No, sympathetic/parasympathetic systems work simultaneously in a push/pull mechanism
Describe the general autonomic efferent pathway
Two neuron pathway.
Preganglionic neuron – cell body in CNS, synapses with postganglionic neurons in the autonomic ganglion (located in the PNS). Always releases ACh to postganglionic neuron.
Postganglion neuron – cell body in autonomic ganglion (always
contain Nicotinic AChR – excitatory response
), synapses with effector organ
How do autonomic efferent pathways differ from somatic efferent pathways?
Autonomic pathways have two motor neurons, while somatic pathways have just one.
Autonomic pathways originate in the hypothalamus, somatic pathways the precentral gyrus
Autonomic pathways are involuntary, somatic pathways are voluntary
Autonomic pathways can use NE as a neurotransmitter, somatic pathways only use ACh
Autonomic pathways use “spray mechanism,” somatic pathways directly innervate a single muscle fiber
Relationship between adrenal medulla and autonomic system?
The adrenal medulla is innervated by sympathetic pre-ganglionic fibers. When they fire, the secretory cells in the medulla release adrenaline into the blood stream. Adrenaline activates the same receptors as norepinephrine from the postganglionic sympathetic axon terminals
Efferent pathway of sympathetic division in detail
Preganglionic cell bodies in spinal cord T1-L2 levels
Preganglionic axons enter sympathetic chain ganglia (also T1-L2 levels) just lateral to spinal cord through the spinal rami communicantes
Synapse with postganglionic motor neurons in sympathetic chain ganglia
Postganglionic neurons send axons to effector organs
Postganglionic neurons use NE (norepinephrine) for neurotransmitter (adrenergic synapse)
Adrenergic receptors also activated by adrenaline released from adrenal medulla
Efferent pathway of parasympathetic division in detail
Preganglionic cell bodies in brainstem and sacral cord
Preganglionic axons synapse with postganglionic neurons at terminal ganglia (adjacent to or within the target organ)
Postganglionic neurons send axons to effector organs
Postganglionic neurons use ACh for neurotransmitter (cholinergic synapse) to Muscarinic AChR
Sympathetic vs. Parasympathetic Pre/Postganglionic lengths
Sympathetic – short preganglionic, long postganglionic
Parasympathetic – long preganglionic, short postganglionic
Describe dual innervation
Many organs receive both sympathetic and parasympathetic input
Give examples of the varied responses gained by dual innervation
Fixed, convex (curves outward) lens that bends light inward
Covers the anterior chamber
Anterior chamber vs Posterior chamber vs Vitrious chamber (location and fluid).
Anterior chamber – space between cornea and iris (aqueous humor)
Posterior chamber – space between iris and ciliary body/lens (aqueous humor)
Vitrious chamber – space behind ciliary body/lens (vitrious humor)
Iris structure and function
Thin ring of pigment and smooth muscle in front of lens
Alters pupil size to regulate the amount of light that passes into the eye
Pupil structure and function
Opening at the center of the iris
Allows light into the eye
Which iris muscles control the pupil in which ways? Which autonomic system?
Radial (dilator) muscles – open the pupil to allow more light (sympathetic)
Circular (sphincter) muscles – close the pupil in response to bright light or close objects (parasympathetic)
Ciliary body structure and function
Ring-shaped smooth muscle encircling the lens, attached to lens by suspensory ligaments
Secretes aqueous humor, adjusts the shape of the lens to focus light (via suspensory ligaments)
Choroid layer structure and function
Vascular and melanin-pigmented layer between the sclera (outer) and retina (inner)
Supplies nutrients to photoreceptor cells, pigment absorbs stray light in eye
Lens structure and function.
Elastic and flexible mass in the eye. Cells made mostly of protein (crystallin)
Used to focus light onto the retina
Vitreous humor characteristics and function
Viscous, transparent fluid in the vitreous chamberAllows light rays to pass freely. If humor is cloudy then light rays are bent/interfered with)
What is the accommodation reflex?
The ability for our eyes to focus on close objects.
Achieved by contracting the ciliary body in varying degrees, pupil constriction (for close objects), and bilateral contraction of the medial rectus muscles (for close objects)
Explain how the accommodation reflex works for far objects.
Light from object enters eye from narrow range of angles.
Ciliary body relaxes which increases tension on suspensory ligaments which causes the lens to flatten
A flatter (less convex) lens results in less refraction (bending of light) from the lens
Explain how the accommodation reflex works for close objects.
Light from object enters eye from a wide range of angles
Ciliary body contracts which decreases tension on suspensory ligaments which causes the lens to thicken
A more convex lens results in more refraction (bending of light) from the lens
Parasympathetic firing causing simultaneous pupil constriction and ciliary muscle constriction
Describe myopia, its causes, and its correction
Nearsightedness – a distant object is brought into focus in front of the retina (too much refractive power to see distant objects)
Caused by elongated eyeball or abnormally high curvature of cornea or lens
Corrected with biconcave (curved inward) lenses
Describe the flow of aqueous humor and its function
Secreted by ciliary body -> posterior chamber (provides nutrients to lens) -> anterior chamber -> drainage (continuous flow)
Maintains intraocular pressure/ eye shape and provides nutrients to avascular lens
What is glaucoma?
Buildup of pressure from aqueous humor buildup in eye. (eye carries no pain receptors, so affected person may have no idea it is happening)
Describe hyperopia, its causes, and its correction.
