Lecture Quiz 3 Flashcards
How is the brain protected in general?
bone, meninges, cerebrospinal fluid
harmful substances are shielded from the brain by the blood-brain barrier
What are the meninges?
three connective tissue membranes that lie external to the CNS
dura mater
arachnoid mater
pia mater
What are the functions of the meninges?
cover and protect the CNS
protect blood vessels and enclose venous sinuses
contain CSF
form partitions within the skull
Describe the dura mater
leathery, strong meninx composed of two fibrous connective tissue layers (periosteal and meningeal layers)
the two layers separate in certain areas and form dural sinuses
Describe the three dural septa of the dura mater
falx cerebri - fold that dips into longitudinal fissure
falx cerebelli - runs along the vermis of the cerebellum
tentorium cereblli - horizontal dural fol that extends into transverse fissure
Describe the arachnoid mater
Middle meninx which forms a loose brain covering
it is separated from the dura mater by the subdural space
Describe the subarachnoid space
beneath arachnoid layer
filled with CSF and\\large blood vessels
arachnoid villi protrude superiorly and permit CSF to be absorbed into venous blood
Describe the pia mater
deep meninx composed of delicate vascularized connective tissue that clings tightly to the brain
What is cerebrospinal fluid?
watery solution similar in composition to blood plasma
contains less protein and different ion concentrations than plasma
What does CSF do?
forms a liquid cushion that gives buoyancy to the CNS organs
prevents the brain from crushing under its own weight
protects the CNS from blows and other trauma
nourishes the brain and carries chemical signals throughout it
What are choroid plexuses?
hang from the roof of each ventricle
cluster of capillaries that form tissue fluid filters
What do choroid plexuses do?
have ion pumps that allow them to alter ion concentration in the CSF
help cleanse CSF by removing wastes
Describe CSF circulation
choroid plexus produce CSF
CSF flows through the ventricles and into the subarachnoid space via median and lateral apertures
CSF flows through the subarachnoid space
CSF is absorbed into the dural venous sinuses via the arachnoid villi
What is the blood-brain barrier?
protective mechanism that helps maintain a stable environment for the brain
What helps the blood brain barrier separated substances from neurons by?
continuous endothelium of capillary walls
relatively thick basal lamina
bulbous feet of astrocytes
What are the functions of the blood-brain barrier?
selective barrier that allows nutrients to pass freely
What is the BBB ineffective against?
substances that can diffuse through plasma membranes
explains how alcohol and drugs affect brain
Where is BBB absent from and why?
vomiting center and the hypothalamus
this allows these areas to monitor the chemical composition of the blood
What weakens the BBB?
stress increases the ability of chemicals to pass through the BBB
What is a concussion?
traumatic brain injury
temporary alteration in function
What is a contusion?
traumatic brain injury
permanent damage
What does a subdural or subarachnoid hemorrhage result in?
may force brain stem through foramen magnum, resulting in death
What is cerebral edema?
swelling of the brain associated with traumatic head injury
What is ischemia?
cerebrovascular accident aka stroke
tissue deprived of blood supply
brain tissue dies
ex: blockage of cerebral artery by blood clot
What is hemiplegia?
cerebrovascular accident aka stroke
paralysis on one side
sensory or speech deficits
What is a transient ischemic attack?
cerebrovascular accident aka stroke
temporary episode of reversible cerebral ischemia
What is tissue plasminogen activator?
the only approved treatment for stroke
What is Alzheimer’s?
a progressive, degenerative disease of the brain that results in dementia
causes memory loss, short attention span, disorientation, eventual language loss, irritable, moody, confused, hallucinations
plaques of beta-amyloid peptide form in brain
toxic effects may involve prior proteins
neurofibrillary tangles inside neurons and kill them
brain shrinks
What is Parkinson’s disease?
degeneration of dopamine releasing neurons of substantia nigra
basal nuclei deprives of dopamine become overactive resulting in tremors
cause unknown
treatment with L-dopa, deep brain stimulation, gene therapy, stem cells seem promising
What is Huntington’s disease?
fatal hereditary disorder
caused by accumulation of protein huntington
leads to degeneration of basal nuclei and cerebral cortex
initial sx wild, jerky “flapping” movements
later marked mental deterioration
treated with drugs that block dopamine effects
stem cell research promising
Describe embryonic development of the spinal cord
develops from caudal portion of neural tube
by week 6 there are two clusters of neuroblasts
What are the three things that form from the clusters of neuroblasts in embryonic spinal cord development?
alar plate - will become interneurons
basal plate - will become motor neurons
neural crest cells form the dorsal root ganglia
Where is CNS tissue found?
within the vertebral column from the foramen magnum to L1 or L2
What is the overall purpose of the spinal cord?
provides two-way communication to and from the brain
What is the spinal cord protected by?
bone, meninges, and CSF
What is the epidural space?
space between the vertebrae and the dural sheath (dura mater) filled with fat and a network of veins
this is not found in the brain
What is the conus medullaris?
terminal portion of the spinal cord
What is the filum terminale?
fibrous extension of the pia mater
anchors the spinal cord to the coccyx
What are denticulate ligaments?
delicate shelves of pia mater
attach the spinal cord to the vertebrae
How many spinal nerves are found from each part of the spine?
