Chapter 14 - Brain & Cranial Nerves Flashcards
What are the 4 major parts of the brain?
- Brain stem
- Cerebellum
- Diencephalon
- Cerebrum
What does the brain stem consist of?
Medulla Oblongata
Pons
Midbrain
- continuous with the spinal cord
What does the diencephalon consist of?
Thalamus
Hypothalamus
Epithalamus
- superior to the brain stem
What does the cerebellum do?
Coordinates and regulates muscular activity
- located at the back of the skull
What does the cerebrum do?
Integration of complex sensory and neural functions
Initiation and coordination of voluntary activities
- the principal and most anterior part of the brain
What are the cranial meninges?
Protective layer of the brain
- consists of three layer
(Dura mater, arachnoid mater & pia mater)
- continuous with spinal meninges
What are the names of the three craninal meninges?
outer layer to inner layer
- Dura Mater
- Arachnoid Mater
- Pia Mater
What two things protect the brain?
- Cranial bones
2. Cranial meninges
How is the cranial dura mater different from the spinal cord dura mater?
Cranial has two layers instead of one
What are the two layers of the cranial dura mater called?
- Periosteal layer (external)
2. Meningeal layer (internal)
What separates the two hemispheres of the cerebrum?
Falx cerebri
What separates the two hemispheres of the cerebellum?
Falx cerebelli
What separates the cerebrum from the cerebellum?
Tentorium cerebelli
What does the blood-brain barrier consist of?
Mainly of tight junctions that seal together the endothelial cells of brain blood capillaries and a thick basement membrane that surrounds the capillaries
What substances can and cannot cross the BBB?
Yes - glucose - active transport
Yes - oxygen, carbon dioxide, alcohol - cross easily
Yes - urea, most ions - diffuse very slowly
No - proteins, antibiotics
What is cerebrospinal fluid? (CSF)
Clear, colourless liquid composed primarily of water
- protects the brain and spinal cord from chemical and physical injuries
Where is cerebrospinal fluid in the body?
Circulates continuously in cavities in the brain & spinal cord and in the sub-arachnoid space
What does the cerebrospinal fluid contain?
Small amounts of glucose, proteins, lactic acid, urea, cations (K+, Na+, Ca+2, Mg+2) and anion (Cl- and HCO3-)
- some white blood cells
What is the sub-arachnoid space?
Space between arachnoid and pia mater
What is the name for cavities in the brain that are filled with cerebrospinal fluid?
Ventricles
How many ventricles are in the brain?
Four
- Lateral ventricle - right hemisphere of cerebrum
- Lateral ventricle - left hemisphere of cerebrum
- Third ventricle - between the right and left halves of the thalamus
- Fourth ventricle - between brain stem and the cerebellum
What are the functions of cerebrospinal fluid?
- Mechanical protection - shock absorption
- Homeostatic function - pH of CSF affects pulmonary ventilation and cerebral blood flow
- Circulation - medium for minor exchange of nutrients & waste products
What is the choroid plexuses?
What does it do?
Networks of blood capillaries in the walls of the ventricles
- production of cerebrospinal fluid
What does the blood-cerebrospinal fluid barrier do?
Permits certain substances to enter the CSF but excludes others
- protects the brain & spinal cord from harmful substances
How is the blood-cerebrospinal fluid barrier formed?
Tight junctions of ependymal cells
How is the blood-brain barrier formed?
Tight junctions of brain capillary endothelial cells
Describe how the cerebrospinal fluid flows in the body.
- See summary on page 535
Produced in the choroid plexuses of each lateral ventricle - flows into third ventricle (through two narrow openings, called interventricular foramina)
- more CSF is added by the choroid plexsus of the third ventricle
- flows through aqueduct of the midbrain, into the fourth ventricle
- choroid plexsus of fourth ventricle adds more fluid
- enters subarachnoid space through three opening in the roof of the fourth ventricle
- then circulates the central canal of the spinal cord
What is the name of the opening(s) between the lateral (1st and 2nd) ventricles and the third ventricle?
Interventricular foramina
What is the name of the opening between the third and fourth ventricle?
Aqueduct of the midbrain (cerebral aqueduct)
What is the name of the opening(s) between the fourth ventricle and the sub-arachnoid space?
Three openings:
- single median aperture
- paired lateral apertures
Where is cerebrospinal fluid reabsorbed into the blood?
Arachnoid villi
- fingerlike projections of the arachnoid that project into the dural venous sinuses
- absorbed as fast as it is produced
The brain stem consists of what three parts?
- Medulla oblongata
- Pons
- Midbrain
Where is the brain stem located?
Between the spinal cord and the diencephalon
What is the medulla oblongata continuous with?
