50 Sensory and Motor Mechanisms Flashcards
What is the purpose of the star on the star-nosed mole?
These 11 pairs of appendages are sensitive to touch. (not smell or light and thy can’t be used for grasping)
What are the basic stages of the sensory pathways?
Sensory reception, transduction, transmission and perception.
What is sensory reception?
The detection of a stimulus by sensory cells.
What are most sensory cells?
Specialised neutrons or epithelial cells.
What are some examples of internal stimuli detected by sensory receptors?
Blood pressure, temperature and body position.
What is transduction?
The conversion of a physical or chemical stimulus to a change in membrane potential.
How does sensory transduction occur?
In all cases the stimuli triggers ion channels of the receptor to open or close. This affects membrane potential. This change is called ‘receptor potential’ and acts are a form of graded potential.
What are the two classes of sensory receptors based on how the signal reaches an afferent neuron?
1) The ‘receptor is afferent neuron’
2) ‘Receptor regulates afferent neuron’
What happens in neurons where ‘receptor is afferent neuron’?
The influx/outflow of ions in the ‘receptor potential’ triggers an action potential that carries the signal to the spinal cord.
What happens in neurons where ‘receptor regulates afferent neuron’?
When the ’sensory receptor cell’ detects a stimulus the movement of ions leads to a receptor potential.
This triggers the release of neurotransmitters form vesicles. These neurotransmitters bind to ‘receptor proteins’ on the afferent neuron which carry the signal to the CNS.
How is stimulus intensity portrayed?
Since action potentials are ‘all or nothing’ the strength of each signal can not be adjusted.
One alternative is for sensory receptors to trigger action potentials to send action potentials at a low frequency when the stimulus is low. When the stimulus increases action potentials are sent at a higher rate.
The stronger the pressure is on the skin, the more receptors it will activate. Therefore the strength of some stimuli can be conveyed through the number of receptors activates.
What is perception in terms of sensory reception?
The conversion of the stimuli to perceptions i.e. colours, smells, sounds and tastes.
How is the source of the action potential identified?
Each sensory neuron has its own nerve fibres. Therefore when that fibres is activated, the brain knows which specific receptor it came form.
What is the collection of multiple inputs called?
Integration
What is an important feature of the sensory transduction pathway?
It amplifies the signal so that a low-energy photon can still yield a meaningful response.
Besides amplification, what can effect the strength of the signal before it reaches the brain?
Adaption.
What is adaptation and why is it important?
After continued stimulation many receptors undergo a decrease in sensitivity called adaption. This is important as otherwise one would be aware of every heartbeat etc.
This would distract the person from important stimuli.
What are the basic types of sensory receptors?
Mechanoreceptors, chemoreceptors, electromagnetic receptors, thermoreceptors and pain receptors.
What is the basic change mechanorecepotrs detect?
Physical deformation caused by mechanical energy such as pressure, touch, stretch, motion and sound.
What is the typical structure of a mechanoreceptor and thus how does it sense deformation?
Ion channels that are linked to structures outside of the cell such as cilia. The ion channels may also be attached to the cytoskeleton.
If the surrounding tissue is deformed tension will be present in the cilia/cytoskeleton. This opens ht sion channels leading to a ‘receptor potential’ and thus the stimulus has been transduced.
Where is a specific place mechanoreceptors are found outside the skin?
“Vertebrate stretch receptors” are dendrites of sensory neutrons that spiral round some skeletal muscle fibres. Groups of about 2 to 12 of these fibers, formed into a spindle shape and surrounded by connective tissue, are distributed throughout the muscle.
When the muscle is stretched, the spindle fibres also leading to a signal being transuded.
Where is a large concentration of mechanoreceptors found?
In the skin.
What are the layers of the skin?
Form top to bottom: Epidermis, Dermis and Hypodermis
What is the hypodermic of the skin?
The bottom layer of the skin that contains the nerves.
Where are the various mechanoreceptors of the skin found?
Receptors that detect gentle pressure, vibration, and temperature are close to the surface of the skin. Receptors that respond to strong pressure are in deep skin layers.
“Naked dendrites” (dendrites on their own) wind around the base of hairs to detect movement of that hair. Naked dendrites in the epidermis respond to pain
All of these receptors, except the naked dendrites of the epidermis, are found in the dermis layer of the skin.
