Unit 3: Cranial system Pt. 3 Flashcards
What are the five brain structures to form the brain?
- Telencephalon
- Diencephalon
- Mesencephalon
- Metencephalon
- Myelencephalon
What does the telencephalon develop into?
It develops into the cerebrum and lateral ventricles.
What does the diencephalon form?
It forms the thalamus, hypothalamus, epithalamus, and third ventricle.
What does the metencephalon become?
It becomes the pons, cerebellum, and upper part of the fourth ventricle.
what does the myelencephalon form?
It forms the medulla oblongata and the lower part of the fourth ventricle.
What are the four major parts of the adult brain?
- Brainstem
- Cerebellum
- Diencephalon
- Cerebrum
What is the largest part of the brain?
Cerebrum
What protects the brain?
The cranium and the meninges
Name the three meninges:
- Dura mater
- Arachnoid mater
- Pia mater
What are the two layers of the dura mater?
- Periosteal layer
- Meningeal layer
Name the three extensions of the dura mater that separates parts of the brain and what it separates:
- Falx cerebri: separates the two hemispheres of the
cerebrum - Falx cerebelli: separates the two hemispheres of the
cerebellum - Tentorium cerebelli: separates the cerebrum from the
cerebellum
How does the blood flow through the brain and where does it brain into?
Blood flows to the brain mainly via the internal carotid and vertebral arteries, the dural venous sinuses drain in to the internal jugular veins to return blood from the head to the heart.
How much does the brain represent the body? How much does the brain consume?
The brain represents only 2% of total body weight, but it consumes about 20% of total oxygen and glucose used by the body, even when you’re resting.
What happens when there is an interruption in blood flow into the brain?
An interruption in blood flow for 1 to 2 minutes, impairs neuronal function, and total depravation of oxygen for about 4 minutes causes permanent damage. Because virtually no glucose is stored in the brain, the supply of glucose also must be continuous.
Explain what the blood brain barrier is.
Consists mainly of tight junctions that seal together and endothelial cells of brain blood capillaries and a thick basement membrane that surrounds the capillaries. The process of many astrocytes press up against the capillaries and secrete chemicals that maintain the ‘tightness’ of the tight junctions.
Why is the blood brain barrier important?
The blood brain barrier is a semi permeable substance that only allows certain things into the brain and keeping the bad stuff out.
Explain what the cerebrospinal fluid is.
It is a clear, colourless liquid composed primarily of water that protects the brain and spinal cord from chemical and physical injuries. CSF continuously circulates through cavities in the brain and spinal cord and around the brain and spinal cord in the subarachnoid space.
What does the cerebrospinal fluid contain?
It contains small amounts of oxygen, glucose, and other needed chemicals form the blood to neurons and neuroglia.
Explain what the ventricles in the brain are.
Ventricles are cavities within the brain that are filled with cerebrospinal fluid.
Name the ventricles in the brain and what are they?
There is one lateral ventricle in each hemisphere of the cerebrum. The third ventricle is a narrow, slitlike cavity along the midline superior to the hypothalamus and between the right and left halves of the thalamus. The fourth ventricle lies between the brainstem and the cerebellum.
Explain what the septum pellucidum.
The lateral ventricles are separated by a thin membrane called the septum pellucidum.
Explain the three functions of the cerebrospinal fluid.
- Mechanical protection: CSF serves as a shock absorbing
medium that protects the delicate tissues of the brain
and spinal cord from jolts that would otherwise cause
them to hit the bony walls of the cranial cavity and
vertebral canal. The fluid also buoys the brain so that it
floats in the cranial cavity. - Chemical protection: CSF provides an optimal chemical
environment for accurate neuronal signalling. Even slight
changes in the ionic compositions of CSF within the brain
can seriously disrupt production of action potentials and
post synaptic potentials. - Circulation: CSF is a medium for minor exchange of
nutrients and waste products between the blood and
adjacent nervous tissue.
Explain where cerebrospinal fluid is produced form. And how its produced.