The superior part of the spinal cord
It forms the inferior part of the brain stem
What does the medulla oblongata’s white matter contain?
All sensory (ascending) tracts and motor (descending) tracts that extend between the spinal cord and other parts of the brain
What are pyramids?
White matter that has formed bulges on the anterior aspect of the medulla
What are pyramids formed by?
Formed by the large corticospinal tracts that pass from the cerebrum to the spinal cord
- control voluntary movements of the limbs and trunk
What is the decussation of pyramids?
Where 90% of the axons cross over from the left/right and right/left sides
- why each side of the brain controls voluntary movements on the opposite side of the body
Where is the decussation of the pyramids located?
Just superior to the junction of the medulla oblongata with the spinal cord
What is the cardiovascular center?
Regulates the rate and force of the heartbeat and the diameter of the blood vessels
- in the medulla
What is the function of the respiratory medullary rhythmicity area of the respiratory center?
Adjusts the basic rhythm of breathing
- in the medulla
Where is the pons located?
Directly superior to the medulla and anterior to the cerebellum
What does the pons consist of?
Consists of both nuclei and tracts
- is a bridge that connects parts of the brain with one another
- connect left and right sides of the cerebellum
What are the two major structural components of the the pons?
- Ventral region - forms a large synaptic relay station consisting of scattered gray centers
- Dorsal region - consists of ascending and descending tracts along with nuclei of cranial nerves
What do the pneumotaxi and apneustic areas do?
Help control breathing
Where is the midbrain? (mesencephalon)
Extends from the pons to the diencephalon
- about 2.5 cm long
What is the function of the midbrain?
Portion of the CNS associated with vision, hearing, motor control, sleep/wake, arousal (alertness), and temperature regulation.
What is the function of the pons?
Primarily with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture.
What is the function of the brain stem?
Regulation of heart rate, breathing, sleeping, and eating
What is the function of the medulla oblongata?
Responsible for the regulation of your heart rate, breathing, and blood pressure as well as reflexes such as vomiting, sneezing, and coughing.
What is the reticular formation?
Broad region where white matter and gray matter exhibit a netlike arrangement in the brainstem connecting the spinal cord, cerebrum, and cerebellum, and mediating the overall level of consciousness
What is the RAS (reticular activating system)?
Ascending portion of the reticular formation
- consists of sensory axons that project to the cerebral cortex, both directly and through the thalamus
- visual and auditory stimuli, mental activities, stimuli from pain, touch, and pressure receptors
What is the most important function of RAS (reticular activating system)?
Consciousness!
- a state of wakefulness in which an individual is fully alert, aware, and oriented
What are the other functions of the RAS?
- Consciousness
- Arousal & awakening from sleep
- Attention & alertness
- Prevents sensory overload
What is the cerebellum?
Occupies the inferior and posterior aspects of the cranial cavity
- highly folded surface area
- 1/10th of overall brain size but 1/2 the total neurons in the brain
What is the function of the cerebellum?
Cerebellum receives information from the sensory systems, the spinal cord, and other parts of the brain and then regulates motor movements.
Cerebellum coordinates voluntary movements such as posture, balance, coordination, and speech, resulting in smooth, balanced muscular activity.
What is the transverse fissure?
Deep groove which supports the superior part of the cerebrum and separates the cerebellum from the cerebrum
What is the vermis?
Central constricted area on the cerebellum
What are the cerebellar hemispheres?
The lateral “wings” or lobes of the cerebellum
What is the cerebellar cortex?
Superficial layer of the cerebellum
- consists of gray matter in a series of slender, parallel folds
What are folia?
Slender parallel folds of gray matter in the cerebellum
What are arbor vitae?
Tracts of white matter in the cerebellum
- deep to the gray matter (in the cerebellar cortex)
What is the diencephalon?
Central core of brain tissue just superior to the midbrain
- extends from brain stem to cerebrum and surround the third ventricle
What does the diencephalon consist of?
Thalamus (80%)
Hypothalamus
Epithalamus
What is the thalamus?
Major relay station for most sensory impulses and motor signals
- regulation of consciousness and sleep
- gray matter organized into nuclei with interspersed tracts of white matter
Where is the thalamus located in the brain?
Just above the brain stem
- between the cerebral cortex and the midbrain
What is the hypothalamus?
Consists of 4 regions:
- Mammillary
- Tuberal -
- Supraoptic
- Preoptic
Where is the hypothalamus located?
Inferior to the thalamus
What are the functions of the hypothalamus?
- Control of ANS
- Production of hormones
- Regulation of emotional and behavioural patterns
- Regulation of eating and drinking
- Control of body temperature
- Regulation of circadian rhythms and states of consciousness