CNS- Spinal Cord Flashcards
what does the spinal cord do
conveys signals from sensory receptors to brain and from brain to muscles
what does “You Can Only Control What You Sense” mean
if sensory inputs are lost(de-afferentation), control is severely impacted
what is the dorsal root
sensory afferents cell bodies are located here, enter via dorsal roots
what is the interface b/w the PNS and CNS (sensory afferents)
sensory afferents enter spinal cord via the dorsal root, they’ll split into ascending–>form dorsal columns which will go into the brainstem(carry sensory info) and descending axons–>travel caudally for
what do ascending and descending axons do in the interface b/w PNS and CNS
send branches into grey matter of spinal cord that synapse onto interneurons and motorneurons
what is the interface b/w the PNS and CNS (motorneurons)
motorneuron cell bodies are located in the ventral horn, motor efferent axons leave spinal cord and form ventral roots
spinal cord tract–> grey matter
butterfly shape–> motorneurons, interneurons, dendrites and axons
spinal cord tract–> white matter
bundles of axons–> tracts
conveys sensory signals ascending to brain or motor commands descending from brain
what are the ascending tracts
sensory info from peripheral nerves is transmitted to cerebral cortex
what are the descending tracts
motor signals are sent from brain to lower motor neurons–> innervate muscles and produce movement
how is the spinal cord organized
31 spinal nerves–> 8 cervical(C1-C8), 12 thoracic(T1-T12), 5 lumbar(L1-L5), 5 sacral(S1-S5) and 1 coccygeal
what do the cervical nerves do
sensory input from head, neck, shoulders, arms and hands
what do the thoracic nerves do
sensory info from abdomen (trunk)
what do the lumbar nerves do
sensory info from waist, front of legs and feet
what do the sacral and coccygeal nerves do
sensory info from butt, genitals, anus, back of legs and feet
what is shingles
when the neurons in the dorsal root ganglia, 1 or 2 segments of S.C, become infected with the chicken pox virus that lies dormant until mutated–> those who have chicken pox when young more susceptible
why are dermatones important
clinically used to determine the level of a spinal cord injury
how do spinal cord injuries work
when the spinal cord gets damaged at a certain level, all sensation and motor function become absent or abnormal, depending on the severity of damage
what happens if there is a complete cut of spinal cord at levels C7-C6
paralysis of hand and finger movements but not of breathing control and heart rate, everything below C6-C7 will be impacted
what is modality
type of sensory info that is being transmitted
ex. vision, sense of tough, hearing, movement
what does structure of a sensory receptor determine
modality of stimulus
what do Meissner’s corpuscles do
respond to light touch of skin
what do Merkel’s corpuscles do
respond to touch
what is the adequate stimulus
modality activating a given receptor
what do free nerve endings do
respond to pain
what does the Pacinian corpuscles do
respond to vibration or deep pressure
what do ruffini corpuscles do
respond to skin stretch
act as thermoreceptors–> warm receptors–> increase firing rate as temp. rises
cold receptors–> increase firing as temp. falls
what are the different sensory receptors
specialized endings of afferent axons
separate cells that respond to the stimulus and transmit signals via synapses with the afferent neurons
what are somatosensory receptors
somatosensory–> sensations coming from body
cover surface of body and signal different sensory modalities to CNS
what are mechanoreceptors
sense local tissue deformation in skin and vice versa
what are thermoreceptors
sense temperature in skin and brain
what are nociceptors
sense pain(tissue damage) in skin, vice versa, muscle
what are proprioceptors
sense movement and force in muscles and joints
what are vestibular receptors
head acceleration and tilt
how does information transfer in NS vary b/w invertebrate and vertebrae
mechanism for information transfer in NS is the same for vertabraes and invertabraes, sensory receptors signal stimuli with action potentials in wide range of species (humans, invertebraes and vertabraes)
the
what happened in vertebrae and not invertebrates
development of the myelin sheath around nerve axons which increases their conduction velocity
what are the sensory axons with the fastest conduction velocities
type Ia
muscle spindle primary endings
Golgi tendon
what are the sensory axons with the slowest conduction velocities
type IV
nociceptors
warmth receptor
what are the autonomic axon with the fastest conduction velocities
