✅Sensory Receptors Flashcards
What are sensory receptors?
Specialized cells or cell processes that provide the CNS with information (stimuli) about conditions inside or outside the body.
What does Activation of a sensory receptor by an adequate stimulus result in?
depolarization or graded potentials that trigger nerve impulses along the afferent fibres coursing to the CNS
What is sensation?
The arriving information
What is perception?
The conscious awareness of a sensation
What are the two classes of sensory receptors?
Special senses
General sensor receptors
Describe special senses
provided by receptors that are localised and more complex in structure. This information is distributed to specific areas of the cerebral cortex and to centres throughout the brain stem
What are the four special senses?
Hearing and balance- ear- cochlea & labyrinth
Smell - nose - olfactory receptors
Taste - tongue - gustatory receptors
Vision- eye - photoreceptors
Describe general sensor receptors
widely distributed, simple in structure. Some of the information they send to the CNS reaches the primary sensory cortex and our conscious awareness.
What are the four general sensor receptors?
- Nociceptors (pain)
- Thermoreceptors (temperature)
- Mechanoreceptors (physical distortion)
- Chemoreceptors (chemical concentration)
What are the 3 functional categories of the general senses?
Exteroceptors
Proprioceptors
Interoceptors
What do exteroceptors provide?
provideinformationaboutexternal environment (touch, pressure, vibration, pain, temperature, special sense receptors)
What do proprioceptors provide?
provide information about body position and movement by monitoring the degree of stretch
What do interoceptors provide?
provide information about internal systems (sensitive to chemical changes, tissue stretch and temperature changes)
What do guard and down hair follicles contain?
Guard hair (G-hair) and down hair (D-hair) follicles contain nerve endings that form a circumferential array of unmyelinated nerve terminals derived from myelinated axons.
Describe g-hair and d-hair
These receptors are rapidly adapting (RA), low threshold (LT) afferents and detect light touch
Describe pacinian corpuscles
have the typical structure of an encapsulated receptor. They are RA LTMs that allow perception of distant events through transmitted vibrations
Describe merkel cell-neuritis complexes
lie at the base of the epidermis and are formed of clusters of 50–70 cells connected to terminals of a myelinated Aβ axon. They function as slowly adapting (SA) LTMs and are responsible for form and texture perceptions
Describe ruffini corpuscles
lie in the dermis, with the distinct outer capsule surrounding a fluid- filled capsule space. They are SA cutaneous mechanoreceptors and contribute to the perception of object motion
What are C-fibre LTM?
Free nerve endings and unmyelinated receptors terminate in the subepidermal corium
Describe C-fibre LTMs
respond to innocuous tactile stimulation and signal pleasant stimulation in affiliative social body contact in humans. The perception of painful touch is initiated by high-threshold (HT) C-fibre and Aδ nerve endings (g), which can be mechanosensitive or polymodal in nature
What are the three types of cutaneous afferents?
Type Aβ
Type Aδ
Type C
What is Type Aβ?
Various rapidly and slowly adapting mechanoreceptors
What is Type Aδ?
Pain,temp, certain hair receptors
What is type C?
Unmyelinated (pain)
What can muscle spindles be thought as?
Length detectors
What are the two groups of muscle spindles?
Group IA: Velocity + direction Group II: Sustained, static position
What can golgi tendons be thought of?
Force detectors
What is Group Ib (golgi)
Branched in collagen fibres to form tendons
What are the two somatic efferents?
Alpha motoneurons
Gamma motoneurons
What are alpha motoneurons?
Large diameter Type A large anterior horn cells/motoneurones innervate skeletal muscle
What are gamma motoneurons?
Small diameter Type A axons innervating intrafusal muscle fibres. Peripheral Nerves are classified according to conduction velocity/fibre diameter
Diameter of afferent fibres innervating muscle have a different distribution from what?
Those innervating the skin
How are the muscle afferents classified?
Group I (Aα) large myelinated (proprioceptors) Group II (Aβ) small myelinated (proprioceptors) Group III (Aδ) smallest myelinated (proprioceptors/pain) Group IV (C) unmyelinated (pain)
What to the receptive fields of three primary sensory neurons do?
