[OT 104] Lec. 4: Brain Stem and Spinal Cord

What is the brainstem like?

• stalk-like

Where is the brainstem located?

• at the posterior fossa of the skull

What does the brainstem connect?

• the brain, cerebellum, and spinal cord

Subdivisions of the brain stem

• midbrain

• pons

• medulla oblongata (deglutition and respiratory center)

Functions of the brainstem

• pathway of tracts

• regulatory functions - autonomic nervous system (swallowing, breathing, blood pressure, heart rate, consciousness, and sleep)

• reflexes

• origin of cranial nerves

Carotid body

• baroreceptors that regulate blood pressure

• important for distension (vasoconstriction and vasodilation)

• reticular active system (RAS): for consciousness and sleep-wake cycle system

What originates from the midbrain?

• CN 3 and CN 4

What is the anatomy/divisions of the midbrain?

• crus cerebri

• cerebral aqueduct

• tectum (roof)

• tegmentum

Crus cerebri

• cerebral peduncle for sensorimotor integration from corticospinal fibers

• where interpeduncular fossa is found between the cerebral crura

Cerebral aqueduct of sylvian fissure

• where cerebrospinal fluid passes

• channel connecting 3rd (superiorly) and 4th (inferiorly) ventricle

Tectum

• roof of midbrain

• contains 4 round swellings called colliculi called corpora quadrigemina (eyes over ears)

Corpora Quadrigemina: Superior Colliculi (2)

• SUPERIOR COLLICULI (2)

  • for visual and ocular reflexes

  • gaze and vergence centers (divergence: eyes outwards, convergence: eyes inwards)

  • connected to lateral geniculate body

Corpora Quadrigemina: Inferior Colliculi (2)

• INFERIOR COLLICULI (2)

  • auditory reflexes

  • sound localization: knowing where the sound comes from

  • connected to medial geniculate body

Tegmentum

• floor of the midbrain

Tegmentum: Nuclei

• oculomotor

• edinger westphal nucleus

• red nucleus: passage of ascending tract fibers that connect to the primary motor cortex (BA 4)

  • for fine tuning and coordination of motor movements

Raphe Nuclei

• extend from midbrain to spinal cord

• part of the RAS

• major serotonin-producing neurons in the CNS

  • serotonin: happy hormone

• modulates sleep-wake cycle, level of arousal, sensory input

Superior Cerebellar Peduncle

• connect the brainstem to the cerebellum

• main OUTPUT pathway of the cerebellum

Ventral Tegmental Area (VTA) and Substantia Nigra

• main producer of dopamine in the CNS

  • low dopamine levels = less initiation from muscle groups = balance difficulties (parkinson’s)

Substantia Nigra

• pars reticulata: contains GABA

• pars compacta: contains dopamine and projects to the striatum , putamen, and the caudate nuclei.

Pons

• anterior to the cerebellum

• connects midbrain and medulla oblongata

• origin of CN 5 to 8

• has the basilar groove at midline and middle cerebellar peduncle

Pons: Seat of ?

• seat of consciousness

What is ARAS?

• Ascending Reticular Activating System (ARAS)

• responsible for overall level of consciousness and the wakeful-sleep states.

  • Comatose can be associated to problems in the ARAS

What is the Reticulospinal tract?

• originates from the pons and spinal cord

  • “reticulo” = reticular activating system in pons

  • “spinal” = spinal cord

• for locomotion and postural control

Medulla oblongata

• connects pons and spinal cord at the level of the foramen magnum

  • foramen magnum: large opening in base of skull

• conical in shape, superior part is broader

• origin of C7-12

  • C7 and 8 are under pons and MO

• respiratory and deglutition center

Cranial nerves in the Midbrain

• CN 3

• CN 4

Cranial nerves in the Pons

• CN 5

• CN 6

• CN 7

• CN 8

Cranial nerves in the medulla oblongata

• CN 7

• CN 8

• CN 9

• CN 10

• CN 11

• CN 12

Anatomy of MO: Pyramids

• paired bundles of motor nerve tracts

• decussation of the pyramids

  • crossing of motor nerve fibers to other side

  • why motor areas affect C/L side of body

  • location of decussation depends on the tract, but lots of motor nerve tracts decussate at the MO

  • pyramidal tracts: corticospinal tract (CST) and corticobulbar tract (CBT) which pass through the pyramids unlike the extrapyramidal tracts

Anatomy of MO: Olives

• posterolateral to pyramids

• produced by inferior olivary nuclei

  • important for control of movement

• inferior cerebellar peduncle is located behind the olives

Anatomy of MO: Nucleus Gracilis

• found on each side of the posterior median sulcus

• forms the gracile tubercles

Anatomy of MO: Nucleus Cuneatus

• found laterally to the nucleus gracilis

• forms the cunate tubercles

Anatomy of MO: Nucleus Ambiguus

• mainly for swallowing and speaking

• contains motor nerves that innervate the ipsilateral muscles of the soft palate, pharynx, larynx, and upper esophagus

• contains vagal (CN 10) efferent neurons which inhibit the heart rate

Anatomy of MO: Nucleus Solitarius

• purely sensory

• receive taste, chemoreceptor, baroreceoptor inputs in the aortic arch and carotid body.

