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Human Anatomy > Nervous System II: Blood Supply, CSF, and Cranial Nerves > Flashcards

Nervous System II: Blood Supply, CSF, and Cranial Nerves Flashcards

1
Q

How much does the brain account for?

A

The brain accounts for only 2% of body weight, but it consumes 20% of the oxygen.

(connot get enough blood; hungry)

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2
Q

Does the CNS store energy?

A

Unlike other organs, the CNS doesn’t store energy.

Therefore, it requires a constant, uninterrupted flow
of blood.

(no fat storages for ex)

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3
Q

What is the blood supplied by?

A

the internal carotid arteries and vertebral arteries.

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4
Q

Internal carotids (anterior circulation):

A

supply the telencephalon (anterior, medial, & lateral surfaces) and diencephalon.

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5
Q

Vertebrals (posterior circulation):

A

supply the posterior & inferior parts of telencephalon (occipital lobe and inferior temporal lobe), brainstem, cerebellum, and cervical spinal cord.

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6
Q

What are the major branches of internal carotid arteries (ANTERIOR circulation)? Describe them

A
  1. Posterior communicating arteries – connect the anterior circulation to the posterior circulation. (1st to branch off)
  2. Anterior cerebral arteries – supply the medial and superior surfaces of the frontal and parietal lobes. The two anterior cerebral arteries are connected by the anterior communicating artery (very small - few mm).
  3. Middle cerebral arteries – largest branches of the internal carotids. They supply most of the lateral surface of the cerebral hemispheres, as well as subcortical areas.
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7
Q

What does the Middle cerebral arteries supply?

A
  • largest branches of the internal carotids. They supply most of the lateral surface of the cerebral hemispheres, as well as subcortical areas

Supply a large portion of the motor and pre-motor areas in the frontal lobe.

Supply a large area in the parietal lobe.

Supply the superior surface and anterior pole of the temporal lobe.

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8
Q

What are the Vertebral arteries (Posterior circulation)?

A

The VERTEBRAL ARTERIES enter the skull and merge to form the single BASILAR ARTERY at the junction of the pons and medulla.

Branches of the vertebral and basilar arteries supply the SPINAL CORD, CEREBELLUM and PONS.

The basilar artery travels on the anterior surface of the pons before before splitting into the POSTERIOR CEREBRAL ARTERIES (left and right).

The posterior cerebrals supply the MIDBRAIN, OCCIPITAL LOBE and INFERIOR SURFACE OF THE TEMPORAL LOBE.

The posterior cerebrals are connected to the anterior circulation via the POSTERIOR COMMUNICATING ARTERIES.

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9
Q

Describe the motor homunculus of motor cortex concept

A

finer motor control (i.e. more neurons needed)
- therefore, exaggerated hands & face

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10
Q

What is the Circle of Willis

A

Acts as a backup system for cerebral blood flow.

If there is a blockage somewhere in the circle, blood can flow in the opposite direction to compensate (not perfect, but it helps).

(circle formed by the arteries)

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11
Q

What are the arteries that make up the circle?

A
  1. Anterior cerebral arteries
  2. Anterior communicating artery
  3. Internal carotid arteries
  4. Posterior communicating arteries
  5. Posterior cerebral arteries
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12
Q

Describe the venous drainage of the brain

A

Superficial veins (SUPERIOR CEREBRAL VEINS) - drain the lateral surfaces of the cerebral cortex (external).

Deep veins (INTERNAL CEREBRAL VEINS and BASAL VEIN) – drain the deep structures of the brain (basal nuclei and diencephalon).

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13
Q

Where do all veins drain into?

A

dural venous sinuses.

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14
Q

What are the dural venous sinuses

A

A sinus is a channel within the dura that carries VENOUS BLOOD.

A sinus is functionally similar to a vein but has a different structure. (just dura)

Venous blood in the brain is initially carried by veins, which then drain into venous sinuses (there are several venous sinuses in the cranial cavity).

The sinuses convey venous blood to the internal JUGULAR VEINS, where it returns to the normal circulation.

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15
Q

Dural venous sinuses - unpaired

What are the three midline sinuses carry the bulk of the brain’s venous blood:

A
  1. Superior sagittal sinus
  2. Inferior sagittal sinus
  3. Straight sinus

• The superior sagittal and straight sinuses meet at the CONFLUENCE OF SINUSES.

(unpaired means largest ones & all found at midline)

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16
Q

Superior sagittal sinus:

A

found at the superior margin of the falx cerebri.

