PHYS335: Lab 7

Photons of light

adequate stimulus for the eye

No

Can the human eye detect the full electromagnetic spectrum?

Sclera

outermost, toughest layer of the eye gives rise to white

muscles attach here to alter the direction of our gaze

Cornea

most light refraction occurs at the part of the eye

clear area of sclera at eye’s front

Choroid

dark pigmented region at the back of the eyeball

prevents reflection by absorbing incoming light

Iris

part of eye responsible for its coloration

part of the choroid at the front of the eye

Pupil

adjustable opening of the eye that allows light entry to the back of the eye

Lens

part of the eye behind the pupil

clear/crystalline object that changes shape and amount of light refraction in doing so

Ciliary muscle / zonular fibers

work together to change the shape of the lens

Retina

innermost layer of the eye

neural tissue extending out from brain- sensory neurons with photoreceptors located here

Macula lutea

small region in center of retina with no blood vessels; no blurring of photons light there

Fovea centralis

shallow pit in center of macula with the highest density of cone receptors and highest visual acuity

Optic disk

site of blood vessel/optic nerve entry and exit in the eye

lacks photoreceptors which causes a blind spot

Rods

photoreceptors in periphery of retina that respond in dim light

low acuity with NO colored vision

Cones

photoreceptors that are dense around the fovea centralis and respond in bright light

high acuity, entirely responsible for color vision

Outer segment

part of rods/cones where phototransduction actually occurs

Inner segment

part of rods/cones where majority of organelles are located

No, cGMP is

Is GMP an activating ligand for a cation channel?

Repolarizes; depolarizes

In the presence of light, cell ___. In the absence of light, cell ___.

• Retinal bound to opsin

• cGMP is high

• cation channels are open

• membrane is depolarized

What are the characteristics of a photoreceptor in the dark?

• Retinal dissociates

• phosphodiesterase is activated so cGMP is reduced

• cation channels are closed

• membrane is repolarized

What are the characteristics of a photoreceptor in the light?

Guanylyl cyclase

enzyme that creates cGMP constantly

cGMP gated channels

cation channel that opens in response to GMP, keeps membrane potential depolarized in the dark

Retinal bound to opsin

two elements that are activated by light; otherwise remain bound to each other

Transducin

G protein activated by photopigment (opsin)

cGMP phosphodiesterase

enzyme that breaks down cGMP, cells repolarize; activated by transducin

Somatic motor neuron

single neuron between CNS and skeletal muscle cells innervating that muscle; only leads to excitation

operated largely under conscious control

Autonomic motor neuron

2 neuron chain between CNS and effector organ; innervates smooth/cardiac muscle, glands; can be excitatory or inhibitory

operates largely outside conscious control

Sympathetic nervous system

division of autonomic system that prepares body for emergency/stressful situations; “fight or flight”

activates processes facilitating physical exertion

diffuse signaling (specific); tonically active

Thoracolumbar regions

Where do cell bodies of the sympathetic nervous system originate?

Short PREganglionic neuron, long POST

How do the two neuron lengths measure in the sympathetic nervous system?

Parasympathetic nervous system

division of autonomic system that is responsible for day to day activities and quite/relaxed situations; “rest and digest”

discrete signaling (specific); tonically active

Cranial and sacral regions

Where do cell bodies of the parasympathetic nervous system originate?

Long PREganglionic neuron, short PRE

How do the two neuron lengths measure in the parasympathetic nervous system?

Varicosities

swellings on branches of postganglionic neuron; vesicles with neurotransmitter inside

Acetylcholine; nAchR

In the somatic nervous system, motor neurons release ___ that binds to ionotropic receptor, ___.

Acetylcholine; MACHR

In parasympathetic nervous system, both pre AND postganglionic neurons release ___ that binds to receptor, ____.

Acetylcholine; norepinephrine; adrenergic receptor

In sympathetic nervous system, the preganglionic neuron releases ___, while the postganglionic neuron releases ___. The latter is received by ___.

Adrenal medulla

acts as a ganglion for gland of the same name

releases epinephrine into bloodstream, responsive to sympathetic innervation

Adrenergic receptor

What kind of receptor does epinephrine respond to?

Highest level

this level of motor control forms complex plans and includes areas involved in memory, emotions, and motivation

Middle level

this level of motor control determines how to enact/maintain motor programs and includes structures like sensorimotor cortex, basal nuclei, thalamus, some of the brainstem, and cerebellum

information transmitted through descending pathways

Local level

this level of motor control is responsible for the execution, final modifications, and reception of movement and includes structures like the brainstem/spinal cord interneurons, receptors, and muscle fibers

this level’s interneurons engage in a lot of convergent activity

1. Tap on knee stretches patellar tendon, pulling extensor muscle down

2. Action potential moves from afferent peripheral process up to spinal cord (and through dorsal column system)

3. 4 axon collaterals are affected; one activates extensor muscle, making knee extend, while another inhibits knee flexors

What is the mechanism of your knee jerk reflex?

Withdrawal reflex

reflex active when you step on something painful (travels up the anterolateral path)

on the same side as the painful stimulus, flexors are activated and extensors are inhibited

on the opposite side as the painful stimulus, extensors are activated and flexors are inhibited