Chapter 14: Brain and Cranial Nerves Flashcards
Telencephalon.
Forms cerebrum and lateral ventricles.
Diencephalon.
Forms thalamus, hypothalamus, epithalamus and third ventricle. Superior to brainstem.
Mesencephalon.
Forms midbrain and cerebral aqueduct.
Metencephalon.
Forms pons, cerebellum and upper fourth ventricle.
Myencephalon.
Forms medulla oblongata and lower fourth ventricle.
Brainstem.
Continuous with spinal cord. Consists of medulla oblongata, pons and midbrain.
Where is the cerebellum?
Posterior to brainstem.
What is the largest part of the brain?
Cerebrum.
Describe the dura mater in the brain, and its layers.
Continuous with the dura mater in the spinal cord. Consists of an outer periosteal layer and an inner meningeal layer. These layers are fused together except for where they separate to enclose the dural Venus sinuses that drain venous blood from the brain.
What are the 3 extensions of the dura mater in the brain that separate parts of the brain?
Falx cerebri: separates the 2 sides of the cerebrum. Falx cerebelli: separates the 2 sides of the cerebellum. Tentorium cerebelli: separates the cerebrum from the cerebellum.
What is present in the spinal cord, but not in the brain?
Epidural space.
What are the main routes of blood flow to the brain?
Internal carotid artery and vertebral arteries.
What is the main route of blood flow from the brain?
The dural venous sinuses drain into the internal jugular veins.
How much oxygen and glucose does the brain consume?
20% of the body’s supply.
An interruption of blood flow for how many minutes distinguishes between impaired function vs. permanent damage?
Impaired neuronal function: 1-2 minutes. Permanent injury: 4 minutes.
Why must the supply of glucose to the brain be continuous?
No glucose is stored in the brain.
What are the components of the blood brain barrier?
Tight junctions between endothelial cells, and a thick basement membrane that surrounds the capillaries.
Which substances can diffuse across the BBB?
Lipid soluble, steroid hormones, alcohols, barbiturates, nicotine, caffeine, water molecules.
What causes breakdown of the BBB?
Trauma, toxins, inflammation.
Cerebrospinal fluid.
Clear and colourless liquid composed of mostly water. Protects the brain and spinal cord from chemical and physical injuries.
What are the components of CSF?
Water, oxygen, glucose, proteins, lactic acid, urea, cations, anions, WBCs.
How much CSF is in the body at all times, and how much is produced?
80-150 mL. Body produces 20 mL / hour.
What are the CSF-filled cavities in the brain?
Lateral ventricle 1, lateral ventricle 2, third ventricle and fourth ventricle.
What is the difference between lateral ventricles 1 and 2?
Each one is in its own hemisphere of the cerebrum.
What separates the lateral ventricles 1 and 2?
Septum pellucidum.
Third ventricle.
Narrow slit-like cavity along the midline. Located superior to the hypothalamus between the right and left halves of the thalamus.
Where is the fourth ventricle located?
Between brainstem and cerebellum.
What are the 3 functions of the CSF?
1) Mechanical protection: shock-absorbing. 2) Chemical protection: provides a chemical environment optimal for neuronal signalling. 3) Circulation: exchange of nutrients and waste between blood and nervous tissue.
How is CSF produced?
By ependymal cells of choroid plexuses in the ventricle walls.
What is the blood-CSF barrier?
Formed by tight junctions between ependymal cells.
Describe CSF circulation.
CSF flows from lateral ventricles to third ventricle through interventricular foramina –> more CSF is added by choroid plexus in roof of third ventricle –> flows through cerebral aqueduct –> midbrain –> fourth ventricle –> more CSF is added by choroid plexus in fourth ventricle –> flows to subarachnoid space through a single median aperture and paired lateral apertures –> to central canal of spinal cord –> gradually reabsorbed into blood through arachnoid villi.
Medulla oblongata.
Continuous with the superior part of the spinal cord, and forms the inferior part of the brainstem. Begins at the foramen magnum and extend to the inferior border of the pons.
Describe the white matter of the medulla oblongata.
Contains all sensory and motor tracts that extend between the spinal cord and the brain. Some of the white matter forms pyramids.
Pyramids.
Formed by large corticospinal tracts that pass from cerebrum to spinal cord.
Decussation of pyramids.
90% of axons in the left pyramid cross to the right side, and 90% of axons in the right pyramid cross to the left side. Explains why each side of the brain controls voluntary movements on the opposite side of the body.
Where is the cardiovascular centre, and what is its function?
Medulla oblongata. Regulates rate and force of heartbeat and diameter of blood vessels.
Where is the medullary respiratory centre, and what is its function?
Medulla oblongata. Adjusts basic rhythm of breathing.
Where is the vomiting centre?
Medulla oblongata.
Where is the deglutition centre, and what is its function?
Medulla oblongata. Promotes swallowing.
Which brain structure controls sneezing, coughing and hiccupping reflexes?
Medulla oblongata.
Olive.
Lateral to each pyramid. Contains an inferior olivary nucleus, which receives input from the cerebral cortex, red nucleus and spinal cord, and sends output to the cerebellum.
What is the function of the inferior olivary nucleus?
Provides instructions for the cerebellum to make adjustments to muscle movement.
Where are the gracile nucleus and cuneate nucleus, and what are their functions?
Posterior medulla oblongata. Monitor touch, pressure, vibration and conscious proprioception, and send impulses to thalamus on opposite side of the brain in a medial lemniscus.
