Blood Supply and Spinal Cord Vocabulary

Blood Supply to the Brain

• We'll discuss blood supply to the brain and then the spinal cord.

• Focus on the inferior side of the brain, looking at vessels from posterior and anterior directions.

• Two major pairs of arteries include the vertebral arteries (posterior) and internal carotid arteries (anterior).

Vertebral Arteries (Posterior Circulation)

• Vertebral arteries supply the posterior side of the brain.

• They pass through the transverse foramina of the cervical vertebrae.

• These arteries are branches of the subclavian artery.

• They supply the brainstem and cerebellum.

• Subclavian arteries give rise to vertebral arteries that ascend through transverse foramina of cervical vertebrae and enter the foramen magnum.

Internal Carotid Arteries (Anterior Circulation)

• Supply the anterior side of the brain, specifically approximately 80% of the cerebrum.

• These are branches of the common carotid artery.

• The internal carotid enters the skull through the carotid canal.

Arteries and the Aortic Arch

• Differences between right and left sides of the body.

• On the left side, the left common carotid comes off separately from the left subclavian.

• The anterior circulation involves the common carotids branching into external and internal carotids.

• The internal carotid continues up into the brain, entering through the carotid canal.

Inferior View of the Brain

• Anterior portion is the frontal lobe.

• Internal carotids bring blood to the anterior part, while vertebral arteries supply the posterior part.

• Understanding anterior vs. posterior circulation is important for determining affected areas in case of blockage.

Branches of the Internal Carotid Artery

• Internal carotid relates to anterior circulation.

• Major branches include the anterior cerebral and middle cerebral arteries.

• These supply about 80% of the cerebrum.

Branches Overview

• The continuation of the internal carotid becomes the middle cerebral artery.

• Anterior cerebral arteries branch anteriorly and dive between the two hemispheres.

• Posterior communicating artery communicates with the posterior circulation.

Vertebral Artery Branches

• Vertebral artery relates to posterior circulation.

• Major branches include the basilar artery, cerebellar arteries, and posterior cerebral artery.

• After the vertebral arteries enter the foramen magnum, they merge to form the basilar artery, which then branches into the posterior cerebral arteries.

Cerebellar Arteries

• Posterior inferior cerebellar artery comes off the vertebral arteries.

• Anterior inferior cerebellar artery comes off right after the basilar artery starts.

• Superior cerebellar artery branches off right before the posterior cerebral artery.

• The names of these arteries often reflect the parts of the brain they serve.

Circle of Willis

• Important anastomosis providing collateral circulation to the brain.

• Allows blood to flow in different directions; no valves present.

• Effective for slow, partial obstructions, allowing connection points to increase in size over time.

• Not effective for sudden occlusions.

• Individuals may have different blood flow, with one side (e.g., right internal carotid) being larger.

• Connection points include the anterior communicating artery (between anterior cerebral arteries) and the posterior communicating artery (connecting anterior and posterior circulation).

Drawing the Circle of Willis

• Start with two internal carotid arteries.

• The continuation of these becomes the middle cerebral arteries.

• The anterior cerebral arteries come off and are connected by the anterior communicating artery.

• Vertebral arteries join to form the basilar artery.

• Posterior branches are the posterior cerebral arteries.

Areas of the Cerebrum Supplied

• Anterior and middle cerebrum supplied by the internal carotid.

• Posterior cerebrum supplied by the vertebral arteries via the basilar artery.

Blood Flow and Pressure

• One side may be larger with more blood flow, affecting blood supply to different areas.

• For example, a large right internal carotid artery may result in posterior cerebral blood flow coming from the anterior circulation.

Blood Flow from the Heart

• On the right side, the brachiocephalic artery splits into the right subclavian and right common carotid arteries.

• Off of the subclavian, the vertebral arteries provide posterior circulation.

• On the left, the left common carotid comes straight off the aorta.

• Common carotids split into external and internal carotids, with the internal carotids providing anterior circulation.

Lateral View of the Brain

• The internal carotid artery leads to the middle cerebral artery, which branches out across the cerebrum.

• A smaller branch coming anteriorly is the anterior cerebral artery.

Flipped View of the Brain

• Middle cerebral artery covers a large region in purple.

• Anterior cerebral artery (in green) covers the area between the hemispheres.

• Posterior cerebral artery (in yellow) is also between the hemispheres but posteriorly.

Blockage Implications

• A blockage of the right anterior cerebral artery will affect the area it supplies.

• The homunculus concept can help understand what problems may arise (e.g., issues with knee and leg control).

Vertebral Artery Branching

• Vertebral arteries branch off the subclavian arteries.

Dealing with Blockage

• If there's a blockage, blood can reach the right anterior cerebral artery via the anterior communicating artery from the left anterior cerebral artery.

• The greatest pressure will generally fill that gap, with larger vessels closer to the blockage providing the flow.

Spinal Cord

Spinal Cord Exit Point

• The spinal cord exits the skull through the foramen magnum.

Other Foramina

• Spinal canal: where the spinal cord goes through, vertebral foramen stacked.

