Title: BV4 / Modul 2 / General sensory physiology

Q: What is meant by modality?
A: Stimuli from the external and internal environment are detected by specific/specialized receptor cells - these receptor cells respond to a specific modality
(main senses: sight, hearing/vestibular, taste/smell, touch/proprioception/pain/temperature)

Q: Which are the main senses?
A: - sight
- hearing/vestibular
- taste/smell
- touch/proprioception/pain/temperature

Q: what else can be said more specifically about modality?
A: There is also submodality

Q: What are ex of submodality?
A: - For vision: colour vision or night vision
- For touch: Discriminative touch

Q: What is meant by adequate stimulus?
A: A stimulus has to be adequate in terms of type of modality - a stimulus has to have a specific intensity or strength to activate a specific receptor cell and produce a conciousness or awarenes of this stimulus

Q: What is meant by transduction of stimulus?
A: Transduction of the stimuli to graded potentials and action potentials firing in neurons

Q: How dos transduction of a stimulus generally occur?
A: a stimulus is transduced into a signal, which will be used by the brain (it's a neuronal signal), this signal is a charge in the membrane which is either a graded potential or action potential

Q: What is sesnory transduction?
A: Sensory transduction is a conversion of energy associated with stimulus into a neuronal electrical signal

Q: What happens after transduction of a stimulus?
A: AP are then conducted to the CNS and to specific parts of the cortex that process information from specific modalities

Q: Which features of the stimulus are featured in the brain?
A: All the different features of the stimulus are processed and represented in the brain

Q: How are different features of the stimulus processed in the brain, which factors are taken into acc.?
A: - Modality (What?)
- Intensity (How strong?)
- Duration (When?)
- Location (Where?)

Q: What can our sensory receptors/-neurons be classified based on?
A: Can be classified based on their location

Q: Where are the receptorcells for somatosensory function located?
A: For somatosensory function, touch and pain, the receptorcells that detect the stimuli are located in our skin

Q: Which receptor cells sense pain?
A: Free nerve endings

Q: Which receptor cells sense touch?
A: Encapsulated endings

Q: Which types of sensory receptors are there in the skin?
A: - Free nerve endings
- Encapsulated endings

Q: Which types of sensory receptors are there in the muscles and tendons?
A: - Muscle spindles
- Golgi tendon organs

Q: Which types of sensory receptors are there in the eye?
A: - Rods
- Cones

Q: Which types of sensory receptors are there in the ear?
A: - Hair cells (hearing and vestibular system)

Q: Which types of sensory receptors are there on the tongue?
A: Receptor cells in taste buds

Q: Which types of sensory receptors are there in the nose?
A: Olfactory receptor neurons

Q: WHat do free nerve endings look like?
A: They have no special structure around the nerve ending

Q: How do encapsulated endings look?
A: The receptors that detect touch have special capsules or cels around the nerve endings

Q: Where do we have sensory receptors cells?
A: - Skin
- Muscls and tendons
- Eyes
- Ears
- Tongue
- Nose

Q: Which types of receptors are there?
A: - Mechanoreceptors
- Thermo receptors
- Chemoreceptors
- Photoreceptors

Q: What do mechanoreceptors sense?
A: Pressure and Mechanical forces such as touch, position of the body (muscle length, tension), and hearing

Q: What do thermoreceptors sense?
A: Temperature - warmth and cold

Q: What do chemoreceptors sense?
A: Chemicals - taste, smell

Q: What do photoreceptors sense?
A: Light - vision

Q: Which receptorcells do we have for proprioception?
A: For proprioception we hav specialized receptor cells that detect tension in our tendons and changes in muscle length

Q: What are sensory receptors classified based on?
A: They are all calssified based on their function or based on type of stimuli that activates these sensor receptors

Q: Where do we have photoreceptors?
A: In our retina

Q: What  should we not confuse sensory receptorcells with?
A: Here the entire cell is called receptor cell, not to be confused with the protein receptors that are in the plasmamembrane of the cell and binds to NT etc.

