Chapter 10 Part 1: The Nervous system's Sensory System Study Question

Vallinoid receptors respond to high temps and acidity and some chemicals

- High temperature (>43°C (109°F) - pH <6 -Capsaicin, the active ingredient in hot peppers: Capsaicin doesn't actually cause a chemical burn or damage tissue. The brain just thinks it does because capsaicin depolarizes a temperature sensor.

Chemoreceptors

- Sensitive to specific chemicals - Includes receptors for smell, taste - Chemical content in the digestive tract - Detection of O2 and CO2

Generalized PATHWAY for Sensory Systems

1 st order neuron is the neuron that carries a signal from the periphery to the spinal cord or brainstem 2 nd order neuron is an interneuron in the spinal cord, takes the signal to the thalamus 3 rd order neuron is the interneuron that takes the signal from thalamus to cortex

How does a baro-receptor get stimulated?

1)An increase in blood pressure stretches the wall of blood vessels 2)This distorts the baroreceptor which triggers depolarization

Thermoreceptors

Different receptors for hot and cold

What's the difference between AP freq and AP transmission?

Frequency is how often we are firing the action potential. And the transmission is how fast the action potential is moving down the axon.

Stimuli include chemicals and various forms of energy such as:

Light and sound waves, pressure, and temperature

Proprioceptors detect _____.

Limb and body positions

How does the nervous system identify stimulus type?

Most stimuli activate a specific receptor

How does Enkephalin, an endogenous pain reliever, counters substance P?

Nociceptor depolarizes afferent neuron, glutamate and substance P released onto 2nd order ascending interneuron to notify the brain • Pain-induced stress releases enkephalin from an efferent interneuron onto the 1 st order afferent neuron & 2 nd order interneuron: - Blocks release of substance P - Hyperpolarizes 2nd order ascending interneuron

Nociceptors detect _____.

Pain

$$$How does the natural analgesic encephalin counteract the action of the pain perception neurotransmitter substance P?

Pain-induced stress triggers the release of enkephalin from an efferent interneuron onto the afferent 2nd order neurons and blocks the release of substance P and hyperpolarizes the 2nd order ascending interneuron.

When is substance P released?

Released e.g. onto the site of injury to stimulate vasodilation. The greater the injury, the greater the release of substance P and the greater the pain perception.

$$$ How does the nervous system determine stimulus strength? What is population coding?

Stimulus intensity is determined by the frequency of the AP generated which is directly correlated with the strength of the stimulus. The stronger the stimulus the more receptors and afferent neurons involved. When multiple receptors are involved, it's referred to as population coding.

How does the nervous system determine stimulus strength (intensity)?

Stimulus intensity is determined by the frequency of the APs generated by the stimulus - Can involve one or more afferent neurons - The stronger the stimulus, the more receptors and afferent neurons involved - When multiple receptors are involved, it's referred to as population coding - Ex: a population of receptors in a receptive field are stimulated

What is referred pain?

The pain feels like its coming from somewhere else. Ex: When having heart attack, we have pain in our hand.

$$$How does the gate-control hypothesis explain the fact that rubbing the area around an injury can reduce the sensation of pain?

The spinal cord has interneurons that inhibit 2nd order neurons that transmit pain info from 1st order nociceptor. Rubbing activates pressure receptors that activate these inhibitory interneurons so a lower AP frequency is sent to the brain and less pain is percieved.

Somatosensory receptors detect _____.