• ex. When heart rate is too fast, the nucleus solitarius receives input from the baroreceptors and relays information to the brain to reduce heart rate and cause vasodilation

Functions of Nucleus Ambiguus and Solitarius

changes in BP > nucleus ambiguus and solitarius > adjust heart rate, BP, respiration

changes in oxygen levels > nuc. a and s. > increase or decrease respiration

Changes in BP and oxygen levels are received by the nucleus ambiguus and solitarius, which process and relay this information within the brainstem, leading to necessary adjustments

Spinal cord

• information highway

• located in the spinal canal

• occupied 2/3 of the spinal canal

  • length: 42-45 cm in adults

  • diameter: 10 mm

• expands laterally in the cervical enlargement and the lumbosacral enlargement

SC: Conus medullaris

• conical distal end

• at the level of L1 or L2 in adults

SC: Cauda equina

• “Horsetail”

• bundle of spinal nerves and rootlets that start at L2 and extend towards the lumbar, sacral, and coccygeal levels

SC: Filum terminale

• pia mater within equina that extends from the conus to the distal dural sac

SC: Denticulate ligament

• band of fibrous pia mater extending along spinal cord on each side

• found between the dorsal and ventral roots

• keeps the spinal cord attached to the arachnoid and dura mater to stabilize it

SC: Meningeal Layers

• dura, arachnoid, pia mater'

• protect the CNS as a shock barrier or cushion

• contain CSF which nourishes the brain and SC

SC: Cross section

• ventral median fissure

• dorsal median sulcus

• central/ependymal canal - where CSF passes through

• ventral roots (2) - motor nerves, outflow

• dorsal roots (2) - sensory nerves

SC: Cross section (Gray and White Matter)

Gray:

• Ventral Gray Column/Horn

• Lateral Gray Column/Horn

• Dorsal Gray Column/Horn

White:

• Ventral Gray Column

• Lateral Gray Column

• Dorsal Gray Column

SC: Dermatomes vs. Myotomes

Dermatomes: skin innervated by single spinal nerve

Myotomes: groups of muscles innervated by single nerve roots

SC: Vertebrae

Cervical: 7
Thoracic: 12
Lumbar: 5
Sacral: 5

Coccygeal: 3-4

Total: 33 bones

SC: Spinal nerves

Cervical: 8 pairs

Thoracic: 12 pairs

Lumbar: 5 pairs

Sacral: 5 pairs

Coccygeal: 1 pair
Total: 31 pairs

SC: Exit points

CerVelow
TaaSic

SC: Gray matter laminas

• Rexed’s Laminae

• follows a topographic organization

• based on the types and functions of the neurons in each laminae

SC: White matter

• 3 columns

• transmits information between brain and body

• important for coordination and processing

SC: Reflexes

• subconscious stimulus-response

• important for diagnosing and localizing neurologic lesions

SC Reflexes: Crossed-extensor reflex

• present until two months of age

• examiner holds one of the baby’s legs extended and applies firm pressure to the sole of the foot of the same leg.

• baby’s free leg flexes, adducts, then extends

• grasp reflex

SC Reflexes: Reciprocal innervation

• flexor and extensor reflexes of the same limb cannot contract simultaneously

• afferent nerve fibers for flexor reflex ms must have branches for extensor motor neurons

SC Lesions: Ant. horn of gray matter downwards are damaged

Affected: striated skeletal ms activity

Cause: trauma, toxins, infections

S/sx:

• flaccid paralysis

• ms atrophy

• diminished or absent DTR

• fasciculations and fibrillations

SC Lesions: Damage to lateral white column

S/sx:

• spastic paralysis/paresis (tightness/stifness)

• disuse atrophy (muscles decrease in size)

• hyperactive DTR

• diminished or absent superficial reflexes

• pathologic reflex (abnormal/primitive reflexes appear in adults)

SC Lesions: Things to consider

• what level does abnormality begin (sensory, motor)?

• what tracts are affected?

• which side are these tracts located?

• what sensory modalities are involved?