Nerves, Reflexes & Circadian Rhythms

What is a nerve?

A bundle of axons held together by connective tissue with blood vessels

Why is a nerve not the same as a neuron?

A nerve contains many neuron axons

What structures are visible in a nerve cross-section?

Fascicles, myelinated/unmyelinated axons, blood vessels

Can nerves contain both sensory and motor neurons?

Yes

What is a reflex?

A rapid, involuntary response to a stimulus

What is a reflex arc?

The neural pathway mediating a reflex

List the components of a reflex arc

Receptor, sensory neuron, integration center, motor neuron, effector

What is the function of the cerebellum?

Coordinates balance and unconscious muscle movement

What are circadian rhythms?

Physiological responses to the 24-hour day-night cycle

What hormone regulates circadian rhythms?

Melatonin

Where is melatonin produced?

Pineal gland

What is the role of the SCN?

Acts as a central pacemaker synchronizing circadian rhythms

When is melatonin secretion highest?

During darkness

How does light affect melatonin secretion?

Bright light suppresses melatonin

How does melatonin affect nocturnal vs diurnal animals?

Promotes activity in nocturnal animals and sleep in diurnal animals