finalbrainstem

2. The brain stem is the part of the brain between the spinal
cord and the diencephalon.
It consists of three structures:
(1) Medulla oblongata,
(2) Pons, and
(3) Midbrain.
Extending through the brain stem is the reticular formation,
a net like region of interspersed gray and white matter.

5. Medulla Oblongata

6. The medulla oblongata, or more simply the medulla, is
continuous with the superior part of the spinal cord; it forms
the inferior part of the brain stem.
The medulla begins at the foramen magnum and extends to the
inferior border of the pons, a distance of about 3 cm (1.2 in.).

7. The medulla’s white matter contains all sensory (ascending) tracts and
motor (descending) tracts that extend between the spinal cord and
other parts of the brain.
Some of the white matter forms bulges (knobs) on the anterior
aspect of the medulla.
These knobs, called the pyramids are formed by the large
corticospinal tracts that pass from the cerebrum to the spinal
cord.
The corticospinal tracts control voluntary movements of the
limbs and trunk.

9. Just superior to the junction of
the medulla with the spinal cord,
90% of the axons in the left
pyramid cross to the right side,
and 90% of the axons in the right
pyramid cross to the left side.
This crossing is called the
decussation of pyramids and
explains why each side of the
brain controls voluntary
movements on the opposite side
of the body.

10. Just lateral to each pyramid is an oval-shaped swelling called an
olive.
Within the olive is the inferior olivary nucleus, which receives input
from the cerebral cortex, red nucleus of the midbrain, and spinal
cord.
Neurons of the inferior olivary nucleus extend their axons into the
cerebellum, where they regulate the activity of cerebellar neurons.
By influencing cerebellar neuron activity, the inferior olivary
nucleus provides instructions that the cerebellum uses to make
adjustments to muscle activity as you learn new motor skills.

13. The medulla also contains several nuclei. (Recall that a nucleus
is a collection of neuronal cell bodies within the CNS.)
Some of these nuclei control vital body functions. Examples of
nuclei in the medulla that regulate vital activities include the
Cardiovascular center and
The medullary rhythmicity area.
The cardiovascular center regulates the rate and force of the
heartbeat and the diameter of blood vessels.
The medullary rhythmicity area of the respiratory center
adjusts the basic rhythm of breathing.

14. Nuclei for vital functions
Cardiovascular center regulates
the rate and force of the
heartbeat and the diameter of
blood vessels.
The medullary rhythmicity
area of the respiratory
center adjusts the basic
rhythm of breathing.

15. Besides regulating vitals, nuclei in the medulla also control
reflexes for
Vomiting
Swallowing
Sneezing
Coughing and
Hiccupping

16. Stimulation of vomiting center of the medulla
causes vomiting, the forcible expulsion of the
contents of the upper gastrointestinal (GI) tract
through the mouth.
The deglutition center of the medulla promotes
swallowing of a mass of food that has moved
from the oral cavity of the mouth into the
pharynx (throat).
Sneezing involves spasmodic contraction of
breathing muscles that forcefully expel air
through the nose and mouth.

17. Coughing involves a long pinched and deep
inhalation and then a strong exhalation that
suddenly sends a blast of air through the upper
respiratory passages.
Hiccupping is caused by spasmodic contractions
of the diaphragm (a muscle of breathing) that
ultimately result in the production of a sharp
sound on inhalation.

18. Nuclei associated with sensations of touch, pressure, vibration,
and proprioception (conscious awareness of position) are
located in the posterior part of the medulla.
These nuclei are the right and left gracile nucleus and cuneate
nucleus.

20. The medulla also contains nuclei that are components of sensory
pathways for gustation (taste), audition (hearing), and
equilibrium (balance).
The gustatory nucleus of the medulla is part of the
gustatory pathway from the tongue to the brain; it
receives gustatory input from the taste buds of the
tongue.
The cochlear nuclei of the medulla are part of the
auditory pathway from the inner ear to the brain;
they receive auditory input from the cochlea of
the inner ear.

21. The vestibular nuclei of the medulla and
pons are components of the equilibrium
pathway from the inner ear to the brain; they
receive sensory information associated with
equilibrium from proprioceptors in the
vestibular apparatus of the inner ear.

22. Finally, the medulla contains nuclei associated with five pairs of
cranial nerves :
Vestibulocochlear (VIII) nerves,
Glossopharyngeal (IX) nerves,
Vagus (X) nerves,
Accessory (XI) nerves (cranial portion), and
Hypoglossal (XII) nerves.

25. The brain stem is the
part of the brain
between the spinal
cord and the
diencephalon.
It consists of three
structures:
(1) Medulla
oblongata,
(2) Pons, and
(3) Midbrain.

26. Location of medulla oblongata: superior to the spinal cord;
inferior to the pons, 3 cm Long.

27. Anterior aspect of the medulla:
Known as the pyramids,
Formed by the large corticospinal tracts.
Function: Control voluntary movements of the limbs and trunk

28. Decussation of pyramids: A cross over of neurons, Superior to
the junction of the medulla with the spinal cord.
It explains why each side of the brain controls voluntary
movements on the opposite side of the body.

