Autonomic Nervous System: Structure, Function, and Sensory Integration

Autonomic Nervous System

The motor portion of the peripheral nervous system (PNS) that controls the viscera and operates without conscious effort.

Regulation of the autonomic nervous system

The ANS regulates the actions of smooth muscle, cardiac muscle, and glands. It also plays a role in regulating heart rate, blood pressure, breathing rate, body temperature, and other activities that maintain homeostasis.

Sympathetic Division

Prepares the body for energy-expending, stressful, or emergency situations. Known as the 'fight or flight' response. Origin: thoracic & lumbar segments.

Parasympathetic Division

Prepares the body for restful conditions to facilitate digestion and relaxful bodily functions. Known as the 'rest-and-digest' response. Origin: brainstem & sacral segments.

Sensory signals associated with the autonomic nervous system

Sensory signals in the viscera and skin receptors.

Ganglia

Processes and relays integrated signals, which indicates that ganglia serves as the integration center for the autonomic nervous system, not the CNS.

Preganglionic neuron

originate in the CNS and terminate in an autonomic ganglion.

Postganglionic neuron

has its cell body in the ganglion and sends its axon to the visceral effector.

Cholinergic fibers

secrete the neurotransmitter acetylcholine (ACh) and are involved in the sympathetic and parasympathetic divisions of the ANS.

Adrenergic fibers

secrete norepinephrine (NE) and are mostly applied to the sympathetic division of the ANS.

Structures controlling the autonomic nervous system

1. Brain 2. Spinal Cord 3. Medulla Oblongata 4. Hypothalamus 5. Limbic System

General Senses

Touch, temperature, pressure, and pain.

Special Senses

Taste, smell, vision, hearing, and balance.

Chemoreceptors

Respond to changes in chemical concentration.

Nociceptors (Pain Receptors)

Activated by tissue damage signals.

Thermoreceptors

Respond to temperature fluctuations (warm and cold receptors).

Mechanoreceptors

Triggered by pressure or movement changes.

Photoreceptors

Respond to light stimuli.

Sensation

An awareness that an impulse from a sensory nerve has been received by the brain.

Perception

How the brain perceives the sensation that came from the sensory nerve.

Projection of a sensation

The process by which the brain projects the feeling or sensation back to its apparent source.

Sensory adaptation

The ability of the nervous system to become less responsive to a maintained stimulus.

Touch receptor

A sensory nerve ending that responds to mechanical stimuli.

Referred pain

Pain that feels as if it is originating from a part other than the site being stimulated.

Example of referred pain

Heart-originated pain referred to the left shoulder or upper limb.

Types of receptors for touch

1. Free nerve endings 2. Tactile (Meissner's) Corpuscles 3. Lamellated (Pacinian) Corpuscles

Proprioception

The continuous sense of where the body is in space and time.

Neurotransmitters released by nociceptors

1. Substance P 2. Glutamate

Prostaglandins

Chemical that is released when tissue is damaged, causing an increase in sensitivity of nociceptors.

Inhibitors of prostaglandins

Ibuprofen and aspirin.

Fast pain fibers

Travel on myelinated neurons and are responsible for immediate, sharp pain from a specific skin area.

Slow pain fibers

Travel on unmyelinated neurons and are responsible for delayed, dull, aching sensations from deeper in the tissue.

Eyelids

Protects the eye and is made up of four layers: skin, muscles, connective tissues, conjunctiva.

Lacrimal Gland

Secretes tears.

Extrinsic Muscles

Six muscles that are attached to the sclera that move the eye in different directions.

Cornea

Transparent layer in the anterior part of the eye that refracts (bends) light entering the eye.

Sclera

Tough, white fibrous outer layer that protects the eye and is the attachment point for the extrinsic muscles.

Choroid coat

Layer between the sclera and retina that contains many blood vessels and melanocytes.

Ciliary Body

Houses the ciliary muscles which change the shape of the lens with the suspensory ligaments and secretes aqueous humor.

Lens

Transparent elastic disc located behind the iris and pupil that focuses light on the retina.

Iris

Colored, muscular part of the eye around the pupil that regulates its size.

Aqueous Humor

Watery fluid secreted by the ciliary body filling the anterior cavity of the eyes which maintains the shape of the eye and helps with nourishment.

