Neuroanatomy Exam 2 Flashcards
Why are arteries black on a T2 weighted MRI?
Fluids are usually white on a T2 MRI. However, the blood within arteries is moving relatively quickly, which makes it appear darker on the image.
What regions of the brain (think vesicles) do the internal charotid arteries supply?
Most of the telencephhalon and diencephalon
What does the vertebral system supply?
Brainstem, cerebellum and parts of the diencephalon, spinal cord, and occipital and temporal lobes
Desrcibe the path the internal chharotid artery takes to reach the brain.
Ascends through each side of the neck, traverses the petrous temporal lobe, passes through the cavernous sinus, and finally reaches the subarachnoid space at the base of the brain
What is the ophthalamic artery?
Off shute of the internal charotid artery as it leaves the cavernous sinus. This artery travels along the optic nerve to th orbit to supply the eye and other orbital structures.
What happens after the internal charotid artery passes the optic chiasm?
Bifurcates into the middle and anterior cerebral arteries
Which artery is often involved in cerebrovascular accidents?
The anterior choroidal artery
What artery supplies the amygdala and portions of the internal capsule?
Anterior Choroidal Artery
What artery supplies the optic tract?
Anterior Choroidal Artery
What artery supplies the choroid plaxus of the inferior horn of the lateral ventricle?
Anterior Choroidal Artery
Describe the general travel of the posterior communicating artery.
Passes posteriorly, inferiorily to the optic tract and toward the cerebral peduncle. Joins the posterior cerebral artery
What connects the two anterior cerebral arteries?
Anterior Communicating Artery
What structure does somatosensory information have to pass through going from the thalamus to the somatosensory cortex?
The internal capsule
What are lenticulostriate arteries?
Branches of the middle cerebral artery that penetrate the brain near their origin and supply deep brain structure of the telencephalon and diencephalon
Where doo the two vertebral arteries fuse to give rise to the basilar artery?
At the junction of the pons and medulla
What branches does the vertebral artery give rise to?
Posterior Spinal Artery
Anterior Spinal Artery
Posteriior Inferior Cerebellar Artery
(Each one gives rise to these 3)
What does the posterior spinal artery supply?
The posterior third of the spinal cord
What does the anterior spinal artery supply?
Anterior two thirds of the spinal cord
What does the posterior inferior cerebellar artery (PICA) supply?
Much of the interior surface of the cerebellar hemispheres
What artery supplies the more anterior portions of the inferior surface of the cerebellum (like the Flocculus) and parts of the caudal pons?
Anterior Inferior Cerebellar Artery (AICA)
What does the superior cerebelar artery supply?
the superior surface of the cerebellum and much of the caudal midbrain and rostral pons
What artery supplies the inner ear?
Internal auditory/labyrinthine artery; occlusion can lead to vertigo and ipsilateral deafness
Which artery sends branches to the thalamus and the splenium?
Posterior Cerebral Artery
What do the posterior choroidal arteries supply?
Choroid plexus of the third ventricle and body of the lateral ventricle
What is cerebral angiography?
uses the intravenous injection of iodinated dyes to make blood much more opaque than brain to x-rays
What is autoregulation?
A way to control cerebral blood flow. Arterial and arteriolar smooth muscle cells are directly stretch sensitive, so the vessels constrict (thus increasing their resistance) in response to increased blood pressure, and they relax in response to decreased pressure
What types of vibers innervate cerebral vessels?
sympathetic autonomic fibers and fibers from several locations within the brain
What is an ischemic infarct?
A necrotic region of tissue resulting from the lack of blood supply
What are the two types of strokes?
Hemorrhagic and Ischemic Infarct
What is a hemorhhagic stroke?
due to either a bursting of a brain aneurysm (an excessive localized enlargement of an artery) or a weakened blood vessel leak
What is the difference between a transient ischemic stroke and an ischemic stroke?
deficits associated with a transient ischemic attack (as the name implies) persist for only a few minutes to a few hours and are followed by an essentially complete recovery
What are the three regions of the blood brain barrier?
(1) the arachnoid barrier layer
(2) the blood–cerebrospinal fluid (CSF) barrier
(3) the true blood brain barrier
What is the Blood-CSF barrier formed by?
tight junctions of the choroid epithelial cells
What forms the “true blood brain barrier”?
rows of tight junctions between adjacent endothelial cells of CNS capillaries together with a lack of pinocytotic vesicles in these endothelial cells
How is the blood-CSF barrier selective?