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17
Q

Inferior sagittal sinus:

A

found at the inferior margin of the falx cerebri. It flows into the: Straight sinus

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18
Q

Straight sinus:

A

found at the junction of the falx cerebri and tentorium cerebelli.

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19
Q

Dural venous sinuses - paired

What are the major paired sinuses?

A

(the unpaired flows into the paired sinuses)

  1. Transverse sinus
  2. Superior petrosal sinus
  3. Inferior petrosal sinus
  4. Sigmoid sinus - joins with the inferior petrosal to drain into the internal jugular vein.

• The locations of these sinuses can be seen as grooves on the inner surface of the skull.

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20
Q

Describe blood flow in the dural venous sinuses

A
  • The superficial veins drain into the superior sagittal sinus.
  • The inferior sagittal sinus and deep veins drain into the straight sinus.
  • Blood then flows from these sinuses into the confluence of sinuses and follows this direction: confluence → transverse → sigmoid → internal jugular.
  • The superior and inferior petrosal sinuses drain smaller veins coming from the brainstem and cerebellum (and the orbit).
21
Q

Describe the ventricular system

A

Consists of 4 fluid-filled cavities within the brain and brainstem:
- 2 lateral ventricles
- 3rd ventricle
- 4th ventricle

22
Q

2 lateral ventricles:

A

C-shaped cavities - one within each cerebral hemisphere, separated anteriorly by a membrane called the SEPTUM PELLUCIDUM.

23
Q

3rd ventricle:

A

a slit-like cavity found at the midline at the level of the diencephalon (between the two halves of the thalamus).

24
Q

4th ventricle:

A

a diamond-shaped cavity found between the pons/medulla (anterior) and the cerebellum (posterior).

25
Q

What is Cerebrospinal fluid (CSF)?

A
  • CSF is a clear fluid derived from plasma.
  • It is produced by the CHOROID PLEXUS, which is
    found in all 4 ventricles.
  • Choroid plexus consists of tufts of capillaries that protrude into the ventricles and are surrounded by a specialized epithelium.
  • The epithelium filters the plasma and determines which solutes enter the CSF.
  • CSF is primarily water and ions (Na, Cl, Mg), with low amounts of protein and glucose. (compared to plasma)
26
Q

What are the CSF functions?

A
  1. Protection - provides buoyancy for the brain within the skull and acts as a shock absorber.
  2. Nourishment - provides nutrients, ions, and growth factors.
  3. Cleansing - removes cellular waste products.
    - The composition of CSF is relatively consistent, so changes can be an indication of pathology (CSF samples for testing are obtained by lumbar puncture, aka. spinal tap).
    - should never see blood &/or bacteria in CSF for ex (menigitis)

(brain is weightless inside skull b/c of CSF (floating inside))

27
Q

Describe the CSF flow

A
  • Imagine CSF that is produced in the lateral ventricles.
  • The 2 lateral ventricles drain into the 3rd ventricle via the INTER-VENTRICULAR FORAMINA (aka. FORAMINA OF MONRO).
  • The 3rd ventricle drains into the 4th ventricle via the CEREBRAL AQUEDUCT (narrowest part of the ventricular system – located in the midbrain).
  • The 4th ventricle drains into the SUBARACHNOID SPACE (between arachnoid and pia) via 3 openings - the MEDIAN APERTURE and 2 LATERAL APERTURES.
28
Q

What is the Subarachnoid space?

A

Once CSF exits the 4th ventricle, it enters the subarachnoid space and circulates around the brain and spinal cord. (how it does what it does)

29
Q

What is CSF Reabsorption?

A
  • CSF is constantly produced by the choroid plexus (~ 500 ml/day)
  • The volume of the ventricles and subarachnoid space is ~150 ml.
  • Therefore, CSF can accumulate rapidly if it is not removed from the subarachnoid space.
  • CSF is reabsorbed into the blood by ARACHNOID VILLI.
  • Arachnoid villi are extensions of the subarachnoid space that protrude through the dura into a venous sinus. They are most numerous within the SUPERIOR SAGITTAL SINUS.
30
Q

What is the Pathology related to CSF? & what are 2 main causes?

A

Abnormal accumulation of CSF within the ventricles is called HYDROCEPHALUS.

Two main causes:
1. Impaired absorption of CSF (can be acquired).
2. Blockage within the ventricular system (often congenital). (esp. in paediatrics)
• Ventricles become enlarged. (pressure –> fatal)

31
Q

What are the Cranial Nerves?

