2: Cortical and subcortical structures of the adult healthy brain

Question 1

1.

The nervous system has two different major parts; what are they?

Answer 1

1) Central Nervous System (CNS): Brain and spinal cord
2) Peripheral Nervous System (PNS):

Question 2

2.

What does the Central Nervous System (CNS) include?

Answer 2

Brain and spinal cord

Question 3

3.

What are the two key parts to the Peripheral Nervous System (PNS) include?

Answer 3

The PNS is the part of the nervous system that consists of the nerves and ganglia outside of the brain and spinal cord.

The PNS is divided into the somatic nervous system and the autonomic nervous system.

Question 4

4.

Describe the somatic nervous system

Answer 4

• It conveys sensory information (from skin, muscles, bones, joints, eyes and ears) to and from the CNS
• It sends motor stimuli from CNS to muscles (voluntary movement)
• The somatic nervous system (SoNS or voluntary nervous system) is the part of the peripheral nervous system associated with skeletal muscle voluntary control of body movements. The SoNS consists of afferent and efferent nerves.

Question 5

5.

Describe the Autonomic nervous system

Answer 5

• It regulates involuntary movement activity
• It controls functions such heart rate, blood pressure, kidney function and breathing
• It is composed by the sympathetic and the parasympathetic nervous systems

Question 6

6.

Name the different planes used to slice the brain:

What is the coronal plane?

Answer 6

A coronal plane (also known as the frontal plane) is any vertical plane that divides the body or brain into ventral and dorsal (belly and back) sections.

Question 7

7.

What is a sagittal plane?

Answer 7

A sagittal plane is a vertical plane which passes from anterior(front) to posterior(back), dividing the body into right and left halves.

Question 8

8

What is the transverse plane?

Answer 8

The transverse plane (also called the horizontalplane, axial plane, or transaxial plane) divides the body into superior (top) and inferior (bottom) parts. It is perpendicular to the coronal and sagittal planes.

Question 9

9.

List the key brain regions divided into:

Forebrain and Brain stem

Answer 9

Forebrain:

1. Neocortex
2. Basal Ganglia
3. Lateral Ventricles
4. Limbic System
5. Thalamus,
6. Epithalamus
7. Hypothalamus

Brainstem:

1. Pineal body
2. Third Ventricle
3. Tectum
4. Tegmentum
5. Aqueduct of Sylvius
6. Pons
7. Cerebellum
8. Medulla oblongata
9. Fourth Ventricle

Question 10

10.

What does the hindbrain consist of?

Answer 10

• the MEDULLA contains important nuclei responsible for regulation of breathing and cardiac functions
• the PONS contains many ascending and descending fibre tracts and fibres linked to cerebellum
• the CEREBELLUM coordinates movements

Question 11

11.

What does the midbrain consist of?

Answer 11

MIDBRAIN includes:

• tectum(colliculi)
• tegmentum (red nuclei and substantia nigra)
• cerebral aqueduct

Image on transverse plane.

Question 12

12.

The forebrain is split into 2 sections:

What are they?

Note - the Limbic system and Cerebral cortex are part of the same overal section!

Answer 12

Telencephalon , which contains:

• Neocortex
• Basal ganglia
• Limbic system
• Olfactory bulb

Diencephalon, which contains:

• Thalamus
• Hypothalamus

Question 13

13.

Describe the neocortex

Answer 13

• The neocortex is made up of six layers, labelled from the outer in, I to VI.
• In humans, the neocortex is involved in higher functions such as sensory perception, generation of motor commands, spatial reasoning, conscious thought and language.
• It is the most recent part of the cerebral cortex.

Fissure: it extends deeply into the brain

Sulcus: it is shallower Gyrus

Question 14

14.

What are the 4 lobes of the neocortex?

Answer 14

Lobes in Hemispheres Left and RIght:

1. Frontal (more developed in humans)
2. Parietal
3. Occipital
4. Temporal

Question 15

15.

