Final Page 4

Autonomic Nervous System (ANS)

Overview of the ANS

The Autonomic Nervous System (ANS) is a division of the peripheral nervous system that regulates involuntary physiological processes, including heart rate, blood pressure, respiration, digestion, and sexual arousal. It consists of the sympathetic and parasympathetic divisions, which often have opposing effects.

• Sympathetic Division: Prepares the body for 'fight or flight' responses.

• Parasympathetic Division: Promotes 'rest and digest' activities.

Origin of Sympathetic and Parasympathetic Nerves

• Sympathetic nerves: Originate from the thoracolumbar region of the spinal cord (T1-L2).

• Parasympathetic nerves: Originate from the craniosacral regions (cranial nerves III, VII, IX, X and sacral spinal cord S2-S4).

Neurons in the ANS

• Preganglionic Neuron: The first neuron in the autonomic pathway; its cell body is in the CNS.

• Postganglionic Neuron: The second neuron; its cell body is in an autonomic ganglion outside the CNS.

• Long Preganglionic, Short Postganglionic: Characteristic of the parasympathetic division.

• Short Preganglionic, Long Postganglionic: Characteristic of the sympathetic division.

Neurotransmitters of the ANS

• Acetylcholine (ACh): Released by all preganglionic neurons and by parasympathetic postganglionic neurons.

• Norepinephrine (NE): Released by most sympathetic postganglionic neurons.

Functions and Effects of the ANS

• Sympathetic Effects: Increases heart rate, dilates pupils, inhibits digestion, stimulates sweat glands.

• Parasympathetic Effects: Decreases heart rate, constricts pupils, stimulates digestion, promotes glandular secretion.

Primary Neurotransmitter Throughout the ANS

• Acetylcholine (ACh): Used by all preganglionic neurons and parasympathetic postganglionic neurons.

• Norepinephrine (NE): Used by most sympathetic postganglionic neurons.

Special Senses: The Eye

Functions of Eye Structures

• Sclera: The white, protective outer layer of the eye.

• Cornea: Transparent front part that refracts light.

• Choroid: Vascular layer providing oxygen and nutrients.

• Pupil: Opening that regulates the amount of light entering the eye.

• Lens: Focuses light onto the retina.

Retina and Visual Pathways

• Retina: Contains photoreceptor cells (rods and cones) that detect light and initiate vision.

• Optic Nerve: Transmits visual information from the retina to the brain.

Visual Cortex

• Location: Occipital lobe of the cerebrum.

• Function: Processes visual information received from the eyes.

Autonomic Effects on Organs

Responses to Sympathetic and Parasympathetic Stimulation

Organ	Sympathetic Response	Parasympathetic Response
Pupil	Dilation (mydriasis)	Constriction (miosis)
Heart	Increased rate and force	Decreased rate
Stomach	Decreased motility	Increased motility
Urinary Bladder	Relaxation (inhibits urination)	Contraction (promotes urination)

Peripheral Nerves and Cranial Nerves

Major Cranial Nerves and Their Functions

• Optic Nerve (II): Vision.

• Oculomotor Nerve (III): Eye movement, pupil constriction.

• Trochlear Nerve (IV): Eye movement.

• Trigeminal Nerve (V): Sensation in the face, chewing muscles.

• Abducens Nerve (VI): Eye movement.

• Facial Nerve (VII): Facial expression, taste, salivary glands.

• Vestibulocochlear Nerve (VIII): Hearing and balance.

• Glossopharyngeal Nerve (IX): Taste, swallowing.

• Vagus Nerve (X): Autonomic control of heart, lungs, digestive tract.

Spinal Nerves and Innervation

• Spinal Nerves: Arise from the spinal cord and innervate the trunk and limbs.

• Somatic Motor Nerves: Control voluntary muscle movements.

• Autonomic Motor Nerves: Control involuntary functions.

Additional info:

• Some content inferred from standard Anatomy & Physiology curriculum regarding ANS neurotransmitters and cranial nerve functions.

• Table entries for organ responses are based on typical textbook comparisons.