A
  • There are 12 pairs of cranial nerves that innervate structures in the head and neck. (exception) Cranial nerve X also innervates structures in the thorax and abdomen.
  • 2 cranial nerves arise from the brain: I and II.
  • 10 of the 12 arise from the brainstem: midbrain (III and IV), pons (V, VI, VII, VIII), and medulla (IX, X, XI, XII).
  • Cranial nerves may be MOTOR, SENSORY, or MIXED (both sensory and motor fibres).

(in PNS)

32
Q

Cranial Nerves: Sensory (n=3)

A

CN I: Olfactory nerve

CN II: Optic nerve

CN VIII: Vestibulocochlear nerve

33
Q

Cranial Nerves: Motor (n=5)

A

3 cranial nerves innervate the 6 extraocular muscles of the eye: (up-down, side-to-side)
CN III: Oculomotor nerve

CN IV: Trochlear nerve

CN VI: Abducens nerve

CN XI: Spinal Accessory nerve

CN XII: Hypoglossal nerve

34
Q

Cranial Nerves: Mixed (n=4)

A

CN V: Trigeminal nerve (3 divisions: V1, V2, V3)
• V1 (Ophthalmic nerve)
• V2 (Maxillary nerve)
• V3 (Mandibular nerve)
CN VII: Facial nerve
CN IX: Glossopharyngeal nerve
CN X: Vagus nerve

35
Q

CN I: Olfactory nerve

A

– carries olfactory information from the olfactory epithelium to the olfactory bulb.

36
Q

CN II: Optic nerve

A
  • carries visual information from the retina to the thalamus. (thalamus will than relay it)
37
Q

CN VIII: Vestibulocochlear nerve

A

– carries balance and hearing from the inner ear (cochlea and vestibular apparatus) to the brainstem.

38
Q

CN III: Oculomotor nerve

A

– innervates 4 of the 6 extraocular muscles (eye movements), and the intrinsic muscles that control pupil size (iris) and lens accommodation (parasympathetic).

39
Q

CN IV: Trochlear nerve

A
  • innervates the superior oblique muscle of the eye.
40
Q

CN VI: Abducens nerve

A
  • innervates the lateral rectus muscle of the eye.
41
Q

CN XI: Spinal Accessory nerve

A

– innervates the sternocleidomastoid (rotates the head) and trapezius muscles (shrugs the shoulders). (innervates the ‘idk muscles”)

42
Q

CN XII: Hypoglossal nerve

A

– innervates the intrinsic and extrinsic muscles of tongue. (sticking out your tongue).

43
Q

CN V: Trigeminal nerve

A

(3 divisions: V1, V2, V3)

44
Q

CN V: Trigeminal nerve (3 divisions: V1, V2, V3)
• V1 (Ophthalmic nerve)

A

– Sensory innervation of the cornea, upper eyelid, nose, and forehead.

45
Q

CN V: Trigeminal nerve (3 divisions: V1, V2, V3)

• V2 (Maxillary nerve)

A

– Sensory innervation of the lower eyelid, maxilla, upper lip and teeth, hard palate, skin of the face.

(detects iced/hot coffee)

46
Q

CN V: Trigeminal nerve (3 divisions: V1, V2, V3)

• V3 (Mandibular nerve)

A

Sensory innervation of the mandible, lower lip and teeth, anterior 2/3 of the tongue, skin of the face; Motor to the muscles of mastication (chewing).

47
Q

CN VII: Facial nerve

A

• Sensory – Taste from the anterior 2/3 of the
tongue. (detects sugar in coffee for ex)
• Motor – Muscles of facial expression.
• Parasympathetic - Lacrimal gland and all salivary glands except the parotid gland.

48
Q

CN IX: Glossopharyngeal nerve

A

• Sensory – Taste and general sensation from the
posterior 1/3 of the tongue (gag reflex).
• Motor – Stylopharyngeus muscle (assists in swallowing).
• Parasympathetic – Parotid gland..

(glosso - tongue, pharynx - throat)

49
Q

CN X: Vagus nerve

A

• Sensory – Taste from the epiglottis, general sensation from the pharynx and larynx. It also carries “visceral sensation” from the organs of the thorax and abdomen.

• Motor – muscles of the pharynx (swallowing) and muscles of the larynx (speech).

• Parasympathetic – Respiratory tract, heart, esophagus, stomach, small and large intestine.

Human Anatomy (15 decks)

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