HNS05 Thalamus And Cerebral Cortex

Question 1

Thalamus

Answer 1

• Large ovoid mass of gray matter —> forms major part of Diencephalon
  —> Anterior end: narrow, rounded
  —> Posterior end: expanded to form the Pulvinar
• Situated on each side of ***Third ventricle (將Third ventricle夾係中間)
• 2 halves of thalamus joined by ***interthalamic adhesion
• very important RELAY station of most sensory systems

Question 2

Topographic location of thalamus

Answer 2

Anterior: Interventricular foramen
Posterior: Pulvinar
Superior: Stratum zonale (White mater) and Stria terminalis
Inferior: Tegmentum of **midbrain
Medial: Lateral wall of **third ventricle
Lateral: Nerve fibres of ***internal capsules

Question 3

Topological location of Thalamus

Answer 3

Dissection from lateral side has to go through Caudate nucleus and Putamens

Question 4

Dorsal view of Diencephalon and Mesencephalon

Answer 4

兩邊Thalamus夾住中間下面Mesencephalon (見到Superior and Inferior colliculi)

Question 5

Coronal sections for Diencephalon

Answer 5

see slides

Question 6

***4 components of Diencephalon

Answer 6

1. Epithalamus
   - **Pineal gland: secretes **melatonin
   - smallest region of diencephalon
2. Thalamus
   - relays **ALL sensory input (perception of touch, pressure, temperature) to all parts of cortex
   - **movement control
3. Subthalamus
   - connects Subthalamic nuclei + Basal ganglia (Caudate nucleus + Putamen + Globus pallidus)
   —> control body movement and emotion control
4. Hypothalamus
   - **release hormones to regulate **Pituitary gland
   - controls body ***temperature
   - eating and drinking behaviour
   - emotion
   - circadian rhythms + wake/sleep pattern

Question 7

***Thalamic nuclei

Answer 7

Left/Right connected by interthalamic adhesion
Groups separated by internal / external medullary lamina

Anterior group:

• part of ***limbic system
• **memory and **emotion

Medial group:

• **emotional output to **prefrontal cortex
• awareness of emotions
• subgroups: Medial dorsal (MD), Medial group (M), Midline nuclei

Ventral group:

• **somesthetic output to **postcentral gyrus
• signals from Cerebellum and Basal nuclei —> ***motor areas of cortex
• subgroups: VA, VL, VP (VI+VPM+VPL)

Lateral group:

• **somesthetic output to **association areas of cortex
• contributes to ***emotional function of limbic system
• subgroups: LD, LP

Posterior group:

• relay of **visual signals to occipital lobe (via **lateral geniculate nucleus)
• relay of **auditory signals to temporal lobe (via **medial geniculate nucleus)

Question 8

Internal medullary lamina

Answer 8

Intralaminar nuclei + Centromedian nuclei

Question 9

***Anterior, VA, VL, VP, Lateral geniculate, Medial geniculate, MD

(Receives signals FROM, Send signals TO)

Answer 9

Learning and Memory:

1. Anterior (part of Limbic system):
   - from Mammillothalamic tract, Fornix (learning, memory) —> ***Cingulate cortex (posterior part)

Emotion:

1. MD:
   - from Substantia nigra, Ventral pallidum, Olfactory cortex, Amygdala —> ***Prefrontal cortex

Motor:

1. ***VA:
   - from Globus pallidus —> Prefrontal cortex (motor)
2. ***VL:
   - from Globus pallidus —> Supplementary motor area
   - from Cerebellum —> Motor cortex

Sensory:

1. ***VP (most important):
   - from Spinothalamic tract, Trigeminothalamic tract, Dorsal column-medial lemniscus pathway —> Somatic sensory cortex
2. ***Lateral geniculate:
   - from Optic tract —> Primary visual cortex
3. ***Medial geniculate:
   - from Inferior colliculi —> Primary auditory cortex