Lipid-soluble substances can diffuse across it, and glucose can cross it by a process of facilitated diffusion, but other molecules of similar size and solubility cannot. In addition, various substances can be actively transported in both directions across this endothelial wall.
What are circumventricular organs?
Locations where cerebral capillaries are fenestrated and allow free communication between the blood and the brain’s extracellular fluid.
Areas lakcing the red line on the attached picture are where there is no BBB
Name the 6 circumventricular organs
Pineal Gland, Median Eminence (of the hypothalamus), posterior lobe of the pituitary gland, area postrema of the brainstem, and the subfornical organ and lamina terminalis of the hypothalamus
What are tanycytes?
Specialized ependymal cells that overlie each circumventricular organ and form a barrier b/w the organ and the ventricular CSF
What do the dural venous sinuses ultimately drain into?
The internal jugular veins
What is unique about cerebral veins as compared to veins in the rest of the body?
They are valveless
The superficial veins drain the lateral surfaces of the cerebral cortex by way of the….
Superior Sagittal Sinus
The blood-brain barrier (BBB) is present in
The arachnoid barrier and the endothelial cells within the brain parenchyma
What are sensory receptor?
cells that detect various stimuli and produce receptor potentials in response
What are interoceptors?
monitor events within the body, such as distention of the stomach or changes in the pH of blood
What ar exteroceptors?
respond to stimuli that arise outside the body, such as the receptors involved in touch, hearing, and vision
What are nociceptors?
Receptors that respond to pain
What is receptor adaptation?
receptors become less sensitive during the course of a maintained stimulus; can be slowly adapting (don’t change sensitivty much) or rapidly adapting
What are the three parts of a sensory receptor?
1) Receptive Area
2) Area rich in mitochondria (near receptive area)
3) Synaptic Area
Where do the cell bodies of somatosensory receptors lie?
The dorsal root ganglia of the spinal cord
Where do the central processes of somatosensory receptors terminate?
Either in the spinal cord, or in the brainstem
What is a capsule on a receptor?
serves as a mechanical filter, modifying mechanical stimuli before they reach the sensory ending. For example, receptors with layered capsules are rapidly adapting, in large part because of these mechanical properties of the capsules. The capsules also have barrier properties
What is a merkel ending?
found in hairy and non-hairy skin. Terminates on a Merkel Cell which is situated in the basal layer of the skin. It is VERY sensitive to deformation (and general tactile information such as pressure, indentation, etc.)
What are Meissner Corpuscles?
Located in the dermal paillae of hairless skin just beneath the epidermis (responds to touch). It is encapsulated and rapidly adapting.
What are Meissner Corpuscles primarily responsible for?
Feeling pressure; work with merkel endings to perform fine tactile discriminations with FINGERTIPS
What type of receptor is reposnible for feeling vibrations?
Pacinian Corpuscle; the’re also all over the body.
What are polymodal nociceptors?
Nociceptors that respond to multiple modalities (intense mechanical stimuli, high levels of heat or cold, and chemicals released by damaged tissues - these are three modalities, like different types of pain)
What are delta fibers?
Fast conducting (myelinated) fibers for pain, reponsible for that initial sharp feeling of pain
What are C fibers?
Unmyelinated fibers that are slow to conduct pain information, thus resulting in an aching pain usually following an abrupt pain.
What receptors supply muscles?
Muscle spindles
Golgi Tendon Organ (similar to Ruffini Ending)
**These are both encapsulated**
What are muscle spindles?
long, thin stretch receptors scattered throughout almost every striated muscle in the body. These muscle spindles sense muscle length and proprioception
What are the two types of intrafusal muscle fibers?
Nuclear Chain Fibers: nuclei are lined up single file
Nuclear Bag Fibers: nuclei are not single file, they are several apart
What are the two types of sensory endings in the muscle spindle?
1) Primary Ending
2) Secondary Ending
Describe primary endings in muscle spindles.
Selectively sensitive to the onset of muscle stretch but discharge at a lower rate while the stretch is maintained. Sensitive to vibration
Describe secondary endings in muscle spindles
Less sensitive to onset of stretch, but discharge rate does not decline much while stretch is maintained
What are alpha motor neurons?
large motor neurons that supply extrafusal muscle fibers in muscle spindle
What are gamma motor neurons?
the smaller motor neurons supplying the contractile portions of intrafusal fibers
What do golgi tendon organs detect?
