Nervous System Flashcards
What is the CNS encased in?
The CNS (brain and spinal cord) is encased in connective tissue layers, the meninges, but CNS tissue contains very little collagen, making it soft and easily damaged by injuries.
What does white matter contain?
White matter includes myelinated axons, often grouped together as tracts, and the myelin-producing oligodendrocytes.
What does gray matter contain?
Gray matter contains abundant neuronal cell bodies, dendrites, astrocytes, and microglial cells, and is where most synapses occur.
The major structures of the CNS
The major structures
comprising the CNS are the cerebrum, cerebellum, spinal cord, and brain stem
Nerve cell bodies of the CNS
Nucleus (mostly brain)
Nerve cell bodies of the PNS
Ganglion
Nerve cell fibers of the CNS
Tract (mostly spinal cord)
Nerve cell fibers of the PNS
Nerve
The major structures of the PNS
Cranial nerves, spinal nerves, and ganglia
Cauda Equina
The long bundle of nerves that extend to form lumbar, coccygeal, and sacral spinal nerves.
Clinically important because of lumbar punctures (spinal tap) used to access subarachnoid space
The two anterior projections (horns) of gray matter in the spinal cord
Contain cell bodies of motor neurons whose axons make up the ventral roots of spinal nerves.
The two posterior projections (horns) of gray matter in the spinal cord
Contain interneurons which receive sensory fibers from neurons in the spinal
(dorsal root) ganglia.
What does the central canal develop from?
Near the middle of the cord the gray matter surrounds a
small central canal, which develops from the lumen of
the neural tube, is continuous with the ventricles of the brain, is lined by ependymal cells, and contains CSF
The dorsal root of spinal
cord contains what fibers?
The dorsal root of spinal
cord has only sensory
fibers.
The ventral root of spinal
cord contains what fibers?
The ventral root has only
motor fibers.
What do the fibers of the dorsal and ventral roots become?
The fibers of the dorsal and ventral roots mix together, and then divide distally into the posterior (dorsal) ramus and anterior (ventral) ramus. Each ramus has a mixture of sensory and motor fibers.
Meningeal layers
Dura mater (most external), Arachnoid, Pia mater (most internal)
What is in the subarachnoid space?
CSF
Extradural or Epidural Hermatoma
Blood from torn branches of a middle meningeal
artery collects between the external periosteal layer of the dura and the skull bones, usually after a blow to the head.
Dural border or Subdural Hematoma
Classically is called a subdural hematoma; however, this term is a misnomer because there is no naturally occurring space at the dura-arachnoid junction. The “space” is called a potential space. The blood creates a
space at the dura-arachnoid junction.
Subarachnoid hemorrhage
An extravasation (escape) of blood, usually arterial, into the subarachnoid space, where CSF is found.
Blood-brain Barrier (BBB)
Allows very tight control of the passage of substances from blood into the CSF of the CNS. It is extremely important clinically because it blocks or slows down the transport of many types of
drugs, such as those that might be used to treat Alzheimer’s, Parkinson’s
Disease and brain cancer, into the brain.
Choroid Plexus
Removes water from blood and releases it as the CSF (cerebrospinal fluid); in this sense, it “produces” CSF.
Choroid Plexus location and composition
The choroid plexus consists of folds of highly vascular tissue, projecting into the large ventricles of the brain. Ependyma and vascularized pia mater
It is found in the roofs of the third and fourth ventricles and in
parts of the two lateral ventricular walls.
Node of Ranvier (or nodal gap)
The gap between two
Schwann cells.
These regions are uninsulated and but rich in ion channels, allowing them
to regenerate the action
potential.
Endoneurium
Surround axons and Schwan cells
Perineurium
Surrounds fascicles or bundles of nerve fibers
Epineurium
Surrounds multiple fascicles of nerve fibers.
Ascending Tracts (Afferent/Sensory)
Conscious tracts – The dorsal column-medial lemniscal pathway and the anterolateral system,
for touch and some types of proprioception.
Unconscious tracts – The spinocerebellar tracts, for muscle proprioception.
Dorsal column–medial lemniscus pathway (DCML)
Conveys sensations of fine touch, vibration, two-point discrimination, and proprioception (position) from the skin and joints.
Spinothalamic tract (part of the anterolateral system)
The spinothalamic tract consists of two pathways: anterior and lateral. The anterior spinothalamic tract
carries information about crude touch. The lateral spinothalamic tract conveys pain and temperature.
Spinocerebellar tracts
Carry unconscious proprioceptive information from the muscles to the
cerebellum. We cannot mentally acknowledge these signals, but they help the brain coordinate and refine motor actions.
Somatosensory Cortex of the brain
Postcentral Gyrus
Somatomotor Cortex of the brain
Precentral Gyrus
Descending Tracts (Efferent/Motor)
Pyramidal tracts and Extrapyramidal tracts
Pyramidal tracts
Originate in the cerebral cortex, carrying motor fibers to the spinal cord
and brain stem. They are responsible for the voluntary control of the musculature of the
body and face.
Extrapyramidal tracts
Originate in the brain stem, carrying motor fibers to the spinal cord. They are responsible for the involuntary and automatic control of all musculature, such as muscle tone, balance, posture and movement.
Autonomic Nervous System (ANS)
It is structurally a division of the peripheral nervous
system that supplies smooth muscle and glands,
and influences the function of internal organs.
It is functionally a system that acts unconsciously
to regulate “visceral” bodily functions.
Two divisions of ANS
Sympathetic and Parasympathetic
Parasympathetic Nervous System
A division of the ANS used for “rest-and-digest” or “feed-and-breed.”
Structure: The parasympathetic division has craniosacral “outflow,” meaning that the neurons begin at the cranial nerves (ie, the oculomotor nerve, facial nerve, glossopharyngeal nerve
and vagus nerve) and sacral (S2-S4) spinal cord.
Sympathetic Nervous System
A division of the ANS used for “fight-or-flight-or-freeze.”
Structure: The sympathetic division has thoracolumbar
“outflow,” emerging from the spinal cord in the thoracic and lumbar areas, terminating around L2-L3
Which of these general effects is associated with the sympathetic division of the ANS?
Quick response
The pia mater is closely applied to the entire surface of the CNS tissue. What is its function?
It forms a physical barrier separating CNS tissue from CSF in the subarachnoid space.
Which type of glial cells are associated with ganglia?
Satellite cells
The central canal of the spinal cord and the ventricles of the brain are formed from the embryonic ____________
Neural tube
The Nodes of Ranvier contribute to saltatory conduction. Which is true?
In saltatory conduction the action potential is faster than that in unmyelinated fibers.
Ganglia are clusters of neuron cell bodies in the PNS. In the CNS, clusters of neuron cell bodies are called
Cerebral nuclei
Where in the brain is the somatosensory cortex located?
Postcentral gyrus
Where is the choroid plexus found?
In the roofs of the 3rd and 4th brain ventricles
