brain, PNS and CNS Flashcards
(264 cards)
1
Q
What are the meninges and their general function?
A
Three concentric connective tissue membranes that surround the brain and spinal cord within the skull and vertebral canal.
Function: Support and stabilize the CNS.
2
Q
What are the three layers of cranial meninges?
A
Dura mater (outermost, tough)
Arachnoid mater (middle, web-like)
Pia mater (innermost, delicate)
3
Q
What are the layers of the dura mater in the cranium?
A
Periosteal layer: outer layer, adheres to inner surface of skull.
Meningeal layer: inner layer, adjacent to arachnoid mater.
4
Q
What forms when the two layers of the dura mater separate?
A
Dural venous sinuses → receive cerebral venous blood
5
Q
What are the potential spaces associated with the dura mater?
A
Epidural (extradural) space: superficial to periosteal dura; can fill with blood (epidural hematoma).
Subdural space: between meningeal dura and arachnoid mater; site of subdural hematoma in trauma.
6
Q
What are the dural reflections (septa) and their locations?
A
dura mater folds in on itself
Falx cerebri: between cerebral hemispheres.
Tentorium cerebelli: between cerebrum and cerebellum.
Falx cerebelli: between cerebellar hemispheres.
Diaphragma sellae: covers the pituitary fossa (sella turcica).
7
Q
Describe the arachnoid mater.
A
Flattened outer layer adjacent to meningeal dura.
Arachnoid trabeculae: CT strands extending to pia mater.
8
Q
What separates the arachnoid mater from the pia mater?
A
Subarachnoid space → contains:
Cerebrospinal fluid (CSF)
Major cerebral blood vessels
9
Q
Describe the pia mater.
A
Thin, delicate membrane that closely follows the gyri and sulci of the brain.
Inseparable from brain surface.
10
Q
What are the three spaces associated with the cranial meninges?
A
- Epidural (extradural) space
📍 Location: Between periosteal dura and calvaria (inner skull surface)
🩸 Normally: A potential space
🩸 Clinical note: Can become real space in epidural hematoma (arterial bleed)
- Subdural space
📍 Location: Between meningeal dura and arachnoid mater
🩸 Normally: A potential space
🩸 Clinical note: Site of subdural hematoma (venous bleed)
- Subarachnoid space
📍 Location: Between arachnoid and pia mater
💧 Normally present
💧 Contains:
CSF (cerebrospinal fluid)
Major blood vessels of the brain
🧠 Enlarged in regions known as cisterns (e.g., cerebellomedullary cistern)
11
Q
What are the two major sources of blood supply to the brain?
A
Anterior circulation: from internal carotid arteries
Posterior circulation: from vertebral arteries
12
Q
Where do the internal carotid arteries arise and enter the skull?
A
Originate from common carotid arteries at C4 vertebral level
Enter skull via the carotid canal, pass through:
Petrous part of temporal bone
Cavernous sinus
Exit near optic chiasm into subarachnoid space
13
Q
What are the branches of the internal carotid artery inside the cranium?
A
Ophthalmic artery
Posterior communicating artery
Anterior choroidal artery
Terminates as:
Anterior cerebral artery (ACA)
Middle cerebral artery (MCA)
14
Q
How do the two anterior cerebral arteries connect?
A
Via the anterior communicating artery, anterior to the optic chiasm
15
Q
What is the course of the anterior cerebral artery (ACA)?
A
Travels in the longitudinal fissure
Runs along the medial side of the hemisphere
Follows superior border of corpus callosum
16
Q
What are the major branches of the ACA?
A
Callosomarginal artery — follows the cingulate sulcus
Pericallosal artery — runs adjacent to corpus callosum
17
Q
What does the ACA supply?
A
Medial surface of frontal and anterior parietal lobes
18
Q
What is the course and branching of the middle cerebral artery (MCA)?
A
Enters the lateral fissure
Gives off lenticulostriate arteries
Then splits into:
Superior division
Inferior division
19
Q
What does the MCA superior division supply?
A
Lateral frontal lobe
Anterior parietal lobe (small part)
20
Q
What does the MCA inferior division supply?
A
Temporal lobe
Anterolateral parietal lobe
21
Q
Where do the vertebral arteries arise from, and what do they form?
A
Arise from subclavian arteries
Ascend via transverse foramina of cervical vertebrae
Enter skull via foramen magnum
Merge to form the basilar artery at the pontomedullary junction
22
Q
What is the course of the basilar artery and its major branch?
A
Travels along midline of ventral brainstem
At midbrain level, gives rise to the:
Posterior cerebral artery (PCA)
23
Q
What does the posterior cerebral artery (PCA) supply?
A
Inferior + medial temporal lobe
Occipital lobe
24
Q
What artery connects the PCA to the internal carotid system
A
Posterior communicating artery
25
What is the Circle of Willis?
A circular arterial anastomosis at the base of the brain that connects the anterior and posterior circulations, allowing for collateral blood flow in case of arterial occlusion.
26
Which arteries form the Circle of Willis?
Anterior cerebral arteries (2)
Anterior communicating artery (1)
Internal carotid arteries (2)
Posterior communicating arteries (2)
Posterior cerebral arteries (2)
27
Where is the Circle of Willis located?
