Somatic Sensory System Flashcards
what does the somatic sensory system give us?
body sense - the representation of the body in the brain.
what are to major input components of the somatic sensory system? (basic)
mechanical stimuli - touch / pressure,
pain stimuli / temp.
what do these basic input components of the somatic sensory system allow us to do?
identify shape and texture,
monitor internal and external forces on the body,
detect harmful circumstances,
have a sense of ourselves within our environment.
what are 8 types of sensory receptors in the somatic sensory system?
Meisner corpuscles, Pacinian corpuscles, Ruffini corpuscles, Merkel discs, free nerve endings, hair follicles, muscle spindles, Golgi tendon organs.
what are Meisner corpuscles?
located in the dermal papillae of the skin, especially in the palms, eyelids, lips, and tongue.
they detect light touch and texture,
they are rapidly adapting,
sensitive to 30-50Hz.
what are Pacinian corpuscles?
located deeper in the dermis, joint capsules, and viscera.
they are sensitive to deep pressure, stretch, vibration, and tickle.
they are rapidly adapting,
sensitive to 250-350Hz.
what are Ruffini corpuscles?
located in dermis, joint capsules, and subcutaneous tissue.
they detect heavy touch, pressure, skin stretch, and joint movements.
they are slowly adapting.
what are Merkel discs?
located in the epidermis and superficial layers of the skin.
they are sensitive to light touch, texture, edges, and shapes.
they are slowly adapting.
what are free nerve endings?
they are widespread in the epithelia and connective tissue.
they detect heat, pain, and cold.
what are rapidly adapting / phasic receptors?
after a stimulus is applied, this type of receptor will initially respond but then stop firing even if the stimulus is still there,
gives us info about changes in the stimulus.
what are slowly adapting / tonic receptors?
respond to a stimulus and then stay active / on / continue to respond to the stimulus,
give us info about the persistence of a stimulus.
how are primary afferent axons classified?
according to conduction velocity (which also reflect diameter).
axons from the skin are classified by letters:
A,B,C
A = the fastest / largest,
C = the slowest / smallest.
the A category of axons from the skin is broken down my Greek characters:
α, β, δ
α = fastest,
δ = slowest.
axons coming from the muscles are classified by roman numerals:
I, II, III, IV
I = fastest,
IV = slowest.
how is sensory information relayed to the brain ?
cell bodies of sensory neurons are grouped in the dorsal root ganglion,
their projections are organised into different layers of the dorsal horn.
how do mechanoreceptive and proprioceptive signals reach the brain?
the medial lemniscal tracts carry signals to the thalamus.
how do pain and temperature signals reach the brain?
the spinothalamic tract carries signals to the thalamus.
what are the three neurons that sensory info travels through to reach higher centres?
first-order neurons,
second-order neurons,
third-order neurons.
what do the first-order neurons in the somatic sensory system do?
detect the stimulus and transmits it to the spinal cord.
what do the second-order neurons in the somatic sensory system do?
relay the signals to the thalamus,
they also cross the midline / commissural.
what do the third-order neurons in the somatic sensory system do?
carry signals from the thalamus to the cortex.
what does this mean:
axons in the medial lemniscal pathway are topologically organised.
the spatial arrangement of the objects are relative to one another.
what pathway do the first-order neurons from the upper body in the somatic sensory system follow?
the lateral pathway and synapse on to second-order neurons in the cuneate nucleus.
what pathway do the first-order neurons from the lower body in the somatic sensory system follow?
a more medial pathway and synapse on to neurons in the gracile nucleus.
what pathway do second-order neurons in the somatic sensory system follow?
they cross the midline and ascend in the medial lemniscus.
the topological projection forms a map of the cortex…
it is very fine,
reflects that each dorsal root ganglion innervates a specific domain of the body called a dermatome.
what influences the size of a receptive field?
where it is in the body as some regions will have denser innervation than others.
how can the size of a receptive field of the somatic sensory system be measured?
assessing the ability to discriminate 2 sharp points set apart at different distances,
if the subject can feel the 2 points then the distance between them is larger than the receptive field.
how can the size of a receptive field of the somatic sensory system be measured?
assessing the ability to discriminate 2 sharp points set apart at different distances,
if the subject can feel the 2 points then the distance between them is larger than the receptive field.
what is discrimination like when receptive fields are large?
large receptive field = low discrimination,
arms and legs.
what is discrimination like when the receptive fields are small?
small receptive field = high discrimination,
hands.