Question 10

VP nucleus

Answer 10

1. VPL: receives all somatosensory signals from ***upper + lower extremities (Dorsal column-medial lemniscus pathway + Spinothalamic tract)
2. VPM: receives all somatosensory signals from ***head + neck region (Trigeminothalamic tract)

(Somatosensory signals: Mechanoreception + Proprioception + Thermoception + Nociception)

Question 11

***Functions / Roles of Thalamus in neuro-network

Answer 11

***ALL sensory signals (from Spinothalamic tract + Dorsal-medial lemniscal pathway) has to go through thalamus, but NOT motor control

Sensation:
Example: Pain sensation:
Sensation —> Dorsal horn —> Spinothalamic tract —> Medulla, Pons, Midbrain —> **Thalamus (form synapse) —>
1. **Learning and memory cortex (avoid pain sensation in the future again)
2. ***Sensory cortex (Parietal lobe) —> Motor cortex —> Corticospinal tract —> Brainstem (Cerebral peduncle, Pyramid) —> Ventral horn

Motor control:
1. Corpus striatum, Diencephalon, Cerebellum
—> ***Thalamus
—> Cerebral cortex
—> go straight back to Corpus striatum, Diencephalon, Cerebellum

2. Brainstem, Spinal cord
—> ***Thalamus
—> Cerebral cortex
—> go straight back to Brainstem, Spinal cord
—> Muscle

Question 12

Involvement of Thalamus in Basal Ganglion circuit

Answer 12

Thalamus: modulate eventual motor output (NOT a part of basal ganglia)

Basal ganglia: Fine tuning of motor movement (finger movement, gait)

Basal ganglia components:

• Striatum
• Globus pallidus
• Subthalamic nucleus
• Substantia nigra

Direct pathway:
Cortex —(glutamate)—>
Striatum —(more GABA)—>
Globus pallidus (internal segment) —(less GABA)—>
Thalamus (VL) —(more glutamate)—>
Supplementary motor area

Indirect pathway:
Cortex —(glutamate)—>
Striatum —(more GABA)—>
Globus pallidus (external segment) —(less GABA)—>
Subthalamic nucleus —(more glutamate)—>
Globus pallidus (internal segment) —(more GABA)—>
Thalamus (VL) —(less glutamate)—>
Supplementary motor area

***Balance between direct / indirect pathway go to Thalamus eventually
—> control motor area

Substantia nigra:

• release dopamine (inhibitory/excitatory) —> Striatum
• fine tuning of direct / indirect pathway

Compacta:
- also fine tuning of direct / indirect pathway

Question 13

Cerebral cortex / Telencephalon

Answer 13

凸起: Gyrus
中間d隙: Sulcus

Components:

1. Frontal lobe (***motor control + emotion, also receives input from thalamus to tell how good motor control is)
2. Parietal lobe (ultimate analysis of ALL ***sensory signals from thalamus)
3. Occipital lobe (***vision centre —> primary visual cortex)
4. Temporal lobe (**learning, **memory, emotion)

Central sulcus: separate frontal / parietal lobe
—> gyrus in front (Precentral gyrus): Primary motor cortex
—> gyrus behind (Postcentral gyrus): Primary somatosensory cortex

Question 14

Frontal lobe

Answer 14

1. Primary motor cortex (Area 4)
2. Motor association area (Area 6: Premotor area + SMA)
3. Pre-frontal cortex
4. ***Broca’s area (language area)
   (5. Olfactory association area)

Question 15

Occipital lobe

Answer 15

1. Primary visual cortex

2. Visual association area

Question 16

Temporal lobe

Answer 16

1. Primary auditory cortex
2. Auditory association area
3. Primary olfactory cortex

Question 17

Parietal lobe

Answer 17

1. Primary somatosensory cortex
2. Somatosensory association area
3. Primary gustatory cortex (taste)
4. ***Wernicke’s area (comprehension of language)

Question 18

Grey matter

Answer 18

Collection of Cell bodies

1. Insula (physio, psychological pain, olfactory sensation) (enclosed within other gyrus)
2. Caudate nucleus + Putamen —> Striatum
3. Basal ganglia (Globus pallidus, Substantia nigra)