The majority of CSF production is from the choroid plexuses, networks of blood capillaries in the walls of ventricles.
Selected substances (mostly water) from the blood plasma, which are filtered from the capillaries, are secreted by the ependymal cells to produced the CSF. Because of the tight junctions between ependymal cells, materials entering CSF from choroid capillaries cannot leak between these cells, instead they must pass through the ependymal cells.
Explain how the blood brain barrier and the blood cerebrospinal fluid barrier are similar.
They are similar in a way that they both only permit certain substances to enter the CNS. The blood cerebrospinal fluid barrier is also formed by tight junctions of ependymal cells.
How does the cerebrospinal fluid circulate.
The CSF flows from the choroid plexuses of each lateral ventricles flows into the third ventricles through two narrow, oval openings, the inter ventricular foramina. The fluid then flows through the aqueducts of the midbrain, which passes through the midbrain, into the fourth ventricle. CSF enters the subarachnoid space through the three openings in the roof of the fourth ventricles: a single median aperture and paired lateral aperture, one on each side.
How is the cerebrospinal fluid reabsorbed?
CSF is gradually reabsorbed into the blood stream through arachnoid vili, fingerlike extensions of the arachnoid mater that projects into the dural venous sinuses, especially the superior sagittal sinus. Because the rates of formation and reabsorption are the same, the pressure of CSF normally is constant. For the same reason, the volume of CSF remains constant.
Explain what the arachnoid granulation is.
A cluster of arachnoid vili is called an arachnoid granulation.
Where is the brainstem located? What does it consists of?
The brainstem is the part of the brain between the spinal cord and the diencephalon. It consists of three structures:
- Medulla oblongata
- Pons
- midbrain
Extending through the brainstem is the reticular formation, a netlike region of interspersed grey and white matter.
Explain what the medulla oblongata is.
Also called medulla, is continuous with the superior part of the spinal cord, it forms the inferior part of the brainstem.
The medulla begins at the foramen magnum and extends to the inferior border of the pons.
The medullas white matter contains all sensory (ascending) tracts and motor (descending) tracts that extends between the spinal cord and other parts of the brain.
Explain what the pyramids in the medulla is.
Some of the white matter forms bulges on the anterior aspects of the medulla. These protrusions, called the pyramids, are formed by the large corticospinal tracts that pass from the cerebrum to the spinal cord.
Explain what the decussation of pyramids are.
Just superior to the junction of the medulla with the spinal cord, 90% of the axons in the left pyramid cross to the right side, and 90% of the 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.
What does the corticospinal tract control?
It controls voluntary movements of the limbs and trunk.
Differentiate between the cardiovascular (CV) centre and the medullary respiratory centre.
The medulla also contains several nuclei (a collection of neuronal cell bodies within the CNS). Some of these nuclei control body functions.
The cardiovascular centre regulates the rate and force of the heart beat and the diameter of blood vessles.
The medullary respiratory centre adjusts the basic rhythm of breathing.
Explain what the vomiting centre of the medulla is.
The vomiting centre of the medulla causes vomiting, the forcible expulsion of the contents of the upper gastrointestinal tract through the mouth.
Explain what the deglutition centre.
The deglutition centre of the medulla promotes deglutition (swallow) of a mass of food that has moved from the oral cavity of the mouth into the pharynx.
What does sneezing involve?
Sneezing involves spasmodic contraction of breathing muscles that forcefully expel air through the nose and mouth.
Explain what coughing involves.
Coughing involves a long drawn and deep inhalation and then a strong exhalation that suddenly sends a blast of air through the upper respiratory passages.
What does hiccuping invovle.
Hiccuping is caused by spasmodic contractions of the diaphragm that ultimately result in the production of a sharp sound of inhalation.
Explain what the olive is. What is the inferior olivary nuclues?
Just lateral to each pyramid is an oval shaped swelling called an olive. Within the dive is the inferior olivary nucleus, which receives input from the cerebral cortex, red nucleus of the midbrain, and spinal cord. Neurons of the inferior olivary nucleus extend their axons into the cerebellum, where they regulate the activity of cerebellar neurons.
