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PMU Anatomy > Brainstem: Midbrain, Pons, Medulla Oblongata & Reticular Formation > Flashcards

Brainstem: Midbrain, Pons, Medulla Oblongata & Reticular Formation Flashcards

1
Q

What does the CNS and PNS consist of?

A
  • CNS - brain and spinal cord
  • PNS - peripheral nerves and ganglion
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2
Q

What is the gross divison of the brain

A
  • cerebrum - cerbral hemisphere
  • diencephalon
  • cerebellum
  • brainstem
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3
Q

What is the function of the brainstem?

A

they help to regulate breathing, heart rate, blood pressure, and several other important functions

  • Produce automatic behaviors necessary for survival.
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4
Q

Embryonic development of the brain

A
  • At the front end, the ventricles and cord swell to form three vesicles that are the precursors of the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain)
  • At the next stage, the forebrain splits into two vesicles called the telencephalon (which will contain the cerebral cortex, basal ganglia, and related structures) and the diencephalon (which will contain the thalamus and hypothalamus)
  • At about the same time, the hindbrain splits into the metencephalon (which will contain the cerebellum and pons) and the myelencephalon (which will contain the medulla oblongata)
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5
Q

What does Proscencephalon develop into?

A
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6
Q

What does Mesencephalon develop into?

A
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7
Q

What does Rhombencephalon develop into?

A
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8
Q

Describe the neural tube and how it develops

A
  • (in an embryo) a hollow structure from which the brain and spinal cord form
  • Defects in its development can result in congenital abnormalities such as spina bifida.
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9
Q

brainstem & its location

A
  • between the cerebrum and spinal cord
  • The brainstem is a stalk-like projection extending caudally from the base of the cerebrum. It facilitates communication between the cerebrum, cerebellum, and spinal cord.
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10
Q

3 parts of the brainstem

A

consists of midbrain, pons and medulla oblongata

  • Microscopically, it consists of deep gray matter surrounded by white matter fiber tracts.
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11
Q

What does the brainstem provide?

A
  • provides a pathway for tracts running between higher and lower neural centers
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12
Q

Describe the Basilar portion of the brainstem

A
  • It has importance in the conveyance of motor and sensory pathways from the rest of the brain to the body, and from the body back to the brain

Descending fibers from cerebral cortex:

  • corticospinal and corticobulbar tracts - pyramidal tracts
  • Corticopontocerebellar Fiber: Cortipontine, Pontocerebellar Fibers and Pons Proper (Ventral Pons)
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13
Q

Describe the roof plate of brainstem

A
  • formed by two paired rounded swellings, the superior and inferior colliculi.

Contains

  • Midbrain
  • superior colliculus: vision
  • inferior colliculus: hearing

Closed medulla

  • nucleus gracilis et cuneatus: discriminiative touch sensation
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14
Q

Describe the structure of the tegmentum section of the brainstem

A
  • ventral part of the midbrain
  • located between the ventricular system and distinctive basal or ventral structures at each level
  • forms the floor of the midbrain (mesencephalon)
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15
Q

Describe the function of the tegmentum

A
  • a multisynaptic network of neurons that is involved in many subconscious homeostatic and reflexive pathways
  • It is a motor center that relays inhibitory signals to the thalamus and basal nuclei preventing unwanted body movement

contains:

  • Cranial nerve nuclei
  • precerebellar nuclei
  • reticular formation
  • Ascending cortical pathway
  • cerebellar circuits, descending, composite bundle tracts
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16
Q

Cranial Nerves Column of Brain Stem

A

Motor column

GSE - general somatic efferent?

SVE - special visceral efferent

GVE - general visceral efferent

Sensory Column

VA - Visceral afferent - general and special

GSA - General somatic afferent

SSA -Special somatic afferent

  • A cranial nerve nucleus is a collection of neurons (gray matter) in the brain stem that is associated with one or more cranial nerves
  • In general, motor nuclei are closer to the front (ventral), and sensory nuclei and neurons are closer to the back (dorsal)
  • This arrangement mirrors the arrangement of tracts in the spinal cord.

Close to the midline are the motor efferent nuclei, such as the oculomotor nucleus, which control skeletal muscle. Just lateral to this are the autonomic (or visceral) efferent nuclei.

There is a separation, called the sulcus limitans, and lateral to this are the sensory nuclei. Near the sulcus limitans are the visceral afferent nuclei, namely the solitary tract nucleus.