In the subarachnoid space at the base of the brain
Surrounds the optic chiasm, infundibulum, and mammillary bodies
28
What is the functional significance of the Circle of Willis?
Provides redundant collateral circulation between:
Left and right hemispheres (via anterior communicating artery)
Anterior and posterior circulations (via posterior communicating arteries)
Protects the brain against ischemia from blockage in one part of the system
29
What are the three main components of cerebral venous drainage?
Superficial cerebral veins
Deep cerebral veins
Dural venous sinuses
All ultimately drain into the internal jugular vein.
30
Do cerebral veins or sinuses have valves?
No — none of the cerebral veins or dural sinuses contain valves.
31
Where are the dural venous sinuses located?
Between the periosteal and meningeal layers of the dura mater
32
Which sinus runs along the superior edge of the falx cerebri?
Superior sagittal sinus
→ Drains posteriorly into the transverse sinuses
33
What forms the transverse and sigmoid sinus drainage pathway?
Each transverse sinus continues as the sigmoid sinus,
→ which exits through the jugular foramen and becomes the internal jugular vein
34
Which sinus runs along the inferior edge of the falx cerebri?
Inferior sagittal sinus
→ Joins with the great cerebral vein (of Galen) to form the straight sinus
35
What is the confluence of sinuses?
Junction of:
Superior sagittal sinus
Straight sinus
Occipital sinus
→ All drain into the transverse sinuses
36
What is the cavernous sinus, and where is it located?
Venous plexus on either side of the hypophyseal fossa
Receives:
Ophthalmic veins
Some cerebral and facial venous blood
Drains via:
Superior petrosal sinus → transverse sinus
Inferior petrosal sinus → internal jugular vein
37
Which sinus primarily receives superficial cerebral venous drainage?
Superior sagittal sinus
Cavernous sinus
38
Name three important superficial cerebral veins and their drainage paths:
Superficial middle cerebral vein
→ Drains temporal lobe into cavernous sinus
Superior anastomotic vein (of Trolard)
→ Drains into superior sagittal sinus
Inferior anastomotic vein (of Labbé)
→ Drains into transverse sinus
39
What are the main deep cerebral veins?
Anterior cerebral vein
Deep middle cerebral vein
→ These unite to form the basal vein (of Rosenthal), which courses around the midbrain
40
What veins form the internal cerebral veins?
Formed at the interventricular foramen by joining of:
Septal veins
Thalamostriate veins
41
What forms the great cerebral vein (of Galen)?
Internal cerebral veins + Basal veins (of Rosenthal)
→ Join posterior to the midbrain
42
What forms the straight sinus?
Great cerebral vein (of Galen) + Inferior sagittal sinus
43
What is the thalamus?
A large, egg-shaped mass of gray matter derived from the diencephalon
Acts primarily as a relay center for sensory, motor, limbic, and modulatory information to the cerebral cortex
44
What is the functional role of the thalamus?
Acts as a synaptic relay station for pathways projecting to the cortex
Functions as a gatekeeper, modulating signal transmission based on behavioral/arousal state
45
What structures neighbor the thalamus?
Anteriorly: Interventricular foramen
Laterally: Posterior limb of internal capsule
Medially: Forms the lateral wall of the third ventricle
Dorsally: Body of the lateral ventricle
Caudally: Midbrain
Connected across midline by the interthalamic adhesion
46
How are thalamic nuclei structurally organized?
Divided based on the internal medullary lamina (a Y-shaped band of axons) into:
Anterior group
Medial group
Lateral group
Intralaminar group
47
What are the three functional classes of thalamic nuclei?
Relay nuclei (most of the thalamus)
Specific relay nuclei → project to primary cortical areas (sensory, motor)
Nonspecific relay nuclei → diffuse cortical projections
All sensory modalities except olfaction relay here
Intralaminar nuclei
Located within the internal medullary lamina
Two groups:
Rostral intralaminar nuclei: connect with basal ganglia, receive input from reticular activating system
Caudal intralaminar nuclei (e.g., centromedian nucleus): involved in basal ganglia circuitry
Reticular nucleus
Thin sheet along lateral thalamus
Does not project to cortex
Receives input from cortex and thalamus, then projects back to thalamic nuclei
Composed of GABAergic neurons → modulates thalamic activity
48
What is the function of the reticular nucleus?
Inhibitory regulation of thalamic activity via GABAergic neurons
Acts as a modulatory filter for incoming and outgoing thalamic signals
49
What arteries supply the thalamus?
Penetrating branches from multiple sources:
Anterior cerebral artery (ACA)
Anterior choroidal artery (branch of internal carotid)
Lenticulostriate arteries (from middle cerebral artery)
Thalamoperforator arteries (from posterior cerebral artery)
50
Thalamic nuclei
51
What is the brainstem, and where is it located?
A stalklike structure in the posterior cranial fossa
Connects the forebrain with the spinal cord
Composed of (from rostral to caudal):
Midbrain
Pons
Medulla oblongata
52
What are the three major functions of the brainstem?
Acts as a conduit for ascending and descending tracts
Houses cranial nerve nuclei III–XII (except CN XI, mostly in cervical spinal cord)
Contains autonomic and reflex centers for:
Respiration
Cardiovascular regulation
Consciousness/arousal
53
What does the midbrain connect?
