Nervous System- Neuroscience By Wells

Front 1

Nervous System- Neuroscience Review by Wells

Back 1

Nervous System- Neuroscience Review by Wells

Front 2

parts of the brain

Back 2

forebrain (telencephalon and diencephalon)

midbrain (superior and inferior colliculus, crus cerebri, and peduncles)

hindbrain- cerebellum, pons, medulla

Front 3

parts of telencephalon

Back 3

neocortex
hippocampus
internal capsule

Front 4

parts of diencephalon

Back 4

thalamus
hypothalamus

Front 5

where is broca's area?

Back 5

posterior inferior frontal gyrus (there's a superior, middle and inferior frontal gyrus)

Front 6

precentral gyrus is the

Back 6

primary motor cortex (moving your mouth, coordinating it)

Front 7

where is the primary somatosensory cortex?

Back 7

postcentral gyrus

Front 8

where is wernicke's area?

Back 8

superior temporal gyrus (there's also a middle and inferior temporal gyrus)

sometimes wernicke's goes out of the temporal lobe and into the parietal lobe.

language, and syntax and vocabulary (language comprehension, while broca's does the motor portion)

Front 9

what is the primary visual cortex?

Back 9

calcarine fissure

Front 10

where is the internal capsule

Back 10

lateral border of the diencephalon

if you see thalamus, you're dealing with the posterior limb of the internal capsule.also, if you see the basal ganglia (globus pallidus), you're at the posterior limb

Front 11

considering its location, what can a pituitary tumor push up against and create pathologies with?

Back 11

the optic chiasm. cause visual field loss.

Front 12

what comes out of the interpeduncular fossa?

Back 12

CN III

Front 13

if there's pressure on the superior portions of the skull, how can it be relieved?

Back 13

forcing the temporal lobes down into the tentorium. that's bad. another thing that's going to happen is that medial surface of the temporal lobe (in particular the uncus) will squish down and push on CN III and the crus cerebri.

you'll end up with contralateral motor neuron issues and CN III issues.

Front 14

AKA TIME:

Forebrain
midbrain
hindbrain
cerebellum
pons
medulla

Back 14

prosencephalon
mesencephalon
rhombencephalon
metencephalon (cebebellum and pons)
myelencephalon (medulla)

Front 15

parts of the posterior funiculus and function

Back 15

parts of dorsal column
gracile fasciculus
cuneate fasciculus

involved in touch, vibration, proprioception

Front 16

lateral funiculus parts and function

Back 16

lateral corticospinal tract- clinically most important descending motor tract
-contains axons that already crossed the midline then synapse in ventral horn to activate the lower motor neurons in the ventral horns

rubrospinal tract (fibers)- bicep curls, and that's it (upper arm flexion means the lateral corticospinal tract is damaged somewhere above the rubrospinal tract which starts in the midbrain)

lateral spinothalamic tract (aka anterolateral system)- carries pain and temperature information

Front 17

dorsolateral tract carries what

Back 17

carries branches of the first order pain neurons

aka Lissauer's tract

Front 18

Dorsal Column/ Medial Lembiscus Pathway carries what? Includes which receptors?

Back 18

Dorsal column/ medial lemniscus pathway:
Carries information concerned with fine touch, proprioception, vibration.

Sensory receptors involved include:
Pacinian corpuscles
Joint receptors
Ruffini corpuscles
Meissner’s corpuscles
Golgi tendon organs
Muscle spindles

Peripheral processes of dorsal root ganglion cells provide axons to these receptors. Axons pick up information from the receptors and project to spinal cord.

Front 19

Talk about the organization of the dorsal root ganglion (DRG) and the posterior funiculus

Back 19

Central processes of dorsal root ganglion (DRG) cells enter the spinal cord in the posterior horn and enter the posterior funiculus.
 
As fibers (axons) from higher levels of the cord enter the posterior funiculus, they assume a more lateral position. Ultimately, this provides a somatotopic organization to the posterior funiculus such that sacral fibers are most medial, cervical fibers are most lateral, and lumbar and thoracic fibers occupy intermediate positions.