Overlap
What does the second sensory neuron have?
A large receptive field
What do the primary sensor neurons do?
Converge on one secondary sensory neuron
What is the somatic sensory pathway for the right side of the body?
Receptors for discriminative touch, stereognosis, proprioception, weight discrimination and vibration
First order neuron
Nucleus gracilis
Medial lemniscus
Thalamus
What is the somatic sensory pathway for the left side of the body?
Spinal nerve
Posterior column: fasciculus cuneatus, fasciculus gracilis
Nucleus cuneatus
Second order neuron
Third order neuron
Primary somatosensory area of cerebral cortex
What are the steps of the sensory pathway?
1- pain, temperature and coarse touch cross the midline in the spinal cord
2- fine touch, vibration and propriocption pathways cross the midline in the medulla
- Sensory pathways synapse in the thalamus
- Sensations are perceived in the primary somatic sensory cortex
What does the CNS receive input from?
A large number of sensory receptors
What do somatic motor neurons contract?
Voluntary skeletal muscles
What do autonomic motor neurons (sympathetic) relax?
Involuntary muscles around many internal organs ; accelerates heart
What do autonomic motor neurons (parasympathetic) contract?
Involuntary muscles around many internal organs; slows heart
What do somatic sensory neurons control?
Skin and pain sensors
What do visceral sensory neurons control?
Receptors in internal organs
Where do all sensory and motor neurons go? (PNS)
Spinal cord
Where do all special senses (CNS) go?
Brain
What is the language of the CNS?
electric signals, each of the various types of receptor cells must convert, or transduce, its sensory input into an electric signal.
Structures with sensory receptors provide selectivity to what?
electric signals, each of the various types of receptor cells must convert, or transduce, its sensory input into an electric signal.
What is the pathway of the electric signals? (Radio)
External signal Receptor Transducer Amplifier Response
What is the pathway From stimulus to frequency modulated AP output?
Stimulus Structural change in membrane Conductance change Receptor change Receptor current Receptor potential Modulated impulse frequency in receptor cell axon/ modulated transmitter release from receptor cell Modulated impulse frequency in 2nd order neuron
An adequate stimulus will open channels where?
at the receptor, resulting in an inward flux of Na+ (in most cases) and depolarisation (a receptor potential).
A receptor potential is a type of what?
graded potential: The strongest the stimulus, the greater the graded potential. They have no refractory period so sustained contraction is possible
What is the pathway of an adequate stimulus?
1- reception n
2- transduction
3- transmission
4- perception
Sensory neurones transform what?
A physical stimulus into electrical activity
What are the steps of sensory neurone transformation?
1- receptor potential
2- trigger action
3- action potential
4- output
What is The different responses of different receptors to a similar stimuli is called?
Adaption
Describe tonic receptors
o Always active
o Show little peripheral adaptation
o Slow-adapting receptors
o Remind you of an injury long after the initial damage
has occurred.
o Examples: pain receptors, joint capsules and muscle
spindles.
In tonic receptors, what happens when the stimulus increases or decreases?
The rate of action potential generation changes accordingly
What do tonic receptors generate?
Action potentials at a frequency that reflects the background level of stimulation.
Describe Phasic receptors
o Normally inactive
o Become active for a short time whenever a change occurs
o Provide information about the intensity and rate of change of a stimulus
o Fast-adapting receptors.
o Example: Pacinian corpuscle.
When do phasic receptors become active for a short period of time?
In response to a change in the conditions they are monitoring
How do tonic receptors respond to a stimulus?
For the duration of a stimulus
How do phasic receptors respond to stimuli?
They rapidly adapt to a constant stimulus and turn off. They fire once more when the stimulus is turned off
What do local anaesthetic block and how?
Action potential propagation by acting on NA+ channels
In what order does conduction block occur?
- Small myelinated axons (pain)
2. Non-myelinated axons
3.Large myelinated axons (motor and sensory
What is the order of block?
Pain>Temp>Touch>Proprioception & Motor
What effects are in reverse order?
Pressure block
Electrical stimulation
largest diameter axons blocked by pressure first
largest diameter axons activated at lower currents than smaller axons
