Week 6 - Brainstem functions

Question 1

What is the brainstem

Answer 1

Midbrain, pons and medulla

Question 2

3 main functions of the brainstem

Answer 2

• Conducts all the communication between the brain and spinal cord.
• Target or source of the cranial nerves.
• Regulates the level of consciousness.

Question 3

Origin of dopamine

Answer 3

substantia nigra (pars compacta) and ventral tegmental area (VTA) in the midbrain.

Question 4

Function of dopamine

Answer 4

motor control, motivation reward and cognition.

Question 5

Clinical relevance of dopamine

Answer 5

degeneration of dopaminergic neurons in the substantia nigra is linked to Parkinson’s disease.

Question 6

What is the link between brainstem and neurotransmitter?

Answer 6

Major site for neurotransmitters production

Question 7

Origin of acetylcholine

Answer 7

pedunculopontine nucleus and laterodorsal tegmental nucleus in the midbrain and pons.

Question 8

Function of acetylcholine

Answer 8

Arousal, REM sleep, and motor control.

Question 9

Clinical relevance of acetylcholine

Answer 9

cholinergic deficits are associated with Alzheimer’s disease and other cognitive disorders.

Question 10

Origin of norepinephrine

Answer 10

locus coeruleus in the pons

Question 11

Function of norepinephrine

Answer 11

attention, arousal, stress response, and autonomic regulation.

Question 12

Clinical relevance of norepinephrine

Answer 12

Involved in ADHD, anxiety, and stress-related disorders.

Question 13

Origin of serotonin

Answer 13

Raphe nuclei, located throughout the midbrain, pons, and medulla.

Question 14

Function of serotonin

Answer 14

mood regulation, sleep, appetite, pain perception.

Question 15

Clinical relevance of serotonin

Answer 15

implicated in depression, anxiety, and sleep disorders.

Question 16

Origine of glutamate

Answer 16

widespread throughout the brainstem

Question 17

Function of glutamate

Answer 17

primary excitatory neurotransmitter; involved in sensory and motor signaling.

Question 18

Clinical relevance of glutamate

Answer 18

Excessive glutamate activity can lead to excitotoxicity, implicated in stroke and neurodegeneration.

Question 19

Origin of Gamma-Aminobutyric Acid (GABA)

Answer 19

also widespread in the brainstem.

Question 20

Functions of Gamma-Aminobutyric Acid (GABA)

Answer 20

primary inhibitory neurotransmitter; modulates neuronal excitability and muscle tone.

Question 21

Clinical relevance of Gamma-Aminobutyric Acid (GABA)

Answer 21

altered GABAergic function is linked to epilepsy, anxiety, and sleep disorders.

Question 22

Pain modulation circuit

Answer 22

1. Inputs to the Periaqueductal gray:
   * From the amygdala (emotional processing — fear, stress)
   * From the hypothalamus (autonomic and hormonal control)
   * From the somatic sensory cortex (pain perception)
   * From the anterolateral system (ascending pain signals)
2. The PAG integrates all of these signals and decides how to modulate pain and stress responses.
3. Outputs from the PAG:
   * It sends descending projections to:
   o Parabrachial nucleus
   o Medullary reticular formation
   o Locus coeruleus
   o Raphe nuclei
   * These nuclei then project down to the dorsal horn of the spinal cord.
4. End result:
   * These lower brainstem nuclei release neurotransmitters (like serotonin, norepinephrine, and endorphins) that inhibit or increase pain transmission at the spinal level.

Question 23

What is the function and content of the medulla

Answer 23

• Lower part of the brain
• Merges into the spinal cord
• Heart rate, blood pressure, breathing, temperature (stroke is devastating)
• Reflexes: vomiting, sneezing, digestion, balance
• Crossing fibers:
  Medial lemniscus
• Medullary pyramids
• Inferior olive

Question 24

What is the role of the medullary pyramids?

Answer 24

o Descending corticospinal tract. These are the motor fibers coming from the cerebral cortex that control voluntary movement of the body.

Question 25

What are the crossing fibers in the medulla?

Answer 25

o Pyramidal decussation o Internal arcuate fibers – Medial lemniscus

Question 26

What is the role of the inferior olive in the medulla?

Answer 26

o Fine motor behavior o Major source of input to the cerebellum o Coordination of signals from the spinal cord to the cerebellum to regulate motor coordination and learning.

Question 27

What structure is in the caudal medulla?

Answer 27

* Nucleus gracilis * Nucleus cuneatus * Spinothalamic tract (anterolateral system) * Pyramids

Question 28

What is the pons?

Answer 28

Mass of decussating fibers that cross the midline

Question 29

What structure is in the pons

Answer 29

* Pontine nuclei o Involved in motor activity (relay info from M1 to the cerebellum) * Cerebellar peduncles o Contains the tracts between the brain and cerebellum. * Mesopontine cholinergic system (ACh) o Arousal, attention, learning, reward, voluntary movement and locomotion * The locus coeruleus (NE) – reticular system o Arousal, emotions, mood and autonomic system

Question 30

What structure is in the midbrain?

Answer 30

* Superior colliculus * Inferior colliculus * Substancia nigra (dopamine) * Red nucleus * Cerebral peduncles (crus cerebris)

Question 31

What is the role of the superior colliculus?