Forebrain anteriorly
Pons caudally
Cerebellum posteriorly
54
How long is the midbrain?
~2 cm in length
55
What is the interpeduncular fossa?
A deep midline depression on the anterior surface of the midbrain
Contains perforations where small vessels enter the brainstem (posterior perforated substance)
56
What structures lie lateral to the interpeduncular fossa?
Crus cerebri (cerebral peduncles)
Contain descending motor tracts (e.g., corticospinal, corticobulbar)
57
Which cranial nerve emerges medially between the crus cerebri?
Cranial Nerve III — Oculomotor nerve
58
What are the major landmarks on the posterior surface of the midbrain?
Superior colliculi: involved in visual reflexes
Inferior colliculi: involved in auditory processing
59
Which cranial nerve emerges posteriorly from the midbrain?
Cranial Nerve IV — Trochlear nerve
Only cranial nerve to exit dorsally, then wraps around the midbrain laterally
60
What are the brachia of the midbrain?
Superior brachium: connects superior colliculus to lateral geniculate body (visual system)
Inferior brachium: connects inferior colliculus to medial geniculate body (auditory system)
61
What is the pons, and where is it located?
Part of the brainstem, located caudal to the midbrain and rostral to the medulla
Connects the midbrain to the medulla oblongata
~2.5 cm in length
62
What runs along the midline of the anterior surface of the pons?
Basilar groove — houses the basilar artery
63
Why is the anterior pons convex?
Due to the large number of transverse pontocerebellar fibers
These fibers project to the cerebellum via the middle cerebellar peduncle
64
Which cranial nerve emerges from the anterolateral surface of the pons?
Cranial Nerve V — Trigeminal nerve
Emerges with both motor and sensory roots
65
Which cranial nerves emerge at the pontomedullary junction?
(Medial → Lateral)
CN VI – Abducent nerve
CN VII – Facial nerve
CN VIII – Vestibulocochlear nerve
66
What forms the posterior surface of the pons?
Faces the cerebellum
Forms the floor of the fourth ventricle
67
What is the facial colliculus?
A prominent midline bump on the posterior pons
Caused by facial nerve fibers looping around the abducent nucleus
68
What is the medulla oblongata and where is it located?
The lowest portion of the brainstem, ~3 cm in length
Located caudal to the pons, continues into the spinal cord at the level of the foramen magnum
Connects brainstem with spinal cord
69
What is the anterior median fissure?
A midline groove on the anterior surface of the medulla
Continuous with the anterior median fissure of the spinal cord
70
What lies lateral to the anterior median fissure?
The medullary pyramids — bundles of corticospinal (motor) fibers descending from the cortex
71
What happens at the decussation of the pyramids?
Most motor fibers in the corticospinal tract cross to the contralateral side
72
What structure lies lateral to the pyramids?
The olive, which overlies the inferior olivary nucleus
73
Which cranial nerve emerges between the pyramid and the olive?
Cranial Nerve XII — Hypoglossal nerve
74
What lies posterior to the olives?
The inferior cerebellar peduncles, which connect the medulla to the cerebellum
75
Which cranial nerves emerge between the olive and the inferior cerebellar peduncle (rostral to caudal)?
CN IX – Glossopharyngeal
CN X – Vagus
CN XI – Spinal accessory
76
What does the posterior medulla form?
The inferior portion of the floor of the fourth ventricle
77
What is the posterior median sulcus?
A midline groove on the posterior medulla, continuous with the spinal cord’s posterior median sulcus
78
What are the gracile and cuneate tubercles?
Longitudinal elevations on either side of the posterior median sulcus
Formed by the underlying:
Gracile nucleus (medial)
Cuneate nucleus (lateral)
79
What are the three general regions of brainstem internal anatomy?
Tectum – "roof"
Tegmentum – "covering" (central core region)
Basis – ventral portion (contains descending motor tracts)
80
What are the major components of the midbrain tectum?
Superior colliculi (rostral) → visual reflexes
Inferior colliculi (caudal) → auditory processing
Cerebral aqueduct runs beneath the tectum
81
What nuclei are found in a rostral section of the midbrain (superior colliculus level)?
Oculomotor nucleus (CN III)
Edinger–Westphal nucleus (parasympathetic CN III)
Red nucleus (motor coordination, rubrospinal tract origin)
Mesencephalic nucleus of CN V (proprioception of face)
82
What nuclei are found in a caudal section of the midbrain (inferior colliculus level)?
Trochlear nucleus (CN IV)
Inferior colliculus
Mesencephalic nucleus of CN V
Substantia nigra
83
What is the basis of the midbrain and what does it contain?
Known as the crus cerebri
Contains descending motor fibers:
Corticospinal tract
Corticobulbar tract
Corticopontine fibers
84
Red nucleus
Found in: rostral midbrain
Function: Motor coordination, gives rise to rubrospinal tract
85
Substantia nigra
Present in both rostral and caudal midbrain
Function: Dopaminergic modulation of movement (projects to striatum)
Clinical relevance: Degenerates in Parkinson’s disease
86
Edinger–Westphal nucleus
Associated with: CN III
Function: Parasympathetic innervation to pupillary constrictor and ciliary muscles
87
What are the two main zones of the internal pons?
