Chapter 14 The Brain and Cranial Nerves Part 1

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Terms in this set (...)

Cerebrum
- 83% of brain volume
- Includes cerebral hemispheres, gyri and sulci, longitudinal fissure, corpus callosum
Cerebellum
- Second largest brain region, located in posterior cranial fossa
- Contains 50% of the neurons
Diencephalon
- Includes thalamus, hypothalamus, and epithalamus
Brainstem
- Includes midbrain, pons, and medulla oblongata
Longitudinal fissure
deep groove that separates cerebral hemispheres
Corpus callosum
thick nerve bundle at bottom of longitudinal fissure that connects hemispheres
Gyri
thick folds
Sulci
shallow grooves between the folds
Gray matter
contains neuron cell bodies, dendrites, and synapses
- Dull white color when fresh, due to little myelin
- Forms surface layer (cortex) over cerebrum and cerebellum
- Forms centers of gray matter (nuclei) deep within brain
White matter
bundles of axons
- Lies deep to cortical gray matter (opposite from set up
in the spinal cord)
- Pearly white color from myelin around nerve fibers
- Composed of tracts, or bundles of axons, that connect
one part of brain to another, and to spinal cord
Meninges
three connective tissue layers that surround the brain
• Include dura mater, arachnoid mater, and pia mater
• Protect the brain and provide structural framework for its arteries and veins
Dura mater
in the cranial cavity has two layers
-folds inward to extend between different parts of the brain
- Falx cerebri separates the two cerebral hemispheres
- Tentorium cerebelli separates cerebrum from
cerebellum
Outer periosteal
in contact with cranial bones; no epidural space
Inner meningeal
continues into vertebral canal and forms dural sheath around spinal cord
Dural sinuses
collection site for blood and CSF that has circulated through the brain
Arachnoid mater
- Transparent membrane over brain surface
- Subarachnoid space separates it from pia mater below
• Cerebrospinal fluid circulation
- Subdural space separates it from dura mater above
Pia mater
- very thin membrane that follows contours of brain
and into sulci
- Not usually visible without a microscope
Meningitis
inflammation of the meninges of the brain and spinal cord
• Caused by bacterial and virus infection of CNS
- Can result in brain swelling, ventricle enlargement,
and hemorrhage
Symptoms of Meningitis
high fever, stiff neck, drowsiness, intense headache; may progress to coma then death within hours of onset
Diagnosis of Meningitis
examination of CSF for infection
- Lumbar puncture (spinal tap) to draw fluid from
subarachnoid space between two lumbar vertebrae
Ventricles
function in production and circulation of CSF
Two lateral ventricles
one in each cerebral hemisphere; surrounded by corpus callosum
Interventricular foramen
connects to third ventricle
Third ventricle
located beneath corpus callosum
Cerebral aqueduct
connects to fourth ventricle
Fourth ventricle
located between pons and cerebellum
- Connects to central canal that runs down through spinal cord
Choroid plexus
- Spongy mass of blood capillaries
- Provides blood flow for production of CSF
- Each ventricle has its own
Ependymal cells (ependyma)
- Resembles a simple cuboidal epithelium
- Lines the ventricles and cover choroid plexus
- Filters blood from capillaries in choroid plexus and
produces cerebrospinal fluid (CSF)
Cerebrospinal fluid (CSF)
clear, colorless liquid that fills ventricles and canals of CNS
Functions of CSF
- Buoyancy
- Protection
- Homeostatic regulation
Buoyancy
prevents the brain from resting too heavily on the floor of the cranium which would cause to much pressure and kill the nervous tissue
Protection
protects the brain from striking the cranium when the head is jolted
Homeostatic regulation
flow of CSF rinses away metabolic wastes and regulates chemical environment of nervous tissue
Step #1 of Flow of Cerebrospinal Fluid
CSF secreted by the ependyma and choroid plexus in
lateral ventricles
Step #2 of Flow of Cerebrospinal Fluid
CSF flows through interventricular foramen into third
ventricle
- Ependyma and choroid plexus in third ventricle secrete additional CSF
Step #3 of Flow of Cerebrospinal Fluid
Continues down cerebral aqueduct into fourth ventricle
- Ependyma and choroid plexus in fourth ventricle secrete additional CSF
Step #4 of Flow of Cerebrospinal Fluid
Flows through apertures into subarachnoid space
- Circulates over surfaces of brain and spinal cord
