Sensory receptors Flashcards
What is the role of sensory receptors?
Sensory receptors change sensory stimuli (touch, temperature, etc) into nerve signals that ate conveyed and processes in the CNS
This can be about the External or Internal environment
What are mechanoreceptors?
Mechanoreceptors detect mechanical compression or stretching of the receptor or of tissues adjacent to the receptor
What are the 2 types of Mechanoreceptors and their features?
Skin tactile sensibilities (epidermis and dermis)
- Free nerve endings (touch)
- Expanded tip endings (Merkels dics)
- Spray endings (Ruffini’s endings)
- Encapsulated endings (Meissners corpuscles + pacinian corpuscle)
- Hair end organs Deep tissue sensibilities
- Muscle spindles
- Golgi tendon receptors
Name all of these different types of Mechanoreceptors found in the skin or deep tissues of the body?
Below
What do free nerve endings sense?
Pain (mechanically-induced)
What are the features of Meissners corpuscle?
Encapsulated nerve endings similar to Pacini’s but much smaller;
Detects touch, flutter and low frequency vibration(2-40 Hz)
Aβ fibres- glabrous (non-hairy) skin types
Has low activation threshold so is sensitive
Rapidly adapting mechanoreceptor, touch and pressure
What are the features of Merkel disks?
Non-encapsulated nerve endings;
Aβ fibres- all skin types
Consists of a specialised epithelial cell + nerve fibre
Found just under the skin surface (e.g finger tips - good discrimination) - detect static touch and light pressure;
Slowly adapting mechanoreceptor, touch and pressure (low activation threshold- sensitive)
Multiple branches often found in an ‘Iggo Dome’
They work with Meissners corpuscles to help determine texture
What are the features of Free neuron ending ?
Slowly adapting, some are nociceptors, some are thermoreceptors, and some are mechanoreceptors
What are the features of Pacinian/pacini’s corpuscle?
Onion like encapsulation nerve endings
Largest mechanoreceptor- 2mm long
Found in deep layers of dermis and detects high frequency vibration (40-500 Hz)
Rapidly adapting mechanoreceptor due to a slick viscous fluid between the layers
Aβ fibres- Glabrous and hairy skin types
Has a low activation threshold (i.e is sensitive) - Doesn’t need much stimulus
What are the features of Ruffini corpuscle?
Responds to skin stretch and is located in the deeper layers of the skin as well as tendons and ligaments
Encapsulated nerve endings in all skin types but especially abundant in hands and fingers as well as soles of feet
What kind of sensory receptors are found in the Glabrous and hairy skin (making them cutaneous receptors)?
The cutaneous receptors are;
- Merkels cells (touch)
- Free nerve endings (pain, temperature)
- Meissners corpuscles (vibration)
- Ruffini’s corpuscles (lateral stretch)
- Pacinian corpuscles (rapid vibration)
What 2 sensory receptors work together to help determine texture?
Merkel disks and Meissners corpuscles
What do skin hair cell receptors do?
Skin hair cell receptors; - There are a number of types of skin hair cell, and each has a mechxnosensitive receptor wrapped around its follicle - These detect both the muscular movements of hair (erector muscle) and the external displacements of the hair
What receptors are involved in the second group of mechanoreceptors and what are their functions?
Hearing - Sound receptors of cochlea
Equilibrium - Vestibular receptors for balance and equilibrium
Arterial pressure - Baroreceptors of carotid sinuses and aorta
What is the role of thermoreceptors?
Thermoreceptors detect changes in temperature, with some receptors detecting cold and other warmth (has them internally and externally)
What is the role of Nociceptors ?
Nociceptors are pain receptors which detect physical or chemical damage occurring in the tissues; Free nerve endings
What its the role of Electromagnetic receptors?
Electromagnetic receptors detect light on the retina of the eye; Vision via rods and cones
What is the role of Chemoreceptors ?
Chemoreceptors detect taste in the mouth, smell in the nose, oxygen level in the arterial blood, osmolality of the body fluids, carbon dioxide concentration, and other factors that. make up the chemistry of the body.
What is the function of chemoreceptors and where are they found ?
• Taste — Receptors of taste buds • Smell — Receptors of olfactory epithelium • Arterial oxygen — Receptors of aortic and carotid bodies • Osmolality — Neurons in or near supraoptic nuclei • Blood CO2 — Receptors in or on surface of medulla and in aortic and carotid bodies • Blood glucose, amino acids, fatty acids — Receptors in hypothalamus
What are the 2 types of Receptors from sensory I impulses ?
- Can go straight from stimulus energy to receptor membrane into CNS via afferent neuron - Can go from stimulus energy via a receptor cell which releases vesicles containing neurotransmitters to fuse with the synapse of an afferent neuron to the CNS
What is the immediate effect once a sensory receptor has been simulated ?