More lateral, but also less posterior, are the general somatic afferent nuclei. This is the trigeminal nucleus. Back at the dorsal surface of the brainstem, and more lateral are the special somatic afferents, this handles sensation such as balance.

Another area, not on the dorsum of the brainstem, is where the special visceral efferents nuclei reside. These formed from the pharyngeal arches, in the embryo. This area is a bit below the autonomic motor nuclei, and includes the nucleus ambiguus, facial nerve nucleus, as well as the motor part of the trigeminal nerve nucleus.

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17
Q

Cranial Nuclei

A
  • A cranial nerve nucleus is a collection of neurons (gray matter) in the brain stem that is associated with one or more cranial nerves
  • In general, motor nuclei are closer to the front (ventral), and sensory nuclei and neurons are closer to the back (dorsal)
  • This arrangement mirrors the arrangement of tracts in the spinal cord.

Close to the midline are the motor efferent nuclei, such as the oculomotor nucleus, which control skeletal muscle

  • Just lateral to this are the autonomic (or visceral) efferent nuclei.

There is a separation, called the sulcus limitans, and lateral to this are the sensory nuclei

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18
Q

Components of the cranial nerves

A
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19
Q

Ventricles in brainstem

A
  • Mesencephalon - ceberal aqueduct
  • Mentencephalon - 4th ventricle
  • Mylencephalon - 4th ventricle
  • The fourth ventricle is one of the four connected fluid-filled cavities within the human brain
  • These cavities, known collectively as the ventricular system, consist of the left and right lateral ventricles, the third ventricle, and the fourth ventricle
  • The fourth ventricle extends from the cerebral aqueduct to the obex, and is filled with cerebrospinal fluid (CSF).
  • characteristic diamond shape in cross-sections of the human brain
  • It is located within the pons or in the upper part of the medulla oblongata
20
Q

Anterior view of brainstem

A
21
Q

Posterior view of brainstem

A
22
Q

Lateral view of brainstem

A
23
Q

Components of the brainstem

A

Sensory ascending pathways (dorsal)

  • relay nuclei, tracts

Motor descending pathways (ventral)

  • tracts, motor nuclei brainstem

Cerebellar pathways

  • tracts, cerebellar afferent and efferent nuclei

Cranial Nerve sensory and motor tracts

  • cranial nerve nuclei, nerve entry and exit points

CPGs: rhythmic chewing, respiration, cardiovas regulation and gain adjustment for reflexes

Modulatory systems: locus coeruleus, raphe and substantia nigra

  • Chemically coded nuclei
24
Q

Describe the ventral side of the midbrain (mesencephalon) of the brainstem

A
  • located between diencephalon and pons
  • 2 bulging cerebral peduncles on ventral side which contain:
  • descending fibers that go to the cerebellum via pons
  • decending pyramidal tracts
25
Q

Describe the cerebral aqueduct of brainstem

A
  • runs through the midbrain
  • connects 3rd and 4th ventricles of the brain
26
Q

Describe the roof (tectum) of the aqueduct of the brainstem

A
  • contains corpora quadrigemina
  • 4 colliculi:
  • 2 superior - control reflex movements of the eyes, head and neck in response to visual stimuli
  • 2 inferior - control reflex movements of the head, neck and trunk in response to auditory stimuli
27
Q

What cranial nerves exit from the midbrain?

A

3 (oculomotor) and 4 (trochlear)

  • also contains the headquarters of the reticular activating system
28
Q

What is on each side of the brainstem?

A
  • contains a red nucleus - contains numberous blood vessels and receives info from cerebrum/bellum, gives subconscious motor commands concerned with muscle tone and posture
  • substantia nigra - lateral to nucleus, melanin-containing, secretes dopamine to inhibit the excitatory neurons of basal nuclei (responsible for body movement and coordination)
29
Q

Where is the Pons?

A
  • literal meaning: bridge
  • between midbrain and medulla
30
Q

What does the Pons contain?