31 total 8 cervical 12 thoracic 5 lumbar 5 sacral
What are the cervical and lumbar enlargements?
sites where nerves serving the upper and lower limbs emerge
What is the cauda equina?
collection of nerve roots at the inferior end of the vertebral canal
What does the anterior median fissure do in the spinal cord?
separates anterior funiculi
What does the posterior median sulcus do?
divides posterior funiculi
What does gray matter consist of in the spinal cord?
soma
unmyelinated processes
neuroglia
What is the gray commissure?
connects masses of gray matter
encloses central canal
what are the posterior horns of the spinal cord?
interneurons
what are the anterior horns of the spinal cord?
interneurons and somatic motor neurons
What are the lateral horns of the spinal cord?
contain sympathetic neurons
What is the dorsal half of the gray matter responsible for in the spinal cord?
sensory roots and ganglia
sensory afferent
What is the ventral half of the gray matter responsible for in the spinal cord?
motor roots
motor efferent
What do the dorsal and ventral roots do outside CNS?
fuse together laterally to form spinal nerves
What are the four zones that are evident in the gray matter?
somatic sensory (SS) visceral sensory (VS) Visceral motor (VM) somatic motor (SM)
Describe white matter in the spinal cord
fibers run in three directions - ascending, descending, and transverse
divided into three funiculi - posterior, lateral, and anterior
Describe the funiculi in white matter in the spinal cord
contain several fiber tracts
fiber tract names reveal their origin and destination
fiber tracts are composed of axons with similar functions
What are the four generalizations we can make about pathways of the spinal cord?
pathways decussate - cross from one side of the CNS to another
most consist of two or three neurons
most exhibit somatotoopy - precise spatial relationships
pathways are paired - one on each side of the spinal cord or brain
What are dermatomes?
areas on the skin innervated by the cutaneous branches of a single spinal nerve
all spinal nerves except C1 participate in dermatomes
What are first-order neurons?
cell bodies reside in a ganglion synapse with second order neurons in the spinal cord or brain stem
What are second-order neurons?
cell bodies reside in the spinal dorsal horn or in medullary nuclei
synapse with third-order neurons in the thalamus or cerebellum
What are third-order neurons?
cell bodies reside in the thalamus
conduct impulses to the somatosensory cortex of the cerebrum
How do neurons branch as they enter the spinal cord?
central processes of first-order neurons branch diffusely as they enter the spinal cord and medulla
Where are nonspecific ascending pathways found?
within the lateral and anterior spinothalamic tracts
Where do the fibers cross in nonspecific pathways?
in the spinal cord
What do nonspecific ascending pathways do?
convey information about pain, temperature, and crude touch to the sensory cortex
Where are specific ascending pathways found?
within the fasciculus gracilis and fasciculus cuneatus tracts, and their continuation in the medial lemniscal tracts
Where do the fibers cross in specific ascending pathways?
in the medulla
What do specific ascending pathways do?
convey information about precise localizations of discriminative touch and vibrations to the sensory cortex
Where are the spinocerebellar tracts found?
within the lateral and anterior spino thalamic tracts
Where do spinocerebellar fibers cross?
do not cross or cross twice
What do spinocerebellar tracts do?
convey proprioceptive information about muscle or tendon stretch to the cerebellum to coordinate muscle activity
Where are the second-order neurons found in nonspecific ascending pathways?
interneuron of dorsal horn
Where are the second-order neurons found in specific ascending pathways?
medulla - nucleus gracilis and nucleus cureatus
Where are first-order neurons found in all ascending pathways?
dorsal root ganglion
What do the descending pathways do?
deliver efferent impulses from the brain to the spinal cord
divided into two groups - direct and indirect pathways
involve two neurons - upper and lower
What are the three steps of the direct system?
originate with the pyramidal neurons in the central gyri
impulses are sent through the corticospinal tractts and synapse in the anterior horn
stimulation of anterior horn neurons activates skeletal muscles
What are corticobulbar tracts?
parts of the direct pathway
innervate cranial nerve nuclei
What does the direct system regulate?
fast and fine movements
What is included in the indirect system?
brain stem, motor nuclei, and all motor pathways not part of the pyramidal system
rubrospinal, vestibulospinal, reticulospinal, and tectospinal (name = origin + termination site)
What do indirect systems do?
regulate axial muscles that maintain balance and postur
regulates muscles controlling coarse movements of the proximal portions of limbs
heck, neck, and eye movement
