CH 1: Intro to NS Flashcards
neuron (nerve cell)
constitutes the primary functional and anatomic unit of the NS
all consist of a cell body containing a nucleus and surrounding cytoplasm
dendrites
consist of afferent neuronal processes with branches that receive signals.
usually the signals consist of chemicals acting as NEUROTRANSMITTERS that interact with specific molecular receptors
these signals transiently alter the electrochemical gradient across the membrane of the dendritic process, and this transient change moves along the dendrites
axon
on a nerve cell
consists of a single fiber extending to other parts of the NS or to a muscle or gland
“axon” aplies to a fiber that conducts impulses (actively propagated electrochemical changes called ACTION POTENTIALS away from the dendrites
EFFERENT fiber or process
at its end, branches of the axon make synaptic contact with other neurons
nerve cell bodies usually cluster together
outside the brain and SC= ganglia of the PNS
within the brain and SC (CNS)= nuclei
cerebral and cerebellar cortex are made up of?
the layers (laminae) of nerve cell bodies on the surface of the cerebrum and cerebellum
gray matter
regions of the brain and SC that contain aggregations of nerve cell bodies
white matter
areas of the brain and SC that consist primarily of myelinated axons
tract=
in the CNS
groups of axons that have a common origin (cell bodies in the same nucleus) and a common destination (axonal endings in the same area of gray matter)
specific bundles of nerve fibers in the PNS=
nerve, nerve root, nerve trunk, nerve cord, and ramus
3 types of neuroglia/glial cells in the CNS=
= NEUROGLIA or GLIAL CELLS
1- astrocytes
2- oligodendrocytes
3- microglia
oligodendrocytes
form and maintainthe myelin sheaths of axons in the CNS
astrocytes
contribute in a variety of important ways to the metabolism of the CNS:
1: can’t develop APs but are highly permeable to potassium (K+) ions and become depolarized if the extracellular concentration of K+ increases.
2: take up extracellular K+ during intense neuronal activity and thereby buffer K+ activity
3: take up and store neurotransmitters- regulate extracellular concentrations of neurotransmitters
4: transfer metabolites from capillaries to the extracellular space
5: sensitive to many different insults to CNS tissue: may respond to injury with cytoplasmic swelling, accumulation of glycogen, fibrillar proliferation with the cytoplasm, cell multiplication or a combo
- they frequently have a permanent scar or plaque after destruction of neuronal elements have occurred
microglia
phagocytic cells that form part of the NS’s defense against infection and injury
nonneural cells=
neuroglia or glial cells
glial cells of the PNS
Schwann cells
satellite cells
Schwann cells
produce myelin
satellite cells
found in ganglia associated with the peripheral nerves
PNS is composed of..
12 pairs of cranial nerves
31 pairs of spinal nerves
and associated ganglia
2 types of efferent fibers of peripheral nerves
1: somatic motor fibers: terminate in skeletal muscles
2: visceral motor (autonomic) fibers: which innervate cardiac muscle, smooth muscle, glands and adipose tissue
Termination of a somatic motor fiber on a skeletal muscle fiber occurs at the?
motor end plate or neuromuscular junction
which resembles a synapse
efferent
motor
afferent
sensory
2 types of afferent fibers of PNS
each afferent fiber conducts impulses toward the SC or brain from the particular sensory receptor (touch, pain, auditory, taste)
1: somatic sensory fibers: arise in sensory receptors of the body wall (skin, muscle and bone)
2: visceral sensory fibers: arise in the internal organs and in the walls of blood vessels throughout the body
3 parts of the brain
cerebrum
cerebellum
brain stem
a deep medial longitudinal fissure separates…
the left and right cerebral hemisphere
the surface of each hemisphere is wrinkled by the presence of eminences known as?
gyri and furrows
which are called sulci or fissures
the cerebral cortex consists of..
a layer of gray matter that is 1.3-4.5 mm in thickness and covers the expansive surface of the cerebral hemisphere
this cortex is estimated to contain 14 billion nerve cells
2 major grooves on the lateral surface of the brain
central sulcus (of Rolando)
lateral fissure (of Sylvius)
how many lobes in the cerebral hemispheres?
6
1-FRONTAL LOBE (anterior to central sulcus and above lateral tissue)
2- OCCIPITAL LOBE (caudal to parieto-occipital fissure to preoccipital notch
3- PARIETAL LOBE- (extends from central sulcus to parieto-occipital fissue; separated from temporal lobe by lateral fissure)
4- TEMPORAL LOBE- (below lateral fissure)
5- LIMBIC LOBE- (a ring of cortical tissue consisting of paraterminal gyrus
6- INSULAR LOBE- consists of cortical tissue that forms the floor of the deep lateral fissure
are the gyri and sulci of the frontal, parietal, occipital and temporal lobes continuous on the medial surface of the cerebral cortex as those seen on the lateral surface??
yes
where is the cerebellum attached?
to the dorsal surface of the brain stem at the level of the pons
the surface of the cerebellum is similar to the cerebrum because it..
consists of a layer of gray matter (CEREBELLAR CORTEX) which is arranged in ridges and grooves
folia=
the ridges of cortical gray matter
the brainstem consists of..
medulla
pons
midbrain
do all pairs 12 pairs of the cranial nerves attach to the brain stem?
