Chapter 10

Which branch of the peripheral nervous system is responsible for perception?

Afferent

Explain the law of specific nerve energies (mention modality and adequate stimulus).

The type of sensation felt when a nerve fiber is stimulated depends on the modality of the receptor it innervates, not the stimulus itself. An adequate stimulus is the specific type of stimulus to which a receptor is most sensitive.

modality

The type of sensory information or sensation being perceived (e.g., vision, hearing, touch, pain, taste). It is determined by the specific neural pathway activated.

adequate stimulus

The specific form of energy or type of stimulus to which a sensory receptor is most sensitive and naturally responds to (e.g., light for photoreceptors, pressure for mechanoreceptors).

Photoreceptors

Detect light.

Chemoreceptors

Detect chemicals.

Thermoreceptors

Detect temperature.

Mechanoreceptors

Detect mechanical pressure, movement, and vibration.

Baroreceptors

Detect blood pressure (stretch of blood vessels).

Proprioceptors

Detect body position and movement.

Tonic receptors adapt ________, while phasic receptors adapt ________.

Slow; fast

First-order neuron: Where is it located (PNS or CNS)?

PNS

First-order neuron: Where is information being carried to and from?

From the sensory receptors to the CNS

First-order neuron: Where is the synapse occurring?

In the spinal cord or brainstem

Second-order neuron: Where is it located (PNS or CNS)?

CNS

Second-order neuron: Where is information being carried to and from?

From the spinal cord/brainstem to the thalamus

Second-order neuron: Where is the synapse occurring?

In the thalamus

Third-order neuron: Where is it located (PNS or CNS)?

CNS

Third-order neuron: Where is information being carried to and from?

From the thalamus to the cerebral cortex

Third-order neuron: Where is the synapse occurring?

In the cerebral cortex

Dorsal column-medial lemniscal pathway - What does it detect?

Discriminative touch, vibration, and conscious proprioception.

Dorsal column-medial lemniscal pathway - Where do the 1st and 2nd order neurons synapse?

In the medulla oblongata.

Dorsal column-medial lemniscal pathway - Where does decussation occur?

In the medulla oblongata.

Spinothalamic tract (lateral) - What does it detect?

Pain and temperature.

Spinothalamic tract (lateral) - Where do the 1st and 2nd order neurons synapse?

In the dorsal horn of the spinal cord.

Spinothalamic tract (lateral) - Where does decussation occur?

In the spinal cord (anterior white commissure).

Spinothalamic tract (anterior) - What does it detect?

Crude touch and pressure.

Spinothalamic tract (anterior) - Where do the 1st and 2nd order neurons synapse?

In the dorsal horn of the spinal cord.

Spinothalamic tract (anterior) - Where does decussation occur?

In the spinal cord.

Pain receptors are called

Nociceptors.

What are A-delta fibers? Do they transmit fast pain or slow pain? Briefly describe the type of pain.

Myelinated fibers that transmit fast pain; associated with sharp, well-localized pain.

What are C fibers? Do they transmit fast pain or slow pain? Briefly describe the type of pain.

Unmyelinated fibers that transmit slow pain; associated with dull, aching, poorly localized pain.

What neurotransmitters does the 1st order neuron release for pain?

Substance P and glutamate.

What types of nerve fibers make up the 1st order neuron for pain?

A-delta or C fibers.

Where does the 1st order neuron for pain synapse?

In the spinal cord (with the 2nd order neuron).

After synapsing in the spinal cord, what specific pathway can the 2nd order neuron follow?

The lateral spinothalamic pathway.

After synapsing in the spinal cord, what nonspecific pathway can the 2nd order neuron follow, and where does it project to?

It projects to the reticular formation, hypothalamus, and limbic system.

Outline the sequence of the pain pathway from the 1st order neuron.

1st order neuron (A-delta or C fibers) -> synapses with 2nd order neuron in the spinal cord -> follows lateral spinothalamic pathway OR nonspecific pathway to reticular formation, hypothalamus, and limbic system.

Fovea

The area of highest visual acuity containing only cones, located at the center of the macula lutea in the posterior retina.

Optic disk

The blind spot where the optic nerve exits, located at the posterior pole of the eye.

Muscle (Ciliary muscle)

Smooth muscle that controls the shape of the lens, located in the ciliary body encircling the lens.

Cornea

The transparent outer layer that refracts light, located at the very front of the eye.

Iris

The colored muscular ring that controls pupil size, located behind the cornea and in front of the lens.

Pupil

The central opening that allows light to enter, located in the middle of the iris.

Anterior segment (aqueous humor)

A space filled with watery fluid that nourishes the front of the eye and maintains intraocular pressure, located between the cornea and the iris/lens.

Lens

The structure that fine-tunes the focus of light, located directly behind the iris and pupil.

