Vision and Hearing, Reflex Activity, Autonomic Nervous System Test #4 LACC Gonzalves

electromagnetic radiation

a form of energy that exhibits wavelike behavior as it travels through space

what is a reflex ?

a rapid, "wired" motor response to a specific stimulus; involuntary, subconscious

Major Functions of ANS

maintain optimal performance of visceral organs, glands, smooth muscle, and cardiac muscle in order to maintain homeostatic state within body

electromagnetic radiation scale

-Short (10^-5 nm)

-Medium (380-750 nm)

-Long (10^2 nm)

A somatic reflex refers to:

skeletal muscle

involuntary nervous system

not under conscious control: regulates heart rate, blood pressure, respiratory rate, body temperature, smooth muscle contraction, glandular function, and secretions

wave-photon duality

light travels in wave-like fashion with "single packets" of energy called photons

A visceral (autonomic) reflex refers to:

smooth muscle, cardiac muscle, visceral organs, glands

General visceral motor system

most "effectors" (organs & tissues regulated) are visceral (as opposed to somatic - skeletal muscle & joints)

visible spectrum

*Different colors of light have different wavelengths;

-Violet 380nm

-Blue 480nm

-Green 550nm

-Yellow 630nm

-Orange 680nm

-Red 730nm

Components of a Typical Reflex Arc

-Receptor

-Sensory Neuron

-Integration Center

-Motor Neuron

-The Effector

Effectors (Target of Motor Neuron)

a.) SOMATIC - skeletal muscle

b.) AUTONOMIC - organs, glands, smooth & cardiac muscle

Efferent (Motor Neuron) Pathway

a.) SOMATIC - one motor neuron from CNS to skeletal muscle

b.) AUTONOMIC - two neurons in the motor pathway

Receptor

site where stimulus is received

How is the color of an object is determined?

its determined by which wavelengths are REFLECTED back to the retina (not absorbed by the object)

Does "white" absorb or reflect all wavelengths?

Reflect

Mechanoreceptors

sensitive to touch, pressure, vibration and stretch

Preganglionic neuron

located in the CNS, sends its axon to an autonomic ganglion located outside the CNS; lightly myelinated, thin axon

Does "black" absorb or reflect all wavelengths?

absorb

Meissner's corpuscles ( Mechanoreceptor)

receptors for discriminative touch, below skin epidermis

Postganglionic neuron

located in the autonomic ganglion, sends it axon to the effector (tissue to be effected); unmyelinated, very thin axons

light refraction of lens

light will bend when it passes from one medium (air) into another (lens) e.g. pencil in glass of water

Merkel's discs ( Mechanoreceptor)

light touch receptors in deep layers of epidermis

Action of Neurotransmitters;

"Somatic"

acetylcholine (ACh); stimulatory

Action of Neurotransmitters;

"Autonomic"

post ganglionic neurons may release either ACh or Norepinephrine (NE); whether response is stimulatory or inhibitory depends on the effector

Pacinian corpuscles (Mechanoreceptor)

respond to skin pressure/vibration, deep in the dermis

convex lens

*causes light to bend so that it comes together at a focal point

-(thicker at center, tapered at edge)

Somatic and Autonomic Systems send their motor neurons to effectors via:

the 31 pairs of spinal nerves and 12 pairs of cranial nerves

What is known as a real image?

Its an image at focal point of convex lens ---> inverted & reversed

Ruffini's corpuscles (Mechanoreceptor)

Respond to stretch of dense connective tissues

The ciliary muscles change:

Convexity of the lens

Krause's End Bulbs (Mechanoreceptor)

respond to pressure and touch, in mucous membranes

When skeletal muscle is active, what system regulates other body activities for sufficient blood, oxygen and waste removal?