Why are the naked dendrites that surround the hairs important?
They allow the deflections of the hair to be detected. This is especially important in cats etc. that use their whiskers to feel around.
What are chemoreceptors divided into?
‘General receptors’ that measure total solute concentration and ’specific receptors’ that respond to specific chemicals.
What is an example of a ‘general receptor’ chemoreceptor?
“Osmoreceptors” in the brain that detect changes in the solute concentration of the blood and use this to stimulate thirst when osmolarity increases.
What are some examples of specific molecules that ’specific receptors’ are often found for?
Glucose, oxygen, carbon dioxide and amino acids.
Also H+ ions to detect pH.
What is a common use of chemical receptors outside of mammals?
To detect pheromones.
What are electromagnetic receptors?
Sensory receptors that detect electromagnetic energy such as in the forms of light, electricity and magnetism.
What are some examples of electromagnetic receptors that detect light?
Photoreceptors in eyes.
Snakes have photoreceptors that are specialised to detect infrared and thus act as thermal cameras to detect the heat of their prey.
What are some examples of electromagnetic receptors that detect electricity?
Platypuses have electroreceptors on their bill that detect the electric fields generates by the muscles of crustaceans, frogs and fish etc.
Some fish generate electric currents and then use their electroreceptors to locate prey or other objects that disturb those currents.
What are some examples of electromagnetic receptors that detect magnetism?
Many animals such as salmon, pigeons, sea turtles, HUMANS, bees, some molls and a few protists/prokaryotes contain the mineral magnetite.
This magnetite can then be used to detect the earths magnetic field for navigation etc.
Where are the thermoreceptors of the skin primarily located?
In the anterior hypothalamus and in the skin.
What is the purpose of thermoreceptors in the anterior hypothalamus?
They detect the temperature of the blood and relay this to the posterior hypothalamus (the bodies ’thermostat’)
How does thermoreception work?
Mammals have a number of kinds of thermoreceptors, each specific for a particular temperature range. At least 6 types of thermoreceptors belong to the TRP (transient receptor potential) family of ion channel proteins.
Why does ‘capsacin’ feel hot? What other chemical triggers an opposite response>
It activates the same receptor that is also activated in temperatures greater than 42º C
Menthol (found in mint) feels cold as it activates the same receptors as when temperatures are less than 28ºC
How are different temperatures senses?
They body has at least 6 receptors that are activated with different thresholds. For example one activates in temperatures greater than 42ºC and another activates at temperatures less than 28ºC.
What are pain receptors formerly called?
Noccioceptors.
In humans what form are most noccioceptors?
Naked dendrites that act as nociceptors by detecting noxious thermal, mechanical, or chemical stimuli.
How does the inflammatory response directly lead to pain?
The damaged tissues release ‘Prostaglandins’ what make nearby noccioceptors more sensitive and thus increase the pain felt.
How is gravity detected in animals?
By statocysts.
How do statocysts work?
They consist of a sac covered by cilia on the inside of the wall. The stack contains balls called ’statoliths’ which are grains of sand etc.
As the animal’s orientation changes the statoliths move around the statocyst. This means different cilia and thus different ‘ciliated receptor cells’ are activated.
What is the basic principle of sound transduction?
Cilia vibrate in response to sound waves and thus can trigger mechanoreceptors.
Different frequencies cause cilia of different lengths to vibrate and thus pitch can be determined.
How do males detect female insects besides with pheromones?
The males have hairs that are tuned to the specific frequency of the wings of a female beating.
What is the structure of the ear divided into?
The ‘outer ear’, ‘middle ear’ and the ‘inner ear’
What does the ‘outer ear’ include?
The ‘pinna’ (the fleshy bit we see) and the auditory canal which carries sounds collected by the pinna and carries it to the inner ear.
What does the middle ear include?
The ’tympanic membrane’ (eardrum) which vibrates as it is hit by sound waves from the auditory canal.
These vibrates hit the malleus (hammer) bone which strikes the incus (anvil bone) and in turn the stapes (stirrup) bone.
The stapes then hits the ‘round window’ causing the sounds to be transferred into the fluid drilled cochlea.
The middle ear is connected to the ‘Eustachian tube’ which leads to the pharynx and thus equalises the pressure of the inner ear to prevent the ’tympanic membrane’ from bursting.
