Lecture #15 Flashcards
which nerves belong to both sensory and motor neurons?
mixed nerves
describe the blind spot in the eye:
in the optic disk region (in the center) in which axons from the sensors are invaginating in the retina and are forming the optic nerve, there is place with no receptors
describe peripheral vision:
in the corner regions the cone start to diminish, and there is also a reduction in the number of rods → this is why lateral vision is more blurry compared to the central region
what are the three somatosensory categories?
proprioreception, exteroception, and interception
describe the function of proprioreception:
in charge of the reception of muscles, tendons, and the position of our arms / fingers in space
describe the function of exteroception:
senses the external world - tactile sensations, vibrations, smell, light, sounds etc
describe the function of interoception:
to sense the internal organs → important for the cardiovascular, digestive, and renal system
relies specific sensory fibers and in the visceral or autonomic nervous system (not voluntary)
what neurons do mechanoreceptors come from?
dorsal root ganglion neurons
what three categories can mechanoreceptors be divided into?
thermal receptors, nociceptors, and chemoreceptors
what proprioreception fibers have the largest diameter?
Ia and fiber II → conduction velocity is (80-100 m/s) and they usually innervate specific fusal fibers of the muscle
what are the function of Aβ fiber and what is their speed?
usually involved in touch sensation and have a big diameter (30-50 m/s)
Merkel, Meissner, Pacinian, Ruffini
what are the function of Aδ receptors and what is their speed?
poorly myelinated, with a small caliber and low speed, involved in pain sensation (10-30 m/s)
what are the function of C fibers?
free of myelin wrapping and are very small, fundamental in long-term perception of pain
what are the four mechanoreceptors under the skin?
Ruffini, Pacinian, Meissner, and Merkel
where are Ruffini cells located?
in the depth of the skin - ruffini corpuscles are in the dermis
where are the Pacinian cells located?
in the depth of the skin - sub-cutaneous layer
where are the Meissner cells located?
close to the surface - interdigitaion of the epidermis cell layer
where are the Merkel cells located?
close to the surface - in the groove
in what area can all four mechanoreceptors of the skin found?
in the glabrous skin (finger and palm)
what is poor in Pacinian and Ruffini cells?
poor spacial acuity
what cells make up around 25% of the mechanosensory cells present in the hand?
Merkel cells
what channel do Merkel cells use?
PIEZO 2 (two are present in the body)
what do the PIEZO 2 channels measure?
can sense the variation in stretching in the skin → closed when the membrane is not being touched and open when a mechanical force is applied and stretching occurs
describe the sensitivity and the functionality of Merkel cells:
highest spacial resolution
they are slowly adapting fibers, which means they fire during the whole period even if the sensation is steady
what percentage of the mechanoreceptors in the hand do Meissner cells make up?
40%
describe the functionality of Meissner cells:
they are rapidly adapting neurons → they are on - off cells, so if the pressure is kept the sensation will not come from the Meissner cells but from the Merkel cells
describe Pacinian cells:
- bi-onion (many layers of membranes wrapping the sensor)
- they are in the depth of the skin and the laminar capsule is composed of many laminae
- they sense vibrations
- very sensitive: only a 10nm vibration is required for their activation
what percentage of cells in the hand do Ruffini corpuscles make up?
20%
describe Ruffini corpuscles:
slow adapting cells in very deep regions of the skin and tendons
which are the fastest and most accurate mechanoreceptors?
Meissner cells
which is the most accurate system to sense pressure?
Merkel cells
which cells are invalid in sensing vibration?
Pacinian
which mechanoreceptors are involved in the sensation of stretch?
Ruffini
what mechanoreceptors allow a blind person to read braille?
Merkel cells
what two types of sensors surround hair follicles?
touch domes and Lanceolate / circumferential endings
what doe the Lanceolate / circumferential endings help us sense?
how we perceive the movement of hairs
longitudinal lanceolate endings are involved in the specific behavior feeling that comes from caress
what type of sense will a blunt object create?
pressure
what type of sense will a pinprick create?
activation at the beginning of pressure, and then the sensation of pain as there is activation of other receptors
describe the ion channels connected to hearing:
have a sort of molecular coil connected with a gate, and when there is a force moving an object connected with the coil there will be the opening of the ion channel and the crossing of ions from the pore
what are the two main receptors connected to proprioreception?
muscle spindles and Golgi tendon organs
what information do muscle spindles and Golgi tendon organs provide?
