Brainstem and Spinal Cord

Brainstem

• Stalk-like structure

• located at the posterior fossa of the skull

• connects the brain, cerebellum, and spinal cord

• Functions: pathway of tracts, regulates functions, reflexes, origin of cranial nerves

Midbrain

• Consists of:

  • Crus Cerebri

  • Cerebral Aqueduct

  • Tectum

  • Tegmentum

Midbrain

• Origin of CN 3 and 4

Tectum

• the roof

• Has 4 round swellings (colliculi) which are known as the Corpora Quadrigemina

Tegmentum

• the floor

• consists of fiber tracts and 3 nuclei distinguished by color

  • Edinger-Westphal

  • Oculomotor

  • Red nucleus

Superior Colliculi

• For visual and ocular reflexes

• Gaze and vergence centers

• Connected to the Lateral Geniculate Body

Inferior Colliculi

• For auditory reflexes

• Sound localization

• Connected to the Medial Geniculate Body

Red Nucleus

• Passage of ascending tract fibers that connect to the primary motor cortex

Raphe Nuclei

• Extend from the midbrain to spinal cord

• Part of the Reticular Activating System

• Major serotonin-producing neuron in CNS

• Modulates sleep-wake cycle, level of arousal, sensory input (pain)

Superior Cerebellar Peduncle

• Connect the brainstem to the cerebellum

• Main OUTPUT pathway of the cerebellum

Ventral Tegmental Area and Substantia Nigra

• Major producer of dopamine in the CNS

Pars Reticulata

• Contains GABA

Pars Compacta

• Contains dopamine

• Projects to the striatum, putamen, and caudate nuclei

Pons

• Anterior to the cerebellum

• Connects the midbrain and medulla oblongata

• has the:

  • basilar groove at midline

  • middle cerebellar peduncle

Pons

• Origin of CN 5 - 8

Pons

• Seat of consciousness

• Consists of the ARAS and Reticulospinal Tract

Ascending Reticular Activating System

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

Medulla Oblongata

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

• conical in shape, with superior part broader

• respiratory and deglutition center

Medulla Oblongata

• Origin of CN 7-12

Pyramids

• paired bundles of motor nerve tracts

• Decussation

Olives

• Posterolateral to pyramids

• Produced by inferior olivary nuclei, which are important for the control of movement

Nucleus Gracilis

• Found on each side of the posterior median sulcus

• Forms the gracile tubercles

Nucleus Cuneatus

• Found laterally to the nucleus gracilis

• Forms the cunate tubercles

Nucleus Ambiguus

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

• Mainly responsible for swallowing and speaking

• Contains vagal efferent neurons that inhibit the heart rate

Nucleus Solitarius

• Receive taste, chemoreceptor, baroreceptor inputs in the aortic arch and carotid body

Spinal Cord

• information highway

• Occupies 2/3 of the spinal canal

• Expands laterally in the cervical and lumbosacral enlargement

Conus Medullaris

• conical distal end

• at the level of L1 or L2 in adults

Cauda Equina

• bundle of spinal nerves and rootlets

• Start at L2, extend towards the lumbar, sacral, and coccygeal levels

Filum Terminale

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

Denticulate Ligament

• band of fibrous pia mater extending along the 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

Meningeal Layers

• Protect the CNS by acting as a shock barrier or cushion

• Protects the vessels that supply the brain

• Contain CSF which nourishes the brain and spinal cord

Central Canal

• space where CSF runs through the SC

Marginal Layer / Layer 1

• Dorsal

• Contains neurons that respond to noxious stimuli

• Sends axons to the contralateral spinothalamic tract

Substantia Gelatinosa / Layer 2

• Dorsal

• Small neurons that respond to noxious stimuli

Nucleus Proprius / Layers 3 and 4

• Dorsal

• Receives information position and light touch sense

Layer 5

• Dorsal

• Responds to visceral noxious and afferent stimuli (mechanical signals from joints and skin)

Layer 6

• Dorsal

• Deepest layer of the dorsal horn

• Responds to mechanical signals of joints and skin

Dorsalis or Clarke’s nucleus or column / Intermediolateral cell column / Zona Intermedia / Layer 7

• Lateral

• Contains the intermediolateral nucleus (or intermediolateral cell column) in thoracic and upper lumbar regions from which the preganglionic sympathetic fiber project to the sympathetic ganglia’

• Gives rise to posterior spinocerebellar tract (relays unconscious, proprioceptive information to the cerebellum)

Layers 8 and 9

• Ventral

• Contains the cell bodies of motor neurons innervating skeletal ms

• Contains the motor interneurons part of reflex pathway in the spinal cord

Layer 10

• Small neurons around the central canal and their remnants

Upper motor neurons in the cerebral cortex or brainstem

• First order of the Motor Tracts (Descending) Pathway

Interneurons in the spinal cord

• Second order of the Motor Tracts (Descending) Pathway

Lower Motor Neurons

• Third order of the Motor Tracts (Descending) Pathway

Dorsal Root Ganglion

• First order of the Sensory Tracts (Ascending) Pathway

Decussates and ascends

• Second order of the Sensory Tracts (Ascending) Pathway

Thalamus

• Third order of the Sensory Tracts (Ascending) Pathway

Reflexes

• Subconscious stimulus-response mechanisms.

• Extremely important in the diagnosis and localization of neurologic lesions

Crossed-extensor Reflex

• Typically 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. The baby's free leg flexes, adducts and then extends.

Reciprocal Innervation

• Flexor AND extensor reflexes of the SAME limb cannot contract simultaneously

• Afferent nerve fibers for flexor reflex muscle MUST have branches for extensor motor neurons

Anterior 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

Damage to lateral white column

• S/Sx:

  • Spastic paralysis/paresis

  • Disuse atrophy

  • Hyperactive DTRs

  • Diminished or absent superficial reflexes

  • Pathologic reflex