Where is the gustatory nucleus, and what is its function?
Medullary oblongata. Receives gustatory input from the tongue taste buds.
Where are the cochlear nuclei, and what is their function?
Medulla oblongata. Receive auditory input from cochlea of inner ear.
Where are the vestibular nuclei, and what is there function?
Medulla oblongata. Receive equilibrium input form proprioceptors in vestibular apparatus of inner ear.
Which pairs of cranial nerves are associated with the medulla oblongata?
Vestibulocochlear, glossopharyngeal, vagus, accessory (cranial part), and hypoglossal.
Pons.
Superior to medulla, and anterior to cerebellum. Works as a bridge that connects parts of the brain.
Ventral region of the pons.
Forms a synaptic relay station of pontine nuclei. Coordinates and maximizes the efficiency of voluntary motor movements.
What enters and exits the pontine nuclei?
White matter tracts, which connect one cerebral hemisphere to the opposite cerebellar hemisphere.
Dorsal region of the pons.
Contains ascending and descending tracts, and nuclei of cranial nerves.
Pontine respiratory group.
Controls breathing alongside the medullary respiratory centre.
Which pairs of cranial nerves are associated with the pons?
Trigeminal, abducens, facial and vestibulocochlear.
Midbrain.
Extends from pons to diencephalon.
What structure passes through the midbrain and connects the third and fourth ventricles?
Cerebral aqueduct.
Anterior midbrain.
Contains cerebral peduncles, and axons of the corticospinal, corticobulbar and corticopontine tracts which relay impulses from motor areas in cerebral cortex to the spinal cord, medulla and pons.
Posterior midbrain.
Also called the tectum. Contains 4 rounded elevations (colliculi).
Superior colliculi.
Two. Reflex centres for visual activities. Responsible for reflexes that govern movements of the head, eyes and trunk.
Inferior colliculi.
Two. Reflex centres for the startle reflex stimulated by a loud noise. Responsible for relaying impulses from auditory receptors in inner ear to brain.
Where is the substantial nigra, and what is its function?
Midbrain. Contains neurons that release DA for control of subconscious muscle activities. Loss of these neurons is associated with PD.
Where are the red nuclei, and what are their functions?
Midbrain. Axons from cerebellum and cerebral cortex form synapses in the red nuclei to control muscle activities.
What gives the red nuclei their colour?
Rich blood and iron supply.
Which pairs of cranial nerves are associated with the midbrain?
Oculomotor and trochlear.
Reticular formation.
Broad region where white matter and gray matter form a netlike arrangement. Extends throughout the brainstem from the spinal cord to the diencephalon.
Reticular activating system (RAS).
Ascending portion of the reticular formation. Sensory axons project through the thalamus to the cerebral cortex. Activated by visual, auditory, pain, touch, pressure, limb and head receptors, and mental activities.
What is the most important function of the RAS?
Consciousness.
How does RAS prevent sensory overload?
Filters out insignificant information so that it does not reach consciousness.
Inactivation of RAS produces:
Sleep.
Damage to RAS produces:
Coma.
Descending RAS.
Connects to cerebellum and spinal cord to regulate muscle tone, HR, BP, RR.
What is the second biggest structure of the brain?
Cerebellum. Contains almost half of the neurons in the brain.
Cerebellum.
Posterior to medulla and pons. Inferior to cerebrum. Highly folded to increase surface area of outer gray matter cortex.
Transverse fissure.
Deep groove that separates the cerebellum from the cerebrum.
Tentorium cerebelli.
Separates the cerebellum from the cerebrum, and supports the posterior cerebrum.
Vermis.
Medial portion of the cerebellum that connects the two hemispheres.
Anterior and posterior cerebellar lobes.
Involved in subconscious skeletal muscle movements.
Flocculondular lobe of cerebellum.
Involved in equilibrium and balance.
Cerebellar cortex.
Superficial layer that consists of gray matter folia. Deep to the gray matter are arbor vitae (white matter). Deeper to the gray matter are cerebellar nuclei (gray matter).
Cerebellar peduncles.
Bundles of white matter that attach the cerebellum to the brainstem.
Superior cerebellar peduncles.
Contain axons that extend from the cerebellum to red nuclei and thalamus.
Middle cerebellar peduncles.
Largest peduncles. Contain axons that extend from the pontine nuclei to the cerebellum for voluntary movement control.
Inferior cerebellar peduncles.
Contain axons of the spinocerebellar tract that extent from proprioceptors in trunk and limbs to cerebellum. Contain axons that extend from the vestibular apparatus of the inner ear and the vestibular nuclei of the medulla and pons to the cerebellum. Contain axons that extend from the inferior olivary nucleus of the medulla to the cerebellum. Contain axons that extend from the cerebellum to the vestibular nuclei of the medulla and pons. Contain axons that extend from cerebellum to reticular formation.
What is the main function of the cerebellum?
Coordinate movements, and regulates posture and balance.
Thalamus.
Major relay station of the brain. Makes up 80% of diencephalon. Consists of paired oval masses of gray matter organized into nuclei with interspersed white matter tracts.
Interthalamic adhesion.
A bridge of gray matter between the right and left halves of the thalamus. Present in 70% of human brains.
Internal medullary lamina.
Vertical Y-shaped sheet of white matter that divides the gray matter of the right and left sides of the thalamus. Consists of myelinated axons that enter and exit the thalamic nuclei.
Internal capsule.
Thick band of white matter lateral to the thalamus. Axons that connect thalamus to cerebral cortex pass through this structure.