information on the stretch of our muscles, the position of our limbs, and are also important for the accuracy of complex movements
with are the two types of fibers in muscle spindles?
extrafusal and intrafusal
describe intrafusal fibers of muscle spindles:
in the middle (4-7 muscle fibers) and are innervated by a specific group (1A afferents) deriving from the DRG
there are also other DRG axons innervating this intrafusal called group II
where are group 1 intrafusal fibers located?
coil around the fiber
describe how muscle spindles work:
there is two sense fiber sensing: when you stretch the muscles you are elongating the extrafusal fibers but at the same time you are elongating the intrafusal fibers → the stretch activates these fibers and they start to send action potentials to the dorsal root ganglia
ion channels involved in this process have a gain of PIEZO2
what are the type I muscle spindle fibers connected to?
associated with velocity and direction of movement
what are the type II spindle fibers provide information on?
static position of the limbs
what do the intrafusal muscle fibers receive their information from?
a specific subset of ventral or voluntary motoneurons which are called gamma motoneurons and are smaller than the classical ⍺-mn
describe what the amount of intrafusal fibers is linked to
in muscles that are governing something that must be precisely regulated, we have a huge number of intrafusal terminals because we need to know exactly how these muscles are moving and the precise amount of stretch in these fibers
where are the Golgi tendon organs located?
in a position between the extra/intrafusal muscle dn the tendon
afferents fro the dorsal root ganglionic neurons innervating the tendons
what are the Golgi tendon organs important for?
providing an accurate sense of the position of the muscles and therefore the position of our organs
where does the innervation of the Golgi tendon organs come from?
DRG neurons
where do the mechanoreceptors send their information?
dorsal grey matter of the spinal cord can be divided into several stripes → mechanoreceptors usually send their information to layers 3-4 and make one or two synapses with the individual neurons
what are very thin, unmyelinated fibers the send information to several layers?
C fibers
why are there some areas of the body where we are unable to distinguish the specific point of pain?
the fibers propagating the pain are not connected to a single neuron and therefore the information is not relayed in a precise way (C fibers)
how can the information move from the periphery (DRG) to the CNS?
- axons enter the dorsal root and interact with layers 3-4 neurons, but sometimes the shappens in the same cells that can make long axons, which turn 90 and start to ascend through the spinal cord
this ascending information starts from the lumbar spinal cord and is collected in a very big nerve called the Gracilis nerve
when it arrives at the medulla it starts to synapse with specific nuclei and the send axons in complex trajectories that eventually will reach the thalamus
what collects the information ascending, starting from the lumbar spinal cord and travels to the thalamus?
Gracils nerve
what are nerves that have very complex trajectories called?
arquate fibers - make an arch
where do DRG neurons that receive information from the upper limbs send their information?
enter the spinal cord and make synapses with the neurons in the ventral grey matter, but at the same time extend a relatively short axon reaching the medulla in another nucleus called the nucleus cuneatus
what is the homunculus?
a schematic representation of where there are the most touch sensors located in the body (large hands, lips etc)
what are the terminals of dorsal rot ganglionic neurons that innervate the skin or other organs that are in charge of sensing pain stimulation?
nociceptors
what two fibers to nociceptors have?
they end with free nerves with our any specific cells surrounding and the pain is running through small diameter fibers either Aδ (pure myelinated) or C fibers (completely unmyelinated)
what are the two types of pain?
first acute pain and second pain
describe first acute pain:
coming from fibers that are purely myelinated but with little myelin - faster pain stimulation
what fibers are responsible for second pain?
C fibers
at what point are our thermal pain sensors activated?
43 degrees
at 43 degrees what is activated in thermal pain receptors?
specific ion channels called TRPV1 that flux calcium
besides heat, how also can TRPV1 channels be activated?
capsaicin which is the active principle in hot chili peppers
what does the repeated activation of TRPV1 channels cause?
desenitization of the channel → the activated channel begins to need more capsaicin to create the same effect until it cannot activate the channel anymore
what can chronic activation of the TRPV1 channel be used for?
to develop an anti-pain action
what are ASICs channels?
acid sending ion channels → inotropic channels that sense protons
pH sensitive channels involved in the perception of peripheral inflammation through the pain circuit
what is able to block ASICS 1a/2a channels?
mambalgin-1 - black mamba venom
what is Amiloride used for?
a classic diuretic drug that blocks a huge number of ASIC channels and has been used to treat MS
what short peptide activates ASICS3?
RPRF amide derived from snail venom
