neuron and one motor neuron, while a polysynaptic neuron consists of multiple reflex pathways with one or more interneurons connecting afferent and efferent signals.