0331 - Intro to the Brain - CS

Question 1

1. Outline the three embryonic brain vesicles, their subdivisions, and the structures derived from each

Answer 1

• The brain develops from a tubular structure called the neural tube. * At the head end of this tube three swellings called primary vesicles appear and these give rise to the adult brain.* These primary vesicles differentiate into the hindbrain, midbrain and forebrain of the adult:1. Forebrain-Telencephalon –>Cerebral hemispheres,Limbic structures (+ lat vent)-Diencephalon –>Thalamus,Hypothalamus,Retina (+ 3rd ventr)2. Midbrain:-Mesencephalon –>Tectum,Tegmentum (+ cerebral aqueduct)3. Hindbrain:-Metencephalon –>Pons,Cerebellum (+ 4th vent)-Myelencephalon –>Medulla (+4th ventricle)

Question 2

2. Discuss, in general terms, the relationship between the brain ventricles and the embryonic brain vesicles

Answer 2

• The mature brain comprises collections of cells and cell processes (grey and white matter) arranged around a central complex of spaces called ventricles.* The ventricles are remnants of the cavity of the neural tube* The shape of the lateral ventricles reflects the growth patterns of the forebrain during foetal life

Question 3

3a. Discuss in general terms, the functions of the cerebral hemispheres

Answer 3

• Each hemisphere is covered by a sheet of grey matter known as the cerebral cortex (see question on cerebral cortex for its function)* A thick layer of white matter can be seen beneath the cortex. This is made up of fibres passing in both directions between the cortex and lower structures (eg thalamus, brainstem and spinal cord), fibres connecting different parts of the one hemisphere and fibres interconnecting corresponding parts of the two hemispheres. * Masses of grey matter are embedded within the white matter. These are known collectively as basal ganglia & are important in the control of movement.

Question 4

3b. Discuss in general terms, the functions of the cerebral cortex

Answer 4

• The site where the highest level of neural processing takes place.* It enables us to consciously perceive sensory stimuli, to think and to make decisions.* Because its surface area is so great the cerebral cortex is highly folded.* The grooves are known as sulci and the bumps between the sulci are known as gyri

Question 5

3c. Discuss in general terms, the names and functions of the deep nuclei in the cerebral hemispheres

Answer 5

• Deep nuclei including the caudate and putamen, substantia nigra and red nucleus are involved in regulating motor activity

Question 6

3d. Discuss in general terms, the functions of the hippocampus

Answer 6

• Part of the limbic lobe, buried in the medial temporal lobe* Essential for acquiring and retaining new learning and memories* Major output tract is the fornix which terminates in the mammillary bodies

Question 7

3e. Discuss in general terms, the functions of the corpus callosum

Answer 7

White matter made of axons connecting the two cerebral hemispheres and connecting homologous regions of cortex

Question 8

3f. Discuss in general terms, the functions of the tectum

Answer 8

• Co-ordinates visual and auditory reflexes (eg. orienting gaze to a sound or movement)* Contains:-Superior colliculus - receives input from retina that is mapped to visual field-Inferior colliculus - gets input from auditory field. Projects to thalamus* Both colliculi output to other brainstem pathways

Question 9

3g. Discuss in general terms, the functions of the thalamus

Answer 9

• Gateway to the cerebral cortex (sensory info that reaches the cortex 1st passes through thalamus)* Comprises distinct groups of nuclei with specific functions, some from a specific modality, relayed to a specific cortical area:-visual pathway-auditory pathway-somatosensory pathway

Question 10

3h. Discuss in general terms, the functions of the hypothalamus

Answer 10

• The central control centre for the maintenance of homeostasis (a constant internal body environment). It does this either by direct neural connections with other brain structures or by controlling the levels of hormone production in the body* A major regulator of the ANS* Output is mainly via hormones released by the pituitary gland.* Major input is from the limbic system via the fornix into the mammillary bodies* Lies just beneath the thalamus.* Is surprisingly small considering its importance

Question 11

3i. Discuss in general terms, the functions of the pons

Answer 11

• Form the middle cerebellar peduncle, one of three bundles of fibres that connects the brainstem to the cerebellum* CN V emerges from the lateral pons* Comprises the axons that cross the midline to enter the cerebellum* Post-synaptic to descending motor fibres (corticopontine) which terminate on cells deep in the pons (the pontine nuclei)* CN VI - VIII emerge in the groove between the pons and medulla

Question 12

3j. Discuss in general terms, the functions of the cerebellum

Answer 12

• Major role in the- learning and coordination of voluntary movements- control of posture (including balance)- control of muscle tone* Gets input from joints and muscles (via spinocerebellar tracts), from CN VIII and from the cortex via pontocerebellar fibres* Major output is from deep nuclei (eg dentate nucleus) to the thalamas and ‘red’ nucleus (motor nucleus) via the cerebellar peduncle

Question 13

3k. Discuss in general terms, the functions of the medulla oblongata

Answer 13

• Cardiac regulation (cardiac centre),* reflex regulation (reflex centres), * blood pressure/vasodilation regulatin (vasomotor centre)* respiratory regulation.* Contains nuclei and is site of brain exit for 8 of 12 cranial nerves

Question 14

4. Describe, using anatomical terms, the areas of the cortex that are ‘mapped’ and those that are ‘unmapped’ and explain the relevance of this distinction

Answer 14

• Mapped cortical areas:- represent a specific modality- map that modality to create an ‘image’- include primary and secondary cortical areas* Unmapped cortical areas are referred to as “association cortex” and they- Get input from other areas of the cortex- Include a mix of modalities- Are highly interconnected with the frontal lobeMapped areas examples and locations:* Primary motor cortex (precentral gyrus/paracentral lobule)* Primary somatosensory area (postcentral gyrus/paracentral lobule)* Primary auditory area (superior temporal gyrus, posterior)* Receptive speech (Wernicke’s) area (posterior to superior temporal gyrus* Primary visual area (banks of calcarine sulcus)* Primary olfactory area (uncus and parahippocampal gyrus, anterior)

Question 15

5. Explain the functional significance of each of the mapped regions of the cortex

Answer 15

• Mapped areas are characterised by a topographical organisation in which body surface, the range of audible frequencies or the outside world is represented on (“mapped” onto) the cortical surface.* Maps are distorted so that highly discriminating or finely controlled items have a disproportionately large representation- Primary motor cortex - gives rise to motor neurones for adjacent muscles of the body- Primary somatosensory area - Sensation from adjacent areas of the body represented in adjacent cortical areas- Primary auditory area - Related tones represented in adjacent cortical areas- Receptive speech (Wernicke’s) area – Primary visual area – Primary olfactory area -

Question 16

2b. List the embryonic brain vesicles.For each vesicle, indicate the mature brain ventricle/s that it develops into

Answer 16

Telencephalon —> cavity inside becomes the lateral ventricles within the cerebral hemispheres-Diencephalon —> cavity inside becomes the third ventricle between the two halves of the thalamus?-Mesencephalon —> cavity inside becomes the cerebral aqueduct between the tectum and tegmentum-Metencephalon —> cavity inside becomes the fourth ventricle between the cerebellum and pons