Basilar (ventral) pons
Tegmental (dorsal) pons
Separated by the medial lemniscus.
88
What fibers dominate the basilar pons?
Transversely running pontocerebellar fibers
→ Arise from pontine nuclei
→ Cross to contralateral cerebellum via middle cerebellar peduncle
Longitudinal corticospinal fibers
→ Descending motor tracts from the cortex
89
What does the medial lemniscus represent in the pons?
A horizontally oriented bundle dorsal to pontocerebellar fibers
Conveys fine touch, proprioception, vibration from the contralateral body
Separates the basilar and tegmental portions
90
What tract lies lateral to the medial lemniscus?
Spinothalamic tract
→ Conveys pain and temperature from contralateral body
→ Located near the superior cerebellar peduncle
91
What is the medial longitudinal fasciculus (MLF)?
A longitudinal bundle near the midline, ventral to periaqueductal gray
Coordinates eye and head movements (connects CN III, IV, VI, and vestibular nuclei)
92
What cerebellar peduncles are visible at mid-pontine level?
Middle cerebellar peduncles (lateral)
Superior cerebellar peduncles (form lateral walls of 4th ventricle
93
What cranial nerve nuclei are found at mid-pontine level?
Motor nucleus of CN V (trigeminal)
Principal sensory nucleus of CN V
94
What nucleus is found just lateral to the medial longitudinal fasciculus?
Abducent nucleus (CN VI)
→ Controls lateral rectus muscle of eye
95
What vestibular and auditory nuclei are found in the caudal pons?
Medial vestibular nucleus
→ Balance, spatial orientation
Anterior and posterior cochlear nuclei
→ Auditory processing
96
What are the three transverse levels of internal medulla anatomy?
Level of the inferior olivary nucleus (rostral)
Level of the decussation of internal arcuate fibers (middle)
Level of the decussation of pyramids (caudal)
97
What major nuclei are visible at this level?
Cranial nerve nuclei:
CN VIII – Vestibulocochlear
CN IX – Glossopharyngeal
CN X – Vagus
CN XI – Spinal accessory
CN XII – Hypoglossal
98
What major tract and nucleus landmarks are present?
Inferior cerebellar peduncle → connects medulla to cerebellum (posteriorly)
Medial lemniscus → positioned vertically, adjacent to midline
Medial longitudinal fasciculus (MLF) → dorsal to medial lemniscus
Hypoglossal nucleus → near MLF
99
What dorsal nuclei are seen here?
Gracile nucleus (medial)
Cuneate nucleus (intermediate)
Spinal trigeminal nucleus (lateral)
100
What occurs at this level with sensory axons?
Decussation of internal arcuate fibers (from gracile and cuneate nuclei)
→ These fibers cross the midline and form the medial lemniscus
101
What tracts are seen lateral and ventral to this?
Spinocerebellar tracts
Anterolateral system (spinothalamic tract)
→ Located around the perimeter of the medulla
102
What happens at the pyramidal decussation?
Corticospinal fibers cross to the contralateral side
→ Becomes the lateral corticospinal tract in the spinal cord
103
What dorsal structures begin appearing here?
Gracile and cuneate nuclei, and their associated fasciculi
→ Continue rostrally toward the internal arcuate fiber level
104
Where is the spinal accessory nucleus located?
NOT in the medulla, but in the cervical spinal cord
105
What major arterial system supplies the brainstem?
The vertebrobasilar system
Formed by vertebral arteries → merge into basilar artery
Basilar artery ends at pontomesencephalic junction, giving rise to posterior cerebral arteries (PCAs)
106
Where do the vertebral arteries originate and how do they enter the skull?
Originate from subclavian arteries
Ascend through foramina transversaria of C6–C2
Enter skull via the foramen magnum
107
What are the branches of the vertebral arteries that supply the medulla?
Posterior inferior cerebellar artery (PICA)
→ Supplies lateral medulla, inferior cerebellum
Anterior spinal artery
→ Supplies medial medulla
Posterior spinal artery
→ Assists in posterior medulla/cervical cord supply
Paramedian branches (from vertebral + anterior spinal arteries)
→ Supply anteromedial medulla
108
What branches supply the caudal pons?
Anterior inferior cerebellar artery (AICA)
→ Supplies lateral caudal pons
109
What supplies the rostral lateral pons?
Circumferential branches of the basilar artery
110
What supplies the medial pons?
Paramedian branches of the basilar artery
111
What artery supplies the caudal dorsal midbrain?
Superior cerebellar artery (SCA)
→ Also supplies superior cerebellar peduncles and superior cerebellum
112
What supplies the medial midbrain?
Paramedian branches of the basilar artery
113
What artery supplies the lateral midbrain?
Posterior cerebral artery (PCA)
→ Also supplies thalamus, medial occipital, and inferior temporal lobes
114
What are the basal nuclei?
A group of deep gray matter structures at the base of the forebrain
Involved in voluntary movement, posture, behavior, and motivation
115
What are the core motor-related basal nuclei?
Caudate nucleus
Putamen
Globus pallidus
Subthalamic nucleus (diencephalon)
Substantia nigra (midbrain)
116
What is the corpus striatum?
Caudate nucleus + Lentiform nucleus (putamen + globus pallidus)
Named for striated appearance (white matter tracts pass through it)
117
What is the lentiform nucleus?