No
CN I (olfactory) and CN II (optic) do not
what are ventricles?
cavities within the brain
filled with cerebrospinal fluid (CSF) (produced by specialized tissue inside the ventricles called choroid plexus)
through 3 openings in the medulla, CSF flows from the ventricles into the…
subarachnoid space- which surrounds the brain and SC
what are the 3 CT membranes that enclose the CNS and constitute the meninges? (meningial layers)
1- pia matter- intimately attached to the surface of the brain and SC
2- arachnoid
3- Dura matter- tough, lines the bony cranial cavity around the brain and the vertebral canal around the SC
subarachnoid space is located ..
between the pia mater and the arachnoid (2 layers of the 3 CT membranes that enclose the CNS
the SC is anchored through the arachnoid to the dura mater by…
paired lateral septa of pia called DENTICULATE LIGAMENTS
the SC is divided arbitrarily into 5 regions..
cervical thoracic lumbar sacral coccygeal
enlargements in the lower cervical region and in the lumbosacral region of the SC contain..
the cell bodies of nerve fibers supplying the upper and lower limbs
spinal nerves are attached to the SC in pairs:
8 cervical pairs 12 thoracic pairs 5 lumbar pairs 5 sacral pairs 1 coccygeal pair
each nerve is formed by..
the union of dorsal root and a ventral root
a dorsal root is composed of?
sensory or afferent fibers
the sensory fibers of the dorsal root are processes of sensory neuron cell bodies in the dorsal root ganglia
a ventral root is composed of?
motor or efferent fibers
the motor fibers in the ventral root are axons of neuron cell bodies in the spinal cord
conus medullaris=
the tapered end of the SC since it does not extend to the lowest level of the bony vertebral canal but rather ends at the level of the lower border of the 1st lumbar vertebra
because the SC is ~25 cm shorter than the verebral column, the lower segments of the SC are not aligned opposite corresponding vertebrae–> the lumbar and sacral spinal nerves have very long roots, extending from ther respective segments in the SC to the lumbar and sacral INTERVERTEBRAL FORAMINA
filum terminale=
the pia mater that continues caudally as a CT filament over the conus medullaris
it passes through the subarachnoid space to the end of the dural sac at the level of vertebra S1 where it receives a covering of dura and continues to its attachment to the coccyx
at each intervetebral foramina…
a dorsal root and a ventral root join to form a spinal nerve
the spinal nerve roots descend in a bundle from the conus (resembles the tail of a horse)= CAUDA EQUINA
cauda equina=
a bundle of spinal nerves descending from the conus medullaris
the white matter of the SC gets divided into?
dorsal, lateral and ventral funiculi
by the dorsal median sulcus, ventral median fissure, dorsolateral and ventrolateral sulcus
the ratio of white matter to gray matter in the SC is greater at..
at cervical levels because the white matter in the cervical region contains fibers connecting the entire SC with the brain- fibers must pass through ( the lumbosacral cord contains only fibers serving the caudal end of the SC
gray matter of the SC contains..
dorsal and ventral horns and small lateral horns (found in the thoracic and upper lumbar segments
ventral horns are larger in the…
cervical and lumbosacral regions than in the thoracic region because the muscle mass of the limbs is greater than that of the trunk and these horns are made up largely of cell bodies of neurons that innervate skeletal muscles
laminae=
distinctive layers or “laminae”, are arranged from dorsal to ventral within the gray matter (longitudinal cell columns when the SC is cut along its length)
each lamina extends the length of the cord
lamina I-VI are confined to the dorsal horn (lamina I is the most dorsal)
lamina IX is restricted to the ventral horn and consists of several different columns of cells
cells in laminae I-VI..
receive and transmit information concerning sensory input from the spinal nerve afferents
fiber pathways from other SC levels and the brain also synapse on cells in these laminae
the columns of cells in lamina XI consist of..
each cell column consists of alpha, beta and gamma motoneurons which send their axons into the ventral roots of the spinal nerves and innervate skeletal muscles
the adult human NS originates in the?
ectoderm of the embryo
initially, a rostrocaudal groove appears in the midline of the embryonic ectoderm, then…
this NEURAL GROOVE is flanked by NEURAL FOLDS which then close to form a NEURAL TUBE
the rostral end of this tube develops into the brain and the remainder differentiates into the SC
the neural tube closes first at the..
level destined to be the upper cervical region of the SC
from this point, closure proceeds both rostrally and caudally
the final closure at the ends of the neural tube typically occurs during?
the 4th week of embryonic life
partial or complete failure of closure of the posterior neuropore results in?
spina bifida- a common deveopmental abnormality
the tissue comprising the neural tube contains several different types of cells..
neuroblasts- primordial neurons
glioblasts- primordial astrocytes and oligodendrocyts
the single layer of cells lining the tube later becomes the?
ependyma- which lines the ventricles of the adult brain
ectodermal tissue lateral to the neural tube constitutes the?
NEURAL CREST
a collection of cells that differentitate into the neurons and glia of the PNSas well as a variety of nonneural structures
elements derived from the neural crest ultimately give rise to autonomic ganglia and most of the sensory ganglia of the body and head as well as glial cells of the PNS
development of the brain begins with differentiation of 3 swellings/vesicles as the rostral end of the neural tube:
prosencephalon
mesencephalon
rhombencephalon
5 vesicle stage of development consists of
the first 3 of these vesicles eventually differentiate into the cerebral hemispheres
telencephalon
diencephalon: thalamus & hypothalamus & midbrain
mesencephalon:
metencephalon: becomes the cerebellum & pons
myelencephalon: becomes the medulla oblongata
the arrangement of 5 vesicles is established by the time the embryo is
6 weeks
what is the major change in form that produces the adult human brain after 6 weeks?
tremendous growth of the cerebral hemispheres and cerebellum relative to other parts of the brain