Where is the nuclei associated with sensation, pressure, vibration, and conscious proprioceptors are located?
It is located in the posterior part of the medulla.
Differentiate between the gracile fasciculus and cuneate fasciculus.
Ascending sensory axons of the gracile fasciculus and the cuneate fasciculus, which are two tracts in the posterior columns of the spinal cord, form synapses in these nuclei.
Explain what the medial lemniscus and how the posterior column medial lemniscus pathway is related.
The axons ascend to the thalamus in a band of white matter called the medial lemniscus, which extends through the medulla, pons and the midbrain. The tracts of the posterior columns and the axons of the medial lemniscus are collectively known as the posterior column medial lemniscus.
Explain what the gustatory nucleus is.
The gustatory nucleus (taste) of the medulla is part of the gustatory pathway from the tongue to the brain; it receives gustatory input from the taste buds of the tongue.
Explain what the cochlear nuclei is.
The cochlear nuclei of the medulla are part of the auditory pathway from the inner ear to the brain; they receive auditory input from the cochlea of the inner ear.
Explain what the vestibular nuclei is.
The vestibular nuclei of the medulla and pons are components of the equilibirum pathway from the inner ear to the brain; they receive sensory information associated with equilibrium from proprioceptors in the vestibular apparatus of the inner ear.
What are the five pairs of cranial nerves the medulla is associated with?
- Vestibulochochlear (VIII) nerve
- Glossopharyngeal (IX) nerve
- Vagus (X) nerve
- Accessory (XI) nerves (cranial portion)
- Hypoglossal (XIII) nerve
Explain what the pons is.
The pons lies directly superior to the medulla and anterior to the cerebellum. The pons consists of both nuclei and tracts. It is a bridge that connects parts of the brain with one another. These connections are provided by bundles of axons. Some axons of the pons connect the right and left sides of the cerebellum. Others are part of ascending sensory tracts and descending motor tracts.
Explain the two major structural components of the pons.
the central region of the pons forms a large synaptic relay station consisting of scattered grey centres called the pontine nuclei.
The dorsal region of the pons is more like the other regions of the brainstem, the medulla and midbrain.
Explain what the pontine respiratory group is.
Also within the pons is the pontine respiratory group. The pontine respiratory group helps control breathing,
What are the four cranial nerves associated with the pons.
- Trigeminal (V) nerve
- Abducens (VI) nerve
- Facial (VII) nerve
- Vestibulocochlear (VIII) nerve
Explain what the midbrain is.
The midbrain or mesencephalon extends form the pons to the diencephalon. The aqueducts of the midbrain passes through the midbrain, connecting the third ventricles above with the fourth ventricle below. The midbrain contains both nuclei and tracts.
Explain what the cerebral peduncles are.
The anterior part of the midbrain contains paired bundles of axons known as the cerebral peduncles. The cerebral peduncles consists of axons of the corticospinal, corticobulbar, and corticopontine tracts, which conduct nerve impulses from motor areas in the cerebral cortex to the spinal cord, medulla, and pons.
Explain what the tectum and the superior colliculi is.
The posterior part of the midbrain, called the tactum. The two superior elevations, nuclei known as the superior colliculi, serves as reflux centres for certain visual activities.
The superior colliculi are also responsible for reflexes that govern movements of the head, eyes, and trunk in response to visual stimuli.
Explain what the inferior colliculi is.
The two inferior elevations, the inferior colliculi, are part of the auditory pathway, relaying impulses form the receptors for hearing in the inner ear to the brain. The superior and inferior colliculi are also reflex centres for the startle reflex.
Explain what the substantia nigra is.
The midbrain contains several other nuclei, including the left and right substantia nigra, which are large and darkly pigmented. Neurons that release dopamine, extending from the substantia nigra to the basal nuclei, help control subconscious muscle movements. Loss of these neurons is associated with parkinsons disease.