What are the two main cell types in the neocortex?

Answer 15

Pyramidal cells: large multipolar neurons – large dendrites and long axon – projection neurons

Stellate (or star-shaped) cells: smaller soma – shorter axon – local information processing

• Size and density of cell bodies varies across layers For example, in Layer III large pyramidal cells – efferent (away) to other cerebral area; IV layer has many stellate cells – it receives afferent (receive) information from thalamus;
• The thickness of each layer varies across different cortical areas, according to the local function
• Sensory areas > thick layer IV
• Motor area > thick layer V

Question 16

16.

What is CYTOARCHITECTONICS?

Answer 16

Cytoarchitectonics, is the study of the cellular composition of the body’s tissues under the microscope.

The variation of thickness and cell composition of each of the six layers of neocortex is known as CYTOARCHITECTONICS. On this basis Korbinian Brodmann developed Brodmann’s map.

Neocortex Brodmann map consists of 52 areas (BA).

Question 17

17.

What Brodmann numbers correspond to:

1. Primary motor area (cortex)
2. Primary somatosensory area
3. Primary Visual area
4. Primary auditory area

Answer 17

1. Primary motor area (cortex) = Area 4
2. Primary somatosensory area = Area 1, 2 & 3
3. Primary Visual area = Area 17
4. Primary auditory area = Area 22

Question 18

18

What are associative fibers?

Answer 18

Association fibers are bundles of axons within the brain that unite different parts of the same cerebral hemisphere.

1. Arcuate fasciculus
2. Uncinate fasciculus
3. Superior and inferior longitudinal fasciculi
4. Cingulate fasciculus
5. Superior and inferior occipital frontal fasciculus

Question 19

19

What are the Commissural fibres?,

Answer 19

They connect the same areas in the two hemispheres.

1. Corpus callosum
2. Anterior commissure (used in fMRI scans as landmark)
3. Posterior commissure

Question 20

20.

What are projection fibers?

Answer 20

The projection fibers consist of efferent and afferent fibers uniting the cortex with the lower parts of the brain and with the spinal cord.

They send (efferent) receive (afferent) information between the cortex and other structures of the brain (e.g. mainly thalamus through internal capsula)

Question 21

21.

Primary ________ and ________ areas mediate ______________________________________

List the 5 key ares:

Answer 21

Primary Sensory and Motor areas mediate elementary sensory or motor functions

1. Visual area
2. Auditory area
3. Primary somatosensory area
4. Motor area
5. Olfactory area

Question 22

22.

A few important issues about cortical and subcortical areas:

(Schmahmann & Pandya, 2008)

Answer 22

• Lesions in basal ganglia and thalamus mimic deficits resulting from cortical lesions

Due to disruption of the interaction of domain-specific subcortical nuclei with the sensorimotor, association cortical areas.

• However there are qualitative differences between the manifestations of lesions in functionally related area of cortical and subcortical areas

Examples:

Lesion of primary motor cortex -> hemiparesis

Lesion of putaman -> slowness in movements

Lesion of thalamus (VL) -> ataxia

Lesion of cerebellum -> lack of motor coordination

Question 23

23.

Subcortcial areas are topographically arranged describe the parrallel loops involved in cortical to subcortical communicaton.

Answer 23

-Segregated loops:

• Multiple parallel loops between cortical and subcortical areas with no cross-modal communication within subcortical nuclei
• Complex behaviour required interaction between different functional domains (Cortex in particular associative areas)

A set of parallel, unidirectional chains link the cortex to a set of its appendages, each with a special structure – the cerebellum, the basal ganglia, and the hippocampus. (Edelman; Universe of Consciousness, 45)

Each of the striatatum and _cerebellum subcortica_l structures forms a nodal point in a major circuit loop than begins with downward projections from the cortex and ends in a route from the thalamus back to the cortex. (Eichenbaum;Neuroscience of Memory, 238)

Question 24

24.

