Peripheral Receptors Flashcards
What do peripheral nerves contain?
Axons, supporting Schwann cells, connective tissue and blood vessels
What is the range of diameter of axons?
0.2-20um
What axons are myelinated?
Axons above 1-1.5um
What produces a myelin sheath?
Schwann cells
The minimum strength that a receptor can detect is called?
The sensory threshold
What is conveyed to the CNS in the frequency of action potentials?
Intensity
The minimum distance between two stimuli that can be detected as separate is defined as?
Two-point discrimination
If a stimulus is continuous for a period of time, the neural response becomes diminished. What is this termed?
Receptor adaptation
What do tactile receptors associated with the skin perceive?
Touch, pressure and vibration
What are the receptors associated with the skin?
Hair follicle receptors, Meissner’s corpuscles, Pacinian corpuscles, Ruffini’s endings, Merkel’s nerve endings and Free nerve endings.
What receptors are termed encapsulated endings?
Meissner’s corpuscles, Pacinian corpuscles and Ruffini’s endings
What are the encapsulated endings surrounded by?
Connective tissue capsule
How are hair follicle receptors formed?
From axons that surround or run parallel to hair follicles
What do hair follicle receptors respond to?
The bending of the hair shaft and serve as receptors for light touch
What are hair follicle receptors also called?
Peritrichial endings
Where are Meissner’s corpuscles found?
Concentrated in glabrous skin in the dermal papillae
Are the axons myelinated or unmyelinated in Meissner’s corpuscles?
Unmyelinated
What surrounds the Meissner’s corpuscles?
Surrounded by a connective tissue sheath
What are Meissner’s corpuscles sensitive to?
Touch and vibration
Are Pacinian corpuscles large or small?
Large (more than 1000um)
Where are Pacinian corpuscles found?
Deep in the dermis or in the hypodermis
What are Pacinian corpuscles made of?
Concentric layers of flat cells with fluid and connective tissue between the layers
Is the innervating fiber in the Pacinian corpuscle myelinated or unmyelinated?
Myelinated
What do Pacinian corpuscles respond to?
Pressure and vibration
Are Ruffini’s endings small or large?
Small (1-2um)
Where are Ruffini’s endings found?
Dermis
What do the Ruffini’s endings consist of?
A capsule that surrounds fluid and collagen fibrils which are continuous with the surrounding collagen of the dermis
Does a myelinated or unmyelinated axon enter the capsule of the Ruffini’s ending?
Myelinated
What do Ruffini’s endings respond to?
Stretch of the collagen fibres
Where are Merkel’s disks found?
Lips, fingers, toes and genitalia
What do Merkel’s disks consist of?
Specialised large epithelial cell in the basal layer of the epidermis which is in contact with a disk-like ending of an axon
What are Merkel’s disks sensitive to?
Pressure
Where are free nerve endings found?
Skin, ligaments, meninges and organ capsules
If the nerve endings are myelinated what does that mean for the diameter?
Small
What do free nerve endings respond to?
Light touch, heat/cold and act as pain receptors
What fibres are present in muscle spindles?
Intrafusal fibres
What are normal contractile muscle fibres called?
Extrafusal fibres
What are the two types of intrafusal fibers?
Nuclear chain fibres and nuclear bag fibres
Describe the nuclei in nuclear chain fibres?
In a line
Describe the nuclei in nuclear bag fibres?
Swelling in the middle where the nuclei congregate
Are intafusal fibres contractile?
Yes
What are intrafusal fibres innervated by?
Smaller motor neurons
What are the two types of sensory axons within the muscle spindle?
Annulospiral endings and flower spray endings
What do the sensory axons respond to?
Stretch
What do the sensory axons influence?
The alpha motor neurons of the muscle in a reflex
Muscles that exhibit fine control have a higher?
Density of muscle spindles
Where are golgi tendon organs found?
In tendons near the myotendonous junction
What are skeletal muscle fibres innervated by?
Motor neurons
Where are the cell bodies found in motor neurons?
In the brainstem or in the ventral horn of the spinal cord
What are the three cells involved in the neuromuscular junction?
Motor neuron, muscle fibers and schwann cell
What vesicles are present in the motor neuron?
Synaptic vesicles
The specialised region of the muscle finer that receives the nerve terminal is called?
Sole plate
What does the sole plate form?
Postsynaptic element of the synapse
Each nerve terminal sits in a depression in the muscle fibre surface called?
A primary synaptic cleft
What are the main glial cells in the peripheral nervous system?
Schwann cells
What is the name given to the schwann cell essentially covers over the cell processes forming the synapse?
Perisynaptic
What happens at the neuromuscular junction?
Motor axons terminate at a motor end-plate and action potentials arriving in the axon cause release of ACH and initiate an action potential in the sarcolemma
