Brainstem and blood supply to the brain

Describe the location of the three components of the brainstem and their anatomical relations.

Locate and identify the key structures that are visible on the midbrain (including in cross-section), pons and medulla oblongata.

Outline the course and appreciate the functional significance of some of the major ascending and descending neural pathways that pass through the brainstem, linking the cerebral hemispheres and the spinal cord.

Describe the formation of the Circle of Willis, naming its major contributing arteries and identifying all major communicating and cerebral artery components.

Describe the origin, course, and recall the specific cortical supply territories of the anterior, middle and posterior cerebral arteries.

Describe the venous drainage of the brain and locate the major venous sinuses.

What are the 3 components of the brainstem ?

midbrain, pons and medulla oblongata

What is the bulb another term for?

medulla oblongata

What are some functions of the brainstem?

• Condit for tracts (sensory and motor)

• Head and neck sensory, motor and autonomic (CN III-XII) 

• Consciousness, cardiovascular system, respiratory system, pain perception (reticular formation)

• Damage is life-threatening

What structure and view is this? Which landmarks are visible?

ventral view of the brainstem

crus cerebri, olive, pyramid visible, transverse fibres of pons

Function of crus cerebri

voluntary motor control, coordination because carries crucial motor fibers from the cerebral cortex to the brainstem and spinal cord

Function of brainstem pyramids

carries corticospinal tract fibres

Function of olive

coordination of movement, link to cerebellum

What structure and view is this? Which landmarks are visible?

dorsal view of the brainstem

cerebellum mostly removed here, Thalamus, pineal gland, colliculi sup and inf,  trochlear nerve, dorsal columns sensory from spine terminate in the gracile and cuneate nuclei seen as tubercles

Function of superior vs inferior colliculus

reflexes linked to auditory vs sensory - very old response eg i see lion, i must run away from lion, together coordinate sensory-motor responses

Function of gracile vs cuneate nuclei

process information from lower limb vs upper body (c for side and cephalic so lateral to gracile and for top of body)

What is the obex?

(Latin for "barrier") is the point in the caudal medulla of the human brain where the fourth ventricle narrows to become the central canal of the spinal cord

Label these

superior, middle and inferior cerebellar peduncle

What view is this ? Label structures

horizontal section of the midbrain

Describe the volume and pathways of the brainstem’s connections to surrounding structures

numerous and bidirectional, links between the brain and spinal cord, brainstem and cerebellum and cerebellum and spinal cord

Some pass through e.g., corticospinal, spinothalamic, Some have origins in, or terminate in, the brainstem nuclei

What are 2 motor pathways spanning through the midbrain?

corticospinal and corticonuclear

What is the function of the corticospinal and corticonuclear pathways ?

voluntary/conscious control over skeletal muscles

What area does the corticospinal motor pathway control?

below the head

What area does the corticonuclear motor pathway control?

head and neck

What are 2 sensory pathways spanning through the midbrain?

reactive spinothalamic and discriminative dorsal column-medial lemniscus (DCML)

What are the 2 systems through which the brain is irrigated?

internal carotid system and vertebral-basilar system (2 internal carotid arteries and 2 vertebral arteries)

What is the function of the spinothalamic pathway?

reactive sensory pathway ie pain, temperature, “crude” touch and pressure 

What is the function of the DCML pathway?

discriminative sensory pathway ie proprioceptive (limb position), fine touch and vibration

Are spinothalamic and DCML ascending or descending?

ascending/afferent tract

How do the internal carotid arteries enter the skull?

through carotid canal

How do the vertebral arteries enter the skull? Where do they arise?

through foramen magnum

from subclavian artery

Branches of the internal carotid and vertebral-basilar systems interconnect to form which structure?

form the cerebral arterial circle (The Circle of Willis)

Which short blood vessels complete the anterior and posterior portions of the circle of Willis respectively?

anterior and posterior communicating arteries - connect left and right anterior cerebral arteries and the posterior and anterior circulation respectively (vertebrobasilar and internal carotid artery systems)

Which main blood vessels are involved in supplying the brain with blood?

cerebral arteries (A, M and P), internal carotid arteries, vertebral artery, communicating arteries

Label the following cortical vascular territories (areas of blood supply)

Where do all venous sinuses drain into?

internal jugular vein

What are the major dural venous sinuses?

• Superior sagittal sinus 

• Inferior sagittal sinus 

• Straight sinus 

• Transverse sinus

• Confluence of sinuses

• Cavernous sinus  

• Sigmoid sinus

What carries out venous drainage in the brain?

Cerebral veins that collect deoxygenated blood and cerebrospinal fluid and channel it into a network of dural venous sinuses, which all drain into internal jugular vein

Which pathways spanning the brainstem are descending vs ascending ?

•  Descending (motor) pathways:

  • Corticospinal tract

  • Corticobulbar tract

•      Ascending (sensory) pathways: 

  • Spinothalamic tract

  • Dorsal column medial lemniscus (DCML)

What is the relationship between the brainstem and the motor and sensory pathways?

Brainstem acts as conduit for the tracts

What splits the midbrain down its centre?

cerebral aqueduct - channel for CSF

What does peduncle mean?

foot/stalk

In which view of the midbrain is the olive visible?

ventral view

What forms the floor of the 4th ventricle?

rhomboid fossa

What is the function and make-up of the red nucleus?

grey matter, involuntary movement, arm swinging during walking, crawling in infants

What is the function and make-up of the substantia nigra?

grey matter, controls voluntary movement, motor planning, and reward-based learning by producing dopamine + regulates muscle tone and movement coordination via the nigrostriatal pathway

Where does the corticonuclear tract originate?

pre-central gyrus ie primary motor cortex