Touch

Having 3 types of A fiber neurons allows you to rapidly respond to injury

You need to detect pain quickly, so pain sensing neurons are myelinated for speed • Once you sense pain, the faster you respond to avoid that pain, the better • This requires being aware of your surroundings by touch and spatial awareness: Touch and proprioceptors use thicker myelinated A-beta and A-delta neurons respectively so they can transmit APs faster

X-rays, microwaves or radio waves are not detected by________

any organism

How do Endorphins and enkephalins, the bodies natural pain relievers act?

by binding to opiate receptors on nerve cells to inhibit pain detection

Sensory receptors are either phasic or tonic, they ________________ be both

cannot

Each sensory receptor is linked to a specific pathway to the _______________ _____________

cerebral cortex

Phasic sensory receptors will start firing again when there is a _________ in stimulation. - Ex: you bump your watch against something

change

Each sensory receptor is specific for a particular _______ or___________

chemical or modality

Temperature is sensed by 2 types of skin thermoreceptors:

cold and hot

Until the stimulus reaches your ___________, you won't be aware of it

cortex

Nociceptors are _____________ by physical acts that cause extreme distortion or damage to tissue

depolarized

Somatosensory receptors

detect the sensation of touch

Hearing compares sound arriving at your left and right ear. You turn your head in the _____ you think the stimulus is coming from.

direction

**?Localizing a stimulus improves with receptive _________

field overlap

Receptor ____________ is very important for tactile sensations(form of the sense of touch, varies according to the type of stimulus: touch, pressure, or vibration.)

field size

Pain modulation:

gate-control hypothesis explains why you rub a painful area

Receptor potentials are like ________________in that they trigger opening or closing of ion channels

graded potentials

Coding of stimulus location: The larger the receptive field size, the ____________ it is to detect the exact location of a stimulus. This is because Stimulus could be anywhere in the receptive field area.

harder

Spinal cord has interneurons to ___________ 2nd order neurons that transmit pain info from peripheral 1st order nociceptors. Rubbing activates pressure receptors that activate these inhibitory interneurons

inhibit

Lateral inhibition enhances _________ within a receptive field

localizing a stimulus

Mechanoreceptors are sensitive to________________

mechanical energy. Ex: 1)Muscle spindles detect when a muscle is stretched - 2)Hair cell receptors for hearing and balance 3)Baroreceptors in blood vessels for pressure changes

Proprioception involves ______________ in your muscles and joints

mechanoreceptors

A ______ intense stimulus leads to a higher frequency of action potentials

more

Pain is perceived by __________

nociceptors

An action potential may result from activation of ______________ of the sensory receptors in that receptive field

one or more

The cerebral cortex has defined areas to interpret ________________

outside stimuli

Enkephalin inhibits axoaxonic synapse and axosomatic synapse to reduce _____________

pain sensation

Somatosensory pathways are direct lines connecting __________ to cortex. These pathways consist of a sensory unit synapsing w/ a chain of neurons leading to the cortex.

peripheral sensors

Tactile receptors are __________ in your skin that adapt to touch sensations from what you are wearing or your jewelry and you eventually stop noticing your jewelry for example, is touching you

phasic receptors

Receptor potentials are just like

postsynaptic graded potentials.

Phasic receptors adapt ________to a stimulus. The response of the cell diminishes and then stops.

rapidly

A sensory unit has a defined ___________

receptive field

Activation of nociceptors in viscera (your insides) produces

referred pain

Smell detection is based on ____________ indicating closer or farther away

scent strength

A __________includes all receptors + the associated afferent neuron

sensory unit

Tonic receptors adapt _______________ to a stimulus and continue to produce APs over the duration of the stimulus

slowly

Receptor potential strength from _____________ determines afferent neuron AP frequency. Or NT amount released from the specialized sensory cell into the synapse.

specialized structure

Sensory receptors are classified according to their _____________

speed of adaption

In receptor potentials, the _________ the stimulus, the greater the change in membrane potential.

stronger

The _________ the afferent neuron graded potential, the higher AP firing rate

stronger

The _________ the stimulus, the greater the receptor potential

stronger

Some sensory neurons release a signaling molecule called __________

substance P

What is a receptive field?

the area in which a sensory unit is activated (the physical location of its sensory receptors)

What is proprioception?

the awareness of position and balance (not movement-that's kinesthetics). Examples: Proprioception makes it possible to walk in total darkness (until you hit something!) You can tell that your right foot is ahead of your left without looking • You can tie a strap behind your neck or touch your fingers with your eyes closed

