Lecture 8: Brainstem Flashcards
What are the structures that make up the brainstem?
1) Midbrain
2) Pons
3) Medulla oblongata
Whats the function of the brainstem?
Controls many essential functions:
- HR, Breathing, Sleeping and Eating
- Pathways of the motor and sensory systems pass through the brainstem
What pathways pass through the brainstem?
Motor:
Corticospinal tract
Corticobulbar tract
Sensation:
Dorsal column medial laminiscus pathway (Fine touch, vibration, sensation, proprioception)
Spinothalamic tracts (Pain, temperature, itch, crude touch)
Cranial nerve contributions
What is the midbrain structure?
Tectum
Cerebral aqueduct
Tegmentum
Crus cerebri (basis penduculi???)
What name is synonymous with the midbrain and what does it sit inbetween?
Mesencephalon
Sits under the diencephalon (thalamus, hypothalamus) and above the metencephalon (Hindbrain, pons+ Cerebellum)
Describe the pons structure:
Two parts:
- Basilar part (ventral)
- Pontine Tegmentum (dorsal pons)
What is the function of the midbrain?
Hearing, vision, sleep/wake cycle, arousal, motor control and temperature regulation
What is the function of the pons?
Contains centres for:
- Respiration
- Involuntary actions
- sensory roles in hearing, equilibrium, taste and facial sensation (touch and pain)
- Motor roles in eye movement, facial expression, chewing, swallowing, saliva and tear secretion (cranial nerves)
- Relay stations
What are the function of the medulla?
Cardiac, respiratory, vomiting, vasomotor centres
Autonomic functions; Breathing, HR and BP
Where is the tegmentum located and what does it contain?
Tegmentum passes thought all layers of the brainstem
Contains:
- Sensory pathways
- Many nuclei
- > Cranial nerve nuclei
- > Homeostatic nuclei
What is the function of the sup. colliculus?
Control modulation of eye movement to stimuli. ‘Scitactic movement’. i.e Shock or surprise, eye moves back towards stimuli.
What is the function of the inf. colliculus?
- Auditory, projects to thalamus
What is the functions of the pars basilaris?
- Many pathways
- Pontine nucleus
- Fibers cross middle cerebral peduncle allowing cerebellar connections
Describe the pathway of the corticospinal / corticobulbar pathway:
Pathway:
- Down the crus cerebri (Somatotopically) (CBT medial, CST lateral)
- Through the pars basilaris (Bundles are formed and separate out)
- Down through the medullary pyramids (CST only, comes back to form pyramids)
- Onto the spinal cord
Corticobulbar pathway sends projections from CST in the pons and medulla to motor nuclei (Cranial nerve motor nuclei)
How is the crus cerebri arranged?
Somatotopically.
- CBT has motor info for the head and is located more medially
- CST is more lateral and contains motor info for rest of body.
What happens to the CST in the spine?
80% of fibers decussate at the medulla/spinal junction forming the lateral CST. Remaining fibres that do not decussate form the anterior CST.
What is the difference in function between the anterior and lateral CST?
Lateral CST = Limbs (more muscles thus more neurons)
Anterior CST = Trunk etc
Describe the pathway of the spinothalamic tract:
- Free nerve endings i.e in hand, sense pain and temperature and via A+C fibers and synapse with second order neurons in the spinal cord.
- The second order neuron decussates at the same level and ascends through the contralateral spinothalamic tract.
- This projects to the intralaminar thalamic nuclei in the thalamus.
- The third order neuron projects to the primary sensory cortex.
Describe the pathway of the dorsal column pathway:
Myelinated A fibers carrying discriminative (fine) touch, vibration, and proprioception i.e mechanoreceptors feed into the spinal cord and travel up to the dorsal nuclei in the tegmentum in the medulla.
The second order neuron decussates and travels up the contralateral side to the thalamus. It synapses with a third order neuron that feeds to the primary sensory cortex.
Describe the corticopontine pathway:
Fibers project down from the cortex through the crus cerebri lateral to the CST. and decussate at the level of the pons before synapsing on pontine nuclei.
In the brainstem how are motor and sensory nuclei arranged?
Motor nuclei are more anterior than sensory.
Motor nuclei are also more medial and sensory more lateral.
These are further arranged based on function.
See if the new slides are uploaded.
What is the periaquaductal grey?
- Area of neurons that surround the cerebral aqueduct
- Involved in pain modulation
- Sends projections down to rex lamina 7 and can turn down pain stimuli.
What is the red nuclei?
Red nuclei
- Part of the rubrospinal tract
- Receives inputs from the brain and cerebellum to coordinate movements
Where is the red nuclei located?
Medial tegmentum of the midbrain
Describe the rubrospinal tract:
Cortex and cerebellum project to the red nuclei in the tegmentum of the mid brain
- It then projects down to the spinal cord and sends projections to the inf. olivary complex enroute.
Rubrospinal tract involved in smooth limb control
ONLY UPPER LIMBS
What body parts is the rubrospinal tract involved in?
Upper limbs only
Describe the inf. olivary complex projections and location:
Located in the tegmentum of the medulla.
- Projects fibers contralaterally to the cerebellum via the inf. cerebral peduncle.
Coordinates movements.
What is the reticular formation?
Loosely defined through the brainstem
- An intricate system of loosely clustered nuclei
- Major integration and relay centers of the brain for coordination of vital brain function
i.e Somatic motor control- Reticulospinal tract. Pain modulation - Raphe nuclei -> Sleep consciousness arousal -> Control of GI, resp, CV function
What nuclei are found in the medulla oblongata?
Cranial nerve nuclei: (IX-XII) i.e inf. salivatory nucleus, spinal nucleus of trigeminal nerve, nucleus ambiguus, dorsal nucleus of vagus, nucleus of accessory and hypoglossal
Relay nuclei: Gracile, cuneate, olivary
Reticular nuclei:
What nuclei are found in the pons?
Cranial nerve nuclei:
- Spinal trigeminal nucleus
- Mesencephalic nucleus
- Abducens nucleus
- Facial nucleus
- Cochlear and vestibular nuclei
CN; 5,6,7,8
What nuclei are found in the midbrain?
Red nucleus (Rubrospinal tract) Raphe nucleus (Serotonin)
Oculomotor nuclei
Trochlear nuclei