Q: How is transduction operated?
A: E.g. mechanoreceptor - encapsulated ending:
1. These nerve endings have ion channels in their membrane which are closed at rest, but whne the membrane is streched or when a pressure is applied the channel opens and allows, in this case, inflow of Na+ ions into the nerve ending and this causes a depolarisation or the membrane - this is called a receptor potential

Q: What is a receptor potential?
A: A small depolarization of the membrane

Q: How is a receptor potential generated?
A: These nerve endings have ion channels in their membrane which are closed at rest, but whne the membrane is streched or when a pressure is applied the channel opens and allows, in this case (encapsulated ending), inflow of Na+ ions into the nerve ending and this causes a depolarisation or the membrane

Q: What are other names for receptor potentials?
A: - Generator potentials
- Graded potentials

Q: What happens with the receptor potential with a weak stimulus?
A: When there is a weak stimulus this receptor potential is too small to reach the threashhold for AP firing

Q: What happens with the receptor potential for stimulus that are too weak and doesn't reach threshold?
A: This small respons will not trigger firing in the nerve ending

Q: What happens with the receptor potential when the stimulus strength and amplitude increases?
A: When the strength of the stimulus increases so does the amplitude of the receptor potential with the strength of the stimulus - when the stimulus is strong enough to depolarize the membrane to threshold an AP is generated in the nerve ending and it will be conducted along the axon to the next neuron

Q: What is the process of transduction for mechanoreceptors called?
A: Mechanotransduction

Q: What is transduction of visual stimuli called?
A: Phototransduction

Q: Which cells/senses only have graded-/receptor potentials?
A: - Hearing
- Vestibular
- Vision
- Taste

Q: Which cells have both graded-/receptor potentials and AP?
A: - Somatosensory system
- Smell

Q: What are the neurons (nerve endings) called for smell?
A: Olfactory receptor neurons

Q: How are ion channels opened in a encapsulated ending (mechanoreceptor)?
A: When the membrane is streched or a pressure is applied the ion channels are open

Q: WHich other classification of receptor cells is there?
A: One especially for the somatosensory system - this classification is based on the firing of AP in receptor neurons, how long a neuron fires AP when stimulus is applied

Q: What are receptors with slow adaptation called?
A: Tonic receptors

Q: What are receptors with rapid adaptation called?
A: Phasic receptor

Q: WHen does the tonic receptor fire?
A: Constant firing during the duration of the stimulus

Q: When does the phasic receptor fire?
A: - Burst at the beginning of the stimulus
- Firing stops if the stimulus remains constant

Q: What is the function of the tonic receptor?
A: Provides information about stimulus that should be continously transmitted to the CNS, spatial feautures (e.g. size, shape), static properties of the stimulus

Q: What is the function of the phasic receptor?
A: Allows to ignore irrelevant information and to infrom about changes in the stimulus (e.g. movement), dynamic properties of the stimulus

Q: What is an ex of a situation where slow adaptation is important?
A: E.g.
when u need ot hold a pen and u dont want to drop it, these cells provide the
information of the static properties of the stimulus

Q: What is an ex of a situation where rapid adaptation is important?
A: These cells will provide information about movement, e.g. when u write with a pen

Q: What is the function of RA cells?
A: Rapidly adapting cells provide information on the temporal properties of the stimulus, and the dynamic properties  of the stimulus

Q: When will RA cells fire?
A: These neurons will informe about when the stimulus starts and sometimes whne it ends but not when it is constant/maintained

Q: What is a receptive field?
A: For touch (skin): It's the area of the skin that when stimulated, induces a change in the activity of the receptor/neuron

Q: What can a receptive field in the skin look like?
A: The surface, with 2 nerve endings - each nerve ending branches in the skin so that it innervates an area of the skin, so there is one axon and several bramches in the skin

Q: How can we define a receptive field?
A: We can define receptive field for a given nerve ending even if we dont see the nerve ending and that skin surface -  we can only see the surface of the skin by applying pressure at different locations on the skin and measuring the firing, the AP firing, of a single nerve ending

Q: HOw can we define the receptive field of a single nerve ending?
A: By appling a stimulus in different locations we can define the lineate of the receptive field for a single nerve ending

Q: WHat can be said about receptive fields next to each other?
A: They overlap

Q: Where else but the skin do we have receptive fields?
A: Neurons located in the spinalcord and brain also have receptive fields, but these receptive fields are more complex than the receptive fields of sensory receptor cells

Q: WHat do we have receptive fields for?
A: - Sensory receptors
- Central neurons

Q: What does the pathway look like for sensory info to reach the cortex?
A: 1. The general idea is that the sensory receptor at the bottom is called the first-order-neuron - enters CNS at the spinal cord
2. 1st order then connects to a 2nd order neuron in the spinal cord or brainstem
3. 2nd order neuron makes a synaps with the 3rd order neuron located in a specific region in the thalamus
4. These 3rd order neurons projects its axons to specific regions in the cortex for somasotsensory function this cortex is the somatosensory coretx or S1

Q: What is the function of 1st order neurons?
A: The sensory receptor at the bottom is called the first-order-neuron, its axon enters the CNS at the spinalcord or the brainstem and synapses onto another neuron which is called the 2nd order neuron