The posterior funiculus on each side is divided by the posterior intermediate septum above T7 into two separate fasciculi - fasciculus gracilis (medial) and fasciculus cuneatus (lateral).

Front 20

at which levels do you see the gracilis and cuneatus fasciculi?

where do these fibers terminate (synapse) and what happens afterwards?

Back 20

Fasciculus gracilis - present at all spinal levels - contains long ascending branches of fibers from sacral, lumbar and lower 6 thoracic dorsal roots.

Fasciculus cuneatus - first appears around T7 - contains long ascending branches of fibers from upper 6 thoracic and all cervical dorsal roots.

Neurons in dorsal root ganglion which send their central processes ascending in fasciculus gracilis and cuneatus are considered to constitute the 1st order neuron for this pathway.

Fibers in the fasciculus gracilis and cuneatus ascend ipsilaterally and terminate (synapse) on nuclei in the medulla - the nucleus gracilis and nucleus cuneatus, respectively.

Nucleus gracilis and cuneatus give rise to 2nd order fibers which project ventromedially as internal arcuate fibers.

Front 21

ok, so what do these internal acruate fibers do from there?

so where does the touch, proprioception, vibration fibers cross the midline? if there's an injury, what does this mean?

Back 21

Internal arcuate fibers decussate (cross the midline) and form a compact fiber bundle located on each side of the brain stem – the medial lemniscus.
 
The medial lemniscus ascends through the contralateral half of the brain stem, and its fibers terminate in the ventral posterolateral (VPL) nucleus of the thalamus.
 
From VPL of thalamus, 3rd order neurons send fibers to postcentral gyrus of cerebral cortex (somatosensory cortex).

cross the midline in the MEDULLA. damage in this pathway inferior to the crossing will cause IPSILATERAL sensory loss, and damage in the pathway at the medulla or above will give CONTRALATERAL sensory loss.

Front 22

where do the third order neurons going from the thalamus to the post central gyrus travel through?

Back 22

the posterior limb of the internal capsule.

Front 23

What does the Anterior Lateral System do?

what does these crazy first order neurons do?

Back 23

Three neuron pathway:
First order neuron- DRG neurons (A-delta and C fibers)
Second order neuron- neuron in dorsal horn to VPL
Third order neuron- VPL to somatosensory cortex



Conducts pain, temperature, and crude touch information.

First order neuron receives input from sensory receptors and projects to the dorsal horn where the neuron bifurcates (splits). These branches travel 1 to 3 segments up and down the cord in the dorsolateral tract, also known as Lissauer’s tract. The axons then enter the dorsal horn, where they synapse (mostly in laminae I and II, but also in V).

Front 24

who crosses the midline and where do they go?

after the ascension up the spinal cord, where is the synapse?

what are some synapses that the second order neurons take along the way through the brain stem? and why.

Back 24

The second order neurons from the dorsal horn send axons that immediately cross the cord in the ventral white commissure. They ascend the spinal cord in the anterior lateral system (sometimes called the lateral spinothalamic tract) and synapse in the VPL. VPL neurons project to the somatosensory cortex.

In the lateral spinothalamic tract new neurons are added on the medial side, thus creating a somatotopic organization.

It should also be noted that the second order neurons make several other synapses along the way through the brainstem. They also synapse in the periaquaductal gray matter in the midbrain (activates descending pain control mechanims) and in the reticular formation and the intralaminar thalamic nucleus (provides emotional and arousal aspects of pain).

Front 25

what's in charge of the fine touch and vibration/ pain and temperature pathways of the face?

Back 25

trigeminal pathway.