A
  • sensory and motor nuclei for 4 cranial nerves:

  • Trigeminal (5), Abducens (6), Facial (7) and Auditory/Vestibular (8)
  • respiratory nuclei - apneustic and pneumotaxic centers work with the medulla to maintain respiratory rhythm
  • nuclei and tracts that process and relay info to/from cerebellum
  • ascending, descending and transverse tracts that interconnect other portions of the CNS
31
Q

Describe the medulla oblongata

A
  • most inferior region of the brainstem
  • becomes the spinal cord at the level of the foreamen magnum
  • ventrally, 2 ridges (medullary pyramids) are visible
  • these are formed by the large motor corticospinal tracts
  • right above the medulla-SC junction, most of there fibers cross-over (decussate)
32
Q

Describe the nuclei in the medulla oblongata

A
  • they are ass. with autonomic control, cranial nerves and motor/sensory relay
  • autonomic nuclei:
  • cardiovas. centers - alter the rate and force of cardiac contractions, alter the tone of vascular smooth muscle
  • respir. rhythmicity centers - receive input from the pons
  • add. centers - emesis, deglutition, coughing, hiccuping, sneezing
33
Q

The sensory, motor and relay nuclei in medulla oblongata

A
  • Auditory/Vestibular (8), Glossopharyngeal (9), Vagus (10), Accessory (11), and Hypoglossal (12)
  • relay nuclei - nucleus gracilis and cuneatus pass somatic sensory information to thalamus
  • olivary nuclei relay info from the SC, cerebral cortex and brainstem to cerebellar cortex
34
Q

Ascending Sensory Pathways - fine discriminative touch, conscious proprioception

A
  • fasciculus gracilis - terminates in the nucleus gracilis (medulla)
  • fasciculus cuneatus - terminate (medulla) in the cuneate and accessory cuneate nuclei
35
Q

Ascending Sensory Pathways - sensations of pain and temp

A
  • lateral spinothalamic tract
  • origin: dorsal horn cells of gray matter
  • fibers cross contralaterally through the anterior commissure and ascend to the ventral posterolateral (VPL) nucleus
36
Q

Ascending Sensory Pathways - transmits sensations of touch

A
  • ventral spinothalamic tract
  • origin: cells of the posterior horn
  • fibers cross to the opp. side in the anterior commissure
37
Q

Descending motor pathways - voluntary movement

A
  • lateral corticospinal tract

  • originates in large pyramidal cells (precentral gyrus)
  • cross to the opp. side of the cord at the pyramidal decussation and terminate in the doral horn cells
  • ventral corticospinal tract
  • originates in the pyramidal cells (motor area of the cortex)
38
Q

Descending motor pathways - impulses related to eqm. and antigravity reflexes

A
  • vestibulospinal tract
  • fibers originate in the vestibular nuclei of the medulla and terminate at level of the sacral SN
39
Q

Descending motor pathways - connects vestib. complex head and eye movement coordination center in medulla

A
  • medial longitudinal fasciculus
  • contains both asc and desc fibers
40
Q

Describe the motor hierarchy - lateral group

A
  • lateral group (extrimities, fine motor control):

  • corticospinal and rubrospinal tract
41
Q

Describe the motor hierarchy - medial group

A
  • axial musculature, rhythmic and postural movements
  • vestibulospinal, tectospinal and reticulospinal tracts
  • final common path - motor pool
42
Q

What is the Reticular formation

A
  • a set of interconnected nuclei that are located throughout the brainstem.
  • not anatomically well defined because it includes neurons located in different parts of the brain
  • complex set of networks in the core of the brainstem that extend from the upper part of the midbrain to the lower part of the medulla oblongata.
  • includes ascending pathways to the cortex in the ascending reticular activating system (ARAS) and descending pathways to the spinal cord via the reticulospinal tracts
  • projects to thalamic nuclei which influence cerebral cortex
43
Q

Structure of Reticular Formation

A

–Midbrain portion of RAS most likely is its center

  • Core of brainstem (midbrain, pons and medulla) composed of loosely organized neurons, outside of the major nuclear groups of the brainstem
  • Medial-to-lateral: raphe nuclei, gigantocellular region, small cell region
44
Q

Function of Reticular Formation

A
  • neurons (esp. ARAS) have an important role in maintaining arousal and consciousness
  • somatic motor control, cardiovascular control, pain modulation, sleep and consciousness, and habituation
  • functions as a net or filter for sensory input: allow passage of infrequent, important stimuli to reach cerebral cortex
  • activates cerebral cortex - keeps it awake
  • rostral continuation of interneural network found in SC
45
Q

Dorsal Column/Medial Lemniscal System

A
  • secondary neuron is in brainstem: nucleus gracilis and cuneatus = dorsal column nuclei
  • output of doral column nuclei crosses midline and forms recognizable bundle: medial lemniscus
  • medial lemniscus fibers synapse in the thalamus in the ventroposterior nuclei
  • thalamic axons synapse in primary somatosensory cortex in several somatotopic maps with some segregation of submodalities

PMU Anatomy (19 decks)

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