Chapter 14: Brain And Cranial Nerves Flashcards
Olfactory (I)
Sensory
Smell
Extends through 20 olfactory foramina in the cribfiform plate of ethmoid bone.
Terminates in the brain in paired masses of gray matter call olfactory bulbs.
Optic (II)
Sensory
Sight
Tract of the brain, conducts nerve impulses for vision through ganglion cells.
Passes through the optic foramen and end in the lateral geniculate nucleus of the thalamus.
Neural Pathway: retina:rod/cones, bipolar cells, ganglion cells, optic nerve.
Oculomotor (III)
Motor
Movement muslce of eye balls and upper lid
Adjusts lens for near vision
Constriction of pupil
Divides into superior and inferior branches that pass through superior orbital fissure into the orbit.
Trochlear (IV)
Motor
Smallest of the 12 cranial nerves
Movement of eye balls
Originates in the midbrain of brain stem, axons cross to opposite side and exit the brain on its posterior aspect. Passes through the superior orbital fissure into orbit.
Innervate superior oblique.
Trigeminal (V)
Both Sensory and Motor
Touch, pain and thermal sensation for scalp, face and oral cavity
Chewing and controls middle ear muscle
Contains 3 nerve branches that enter the Trigeminal ganglion and terminate in the nuclei of the pons.
Abducens (VI)
Motor
Abducts the eyeball in lateral rotation. Named due to the movement it makes.
Passes through the superior orbital fissure of the orbit.
Facial (VII)
Both Sensory and Motor
Taste buds on 2/3 of tongue, touch, pain and thermal sensation from skin
Control of muscles for facial expression
Secretions of tear and saliva
Exits through the stylomastoid foramen to innervate the middle ear.
Vestibulocochlear (VIII)
Sensory
Hearing and equilibrium
Vestibular branch: impulse for equilibrium
Cochlear branch: impulse for hearing
Axons extend to nuclei in the medulla Oblongata and end in the thalamus.
Nerve impulses move medially.
Glossopharyngeal (IX)
Both Sensory and Motor
Taste from 1/3 tongue
Touch, pain, thermal sensations from skin
Propriception and assist in swallowing muscle, secretions of saliva, supply the taste buds.
Monitors BP, O2 and CO2 levels in blood
Pass through the jugular foramen and end in the medulla.
Vagus (X)
Both Sensory and motor. Gets its name due to its wide distribution.
Taste from epiglottis
Swelling, vocalization, coughing
Proprioception from throat and voicebox muscle
Monitors BP, O2 and CO2 in blood
Touch, pain and thermal sensation of skin
Sensation from thoracic and abd organs
Motility and excretion of GI organs
Construction of Resp passageways
Decreases HR
Pass through the jugular foramen to end in the medulla and pons.
Accessory (XI)
Motor
Movement of head and pectoral girdle
Arise from the first 5 segments of cervical portion of the spinal cord. Ascend through foramen magnum and exit through the jugular foramen.
Hypoglossal (XII)
Motor
Speech
Manipulation of food, swallowing
Innervate the tongue.
Exits the cranium through the Hypoglossal canal.
Located at the midline of the medulla.
Brainstem
Continuous with the spinal cord
Contains:
Midbrain
Pons
Medulla Oblongata
Medulla Oblongata
Medulla begins at the foramen magnum and extends to the inferior boarder of the pons.
Contains sensory (ascending) /motor tracts (descending).
Contains nuclei that are vital in control body functions.
Cardiovascular Center: regulates heart beat, blood vessels.
Medullary Resp Center: regulates breathing
Reticular Formation: functions in consciousness and arousal
Vomiting Center: controls reflex’s for vomiting, swallowing, sneezing, coughing and hiccupping.
Pons
Lies directly superior to the medulla and anterior to the cerebellum.
Acts as a bridge that connect the parts of the brain to one another.
Contains sensory and motor tracts.
