Neuro Block 10?

Where do first order neurons terminate in the vestibular pathway?

1. superior vestibular nuclei

2. inferior vestibular nuclei

3. medial vestibular nuclei

4. lateral vestibular nuclei

What 3 pathways connect in order to coordinate movement, posture and balance?

1. visual motor system

2. descending motor system

3. cerebellar pathways

List the Ascending pathway of the vestibular system:

1. Medial Longitudinal Fasciculus

What is the function of the Medial Longitudinal Fasciculus?

• coordination of eye and head movement (visual stabilisation)

Summarise the pathway of the Medial Longitudinal Fasciculus:

oculomotor, trochlear and abducens nuclei → cerebral cortex (VPN of thalamus) → Cerebellum

List the 2 descending Vestibular pathways:

1. Medial Vestibulospinal tract - receives fibres from ipsilateral and contralateral side

2. Lateral Vestibulospinal tract - only receives fibres from ipsilateral side

Where do neurones of the medial and lateral vestibulopsinal tracts synapse?

• in the anterior / ventral grey horn of the spinal cord

Give the resting potential for neurons

• - 70 mV

Give the threshold potential of neurons:

• - 55mV

Give peak depolarisation:

• +30 mV

What causes the neuron to depolarise?

• Na+/K+ pump

• moves 3Na+ out for every 2K+ in

• however, K+ leaks out of the membrane faster than sodium enters so the neuron becomes more negative

What happens once inside the neuron reaches - 55mV?

• voltage gated Na+ channels open and rapid depolarisation occurs

What happens once peak depolarisation has been reached?

• Na+ channels close

• K+ channels open

• potassium leaves the cell and membrane becomes negative again

List 4 key properties of neuron action potentials:

1. All or nothing - must reach threshold to activate a full action potential.

2. One directional - due to refractory period

3. Signal Strength coding; frequency of firing and number of neurons activated.

4. Saltatory conduction - jumps between Nodes of Ranvier

Summarise Synaptic Transmission:

1. action potential arrives at synapse triggering voltage-gated Ca2+ channels to open → influx of calcium

2. Calcium causes vesicles (filled with neurotransmitter) to fuse with the motor membrane (synaptic cleft)

3. neurotransmitter is released and diffuses across the gap

4. neurotransmitter binds to receptors (ligand-gated channels)

What two types of signals can there be?

• excitatory

• inhibitory

Give two examples of an excitatory signal:

• GABA
  Glutamate

What is the difference between spatial summation and temporal summation?

1. Spatial Summation → multiple inputs at different locations

2. Temporal Summation → rapid repeated input

What are the 2 overarching types of neurotransmitter?

1. classical

2. peptide

List the 4 subcategories of classical transmitters:

1. amino acids - glutamate

1. acetylcholine - Ach - mixed

2. monoamines - noradrenaline, dopamine, serotonin

3. purines - adenosine, ATP

Give 6 examples of peptide transmitters:

1. Substance P

2. Met-enkephalin

3. Beta-endorphin

4. Dynorphins

5. Somatostatin

6. Cholecystokinin (CCK)

What occurs at Neuromuscular Junctions?

1. action potential reaches motor neuron terminal

2. Ach is released

3. Ach binds to nicotinc receptors on muscles → opens ion channels → depolarisation → muscle contraction (action-myosin cross linking)

4. Ach is broken down or reuptake into presynaptic terminal occurs

Which illness/toxin affects Ach release at the neuromuscular junction?

• Myasthenia gravis (botulinum toxin)

List where the cranial nerves arise from in the brain:

1. Midbrain - 1, 2, 3, 4

2. Pons - 5, 6, 7, 8

3. Medula - 9,10, 11, 12

Do plexuses have synapses?

• most do not have synapses

List 2 major plexuses:

1. Brachial Plexus

2. Lumbosacral Plexus

List 2 nerves and their roots in the Lumbosacral Plexus:

1. Femoral nerve (L2-4) - repsonsible for knee extension and anterior thigh sensation.

2. Sciatic nerve (L4-S2) - responsible for hip extension and knee flexion

What is a key histological difference between myelin in the CNS and myelin in the PNS?

• no Schwann cells in CNS, only oligodendrocyte glial cells

• Schwann cells in PNS

What is the difference in fibres between sympathetic and parasympathetic tracts?

Sympathetic: short preganglionic fibres but long postganglionic fibres

Parasymapthetic: long preganglionic fibres but short postganglionic fibres