Autonomic

Lens can:

Change refraction and focal length

Muscle spindles (Mechanoreceptor)

respond to stretch in "intrafusal fibers" of skeletal muscle

Divisions of the Autonomic Nervous System

The sympathetic and parasympathetic divisions work in contrasting fashion to stimulate and inhibit effectors

Sympathetic Division - classic "flight-or-fight" response in scary situations:

a.) increased heart rate

b.) rapid, deep breathing pattern

c.) cold, sweaty skin

d.) dilated eye pupils

e.) large burst of energy available (glucose)

f.) constriction of blood vessels

g.) increased blood pressure

h.) dilation of bronchioles (more air)

Golgi tendon organs (Mechanoreceptor)

respond to stretch in tendon, close to muscle insertion point

Far point of vision:

distance beyond which lens will not change its shape (about 20 feet) (flattest point of the lens)

Emmetropic eye

Is known as a normal healthy eye

Parasympathetic Division

The "resting and digesting" system, keeps body calm, stimulates digestion, urination, and defecation

joint kinesthetic receptors (Mechanoreceptor)

monitor position of synovial joints (position)

Accommodation of lens (Close Vision)

lens shape becomes more convex, light rays bend more sharply, shorter focal length for the closer object (ciliary muscles for lens)

Thermoreceptors

respond to changes in temperature

Acetylcholine (ACh) (neurotransmitter)

the same neurotransmitter at the neuromuscular junction is used by autonomic fibers in two places (cholinergic fibers):

near point of vision

shortest distance for focusing (maximum convexity of lens); about 8-10 inches; gets worse with age

Photoreceptors

respond to light ( retina)

Neurotransmitter secreted by ALL preganglionic neurons of the ANS:

ACh

Presbyopia is:

-poor close vision in elderly; in-elasticity of the lens

- farsightedness associated with aging

Chemoreceptors

respond to different molecules in the blood,kidney, tongue, nose, etc.

Neurotransmitter secreted by MOST postganglionic neurons of PARASYMPATHETIC onto target cells:

ACh

Name two Acetylcholine (cholinergic) receptors:

- nicotinic receptors

- muscarinic receptors

Accommodation of pupil (close vision)

constriction of pupils; better focus, less divergent rays (constrictor muscles of iris)

Nociceptors

respond to harmful stimuli (painful); heat, cold, pressure, chemical

Convergence of eyes (Close Vision)

yes rotate medially to keep image on center of the retina (medial rectus muscles of eyeballs)

Sensory neurons (afferent)

transmits the signal from receptors (AFFERENT nerve fiber) to the CNS

Nicotinic receptors are

ACh receptors that can also be activated by nicotine - STIMULATE

Myopia (nearsightedness)

-distant objects are blurred; distant objects are focused in front of the retina, rather than directly on it

a.) eyeball too long; lens too strong

b.) concave lens can correct light before eye

Integration center (CNS)

point where sensory and motor neurons integrate information to respond

Where can Nicotinic receptors be found?

1.) skeletal muscle

2.)located on ALL postganglionic nerve cell bodies of ANS

3.) hormone-producing cells of adrenal medulla

Hyperopia (farsightedness)

-close objects are blurred; close objects are focused beyond the retina, rather than directly on it

a.) eyeball too short; poor refraction of a lens

b.) convex lens can correct light before eye

Monosynaptic pathway

sensory neurons synapse directly with the motor neuron

Muscarinic receptors are

ACh receptors which are activated by mushroom toxin muscarine STIMULATE or INHIBIT depending of target cell

Where are Muscarinic receptors found?

located on the target cells of the body receiving ACh from the parasympathetic division

-cardiac muscle -> INHIBITORY

-smooth muscle of GI tract -> STIMULATORY

Polysynaptic pathway

one or more "interneurons" between sensory and motor neurons

Astigmatism -

-blurry images at all distances; unequal curves on lens and/or cornea, creating discontinuous image on the retina

General Structure of Rods and Cones;

-"pigmented base" of retina

-outer segment (pigmented discs)

-connecting stalk

-inner segment (mitochondria)

-outer fiber

-cell body (nucleus)

-inner fiber

-synaptic ending

Motor neurons (efferent)

transmits motor signal from CNS to the effector organ via EFFERENT nerve

Norepinephrine (noradrenaline)

released by most postganglionic neurons of the SYMPATHETIC system (adrenergic fibers)