Pontine nuclei: relay nerve impulses from motor areas of cerebral cortex to cerebellum.
Pontine resp group: helps control breathing.
Cranial Nerves:
Trigeminal, abducens, facial, vestibular
Midbrain
Or mesencephalon. Extends from the pons to the Diencephalon.
Contains sensory and motor tracts
Tectum: posterior part, contains 4 rounded elevations:
2 Superior colliculi: coordinate movement of heads, eyes and trunk in response to visual stimuli.
2 Inferior colliculi: coordinate movements of head, eyes and trunk in response to auditory stimuli.
Diencephalon 3 Parts
Superior to Brainstem
Contains:
Thalamus
Hypothalamus
Epithalamus
Thalamus
Makes up 80% of Diencephalon
Relays almost all sensory input to cerebral cortex.
Contributes to motor function by transmitting information from cerebellum and basal nuclei to primary motor area of cerebral cortex.
Function: plays a role in maintenance of consciousness.
Hypothalamus
Small part of Diencephalon
Main function: controls body activities and a major regulator of homeostasis.
Other Functions:
1. Controls and integrates activities of ANS
2. Produces and releases hormones.
3. Regulates emotional and behavior patterns.
4 Controls feeding/thirst centers and body temp.
5. Regulation of circadian rhythms.
Epithalamus
Small region of Diencephalon
Consists of pineal gland and habenular nuclei (involved in olfaction).
Cerebrum
Largest part of the brain
Is the seat of intelligence: read, write and speak
Supported on the Diencephalon and Brainstem
Sensory ares: perception of sensory information
Motor areas control execution of voluntary movements.
Complex functions: memory, personality traits and intelligence.
Cerebellum
Occupies the inferior and posterior aspect of the cranial cavity.
Main Function: to evaluate how well movements initiated by motor areas in the cerebrum are actually being carried out.
Also:
Smooths and coordinates contractions of skeletal muscles.
Regulates posture and balance.
Cerebellum Cortex: consists of gray matter in a slender folds called foliage.
Arbor Vitae: white matter, resembles branches of a tree.
4 Major Parts of the Brain
Brainstem
Cerebellum
Diecephalon
Cerebrum
Protective Coverings of the Brain
Cranium and cranial meninges surround and protect the brain.
3 Cranial Meninges
Continuous with spinal meninges and have a similar basic structure.
1. Dura Mater: contains 2 layers:
Periosteal layer (external) and meningeal layer (internal).
2. Arachnoid Mater
3. Pia Mater
3 Extensions of Dura Mater
- Flax Cerebri: separates 2 hemispheres of cerebrum
- Flax Cerebelli: separates 2 hemispheres of cerebellum
- Tentorium Cerebelli: separates cerebrum from cerebellum.
Blood Flow to the Brain
Mainly via the internal carotid and vertebral arteries.
Dura Venous Sinuses
Drain into the internal jugular veins to return blood from the head to the heart.
Adult Brain
2% of total body weight
Consumes about 20% of the O2 and glucose used by the body.
An interruption in blood flow for 1-2 mins impairs neuronal function.
Total deprivation of O2 for about 4 mins causes permanent injury, supply of glucose must be continuous.
Blood Brain Barrier
Or BBB
Consists of :
mainly tight junctions, seal together the endothelial cells of brains blood capillaries
thick basement membrane that surrounds the capillaries.
Antibiotic and proteins cant cross the BBB.
Cerebrospinal Fluid
Or CSF. Production is 20ml/hr.
Is clear, colorless liquid composed of water
formed from blood plasma of ependymel cells
protects the brain and spinal cord from chemical and physical injury.
Found in: subarachnoid space, ventricles and central canals.
Carries: O2, glucose and chemicals from blood to neurons
Contains small amounts : glucose, proteins, lactic acid, urea, cations and anions. Some WBC.
CSF Circulation
CSF is formed in the choroid plexuses of each lateral ventricle.