What does the middle ear include?
The ’semicircular canals’ which which function in equilibrium, and the coiled cochlea, a fluid-filled bony chamber that is involved in hearing.
What is the structure of the cochlea?
When takes in cross section:
The basic structure of the cochlea is a hollow ring of bone.
The upper portion of this ring is the ‘vestibular canal’ and the lower-portion is the ’tympanic canal’. Both canals are enclosed and filled with fluid.
Between the vestibule and tympanic canals is the ‘cochlear duct’ The ‘basilar membrane’ (floor) of this canal has the ‘organ of corti’
What is the structure of the ‘organ of corti’?
The organ of Corti is on the floor (basilar membrane) of the basilar membrane
It contains the mechanoreceptors of the ear in the form of hair cells whose hairs project into the cochlear duct. Many of the hairs are attached to the tectorial membrane, which hangs over the organ of Corti like a canopy..
Sound waves make the basilar membrane vibrate, which results in bending of the hairs and thus depolarisation of the hair cells.
How specifically do the hairs get deformed enough to trigger a signal?
Vibration of the basilar membrane in response to sound raises and lowers the hair cells, bending the hairs against the surrounding fluid and the tectorial membrane.
Why is it important that sound waves travel from the air and into the fluid of the cochlea?
This amplifies them and thus makes them more perceptible.
The ‘hair cells’ also move more in the fluid.
What is the fluid in the cochlea called?
Perilymph
Where do pressure waves travel after being initiated by the stirs striking the oval window?
Upon entering the vestibular canal, the pressure waves push down on the cochlear duct and basilar membrane. This causes the basilar membrane and its attached hair cells to move up and down and thus leading to the detection of sound.
How do the hair cells communicate that they have moved?
In a typical resting state they release a steady stream of neurotransmitters.
As the hairs of the hair cells are hit by the pressure wave they deflect. This triggers mechanoreceptors to increase the rate at which neurotransmitters are being released.
As the pressure wave ends the hairs get pushed in the opposite direction. This causes even less than normal neurotransmitters to be released.
What prevents pressure waves from reverberating within the ear/
Once pressure waves travel through the vestibular canal, they pass around the apex (tip) of the cochlea. The waves then continue through the tympanic canal, dissipating as they strike the round window.
How does the ear convey volume?
A louder sound leads to greater deflection and thus more frequent action potentials of the cells.
How does the ear convey pitch?
The basilar membrane is not uniform along its length: it is relatively narrow and stiff at the base of the cochlea near the oval window and wider and more flexible at the apex.
Therefore each region is tuned to a specific frequency and thus the region with the most action potentials denotes the pitch.
Besides hearing, what is a major function of the ear?
‘Equilibrium’ i.e. sensing motion and orientation
What are the parts of the ear that determine orientation and motion called?
The vestibular system
What are the major structures of the vestibular system?
The semicircular canals, the utricle and the saccule.
What are the primary variables the vestibular system detects?
Anglular motion, linear motion and the direction of ‘up’
With what is angular motion detected?
The semicircular canals.
With what is linear motion detected?
The utricle and saccule
With what is the direction on ‘up’ detected?
The utricle and saccule.
What is the structure of the semicircular canals?
There are three rings with one on each plane i.e. X, Y and Z.
How do the semicircular canals detect angular momentum?
Each of the semicircular canals is filled with fluid (perilymph)
As the canals experience angular momentum this fluid moves through the canal. This causes the hair cells to bend triggering nerve impulses as the frequency of action potentials increases in direct proportion to the angular momentum experienced.
What is the structure of the hair cells in the semicircular canal?
Each hair cell is in a small group. This group is then protected by begin enclosed in a “cupula” which is a gelatinous cap that acts as a ’sail’ to increase the surface area exposed to the moving perilymph
What is the structure of the utricle and how does this allow them to detect linear motion and the direction of gravity?
The utricle are chambers that are filled with a gelatinous material. Hairs from the wall of these chambers protrude into the fluid.
Embedded in the gelatinous material are many tiny pieces of calcium carbonate called ‘otoliths’
As the head moves these otoliths press on hairs protruding into the gel and thus trigger the ‘hair cell receptor’
How are the utricle and saccule arranged and what does this lead to?