• Foramen rotundum: the maxillary division of the trigeminal nerve passes through (cranial nerve V sub 2).

• Foramen Ovale: Transmits cranial nerve V3. Mandibular division of the trigeminal nerve.

• Foramen spinosum: the middle meningeal artery coming through. Associated with epidural hematoma.

Division of the Nervous System

• The spinal cord is part of the central nervous system.

• Central Nervous System: brain and spinal cord; its job is to integrate information.

• Peripheral Nervous System: 31 pairs of spinal nerves and 12 pairs of cranial nerves; its job is to connect and connect; bringing us information from the outside world and telling our body to do things like move.

Spinal Nerves and Information Flow

• Sensory information (afferent): incoming information arriving in the central nervous system. It is monitoring the external environment.

• Motor activity (efferent): outgoing information activating or inhibiting a muscle. It is going from the spinal cord/central nervous system/ PNS, to a muscle. It is moving.

SAME way to remember which sensory is coming and motor is outgoing. Sensory is afferent and motor is efferent. Sensory arrives and the motor exits.

Neurons and Information Flow

• Motor Neuron: It has its cell body here in the central nervous system. Information is going to leave the central nervous system and travel out into the body, into the peripheral nervous system, and then we're going to stimulate some sort of effector.

• Sensory Neuron: It is out here in the peripheral nervous system, where its cell body is found. Information is going to travel back towards the central nervous system, so that the information is afferent. Then we arrive at our central nervous system.

Gross Anatomy

*Communication between the brain and the peripheral nervous system.
*It is a reflex center. It does not require sending the information up to the brain before reacting.

• Extends from the foramen magnum to about L1 to L2. It is not the full length of the vertebral column. They spinal cord doesn't go all the way down to the sacrum.
  Conus Medullaris- end of the spinal cord itself.
  *Cauda Equina - A collection of spinal nerve roots below the spinal cord, so you still send nerve roots out down into your sacrum. Also known as the horse's tail.

• Filum terminale - extension of the pia mater that anchors the conus medullaris to the coccyx. That is the final anchor point to hold the conus medullaris in place in that spinal canal.

Different View

*The end of the spinal cord is between L1 and L2. Those are our conus medularis.
*They all stretch out down to the spinal nerve groups. That is known as the cartaquina. That exits down into their appropriate levels.
The little bit of pia mater there to form our final termite, and that is made up of those spinal nerves coming down.

Enlargements

*We have cervical region and lumbosacral region.
*Cervical- C5 through T1. This refers to what is going to go innovate in the upper limb. Also known as the brachial plexus.
*Lumbosacral - L1 through S3. And that is where we are sending info to the lumbar cycle plexus to the lower limb.

Protection

*Bone
*Layers of the connective tissue/meninges.
*CSF

Meninges of the Spinal Cord

Pia Mater: On the inside directly adhered to the spinal column
*Arachnoid Mater: The next layer. Which is a web-like projection containing CSF
Dura Mater: is sitting right on top of the arachnoid mater which is a single layer as opposed to the brain

Protection of the Spinal Cord Laterally

• Deniticulate ligament- The projections of the pia mater, that stick out laterally, and help anchor it laterally to go around the body.
  *Difference in Meningeal Spaces
  *Epidural space- between the bone and the Dura Mater- is an actual space. It is going to contain a lot of fat and it's always going to contain a venous plexus that is surrounded by the dura mater.
  *Subdural space- Between the dura and arachnoid. It is still just a potential space
  *Subarachnoid space- actual space where CSF is found between the Arachnoid and the Pia space, just like in the brain.

Big difference

In the brain, there is no space in the Epidural space. But there is a space in the Spinal Cord.

Epidural

*An epidural is where they stick a needle into the epidural space.
*Epiduaral space- going into T10-L1 to make that work.
*An Epidural, if you are thinking about it, in the context of labor, what you can do is go into that space and inject some sort of anasetic.

Spinal Tap

*A spinal tap is where we want to go in and grab some CSF.
*You would need to pass the dura and arachnoid matter to get into the space.
*L3-L4 or L4-L5 area when receiving a spinal tap.
*You would need to do a spinal tap to drop fluid in the L3-L4 level, because you want to have the patients feet forward, like on a table so we can flex the bones, so we do not have bone, have those bone parts kind of right next to each other. You would feel 2 punctures because of all those ligaments, but you would see one pop and feel 2 for the spinal cord.

Spinal tap vs spinal cord

*L3 L4 for spinal tap because you passed the konis murais

Vertebral Structures

*The nerve on the posterior side can be impacted if say if we have a part of the annulous fibrosis come out, and impinge the spinal nerves causing a slipped disc.

Spinal Cord Cross Section

*White matter, and gray matter, just like we had at the brain, what will just kind of flip, sloppy where they're at.
*The white matter is going to be in the outside and the gray matter is going to be in the inside.
*Gray Matter- where the cell bodies are found in the central nervous system, motor neurons. Also where interneurons are found- neurons that connect different places internally.
*White matter- Myelinated axons. That is the tracks of information coming up and down the area

Mylan- fatty substance that actually looks white