Pupil

Opening in the iris that allows light to pass through, controlled by circular and radial muscles in the iris.

Retina

Inner layer of the eye that contains visual receptor cells (photoreceptors) and is continuous with the optic nerve.

Optic Disc

Region in the retina that does not contain any photoreceptors, creating a blind spot. The area where nerve fibers exit to form the optic nerve.

Vitreous Humor

Gel-like fluid that fills the posterior cavity of the eye and maintains the shape of the eyeball.

Emmetropia

Normal vision where light rays focus sharply on the retina.

Hyperopia

Farsightedness. Light rays focus past the retina, unable to see objects up close.

Myopia

Nearsightedness. Light rays focus in front of the retina, unable to see objects far away.

Cataracts

Clouding of the lens. Can be treated with an artificial lens.

Glaucoma

Increased pressure within the eye, which causes a gradual loss of vision. Can be treated with eye drops, laser therapy, or surgery.

Astigmatism

Refraction of light is not accurate due to the irregular shape of the cornea or lens. Causes blurred vision. Can be treated with corrective lenses.

Macular Degeneration

Chronic eye disease that causes a loss of vision in the center of the visual eye field due to damage of the macula lutea. No cure, but can be treated to slow the progression.

Rods

Photoreceptors that have one type and provide colorless vision; work well in dim lighting.

Cones

Photoreceptors that have three types and provide color vision. If all cones are stimulated - white color; no cones stimulated - black color.

Nerve Impulse Pathway (Vision)

Photoreceptors - optic nerve - thalamus - cortex of occipital lobe.

Olfactory Organs

Masses of epithelium located in the upper nasal cavity and contains olfactory receptors (chemoreceptors).

Olfactory Receptor Pathway

Olfactory receptor cells (chemoreceptors) - olfactory bulb - olfactory tract - temporal lobe and frontal lobe.

Sense of Smell vs. Taste

One odorant molecule can bind several types of receptors creating a unique code of smell. Each taste sensation binds to one type of receptor.

Anosmia

The partial or complete loss of smell.

Taste Buds

Organs containing chemoreceptors for the sense of taste.

Sweet Taste Sensation

Example(s): Sugar, chocolate, honey, fruits, desserts, etc.

Sour Taste Sensation

Example(s): Lemons, vinegar, sour cream, yogurt, etc.

Salty

Table salt, potato chips, bacon, pickles, pretzels, etc.

Bitter

Coffee, dark chocolate, broccoli, red wine, etc.

Umami (Savory)

Grilled meats, soy sauce, tomatoes, mushrooms, etc.

Spicy foods stimulation

Warm receptors. Can stimulate nociceptors which can cause a burning sensation.

Taste sensation pathway

Chemoreceptor - sensory nerve - medulla oblongata - thalamus - gustatory cortex in the parietal lobe.

Auricle

Outer ear that collects sound waves to focus them down the ear canal (external acoustic meatus).

External Acoustic Meatus

S-shaped tube that carries sound waves from the auricle to the middle ear.

Eardrum

Membrane between the external ear and middle ear. Vibrates back and forth in response to sound waves causing the auditory ossicles to vibrate.

Auditory ossicles

Malleus - Incus - Stapes. Amplifies vibrations and transfers the vibration to the fluid in the inner ear.

Auditory tube (Eustachian tube)

The auditory tube connects the middle ear (tympanic cavity) to the nasal cavity.

Cochlea

Coiled portion of the inner ear containing hearing receptors.

Organ of Corti

Rows of hearing receptors that are stimulated by the movement of the tectorial membrane.

Average human hearing frequency

20-20,000 Hz. Lower frequencies stimulate the hearing receptors at the apex of the cochlea; higher frequencies stimulate the hearing receptors near the base of the cochlea.

Sound sensation pathway

Sound wave - external acoustic meatus - eardrum - malleus - incus - stapes - oval window - cochlea - thalamus - auditory cortex of the temporal lobe.

Equilibrium

A state of balance.

Static Equilibrium

Balance when the head and body are motionless. Part of the Inner Ear: Vestibule (utricle and saccule).

Dynamic Equilibrium

Balance when the head and body are in motion. Part of the Inner Ear: Semicircular canals.

Motion sickness

Occurs when the brain receives mixed signals from different senses.