What are sensory systems responsible for? (3)
- Collecting info regarding external & internal environment
- Conveying info from PNS to CNS
- Sensory info is utilized by CNS in various ways
In what ways is sensory info utilized by the CNS?
- conscious appreciation of specific qualities of sensory stimulus
- appropriate reflex response to a stimulus
What do sensory receptors of the PNS do?
- monitor changes in external & internal environment
- serve as biological transducers- monitor stimuli
- the info generated in PNS gets sent to CNS
What are primary sensory neurons?
Sensory neurons in PNS
Cell bodies of primary sensory neurons are located where?
Peripheral ganglia of spinal and cranial nerves
Peripheral processes innervate what?
Peripheral sensory receptors in peripheral tissues
Central processes project into what?
into the CNS
What are the classifications of stimulus receptors and they’re functions?
Chemoreceptors- monitors changes in concentration of various chemical species in tissues
Photoreceptors- light
Thermoreceptors- temperature
Mechanoreceptors- physical or mechanical stimuli
Nociceptors- noxious stimuli (potentially harmful- chemical, mechanical, or thermal stimuli)
What is the difference between a nonencapsulated and an encapsulated ending?
Nonencapsulated- terminals of axons that lie next to cells or free in the extracellular space
Encapsulated- consist of terminals of axons enclosed by a capsule of non-neuronal cells
What are the 3 types of nonencapsulated ending receptors?
- Free nerve endings- axon terminals distributed between cells
- Merkel endings/discs- associated with cells located in deep layers of epidermis (hairless especially)
- Peritrichial nerve endings- associated with axon terminals distributed along root of hair follicles
What are the 5 types of encapsulated ending receptors?
- Pacinian corpuscles- single axon terminal with layers o non-neural cells
- Meissner’s corpuscles- one or more axons inside capsule- highly branched (long and slender capsule)
- Ruffini endings- single axon inside delicate capsule
- End bulbs- variable size & shape - often round - highly branched - often found at muco-cutaneous junctions
- Others: neuromuscular spindles (skeletal muscle) & neurotendinous spindles (tendons & ligaments- Golgi)
Where are the free nerve endings found in cutaneous areas and what do they monitor?
- epidermis, dermis, subcutaneous tissue
- monitor thermal, painful (noxious), and tactile stimuli
What do the peritrichial endings in cutaneous areas monitor?
Movement of hair (tactile)
Where are Merkel endings found in cutaneous areas and what do they detect?
Deep layer of epidermis
Tactile
Where are Ruffini endings found in cutaneous areas and what do they detect?
Dermis & subcutaneous tissue
Tactile
Where are Meissner’s corpuscles found in cutaneous areas and what do they detect?
Dermal papillae of mostly glabrous (hairless) skin, especially fingertips
Tactile
Where are Pacinian corpuslces found in cutaneous areas and what do they detect?
Dermis & subcutaneous tissues
Mechanoreceptors that detect vibration
What 4 type of receptors are found in joints? Where and what kind of stimuli do they detect?
- Free nerve endings- synovial membrane (proprioception), joint capsule, & periarticular CT (nociception)
- Small pacinian corpuscles- periarticular CT around joint capsule- proprioception
- Ruffini- joint capsular tissue- proprioception
- Neurotendinous spindles (Golgi tendon organ)- in articular ligaments- proprioception
What 2 types of receptors are found in skeletal muscles?
- Free nerve endings- mainly CT around muscle- nociceptor
- Neuromuscular spindles- in muscle near junction with tendon - proprioception
What 2 types of receptors are found in tendons?
Free nerve endings- nociceptors & proprioceptors
Golgi tendon organs- proprioceptors
What 2 types of receptors are found in viscera?
- Free nerve endings- nociceptors, chemoreceptors, stretch/distension
- Pacinian corpuscle- fullness/distension
What are the functions of A-alpha fibers?
- motor to skeletal muscle
- sensory from neuromuscular spindle
What is the function of A-beta fibers?
- sensory from neuromuscular spindles, Ruffini endings, GTO’s, Meissner’s, and Pacinican corpuscles
What is the function of A-gamma fibers?
Motor to neuromuscular spindles
What is the function of A-delta fibers?
- Peritrichial endings, pain and temperature receptors
What are the functions of B fibers?
- Preganglionic autonomic fibers
- Sympathetic & Parasympathetic
What are the functions of C fibers?
- Postganglionic autonomic fibers, pain & temperature receptors
- Nociceptic information
Which of the A, B & C fibers is unmyelinated?
C fibers
What type of receptor is a Ia fiber, and what is it’s equivalent?
Neuromuscular spindle, A-alpha
What type of receptors are Ib fibers, and what it’s equivalent?
Neurotendinous spindle
Ruffini Endings
A-beta
What type of receptors are II fibers, and what it’s equivalent?
Neuromuscular spindle
Meissner’s & Pacinian corpuscles
A-beta
What type of receptors are III fibers, and what it’s equivalent?
Pain and temperature receptors
A-delta
What type of receptors are IV fibers, and what it’s equivalent?
Pain and temperature receptors
C
Which of the two numbered fibers are nociceptive fibers?
III and IV
What tissues monitor somatosensations?
Superficial (skin (epiderm, derm, & subcutaneous tissue)
Deep (muscle, tendons, ligs, bones)
What are the 6 somatosenses?
Pain (nociception) Temperature Light touch= nondiscriitive (poorly localized) Discrimitive touch= fine/2point touch Proprioception Vibration
What are the two main general somatosensory pathways/systems?
Spinothalamic (anterolateral) Medial Lemniscus (Dorsal/posterior column system)
Which types of sensations is the spinothalamic system primarily concerned with?
Pain
Temperature
Light/ Non-discrimitive touch
Which types of sensations is the medial lemniscus system primarily concerned with?
Discrimitive/fine touch
Proprioception
VIbration
Where are primary sensory neurons typically located?
Ganglia of spinal & cranial nerves (DRG)
Where are secondary sensory neurons typically located?
Spinal cord or brainstem
Where are tertiary sensory neurons typically located?
Thalamus
T or F. The concept of only three neurons forming the spinothalamic and medial lemniscus pathways is accurate.
False. It’s more convenient. The modification of the pathways can provide for modification of the experience/perception.
Define 2 point discrimination
The ability to distinguish when 2 points are touched simultaneously even when close together. Fingertips=good, back=poor
Permits recognition of different textures
Define Graphesthesia
Traced figure identification- ability to identify a familiar pattern when traced on the skin (quality of discriminative touch)
Does discriminative touch require Meissner’s corpuscles?
Yes along with other cutaneous receptors such as Merkel cells
Define the qualities of Proprioception.
Info regarding the precise position of a body part and the range of direction of movement (kinesthesia).
Does proprioception, discrimative touch, or light touch permit one to appreciate the shape, size, and weight of objects held in hand?
Proprioception
Where are receptors found for proprioception and which receptors do these include?
Found in articular and periarticular tissues (joint capsules, ligaments) and in muscles and tendons
- Neuromuscular & neurotendinous spindles
- Ruffini-like endings
- Pacinian corpuscles
What receptors are used to monitor vibration?
Mostly pacinian corpuscles