Flows into third ventricle through 2 oval openings, intervenbtricular foramina.
Then flows through the aqueduct of the midbrain in fourth ventricle.
CSF enters subarachnoid space through openings of the fourth ventricle.
Then is gradually reabsorbed into blood through arachnoid villi.
4 CSF Filled Cavities in the Brain
Known as: Ventricles
2 Lateral Ventricles: one is each hemispheres of the cerebrum ( ventricles 1 and 2).
1 Third Ventricle: narrow, slit like cavity along the midline superior to the hypothalamus.
1 Fourth Ventricle: lies between the brain and the cerebellum.
Septum Pellucidrum
Thin membrane that separates the lateral ventricles.
Functions of CSF
- Mechanical Protection: serves as shock absorbing medium that protects the tissue of the brain and spinal cord. creates a buoys so the brain floats in cranial cavity.
- Chemical Protection: provides optimal chemical environment for accurate neuronal signaling.
- Medium for minor exchange of nutrients and waste products between blood and adjacent nervous tissue.
Formation of CSF in Ventricles
Majority of CSF is produced from the choroid plexuses
Network of blood capillaries in the walls of the ventricles.
Selected substances (mostly water) from blood plasma
Filtered from capillaries
Then secreted by the ependymal cells to produce CSF.
Blood-Cerebrospinal Fluid Barrier
Permits certain substances to enter CSF
excludes others to protect the brain and spinal cord from potentially harmful blood-borne substances.
Interventricular Foramina
2 narrow openings where CSF fluid flows from lateral ventricle into the third ventricle
Arachnoid Villi
Finger like extensions of the arachnoid mater where CSF is gradually absorbed.
These extensions project into the rural venous sinuses, especially superior sagittal sinus.
Arachnoid Granulation
Cluster of arachnoid villi
Pyramids
White matter on anterior portion in medulla Oblongata that bulges forming protrusions.
These protrusions are formed by large corticospinal tracts.
Decussation of Pyramids
Crossing where:
90% of axons in left pyramid cross to the right side
90% of axons in the right pyramid cross to the left side.
This crossing explains why each side of the brain controls voluntary movements on the opposite side of the body.
Medulla Oblongata Anatomy
Olive: oval shaped sweeping, lateral to each pyramid
Inferior Olive: recieve input from cerebral cortex, red nucleus and spinal cord.
Gracile Nucleus and Cuneate Nucleus: associated with sensation of touch, pressure, vibration and conscious proprioception.
Gracile Fasciculus: ascending sensory axons
Cuneate Fasciculus: two tracts in spinal cord, form synapses.
Medial Lemniscus
Part of medulla Oblongata
Band of white matter where axons ascend to the thalamus, which extends through medulla, pons and midbrain’.
Gustatory Nucleus
Part of medulla of gustatory pathway from the tongue to the brain.
Recieves input from taste buds on the tongue.
Cochlear Nuclei
Part of the medulla of the auditory pathway from the inner ear to the brain. Receives auditory from the cochlea to the inner ear.
Vestibular Nuclei
Part of the medulla and pons. Components of the equilibrium pathway from the inner ear to the brain. Receives sensory information associated with equilibrium.
5 Cranial Nerves associated with Medulla Oblongata
- Vestibulocochlear VIII
- Glossopharyngeal IX
- Vagus X
- Accessory XI
- Hypoglossal XII
4 Cranial Nerves Associated with Pons
- Trigeminal (V)
- Abducens (VI)
- Facial (VII)
- Vestibulocochlear (VIII)
Cerebral Peduncles
Paired bundles of axon.
Found in the anterior part of the midbrain.
Consists of axons of : corticopspinal, corticbular, and corticopontine tracts. These tracts conduct nerve impulses from motor areas in cerebral cortex to spinal cord, medulla and pons.
Red Nuclei
Found in the midlbrain on left and right side.
Appear red due to the rick blood supply and an iron containing pigments in their neuronal cell bodies.
