7.1 efferent pathways

The cardiovascular system is made up of 

• The blood, the heart & the blood vessels.

• It is in charge of ensuring the delivery of oxygen & nutrients to all tissues in the body.

Autonomic control of the cardiovascular system

• heart & blood is under control

Heart

• pump that pushes blood through the blood vessels

The heart beats spontaneously thanks to its

• intrinsic pacemaker (SA node) at about 100 bpm.

 The parasympathetic NS (heartbeat)

• inhibits the SA node via muscarinic receptors

• lowering HR

• resting heart rate (HR) is 60-80 bpm.

The sympathetic NS (HR)

• increases heart rate and blood pressure via β- adrenergic receptors in the SA node & ventricles

 blood vessels can constrict or dilate to 

• regulate blood pressure & blood flow to different tissues.

Vasoconstriction

• the smooth muscle of the arteriole contracts.

• Vessel diameter decreases → blood pressure increases

Vasodilation

• The smooth muscle of the arteriole relaxes.

• Vessel diameter increases → blood pressure decreases.

The sympathetic NS innervates the 

• smooth muscle of arterioles.

Sympathetic stimulation causes

• Vasoconstriction in most arterioles, but vasodilation in those supplying oxygen to skeletal muscle, liver, lungs, &heart.

• Overall ↑BP*

Breathing is

• Automatic

• generated by centers in the brainstem that set the basic rhythm in response to many inputs

• including chemoreceptors that detect O2/CO2/pH in the blood.

Autonomic input modulates

•  airway diameter, affecting resistance & airflow

Sympathetic activation 

• β₂ adregnergic receptors → ↑diameter → more airflow

 Parasympathetic activation:

• Muscarinic receptors → ↓diameter → less airflow

The physiology of anxiety symptoms

•  Emotional/stress threat signals (amygdala → hypothalamus)

Hypothalamus responds to this threat in several ways:

• influences the brainstem respiratory centers

• activates the sympathetic nervous system

• activates the HPA axis

Panic attack

• A transient dysregulation of limbic–brainstem coupling, producing exaggerated autonomic & respiratory output

The hypothalamus & brainstem control 

• balance between both autonomic branches 

Most organs & glands are

• innervated by both branches with opposite effects (dual innervation)

Single innervation (just by sympathetic) in

• Medulla of the adrenal gland

• Kidneys

• Sweat glands

• Piloerector muscle in the skin

• Most blood vessels

Muscarinic (Ach) antagonists

• Atropa belladonna (atropine).

• Block the muscarinic ACh receptor

Muscarinic agonist

• Amanita muscaria (muscarine)

• Binds to the muscarinic ACh receptor

The control that an AUTONOMOUS NEURON exerts in its target depends on:

• Neurotransmitters concentration

•  Type & number of receptors 

Autonomic reflexes

• adjust organ function automatically

Autonomic reflexes adjust organ function automatically →

• a stimulus is detected by sensory receptors, processed in the CNS, & then sympathetic or parasympathetic responses are triggered to maintain homeostasis

Central control of ANS responses

• Forebrain

• Cingulate Cortex

• Insular Cortex

• Amygdala

• Hypothalamus 

• Brainstem

• Spinal cord / Autonomic nerves 

Control by hormones/NTs:

• Cortisol, adrenalin: ↑Sympathetic

• Oxytocin, endogenous opioids: ↑ Parasympathetic