Title: Physiology 2130 / Module 7: Sensory System

Q: Signals from outside the body must be converted into [...].
A: action potentials

Q: Special receptors that convert stimuli to AP are:
1. [...] in the visual system.
2. [...] for somatosensory system.
3. [...] in the auditory system.
A: Photoreceptors; Free-Nerve Endings; Auditory Hair Cells
Extra: Photoreceptors are sensitive to light, free nerve endings detect heat & pain, & auditory hair cells can detect sound waves in the air.

The sensory systems are:
1. Somatosensory System (Touch)
2. Visual System
3. Auditory System
4. Vestibular System
5. Olfactory System (Smell)
6. Gustatory System (Taste)

Q: The [...] of environmental info is how info from external environment is turned into action potentials.
A: transduction

Q: Envrionmental stimuli is turned into APs by [...].
A: sensory receptors

Types of Environmental Stimuli:
1. Mechanical - touch, pressure, vibration, proprioception, sound;
2. Chemical - taste, pain, odors;
3. Electromagnetic - light; &
4. Other - gravity, motion, acceleration, heat

Q: An [...] is the particular form of environmental stimulus to which the sensory receptor is most sensitive.
A: adequate stimulus
Extra: Sensory receptors do respond to other forms of energy, but not in an optimal way. When the stimulus is adequate, it will respond in an optimal way.

Q: When a sensory receptor is stimulated by environmental stimulus there is a change in ion permeability that creates a local depolarization, this is a [...] or [...].
A: generator; receptor potential

Q: Receptors do not have [...], so receptor potentials must spread to the [...] for an action potential to be generated.
A: voltage-gated ion channels; axon (usually the node of ranvier)

Q: In order for neurotransmitters to be released, action potentials must spread to a [...].
A: synapse

Characteristics of Receptor Potentials:
1. Usually depolarizing but can also be hyperpolarizing.
2. Caused by an increase in permeability to sodium ions (or K+ ions if hyperpolarization).
3. Local, do not propogate like action potentials. They decrease with time and distance.
4. Proportional to the strength of stimulus, stronger stimulus = larger receptor potential and more likely to fire an action potential.
Extra: These are shared characteristics with EPSP and IPSP.

Q: Heavy weight = [...] receptor potential = [...] action potentials [...].
A: large; many; (burst of many)
Extra: The many action potentials will reach the brain and make you conciously aware of the heavier weight in your hand.

Q: The [...] detects touch, vibrations, temperature and pain which all originate in the skin.
A: somatosensory system

Q: Receptors in the skin are called [...] receptors.
A: cutaneous

Q: Although the skin is covered with sensory receptors, each receptor will only respond to a stimulus within a certain region on the skin. This is the [...].
A: receptive field

Q: The receptive field is the [...] where an [...] stimulus will activate a particular receptor to fire an action potential in the neuron.
A: area of the skin; adequate

Q: Any stimulus applied [...] of the receptive field will not generate an action potential.
A: outside

Q: The somatosensory pathway from the periphery to the brain is the [...].
A: spinothalamic tract
Extra: aka the anterolateral tract

Q: The spinothalamic tract trnasmits info dealing with basic sensations like [...], [...] and [...].
A: pain; temperature; crude touch

Information from sensory neuron is passed on through the spinothalamic tract as follows:
1. Enters the spinal cord from the sensory neuron.
2. Synapses with the 2nd order neuron.
3. 2nd order neuron crosses to the contralateral side of the spinal cord.
4. Information ascends to the thalamus.
5. There is another synapse with a 3rd order neuron.
6. Information travels to the somatosensory cortex.

Q: The [...] and [...] transmits info associated with advanced sensation from the somatosensory pathway.
A: dorsal column; medial lemniscal system
Extra: Advanced Sensations = fine detailed touch, proprioception (muscle sense), and vibration.

Information from the dorsal column, medial lemniscal system is transmitted to the somatosensory cortex as follows:
1. Sensory neuron (1st order) enters spinal cord.
2. Immediately travels up spinal cord.
3. Synpases with 2nd order neuron.
4. Now crosses to the contralateral side of the spinal cord.
5. Info goes to thalamus.
6. Synapses with 3rd order neuron and travels to somatosensory cortex.

Q: The primary somatosensory cortex is located in the [...] lobe on the postcentral [...] behind the central [...].
A: parietal; gyrus; sulcus

Q: The [...] refers to the topographical representation of the body on the surface of the primary somatosensory cortex.
A: somatosensory homunculus

Q: Some areas of the somatosensory cortex receive more sensory info and require more [...] of the brain to process this info.
A: area
Extra: ie. tongue, lips and hands have more sensory info so need more brain to process, they have more sensory receptors than any other part of the body.