Putamen (lateral) + Globus pallidus (medial)
Appears lens-shaped in horizontal/axial sections
Lateral to internal capsule, medial to external capsule and claustrum
118
What is the striatum?
Caudate nucleus + Putamen
Main input center of the basal nuclei
119
Describe the structure and path of the caudate nucleus.
C-shaped structure with:
Head: forms lateral wall of anterior horn of lateral ventricle
Body: forms floor of lateral ventricle
Tail: curves into inferior horn of lateral ventricle, ends in amygdala
120
What separates the caudate from the lentiform nucleus?
The internal capsule
121
Where does input to the basal nuclei primarily go?
To the striatum (caudate + putamen)
122
Where does output from the basal nuclei primarily originate?
From the globus pallidus (especially the internal segment)
123
What are the major sources of input to the striatum?
Cerebral cortex (all areas)
Thalamic nuclei
Subthalamic nucleus
Substantia nigra (dopaminergic)
Brainstem
124
What is the direct pathway, and what is its effect on movement?
Striatum → Globus pallidus → Thalamus → Cortex
Facilitates movement (increases motor activity)
125
What is the indirect pathway, and what is its effect?
Striatum → Globus pallidus (external) → Subthalamic nucleus → Globus pallidus (internal) → Thalamus
Inhibits movement (decreases motor activity)
126
Where is the cerebellum located?
In the posterior cranial fossa, beneath the tentorium cerebelli
Connected to the brainstem via:
Superior cerebellar peduncle
Middle cerebellar peduncle
Inferior cerebellar peduncle
127
What are the functions of the cerebellum?
Balance and posture
Coordination of voluntary movement
→ Synchronizes contraction and relaxation of muscles
Motor planning and timing
Affects ipsilateral side of body
128
What connects the cerebellar hemispheres?
The vermis (midline structure)
129
What are the three cerebellar lobes and their landmarks?
Anterior lobe
→ Separated from posterior lobe by primary fissure
Posterior lobe
→ Largest lobe
Flocculonodular lobe
→ Separated by posterolateral fissure
→ Includes flocculus + nodulus
🔹 A third, surface-based fissure — the horizontal fissure — separates superior/inferior cerebellar surfaces.
130
What is the arbor vitae?
The branching white matter core of the cerebellum seen in sagittal sections
Surrounded by superficial gray matter cortex
131
What are the deep cerebellar nuclei (lateral to medial)?
Dentate nucleus
Emboliform nucleus
Globose nucleus
Fastigial nucleus
🟢 Emboliform + Globose = interposed nuclei
132
Where does output from the cerebellum originate?
From one of the four deep cerebellar nuclei
Mostly exits via the superior cerebellar peduncle
133
What are the three functional regions of the cerebellar cortex?
Vermis
→ Controls axial muscles (trunk, neck, pelvis)
Intermediate zone
→ Controls distal limb muscles
Lateral zone
→ Involved in motor planning and coordination
134
What are the input sources to the cerebellum?
Cerebral cortex (via pontine nuclei)
Spinal cord
Brainstem (vestibular, olivary nuclei)
→ Enter mostly via middle and inferior cerebellar peduncles
135
What are the three layers of the cerebellar cortex (from deep to superficial)?
Granular layer
Contains granule cells, receives mossy fibers
Purkinje cell layer
Contains large Purkinje neurons
Only output cells of cerebellar cortex → project to deep nuclei
Molecular layer
Contains parallel fibers and Purkinje dendrites
136
What are mossy fibers?
Afferent fibers from various sources (spinal cord, brainstem)
Synapse on granule cells in the granular layer
137
What are climbing fibers?
Afferent fibers from the inferior olivary nucleus
Form strong excitatory synapses directly on Purkinje cells
138
Where does cerebellar output originate?
From the deep cerebellar nuclei:
Dentate
Interposed (emboliform + globose)
Fastigial
139
What is the primary output path of the dentate nucleus?
Projects to contralateral ventral nucleus of thalamus
→ Thalamus projects to motor cortex
→ Pathway decussates in superior cerebellar peduncle
→ Function: Voluntary movement planning and posture
140
What is the output of the interposed nuclei (emboliform + globose)?
To contralateral:
Ventral thalamic nucleus
Red nucleus (midbrain)
→ Red nucleus → inferior olivary nucleus (medulla)
→ Function: Correction of limb movements
141
What are the outputs of the fastigial nucleus?
To:
Ipsilateral vestibular nuclei
Contralateral vestibular nuclei (via uncinate fasciculus)
Reticular formation
Contralateral tectum
Contralateral ventral thalamus
→ Inferior cerebellar peduncle: to vestibular nuclei, reticular formation
→ Superior cerebellar peduncle: to thalamus and tectum
142
Summary: What do the three cerebellar nuclei primarily influence?
Nucleus | Main Targets | Function
Dentate | Thalamus → Cortex | Motor planning & posture
Interposed | Thalamus + Red nucleus → Olive | Movement correction (limbs)
Fastigial | Vestibular nuclei, RF, tectum, thalamus | Balance, postural reflexes, eye-head sync
143
What arterial system supplies the cerebellum?
The vertebrobasilar system
144
What are the three main arteries supplying the cerebellum?