preganglionic fibers
what are the autonomic axon with the slowest conduction velocities
postganglionic fibers
what happens as stimulus intensity increases
membrane potential at the initial segment of the sensory receptor’s afferent axon increases until AP are generated
how are sensory receptors recruited
as the stimulus intensity increases it will increase the rate of the AP causing recruitment
how are stimulus intensities encoded
Frequency code–> bigger the stimulus the more the membrane channels in the sensory endings are distorted, the greater the number of AP/s
Population code–>bigger the stimulus, more sensory neurons are recruited into activity, more AP/s
Temporal pattern code–> variability of firing rate(bursts vs. steady firing) may mediate certain types of sensation
what is the duration of stimulus processing
slowly adapting (tonic) receptors respond the entire time a stimulus is applied
rapidly respond briefly each time as stimulus changes
what does a rapidly adapting receptor do
respond briefly whenever the stimulus changes quickly–> Pacinian corpuscles and Meissner’s corpuscles
what does a slowly adapting receptors do
tonic receptors, respond during the entire time that the stimulus is applied, seen by the continual production of action potentials–> Merkel’s corpuscles, free neuron endings and Ruffini corpuscles
what does localization of stimuli depend on
density of receptors and sizes of their receptive fields
convergence (one neuron receives inputs from many sensory afferents) and divergence (each sensory afferent sends branches to many neurons in the CNS)
Lateral inhibition
what is lateral inhibition
sharpens contrast by focusing activation of CNS neurons
stimulus location is perceived more precisely–> increase spatial acuity
remember slide
A and C inhibit B but since B is firing at a higher frequency it will inhibit A and C to a greater extent than A and C to B
what is two-point discrimination and how does it relate to acuity
a smaller receptive field provides greater spatial acuity
due to the receptors being tightly packed
on lips able to tell that a set of pliers has two tips while on the back receptors are not as tightly packed and the two tips are felt as one –> sensory acuity is relatively low on the back compared to the lips
where is two-point discrimination the best and why
hands and face, worst on abdomen and proximal parts of limbs
density of receptors is highest in skin areas with the best 2-point discrimination
surface area of sensory cortex is largest in regions to which receptors from skin areas with the best 2-point discrimination project
what is sensation
the conscious awareness of a stimulus
what is perception
sensation combined with an understanding of its meaning
where do sensation and perception result
processing in cerebral cortex
which body areas have the greatest representation in sensory cortex
face and hands
what provides general information about location of a stimulus
overlapping stimulation b/w neighbouring receptive fields
which body areas have the least representation in sensory cortex
abdomen, legs and feet
what does descending inhibition do
can reduce the intensity of a perceived sensation because it can screen out certain types of sensory information by inhibiting neurons in afferent pathway
two types–> presynaptic inhibition and postsynaptic inhibition
what is presynaptic inhibition
acts by reducing transmitter release at synapse b/w first and second order sensory neurons
inhibits specific sensations–> pain
lasts several ms
what postsynaptic inhibition
acts by hyper-polarizing membrane of second-order sensory neurons
non-selective: reduces effect of all synaptic inputs
lasts less than 1 ms
what is the process of pain
painful stimulus causes tissue damage and releases prostaglandins and histamine–> activate pain receptors, fire APs which travel to the dorsal part of spinal cord–> in the spinal cord, activity of pain fibers causes the release of Substance P which activates interneurons called projection neurons–> signal pain and excite neurons in the thalamus and cortex which results in sensation of pain
what is Analgesia
suppression of pain transmission
how does aspirin work to suppress pain
blocks production of prostaglandins which are released as a result of damaged tissue
how does Gabapentin work to suppress pain
block conduction in nociceptive afferents–> C-fibre axons
how does opioids work to suppress pain
in CNS will block release of Substance P onto the projection neurons in spinal cord
what is referred pain
sensation of pain that is experienced at a site other than the injured or damaged tissue