Farsightedness – a close object is brought into focus behind the retina (too little refractive power to see near objects)
Caused by shortened eyeball or abnormally low curvature of cornea or lens
Corrected with biconvex (curved outward) lenses
Describe presbyopia, its causes, and its correction
Close objects are blurry.
With age (~45-50 years) the proteins making up the lens lose their flexibility, and can no longer thicken for accommodation (even when the ciliary muscle contracts).
Correction with reading glasses or bifocals (convex lenses)
Retina structure and function (basic) + major substructures (macroscopic).
Inner layer of eye (lining of the vitreous chamber) that contains photoreceptors.
Fovea centralis – point where light from the center of the visual field is focused (highest desnity of cone cells, sharpest visual acuity). Macular degeneration (degeneration of that area) can cause blindness)
Optic disc – where optic nerve joins the eye. “blind spot”
Describe the layers of retinal cells (in order) and their functions
Pigmented epithelium – supporting cells (absorb some stray light and various activities)
Photoreceptors (rods and cones) – sensitive to light
Bipolar cells – interneurons between photoreceptors and ganglion cells
Ganglion cells – receive signals from bipolar cells. Axons for CN II and send signals to the thalamus and other visual centers (eg superior colliculus)
What does the term inverted retina mean?
The photoreceptors are “buried” underneath the other cells, so the electrical signal is sent in the opposite direction (up) of incoming light (down)
General rod information? Synapse structure? Function in detail?
More numerous than cones, cannot distinguish between colors, night vision.
Many rods converge onto several bipolar cells which synapse with one ganglion cell, causing massive summation, high sensitivity to low light levels, low visual acuity, and a large visual field per ganglion cell
General cone information? Synapse structure? Function in detail?
Found mainly in fovea centralis, can distinguish colors, day vision.
One or very few cone cells per ganglion cell (little to no convergence), causing a higher threshold of light than rods (less sensitivity), high visual acuity, and a small visual field per ganglion cell
Describe photoreceptor structure
Outer segment of photoreceptors have many discs with photopigments (visual pigments).
Rods have rhodpsin
Cones have opsins (3 kinds: red, green, or blue) – each cone has mostly one opsin and will respond more to a certain wavelength of light (similar to taste buds)
How does rhodopsin respond to light?
Light stimulous causes a change in the shape of the molecule (retinal + opsin) which leads to a membrane potential change. This molecule is “used” and must be reformed before it can fire again.
How does opsin respond to light?
Opsin responds to various wavelengths of light (either red, green, or blue)
Describe the two different pathways from the eye (from CN II)
Horizontal Gaze Nystagmus, Walk and Turn, and One Leg Stand
Describe the HGN test (including indicators of impairment and # needed for a positive test). Any other possibilities for a positive test?
Alcohol impaired person has exaggerated nystagmus and difficulty smoothly tracking a moving object.
Test: Observe eyes of suspect as suspect follows a slowly moving object (pen or flashlight)
Three indicators (per eye): eye cannot follow moving object smoothly, jerking is distinct when eye is at maximum deviation, angle of onset of jerking within 45 degrees of center.
Positive test: 4+ indicators between two eyes. (88%)
Could also indicate consumption of seizure medications, phencyclidine, inhalants, barbiturates, and other depressants.
Describe the WAT test (including indicators of impairment and # needed for a positive test)
Divided attention test, requires subject to follow instructions while performing simple physical movements.
Test: subject is directed to take nine steps (heel-to-toe) along a straight line, turn on one foot, and return in the same manner.
8 indicators: suspect cannot keep balance, begins test before instructions are completed, stops while walking to regain balance, does not touch heel-to-toe, steps off the line, uses arms to balance, makes an improper turn, takes an incorrect number of steps.
Positive test: 2+ indicators (79%
Describe the OLS test (including indicators of impairment and # needed for a positive test)
Divided attention test, requires subject to follow instructions while performing simple physical movements
Test: subject is instructed to stand with one foot ~6in off the ground and count aloud by the thousands. Officer times subject for 30 seconds.
4 indicators: swaying while balancing, using arms to balance, hopping to maintain balance, putting the foot down
Positive test: 2+ indicators (83%)
Describe the Rinne test. What does it test for? What test should accompany a Rinne test and why
Compares the perception of sounds transmitted by
air vs conducted through the mastoid
Test: Tuning fork is placed on mastoid until sound is no longer heard, then held to ear.
tests for conductive hearing loss
A Weber test should accompany to detect sensorineural hearing loss
What are the possible results of a Rinne test?
Normal ear: positive (AC>BC)
Conductive hearing loss: negative (BC>AC)
Sensorineural hearing loss: should give positive (equal depreciation) but could give false neg
Describe the Weber test. What does it test for?
Compares the perception of sounds transmitted by each ear. Can detect unilateral conductive hearing loss and unilateral sensorineural hearing loss.
Test: Stem of tuning fork is placed centrally on either the top of a patients skull, forehead, or above upper lip. Patient reports which ear hears the sound louder
Weber test results: unilateral conductive vs unilateral sensorinueral and why?
Conductive: tuning fork loudest in the affected ear.
Conduction problem masks the ambient noise of the room, but inner ear picks up vibrations through the bone.
Sensorineural: tuning fork loudest in the unaffected ear. Affected ear is less effective at picking up sound even when vibrating through the bone