PICA – Posterior inferior cerebellar artery
AICA – Anterior inferior cerebellar artery
SCA – Superior cerebellar artery
145
Where does the PICA originate?
From the vertebral artery, before it merges into the basilar artery
146
What does the PICA supply?
Inferior portion of the cerebellum
Also contributes to lateral medulla (clinically important in Wallenberg syndrome)
147
Where does the AICA originate?
From the basilar artery at the level of the caudal pons
148
What does the AICA supply?
Anterior and lateral cerebellum
Middle and inferior cerebellar peduncles
149
Where does the SCA originate?
From the basilar artery, just before it divides into posterior cerebral arteries (PCAs)
150
What does the SCA supply?
Superior portion of cerebellar hemispheres
Superior cerebellar peduncles
151
Which cerebellar peduncle is supplied by all three arteries?
Inferior cerebellar peduncle
PICA and AICA both contribute partially
SCA supplies superior peduncle
152
What are the primary functions of the visual system?
Visual perception
Spatial awareness
Recognition of shapes and object features
153
What is the first structure light passes through when entering the eye?
The cornea
154
What is the function of the pupil?
Controls how much light enters the eye
Aperture of the iris
155
What structure focuses light and separates the anterior from the posterior eye?
The lens
156
What controls the shape of the lens for accommodation?
Ciliary muscle and suspensory ligaments
Controlled by parasympathetic input (CN III → Edinger–Westphal nucleus)
157
What is accommodation?
Rounding of the lens to focus on near objects
Occurs via contraction of the ciliary muscle
158
After the lens, where does light pass through?
The vitreous humor → onto the retina
159
What is the role of the choroid and pigmented epithelium?
Absorb stray light and prevent reflection inside the eye
Aid in clarity and contrast of the image
160
What is phototransduction?
The process by which photoreceptors convert light into electrical signals
161
How is the retinal image oriented?
Inverted both vertically and laterally
Visual field is divided into 4 quadrants
162
What are the two types of photoreceptors?
Rods – very sensitive to light, used in dim light, located in peripheral retina
Cones – responsible for color vision and high acuity, concentrated in macula, especially the fovea
163
Where is visual acuity highest?
At the fovea centralis (contains only cones)
164
What are the three parts of a photoreceptor?
Outer segment – detects light
Inner segment – metabolic activity
Synaptic terminal – contacts bipolar cells
165
What is the first-order neuron in the visual pathway?
Bipolar cells
166
What is the second-order neuron in the visual pathway?
Ganglion cells → axons form the optic nerv
167
What other interneurons are present in the retina?
Horizontal cells – modulate input from photoreceptors to bipolar cells
Amacrine cells – modulate bipolar-to-ganglion synapses
168
Where do ganglion cell axons converge to exit the retina?
At the optic disc (blind spot — no photoreceptors)
169
What forms the optic nerve?
Axons of retinal ganglion cells
Covered by oligodendrocyte-derived myelin and meninges → CNS tissue
170
Where do the optic nerves converge?
At the optic chiasm, anterior to the infundibular stalk
171
What happens at the optic chiasm?
Nasal retinal fibers decussate to the contralateral optic tract
Temporal retinal fibers remain ipsilateral
🧠 Due to retinal inversion, nasal retina sees temporal visual field, and vice versa.
172
Where do the optic tracts project?
Mostly to the lateral geniculate nucleus (LGN) of the thalamus
173
What additional brain areas receive minor input from the optic tract?
Pretectal area and superior colliculus
→ Mediate pupillary light reflex and visual tracking
174
What structure do axons leaving the LGN form?
Optic radiations → project to the primary visual cortex in the occipital lobe
175
How are optic radiations organized?
Lower fibers (from upper visual field) → project to lower half of primary visual cortex
Upper fibers (from lower visual field) → project to upper half of cortex
176
Why does each visual cortex receive information from the contralateral visual field?
Because nasal retinal fibers cross, and the retina sees an inverted/reversed image
→ Each optic tract, LGN, optic radiation, and cortex processes the contralateral visual field
177
What kind of visual field defect results from:
178
What nerve carries auditory information?
Cranial Nerve VIII — Vestibulocochlear nerve
179
What are the two functional divisions of CN VIII?
Cochlear nerve → hearing
Vestibular nerve → balance
180
Where does CN VIII enter the brainstem?
At the pontomedullary junction, in the cerebellopontine angle
181
What structures make up the outer ear?
Pinna + external acoustic meatus
182
What structure vibrates in response to sound waves?
The tympanic membrane
183
Which bones transmit vibrations through the middle ear?
Malleus
Incus
Stapes
184
What window does the stapes connect to?
The oval window of the cochlea
185
What muscles reduce movement of ossicles in loud sounds?
Tensor tympani (malleus)
Stapedius (stapes)
186
What fluid-filled chambers are present in the cochlea?
Scala vestibuli (perilymph)
Scala media (endolymph)
Scala tympani (perilymph)
187
What separates the scala vestibuli and scala tympani?
The scala media, bordered by:
Vestibular membrane (Reissner’s)
Basilar membrane
188
What structure sits on the basilar membrane?
The organ of Corti
→ Contains hair cells, the auditory sensory receptors
189
What happens when the basilar membrane moves?
