Study Guide: Special Senses and Autonomic Nervous System

Chapter 15: The Special Senses

Development and Anatomy of the Eye

The eye is a complex sensory organ responsible for vision. Understanding its development and structure is essential for comprehending how visual information is processed.

• Embryonic Development: The eye develops from the optic vesicle, which forms from the neural tube in the embryo.

• General Anatomy: The eye consists of three main layers and several accessory structures.

Layers of the Eyeball

• Fibrous Layer: Outermost layer; includes the sclera (white of the eye) and cornea (transparent front part).

• Vascular Layer: Middle layer; includes the choroid (provides blood supply), ciliary body (controls lens shape), and iris (regulates pupil size).

• Inner Layer: Also called the neural layer; consists of the retina, which contains photoreceptor cells (rods and cones).

Accessory Structures

• Lacrimal Apparatus: Produces and drains tears.

• Eyelids and Eyelashes: Protect the eye from debris and injury.

Retina and Photoreceptors

The retina is the light-sensitive layer of the eye, containing two main types of photoreceptors:

• Rods: Sensitive to low light; responsible for night vision.

• Cones: Detect color and provide sharp central vision.

Photoreceptors convert light into electrical signals, which are processed by the brain to form images.

Adaptation to Light and Dark

• Light Adaptation: Adjustment of the eye to bright light; involves the constriction of pupils and decreased sensitivity of photoreceptors.

• Dark Adaptation: Adjustment to low light; involves dilation of pupils and increased sensitivity of rods.

Visual Pathways

• Signals from the retina travel via the optic nerve to the brain's visual cortex.

Anatomy and Physiology of the Ear

The ear is responsible for hearing and balance. It consists of three main regions:

• Outer Ear: Collects sound waves.

• Middle Ear: Transmits vibrations via ossicles (malleus, incus, stapes).

• Inner Ear: Contains the cochlea (hearing) and vestibular apparatus (balance).

Hearing Mechanism

• Sound waves cause vibrations in the tympanic membrane, which are transmitted through the ossicles to the cochlea.

• Hair cells in the cochlea convert vibrations into nerve impulses.

Balance and Equilibrium

• Vestibular Apparatus: Includes the semicircular canals and vestibule, which detect head movement and position.

• Key Structures: Maculae (detect linear acceleration), Crista Ampullaris (detect rotational movement).

Other Special Senses: Taste and Smell

Taste and smell are chemical senses that detect molecules in food and the environment.

• Taste Buds: Located on the tongue; detect five basic tastes: sweet, sour, salty, bitter, umami.

• Olfactory Receptors: Located in the nasal cavity; detect airborne chemicals.

Taste and smell work together to create the perception of flavor.

Chapter 14: The Autonomic Nervous System (ANS)

Overview of the ANS

The autonomic nervous system controls involuntary functions such as heart rate, digestion, and respiratory rate. It is divided into the sympathetic and parasympathetic divisions.

• Somatic vs. Autonomic Motor Systems: The somatic system controls voluntary skeletal muscles, while the ANS controls involuntary smooth and cardiac muscles and glands.

Sympathetic vs. Parasympathetic Divisions

• Sympathetic Division: Prepares the body for 'fight or flight' responses; increases heart rate, dilates pupils, inhibits digestion.

• Parasympathetic Division: Promotes 'rest and digest' activities; decreases heart rate, stimulates digestion.

Anatomy of the ANS

• Preganglionic Neurons: Originate in the CNS and synapse in autonomic ganglia.

• Postganglionic Neurons: Originate in ganglia and innervate target organs.

• Sympathetic Ganglia: Located near the spinal cord.

• Parasympathetic Ganglia: Located near or within target organs.

Neurotransmitters of the ANS

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

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

Receptors

• Cholinergic Receptors: Bind acetylcholine; include nicotinic and muscarinic receptors.

• Adrenergic Receptors: Bind norepinephrine; include alpha and beta receptors.

Autonomic Reflexes

• Involve two neurons (preganglionic and postganglionic) and regulate functions such as heart rate and digestion.

Comparison Table: Somatic vs. Autonomic Nervous System

Feature	Somatic NS	Autonomic NS
Control	Voluntary	Involuntary
Effector Organs	Skeletal Muscle	Smooth & Cardiac Muscle, Glands
Number of Neurons	One	Two (pre- and postganglionic)
Main Neurotransmitter	Acetylcholine	Acetylcholine, Norepinephrine

Example:

• During exercise, the sympathetic division increases heart rate and redirects blood flow to muscles.

• After eating, the parasympathetic division stimulates digestion and nutrient absorption.

Additional info: The study guide also references the use of tables for comparing sympathetic and parasympathetic effects on organs, which is a common exam topic.