Lower Brainstem Functions

Front 1

Medulla Functions

Back 1

- contains tracts
- REGULATES:
1. breathing
2. BP
3. others (swallowing, vomitting)

Front 2

Pons

Back 2

- contains tracts
- relays signals from cerebellum to the forebrain
- also important in breathing regulation

Front 3

What central mechanisms generate respiratory rhythm?

Back 3

basic respitratory rhythm via RESPIRATORY CENTRE
- INSPIRATION: inc. firing rate
- rate and depth regulated by inputs from
1. PCO2, pH, PO2 via resp. centre
2. Afferents from lungs
3. Inputs from higher brain centres (eg motor cortex)

Front 4

Where is the CO2 level sensed and how does it drive breathing?

Back 4

- medullary chemoreceptors (currently thought to be in the retrotrapezoid nucleus (RTN) in caudal pons/rostral medulla
- INC. CO2 v.powerful stimulus to breathing

Front 5

Where is the blood O2 level sensed and how does it drive
breathing?

Back 5

Peripheral Chemoreceptors
- in the carotid body that respond to levels of O2 in the blood (also in arotic bodies)
- via CN IX

Front 6

Breathing increases during exercise, fear or arousal. What mechanisms cause that?

Back 6

Forebrain centre feeds onto RTN

Front 7

The pattern of breathing (i.e. duration of inspiration) is reflexly affected by afferent inputs from lungs. What are the receptors and reflex pathways?

Back 7

Hering-Breuer reflex
- Pulmonary stretch receptors in the bronchi & bronchioles that are excited when the lungs inflate
- this messages travels to resp. centre inthe brainstem via vagus and cause inhibition of inspiration via pneumotaxic centre
- thus limits inspiration and reduce the depth of breathing and increases its rate
- protective against lung overinflation and also min. work
- there are also inputs from the receptors in the chest wall that play a role in min. resp. work

Front 8

EMG of diaphragm

Back 8

Front 9

Respiratory Centres in Brainstem

Back 9

- Dorsal Respiratory Group DRG: consist mainly inspiratory neurons
- Ventral Respiratory Group VRG: both inspiratory and expiratory neurons
- Pneumotaxic Centre (PONS): inhibit inspiratory neurons, thus limit inspiration
- Apneustic centre (PONS): excite inspiratory neurons
- INSPIRATORY neurons many descend spinal cord to control motoneurons to inspiratory muscles
- EXPIRATION is a passive process but some neuroms also descend to drive expiration

Front 10

2 theories for Respiratory Rhythmogenesis

Back 10

1. pacemaker theory
2. Network theory

Front 11

BP regulation (rat)

Back 11

NA: vagal preganglionic regulates HR
RVLM (rostral ventrolateral medulla): regulating sympathetic outflow to heart, blood vessels, adrenal medulla
NTS: BP and breathing; termination site of inputs for a whole range of receptor, IX and X afferent fibres
from visceral receptors in CV system, lungs, gut etc
(e.g. from baroreceptors, chemoreceptors and lung
inflation receptors)
Area Postrema: lacks BBB so circulating substances (eg AngII act directly here)

Front 12

RVLM neurons

Back 12

• project directly to sympathetic preganglionic neurons in spinal cord
• are tonically active, and this tonic activity maintains resting sympathetic activity and hence resting blood pressure
• receive inputs (excitatory and inhibitory) from a wide range of peripheral receptors and from cardiovascular nuclei in the pons, midbrain, and forebrain
• are a critical component of baroreceptor and other cardiovascular reflex pathways, as well as pathways mediating cardiovascular responses from higher centres

Front 13

How is BP to different areas of the body regulated?

Back 13

Premotor sympathetic neurons in RVLM consist of subgroups that regulate specific vascular beds

Front 14

Reflexes for cardiovascular Challenges

Back 14

Cardiovascular challenges evoke reflex changes in sympathetic nerve activity which tends to restore homeostasis

DEPENDS on baroreceptors and RVLM

Front 15

Baroreceptors Reflex

Back 15

- via DISINHIBTION