Hair cells bend → generate electrical signal
Synapse with neurons of spiral ganglion
190
Where is the spiral ganglion located?
In the modiolus of the cochlea
191
What do axons from spiral ganglion form?
The cochlear nerve
→ Exits through the internal acoustic meatus
192
Where do first-order cochlear nerve fibers terminate?
On the dorsal and ventral cochlear nuclei (ipsilateral)
193
What is the first major site of bilateral auditory integration?
The superior olivary nucleus (in the pons)
🧠 Important for sound localization
194
What tract carries auditory fibers from the pons to midbrain?
The lateral lemniscus
195
What is the midbrain target of the auditory pathway?
The inferior colliculus
196
Where do fibers go after the inferior colliculus?
To the medial geniculate nucleus (MGN) of the thalamus
197
Final projection site of auditory input?
Primary auditory cortex (in the superior temporal gyrus, Brodmann areas 41 & 42)
198
What is tonotopic organization?
Frequency-specific mapping maintained from cochlea to cortex
→ Similar to somatotopy in sensory/motor systems
199
What descending pathway originates from auditory cortex?
Feedback to superior olivary nucleus → projects inhibitory olivocochlear fibers to the organ of Corti
200
Which cranial nerves mediate reflexive ossicle contraction?
CN V (tensor tympani) and CN VII (stapedius)
→ Protect from loud sounds
201
What structures detect head movement and position?
Semicircular ducts – angular acceleration
Utricle and saccule – linear acceleration and gravity
202
Where are vestibular sensory cell bodies located?
In Scarpa’s ganglion (vestibular ganglion) in the internal acoustic meatus
203
Where does the vestibular nerve enter the brainstem?
At the cerebellopontine angle, alongside the cochlear nerve
204
Where do vestibular afferents terminate?
In the four vestibular nuclei (superior, inferior, medial, lateral) in the rostral medulla and caudal pons
205
What is the role of the medial longitudinal fasciculus (MLF)?
Connects vestibular nuclei to CN III, IV, VI
→ Coordinates eye movement with head movement
206
What thalamic relay projects vestibular input to cortex?
Ventral posterior nucleus of the thalamus
→ Helps with spatial orientation awareness
207
What cerebellar structure receives vestibular input?
The cerebellum via the inferior cerebellar peduncle
208
What spinal pathways arise from vestibular nuclei?
Medial vestibulospinal tract
→ Head and neck posture
Lateral vestibulospinal tract
→ Whole-body posture and balance
209
What is the hypothalamus?
A neuroendocrine center of the diencephalon
Regulates homeostasis, behavioral drives, and endocrine function
210
What physiological functions are controlled by the hypothalamus?
Feeding and drinking behavior
Temperature regulation
Sleep–wake cycle
Growth and reproduction
Autonomic nervous system regulation
211
What is the general anatomical location of the hypothalamus?
Inferior part of the diencephalon, surrounding the third ventricle
212
What are the major boundaries of the hypothalamus?
Anterior: Optic chiasm
Posterior: Mammillary bodies
Lateral: Optic tracts and crus cerebri
213
What are mammillary bodies?
Paired hypothalamic nuclei involved in limbic system and memory circuits
Part of the Papez circuit
214
What types of connections does the hypothalamus have?
Neural: with limbic system, brainstem, thalamus, spinal cord
Endocrine: to pituitary gland via infundibulum and hypophyseal portal system
215
What structure connects the hypothalamus to the pituitary gland?
The infundibulum and hypophyseal stalk
216
Where is this connection located anatomically?
Caudal to the optic chiasm
217
How does the hypothalamus control the anterior pituitary?
Via the tuberoinfundibular tract, which delivers releasing/inhibiting hormones into the hypophyseal portal system
218
What kind of connection is this: neural or vascular?
Vascular connection (via portal circulation
219
Which hormones are regulated by the hypothalamus through this route?
ACTH – adrenocorticotropic hormone
LH – luteinizing hormone
FSH – follicle-stimulating hormone
TSH – thyroid-stimulating hormone
GH – growth hormone
Prolactin
220
How does the hypothalamus communicate with the posterior pituitary?
Through the hypothalamo-hypophyseal tract
→ Axons from supraoptic and paraventricular nuclei
221
What kind of connection is this: neural or vascular?
Neural connection
222
What hormones are released into circulation from the posterior pituitary?
Oxytocin
Vasopressin (ADH)
→ Synthesized in hypothalamic nuclei, released via axon terminals in posterior pituitary
223
What are the three longitudinal zones of the hypothalamus?
Lateral zone
Medial zone
Periventricular zone
224
What anatomical landmarks divide the lateral and medial zones?
The columns of the fornix
The mammillothalamic tract
225
What fiber bundle runs through the lateral zone?
The medial forebrain bundle (MFB)
226
What is the function of the lateral hypothalamic area?
Promotes feeding behavior
Lesion = aphagia (loss of desire to eat)
227
What are the tuberal nuclei of the lateral zone involved in?
Connect to anterior pituitary (via tuberoinfundibular tract)
Also connect to cerebellum for motor modulation
228
What are the 4 main nuclei and their functions?
Supraoptic nucleus
→ Synthesizes vasopressin (ADH)
Paraventricular nucleus
→ Synthesizes oxytocin and ADH
Suprachiasmatic nucleus
→ Receives retinal input
→ Controls circadian rhythms
Anterior nucleus
→ Involved in heat dissipation (thermoregulation)
229
What are the 3 main nuclei and their functions?