Front 26

Orofacial Fine Touch and Vibration Pathway

Back 26

The primary sensory neuron has its soma in the trigeminal ganglion, and projects into the pons where it synapses in the chief (principle) sensory nucleus on the ipsilateral side. The second order neuron (with its soma in the chief sensory nucleus) projects through the brainstem and synapses bilaterally in the ventral posterior medial thalamic nucleus (VPM) of the thalamus. The third order neuron, with its soma in the VPM, projects to the primary somatosensory cortex. More details to follow…

Front 27

Orofacial Pain and Temperature Pathway

Back 27

The primary sensory neuron has its soma in the trigeminal ganglion, and projects into the brainstem where it synapses in the spinal trigeminal nucleus on the ipsilateral side. The second order neuron (with its soma in the spinal trigeminal nucleus) projects to the contralateral side of the brainstem and ascends in the ventral trigeminal tract to synapse in the VPM. The third order neuron (with its soma in the VPM) projects an axon to synapse in the primary somatosensory cortex.
More details to follow…

Front 28

both eyes see both visual fields

Back 28

yeah, so? right sees left visual field and right visual field, and left eye sees right and left visual field

Each optic tract carries information from the lateral ipsilateral retina and the medial contralateral retina.

Stated another way, each optic tract carries information from the contralateral visual field.

Retinotopic organization is maintained throughout the visual pathway.

Front 29

what's going on at the optic chiasm

Back 29

cross over of visual field info so that the right optic tract has only information from the left visual field and the left optic tract has information from only the right visual field

the optic tracts synapse at the lateral geniculate body of the hypothalamus

then they go to the occipital lobe at the calcarine fissure via the geniculo-calcarine tract (to the primary visual cortex)

Front 30

what is Meyer's loop?

Back 30

axons from the lateral geniculate to the calcarine fissure containing superior visual field information. take a wide (lateral inferior) loop to the calcarine fissure. they sweep down through the temporal lobe. it's then possible for MCA (middle cerebral artery) lesion to take out wernicke's area, auditory area, and visual field information (so it can take out language and vision all at the same time)

so the inferior visual information comes in to the calcarine fissure in a more medial loop.

Front 31

what visual loss do you have if there's a pituitary cancer?

Back 31

since the cancer will press on the optic chiasm, you will lose lateral vision on both eyes.

Front 32

Corticobulbospinal tract..what it does

Back 32

Cell bodies are in the cerebral cortex (mostly pre-central gyrus -Brodmann’s area 4 but also in 6)

They descend through the CNS and make synapses in the brainstem (corticobulbar axons) and in the ventral spinal cord (corticospinal axons).

Somatotopy of motor humunculus is maintained in descending fibers.

Corticobulbal synapses are made on red nucleus and cranial nerve nuclei III, IV, V, VI, VII, X, XI, XII.

Front 33

Corticobulbospinal tract pathway

a lot of detail, but where do the axons cross the midline in the medulla?

Back 33

From cortex, fibers converge in the corona radiata and travel in the posterior limb (corticospinal) and genu (corticobulbar) of the internal capsule. At midbrain levels, the corticospinal fibers form the middle 1/3 of the crus cerebri (cerebral peduncles), while the corticobulbar fibers are located just medial to the corticospinal fibers.

In the pons, the fibers of the corticobulbospinal system are broken up into scattered fiber bundles in the basilar (ventral) portion of the pons.

In the medulla, the fibers of this system coalesce again into the medullary pyramids. Nearly all of the axons cross the midline in the medulla at the pyramidal decussation. The crossed fibers travel through the spine in the lateral corticospinal tract and the uncrossed fibers (<10%) travel in the anterior corticospinal tract.

Front 34

The lateral corticospinal tract... is clinically the most important descending motor pathway. why's that?

Back 34

it's the movement of the extremities (running, jumping, etc)

The fibers of the lateral corticospinal tract enter into the ventral horn at all spinal levels and synapse on motor neurons and interneurons. The fibers in the anterior corticospinal tract cross the midline in the anterior white commissure at the same level they enter the ventral horn and make similar synapses as the lateral corticospinal tract.

Anterior corticospinal tract (uncrossed axons that cross the midline right before they synapse), on the other hand, involves movement of the axial (trunk) muscles.