Muscle tension; make fine adjustments in muscle tension when called for (such as when handling a raw egg)
T/F: Extensions of the Meninges Envelop Peripheral Nerves
True (see picture)
What does the perineurium form?
perineurial cells are connected to one another by tight junctions - isolate the epineurial spaces from the endoneurial spaces around peripheral nerve fibers. The endothelial cells of capillaries within the perineurium are connected to one another by tight junctions too.
FORMS BLOOD-NERVE BARRIER
How does axon diameter relate to conductance?
Larger diamters mean faster conductance
What are A fibers?
Myelinated sensory and motor fibers
What are B Fibers?
Myelinated visceral fibers, preganglionic autonomic fibers and some visceral afferents (toward CNS).
What are C fibers?
Unmyelinated and the slowest out of the A, B and C fibers
Where do the dorsal rootlets enter on the spinal cord?
The posterolateral sulucs
Where do the ventral rootlets exit on the spinal cord?
The anterolateral sulcus
What does the dorsal root ganglion contain?
the cell bodies of the primary sensor neuons
What is the conus medullaris?
Caudal enlargment due to the presence of an increased number of motor and interneurons.
What does the lumbar enlargementt supply?
The lower extremeties
Each spinal cord segment innervates a……
Dermatome
What is a dermatome?
A systematic pairing of a spinal cord segment (and nerves) to areas of skin, muscles, and sometimes bones
How can understanding the segmental innervation of muscles be beneficial in diagnosing the site of damage in or near the spinal cord?
As an example, compression of a dorsal root (sennosry neurons) can cause pain in its paired dermatome. This allows pain to be distinguished between peripheral nerve damage versus an actual pinching in the spinal cord. You can memorize what sgement goes with which dermatome.
Which grows longer; the spinal cord or the vertebral column?
Ultimately, the vertebral column grows longer than the spinal cord
What is the impact of the vertebral canal growing longer than the spinal cord?
Proceeding from cervical to sacral levels, the dorsal and ventral roots become progressively longer because they have longer and longer distances to travel before reaching their sites of exit from the vertebral canal.
There is also the formation of the lumbar cistern.
What is the lumbar cistern?
A cistern (filled with CSF) that contains a collection of free danling dorsal and ventral roots. Collectively, because they are free floating on one end, they are known as the cauda equina because it resembles a horse’s tail
Where do each of the first seven cervical canals leave the vertebral canal?
Above the corresponding vertebra. So, for example, the second cervical nerve leaves between the first and second vertebra, the third leaves between the second and third and so on.
Where does the leaving of nerves change from above the corresponding vertebra to below?
The eight cervical nerve leaves between the seventh cervical and the first thoracic vertebrae, and each of the subsequent nerves leaves below the corresponding vertebrae.
What are denticulate ligaments?
Exetensions of pia-arachnoid that suspend the spinal cord within an arachnoid-line dural tube
What is the filum terminale?
Anchors the caudal end of the cord to the end of the dural tube in which it is suspended
How do afferent fibers enter the cord?
Via dorsal roots
Describe the projection of dorals roots to the cortex
may reach their site of termination either by synapsing on neurons in the ipsilateral gray matter of the spinal cord or by ascending directly and uncrossed to relay nuclei in the medulla. The relay cells in the spinal gray matter or the medulla then project their axons through defined sensory pathways to more rostral structures
Where are motor neurons located in the cord?
In the anterior horns
Describe how motor neurons “leave” the spinal cord
Project their axons via the ventral roots
What type of matter corresponds to the horns of the spinal cord?
The gray matter
What ype of matter corresponds to the funniculi of the spinal cord?
The white matter
The posterior horn consists mainly of…..
1) Sensory Interneurons whose processes remain within the spinal cord
2) Projection neurons whose axons collect into long, ascending pathways
What are the two parts of the posterior horn?
Substantia Gelatinosa and the Body of the posterior horn (both are present at all levels of the cord)
What is the substantia gelatinosa?
A distinctive region of gray matter that caps the posterior horn
What types of sensory information is generally assoiciated with the region of the substantia gelatinosa?
Pain and Temperature
Why does the substantia gelatinosa look pale in myelin stains?
Compared with the rest of the gray matter, the SG is severely defficient in myelin. The sensory fibers are mostly unmyelintaed with some fine myelination.