Step #5 of Flow of Cerebrospinal Fluid
After circulation around entire CNS, CSF reabsorbed from subarachnoid space at arachnoid villi; mixes with
venous blood in the superior sagittal sinus
Blood Supply and the Brain
Brain tissue has a high demand for ATP, oxygen, and glucose, so constant supply of blood is critical
Blood-brain barrier (BBB)
strictly regulates what substances can pass from the bloodstream into the brain
- Highly permeable to water, glucose, and lipid-soluble
substances (oxygen, carbon dioxide, alcohol, caffeine,
nicotine, and anesthetics)
- Presents an obstacle for delivering some types of
medications such as antibiotics and cancer drugs
- Trauma and inflammation can damage BBB and allow
pathogens to enter brain tissue
Blood-brain barrier (BBB)
Consists of tight junctions between endothelial cells that form the capillary walls
- Astrocytes reach out and contact capillaries with their perivascular feet
- Induce the endothelial cells to form tight junctions that completely seal off gaps between them
- Anything leaving the blood must pass through the cells, not between them
- Excludes harmful substances from passing to the brain tissue while allowing necessary ones to pass
Reticular formation
loosely organized web of gray matter that runs vertically through all levels of the brainstem (found in pons, midbrain, and medulla)
• Consists of more than 100 nuclei (small neural
networks without distinct boundaries)
• Reticular nuclei control important functions
of the body
• Has connections with many areas of cerebrum
Somatic motor control
- Integrates visual, auditory, balance, and motion stimuli into motor coordination
- Gaze center: allows eyes to track and fixate on objects
- Central pattern generators: neural pools that produce rhythmic signals to the muscles of breathing and swallowing
Cardiovascular control
- Includes cardiac and vasomotor centers of medulla
oblongata
Pain modulation
- Provides one route by which pain signals from lower body reach the cerebral cortex
- Origin of descending analgesic pathway (reticulospinal
tract) that can oppose pain signals ascending up the
spinothalamic tract (more in Chap 16)
Sleep and consciousness
- Plays central role in states of consciousness, such as
alertness and sleep
- Injury to reticular formation can result in irreversible coma
Habituation
Process in which the brain learns to ignore repetitive, inconsequential stimuli while remaining sensitive to others
Medulla Oblongata
• Medulla begins at foramen magnum of the skull
• All nerve fibers connecting brain to spinal cord pass through medulla
- Includes ascending and descending tracts (Chap. 13)
- Also connections to some cranial nerves (IX, X, XI, XII)
• Pyramids)
• Olives
Pyramids
pair of external ridges (anterior surface)
- Contain corticospinal tracts (site of decussation)
Olives
prominent bulges lateral to each pyramid
- Contain inferior olivary nuclei; act as relay centers for signals going to cerebellum
Cardiac center
Adjusts rate and force of heart
Vasomotor center
Adjusts blood vessel diameter
Respiratory centers
Control rate and depth of breathing
Reflex centers
For coughing, sneezing, gagging, swallowing,
movements of tongue and head, in addition to others
Pons
located superiorly to the medulla and inferiorly to the midbrain (in the middle of brainstem)
• Contains continuations of some ascending and descending nerve tracts
• Also relays signals via other tracts:
- Some cross between right and left (transverse fascicles)
- Some carry signals up and down the brainstem (longitudinal fascicles)
• Contains additional reticular formation nuclei
Pons
Contains connection points for cranial nerves V, VI, VII, and VIII
- Sensory roles
- Motor roles
Sensory roles
hearing, equilibrium, taste, facial sensations
Motor roles
eye movement, facial expressions, chewing, swallowing, urination, and secretion of saliva and tears
Cerebellar peduncles
connect cerebellum to pons and midbrain
Midbrain
located superiorly to the pons
Cerebral peduncles
connect cerebrum to midbrain and brainstem; anterior to cerebral aqueduct
• Contains connections to cranial nerves III and IV (control eye movements)
• Also contains continuation of the reticular formation
Tectum
roof-like part of the midbrain
Colliculi
prominent bulges (4)
Superior colliculi (2)
relays signals for movement of eyes, head and neck in response to visual stimuli
Inferior colliculi (2)
relay signals for movements of head and neck in response to auditory stimuli