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the somatosensory system Flashcards

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1
Q

what is the role of the vestibular system?

A

provides the brain with information about balance, posture and where our body is in space
it does this by communicating with the cerebellum and keeping our eyes still as we move

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2
Q

what are the 2 main parts of the vestibular system?

A

the otolith organs: the utricle and saccule that detect linear motion
the semi-circular canals: made up of 3 canals that detect head rotation

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3
Q

what is the structure of the vestibular system?

A

the otolith organs and the semi-circular canals
the ampulla which contains the hair cells
vestibular nerves that carry information to the brainstem
the vestibular labyrinth (the whole system) contained within a bony skeleton and filled with endolymph

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4
Q

what is the structure of vestibular hair cells?

A

they have a hair bundle with stereocilia and tip links however they are more clumped together to detect low frequency movement
they have a kinocilium that gives them polarity
the stereocilia can be placed in different directions to detect movement from all directions

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5
Q

what are the 2 types of vestibular hair cells?

A

type I have calyx dendrite terminals that surround the cell for more reliable transmission
type II have normal dendrite terminals

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6
Q

what is the structure and role of the saccule and utricle?

A

they detect head tilt and linear acceleration using a structure called the macula
the macula is a sensory patch containing hair cells, it has a line across it called the striola where hair cells line up in opposite directions

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7
Q

what is the gelatinous otolithic membrane in the otolith organs?

A

a membrane above the hair bundles covered with otoconia (crystals) that pulls hair cells down when we move our head

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8
Q

how do we distinguish between head tilt and linear acceleration?

A

using input from other sensory systems such as the visual system and proprioception

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9
Q

what is the structure of the ampulla and what happens when we spin?

A

it contains a gelatinous structure called the cupula that contains hair cells
the cupula is surrounded by endolymph that moves when we spin
the endolymph pushes the cupula and hair bundles in the opposite direction of our spinning

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10
Q

how does the semi-circular canal detect spinning?

A

when the cupula and hair bundles are pushed in the opposite direction of spinning it allows the canals to detect angular acceleration
they work in pairs, one side is activated and the other is inhibited to detect the direction of movement

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11
Q

where does the vestibular system output?

A

to the vestibular nuclei in the brainstem it can also go to:
the cerebral cortex and cerebellum for posture
the spinal cord and the oculomotor nuclei to keep eyes straight

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12
Q

why is vestibular input faster than ocular input?

A

the vestibular system relies on ion channels and has a less complex circuit so it is faster

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13
Q

what are reflexes?

A

a reflex is a rapid, involuntary and coordinated response to a sensory stimulus
it usually involves muscles or glands and happens the same way each time

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14
Q

what are somatic reflexes?

A

unlearned reflexes that involve the spinal cord (so they are also known as spinal reflexes)
they require sensory input and are fast because there are few synapses involved
they are hard to supress because there is not much input from the brain

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15
Q

what is the route of the patellar reflex (knee jerk)?

A
  1. the sensory stimulus is relayed by the primary afferent neuron to the dorsal root ganglion
  2. dorsal root ganglion axons project into the periphery and the ventral horn where it synapses onto a motor neuron
  3. the motor neuron relays to the muscle causing it to contract
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16
Q

what causes our knee to jerk in the patellar reflex?

A

an extensor muscle allows the limb to extend
a flexor muscle causes the limb to bend

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17
Q

what is a monosynaptic circuit?

A

a circuit containing one synapse

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18
Q

what is the stretch reflex (when we are holding an empty cup and it is filled)?

A
  1. muscle spindles detect muscle stretch and send signals to the spinal cord
  2. the brain activates motor neurons causing the bicep to contract
  3. at the same time inhibitory interneurons synapse to motor neurons causing the tricep to relax
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19
Q

what is an antagonistic muscle and what is reciprocal inhibition?

A

an antagonistic muscle acts in the opposite direction of the agonist muscle
reciprocal inhibition is the process of the antagonistic muscle being inhibited as the agonist muscle contracts

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20
Q

what are muscle spindles?

A

proprioceptors that monitor the movement and position of body parts
they are found in all striated muscle especially muscles involved in fine moto control

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21
Q

how are muscle spindles innervated?

