The Senses Flashcards
What is a sensory system?
A sensory system is a part of the nervous system responsible for processing sensory information.
What does a sensory system consist of?
Sensory receptors detect the signal that is around us.
Neural pathways transfer the signal from the sensory receptor up to the brain.
Brain areas that are activated by the sensory modality.
What is a sensation?
The process through which the senses pick up visual, auditory, and other sensory stimuli and transmit them to the brain; sensory information that has registered in the brain but has not been interpreted.
What is perception?
The process by which sensory information is actively organized and interpreted by the brain.
What are three common characteristics of all sensory processes?
- Apparence of adequate physical stimulus (respond to a certain type of stimulus and not others, each sensory system can only respond to a certain type of stimuli).
- Processes that convert information contained in physical stimulus into information encoded by neural signals (sensory processing needs to convert physical energy into AP’s).
- Apparence of specific body response to the message as conscious sense (perception) – conscious awareness of the stimuli in the environment.
What is transduction?
Process where the receptors change or convert the sensory stimulation into neural impulses.
Describe the steps of sensory processing.
- Sensory receptors collect the signal (note: each receptor is sensitive to special forms of physical energy, i.e., mechanical, thermal, chemical)
- Receptor is translating the energy of stimuli in electrochemical energy of receptor and action potentials –> transduction
- Signal transmitted to the brain
- Brain processing
What is a receptor potential?
Step between the arrival of energy at receptor cell and the initiation of an action potential.
It is usually an EPSP
If there is a stimulus with an energy that is strong enough, it will activate the receptor.
What is the role of a sensory receptor in sensory processing?
The structure of the receptor determines the form of energy to which it will respond. (what allows us to perceive the external environment) – the structure that allowed us to detect physical energy and then communicate the physical energy into our brain, think of it as a gate that allows us to see the external environment.
How many senses are there?
- Vision
- Hearing
- Somatosensory (pressure, pain, temperature)
- Vestibular sense (balance)
- Proprioception (body movement)
- Smell (olfaction)
- Taste (gustation)
Explain the steps of visual processing?
The eye is the first step of visual processing, light goes into the eye and is reflected in the retina.
There are multiple layers in the retina which are the first step of our vision processing. If we zoom into the retina, we can see three different layers. In the final layer we can identify the visual receptor which are called cones and rods.
The visual receptor in the retina that are called rods allow us to process day and night vision and cones which allow us to process colour vision.
There is one type of rod for dark and bright light, and three different types of cones for colours.
What is the role of the visual receptors?
The eye captures light and focuses it on the visual receptors, which convert light energy to neural impulses sent to the brain.
Where are visual receptors located?
Visual receptors are in the retina.
• Four types of photoreceptors: 3 cones, 1 rod
• Rods –> for night vision
• Cones –> for colour vision
What is the structure of the retina?
Photoreceptor layer
Intermediate layer
Ganglion cells layer
(Light coming up from here)
What do rods and cones respond to?
• Rods and cones respond to light intensity
How do the photoreceptors work in darkness and light?
• In darkness, rods & cones constantly release a flow neurotransmitter (glutamate)
(Paradoxically they are activated and release neurotransmitter when there is darkness)
• When light is present it is absorbed by a pigment in rods and cones
• Causes change in shape of photopigment that triggers a G- protein cascade that reduces glutamate release
(This activates a G- protein, which is related to the transmission of a signal, this reduces the amount of neurotransmitter that is normally released)
• So, paradoxically, photoreceptors are inhibited (deactivated) by light!
To summarise there is a lot of the neurotransmitter in the dark but as soon as light reaches the eye, the production of the neurotransmitters is reduced. This allows us to perceive different intensities of light.
What cells does the intermediate layer of the retina contain and what is their role?
Contains bipolar, horizontal, and amacrine cells
Bipolar cells transfer information from rods & cones to retinal ganglion cells
Transforms light (brightness) information into contrast information
Explain the route of the vision pathway?
The light reaches the retina, then the signal crosses at the level of the optic chiasm and then it reaches the lateral geniculate nucleus of the thalamus and then the primary occipital cortex.
Information from the right eye goes into the left hemisphere and the information from the left eye goes into the right hemisphere.
They are crossing and transferring information to the opposite hemisphere.
What we see in the right eye is processed by the left occipital lobe and what we see in the left eye is processed by the right occipital lobe.
Before reaching the visual cortex, the signal reaches the lateral geniculate nucleus of the thalamus.
Briefly explain the vision pathway.
- Eye
- Retina
- Thalamus
- Lateral Geniculate Nucleus (LGN)
- Primary Visual Cortex (striate cortex, V1)
- Secondary Visual Cortex
Where is the thalamus located?
• In the Diencephalon, near the third ventricle.
What is the role of the thalamus in visual processing?
Sensory relay
• The thalamus relays sensory impulses from receptors in various parts of the body to the cerebral cortex.
• A sensory impulse travel from the receptors towards the thalamus.
• This signal is then passed onto the cerebral cortex for further processing.
• Recently been shown to process sensory information which is key to providing a perception of the environment. All sensory signals apart from smell and taste stop in the thalamus and then they go into the cortex
Summarise the vision pathway?
The eye contains the visual receptors which detects the signal and what type of signal it is (light or colour).
After the retina is the optic nerve, which is transferring information to the visual cortex, which is the final station, before the visual cortex is the chiasm where the nerves cross and then the thalamus which is our sensory relay. There are two visual cortexes’: V1 – the primary visual cortex which detects the key features of the signal and the secondary visual cortex which provides perception.
What is the role of the lateral geniculate nucleus (LGN)?
- The lateral geniculate nucleus (LGN) is part of the thalamus and serves as the primary centre for processing visual information.
- Relay station between eye and brain.
- Response properties similar to retinal ganglion cells
- But receives massive feedback from cortex – 10x as many connections as from the eye!
What happens in the visual primary visual cortex?
- Information from the eye goes directly into this area.
- The primary visual cortex detects the signal and can start recognising how a line is oriented, different types of colour and whether there is a type of frequency in the visual information.
- It has a topographic organisation which is called a retinotopic map. This means your eye takes a picture of the external environment and then in the primary visual cortex, there is a retinotopic map of that picture and all the elements are already organised.
- This allows us to interact easily with the environment and know where things are.
Where is the primary visual cortex located?
This is at the bottom of the brain in the occipital lobe and almost adjacent to the cerebellum.
What is the organisation of the primary visual cortex?
Topographic (retinotopic) organisation à contains a “map” of the visual field.
Detailed maps of orientation, colour, spatial scale, motion direction, 3D depth.
What does the primary cortex (V1) compute?
For each part of the visual scene, V1 computes: orientation, spatial frequency, motion, colour, depth
What happens in the extrastriate cortex?
- After the primary visual cortex, there is further processing in the extrastriate cortex. (which is the secondary area in the brain for processing visual information).
- Secondary cortical areas communicate to and from striatal cortex (V1)
- Here the brain can build up a representation of the stimulus in terms of object recognition, location and motion, so it’s a much higher level of processing.
What is the most common type of receptors?
Somatosensory receptors are the most common receptors in the body because they are all around our skin.
What type of tactile receptors are there in somatosensory processing and what do they respond to?
Different type of tactile sensations: many different types of tactile receptors (mechanoreceptors)
Mechanical receptors respond to pressure on our skin and face. (Similar to how visual receptors respond to light.)
What two things define a mechanical receptor?
The receptive field and the stimulus response.
What is the receptive field?
The receptive field (RF) of an individual sensory neuron is the particular region of the sensory space in which a stimulus will modify the firing of that neuron