Front 35

lower motor neurons

Back 35

cell bodies that are directly connected to muscle. so they synapse and activate muscle. so if you damage a lower motor neuron, you have limply paralyzed that muscle, lose deep tendon reflexes,

Front 36

upper motor neurons

Back 36

synapse and activate lower motor neurons. damange to upper motor neuron gives paralysis but it's a spastic paralysis, and hyperresponsive deep tendon reflex.

Front 37

basal ganglia does what

Back 37

The basal ganglia are a set of nuclei that function as a “consultant” to the cerebral cortex.

They provide the crucial physiological link between the idea of movement and the motor expression of that idea.

Neuronal activity in the descending motor systems is closely correlated in time with the expression of a particular motor act. In contrast, most neuronal activity of the basal ganglia occurs before a particular movement begins.

Disturbances in the function of the descending pathways result in paralysis or paresis, but lesions to the basal ganglia causes disturbances in the initiation or cessation of a motor event.

Front 38

parts of the basal ganglia aka corpus striatum

Back 38

neostriatum - caudate nucleus and putamen

paleostriatum- globus pallidus

putamen and globus pallidus= lentiform nucleus

Front 39

direct pathway of the basal ganglia involved in

Back 39

starting movements

This pathway involves a circuit beginning in the cerebral cortex with connections to the caudate and putamen (together: neostriatum), which then project to the medial segment of the globus pallidus (GPm), which projects on to the thalamus, and then back to the cerebral cortex. Without input from other areas, GPm neurons are tonically active and inhibit thalamic neurons with GABA, preventing them from exerting an excitatory influence on the cerebral cortex. Activation of the direct pathway causes excitation of the neostriatum by the cerebral cortex. Neostriatal neurons secrete GABA and are inhibitory to neurons of the GPm. Therefore, when activated, neostriatal neurons will inhibit GPm cells, thus preventing them from inhibiting thalamic neurons (disinhibition). Thus, the result of activation of the direct pathway is increased output from the thalamus with a resultant increase in activation of the motor regions of the cerebral cortex.

Release of dopamine by substantia nigra compacta (SNc) cells onto neostriatal neurons with D1 receptors facilitates activity in the direct pathway.

Front 40

Indirect Pathway

Back 40

stopping movements by forcing the GPm to inhibit the thalamus

This pathway includes an additional loop through the lateral globus pallidus (GPl) and the subthalamic nucleus (ST). As with the direct pathway, the indirect pathway begins with excitatory projections from the cerebral cortex to the neostriatum. However, neostriatal output in this pathway is to the lateral, rather than medial, segment of the globus pallidus. These neostriatopallidal fibers are inhibitory (GABA is transmitter). Neurons of the GPl in turn send inhibitory connections (also GABAergic) to the subthalmic nucleus. These fibers to the subthalamic nucleus show high levels of spontaneous activity and tonically inhibit subthalamic neurons. Inhibition of GPl neurons by the neostriatum prevents GPl cells from inhibiting the subthalamic nucleus (disinhibition of ST). When active, subthalamic neurons are excitatory (glutamate is transmitter) to neurons of the GPm. Remember from the description of the direct basal ganglia pathway, that GPm neurons inhibit thalamic neurons. Thus, when the indirect basal ganglia pathway is activated, the result is decreased activity of the thalamus and therefore decreased activity of the motor regions of cerebral cortex.

Front 41

What happens with the substantia nigra?

Back 41

direct: releases dopamine onto D1 and D1 receptors. job is to depolarize the neostriatum. it's easier to start a movement

indirect: still releasing dopamine, but now releases onto D2 receptors which are inhibitory. so SN on indirect makes it harder to stop movement.

so if the SR goes away, it's now harder to start a movement b/c we've lost that source of activation and also easier to stop a movement because we lost that source of inhibition. so in parkinson's you have bradykinesia (hard to start movement, and once it starts, it's very slow)