Exam 1: Alpha and Beta Receptors, Newborn reflexes and fusion of skull

Alpha and Beta Receptors

These receptors are part of the sympathetic nervous system (fight-or-flight response).

When the body is under stress:

• The adrenal glands release epinephrine (adrenaline) and norepinephrine (noradrenaline).

• These hormones stimulate adrenergic receptors (alpha and beta receptors) located in the heart, blood vessels, and lungs.

Adrenergic simply means related to epinephrine and norepinephrine.

Alpha-1 (α1) Receptors

Location

• Blood vessels

Effect when stimulated

• Vasoconstriction (blood vessels constrict/narrow)

• Increases blood pressure

• Skin becomes:

  • Pale

  • Cool

  • Clammy

Purpose

Constricts blood vessels so blood is redirected to vital organs during the fight-or-flight response.

Remember:

Alpha = Arteries constrict

Beta-1 (β1) Receptors

Location

• Heart

Effect when stimulated

• Increased heart rate

• Increased force of heart contractions

• Increased cardiac output

Purpose

Allows the heart to pump more blood and oxygen throughout the body during stress.

Remember:

Beta-1 = 1 heart

Beta-2 (β2) Receptors

Location

• Lungs (bronchi)

Effect when stimulated

• Bronchodilation (bronchi widen)

Purpose

Allows more air to move into and out of the lungs so:

• More oxygen reaches the alveoli

• More oxygen becomes available to body tissues

Remember:

Beta-2 = 2 lungs

Parasympathetic (Muscarinic) Receptors

Not part of the fight-or-flight response.

Location

• Heart

Effect when stimulated

• Decreased heart rate

• Decreased force of contraction

This is the body's rest-and-digest response.

Easy Comparison Table

Receptor	Location	Effect
Alpha-1	Blood vessels	Vasoconstriction → ↑ Blood pressure, pale/cool/clammy skin
Beta-1	Heart	↑ Heart rate, ↑ Force of contraction, ↑ Cardiac output
Beta-2	Lungs	Bronchodilation → More airflow and oxygen
Muscarinic	Heart	↓ Heart rate, ↓ Force of contraction

 Moro Reflex (Startle Reflex)

Triggered by:

• Sudden noise

• Sudden movement

• Infant being startled

Response:

• Opens arms wide

• Spreads fingers

• Appears to grasp for something

Purpose:

• Normal protective/startle reflex.

 Palmar Grasp Reflex

Triggered by:

• Placing an object in the newborn's palm.

Response:

• Hand instinctively closes around the object.

 Rooting Reflex

Triggered by:

• Touching or stroking the newborn's cheek.

Response:

• Infant turns head toward the side that was touched.

Purpose:

• Helps the infant locate the breast or bottle for feeding.

 Sucking Reflex

Triggered by:

• Stroking the baby's lips with the nipple (or anything touching the lips).

Response:

• Infant begins sucking and latches onto the nipple.

Purpose:

• Allows feeding.

Fusion of the Skull (Fontanelles)

At Birth

The bones of the skull are:

• Not fully developed

• Not fused together

Instead, the spaces between the bones are connected by flexible fibrous tissue called fontanelles ("soft spots").

Purpose of Fontanelles

Fontanelles allow:

• The newborn's head to change shape slightly while passing through the birth canal.

• Continued growth of the brain and skull during infancy.

Closure of the Fontanelles

Posterior Fontanelle

• Located at the back of the skull.

• Normally closes by about 3 months of age.

Anterior Fontanelle

• Located on the top/front of the skull.

• Normally closes between 9 and 18 months of age.

Assessing Fontanelles

Fontanelles can give EMTs important information about an infant's condition.

Depressed (Sunken) Fontanelle

May indicate:

• Dehydration

Bulging Fontanelle

May indicate:

• Increased intracranial pressure (ICP)

This is an important sign of a potentially serious neurologic condition.