Peripheral Nervous System Flashcards
what are the receptors for the pain neurotransmitter glutamate
AMPA and NMDA. The former results in permeability changes which encourages further action potentials to occur. The latter releases calcium when glutamate binds, which causes the post synaptic potential (of dorsal horn) to be hypersensitive through opening calcium channels and a second messenger system, only requiring a little amount of glutamate and substance P to generate an action potential
what are the six types of sensory receptors?
photoreceptors, mechanoreceptors, thermoreceptors, osmoreceptors, chemoreceptors and nociceptors (pain receptors)
compare tonic and phasic receptors
tonic receptors adapt slowly or do not adapt at all to stimuli, where as phasic receptors adapt rapidly to stimuli. For example, tonic receptors are useful for remembering information about the stimulus such as to maintain posture and balance. On the other hand, phasic receptors are useful for stimuli that is not felt after a short while, for example clothing.
What are the five types of tactile receptors (type of mechanoreceptor) and what are each responsible for?
Hair receptors: respond to gentle touch of hairs and are phasic. Merkel’s disc: responds to light, sustained touch and is tonic e.g. reading Braille. Pacinian corpuscle: responds to vibrations and deep pressure and is phasic. Ruffini endings: respond to deep, sustained pressure and stretch of skin like in a massage (tonic). Meissner’s corpuscle: sensitive to light, fluttering touch like tickling with a feather (phasic)
what are the three types of pain receptors (nociceptors)
mechanical nociceptors, thermal nociceptors and polymodal nociceptors: detect all stimuli equally
what are prostaglandins?
prostaglandins sensitise nociceptors, lowering their threshold for activation, meaning less stimuli is needed to feel pain/ pain is felt easier. Drugs like aspirin aim to inhibit the release of prostaglandins and have a pain-relieving or analgesic effect
What kind of afferent nerve fibres carry the pain signals originating at each nociceptor?
Both mechanical and thermal nociceptors transport their signals via small, myelinated A-delta fibers which are phasic (respond rapidly to pain). Polymodal nociceptor signals are carried by small unmyelinated C fibers and are phasic (respond slowly to pain).
what are the two best known pain neurotransmitters?
substance P, which activates ascending pathways that transmit nociceptor signals to higher levels for further processing (for the perception and localisation of pain) and glutamate, which makes the dorsal horn interneuron hypersensitive
How can pain be relieved?
opiates are released via efferent analgesic pathways which can then bind to opiate receptors on the pre-synaptic knob of an afferent pain fibre. this inhibits the release of substance P
what is the name of a single cardiac cell, which are joined by ____ and includes ____
syncytium, joined by intercalated discs, includes gap junctions.
sensory systems convey four types of information. what are they and how do we code for them?
Modality (type): nerve specific not receptor specific according to labelled line theory. location (where) smaller and more dense receptor fields have more acuity. intensity (how strong) depending on AP firing frequency and size of stimulus. and timing (when and how often) measured by when a response/firing begins and ends and impacted by whether receptor is phasic or tonic
what are some examples of reflexes which occur in the body? (including monosynaptic relfexes)
Platellar tendon stretch reflex or knee jerk reflex, crossed extensor coupled with withdrawal reflex, pupillary light reflex and vestibulo-ocular reflex
what are the two types of muscle receptors and what do they detect?
Muscle spindles monitor changes in muscle length. Golgi tendon organs monitor changes in muscle tension. Both are activated by muscle stretch
what are the two types of intrafusal muscle fibers found within a muscle spindle? (these lie parallel to ‘ordinary’ extrafusal fibers where fuses means spindle).
Nuclear bag (muscle length and velocity- dynamic) and Nuclear chain (muscle length- tonic)
How are gamma motor neurons able to change the shape and sensitivity of the muscle spindle
- gamma motor neurons innervate the contractile component of the muscle spindle 2. when the extrafusal muscle contracts, the gamma motor neuron increases the rate of firing, making the spindle more sensitive to stretch and allowing it to shorten (not slacken). 3. if the extrafusal muscle were to relax or stretch, the gama motor neurons would decrease firing, making the spindle less sensitive to stretch, so it can also relax.
