NS

Question 1

What structures form the fourth ventricle?

Answer 1

The pons and medulla coming together with the cerebellum

Question 2

What structures form the third ventricle?

Answer 2

The diencephalon - thalamus and hypothalamus

Question 3

Describe the formation of the lateral ventricles

Answer 3

During embryological development cells of the insula cortex remain quiescent while those around it have a high mitotic division rate leading to the formation of C shaped structures including the lateral ventricles, the roof being the corpus callosum

Question 4

Outline the difference between neurotransmitters and neuromodulators

Answer 4

• Neurotransmitters are released by neurons at the presynaptic terminals and produce rapid excitatory or inhibitory responses in postsynaptic neurons -
• Neuromodulators produce slower responses to regulate presynaptic transmitter release and neuronal excitability. A neurotransmitter can also be a neuromodulator

Question 5

Describe the process of neurulation

Answer 5

• Occurs at ~22 days
• a band of longitudinal ectoderm thickens and divides to become the neural plate, the centre has a high mitotic division rate forming the neural tube and pushing the lateral sides up to its superior portion
• the neural tube becomes the CNS
• the superio-lateral areas are the neural crest cells which form the PNS and other structures
• the most lateral cells of the place are the surface ectoderm and become the skin

Question 6

Describe the processes of anencephaly and spina bifida

Answer 6

• anencephaly involves failure of the anterior neuropore to close and causes failure in brain formation, absence of skull and facial abnormalities. it is not compatible with life
• spina bifida results from failure of the spinal cord to encase itself in the spinal cord
• SB Occulta occurs when the spinal cord is encased in the meninges but the spinous processes of the vertebral bones do not form.
• SB Cystica occurs when a pocket of CSF forms and the spinous processes arent formed (meningeocoele), or where the cauda equina sit out inside the sac (meningiomarleocene)

Question 7

describe some of the complications of spina bifida

Answer 7

• hydrocephalous: due to neural tube not forming correctly leading to a communicating where CSF can get out of the ventricles but cant get into the dural venous sinuses or non communicating where CSF cannot leave the ventricles at all (most commonly due to stenosis of the cerebral aqueduct)

Question 8

Describe the process of Chiari Malformations

Answer 8

• increased ICP –> cerebellum (coning) and medulla into the foramen magnum leading to compression of these centres –> medical emergency

Question 9

Describe the process of neural induction

Answer 9

• the process by which mesodermal tissue (notochord) directs differentiation of the neuroectoderm.
• The notochord becomes the vertebral column
• occurs roughly around d16 –> drives primary neurulation (closure of the anterior and posterior neuropore)
• drives dorso-ventral seperation of the spinal cord (motor and sensory respectively)
• forms the basal plate (motor) and alar plate (sensory)

Question 10

Explain the embryological origins of cranial nerve nuclei development

Answer 10

• in the medulla the fourth ventricle pushes the basal plate medially so that the alar plate now lies laterally to it.
• The motor nuclei sit in the basal plate therefore are medial and the sensory nuclei sit laterally
• the basal and alar plates are divided by the sulcus limitans