What kind of information is transmitted through the body of the posterior horn?
Transmits various types of somatic and visceral sensory information.
What kind of neurons are contained in the anterior horn?
Cell bodies of large Motor neurons that supply skeletal muscle (known as alpha motor neurons and referred to as lower motor neurons)
How do alpha motor neurons generally appear on cross sections and how are they arranged?
Appear as clusters separated from each other by areas of interneurons
The clusters that innervate axial muscles are medial to those that innvervate limbs
What does the intermediate gray matter contain?
Autonomic Neurons (spinal preganglionic autonomic neurons). At some levels of the cord, it includes Clarke’s Nucleus.
What is clarke’s nucleus?
A rounded collection of large cells located on the medial surface of the based othe posterior horn. Relays information to the cerebellum and may play a role in forwarding proprioceptive information (from the leg) to the thalamus
What is reciprocal inhibition?
Reflex activity in a given muscle produces similar activity in its ipsilateral synergists and the opposite activity in its ipislateral antagonists
What are the three nerve fiber types in the white matter of the spinal cord?
- Long, ascending fibers projecting to the thalamus, the cerebellum, or assorted brainstem nuclei
- Long, descending fibers projecting from the cerebral cortex or from several brainstem nuclei to the spinal gray matter
- Shorter propriospinal fibers interconnecting different spinal cord levels, such as the fibers responsible for the coordination of flexor reflexes
Where are descending tracts primarily found?
Lateral and Anterior Funiculi
T/F: When the primary afferents of the posterior columns (Posterior Column - Medial Lemniscus system) terminate in the posterior column nuclei, they maintain their somatotopic organization.
True. For example, the fine touch “shape” is maintained from periphery to CNS
What happens if the medial lemniscus system is damaged via damage to the posterior column?
Impairment, not complete abolition, of touch, pressure, and vibration
Proprioception is completely lost resulting in ataxia (uncordinated movement)
What is stereognosis?
Being able to use somatosensory information to identify objects. Usually very impaired/lost with damage to the Posterior Column
What does the spinothalamic tract convey?
Information about pain and temperature
What is the anterolateral pathway?
Tracts, including the spinothalamic tract, that travel together to convey nociceptive information.
Tracts include the spinoreticular fibers, spinomesencephalic fiber, and the spinohypotahalmic fibers
What are spinoreticualr fibers more responsive to?
Part of the spinothalamic tract, this system is more likely to be important for changes in level of attention in response to pain.
What would happen if the anterolateral system is damaged?
Decreased perception of pain and temperature sensations
What happens if the spinothalamic tract is damaged?
Contralateral analgesia would result
What is the posterior spinocerebellar tract?
Conveys proprioceptive information to the cerebellum ipsilaterally to medial zones through the inferior cerebellar peduncle.
What is the posterior spinocerebellar tract principally concerned with?
The ipsilateral leg
What cells give rise to the anterior spinocerebellar tract?
Cells on the lateral surface of the lumbar anterior horn, called spinal border cells
Does the spinocerebellar tract cross the midline?
No, it ends ipislaterally
Where does the anterior spinocerebellar tract cross the midline?
At the level of the spinal cord
What do the corticospinal tracst mediate?
Voluntary movement
What are corticospinal tracts?
Fibers from the precentral gyrus and other nearby cortical areas that descend through the:
1) Cerebral Peduncles
2) Pons
3) Medullary Pyramids
How is the lateral corticospinal tract formed?
From the pyramidal decussation of the cortiospinal tracts
What are alpha motor neurons?
Neurons that directly contact striated muscle (also called lower motor neurons).
Why are alpha motor neurons so important?
They are the only means by which the nervous system can exercise control over body movements
How is the anterior corticospinal tract formed?
From corticospinal fibers in each pyramid that do NOT cross the pyramidal decussation
T/F: The anterior corticospinal tract affects the activity of motor neurons for medial muscles
FALSE: Anterior Corticospinal Tracts affect the acitivity of motor neurons for axial muscles
What are the three subdivions of the autonomic nervous system?
The sympathetic, parasympathetic, and enteric nervous system.
How do sypmathetic and parasympathetic efferents reach their targets?
Indirectly though a two-neuron chain. First neuron has its cell body in the CNS (preganglionic neurno). Its axon terminates in a peripheral ganglion on the second neuron, called the postganglionic neuron
Are postganglionic fibers myelinated?