Explain what the red nuclei is.
Present in the midbrain is also the left and right red nuclei, which look reddish due to their rich blood supply and an iron containing pigment in their neuronal cell bodies.
Axons from the cerebral cortex form synapses in the red nuclei, which help control muscular movements.
What are the two pairs of cranial nerves associated with the midbrain?
- Occulomotor (III) nerve
- Troclear (IV) nerve
Explain what the reticular formation is.
Much of the brainstem consists of small clusters of neuronal cell bodies interspersed among small bundles of myelinated axons. The broad region where white matter and grey matter exhibit a netlike arrangement is known as the reticular formation. It extends from the superior part of the spinal cord, throughout the brainstem, and into the inferior part of the diencephalon.
Explain what the reticular activation system is.
Neurons within the reticular formation have both ascending (sensory) and descending (motor) functions. The ascending portion of the reticular formation is called the reticular activation system, which consists of sensory axons that projects to the cerebral cortex, both directly and through the thalamus.
Explain what the functions of the reticular activation formation (RAS).
- The most important function of the RAS is
consciousness. Visual and auditory stimuli and mental
activities can stimulate the RAS to help maintain
consciousness. - The RAS is also active during arousal, or awakening from
sleep. - Another function of RAS is to help maintain attention and
alertness. - The RAS also prevents sensory overload by filtering out
insignificant information so that is does not reach
consciousness. Inactivation of the RAS produces sleep. - The RAS also prevents sensory overload by filtering out
insignificant information so that it does not reach
consciousness.
Explain how a coma happens.
Damage to the RAs results in coma. In the lightest stages of coma, brainstem and spinal cord reflexes persists, but in the deepest states even those reflexes are lost, and if respiratory and cardiovascular controls are lost, the patient dies.
What helps regulate muscle tone?
The descending portion of the reticular activation system has connections to the cerebellum and spinal cord and helps regulate muscle tone. This portion of the RAS also assists in the regulation of heart rate, blood pressure and respiratory rate.
What is unique about the reticular activation system in terms of senses?
Even though the RAS receives input from the eyes, ears, and other sensory receptors, there is no input from receptors for the sense of smell.
Explain what the cerebellum is.
The cerebellum, second only to the cerebrum in size, occupies the inferior and posterior aspects of the cranial cavity. The cerebellum has a highly folded surface that greatly increases the surface area of its outer grey matter cortex, allowing for greater number of neurons. It contains nearly half of the neurons in the brain.
Where is the cerebellum located?
The cerebellum is posterior to the medulla and pons and inferior to the posterior portion of the cerebrum.
Explain what the transverse fissure is and how the tentorium cerebelli is related.
A deep groove known as the transverse fissure, along with tentorium cerebelli, which supports the posterior part of the cerebrum, separates the cerebellum from the cerebrum.
Explain what the vermis hemisphere is.
The central part of the cerebellums constricted area is the vermis hemispheres. Each hemisphere consists of lobes separated by deep and distinct fissures. The anterior lobe and posterior lobe governs subconscious aspects of the skeletal muscle movements.
The flocculonodular lobe on the inferior surface contributes to the equilibrium and balance.
Explain what the cerebellar cortex is.
The superficial layer of the cerebellum, the cerebellar cortex, consists of grey matter in a sense of slender, parallel folds called folia.
Explain what is deep in the grey matter and the white matter.
Deep to the grey matter are tracts of the white matter called arbour vitae that resembles branches of a tree. Even deeper, within the white matter, are the cerebellar nuclei, regions of the grey matter, are the carrying impulses from the cerebellum to other brain centres.
Explain what the three paired of cerebellar peduncles are.
Three paired cerebellar peduncles attach the cerebellum to the brainstem.
- The superior cerebellar peduncles contains axons that
extends from the cerebellum to the red nuclei of the
midbrain and to several nuclei of the thalamus.
- The middle cerebellar peduncles are the largest
peduncles; their axons carry impulses for voluntary
movements form the pontine nuclei into the cerebellum.
