Sensory receptors Flashcards
What are the 5 basic types of sensory receptors?
- Mechanoreceptors
- Thermoreceptors
- Nociceptors (pain)
- Electromagnetic receptors
- Chemoreceptors
What are the types of Chemoreceptors?
- Taste: receptors of taste buds
- Smell: receptors of olfactory epithelium
- Arterial oxygen: receptors of aortic and carotid bodies
- Osmolality: neurones in or near supraoptic nuclei
- Blood Co2: receptors on or in the medulla and in aortic bodies
- Blood glucose, amino acids, fatty acids: receptors in hypothalamus
Describe the formation of a receptor potential of a receptor of the Pacinian corpuscle
- Compression changes the membrane and opens the channels allowing more sodium ions to move into the fibre- this is the receptor potential which creates a local current flow within the area
- Greater stimulus= greater amplitude of the receptor potential
What happens in a pacinian corpuscle after the local current has been created
• Local current flow causes depolarisation at the first node of ranvier and this causes the action potential
What happens when there is a low stimulus in comparison to a greater intensity stimulus (touch)
An increased frequency of action potentials
What happens when there is a low stimulus in comparison to a greater intensity stimulus (touch)
An increased frequency of action potentials
How can we tell the modality of sensation
Depends on where the nerve terminates in the CNS
How does phantom limb sensation arrive?
When sensory neurones from absent limbs are spontaneously active and can be mimicked by electrical stimulation
Which receptors are rapidly adapting?
- Hair follicles
- Meissner corpuscle
- Pacinian corpuscle
Which receptors are slow acting?
- Merkel cell-neurite complex
- Ruffini corpuscle
- C-fibre LTM
- Mechano-noiceptor, polymodal noiceptor
What determines the precision of localisation of a particular stimulus?
- Size of the individual nerve fibre receptive field
- Density of sensory units
- Amount of overlap in nearby receptive fields
If there is a greater overlap, how does this influence the precision of localisation
It decreases it
Although it aid stimulus localisation it is thought to muddy the image
What is the role of lateral inhibiton?
• Aids in enabling localisation of the stimulus
How does lateral inhibition work?
• Information from afferent neurones whose receptors are at edge of a stimulus are strongly inhibited compared to information from the stimulus’ centre
What is a mechanoreceptor?
Receptor that detects mechanical compression or stretching of the receptor or the tissues adjacent to the receptor
What are the skin tactile sensibilities (epidermis and dermis)?
- Free nerve endings
- Expanded tip endings (Merkel’s disks)
- Spray endings
- Ruffini’s endings
- Encapsulated endings (meissner’s corpuscles, Krause’s corpuscles)
- Hair-end organs
What are the deep tissue sensibilities?
- Free nerve endings
- Expanded tip endings
- Spray endings (Ruffini’s)
- Encapsulated endings (pacinian)
- Muscle endings
- Muscle spindles
- Golgi tendon receptors
Pacini’s corpuscles
- Largest
- 2mm
- AB fibres
- In the deep layers of the dermis
- High frequency (40-500Hz)
- High sensitivity - low activation threshold
- Glabrous and hairy skin types
- Slick viscous fluid between the layers
Meissner’s corpuscles
- Encapsulated nerve endings
- Stacks of discs interspersed with nerve branch endings
- Found between the dermal papillae
- Detects touch, flutter and low frequencys (2-40Hz)
- AB fibres
- Glabrous (non-hairy) skin types
- Low activation threshold - sensitive
- Work with merkel discs to help determine texture
Merkel discs
- Non-encapsulated nerve endings
- Detect static touch and light pressure
- AB fibres
- All skin types
- Specialised epithelial cell and nerve fibre
- Slowly adapting
- Found just under the skins surface
- Multiple branches are often found in an ‘iggo dome’
- Work with meissners corpuscles to help determine texture
Ruffini corpuscles
- Responds to skin stretch
- Located in the deeper layers of the skin as well as the tendons and the ligaments
- Encapsulated nerve endings
- all skin types
- Abundant in hands, fingers and soles of the feet
- Nerve endings weave between collagen fibres which activate the nerve when pulled longitudinally
Skin hair receptors
- Each type of skin hair receptor has a mechxnosensitive receptor wrapped around its follicle
- Detects muscular movements of the hair (erector muscle)
- Detects the external displacement of the hair
How do we hear?
Sound receptors of the cochlea
How do we sense equilibrium?
Vestibular receptors
How do we sense arterial pressure?
Baroreceptors of carotid sinuses and aorta
Thermoreceptors
Detect changes in temperature, some detect cold, some detect warmth
Nociceptors
Detects physical or chemical damage occurring in the tissues; free nerve endings
Electromagnetic receptors
Detect light on the retina of the eye; vision via rods and cones
Chemoreceptor
Detects taste, smell, oxygen in arterial blood, osmolality of the body fluids, carbon dioxide concentration and other factors
What is a receptor potential?
The change in the membrane electrical potential when the receptor is stimulated
How can a receptor potential be created?
- Mechanical deformation- stretches the receptor membrane and opens ion channels
- Application of a chemical to the membrane which opens ion channels
- Change in membrane temperature which changes the membrane permeability
- Effects of electromagnetic radiation e.g. light on a visual receptor which changes the receptor membrane characteristics, allowing ions to flow through the membrane channels
How do signals from sensory nerve endings get to the CNS?
- Frequency is directly related to its amplitude at any moment
- non damaging stimulus: coded by the frequency of action potentials in the sensory nerve
What is labelled line principle?
Nerves terminate at a specific point in the CNS and there type of sensation felt is determined by the point in the nervous system to which the fibre leads
how is information delivered to the CNS?
In a topographic fashion
What causes 2 point discrimination?
- Receptive field size
* Receptor density in the area
The smaller the receptive field…
… The better the liner discrimination between stimuli is
What is needed for high linear discrimination?
More sensory fibres/neurones to cover the area with small receptive fields
Why do we not have high linear discrimination all over the body?
- Not needed in certain areas e.g. the torso
* Would cause an issue with space in the spinal cord
How is some space saved in places that have a high linear discrimination?
• Multiple same modality sensory neurones with overlapping fields all project to a single ascending neurone