Composed of axons from cerebellum and cerebral cortex that control muscle movement.
2 Cranial Nerves Associated with Midbrain
- Oculomotor (III)
- Trochlear (IV)
Reticular Formation
Found in region of the brain stem
Contains gray matter and white matter arranged in a netlike pattern
Neurons here have both ascending and descending functions.
Reticular Activating System (RAS)
The ascending portion of recticular formation. Consists of sensory axons.
Most important function:
Consciousness (state of wakefulness where one is fully awake).
Other functions:
Maintains attention
Regulates muscle tone
Prevents sensory overload
Inactivation of RAS produces sleep
Damages to RAS results in a coma.
Cerebellar Peduncles
Three pairs, attach the cerebellum to the brainstem. These bundles of white matter consist of axons that conduct impulses between the cerebellum and other parts of the brain.
7 Major Groups of Nuclei of theThalamus
Based on postion and functions
1. Anterior Nucleus: receives input from hypothalamus. Sends output to limbicsystem.
Function: emotion and memory
2. Medial Nuclei: receives input from limbic system. Sends output to cerebral cortex.
Function: emotions, learning, memory and cognition
3. Lateral Group: recieve input from limbic system, superior colliculi, cerebral cortex. Sends output to cerebral cortex.
Function: expressions of emotions and integrates sensory info.
4. Ventral Group: receives input from basal nuclei. Sends output to motor areas of cerebral cortex.
Function movement control
5. Intralaminar Nuclei: lie within internal medullary laminar. Connections are made with reticular formation, cerebellum and basal nuclei.
Function:arousal and integration of sensory and motor info
6. Midline Nucleus: forms thin band adjacent to 3rd ventricle.
Function: memory and olfaction.
7. Reticular Nucleus: surrounds lateral aspect of the thalamus.
Function: monitors, filters, integrates activities of other thalamic nuclei.
Infundibulum
Connects the pituitary gland to the hypothalamus.
Pineal Gland
Part of Epithalamus
Protrudes from the midline of the third ventricle. Part of the endocrine system as it secretes hormone melatonin.
Melatonin
Secreted by the pineal gland.
Helps regulate circadian rhythms.
Habenular Nuclei
Part of Epithalamus
Involved in olfaction, especially emotional response to odors such as a loved ones cologne.
Circumventricular Organs (CVOs)
These organs are part os the diencephalon. They lie in the third ventricle.
Monitor chemical changes in the blood because they lack the BBB.
Includes: hypothalamus, pineal gland, pituitary gland
Cerebral Cortex
Region of gray matter that forms the outer rim of the cerebrum.
Contains billions of neurons arranged in distinct layers.
Longitudinal Fissures
Most prominent fissure of the cerebral cortex.
Separates the cerebrum into right and left halves.
Cerebral Hemispheres
Right and left halves of the cerebrum
Corpus Callosum
Connects the cerebral hemispheres
Largest fiber bundle in the brain (300 million fibers)
A broad band of white matter containing axons that extend between the hemispheres.
Cerebral Hemisphere Lobes
These lobes are named after the bones that cover them.
Central Sulcus separates the frontal lobe from the parietal lobe.
Lateral cerebral sulus separates the frontal lobe from the temporal lobe.
Parieto-occipital sulcus separates the parietal lobe from the occipital lobe.
Insula
5th part of the cerebrum.
Lies within the lateral cerebral sulcus, deep to the parietal, frontal and temporal lobes.
Cerebral White Matter
Consists of primarily of myelinated axons in 3 types of tracts:
1. Association tract: contains axons that conduct nerve impulses between gyro in the same hemisphere.
2. Commissural tracts: contains axons that conduct nerve impulses from gyri in one cerebral hemisphere to corresponding gyri in the other cerebral hemisphere.
3. Projection tracts: contains axons that conduct nerve impulses from the cerebrum to lower parts to the CNS.
Brain Waves
Millions of nerve impulse that are generated by brain neurons.