Describe the Basal Ganglia?

Then list the 4 main sections

Answer 24

• Basal ganglia are a group of subcortical structures which are situated at the base of the forebrain.
• The function of basal ganglia is quite complex. They are strongly involved in movement and motor control.
• They do NOT initiate movements but they are involved in a loop of modulation with the cortex that is constantly active.
• Therefore they are actively involved in monitoring the force to be applied to a task and gross postural adjustments The four main structures:

1. striatum (larger - putman, caudate nucleus)
2. pallidum (globus pallidus larger component of the limbic loop of the basal ganglia)
3. substantia nigra (smaller)
4. subthalamic nucleus (smaller)

Question 25

25. Basal Ganglia: Describe the **Corpus Striathum**

Answer 25

In all primates, the **striatum** is divided by a white matter tract called the **internal capsule** into two sectors called the **caudate nucleus** and the **putamen**. The **lenticular nucleus** refers to the **putamen** together with the **globus pallidus.**

Question 26

26. Does the Basal Ganglia project directly to the cortex? Draw a simple flow chart showing the direction between: * **Cerebral Cortex** * **Thalamus** * **Cerebellum** * **Spinal Chord** * **Basal Ganglia**

Answer 26

**Basal ganglia** receive direct input from cortical areas and limbic system They DO NOT project DIRECTLY to the cortex. Cortical projections travel trough the **thalamus.**

Question 27

27. Main neurotransmitters of Basal ganglia are: Draw a diagram illustrating their integration into the communication with other brain regions.

Answer 27

1. **GABA** 2. **Dopamine** 3. **Glutamate**

Question 28

28. ## Footnote The cortex, thalamus, and the basal ganglia are the three main participants in the **circuit** created by the **basal ganglia**. Draw out the **direct pathway** (less inhibitory)

Answer 28

1. Cortex (stimulates) → 2. Striatum (Caudate/Putamen) (**_inhibits_**) → 3. "SNr-GPi" complex (**_less inhibition of thalamus_**) → 4. Thalamus (stimulates) → 5. Cortex (stimulates) → 6. Muscles, etc. → (hyperkinetic state)

Question 29

29. The cortex, thalamus, and the basal ganglia are the three main participants in the circuit created by the basal ganglia. Draw out the **_indirect pathway_** (**MORE inhibitory**)

Answer 29

1. Cortex (stimulates) → 2. Striatum (inhibits) → 3. GPe (less inhibition of STN) → 4. STN (stimulates) → 5. "SNr-GPi" complex (inhibits) → 6. Thalamus (is stimulating less) → 7. Cortex (is stimulating less) → 8. Muscles, etc. → (hypokinetic state)

Question 30

30. ## Footnote Discuss the difference between the **_direct_** and **_indirect_** pathways of the **Basal Ganglia.** Draw out the full **_direct_** and **_indirect pathway_** and label it carefully.

Answer 30

These pathways have competing effects on movement and there is often thought to be a balance between these systems that is involved in establishing and regulating tone. In both the direct and indirect pathways, the caudate and putamen represent the first synapse in the system. The **_indirect pathway_** is more **inhibitory** to motor cortical activity than the **_direct pathway_**.

Question 31

31. ## Footnote Malfunction or lesion of the **_basal ganglia._** _What brain region is critical?_

Answer 31

Parkinson Disease (rhytmical tremor at rest, bradykinesia, muscles rigidity, difficulty in stopping walking once started; difficulty in motor coordination -\> falls) **Substantia Nigra.**

Question 32

32. ## Footnote Parkinsons Disease - discuss the reasons.

Answer 32

1. Reduction of **dopamina** is mainly due to death of dopaminergic neurons in the substantia nigra. 2. This causes a lack of input (through nigrostriatal path) to putamen 3. then **internal pallidus** more activated 4. Then **thalamus** more inhibited 5. less activation towards the cortex 6. which turns into **_less_** movement.