A

they are innervated by Ia sensory fibres that feedback to alpha motor neurons that cause muscle to contract
they are also innervated by axons from the gamma motor neurons that adjust tension in the muscle spindle to monitor stretch

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22
Q

what is the golgi tendon organ and how is it activated?

A

a proprioceptor that detects muscle tension due to contraction
they are activated by sensory afferent neurons that activate inhibitory interneurons to inhibit alpha motor neurons

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23
Q

how does the golgi tendon organ affect muscles?

A

it acts in a negative feedback loop that regulates muscle tension to protect muscles and tendons from damage
it helps maintain muscle length

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24
Q

what is the flexor reflex and what causes it?

A

it is a reflex that causes quick contraction of flexor muscles to withdraw a limb from harm
it is caused by activation of nociceptive receptors in the skin
it is polysynaptic because there are multiple excitatory neurons

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25
what is the parallel after-discharge circuit?
a circuit where the sensory input is fired through multiple synapses to sustain the response
26
what is the crossed-extensor reflex?
inhibitory interneurons are activated causing the opposite muscle to extend for reciprocal inhibition to maintain balance it is a parallel after-discharge circuit to maintain the response
27
how do mammals walk using an alternating pattern?
extensor and flexor muscles in individual limbs are alternatively activated and inhibited this is done locally within the spinal cord by central pattern generators neurons have different patterns of rhythmic firing to produce alternating activation and inhibition
28
what is the somatosensory system and what are the 2 main inputs?
it is the representation of the body in the brain the 2 main inputs are mechanical stimuli and pain that allow us to detect objects and harm
29
what are the 5 main classes of sensory receptor in the skin, which are encapsulated nerve endings and which are unencapsulated?
meissner, pacinian, ruffini, merkel and free nerve endings meissner, pacinian and ruffini are encapsulated merkel and free nerve endings are unencapsulated
30
where are meissner corpuscles located and what do they detect?
located in dermal papillae (palms, eyelids, lips and tongue) they detect light touch and texture they are rapidly-adapting
31
where are pacinian corpuscles located and what do they detect?
located deeper in the skin, gut and joints detect deep pressure, skin stretch and vibration they only detect high frequency which is why they are layered they are rapidly-adapting
32
where are ruffini corpuscles located and what do they detect?
located in skin and joints they detect heavy touch, pressure, skin stretch and joint movement they are slowly-adapting
33
where are merkel corpuscles located and what do they detect?
located in skin they detect light touch, texture and shapes they are slowly-adapting
34
where are free nerve endings located and what do they detect?
located in epithelia and connective tissue detect pain and temperature they are slowly-adapting
35
how are primary afferent axons divided into subtypes?
by their conduction velocity and diameter (because a larger diameter causes a faster velocity)
36
what is the fastest and slowest axons in the skin and muscles?
in the skin A-alpha axons are fastest and A-delta are slowest in the muscles Ia axons are fastest and Ic are slowest
37
how is sensory input kept separate in the brain?
the axons of sensory neurons project into different layers of the dorsal horn in the spinal cord they are carried to the brain by different pathways
38
how does sensory input travel from neurons to the brain?
1. first order neurons in the dorsal root ganglion detect a stimulus and transmit it to the spinal cord 2. the stimulus passes through second order neurons and is relayed to the thalamus 3. it is synapsed to third order neurons that relay information to the cortex
39
what is the role of the medial lemniscal system and medial lemniscal tracts?
provides the brain with information about fine touch, vibration and proprioception medial lemniscal tracts carry mechanoreceptive information to the thalamus
40
what is the role of the spinothalamic tract?
carries pain and temperature signals to the thalamus
41
what pathway do upper body first order neurons follow and where do they end?
they follow the lateral pathway and synapse onto second order neurons in the cuneatus nuclei in the dorsal column
42
what pathway do lower body first order neurons follow and where do they end?
they follow the medial pathway and synapse onto second order neurons in the gracilis nuclei
43
what pathway do second order neurons follow?
the pathways of the upper and lower body neurons cross and move up into the medial lemniscus this means that lower body neurons travel laterally to the thalamus and upper body neurons travel medially
44
what pathway do third order neurons follow?
the third order neurons cross again so that the lower body neurons synapse medially to the cortex and upper body neurons synapse laterally to the cortex
45
what are dermatomes and how are they derived?