Q: What is the function of 2nd order neurons?
A: These 2nd order neuron then makes a synaps with the 3rd order neuron located in a specific region in the thalamus

Q: What is the function of the 3rd order neuron?
A: These 3rd order neurons projects its axons to specific regions in the cortex for somasotsensory function this coretx is the somatosensory coretx or S1

Q: WHat can be said about the neuronal pathway with the 3 main types of neurons?
A: This is a very simplified pathway but irl so complex coz there are other neuronal circuts that can
modify this transmission along the way up to the cortex, and at each step
of the pathway in addition each of these neurons have receptive fields
that may be modified on the way up to the cortex bc of neuronal circuits

Q: Between what is the 1st order neuron?
A: Receptor - spinal cord or brainstem

Q: Between what is the 2nd order neuron?
A: Spinal cord/brainstem - Thalamus

Q: Between what is the 3rd order neuron?
A: Thalamus - cortex

Q: In which part of the nervous system are the --order neurons?
A: 1st - peripheral
2nd - CNS
3rd - CNS

Q: What is a neuronal circuit?
A: Neuronal circuits are how different neurons are connected with each other and modify their activity and the activity of other neurons

Q: What is an ex. of a neuronal circuit?
A: E.g. convergence, 4 1st order neurons can connect to one 2nd order neuron, so the information of the stimuliu detected by these 4 cells converges onto the same 2nd order neuron, which means that that neuron will take care of the info transmitted by these 4 neurons

Q: Where else can neuronal circuits occur except from between 1st and 2nd order neurons?
A: Can also occur between 2nd order and 3rd order neurons

Q: WHat can be said about receptive fields of higher order neurons in terms of neuronal circuits?
A: The receptive field of higher order neurons can be larger than the receptive field of 1st order neurons, bc they cover receptive fields over several 1st order neurons

Q: What can be said about the receptive field of central neurons?
A: But the receptive field of central neurons are also more complex bc not only do they take care of several cells, they are also influenced by another typ of neuronal circut that affects synaptic transmission and is called lateral inhibition

Q: What is the mechanism of convergence?
A: A mechanism for providing input from many sources to a single neuron

Q: What is lateral inhibition?
A: Inhibition of transmission by neurons with neighbouring receptive fields

Q: What is the purpose of lateral inhibition?
A: Increases acuity (precison)/contrast - sharpens signals

Q: What does acuity mean?
A: Precision

Q: How can lateral inhibition be explained with an ex.?
A: 3 neurons (X1, Y1, Z1), with their own receptive fields that also overlap each others
- If the stimulation is located at Y1 (middle) will fire strongly, but this also stimulates the periphery of the receptive field of the 2 other neighboruing cells (X1 and Z1) - these cells will also be activated and fire action potential but less than Y1
- All 3 1st order neurons will provide information to the 2nd order neurons X2, Y2, Z2, but on the way up at the lever of the connextion between the 1st order and 2nd order neuron there will be and intervention of and inhibitory interneuron, mostly GABAergic interneurons
- Each of these 1st order neurons not only contact a 2nd order neuron but also an inhibitory interneuron, latrelly from axon collaterals - braches from their axons
- These inhibitory interneurons inhibit synaptic transmission between the 1st order and 2nd order neurons in the neighbouring cells - this will lead to a decrease in the firing of these neighbouring 2nd order neurons

Q: How can lateral inhibition be explained briefly?
A: Because Y1 is strongly cativated it will provide a strong lateral inhibition of the neighbouring cells, stronger than the inhibition produced by X1 and Z1

Q: What can be seen in these graph (more specifically the upper one)?
A: In this graph u can see the result of the lateral inhibition - Y1 fires strongly but
the neighbouring neurons fire less coz they have been inhibitoed by the
inhibitory interneuorn

Q: What is lateral inhibition in a nutshell?
A: Lateral inhibition os an inhibition of transmission by neurons with neighbouring receptive fields

Q: What is the use of this lateral inhibition?
A: The mechanism allows to increase acuity (precision) and it allows for an increase in the contrast - it sharpens signals by decreasing the background

Q: What are 2 ex. of situations where lateral inhibition is important?
A: - Tactile acuity
- Visual acuity

Q: Where can lateral inhibition/ these types of neuronal circuits take place?
A: These types of neuronal circuit takes place in higher order neurons in the connecton of 1st and 2nd order neurons e.g. in the spinal cord but also between 2nd and 3rd order neurons in the brain

Q: What are ex. of modality?
A: Somatic sensation, vision, smell etc.

Q: What's the difference between a graded and an action potential?
A: - Graded potentials are the variable-strength signals that can be transmitted over short distances
- Action potentials are large depolarizations that can be transmitted over long distances