PSIO 241 CH 6

information detected by sensory receptors

* regulating motor behavior in accordance with external circumstances
* coordinating internal activities directed at maintaining homeostasis
* cortical arousal and consciousness
* perceptions of the world around us
* changing emotional states

sensory receptors

• Specialized peripheral endings of afferent neurons.

• Each type of receptor responds to its one adequate stimulus.

• **Sensory receptors have graded potentials, called receptor potentials**

photoreceptors

Responsive to visible wavelengths of light

mechanoreceptors

Sensitive to mechanical energy

signal (sensory) transduction

Translates the energy form of the stimulus into electrical signals

thermoreceptors

Sensitive to heat and cold

osmoreceptors

Detect changes in concentration of solutes in body fluids and resultant changes in osmotic activity

chemoreceptors

\- sensitive to specific chemicals; includes receptors:

– For smell and taste

– Detect O2 and CO2 in blood

– Detect chemical content of digestive tract

nociceptors

Pain receptors that are sensitive to tissue damage or distortion of tissue.

perception

the conscious interpretation of the external world

• What the brain perceives from its input is an abstraction and not reality

• The only stimuli that can be detected are those for which receptors are present.

pain

Primarily a **protective mechanism** to bring  awareness that tissue damage is occurring

• Begins with stimulation of **nociceptors**.

• Sensation of _ is accompanied by behavioral responses and emotional reactions.

• Subjective perception can be influenced by other past or present experiences.

afferent pain pathways

Pain signals are transmitted over two afferent pathways:

– fast pathway

–slow pathway

fast pathway

carries sharp, pricking pain signals

slow pathway

carries dull, aching, persistent pain signals

pain pathway

Afferent pain fibers terminate in the spinal cord on ascending pathways that transmit the signal to the brain

substance P

the spinal cord pain neurotransmitter

* Pain messages sent into brain stem then thalamus on their way to the cerebral cortex.

descending pathways

use endogenous opiates to suppress the release of substance P, **blocking pain transmission**

periaqueductal gray (PAG)

Pain suppression originates in the **_** of the brainstem

• Suppression of substance P release in spinal cord

opioid class- endorphin

opioid receptor: mu

opioid class- enkephalin

opioid receptor: delta

opioid class- dynorphin

opioid receptor: kappa

endogenous opioids and receptors

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•**Medulla oblongata—pain and  respiratory regulation**

•**Spinal cord- pain**

•Mesolimbic pathway– reward

•**Periaqueductal gray-pain regulation**

•GI-smooth--muscle contractions

•**Cortex-modulate pain**

morphine, fentanyl

**_** binds to these endogenous receptors, so does _ which has 100 times the analgesic potency of morphine

calcium, substance P

opioid spinal cord pain suppression reduces **_ permeability** which in turn **reduces _ release** from presynaptic  neurons

opioid spinal cord pain suppression

**Hyperpolarize second-order pain transmission neurons** by opening K+ channels, **producing an IPSP**. Less AP into the brain

methadone

* A synthetic opioid, used medically as an analgesic and in the treatment of narcotic addiction
* acts on the opioid receptors (agonist) and produces many of the same effects
* **does not provide** any of the euphoric effects that heroin does when administered.   
* Used for controlled withdrawal from heroin & morphine

overdosing on opioids

* treatment includes the administration of **Naltrexone (Narcan)**
* Because **Narcan is a receptor antagonist**, it blocks the effects of opioids but does not reduce the craving for opioids
* This reverses morphine's effects but **causes immediate onset** of withdrawal in opiate-addicted subjects
* has a much shorter half life than heroin

sclera

• tough outer layer of connective tissue

• forms visible white of the eye

cornea

• anterior, transparent outer anterior layer

• light rays pass through it before entering interior of eye; **bends light rays to begin focusing light**

choroid

• middle layer underneath sclera, contains blood vessels that nourish retina

• Towards the lens, it forms the **ciliary body and iris**

ciliary body

controls lens shape during visual accommodation via the suspensory ligament

iris

contains pigment and **smooth muscle** and controls amount of light entering eye by **adjusting the size of the pupil**

retina

• Innermost coat under choroid.

• Consists of inner nervous-tissue layer and outer pigmented layer.

• **Rods and cones**

• Pigmented layer absorbs light after it passes by the rods and cones.

rods and cones

the light detecting photoreceptors in the nervous tissue layer

rodes and cones

outermost layer contains _

(retina)

bipolar cells

middle layer contains _

(retina)

ganglion cells

inner layer contains _ ; axons from _ join to form optic nerve

(retina)

rods

* coarse detail
* black and white
* 120 million cells
* more sensitive to low light
* used for peripheral and night vision

cones

* fine detail
* color
* 6-7 million cells
* less sensitive to low light
* used for central and detailed vision

macula lutea

a portion of the retina the contains many cones, bipolar and ganglion cells and is the place of fairly high acuity

fovea

small depression in center of macula and has only cones, so it is the point of most distinct vision

optic disc

is point on the retina where the optic nerve leaves, the region of the optic disc is the **blind spot**

refraction

the bending of a light ray

convex; converge

_ surfaces _ light rays

(natural lens in eye)

concave; diverse

_ surfaces _ light rays

cornea and lens

• The cornea and lens are the primary refractive structures that bend incoming light rays.

• The **cornea contributes most** to the total refractive ability of the eye.

• The strength of the lens can be adjusted to **accommodate for differences in near and far vision**.

accommodation

• Ability to adjust strength of lens by changing its shape.

\- Shape is regulated by ciliary muscle

common vision disorders

* astigmatism (mis-shaped cornea)


* nearsightedness (myopia)


* farsightedness (hyperopia)


* presbyopia; age-related reduction in accommodation ability (like farsightedness)

convex lens

lens too weak, correct with _

concave lens

lens too strong, correct with _