Two-point threshold

the minimum distance that must be between 2 points in order to perceive them as separate

Thermoreceptors are temperaturesensitive ________

ion channels

When multiple receptors are involved, it's referred to as _____ ________

population coding

Tonic receptors adapt very ____________

slowly or not at all

Coding of stimulus location: The ________ the field the better able you are to detect the stimulus location.

smaller

All sensory systems except ____________ with thalamus

smell synapse

Tonic Receptors will keep sending action potential to the brain as long as the ________ is there.

stimulus

Phasic receptors will _____________ sending APs even though a stimulus is still present

stop

Proprioception senses position using ___________

stretch receptors (spindles)

Receptive field overlap is more accurate for 2 reasons

• 1) If detected by 2 afferent neurons, the signal must lie w/in the overlap region 2) Lateral inhibition - This involves interneurons

3 categories of nociceptors:

- Mechanical nociceptors respond to cutting, crushing or pinching - Thermal nociceptors respond to temp <45°F & >109⁰F - Polymodal nociceptors respond equally to all kinds of damaging stimuli

Examples of Tonic Receptors

- Muscle stretch receptors - Joint proprioceptors (info on movement and position) - As long as your eyes are open, you detect light - Your ears constantly hear: Your thalamus can decide to not send an AP to your auditory cortex so your brain doesn't perceive a sound

Nociceptors (Latin for pain)

- Sensitive to tissue damage - Detect extreme distortion or temperature changes in tissue

Sensory coding isn't fool proof

-If you close your eyes and press on you eyeball (please don't do that!), you can see light and colors - You see stars when you get hit hard in the head - The applied pressure is stimulating photoreceptors and is therefore perceived as light rather than pressure

How does the thalamus intervenes to prioritize signals?

-Lets you focus on what's important and what you can ignore - All sensory systems except smell synapse w/ thalamus - Inhibitory neurons between the thalamus and cortex block a lot of the incoming sensory info - 1 inhibitory neuron for every 4 excitatory neurons in the cerebral cortex - Lots of inhibitory neurons in the visual system (enhances visual contrast) and olfactory systems (modulates odor signals sent to the olfactory cortex

**??Gate Control Hypothesis (understand Picture in slides)

-Painful stimuli may be prevented from reaching higher levels of the central nervous system by touch stimuli activating an inhibitory interneuron which inhibits the projection of pain

$$$ Explain the difference between rapidly adapting phasic receptors versus tonic receptors that adapt slowly or not at all.

Phasic receptors adapt rapidly to a stimulus. They will stop sending APs even though a stimulus is still present (EX: we get used to odor) and start firing again when there is a change in stimulation. Tonic receptors adapt slowly or not at all. As long as the stimulus is there, the receptor will keep sending action potentials to the brain.

What is modality?

The energy form of a stimulus

Why don't we see X-rays, microwaves, or radio waves?

The environmental levels of each are too low to be of practical use to the biological world. Natural sources of microwaves and radio waves are low energy and would be difficult to detect by an organism No practical way to build in protection for an x-ray detection receptor (or any cell)

Two types of Sensory Receptors

1) 1 st type has a specialized structure at the end of an afferent neuron that gets directly stimulated. -If stimulation depolarizes to threshold, an action potential is generated - The AP is sent by an afferent neuron to the CNS 2) 2 nd type of sensory receptor. Sensory receptor is a separate cell that communicates through a chemical synapse w/ an afferent neuron - Stimulus changes receptor membrane potential and a chemical messenger is released

Describe the steps involved when a sensory unit uses a specialized cell to stimulate an afferent neuron.

1. The cell is depolarized when a ligand binds to a receptor 2. Depolarization opens voltage-gated Ca+2 channels, which triggers neurotransmitter release. 3. Neurotransmitter binds to a neurotransmitter receptor and a signal is sent to the CNS

Hot receptors let the most Na+ in at ________ and less above or below 109°F

109°F

Pain receptors start firing APs at ____

109°F

Humans have _____ color receptors, many insects and birds have 4 and can see UV light

3

Cold receptors let the most Na+ in at _______ and less below or above that

68°F

$$$ A sensory unit is composed of

A sensory unit includes all receptor cell and the associated afferent neuron.