a specific region of the skin innervated by a sensory ganglion in the embryo each dorsal root ganglion is associated with a specific somite that forms the dermatome
46
what are receptive fields?
an area of sensory space that influences the firing rate of a specific neuron when activated their size depends on the location of the neuron in the brain
47
how is the size of a receptive field on our skin measured?
by finding the minimum distance between two points that we can feel
48
why are smaller receptive fields more sensitive?
there are more nerve endings and input from different areas there are more axons per unit area that are represented in the cortex
49
what is the cortical map?
the cortical map is a somatotopic map in the coronal plane of the post-central gyrus it is plastic so can adapt to changes in its input
50
what are Broadmann areas?
regions in the cortex that receive inputs from different types of sensory receptors e.g. auditory system is area 17
51
why is pain different to other senses?
it is discriminative meaning it tells us what is happening around us and it is a graded motivation meaning it affects our behaviour
52
what is the specificity theory?
a theory about how pain is represented in the brain that states that pain is a distinct sensation that is detected and transmitted by receptors and pathways to pain areas in the brain
53
what is the convergence theory?
a theory about how pain is represented in the brain that states that pain is represented by convergent somatosensory activity within a network called the neuromatrix and can be changed by the environment
54
what are lightly myelinated nociceptive fibres?
A-delta fibres that cause fast pain they can be mechanosensitive or mechano-thermal sensitive
55
what are unmyelinated nociceptive fibres?
C fibres that cause slow pain they are polymodal meaning they detect mechanical, chemical and thermal stimuli
56
what do nociceptors detect?
they only detect pain caused by mechanical, chemical or thermal stimuli this means that if nociceptors are activated the mechano/chemo/thermoreceptor has been saturated and the stimuli has become painful
57
what is fast and slow pain?
fast pain is sharp and immediate and is detected by A-delta fibres slow pain is delayed and lasts longer and is detected by C fibres
58
what are molecular pain receptors and what is an example?
specific receptors associated with nociceptive nerve endings that are activated by heat and hot chillis an example is capsaicin receptors that are activated by capsaicin in hot chillis capsaicin mimics molecules released by stressed tissues showing that nociceptors can detect chemicals released from cells
59
what are the 2 components of the central pain pathway?
the sensory discriminative pathway that signals the location, intensity and type of pain stimulus the affective-motivational pathway that signals pain and enables autonomic activation for the flight or fight response
60
how does the sensory discriminative pathway detect the intensity and location of pain?
intensity is determined by the frequency of action potentials fired location is determined because the somatosensory cortex is topographically mapped to areas of the body
61
can the affective-motivational pathway detect location of pain?
no because it is not topographically mapped so it responds to pain anywhere in the body
62
how does pain affect us through the affective-motivational pathway?
it inputs to the limbic lobe which processes emotions and memory so we associate pain with an unpleasant emotion or experience
63
what is hyperalgesia and how can it be treated?
it is an increased response to a painful stimuli e.g. extreme pain from a papercut can be treated using painkillers that block prostaglandin production however this is not very effective
64
what is allodynia?
a more painful response to a normally gentle stimuli e.g. painful response to being tapped lightly
65
what causes hyperalgesia and allodynia?
nociceptors having a lowered pain threshold and the relay neurons becoming sensitive to other inputs
66
what is hyperpathia and what causes it?
a condition where pain is not detected until a certain point and then there is explosive pain it is caused by axon damage that increases the pain detection threshold so when the threshold is met there is extreme pain
67
what is neuropathic pain and when can it be experienced?
central nerve pain that occurs when central pain pathways are damaged it can be experienced after diabetes, strokes, shingles or limb amputations (phantom limb pain)
68
what does phantom limb pain show?
that the central representation of the body is not passive and can be experienced without peripheral input
69
what is referred pain and what causes it?
pain coming from an different area than the stimulus e.g. shoulder pain during a heart attack it is caused by visceral nerve afferents converging on the same pathway
70
how do we modulate pain and what does this show?
by suppressing it e.g. walking over fire this shows that there are mechanisms that can overcome severe pain
71
what are enkephalins and how do they cause pain modulation?
they are opioid peptides that contain endorphins they are released form parts of the midbrain and inhibit nociceptive fibres
72
what is an example of local pain modulation and what does it show?
an example is rubbing an injury this shows that we can inhibit mechanoreceptors locally to stop them inputting to the spinal cord

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