Question 19

Broca’s area + Wernicke’s area

Answer 19

joined by ***Arcuate Fasciculus (several axons grouped together)
—> from Wernicke’s area (Parietal lobe) to Broca’s area (Frontal lobe)

Question 20

Fibres of white matter of Cerebrum

Answer 20

1. Arcuate fibres (最短)
   - interconnect gyri within a lobe
2. Association fibres
   - interconnect cortical areas within same hemisphere / linking several gyri together
3. Longitudinal fasciculi (前後)
   - interconnect frontal lobe with other cerebral lobes
4. Corona radiata (上下)

Question 21

6 layers of cortex

Answer 21

1. Molecular layer
2. External granular layer
3. External pyramidal layer
4. Internal granular layer
5. Internal pyramidal layer
6. Multiform layer

Differ in distribution of neurons

Question 22

Different staining methods

Answer 22

1. Golgi stain: cell bodies + axons
2. Nissl stain: cell bodies only
3. Weigert stain: axons only

Question 23

Corpus callosum

Answer 23

Connect left + right hemisphere

Question 24

Learning and memory

Answer 24

1. Limbic system
2. Basal nucleus of Meynert
3. Septal nucleus (headquarter of cholinergic neuron to pre-frontal cortex)

Question 25

***Limbic system

Answer 25

Learning + Memory + Emotion Diencephalon components: 1. ***Anterior group of thalamic nuclei 2. ***Hypothalamus 3. Mamillary body Cerebrum components: 4. ***Cingulate gyrus 5. ***Hippocampal formation (Hippocampus + Dentate gyrus + Subicular complex) 6. Parahippocampal gyrus 7. Entorhinal cortex Other components: 8. Fornix + Fimbria 9. ***Amygdala (negative emotion)

Question 26

***Learning loop (Papez circuit)

Answer 26

Repeated stimulation of Hippocampus: ``` Cingulate gyrus —> Parahippocampal gyrus —> Entorhinal cortex —> Hippocampus (Dentate gyrus) —> Fimbria —> Fornix —> Mamillary body (of Hypothalamus) —> Mammillothalamic tract —> ***Anterior nucleus of Thalamus —> Cingulate gyrus (posterior) —> Parahippocampal gyrus —> Hippocampus ``` (—> Cingulate gyrus (anterior) —> Basal nuclei —> Occipitofrontal nucleus —> Subcallosal area of cortex)

Question 27

Amygdaloid complex

Answer 27

Amygdala + Stria terminalis Anterior to Hippocampus Functions: 1. Involve in defence and attack, fear, rage (***negative emotions) 2. Influence ***endocrine function of hypothalamus

Question 28

Hippocampal formation

Answer 28

``` Entorhinal cortex (within Parahippocampus gyrus) —> sends signals to Dentate gyrus (within Hippocampus) ``` Functions: 1. ***Learning, recent memory 2. ***Emotion

Question 29

***Summary of memory

Answer 29

Long term memory - Explicit memory (declarative): ***Hippocampus, ***Nucleus Basalis, Medial temporal lobe —> Remembering events (episodic memory) —> Remembering facts (semantic memory) - Implicit memory (non-declarative) —> Skills and habits: ***Striatum, Motor areas of cortex, Cerebellum (muscle memory) —> Emotional associations: ***Amygdala, Insula —> Conditioned reflex: ***Cerebellum Working memory: ***Prefrontal cortex (PFC) —> Non-spatial (colour, shape): Ventrolateral PFC —> Spatial memory: Dorsolateral PFC

Question 30

Clinical relevance of cerebral cortex

Answer 30

1. Alzheimer’s disease - shrinkage / atrophy of whole brain, enlarged lateral ventricle - start with Hippocampus —> temporal lobe: affect memory, language 2. Frontotemporal lobe dementia - atrophy of frontal lobe 3. Creutzfeldt-Jakob disease - prion change brain protein to beta-sheet —> neuron die - vacuoles / holes formed in the cortex - affect mental acuity + memory (limbic system)