Question 33

33. ## Footnote **Huntington’s Chorea** (jerks, muscle tone poor, possible change in personality, dementia) - what are the reasons?

Answer 33

* Degeneration of **_striatum_** * Reduction of **GABA** neurons and increment of external pallidus activity which strongly inhibits subthalamic n. * then less inhibition of the thalamus * more motor activity - involuntary movements

Question 34

34 ## Footnote What is the reason for **Ballismus or hemiballismus** (severe involuntary movements of limbs) ? Why involuntary movements?

Answer 34

Lesion of the subthalamic nucleus In both **Huntington’s Chorea** and **Ballismus syndromes**, the involuntary movements are caused by a **_abnormal discharges of upper motor neurons_** that are not adequately inhibited (modulated) by **_basal ganglia_**.

Question 35

35 ## Footnote Lesions of the **_rostral (head of caudate?_** Rostoral (situated toward a rostrum or toward the beak (oral and nasal region)

Answer 35

Impairment of working memory, strategy formation, flexibility, neglect if right caudate or aphasia if left caudate

Question 36

36. Lesions of the **ventral striatum ?**

Answer 36

Behavioural disorders (e.g. disinhibition, irritability, obsessive compulsive disorder)

Question 37

37. The __________ has a key role in transforming information to and from the cortex. It is a large \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.

Answer 37

The **_thalamus_** has a key role in transforming information to and from the cortex. It is a large **two-lobbed structure**.

Question 38

38. What is the bridge that connects the two lobes of the **thalaums**?

Answer 38

The **_massa intermedia_** is a sort of bridge that connects the two lobes.

Question 39

39. ## Footnote The\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ divides the _____ from the __________ group of nuclei.

Answer 39

The **_internal medullary lamina_** divides the **_medial_** from the **_lateral_** group of nuclei.

Question 40

40. ## Footnote \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ forms the lateral boundary of the thalamus medial to the internal capsule, which contains _________________ nerve fibres passing to and from the \_\_\_\_\_\_\_\_to the \_\_\_\_\_\_\_\_\_\_\_\_\_.

Answer 40

**External medullary lamina** forms the lateral boundary of the thalamus medial to the internal capsule, which contains **_afferent and efferent_** nerve fibres passing to and from the **_thalamus_** to the **_cerebral cortex_**

Question 41

41. ## Footnote The **intralaminar nuclei** are collections of neurons in the **thalamus** name three of the key parts:

Answer 41

1. Media 2. Lateral 3. Anterior nuclei

Question 42

42. Describe the nuclei of the **thalamus:** 1. **Specific nuclei(**Relay Thalamic Nuclei**):** 2. **Associative nuclei:** 3. **Non-specific nuclei:**

Answer 42

1. **Specific nuclei:** Each specific nucleus receives connection from the region of the cerebral cortex upon which it projects (usually **primary motor** and **sensory areas**) 2. **Associative nuclei:** Receive input from several areas and each nucleus projects to one of the three association cortex (P-T-O ass. c.; PreF c.; Limbic c.) 3. **Non-specific nuclei:** Widespread connections also towards other thalamic nuclei and some of these are inhibitory (e.g. **reticular** formation)

Question 43

43. Describe the **_internal capsule_** and how it relates to other brain regions.

Answer 43

* Thalamo-cortical projections run through the **_internal capsule._** * In the **_internal capsule_** there are also the fibers from cortex to medulla and spinal cord. * The internal capsule continues more laterally and superiorly with the **corona radiata** (a white matter sheet), which contains descending axons of the corticospinal tract.

Question 44

44. **Lymbic System:** Name four areas of the **lymbic lobe**? note: the term is ambiguous - some authors differ on what makes up the lymbic lobe.