The immediate effect is to change the membrane electrical potential
What is the change in electrical potential in a sensory stimuli called?
The Receptor Potential
What are the 4 ways to create a receptor potential ?
A receptor potential can be created by: — Mechanical deformation which stretches the receptor membrane and also opens ion channels. — Application of a chemical to the membrane which opens ion channels. — Change in membrane temperature which changes the permeability of the membrane. — Effects of electromagnetic radiation eg light on visual receptor which changes receptor membrane characteristics allowing ions to flow through membrane channels.
No matter what the stimuli is that is caused what will always be created?
A receptor potential
What happens when the receptor potential rises above threshold?
When the receptor potential rises above the threshold for eliciting action potentials in the nerve fiber attached to the receptor, then action potentials occur.
What is a receptor potential ?
A receptor potential is a membrane potential in a receptor (like a photoreceptor or a mechanized-receptor), though the term usually refers to the potential in a receptor generated when the receptor receives the type of stimulation is is designed to detect (e.g., light or touch).
What happens the more the receptor potential rises above the threshold level?
The more the receptor potential rises above the threshold level, the greater the action potential frequency becomes.
What happens to the receptor potential of the Pacinian Corpuscle?
Compression anywhere on the outside of the corpuscle will elongate, indent or deform the central fibre. The fibre will then become more positively charged than it was previously and activate a receptor potential which consequently activates an action potential
Why does the amplitude of receptor potential change on the Pacinian Corpuscle ?
The amplitude of receptor potential changes because there is a progressively stronger mechanical compression being applied to the central core of the Pacinian Corpuscle
If you increase pressure on the Pacinian corpuscle what changes?
The receptor potential increases
What can happen if sensory nerve endings are stimulated?
They produce action potentials that spread to the CNS
What is the frequency of a sensory action potential directly related to?
Its amplitude at any moment
What is the intensity of the stimulus in non-damaging sensory stimului coded by?
For a non-damaging sensory stimulus, the intensity of the stimulus is coded by the frequency of action potentials in the sensory nerve.
How do we work out the modality of sensation (pain, touch, sight, sound) from nerve impulses?
Nerves terminate at specific points in the CNS and the type of sensation felt is determined by the point in the nervous system to which the fibre leads. This is known as THE LABELLED LINE PRINCIPLE
How is modal information delivered to the CNS?
In a topographic fashion (i.e palm from leg is delivered to a particular part of the CNS which is different to, but near, stretch or vibration signals from the leg (E.g - different parts of cortex)
How does Phantom limb sensation arise?
Phantom limb sensation arises when sensory neurones from absent limbs are spontaneously active, and can be mimicked by electrical stimulation
How do some sensory receptors adapt?
Some sensory receptor types adapt rapidly to constant stimuli so their generator potentials do too. (Receptor rapidly adapts are reduces stimulus) - E.g Joint capsule and Muscle spindle receptors Some sensory receptors adapt to generator potentials slowly as well - E.g Pacinian corpuscle and hair receptors
What is the precision of localisation of a particular stimulus determined by?
- The size of the individual nerve fibre receptive field
- The density of sensory units
- The amount of overlap and nearby receptive fields
What is 2 point discrimination?
Working out what thing is touching you
What. does receptor field overlap aid?
Receptor field overlap aids to stimulus localisation
What does the higher the resolution, and the higher the number of modalities for a given situation give?
The better the understanding of information
What 1 things do Meissners corpuscle and Pacini’s corpuscle have in common and 1 thing they differ in?
They are both sensitive but have different receptive field sizes which reflect their differing roles in cutaneous sensation
What do variations in the results of the 2 point discrimination test show?
- They are seen across different regions of the body - Are a result of the receptive field size and receptor density in the area - This does not represent sensitivity to stimulus E.g - Very poor 2 point descrimination in the calf but very good in lips and fingers
What is the role of lateral inhibition?
Lateral inhibition aids in enabling localisation of stimulus Information from afferent neurones whose receptors are at edge of a stimulus are strongly inhibited compared to information from the stimulus’ centre
Draw a diagram showing lateral inhibition?
Below
What does a smaller receptive field result in?
A better linear discrimination between stimuli
Why don’t all areas of the body have high linear discrimination?
High linear discrimination needs more sensory fibres/neurons to cover the area with small receptive fields There is no requirement for the torso to have that level of discrimination, and the extra neurones wouldn’t have enough space to fit in the spinal cord!
What is the pathway that most conscious sensory tracts follow?
1). Primary afferent is a first order neuron and terminates in the spinal cord or brain stem 2). The second order neuron projects to the hypothalamus 3). The third order neuron projects into the brain
Where does all of the sensory information go in the brain?
The sensory information passes through the thalamus and on to the primary sensory cortex which is located in a strip posterior to the post central sulcus of the brain Sensory information is projected in a topographical manor to this area, with areas of higher discrimination having a larger proportion of this space