No, they are unmyelinated
Where do preganglionic parasympathetic fibers originate?
From neurons in the brainstem and the sacral spinal cord
Where are preganglionic sympathetic neurons located?
In thoracic and lumbar spinal segments
What is the reticular formation?
A set of interconnected nuclei responsible for integration of complex motor patterns, aspects of respiratory and cardiovascular activity, and some regulation of consciousness.
It forms the central core of the brainstem
Name the parts of the Medulla
Pyarmids, Olives, and part of the 4th ventricle
What does the cuneate tubercle mark?
Site of the nucleaus cuneatus (Fasciculus Cuneatus)
What does the gracile tubercle mark?
The site of nucleus gracilis
What does the facial colliculus mark (medulla)?
Location of the abducens nucleus
Name the parts of the pons
Includes the Basal Pons, Middle Cerebellar Peduncles, and part of the fourth ventricle
Name the parts of the midbrain
Includes the superior and inferior colliculi, the cerebral peduncles, and the cerebral aqueduct
Name this structure
This is the Medulla
Name this structure
This is the pons
Name this structure
This is the midbrain
Where do the posterior columns terminate?
In the posterior column nuclei (Nucleus Gracilis and Nucleus Cuneatus)
Efferent fibers from the posterior nuclei decussate in the medulla to form the…..
Medial Lemniscus (which reaches the thalamus)
Where does the medial lemniscus form?
In the caudal medulla
The lateral cuneate nucleus deals with what area of extremeties?
The upper extremeties
The rostral medulla contains….
Inferior Oliveray Nucleus and part of the fourth ventricle
What attaches the caudal pons to the cerebellum?
The middle cerebella peduncle
What joins the brainstem in the rostal pons?
The superior cerebellar peduncle
The Superior Cerebellar Peduncles Decussate in the…..
Caudal Midbrain
The rostral midbrain contains the…..
Red Nucleus and Substantia Nigra
Where do spinomesenphalic fibers terminate?
In the periaqueductal gray, adjacent regions of the reticular formation and parts of the superior colliculus
What is the medial zone?
Source of most of the long ascending and descending projections from the reticular formation
What is the lateral zone (in the reticular core)?
Primary concern is cranial nerve reflexes and visceral functions
What is the reticulospinal tract?
Alternative route by which spinal motor neurons are controlle; has direct influence and regulates sensitivity of spinal reflex arcs
The reticulospinal tracts carry descending motor commands generated within the…..
Reticular Formation
The Reticular Formation Modulates…..
Transmission of information in pain pathways
Does the reticular formation contain autonomic reflex circuitry?
Yes, centers controlloing heart rate and blood pressure have been found in the medullary RF
Neurons of the Locus Ceruleus contain….
Norepinephrine
What is the locus ceruleus?
Collection of pigmented cells near the floor of the fourth ventricle; contains noradrenergic neruons
What role does the locus ceruleus play?
Maintaining attention and vigilance
Neurons of the Raphe Nuclei contain….
Serotonin; innervates almost all parts of the CNS
Neurons of the Rostral Brainstem and Basal Forebrain contain….
Acetylcholine
What is the significance of acetylcholine?
Used by alpha and gamma motor neurons in the PNS, preganglionic autonomic neurons, and postganglionic parasympathetic neurons.
What is the basal forebrain?
Area at and near the inferior surface of the telencephalon, between the hypothalamus and the orbital cortex
What are muscarnic receptors?
G-coupled acetylcholine receptors involve in peristalsis, micturation, bronchoconstriction, and other PARASYMPATHETIC actions (act slowly)
What is the basal nucleus?
Major collection of forebrain cholinergic neurons
The brainstem is supplied by what artery system?
The Vertebral-Basilar System
What are somatic sensory fibers (cranial nerve)?
Convey information from receptive endings for pain, temp, and mechanical stimuli in somatic structures such as skin and muscles.
What are visceral sensory fibers?
Convey information from receptive endings in visceral structures such as the walls of blood vessels
What are visceral motor fibers?
Preganglionic autonomic axons
What are somatic motor fibers?
Innervate skeletal muscles (they are the axons of alpha and gamma motor neurons)
Cells concerned with visceral functions tend to be (closer/farther) to/from the sulcus limitans
Closer
What detects muscle tension?
Golgi Tendon Organs
Describe the morphology of Golgi Tendon Organs
Large diameter, afferent, encapsulated