Electroencephalogram (EEG)
Record of brain waves
4 Types of Brain Waves
- Alpha Waves: rhythmic waves, 8-13 cycles per second (Hz).These waves are present during wakefulness, disappear during sleep.
- Beta Waves: 14-30 Hz. Disappear when nervous system is active. (Input/mental activity)
- Theta Waves: 4-7 Hz. Normally occurs in children and adults experience emotional stress.
- Delta Waves: 1-5 Hz. Occurs during sleep in adults. If produced when adult is awake, indicates brain damage.
Occur when infants are awake.
Cranial Nerves
12 pairs
Named because they pass through various foramina in the bones of the cranium and apprise from the brain inside the cranial cavity.
Part of the PNS.
Olfactory Bulbs
Paired masses of gray matter where olfactory nerves end in the brain.
Anterior to olfactory tracts.
Olfactory Tracts
Made up by axons of neurons within the olfactory bulbs. Extend posterior from these bulbs.
Optic Tracts
Formed by regrouped axons, some from each eye.
Ciliary Ganglion
Synaptic relay center for the 2 motor neurons of the PNS.
Found in cranial nerve III.
Trigeminal Ganglion
Swelling of large sensory root in cranial nerve V. Located in a fossa on inner surface of petrous bone of temporal bone.
3 Branches of the Trigeminal Nerve
- Ophthalmic nerve: smallest branch, passes into orbit of superior orbital fissure.
- Maxillary Nerve: intermediate in size, passes through the foramen rotundrum.
- Mandibular Nerve: largest branch, passes through foramen ovale.
Geniculate Ganglion
A cluster of cell bodies of sensory neurons of the facial nerve within the temporal bone, ends in the pons.
Limbic System
Sometime called the emotional brain.
Plays primary role in a range of emotions. Damage to the limbic system causes memory impairment.
Included pain, pressure, docility, affection and anger
Together with cerebrum: fuctions in memory
Hippocampus: memory, learning emotion
Amygdala: fear and rage
Choroid Plexuses
Where CSF is produced in the lateral ventricles.
Substantia Nigra
Contained on the left and right sides of the midbrain. Dark pigmented.
Release dopamine to basal nuclei.
Brain Organization
- Telencephalon: give rise to lateral ventricles and cerebrum
- Metencephalon: delveops pons, cerebellum, fourth ventricle
- Mesencephalon: develops midbrain
- Diencephalon: thalamus, hypothalamus, Epithalamus, 3th ventricle.
Cerebral White Matter - Tracts
White matter consists of myelinated axons in 3 tracts.
1. Association tracts: contains axons that conduct nerve impulses between gyri in same hemisphere.
2. Commissural tracts: contains axons that conduct impulses from gyri in one hemisphere to corresponding gyri in other hemispheres.
3. Projection tracts: contains axons that conduct nerve impulses from cerebrum to lower parts of the CNS.
Astrocytes
Secrete chemical near the capillaries that help maintain the tightness of the tight junctions in endothelial cells.
Gray Matter of the Thalamus
Intermediate Mass or Adhesion.
Joins the right and left halves of the thalamus.
White Matter of the Thalamus
- Interdental Medullary Lamina
Vertical Y shaped sheet of white matter divides the gray matter of the right and left sides of the thalamus. - Internal Capsule
Thick band of white matter lateral to the thalamus.
Axons that connect the thalamus to the cerebral cortex pass through this capsule.
Bells Palsy
Diseased characteristic by facial paralysis.
Caused by damage to the facil nerve (VII)
Can be due to viral or bacterial infections, trauma or stoke.
Tectum of Midbrain
Contains 4 rounded elevations;
2 superior colliculi
2 inferior colliculi
Insula
Part of the cerebrum that cant be seen on the surface of the brain.
Gray Matter vs White Matter Growth.
Gray matter of the cortex grows faster then white