How does our sensory system work?

Afferent neurons send information from the periphery to the CNS. CNS receives the stimulus and makes a decision about this information. The cerebral cortex then formulates a conscious interpretation of the stimulus. The interpretation is not always accurate and sometimes our brain makes things up.

Where are Baro-receptors located?

Aorta and Carotid Arteries

How do you decrease the frequency of AP in baro-receptor?

Drop in BP decreases AP frequency

_____________, an endogenous pain reliever, counters substance P

Enkephalin

What is the effect of stimulating one vs all of the sensory receptors in receptive field?

Every time we stimulate one of the sensory receptor, we are going to trigger a sensory potential (kind of like graded potential), the more sensory potential there is, the more likelihood that we are going to fire a action potential.

A sensory receptor converts one form of a signal into another form

Ex: a sensory stimulus from light is converted into a membrane potential change. This is called a receptor potential.

$$$$ How is the size of a receptive field, the degree of overlap between sensory units and lateral inhibition used in stimulus localization?

Size: the larger the receptive field size, the harder it is to detect the exact location of a stimulus. The smaller the field the better able you are to detect the stimulus location. The degree of receptive field overlap: localizing a stimulus improves with receptive field overlap because if the signal is detected by two overlapping neurons, the signal must be within the overlap. Lateral inhibition:

Two-point discrimination

The ability to perceive two points on the skin. The smaller the receptive field, the better the resolution • 2-point discrimination varies considerably in different areas on your body

How do you increase the frequency of AP in baro-receptor?

The higher the blood pressure, the greater the frequency of APs generated -

$$$ What is the mechanism behind referred pain? (Slide 53)

Visceral organ sensory neuron synapse with the same 2nd order neurons as peripheral sensory neurons within the external body, so the pain feels like it is coming from somewhere else.

Why do visceral organ produce referred pain?

Visceral organ sensory neurons synapse with the same 2nd order neurons as peripheral sensory neurons within the external body such as your muscles

Slow pain responding receptors (polymodal nociceptors)

• Give the perception of dull aching pain • Poorly localized pain because of a larger receptive field • APs are transmitted by unmyelinated C fibers • Polymodal means they don't really perceive pain differently when caused e.g. by fire or being cut • Polymodal pain receptors job is to notify you that you are still injured

When you stub your toe, pain perception starts out fast and ends slow

• Initial sharp pain is fast pain transmitted by thinly myelinated A-delta fibers (myelinates makes it travel faster) - Reaches sensory cortex sooner - Allows for a rapid response • Followed by prolonged aching pain (slow pain) - Transmitted by slower unmyelinated C fibers - Reaches the cortex after the A-delta signal - Keeps reminding you that you are still injured

Fast-type mechanical and thermo pain receptors

• Pain perceived as a sharp sensation • Small receptive fields to determine the location • Thinly myelinated A-delta fibers (fast transmission but slowest of the A-fibers) • Two other A type nerve fibers that are not pain receptors - A-beta (thicker myelin, faster) nerve fibers are for touch - A-delta (thickest myelin, fastest) fibers are for proprioception

Referred pain is just a misunderstanding

• The brain more often receives pain stimuli from somatic pain receptors • When a pain stimulus comes from a visceral organ, it goes through the same 2nd order neuron to get to the brain • Since the signal came from a 2nd order neuron used most often in the past to indicate muscle pain, the brain assumes it's the same pain source

Accurately detecting where a stimulus is coming from depends on a number of things

• The size of the receptive field • The degree of receptive field overlap • The presence of lateral inhibition

Identifying a stimulus can involve combining multiple sensory receptors

• We don't have receptors for wetness • Instead we combine information about temperature change and touch • The cerebral cortex uses the combined signals from temperature and touch to interpret the feeling of wetness