Ventromedial nucleus
→ Satiety center (inhibits feeding)
Dorsomedial nucleus
→ Aggressive behavior, rage response
Arcuate nucleus
→ Synthesizes releasing hormones for the anterior pituitary
230
What are the 4 nuclei?
Medial mammillary nucleus
→ Receives input from hippocampus (postcommissural fornix)
→ Role in memory
Intermediate mammillary nucleus
Lateral mammillary nucleus
Posterior hypothalamic nucleus
→ Heat conservation and wakefulness
231
Where is the periventricular zone located?
Adjacent to the third ventricle, medial to the medial zone
232
What is the main function of the periventricular zone?
Produces releasing hormones → transmitted via tuberoinfundibular tract to regulate anterior pituitary
233
What makes the olfactory pathway unique among sensory systems?
It bypasses the thalamus before reaching the primary sensory cortex
234
What are the three main cell types in the olfactory epithelium?
Olfactory receptor neurons – detect odorants
Sustentacular cells – support and insulate
Basal cells – stem cells for regeneration
235
Where is the olfactory epithelium located?
Along the lateral and septal walls of the nasal cavity
236
How do olfactory receptor neurons detect odors?
Their olfactory vesicles contain cilia with receptors for odorant molecules
237
Where do the axons of olfactory receptor neurons project?
Through the cribriform plate of the ethmoid bone
→ To the olfactory bulb
238
Where do olfactory receptor neurons synapse?
On mitral cells in the glomeruli of the olfactory bulb
239
What do mitral cell axons form?
The olfactory tract
240
What does the olfactory tract divide into?
Medial olfactory stria
Lateral olfactory stria
241
Where do fibers in the medial olfactory stria go?
Septal area via the diagonal band
Some cross via the anterior commissure to inhibit contralateral olfactory bulb (enhances localization)
242
Where do fibers in the lateral olfactory stria project?
Primary olfactory cortex (piriform cortex, uncus)
Amygdala
243
What tract links the olfactory system to the hypothalamus and brainstem?
The medial forebrain bundle (MFB)
244
What autonomic responses are influenced by olfactory input?
Arousal (via reticular formation)
Salivation
Gastric motility
→ All linked to survival behaviors
245
What makes the olfactory system unique among sensory pathways?
It bypasses the thalamus and projects directly to primary olfactory cortex
246
What are the cell types in the olfactory epithelium?
Olfactory receptor neurons – sensory input
Sustentacular cells – structural support
Basal cells – stem cells for regeneration
247
Where do olfactory receptor axons synapse?
In the olfactory bulb on mitral cells (via glomeruli)
248
What are the two main divisions of the olfactory tract?
Medial olfactory stria → septal area, anterior commissure
Lateral olfactory stria → primary olfactory cortex (piriform cortex, uncus) & amygdala
249
What tract links olfactory regions with hypothalamic and autonomic centers?
The medial forebrain bundle (MFB
250
What are the major cortical components of the limbic system?
Cingulate gyrus, parahippocampal gyrus, subcallosal area, and insular cortex
251
What are the major subcortical nuclei of the limbic system?
Amygdala, hippocampal formation, septal nuclei, nucleus accumbens, anterior and mediodorsal thalamic nuclei
252
What is the amygdala's primary function?
Fear, emotional processing, and autonomic/endocrine responses
253
What are the three amygdala connection pathways?
Uncinate fasciculus – to frontal cortex
Stria terminalis – to septal nuclei and hypothalamus
Ventral amygdalofugal pathway – to thalamus, brainstem, and forebrain
254
What is the nucleus accumbens involved in?
Reward, motivation, and addiction ("gratification center")
255
What are its key inputs and outputs?
Inputs: Amygdala, hippocampus, ventral tegmental area, septal nuclei
Outputs: Hypothalamus, globus pallidus, brainstem
256
What behaviors are associated with the septal area?
Pleasure and positive reinforcement
Lesions may cause rage or displeasure
257
What is the connection between septal nuclei and sleep–wake cycle?
Via habenular nuclei → interpeduncular nucleus (reticular formation)
258
What structures make up the hippocampal formation?
Hippocampus, dentate gyrus, and subiculum
259
What are the hippocampus' main functions?
Episodic memory, short-term memory, working memory, and memory consolidation
260
What are the two afferent pathways from the entorhinal cortex?
Perforant pathway – to dentate gyrus
Alvear pathway – to CA1 and CA3
261
What are Shaffer collaterals?
Axons from CA3 to CA1 within the hippocampus
262
What is the fornix?
A white matter tract that carries hippocampal output to other limbic structures
→ Projects to mammillary bodies, septal area, nucleus accumbens, thalamus
263
What is the flow of the Papez circuit?
Subiculum →
Fornix →
Mammillary bodies →
Mammillothalamic tract →
Anterior nucleus of thalamus →
Cingulate gyrus →
Cingulum →
Parahippocampal gyrus/entorhinal cortex →
Hippocampus
264
What was the original purpose of the Papez circuit?
Proposed as the neural basis for emotion
→ Now known to involve memory, integration, and limbic communication
