blood supply to the brain

• •The brain makes up 2.5% of our body weight

  •However, uses 1/6th of the cardiac output

  •And uses 1/5th of the oxygen!

  •The brain is very sensitive to 02 deprivation, cells start to die within minutes

  We have cerebral and cerebellar blood supply
• Two systems of getting blood to the brain: Carotid and Vertebrobasilar

  which are continuous with one another
• There are two paired arteries responsible for the blood supply to the brain;

  1)The Left and right vertebral arteries

  2)The Left and right internal carotid arteries. 

  These arteries arise in the neck and ascend to the cranium.

  
• Arterial supply to Brain

  Within the cranial vault, the terminal branches of these arteries form an anastomotic circle, called the Circle of Willis.

  From this circle, branches arise which supply the majority of the cerebrum.

  Other parts of the CNS, such as the pons and spinal cord, are supplied by smaller branches from the vertebral arteries

  
• Why do we need blood supply?

  •Change in voltage induced by action potential is determined by the concentration of ions either side of the cell membrane.

  •Maintaining these ionic gradients is an energy consuming process.

  •Requires a constant supply of glucose and oxygen to the neuron.

  Neurones need a lot of energy to allow them to function. Dual Blood supply of the brain aids this as much as possible. 
• Important names to be aware of

  A) cerebrum

  B) cerebellum

  C) brainstem

  D) brainstem

  E) midbrain

  F) pons

  G) medulla oblaganta

  
• Important names to be aware of

  A) Foramen Magnum

  B) TRANSVERSE FORAMINA

  
• Important names to be aware of

  A) The carotid canal

  
• Lobes of the brain

  A) frontal lobe

  B) parietal lobe

  C) occipital lobe

  D) temporal lobe

  E) insula

  F) limbic lobe

  
• Heart anatomy recap

  A) aorta

  B) superior vena cava

  C) right atrium

  D) tricuspid valve

  E) pulmonary valve

  F) right ventricle

  G) septum

  H) left ventricle

  I) aortic valve

  J) mitral valve

  K) left atrium

  L) pulmonary vein

  M) pulmonary artery

  
• The aortic arch and branches

  A) Ascending aorta

  B) Arch of aorta

  C) Descending aorta

  D) Right coronary artery

  E) Left coronary artery

  F) Brachiocephalic artery

  G) Right subclavian artery

  H) Right common carotid artery

  I) Left common carotid artery

  J) Left subclavian artery

  
• The aortic arch and branches

  L&R Subclavian go to supply the L&R upper limbs.

  L&R Common carotids go to supply the head and brain

  Descending aorta takes blood to the rest of the body.

  
• The vertebral arteries

  The L&R vertebral arteries come off the L&R subclavian arteries, respectively.

  
• The vertebral arteries

  •The right and left vertebral arteries arise from the right and left subclavian arteries.

  •They then ascend the posterior aspect of the neck, through holes in the transverse processes of C6-C1 cervical vertebrae, known as the transverse foramina.

  •The left and right vertebral arteries both enter the cranial cavity through the foramen magnum. 

  •Perforate dura and arachnoid to reach subarachnoid space

  
• Course of the Vertebral Artery

  •At caudal border of Pons, L&R vertebral arteries unite to form the Basilar artery

  •Ascends the clivus

  •The basilar artery terminates as the posterior cerebral arteries.

  
• WHAT IS THIS

  A) clivus

  
• The vertebral arteries

  Once in the cranium and before the L&R vertebral arteries unite to form the basilar artery, some branches are given off the vertebral arteries:

  •(x1)Anterior and (x2)posterior spinal arteries – supply blood to the spinal cord

  •Posterior inferior cerebellar artery – supply the posterior inferior aspect of the cerebellum.

  • After this, the left and right vertebral arteries converge to form the Basilar artery.

  •The basilar artery terminates by bifurcating into the Posterior cerebral arteries. which supply the posterior part of the cerebral hemispheres

   

  
• The vertebral arteries

  A) vertebral artery

  B) Posterior inferior cerebellar artery 

  C) posterior spinal

  D) anterior spinal

  E) basilar artery

  F) Posterior cerebral arteries

  
• Branches of the basilar artery

  •Anterior inferior cerebellar arteries.  supply the anterior inferior part of the cerebellum

  •Pontine arteries. supplies the pons

  •Superior cerebellar arteries.   supply the superior part of the cerebellum

  •The basilar artery then terminates as the two posterior cerebral arteries.

  
• Branches of the basilar artery

  A) vertebral artery

  B) Anterior inferior cerebellar arteries.