The utricle is orientated horizontally and the saccule vertically. Therefore motion can be detected in the forward-back and up-down directions
What causes dizziness?
When spinning the fluid and canal eventually come to equilibrium and remain in that state until you stop. At that point, the moving fluid encounters a stationary cupula, triggering the false sensation of angular motion that we call dizziness.
How do fishes hear?
Their hearing apparatus does not open to the outside nor contains an eardrum or cochlea.
Instead they have inner ears inside their head. As pressure waves are conducted through the skeleton in moves ‘otoliths’ in this ear. This stimulates hair cells and thus the perception of sound.
Besides the inner ear, how can fish detect pressure waves?
They have a ’lateral line’ running down their side.
How does a ‘lateral line’ work?
Between their scales is a tube, called the ‘lateral line canal’ through which water can flow.
Along this canal are clusters of hair cells that are encapsulated in a gelatinous cap called the ‘cupula’ Based on the direction and velocity of water flow through the ‘lateral line canal’ the hair cell is depolarised.
What is the lateral line system used for?
It detects how fast the fish is swimming and can gauge the direction and velocity of water currents.
It can also detect water movements or vibrations triggered by prey and predators etc.
What is the hearing system of amphibians?
Many amphibians have lateral lines in the juvenile form i.e. as tadpoles.
As adults on land they have an ear with the tympanic membrane on the body surface. A single bon conducts the sounds from this tympanic membrane to the cochlea.
What is the structure of an eye in simple invertebrates?
They often have two small patches of photoreceptors called ‘ocelli’ on the head region.
A layer of darkly pigmented cells surrounds the ocellus on three sides so that it receives light from only one side.
How are ocelli useful?
Because of the dark pigmented cells they only receive light from one direction. Because there is one ocellus on each side of the head the organism can compare the strength of light on the left or the right to move towards or away from the light.
What is an example of an organism that uses ocelli to see?
Planarians
What type of eyes do insects and crustaceans have?
They have compound eyes made of ‘omatidia’
What is the structure of a compound eye?
It consist of many ‘omatidia’
What is the structure of an omatidia?
Each omatidia has at the top its own ‘cornea’ then below it a ‘crystalline cone’ These together acts as the ‘lens’ to focus the light.
The focused light is sent into a tube called the ‘rhabdom’ which traps the light. The wall of this tube is made of photoreceptors cels which measure the strength of the light.
What are the advantages of ‘omatidia’?
They have a very high “frame rate” so are good at detecting movement which is beneficial in insects.
Besides those with ocelli or omatidia, what type of eyes do invertebrates have?
’Single-lens eyes’
What are some examples of invertebrates with single lens eyes?
Some jellies and polychaete worms, as well as in spiders and many molluscs.
What are the basic structures found in a single lens eyes?
It has a small opening, the pupil, through which light can enter. The pupil can be dilated or contracted by the surrounding iris.
Behind the pupil a single lens per eye focuses this light not the layer of photoreceptors.
What basic type of eye do vertebrates have?
Single lens eyes
How do the signle lens eyes seen in vertebrates differ from this in invertebrates?
In invertebrates and fish the foci is adjusted by moving the lens forward or backwards.
In vertebrate excluding fish this focusing is achieved by muscles which change the actual shape of the lens.
What are ‘omatidia’?
The individual photoreceptor units of a compound eye.
What is the the structure of a human eye?
It has the basic shape of a ball. The front edge of the ball is made up of transparent ‘cornea’ while the rest of the eye ball is surround by white ’sclera.’ Interior to the sclera is a thin layer of chorioid which contains many blood vessels to feed the retina which is interior to it.
Behind the cornea is the iris, with aqueous humour between these structures. Light passes through the pupil, a hole in the iris, and passes through the ‘lens’. The shape of the lens is adjusted by the ’suspensory ligament.’
The light passing through the lens reaches the interior of the eyeball, which is filled with vitreous humour. This light is focused onto the retina, a sheet of cells that covers most of the eyeball.
At the far back of the retina is the ‘optic disk’, a blindspot which has not photoreceptors. Behind this is the optic nerve and the ‘central artery’ and ‘central vein’ which provided blood flow to the eye.
What is the white exterior of the eye called?
Sclera
What is internal to the sclera?
