Exam #1: Neurohistology Flashcards
What are sensory receptors the beginning of?
- Sensory pathways to the brain
- Spinal cord reflex arc
Where are sensory neurons located?
DRG
Ganglia of cranial nerves
What part of the sensory neuron contains the peripheral sensory receptors?
Dendrites of sensory neurons i.e. the peripheral end of the sensory neuron
What are the two types of sensory neurons that have sensory receptors?
Bipolar neurons
Pseudounipolar neurons
What are bipolar neurons associated with?
Special senses:
1) Smell
2) Vision
3) Balance
4) Hearing
What is the difference between olfactory & retinal/ vestibular/ cochlear receptors?
Olfactory receptors ARE the bipolar neurons
- In the other two, bipolar neurons SYNAPSE with sensory receptors (rods/cones & hair cells)
Where are pseudounipolar neurons located?
Not special senses
Describe the two different structural phenotypes of the pseudounipolar terminal.
- Naked
- Encapsulated
What are multipolar neurons? Do multipolar neruons have sensory receptors?
No
What is a sensory receptor?
Specialized terminal at the distal end of a sensory nerve
*Note that sensory receptors generally carry more than one modality
What are the four modalities only carried by the cranial nerves?
1) Olfaction
2) Vision
3) Gustation (taste)
4) Audition
What are the four modalities carried by cranial & spinal nerve?
1) Tactile sensation
2) Nociception
3) Temperature
4) Proprioception
What are the three general classifications of tactile sensation?
1) Touch
2) Pressure
3) Vibration
What are the two different types of touch?
- Light touch
- Discriminative i.e. fine/ detailed touch
What happens at the receptor when a stimulus is applied?
Conversion of the stimulus to an electrical signal
What happens at the nerve terminal in response to an electrical signal from a receptor?
Generation of an action potential
What is the receptive field of a receptor?
Region that a receptor is able to convert stimulus into a receptor potential i.e. region from which stimulation results is signal transduction
Where are there large numbers of sensory receptors? Where are there relatively few sensory receptors?
- Skin of face & hand have a large number of receptors
- Skin of other body parts has few receptors
How do receptors with a wide receptive field compare to receptors with a narrow receptive field?
Precision of perception
- Wide= less precise
- Narrow= more precise
What are exteroreceptors? What are the two categories of exteroreceptors?
Receptors located close to the surface of the body:
1) Teloreceptors
2) Contact receptors
What is a teloreceptor?
Exoreceptors that can be activated at a distance e.g.
- Light–rods/cones
- Sound–auditory hair cells
What are contact receptors?
Exoreceptors that require contact
- Touch
- Pressure
- Pain
- Temp
- Chemicals
What are examples of contact receptors?
- Olfactory
- Taste
- Tactile
Where are proprioceptors located?
- Vestibular apparatus i.e. the inner ear
- Skin
- Muscles
- Tendons
- Joint capsules
What are the two types of proprioception?
1) Static= stationary
2) Kinetic= moving
What are interoreceptors?
Receptors found deep in the body or brain
What are the two categories of interoreceptors? List examples.
Chemoreceptors
- Hypothalamus
- Carotid body
Baroreceptors
- Carotid sinus in urinary bladder
What are the three classifications of receptors according to modality
1) Nociceptors- Aδ or C fibers
2) Thermoreceptor- Aδ or C fibers
3) Machanoreceptors- Aβ
Thus, mechanoreceptors are associated with faster conduction velocities/ fiber types
What are the different types of nociceptors? What fiber types are these receptors associated with?
1) Mechanosensitive= injury- Aδ
2) Temperature= heat or cold- Aδ
3) Polymodal= respond to various noxious stimuli- C
4) Pruriceptors= itching that respons to histamine, associated with C fibers
What are the non-encapsulated mechanoreceptors?
- Free nerve endings
- Peritrichial nerve ending= around hair follicle
- Merkel Disc= dialated & naked pseudounipolar dendrite
*****Associated with Aβ fibers
What are the encapsulsed mechanoreceptors?
Meissner corpuscle= dermal papillae–light touch
Pacinian corpuscle= in skin–vibration & pressure
Ruffini end organ= joint–proprioception
Muscle spindle
Golgi tendon
What is a muscle spindle?
Specialized mechanoreceptor (proprioceptor) unique to skeletal muscle that monitors muscle length
What is an extrafusal fiber?
- This is a typical skeletal muscle fiber that forms the gross muscle
- Innervated by alpha motor neurons to produce contraction
What are nuclear bag and nuclear chain fibers?
These are the two different intrafusal or muscle spindle fiber types i.e. the inner components of the muscle spindle
- Differences are based on morphology
- Have contractile & non-contractile properties
What is the function of nuclear chain fibers?
Detect static changes in muscle length
What is the function of nuclear bag fibers?
Detect static & dynamic changes in muscle length
- Static= detects changes in muscle length
- Dynamic= detect the rate of change
What is an annulospiral ending?
Intrafusal fibers receive two types of sensory innervation, one of which is in the form of annulospiral endings
- Annulopsiral respond to the onset of muscle stretch
- Type Ia
What is a flower spray ending?
This is the second type of sensory innervation to intrafusal fibers
- Flower spray fibers are activated when muscle stretch is in progress
- Type II
What is the golgi tendon organ?
This is a specialized mechanoreceptor located where the muscle inserts into its tendon; the function of the GTO is to monitor the amount of tension applied to a tendon
What happens in response to a central CNS lesion? Why?
No regeneration b/c:
1) Schwann cell are needed to tell axons don’t know where to go–NOT present in CNS
2) Oligodendrocytes INHIBIT axon growth
3) Astrocytes don’t make enough growth factor & form scar tissue
*****No regeneration & permanent neurologic deficits
What is a receptor potential?
Electrical signal produced in response to stimulation of a sensory nerve
What is sensory transduction? How does this differ from a receptor potential?
Sensory transduction is the actual conversion of a stimulus into an electrical signal (vs. the receptor potential, which is the electrical signal)
What is an Aα fiber?
- Myelinated fibers
- Fastest
What is the difference between Type Ia & Ib Aα fibers?
Both are myelinated
- Ia= form annulospiral endings innervating muscle spindles
- Ib= innervate golgi tendon organs (GTO)
What are Aβ or Type II fibers?
Myelinated fibers from flower spray endings
What are Aδ or Type III fibers?
Lightly myelinated fibers that relay:
- Pain
- Temperature
- Crude touch
*****Note that the pain signals transmitted by these fibers are “sharp & well localized (vs. C)
What are C or Type IV fibers?
UNMYELINATED fibers that relay:
- Pain
- Temperature
- Touch
*****Note that the pain signals transmitted by these fibers are “dull & poorly localized (vs. Aδ) & this is the SLOWEST fiber type
What is the difference between cold and warm receptors in terms of fiber type?
Cold= Aδ Warm= C