Zonular fibers

Suspensory ligaments that hold the lens in place and adjust its shape, located extending from the ciliary body to the edge of the lens.

Blood vessels

Vessels that provide oxygen and nutrients to the eye tissues, located within the choroid layer and the retina.

Optic nerve

The nerve that carries visual information to the brain, located exiting the back of the eye through the optic disk.

Vitreous chamber (vitreous humor)

The large space filled with a thick gel-like fluid that maintains the shape of the eyeball, located behind the lens in the posterior cavity.

Sclera

The tough, white outermost layer that provides structural protection, located covering most of the eyeball (except the cornea).

Choroid

The middle vascular layer that provides blood supply to the retina, located between the sclera and the retina.

Retina

The innermost layer containing photoreceptors that convert light into electrical signals, located lining the posterior cavity of the eye.

The ______ is the area of the eye with the highest visual acuity and contains only ______.

Fovea (centralis); cones.

The ______ is also called the blind spot, and contains the optic nerve (CN II).

Optic disk.

What is refraction?

The bending of light rays as they pass from one medium to another.

What is accommodation?

The process by which the eye's lens changes shape (curvature) to focus near or far objects on the retina.

Viewing a distant object: the ciliary muscle is ______.

Relaxed

Viewing a distant object: the zonular fibers are ______.

Tight

Viewing a distant object: the lens is ______.

Flat

Viewing a distant object: is there parasympathetic stimulation?

NO

Viewing a near object: the ciliary muscle is ______.

Contracted

Viewing a near object: the zonular fibers are ______.

Slack

Viewing a near object: the lens is ______.

Rounded

Viewing a near object: is there parasympathetic stimulation?

YES

Emmetropia

Normal vision.

Myopia

Near-sightedness (fixed with a concave lens).

Hyperopia

Far-sightedness (fixed with a convex lens).

Astigmatism

Irregularities of the lens or cornea.

Presbyopia

Hardening of the lens.

Glaucoma

Increased volume of aqueous humor.

Cataract

Opacity caused by protein breakdown.

The ______ is stimulated by the ______ nervous system and causes pupillary constriction.

Circular muscle; parasympathetic.

The ______ is stimulated by the ______ nervous system and causes pupillary dilation.

Radial muscle; sympathetic.

Rods contain the photopigment rhodopsin and are responsible for ______ vision.

Black/white (scotopic).

Cones contain three photopigment types and are responsible for ______ vision.

Color (photopic).

In the dark: cGMP levels are ______ in the cytosol.

High.

In the dark: cGMP opens sodium channels, causing sodium to ______ the cell.

Enter.

In the dark: The cell becomes ______.

Depolarized.

In the dark: The depolarization of the cell causes calcium channels to ______.

Open.

In the dark: Calcium enters the cell causing neurotransmitter release to be ______.

Triggered.

In the light: The photopigment rhodopsin absorbs light, causing retinal and opsin to dissociate. The opsin is now "bleached opsin," causing the photoreceptor to become ______ sensitive to light.

Less.

In the light: The bleached opsin ______ the G protein, transducin.

Activates.

In the light: This activates the enzyme phosphodiesterase, which catalyzes the breakdown of cGMP. The cGMP levels in the cytosol ______.

Decrease.

In the light: The decreased levels of cGMP cause the sodium channels to ______.

Close.

In the light: With no sodium entering the cell, leaky potassium channels cause the cell to ______.

Hyperpolarize.

In the light: The hyperpolarization of the cell causes calcium channels to ______.

Close.

In the light: Because calcium channels are closed, neurotransmitter release ______.

Decreases.

OFF bipolar cells are ionotropic and become ______ by glutamate.

Excited.

In the dark, glutamate release occurs, meaning that the ______ bipolar cells are activated.

OFF.

ON bipolar cells are metabotropic and get ______ by glutamate.

Inhibited.

In the light, there is no glutamate being released, meaning that the ______ bipolar cells are activated.

ON.

Nasal Retina Paths

Fibers from the nasal half of each retina receive light from the temporal visual field. These fibers cross at the optic chiasm and travel to the opposite side of the brain.

Temporal Retina Paths

Fibers from the temporal half of each retina receive light from the nasal visual field. These fibers do not cross at the optic chiasm and stay on the same (ipsilateral) side of the brain.

Optic Nerve (CN II)

Exits the back of the eye (optic disk) and carries visual information toward the optic chiasm.

Optic Chiasm

X-shaped structure where fibers from the nasal retina cross to the opposite side.

Optic Tract

Formed after the optic chiasm; carries visual information to the thalamus.

Lateral Geniculate Body of Thalamus

The synaptic relay center in the thalamus for visual information.

Optic Radiations

Nerve fibers that carry visual information from the thalamus to the primary visual cortex.

Primary Visual Cortex

Located in the occipital lobe; final destination for conscious visual perception.