Answer 31

o Involved in vision o Involved in multisensory integration o Involved in neck and ocular movement

Question 32

What is the role of the inferior colliculus?

Answer 32

o Involved in auditory system

Question 33

What is the role of the substancia nigra (dopamine)?

Answer 33

o Basal ganglia (Parkinson’s disease)

Question 34

What is the role of the red nucleus?

Answer 34

o Origin of the rubrospinal tract o Upper limb = regulation of flexor and inhibiting extensor

Question 35

What is the role of the cerebral peduncles (crus cerebris)?

Answer 35

o Massive projections from the cerebral cortex to brainstem and spinal cord targets.

Question 36

What is the reticular formation?

Answer 36

* Numerous clusters of neurons scattered among axon bundles The reticular formation is a network of neurons that runs through the entire brainstem, from the medulla, through the pons, up to the midbrain. It isn’t one single structure, but rather a web-like collection (“reticulum”) of nerve cells and fibers that are interconnected and spread among other brainstem tracts. Because of this, it looks like a “mesh” of gray and white matter mixed together, not neatly separated like other brain areas.

Question 37

What are the functions of the reticular formation?

Answer 37

o Emotional processing, sleep and pain regulation, mood  Raphe nuclei / serotonin o Stress, attention, heightening alertness and arousal  Locus coeruleus / norepinephrine o Cardiovascular and respiratory digestive controls. These are handled mainly by autonomic centers in the medulla (part of the reticular formation). They integrate sensory input (like blood pressure, oxygen, stomach distension) and send signals to the heart, lungs, and gut via the vagus nerve and spinal autonomic fibers. o Reticulospinal tract (limb and trunck movements). The reticulospinal tracts coordinate core and limb movements for posture and locomotion, working alongside the cerebellum. o Relay eye and ear signals to the cerebellum. The reticular formation also receives sensory input from visual and auditory pathways. It relays this information to the cerebellum, which uses it for balance and coordination.

Question 38

What is the central autonomic network?

Answer 38

complex neural network in the brain and spinal cord that regulates the ANS – key components are the brainstem (reticular formation), insular cortex, anterior cingulate cortex (ACC) and amygdala.

Question 39

What does the mesencephalic and rostral pontine reticular formation modulate?

Answer 39

Modulates forebrain activity

Question 40

What does the caudal pontine and medullary reticular formation modulate?

Answer 40

Premotor coordination of lower somatic and visceral motor neuron pools

Question 41

What is the pathway of the reticulospinal tract?

Answer 41

1. Starts in the motor cortex (M1 and premotor cortex) o These areas send movement commands not only down the direct corticospinal tract but also to the reticular formation in the pons and medulla. 2. Reaches the reticular formation (in the brainstem) o This area integrates signals about balance, posture, and sensory feedback. o The neurons here form two main reticulospinal tracts:  Pontine (medial) reticulospinal tract  Medullary (lateral) reticulospinal tract 3. Descends to the spinal cord o These fibers travel down through the reticulospinal tracts and end mainly in the medial part of the ventral horn of the spinal cord (as shown at the bottom of the figure). o This area controls axial (trunk) and proximal (shoulder and hip) muscles — the muscles that maintain posture and stabilize the body.

Question 42

What is the function of the reticulospinal tract?

Answer 42

* Posture & Balance: Adjusts your trunk and limb position to keep you upright. * Anticipatory Movements: Activates core muscles before you move your limbs (for example, tightening your abdomen before raising your arm). * Automatic Movements: Coordinates walking, running, and startle reflexes. * Integration with other systems: Works with the vestibulospinal tract (balance) and corticospinal tract (voluntary control) for smooth, coordinated movement.

Question 43

Where on the spinal cord the reticulospinal tract synapse and why?

Answer 43

C. Medial Part of the Ventral Horn = Axial & Proximal Muscles This note means: * The medial (inner) part of the ventral horn in the spinal cord contains motor neurons that control axial (trunk) and proximal (near-the-body) muscles. * The reticulospinal tract primarily synapses on these neurons — so it controls postural and large-scale movements, not fine finger movements.

Question 44

Where is the origin of the vestibulospinal tract?

Answer 44

* These fibers start in the vestibular nuclei, which are located in the rostral medulla and caudal pons. * The vestibular nuclei receive information from the inner ear (vestibular system) about head position and balance.

Question 45

What are the pathway of the two vestibulospinal tract?

Answer 45

There are two vestibulospinal tracts: 1. Lateral Vestibulospinal Tract o Origin: Lateral vestibular nucleus o Function: Controls posture and balance by exciting extensor muscles (like those in your legs and back). o Helps you stay upright when you start to fall — a rapid postural correction. 2. Medial Vestibulospinal Tract o Origin: Medial vestibular nucleus o Function: Coordinates head and neck movements with eye movements, helping stabilize your gaze when your head moves. o Extends mainly to the cervical spinal cord (neck region).

Question 46

What is the rubrospinal tract?

Answer 46

* Role in humans is unclear, few neurons in comparison to non-human primates and other mammals. * Lateral and intermediate parts of the ventral horn = distal muscles.

Question 47

What is the effect of the rubrospinal tract on decerebration and decortication?

Answer 47

Decerebration: there is a lesion in the rubrospinal tract Decortication: the lesion does not affect the rubrospinal tract (Between the cerebral cortex and red nucleus)