Brainstem

Question 1

What are the 3 divisions of the brainstem?

Answer 1

• midbrain (mesencephalon)
• pons and cerebellum (metencephalon)
• medulla (myelencephalon)

Question 2

Motor tracts originating from the brainstem

Answer 2

• rostral colliculus: medial tectospinal tract (visual reflex and auditory reflex to muscles of neck to turn head)
• tectotegmentospinal tract (pupillary dilation, SANS to T1-2 to sympathethic trunk)
• red midbrain: rubrospinal tract (last place where things decessate)
• pons: pontine reticulospinal tracts (extensor muscles)
• medulla: medullary reticulospinal tract (flexor muscles)
• vestibulospinal tract

Question 3

Motor tract originating from the cerebral cortex and its path down the brainstem

Answer 3

• Corona radiata
• Internal capsule
• Crus cerebri
• Longitudinal fibers of the pons
• Pyramids
• Lateral and ventral corticospinal tracts (coming from cortex, down to the spine)

Question 4

What areas of the midbrain function in reflex activity?

Answer 4

Rostral colliculi: visual reflex activity
Caudal colliculi: auditory reflex activity
- go down tectospinal tracts to C spine

Question 5

Reticular formation

Answer 5

Central core of brain stem

• coordinates motor and sensory activities
• basis of consciousness and alertness (ascending reticular activating system)
• no defined organization

Question 6

Reticular functions

Answer 6

• wakefullness/ARAS
• motor function
• respiratory and cardiovascular control
• urination
• vomiting

Question 7

Urination

Answer 7

Pontine micturition center (PSANS)
- to parasympathetic nuclei in sacral spine
- pelvic nerve to contract smooth muscle of bladder
- voiding
Medullary reticulospinal tracts (SANS)
- to sympathetic nuclei in TL spine to viscera
- hypogastric nerve
- inhibitory to detrusory muscle and excitatory to bladder neck and proximal urethra
- filling

Question 8

Vomiting

Answer 8

VC located in medullary reticular formation

• input from vestibular receptors, cerebral cortex, nucleus of solitary tract, chemoreceptor trigger zone
• output to motor nucleus of hypoglossal nerve, parasympathetic nucleus of vagus nerve, spinal cord for abdominal muscles and diaphragm

Question 9

Respiratory and cardio control

Answer 9

• chemoreceptors from carotid (CN 9) and aortic (CN 10) bodies to increase respiration in response to decreased PaO2 or increased PaCO2

Question 10

Motor function

Answer 10

Pontine and medullary reticulospinal tracts

Question 11

Wakefulness

Answer 11

• nonspecific thalamic nuclei

- diffuse cortical projection system