Week 3 Lecture Outline MENINGES BLOOD BRAIN BARRIER BRAIN BLOOD SUPPLY VENTRICULAR SYSTEM CRANIAL NERVES Meninges Meninges Comprised of three layers of connective tissue membranes which surround and protect the CNS (brain and spinal cord). It ensures that the brain is not in direct contact with overlying bone of skull. Meninges Dura Mater – “Hard Mother” Outermost membrane closest to the skull; adheres to the cranium Tough, inelastic consistency Arachnoid Mater – “Web-like Mother” Middle membrane Web-like appearance results from processes called “arachnoid trabeculae” Meninges Subarachnoid space Space between the arachnoid and pia mater, filled with cerebrospinal fluid Pia mater – “Gentle Mother” Innermost membrane that closely adheres to the cerebral cortex of brain Thin and elastic Major blood vessels course through the surface of pia mater and penetrate substance of the brain Blood brain barrier BBB is a specialized system of capillary endothelial cells Endothelial cells are different from those found in peripheral tissues, allowing it to serve as a barrier to the brain Blood brain barrier Anatomy Endothelial cells of brain capillaries are joined by tight junctions Creates high resistant barrier to many molecules Only certain molecules are allowed access, including • • • • • Glucose Oxygen Small fat soluble molecules Critical ions involved in neuron electrical activity Some water soluble molecules Blood brain barrier Anatomy Endothelial cells are in contact with foot processes of astrocytes (glial cells) Essentially separates capillaries from neurons Suspected to play a role in the formation and maintenance of barrier Blood brain barrier Functions 1.Serves as protective layer for brain Prohibits blood borne toxins from entering brain 2.Essential for homeostasis Prevents great fluctuations in ion concentrations in brain ex., BBB buffers movement of excess K+ into extracellular brain fluid, thereby preventing premature/sustained neuron depolarization Will talk more about K+ in the brain next week Blood brain barrier Limitations Some drugs do not cross the blood brain barrier, and so fail to influence the CNS ex., Antiretroviral drugs for HIV treatment cannot cross this barrier Current research looks to develop drugs that are similar in chemical structure to the nutrients that naturally cross BBB ex., As treatment of PD with drug L-DOPA L-DOPA has amino acid structure recognized by transporter in BBB; the drug is then converted to dopamine in the brain Blood brain barrier Mekarsi M M (2009). Bio-Transfer and Metabolism in the Distributed System Under Uncertainty. The Journal of Young Investigators, 19(12). Getting Drugs Past the Blood-Brain Barrier http://www.youtube.com/watch?v=FAdyhOHvu3k& feature=channel_page Brain Blood Supply The entire cerebral blood supply is provided by two major pairs of arteries The vertebral arteries Supplies to posterior structures of brain Internal carotid arteries Supplies to anterior structures of brain Brain Blood Supply Posterior Circulation The pair of vertebral arteries converge at base of pons to form a single basilar artery Near the midbrain, the basilar arteries splits into left and right posterior cerebral arteries Vertebral arteries branch into smaller cerebellar arteries which serve anterior and posterior part of cerebellum Posterior cerebral arteries serve posterior medial wall of cerebrum (medial occipital and temporal lobe) Brain Blood Supply Vertebral arteries converge at base of pons Brain Blood Supply Anterior Circulation The internal carotids branch into middle cerebral arteries and anterior cerebral arteries Middle cerebral arteries serve lateral surface of cerebrum (lateral frontal, temporal and parietal lobes) Middle cerebral arteries also serve basal forebrain structures (basal ganglia, internal capsule, hippocampus) Anterior cerebral arteries serve anterior medial wall of cerebrum (medial frontal and parietal lobes) Brain Blood Supply Circle of Willis The internal carotid and vertebral artery blood supplies are connected in a ring (near hypothalamus of ventral brain) McCaffrey P. (2008). The Circle of Willis. Retrieved from http://www.csuchico.edu/~pmccaffrey//syllabi/CMSD% 20320/362unit11.html Brain Blood Supply Circle of Willis Anatomy posterior cerebral arteries internal carotid posterior communicating arteries anterior cerebral arteries anterior communicating artery Brain Blood Supply Brain Blood Supply Circle of Willis Anatomy This vascular circle is formed with the posterior cerebral arteries connecting to the internal carotids via posterior communicating arteries Internal carotids are in turn directly connected to the anterior cerebral arteries The two anterior cerebral arteries are connected via the anterior communicating artery Brain Blood Supply Circle of Willis Function If one of the major arteries gets blocked, overall blood brain flow is not compromised because blood flows from other artery through circle Serves to equalize blood pressure through brain Bleeding in the Head and Brain 4 main types Epidural hematoma Subdural hematoma Subarachnoid hemorrhage Intracerebral hemorrhage Note: Hematoma is a collection of blood outside of a blood vessel Epidural hematoma Occurs when blood accumulates between your skull and the outermost covering of your brain. Often follows head injury, skull fracture