The ‘choroid’
What is ’sclera’?
The opaque white exterior of the eye
What is ‘choroid’?
The layer of the eye ball between the sclera and the retina. It has many blood vessels to supply the retina.
What is the ‘fovea’?
A concentration of cones on the retina meaning this area has particularly acute visual detail i.e. not-peripheral
What is region of the retina with many photoreceptors called?
The fovea.
What is the outermost layer of the eye through which light can pass?
The cornea.
What is the cornea?
The front transparent bit of the eye through which light can pass.
What are the liquids of the eye called?
The aqueous humour and the vitreous humour
What is the aqueous humour?
The fluid between the cornea and iris
What is the vitreous humour?
The fluid in the main interior of the eye i,e, where the retina is.
What is the fluid between the cornea and iris called?
Aqueous humour
What is the fluid in the main cavity of the eyeball called?
The vitreous humour
What is the structure which adjusts the size of the lens called?
The suspensory ligament
What is the layer of tissue with blood vessels to supply the retina called?
The choroid
What is glaucoma?
A disease in which the ducts which drain the aqueous humour are clogged causing fluid to accumulate.
This puts pressure on the optic nerve, possibly causing blindness.
How does aqueous humour differ from vitreous humour in terms of physical properties?
Aqueous humour has a consistency of water whereas vitreous humour is jellylike.
What causes the blind spot in humans?
The optic nerve is covered by the optic disk, which lacks photoreceptors.
What is the structure of the retina?
The outermost layer is a single-cell thick layer of pigmented epithelium. Photoreceptors i..e rods and cones extend into this layer.
‘bipolar cells’ are neurons that gather input from multiple photoreceptors. Multiple bipolar cells attach to ganglion cells which relay their information to optic nerve fibres.
Horizontal cells integrate information from multiple photoreceptors and convey this to bipolar cells. Amacrine cells integrate information form multiple horizontal cells and sends this to the ganglion cells.
Note that most photoreceptors/bipolar cells link directly to horizontal/ganglion cells whereas in other this information is integrated first by horizontal/amacrine cells.
What are the main cells involved in the conduction of signals from the photoreceptors to the optic nerves?
Horizontal cells, bipolar cells, amacrine cells and ganglion cells.
What are ‘omatidia’?
The individual photoreceptor units of a compound eye.
What is the the structure of a human eye?
It has the basic shape of a ball. The front edge of the ball is made up of transparent ‘cornea’ while the rest of the eye ball is surround by white ’sclera.’ Interior to the sclera is a thin layer of chorioid which contains many blood vessels to feed the retina which is interior to it.
Behind the cornea is the iris, with aqueous humour between these structures. Light passes through the pupil, a hole in the iris, and passes through the ‘lens’. The shape of the lens is adjusted by the ’suspensory ligament.’
The light passing through the lens reaches the interior of the eyeball, which is filled with vitreous humour. This light is focused onto the retina, a sheet of cells that covers most of the eyeball.
At the far back of the retina is the ‘optic disk’, a blindspot which has not photoreceptors. Behind this is the optic nerve and the ‘central artery’ and ‘central vein’ which provided blood flow to the eye.
What is the white exterior of the eye called?
Sclera
What is internal to the sclera?
The ‘choroid’
What is ’sclera’?
The opaque white exterior of the eye
What is ‘choroid’?
The layer of the eye ball between the sclera and the retina. It has many blood vessels to supply the retina.
What is the ‘fovea’?
A concentration of cones on the retina meaning this area has particularly acute visual detail i.e. not-peripheral
What is region of the retina with many photoreceptors called?
The fovea.
What is the outermost layer of the eye through which light can pass?
The cornea.
What is the cornea?
The front transparent bit of the eye through which light can pass.
What are the liquids of the eye called?
The aqueous humour and the vitreous humour
What is the aqueous humour?
The fluid between the cornea and iris
What is the vitreous humour?
The fluid in the main interior of the eye i,e, where the retina is.
What is the fluid between the cornea and iris called?
Aqueous humour
What is the fluid in the main cavity of the eyeball called?
The vitreous humour
What is the structure which adjusts the size of the lens called?
The suspensory ligament
What is the layer of tissue with blood vessels to supply the retina called?
The choroid
What is glaucoma?