29. Olive: Oval-shaped swelling, just lateral to each pyramid.
Within the olive is the inferior olivary nucleus, receiving
input from the cerebral cortex, red nucleus of the midbrain, and
spinal cord.
Neurons of the inferior olivary nucleus regulate the activity
of cerebellar neurons by providing instructions, that the cerebellum
uses to make adjustments to muscle activity as you learn new motor
skills.

30. Nuclei for vital functions
Cardiovascular center regulates
the rate and force of the
heartbeat and the diameter of
blood vessels.
The medullary rhythmicity
area of the respiratory
center adjusts the basic
rhythm of breathing.

32. Gracile and cuneate nucleus: Located in the posterior part of
the medulla, associated with sensations of touch, pressure,
vibration, and conscious awareness of position.

33. • Gustatory pathway from the tongue to the brain; it
receives gustatory input from the taste buds of the
tongue
Gustation (taste)
• Auditory pathway from the inner ear to the brain;
they receive auditory input from the cochlea of the
inner ear
Audition
(hearing)
• Equilibrium pathway from the inner ear to the
brain; they receive sensory information
associated with equilibrium from proprioceptors
in the vestibular apparatus of the inner ear
Equilibrium
(balance)

36. Pons

37. The pons (bridge) lies directly superior to the medulla and
anterior to the cerebellum and is about 2.5 cm (1 in.) long.
As its name implies, the pons is a bridge that connects
different parts of the brain with one another. These
connections are provided by bundles of axons.

38. Like the medulla, the pons consists of nuclei, sensory tracts,
and motor tracts.
Signals for voluntary movements from motor areas of the
cerebral cortex are relayed through several pontine nuclei
into the cerebellum.

40. Pons also contains vestibular nuclei that are components of
the equilibrium pathway from the inner ear to the brain.

41. Other nuclei in the pons are the pneumotaxic area and the
apneustic area of the respiratory center.
Together with the medullary rhythmicity area, the
pneumotaxic and apneustic areas help control breathing.

43. The pons also contains nuclei associated with the following
four pairs of cranial nerves:
 Trigeminal (V) nerves,
 Abducens (VI) nerves,
 Facial (VII) nerves, and
 Auditory (VIII) nerves

45. Location : Anterior to Cerebellum
Superior to Medulla
Inferior to Mid Brain

46. Nuclei Present: Vestibular Nuclei
Respiratory Nuclei
1. The pneumotaxic area and
2. The apneustic area

47. Cranial Nerve:
 Trigeminal (V) nerves,
 Abducens (VI) nerves,
 Facial (VII) nerves, and
 Auditory (VIII) nerves

49. The midbrain or mesencephalon extends from the pons to the
diencephalon and is about 2.5 cm (1 in.)long.

50. The cerebral aqueduct passes through the midbrain,
connecting the third ventricle above with the fourth
ventricle below.

51. The anterior part of the midbrain contains paired bundles of
axons known as the cerebral peduncles.
The cerebral peduncles consist of axons of
Corticospinal,
Corticopontine, and
Corticobulbar tracts, which conduct nerve impulses
from motor areas in the cerebral cortex to the spinal cord, pons,
and medulla, respectively.

52. The posterior part of the midbrain, called the tectum,
contains four rounded elevations.
Two superior elevations: Superior Colliculi
Two inferior elevations: Inferior Colliculi

53. The superior colliculi serves as reflex centers for certain
visual activities.
Visual activities like, eye movements for tracking moving
images (such as a moving car) and scanning stationary
images (as you are watching this slide).

54. The superior colliculi are also responsible for reflexes that
govern movements of the head, eyes, and trunk in response
to visual stimuli.

55. The inferior colliculi are part of the auditory pathway, relaying
impulses from the receptors for hearing in the inner ear to the
brain.
These two nuclei are also reflex centers for the startle reflex,
sudden movements of the head, eyes, and trunk that occur when
you are surprised by a loud noise such as a gunshot.

56. The midbrain contains several other nuclei, including the
left and right substantia nigra.
Neurons that release dopamine, extending from the
substantia nigra to the basal ganglia, help control
subconscious muscle activities.
Loss of these neurons is associated with Parkinson disease.

58. Also present are the left and right red nuclei, which look
reddish due to their rich blood supply and an iron-
containing pigment in their neuronal cell bodies.

59. Axons from the cerebellum and cerebral cortex form synapses in
the red nuclei, which help control some voluntary movements of
the limbs.

61. Mid Brain Location:
Superior to pons and inferior to diencephalon

62. Anterior part of Mid brain:
Cerebral Peduncles which contains
Corticospinal,
Corticopontine, and
Corticobulbar tracts
Posterior part of mid brain: Known as
Tectum and contains 4 elevations.
2 superior colliculi: serving as reflex
center for serval visual activity
2 inferior colliculi: part of auditory
pathway.

63. Substantia nigra: Posterior to
cerebral peduncles, contains
dopaminergic neurons and having
role in controling subconscious
muscle activity
Red Nuclei: Next to substantia nigra
there is red nuclei involved in
voluntary movements of limbs.