Answer 44

1. **parahippocampal gyrus** 2. **cingulate gyrus** 3. **subcallosal gyrus** (anterior and inferior continuation of the cingulate gyrus) 4. **Hippocampal formation** (hippocampus, dentate gyrus and subiculum) the hippocampus

Question 45

45. Describe the _**lymbic** **system**_?

Answer 45

* The **limbic system** (or paleomammalian brain) is a complex set of brain structures located on both sides of the **thalamus**, right under the **cerebrum**.

Question 46

46. ## Footnote Main sources of limbic afferents and efferents.

Answer 46

Major pathways communicate bidirectionally and contain both **efferent** (away) and **afferent** (towards) fibers from the **_hippocampus._** Outputs or efferents from the hippocampus pass directly from the subiculum to the entorhinal cortex and **_amygdala_** or through the **_fornix_** (a C-shaped bundle of nerve fibers) to a variety of anterior structures.

Question 47

47. Describe the **_amygdala_**

Answer 47

* The **_amygdala_** has two important projections to **_hypothalamus_** and **_dorso-medial thalamic nuclei_** and it receives an important afferent input from the **_olfactory tract_** * emotional processing (e.g. fear) and social behaviour * Bilateral damage of amygdala results in Klüver-Bucy syndrome

Question 48

48. Describe the **_hypothalamus_**

Answer 48

* The **_Hypothalamus_** is a complex structure containing many nuclei and tracts. * It controls the autonomic nervous system and the endocrine system with direct link to the pituitary gland.

Question 49

49. ## Footnote The __________ controls the ______________________ and the ________________ with a direct link to the **pituitary gland**.

Answer 49

The **_hypothalamus_** controls the **_autonomic nervous system_** and the **_endocrine system_** with a direct link to the **_pituitary gland_**. * The **autonomic nervous system (ANS)** is a division of the peripheral nervous system that influences the function ofinternal organs * The **endocrine system** is the collection of glands that produce hormones that regulate metabolism, growth and development, tissue function, sexual function, reproduction, sleep, and mood, among other things.

Question 50

50 List 6 functions of the **_Hypothalamus_**.

Answer 50

1. Much of the **endocrine system** is controlled by hormones produced by cells in the **hypothalamus**. 2. Descending tracts to brain stem to regulate autonomic centres related to cardiovascular and breathing functions 3. Integrating emotions and **autonomic** responses 4. Link to centre for “set points” relating to appetite, body temperature 5. Biological clock and **circadian** rhythms 6. Link to **limbic system**

Question 51

51. ## Footnote **Neuroimaging in computed tomography (CT):** What does the brain looks like?

Answer 51

* Computed tomography (CT). * Various attenuation intensity of x-rays according to type of tissue. This is computerised into numbers. * Positive numbers (+1,000) are represented white (e.g. bone), negative numbers (-1,000) are represented black (e.g. air) The brain and related structures in CT

Question 52

52. ## Footnote Neuroimaging in MRI: What does the brain looks like with T1 and T2?

Answer 52

The brain and related structures in MRI

Question 53

53. List advantages of a CT scan:

Answer 53

1. Clearly shows acute and subacute hemorrhages into the meningeal spaces and brain 2. Better in showing bone and bone fractures 3. Rapid (important for emergency) and cheap

Question 54

54. List advantages of an MRI scan.

Answer 54

1. Excellent spatial resolution. It better differentiates white and grey matter than CT Scan. 2. It clearly shows acute or subacute infarcts or ischemia or brain edema 3. No radiation exposition and, at the present, not known harmful effects

Question 55

55. ## Footnote A sagittal MRI of a 23-year-old woman is located at, or immediately adjacent to, the midline. Which of the following spaces or structures would be in the image and would indicate a midline plane? a) Cerebral aqueduct b) Corpus callosum c) Interventricular fossa d) Superior colliculus

Answer 55

a) **Cerebral aqueduct** (because it is in the middle coming up from the spinal chord)