Q: The [...] system detects light and turns it into action potentials that are sent to the primary visual areas for processing.
A: visual

Q: The Visual System Consists of:
1. The [...] - which contains photoreceptors to convert stimuli into action potentials.
2. [...] - transmits action potentials.
3. [...] (in the occipital lobe) - processes incoming signals.
A: eye; Visual Pathway; Primary Visual Area

How the Eye Processes Light:
1. Light passes through the cornea.
2. The iris regulates the amount of light, can constrict with bright light and dilate in low light.
3. The lens flips the light upside down and backwards and focuses it onto the retina (back of the eye).
4. The retina has photorecepors, rods and cones.
5. Center of vision is focused on the fovea (part of the retina) which has highest concentration of cones.
Extra: Dilate = Widen
Constrict = Narrow

Q: Rods are very sensitive to light, they function best in [...] light conditions.
A: low

Q: Rods have 1 type of [...] and therefore do not detect [...].
A: photopigment; color

Q: Rods are located mostly in the region of the retina outside and around the [...].
A: fovea

Q: Cones function best under [...] light and are ideal for detecting [...].
A: bright; detail

Q: There are 3 types of cone cells, each with a different photopigment, and each sensitive to a [...].
A: primary colour

Q: Cones are found in the highest concentration in the [...].
A: fovea

Q: Rod and cone cells don't have [...] and therefore do not generate action potentials.
A: axons

Q: Rods and cones generate [...] potentials that release [...] neurotransmitters from their synaptic ending.
A: receptor; inhibitory

Q: The retina has a [...] layer at the very back of the eye to abosrb excess light.
A: pigment

Other cells in the retina used for integrating info are:
1. Bipolar Cells
2. Ganglion Cells
3. Horizontal Cells
4. Amacrine Cells
Extra: While rod & cone cells do not generate action potentials, these other cells are responsible for the integration of info from the rods & cones & the production of action potentials.

Q: When rod and cone cells are [...], they shut off bipolar cells.
A: depolarized

Q: When light strikes the retina, it does not [...] and [...] rod and cone cells.
A: excite; depolarize

Q: Light [...] rod and cone cells and shuts them off. Whereas they are [...] in the dark.
A: hyperpolarizes; depolarized

Transduction of light to action potentials:
1. Light strikes and it closes Na+ voltage gated channels in the rod and cone cells.
2.  K+ is still leaking out.
3. The rod and cone cells hyperpolarize,shutting them off so they do not release inhibitory neurotransmitters.
4.. Bipolar cells are activated (they depolarize) which leads to an AP in the ganglion cells.
Extra: Bipolar Cells can depolarize spontaneously.

The 4 primary types of eye movement:
1. Saccades - rapid, jerky eye movements (head held still, eyes moving to object of interest, which is also still ie. words).
2. Smooth Pursuit - the smooth movement of eyes to follow an object and keep image focused on fovea (head is still and eyes follow moving object).
3. Vestibular Ocular Reflex (VOR) - eye movement to focus attention on an object and move your head at the same time (ie. staring at someone and nodding).
4. Vergences - eye movements when object of interest is moving towards (convergence) or away from you (divergence).

Q: [...] turns sound waves into APs that go to auditory area of brain.
A: Auditory System

Q: Humans can hear [...] but best hearing occurs in the range of [...].
A: 20Hz - 20,000Hz; 1000-3000Hz

Q: Auditory System can be divided into 3 parts:
1.[...]
2. [...]
3. [...]
A: External or Outer Ear; Middle Ear; Inner Ear

Q: The outer ear contains the [...] and the [...].
A: auricle; external auditory canal
Extra: Auricle = the ear essentially (what we see on our heads)

Q: The middle ear consits of:
1. [...]
2. [...]
3. [...]
A: Eardrum (Tympanic Membrane); Ear Ossicle; Eustachian Tube

Q: The ear ossicle has 3 bones, the [...], [...] and [...].
A: malleus; incus; stapes

Q: The inner ear consists of:
1. [...] - For Balance
2. [...] - Processing Sound
A: Vestibular apparatus; Cochlea

Q: Sound is not created until a wave of [...] hits parts of the ear (or microphone) and turns it into [...] information (action potentials in the CNS).
A: air pressure; electrical

Q: The cohlea has a hollow area on the inside that can be divided into 3 compartments:
1. Upper [...]
2. Middle [...]
3. Lower [...]
A: Scala Vestibuli; Cochlear Duct; Scala Tympani

Q: The [...] of a sound wave is the # of waves per second.
A: frequency

Q: The intensity or loudness of the sound wave is expressed by its [...].
A: height
Extra: Height = Amplitude

How sound vibrations are transferred and amplified:
1. Sound waves are funneled into external auditory canal.
2. Sound waves strike the tympanic membrane, causes it to flex back and forth.
3. Levering action of ear ossicles amplifies the pressure waves that strike the typanic membrane.
4. The oval window vibrates due to the ear ossicles, amplifies waves 15-20x original amount.
5. Perilymph fluid in the cochlea transmits waves to the hair cells emebedded in the basilar membrane.
6. Hair cells detect vibrations and turn them into APs.