A disease in which the ducts which drain the aqueous humour are clogged causing fluid to accumulate.
This puts pressure on the optic nerve, possibly causing blindness.
How does aqueous humour differ from vitreous humour in terms of physical properties?
Aqueous humour has a consistency of water whereas vitreous humour is jellylike.
What causes the blind spot in humans?
The optic nerve is covered by the optic disk, which lacks photoreceptors.
What is the structure of the retina?
The outermost layer is a single-cell thick layer of pigmented epithelium. Photoreceptors i..e rods and cones extend into this layer.
‘bipolar cells’ are neurons that gather input from multiple photoreceptors. Multiple bipolar cells attach to ganglion cells which relay their information to optic nerve fibres.
Horizontal cells integrate information from multiple photoreceptors and convey this to bipolar cells. Amacrine cells integrate information form multiple horizontal cells and sends this to the ganglion cells.
Note that most photoreceptors/bipolar cells link directly to horizontal/ganglion cells whereas in other this information is integrated first by horizontal/amacrine cells.
What are the main cells involved in the conduction of signals from the photoreceptors to the optic nerves?
Horizontal cells, bipolar cells, amacrine cells and ganglion cells.
What is the structure of a photoreceptor?
It has a synaptic terminal and cell body.
At the other end is a stack of membranous ‘disks’ in which visual pigments are embedded. These disks are surrounded by an ‘outer segment’ membrane. In ‘cones’ the disks and outer segment is conical, in rod it is cylindrical.
What is the structure of a visual pigment in a human eye’s photoreceptor?
Vertebrate visual pigments consist of a light-absorbing molecule called retinal (a derivative of vitamin A) bound to a membrane protein called an opsin. Seven α helices of each opsin molecule span the disk membrane.
How do the visual pigments in a rod work?
The opsin bound to the retinal is called ‘rhodopsisn’
In the absence of light the retinal is in its ‘cis isomer’, existing as a bent chain. The presence of light stimulates its conversion into its ’trans isomer’ form which is a strait chain.
In the absence of light enzymes convert the trans isomer into the cis isomer. Therefore by measuring the ratio of retinal in its ’trans isomer’ to ‘cis isomer’ the light level can be deduced.
What is retinal?
The general term for a light-absorbing molecule in the vertebrate eye.
What from does retinal enter when exposed to light?
It enters its ’trans isomer’ phase which consists of a straight line.
What is ‘rhodopsin’?
The molecule bound to the light-absorbing retinal pigment in rods.
What are the basic stages in the generation of a receptor potential in a rod cell?
Light converts cis-retinal to trans-retinal, activating rhodopsin.
Active rhodopsin activates a G protein called ‘transducer’.
Transducin activates the enzyme phosphodiesterase which detaches cGMP from Na+ channels in the plasma membrane by hydrolysing cGMP to GMP.
The Na+ channels close when cGMP detaches. The membrane’s permeability to Na+ decreases, and the rod hyperpolarizes (becomes more negative), generating a membrane potential.
What is ’transducin’?
The G protein activated by rhodopsin in the rods of a vertebrate eye.
What is the basic difference between rods and cones?
Rods detect light/dark, cones detect colour.
How are signals relayed from the photoreceptors?
When exposed to light the activation of rhodopsin causes Na+ channels to close and thus the rod becomes hyper polarises.
This negative voltage inhibits the release of glutamate into the synapse. This depolarises or hyperpolarises the post-synaptic bipolar cell, depending on it glutamate receptors.
Why are horizontal cells important?
When an illuminated rod or cone stimulates a horizontal cell, the horizontal cell inhibits more distant photorecep- tors and bipolar cells that are not illuminated.
The result is that the region receiving light appears lighter and the dark surroundings even darker. This form of integration is called ‘lateral inhibition’ and improves the sharpness and contrast of the image.
What does ‘receptive field’ refer to?
Is the region of photoreceptors which link to a single ganglion.
Therefore in the peripheral vision areas each ganglion has a large receptive field, whereas in the fovea it is smaller and thus a finer image is formed.
What is the area from which a ganglion revives visual input from photoreceptors called?
Its ‘receptive field’
What is ‘lateral inhibition’?
The idea that when activated horizontal cells inhibit photoreceptors far from the activated photoreceptor to increase the image’s contrast