Subdural hematoma Collection of blood on the surface of your brain Often after a car accident when head moves rapidly forward and stops Subarachnoid hemorrhage Bleeding in arachnoid space Often result of trauma or rupture of a major blood vessel in the brain Intracerebral hemorrhage Bleeding inside the brain Most common in stroke and not usually result of injury Brain Blood Supply Stroke Neurons very sensitive to oxygen and glucose deprivation Ischemic (brief) or sustained disruption of blood supply can cause permanent cell death Strokes can be Thrombotic – occlusion of cerebral blood vessel due to plaque build up Embolic – plugging of cerebral artery with dislodged embolus from heart/plaque from vertebral arteries Hemorrhagic – rupturing of cerebral blood vessel (due to hypertension, aneurysm, etc.) https://www.youtube.com/watch?v=3oWspN_Sv VM Brain Blood Supply Broca’s aphasia (motor/nonfluent aphasia) Speech is highly impaired in patients, and is characterized by Long pauses and anomia - difficulty in finding the correct words Use of mainly content words (nouns, verbs, adjectives) and little or no use of function words (connecting words to make a grammatical sentence) Agrammatism - overall inability to produce grammatically correct speech Comprehension of speech is generally conserved however The Ventricular System What is it? Interconnected fluid-filled spaces Located in the core of the forebrain and brainstem Contains cerebrospinal fluid (CSF) Made by choroid plexus The Ventricular System Do you recognize these ventricles? The Ventricular System Anatomy Lateral ventricles Third ventricle Largest ventricles, one within each cerebral hemisphere Located in the midline space between the right and left diencephalon (thalamus and hypothalamus) Fourth ventricle Located near cerebellum and brainstem The Ventricular System Anatomy Cerebrospinal flow Neuroanimations (2008). Retrieved from http://neuroanimations.com/ Hydrocephalus/Obstruct.html The Ventricular System Functions Protection Buoyancy Excretion of waste Endocrine medium The Ventricles https://www.youtube.com/watch?v=P49ZJWpu06k The Ventricular System Abnormalities Hydrocephalus – water on the brain Developmental disorder Fig 1 – Child with hydrocephalus Note size of skull Fig 2 – MRI of lateral ventricles Note enlargement The Ventricular System Abnormalities Alzheimer’s disease (AD) – neurodegenerative disease where neurons die and shrink so ventricles expand to fill the empty space Fig 1 – Healthy human Note small size of lateral Ventricles Fig 2 – AD patient Note enlarged lateral ventricles and enlarged sulci Cranial Nerves 12 pairs Referred to by their name or by their corresponding number (I – XII) Know both name and number Function Innervate mostly the head Carry different types of signals: Motor information (M) Sensory information (S) Both motor and sensory information (B) Nerves can contain Afferent projections (S) Efferent projections (M) Both Cranial Nerves Cranial Nerves Number & Name Axon Type Functions I II III Olfactory Optic Oculomotor Sensory Sensory Motor IV V Trochlear Trigeminal Motor Both VI VII Abducens Facial Motor Both VIII IX Auditory-Vestibular Glossopharyngeal Sensory Both X Vagus Both XI XII Spinal Accessory Hypoglossal Motor Motor - smell - sight - movement of eye and eyelid - control of pupil size - movements of the eye - sensation of touch to the face - chewing - movements of the eye - facial expression muscles - taste - hearing and balance - muscles of throat - salivary glands - taste - detection of blood pressure - control of heart, lungs, & abdominal organs - muscles of throat and neck - movement of tongue Trochlear Nerve (IV) How could you test for function? Innervates superior oblique muscle Turns eye downward and laterally Trochlear Nerve (IV) Test for function by looking down at the nose Trigeminal Nerve (V) How could you test for function? Trigeminal Nerve (V) Test for function Touch the face (S root) Clench the teeth (M root) Spinal Accessory Nerve (XI) How could you test for function? Spinal Accessory Nerve (XI) Controls trapezius & sternocleidomastoid muscles Test for function by raising shoulders or turning head Cranial Nerves Different nerves work together for different functions Rotate eye in the socket Oculomotor (III) Trochlear (IV) Abducens (VI) Respiration, vocalization, swallowing Glossopharyngeal (IX) Vagus (X) Cranial Nerves "On Old Olympus Towering Tops, A Fiery, Angry Group Viewed Some Hills" I II III IV V VI VII VIII IX X XI XII Olfactory Optic Oculomotor Trochlear Trigeminal Abducens Facial Auditory-Vestibular Glossopharyngeal Vagus Spinal Accessory Hypoglossal On Old Olympus Towering Tops, A Fiery Angry Group Viewed Some Hops Cranial Nerves "Some Say Money Makes Business. My Brother Says Big Business Makes Money." I II III IV V VI VII VIII IX X XI XII Sensory Sensory Motor Motor Both Motor Both Sensory Both Both Motor Motor Some Say Money Makes Business. My Brother Says Big Business Makes Money. Cranial Nerves Cranial nerve damage and dysfunction can result in various problems Parry Romberg Syndrome involves damage to the trigeminal nerve severe pain in affected facial tissues Vestibular neuritis caused by the inflammation of the vestibular nerve main symptom is vertigo (sensation of falling, dizziness) What is a brain's favourite kind of boat?