Q: The basilar membrane is aka the [...].
A: basement membrane

Q: We hear different frequencies because pressure waves will reach [...] at different locations/regions of the [...], which is not consistent along its length.
A: peaks; basilar membrane

Q: The basilar memebrane is wide and thin at the [...] of the [...], and narrow and thick at the [...].
A: top; cochlea; base

Q: Tension is tight at the [...] of the basilar membrane and loose at the [...].
A: base; top

Q: [...] and [...] of the hair cells differs slightly along the length of the basement membrane.
A: Length; stiffness

Q: Low frequencies stimulate hair cells at the [...].
High frequencies stimulate hair cells near the [...].
A: apex of the cochlea; oval window
Extra: Apex = Top
The length & stiffness of the hair cells also differ slightly along the length of the membrane. This is another way that we can detect different frequencies.

Q: When the basilar membrane vibrates, hair cells are bent = [...] and [...] occurs.
A: ion channels open; depolarization

Transduction of sound to action potentials:
1. Basilar Membrane vibrates = bends hair cells.
2. Ion Channels open and cells depolarize.
3. Hair Cells releases neurotransmitters that excite neurons of the auditory nerve.
4. Auditory nerve is excited and fires APs.
5. Signals flow to auditory cortex on the temporal lobe of the brain.

Q: The [...] the sound = the stronger the vibration = more neurotransmitters released = higher frequency of action potentials produced.
A: louder

Q: The vestibular system is located in the [...].
A: inner ear

Q: The [...] is responsible for maintaining balance, equilibirum and postural reflexes.
A: vestibular system

Q: The vestibular system detects [...] and [...] motion and the position of the head relative to the rest of the body.
A: linear; rotational

Q: Each vestibular apparatus has:
1. [...] which detect rotational or angular accelerations of the head; &
2. [...] which detect linear accelerations.
A: Semicircular Canals; Otolith Organs

Q: There are [...] semicircular canals and [...] otolith organs in each apparatus.
A: 3; 2
Extra: 3 Semicircular = 1 for movement in each plane of motion.
2 Otolith = 1 for acceleration in vertical plane & 1 for horizontal plane.

Q: The semicircular canals are filled with a fluid called [...].
A: endolymph

Q: At the end of the semicircular canal there is a swelling called an [...].
A: ampula

Q: The [...] contains a sensory region called the crista ampullaris.
A: ampula

Q: The crista ampullaris contains [...] cells which are fixed at their base while their cilia are embedded in a [...] material called the cupula.
A: sensory hair; gelatinous

Header: What is the utricle and what is the saccule?

Header: What is the utricle and what is the saccule?
Extra 1: The utricle detects horizontal accelerations & decelerations (like when you’re in a car), while the saccule detects vertical accelerations & decelerations (like when you’re in an elevator).

Q: Semicircular canals detect only [...] and [...].
A: rotational accelerations; decelerations

The action of the endolymph:
1. When head moves to the left the endolymph seems to lag behind and move to the right (opposite direction than head movement on the horizontal).
2. Endolymph hits the cupula and bends the hair cells.
3. Hair cells embedded in the cupula will either bend in a way that creates depolarization or hyperpolarization, depending on which signals will either be sent (or not) to the brain.

Q: The endolymph lags due to [...].
A: inertia

Q: The otolith organs detects [...] accelerations and decelerations and the position of the [...].
A: linear; head

Q: The two otolith organs in each vestibular apparatus are:
1. [...] - detect horizontal acceleration and deceleration
2. [...] - detect verticle accelerations and decelerations
A: Utricles; Saccules
Extra: each otolith organ has many hair cells embedded in a gelatinous membrane

Q: The gelatinous membrane has [...] to give it weight and inertia during movements.
A: otolith crystals

Q: When the body is at rest the [...] still has series of APs being produced within it.
A: vestibular nerve

Q: Acceleration/Deceleration on the Vertical/Horizontal Plane:
1.The body accelerates on the vertical or horzontal plane.
2. The [...] intially lag and seem to move in the opposite direction to the acceleration.
3. This bends the cilia and causes an [...] in frequency of APs from vestibular nerve.
IF deceleration, the hair cells bend in the other direction which causes the frequency of action potentials to [...] further from resting state.
A: otolith crystals; increase; decrease

Q: There is [...] ontop of hair cells.
A: cilia

When stereocilia bends towards the larger kinocilium more neurotransmitter is released = more APs.
Sterocilia bends away from the kinocilium = less neurotransmitter = less APs.
Resting and steady APs = vertical sterocilia.

Q: In order for the brain to know what’s happening outside the body, [...] (energy) like light, heat, touch, or sound must first be detected by [...] which then convert the info into action potentials.
A: environmental stimuli; sensory receptors

Cutaneous Receptors include:
1. Hair Follicle receptors that are sensitive to fine touch & vibration;
2. Free Nerve Endings that respond to pain & temperature (hot & cold);
3. Meissner’s Corpuscles that detect low-frequency vibrations (between 30 & 40 cycles/sec);
4. Ruffini’s Corpuscles that detect touch;
5. Pacinian Corpuscles that detect high-frequency vibrations (250 to 300 cycles/sec) & touch.