  C) basilar artery

  D) Pontine arteries

  E) Superior cerebellar arteries

  F) Posterior cerebral arteries

  
• The cerebellar arteries

  •Superior cerebellar a. – supplies the superior surface of the cerebellum

  •Anterior inferior cerebellar a. - supplies the anterior inferior part of the cerebellum

  •Posterior inferior cerebellar a. - supplies the posterior inferior part of the cerebellum

  
• Cerebellar arteries

  •Superior cerebellar a. – supplies the superior surface of the cerebellum

  •Anterior inferior cerebellar a. - supplies the anterior inferior part of the cerebellum

  •Posterior inferior cerebellar a. - supplies the posterior inferior part of the cerebellum

  
• The internal carotid arteries

  A) Descending aorta

  B) Brachiocephalic artery

  C) Common carotid artery

  D) Subclavian A.

  E) Arch of aorta

  F) left external carotid artery

  G) Left internal carotid artery

  H) Right external carotid artery

  I) Right internal carotid artery

  
• The internal carotid arteries

  The common carotid arteries bifurcate( at C4) into an internal carotid artery and an external carotid artery.

  The internal carotid arteries pass into the cranial cavity to supply the brain

  The external carotid arteries stay external to the cranial cavity and supply the face and scalp

  
• •The internal carotid arteries originate at the bifurcation of the left and right common carotid arteries, at the level of the fourth cervical vertebrae (C4).

  •They move superiorly within the carotid sheath and enter the brain via the carotid canal of the temporal bone.

  •The internal carotid arteries DO NOT HAVE ANY BRANCHES BEFORE ENTERING THE CRANIAL CAVITY

  •The external carotid arteries, however, have many branches which go to supply the face and scalp.

  
• THE internal carotid arteries

  A) internal carotid artery

  B) external carotid artery

  C) Bifurcation

  D) bulb

  E) Common carotid artery

  
• The carotid sinus is a neurovascular structure which presents as a dilation at the bifurcation of the common carotid artery and proximal aspect of the internal carotid artery.

  The carotid sinus contains baroreceptors (stretch receptors) which are sensitive to pressure changes in the arterial blood, so the carotid sinus plays a role in the control of blood pressure.

  
• External Carotid Artery branches

  SOME                     Superior thyroid a.

  ANATOMISTS       Ascending pharyngeal a.

  LIKE                        Lingual a.

  FREAKING             Facial a.

  OUT                         Occipital a.

  POOR                      Posterior auricular a.

  MEDICAL                Maxillary a.

  STUDENTS             Superficial temporal a.

  
• External Carotid Artery branches

  A) Superior thyroid a.

  B) Ascending pharyngeal a.

  C) Lingual a.

  D) Facial a.

  E) Occipital a.

  F) Posterior auricular a.

  G) Maxillary a.

  H) Superficial temporal a.

  
• •The L&R internal carotids enter the cranial cavity through the L&R carotid canals.

  •The internal carotids then pass anteriorly through the cavernous sinus. Distal to the cavernous sinus, each ICA gives rise to:

  •Ophthalmic artery 

  •Posterior communicating artery 

  •Anterior choroidal artery 

  •Anterior cerebral artery 

  The internal carotids then continue as the Middle cerebral artery, which supplies the lateral portions of the cerebrum.

  
• •Ophthalmic artery – supplies the structures of the orbit.

  
• •Posterior communicating artery – acts as an anastomotic ‘connecting vessel’ in the Circle of Willis (see ‘Circle of Willis’ below).

  
• •Anterior choroidal artery – supplies structures in the brain important for motor control and vision.

  
• •Anterior cerebral artery – supplies part of the cerebrum.

  
• How do the internal carotid arteries enter the skull?

  The carotid canal

  
• Parts of the internal Carotid Artery

  •Cervical Part: after bifurcation of common carotid a.

  •Petrous part: enters middle cranial fossa through carotid canal, beside dorsum sellae

  •Cavernous part: lies horizontal in cavernous sinus

  •Cerebral part: emerges medial to ant. Clinoid process, enters subarachnoid space (joins arterial circle of willis)

  
• Parts of the internal Carotid Artery

  A) Cerebral part

  B) Cavernous part

  C) Petrous part

  D) Cervical Part

  
• The internal carotid arteries

  A) internal carotid artery

  B) Anterior choroidal artery 

  C) posterior communicating artery

  D) Ophthalmic artery 

  E) Anterior cerebral artery 

  F) middle cerebral artery

  G) anterior communicating artery

  
• Arterial Circle of Willis

  •Anterior cerebral a.

  •Anterior communicating a.

  •Internal carotid a.

  •Posterior cerebral a.

  •Posterior communicating a.

  Function: to provide alternative routes for blood flow if one of the arteries becomes blocked or stenosed.

  
• Arterial Circle of Willis

  Function: to provide alternative routes for blood flow if one of the arteries becomes blocked or stenosed.