General Structure of Rods and Cones;

-"neural layer"

-bipolar cell

-ganglion cell (axons carried to brain by optic nerve)

The Effector

the muscle or organ that responds to signal of the motor neuron

Two norepinephrine (noradrenergic) receptors:

-alpha adrenergic receptors

-beta adrenergic receptors

Outer segment of rods and cones

-contain membrane-bound discs with pigments that absorb and react to light

Intrafusal muscle fibers

special muscle fiber that responds to stretching; center is non-contractile; ends have contractile property

Receptor that generally STIMULATE the effector organ/tissu:

alpha adrenergic receptors

Receptor that generally INHIBIT the effector organ/tissue:

beta adrenergic receptors

type Ia sensory fiber (intrafusal muscle fiber)

wraps around CENTER of intrafusal fiber; respond to rate and degree of stretching of the muscle

Rods

pigment discs stacked like pennies all the way to the base, membranes are DISTINCT from the plasma membrane.

Rod characteristics:

1. ) sensitive to dim light (night vision)

2. ) respond to ALL wavelengths (colors)

3. ) only "grey" information to the brain

4. ) 100 rods per ganglion cell to brain

5. ) widely spread throughout the retina

6. ) not good for visual acuity

type II sensory fiber (intrafusal muscle fiber)

wrap around ends of intrafusal fiber; respond only to degree of stretch of the muscle [records "resting length" of the intrafusal fiber]

Synaptic cleft enzyme inhibitors:

- neostigmine

- tricyclic antidepressants

- beta-blockers

Cones

pigment discs taper off toward the base, membranes are CONTINUOUS with the plasma membrane.

Gamma motor fiber (intrafusal muscle fiber)

synapses on contractile end of intrafusal fiber; maintains level of sensitivity of this stretch receptor, depending on the length of the muscle at any given time [sets the "resting length" of intrafusal fiber]

Neostigmine

Blocks acetylcholinesterase for accumulation of ACh (myasthenia gravis)

Cones Characteristics:

1.) require bright light for stimulation

2.) different cones have different pigments specific for certain wavelengths (colors)

3.) can convey color information to brain

4.) 1-3 cones per ganglion cell to brain

5.) primarily concentrated in fovea (center)

6.) essential for visual acuity

Extrafusal fibers

normal contractile muscle fibers of a skeletal muscle

Tricyclic Antidepressants (TCAs)

prolong the binding of norepinephrine to postsynaptic receptors

Beta Blockers

Block binding of norepinephrine to beta-I receptors; reduce heart rate

Alpha motor fiber ( extrafusal fiber)

synapses on normal extrafusal fibers to allow a response to a stretched muscle

What is opsin?

- a transmembrane protein in the membrane of pigmented discs of rods and cones

Retinal

light absorbing molecule that changes shape when struck by a photon of light

Mechanism of Skeletal Muscle Stretch Reflex:

a.) Excitation of Muscle Spindle (Stretching)

b.) Type Ia and II Sensory Fiber Activation

c.) Regulation of Muscle Spindle Length

"Eye Pupil" ----- Antagonistic Control with Sympathetics & Parasympathetics.

Parasympathetic: Constricts

Sympathetic: Dilates

precursor to retinal:

Vitamin A

External stretch

external force (weight) on muscle or contraction of antagonistic muscle (eg. quadriceps - hamstrings)

" Heart" --- Antagonistic Control with Sympathetics & Parasympathetics

Parasympathetic: Decrease heart rate

Sympathetic: Increase heart rate

What is known as a "11-Cis-isomer of retinal"?

It is a non-activated form of retinal, prior to absorption of photon energy; has a "kinked" double bond

Internal stretch

activated gamma motor neurons cause contraction of intrafusal fiber, stretching midsection of spindle

"Lungs" --- Antagonistic Control with Sympathetics & Parasympathetics

Parasympathetic: Constrict Bronchioles

Sympathetic: Dilates bronchioles

All trans isomer of retinal is a:

activated form of retinal, after struck by photon of light; double bond straightens out