- The inferior cerebellar peduncles
Explain what the inferior cerebellar peduncles consists.
- Axons of the spinocerebellar tracts that carry sensory
information into the cerebellum from proprioceptors in
the trunk and limbs. - Axons from the vestibular apparatus of the inner ear and
from the vestibular nuclei of the medulla and pons that
carry sensory information into the cerebellum from
proprioceptors in the head. - Axons from the inferior olivary nucleus of the medulla
that enters the cerebellum and regulate the activity of
cerebellar nueorons. - Axons that extend from the cerebellum to the vestibular
nuclei from the medulla and pons - Axons that extend from the cerebellum to the reticular
formation.
Explain what the primary function of the cerebellum is.
The primary function of the cerebellum is to evaluate how well movements initiated by motor areas in the cerebrum are actually being carried out. When movements initiated by the cerebral motor areas are not being carried out correctly, the cerebellum detects the discrepancies. It then sends a feedback signal to motor areas of the cerebral cortex, via its connections to the thalamus. The feedback signals helps correct the errors. The cerebellum is the main brain region that regulates posture and balance.
Explain what the diencephalon is.
The diencephalon forms a central core of the brain tissue just superior to the midbrain. It is almost completely surrounded by the cerebral hemisphere and contains numerous nuclei involved in a wide variety of sensory and motor processing between higher and lower brain centres.
The diencephalon extends form the brainstem to the cerebrum and surrounds the third ventricle; it includes the thalamus, hypothalamus, and epithalamus.
Explain what the thalamus is.
The thalamus makes up 80% of the diencephalon, consists of paired oval masses of grey matter organized into nuclei with interspersed tracts of white matter.
A bridge of grey matter called the inter thalamic adhesion joins the right and left halves of the thalamus in about 70% of human brains.
A vertical Y shaped sheet of white matter called the internal medullary lamina divides the grey matter of the right and left sides of the thalamus.
Axons that connects the thalamus and cerebral cortex pass through the internal capsule, a thick bend of white matter lateral to the thalamus.
Why is the thalamus important?
The thalamus is the major relay station for most sensory impulses that reach the primary sensory area of the cerebral cortex from the spinal cord and brainstem.
The thalamus also contributes to motor functions by transmitting information from the cerebellum and basal nuclei to the primary motor area of the cerebral cortex.
The thalamus also plays a role in the maintenance of consciousness.
What are the seven major groups of nuclei on each side of the thalamus?
- Anterior nucleus
- Medial nuclei
- Nuclei in the lateral group
- Five nuclei are part of the ventral group
- Intralaminar nuclei
- Midline nucleus
- Reticular nucleus
Explain what the anterior nucleus of the thalamus does.
The anterior nucleus receives input from the hypothalamus and sends output to the limbic system. It functions in emotions and memory.
Explain what the medial nuclei of the thalamus does.
The medial nuclei receives input from the limbic system and basal nuclei and send output to the cerebral cortex. They function in emotions, learning, memory, and cognition.
Explain what the lateral group of the thalamus does.
Nuclei in the lateral group receive input from the limbic system, superior colliculi, and cerebral cortex and send output to the cerebral cortex.
The lateral dorsal nucleus functions in the expression of emotions.
The lateral posterior nucleus and pulvinar nucleus help integrate sensory information.
Explain what five nuclei of the ventral group of the thalamus.
- The ventral anterior nucleus receives input from the
basal nuclei and sends output to motor areas of the
cerebral cortex; it plays a role in movement control. - The ventral lateral nucleus receives input from the
cerebellum and basal nuclei and sends output to motor
areas of the cerebral cortex; it also plays a role in
movement control. - The central posterior nucleus relays impulses for somatic
sensations such as touch, pressure, vibration, itch, tickle,
temperature, pain, and proprioception from the face and
body to the cerebral cortex. - The lateral geniculate nucleus relays visual impulses for
sight from the retina to the primary auditory area of the
cerebral cortex.
