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Neuroscience > Lecture 5 > Flashcards

Lecture 5 Flashcards

Midterm 2

1
Q

What is the somatosensory system?

A

-the part of the nervous system involved in conscious and unconscious perception of touch, proprioception, temperature and pain

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2
Q

what are the similar anatomical arrangements of pathways that convey somatosensory information (3)

A
  1. receptors in the periphery encode the specific simulation into receptor potentials
  2. if AP is produced, signal is transmitted along axon to soma in dorsal root ganglion and then along the proximal axon to the spinal cord
  3. in the spinal cord the signal ascends via axons in the white matter to the brain where it can be interpreted
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3
Q

What is somatosensation

A

interpreting sensory info from skin (touch, pain and temp) and musculoskeletal systems (proprioception, pain)

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4
Q

3 things that determine the speed of information processing

A
  1. Diameter of axon
  2. Degree of mylenation
  3. number of synapses in the pathway
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5
Q

sensation involves what of sensory stimuli

A

conscious perception

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6
Q

process of somatosensory system

A
  • sensory receptor responds to stimulsu by producing receptor potential
  • sensory neuron: axon conducts impulses from receptor to integrating center
  • intergrating center:relay impulses from sensory to motor neurons
  • motor neuron: axon conducts impulses from integrating center to receptor
  • effector: muslce that responds to nerve impulses
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7
Q

where are sensory receptors located and how are they specialized?

A
  • located at distal ends of peripheral nerves

- specialized to responding responding to specific type of stimulus

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8
Q

3 peripheral receptors

A
  1. mechanoreceptors: sensative to mechanical deformation (touch, pressure, stretch or vibration)
  2. chemoreceptors: sensitive to chemicals released from the cells (includes damaged cells after injury or infection
  3. thermoreceptors: sensitive to heat or cooling
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9
Q

what is the difference in a tonic and phasic receptor

A
  • tonic receptors have a response that last as long as simulation is present
  • phasic receptors have a response that weakens with the duration of simulation
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10
Q

what two axons do peripheral sensory neurons have

A
  1. distal axon: conduct messages from receptor to cell body

2. proximal: projects from cell body into spinal cord or brainstem

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11
Q

how are afferent axons classified

A

according to diameter and transmission speeds

  • Ia, Ib, II or Ab, Ad, c
  • sensory C are slower ia is fastest
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12
Q

where are the cell bodies of most peripheral sensory neurons located

A

-outside the spinal cord in the dorsal root ganglion

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13
Q

cutaneous innervation: receptive fields

A
  • receptive field is area of skin innervated by a single afferent neuron
  • the ability to distinguish two closely applied stimuli require that they activate two different receptive fields
  • receptive fields are smaller distally and larger proximally
  • distal regions of the body have a greater density of receptors than proximal areas which results in a greater ability to distinguish two closely applied stimuli on a fingertip
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14
Q

When are caliper points perceived as two different points

A

when the points are contacting the receptive fields of two neurons

  • receptors close to our skin have smaller receptive fields
  • receptors deeper down have larger receptive field and sense of touch is less fine
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15
Q

what are sensations are available from cutaneous (skin) receptors

A
  1. touch
  2. pain
  3. temperature
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16
Q

how is fine touch information transmitted

A

-through receptors carried by A-Beta afferents

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17
Q

what type of receptive fields do superficial cutaneous receptors have

A
  • small
  • Meissner’s corpuscles-light touch and vibration
  • Merkel’s disks-sensitive to pressure
  • Hair follicles-movement of hair
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18
Q

what type of receptive fields do subcutaneous receptor have?

A
  • large receptive fields
  • Pacinian corpuscles-responsive to touch and vibration
  • Ruffini’s endings-sensitive to stretch of the skin
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19
Q

how is course touch mediated?

A
  • by free nerve endings
  • poorly localized providing feedback about touch to other parts of the brain than the primary somatosensory area
  • sensory will be received as pleasant pressure and/or the sensation of tickle
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20
Q

thermal receptors

A

-specialized free nerve endings respond to heat and cold temperatures within range that does not cause cell damage
-if it gets too hot cell damage happens, receptors don’t fire and they die
-thermal receptors are small myelinated and unmyelinated neurons
A delta fibers: carry impulses produced by cooling
C fibers: carry info regarding heat

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21
Q

2 components of pain

A
  • conscious sensation of painful stimuls

- emotional and autonomic responses to the sensation

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22
Q

what are nociceptors?

A

-free nerve endings responsive to stimuli that damage or threaten tissue

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23
Q

what are the two types of pain responses?

A
  • fast pain or spinthalamic pain: the initial and immediate sharp sensation that indicates the location of the injury (pricking hand with needle)
  • slow pain or spinolimbic pain: the dull and throbbing ache following fast pain that is not well localized (ie broken bone)
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24
Q

muscle spindles

A
  • sensory organs located in muscles
  • respond yo stretch
  • provide info on fiber length and velocity of length change
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25
Q

two endings of muscle spindles

A
  • primary endings: Ia afferents, rate of stretch, length changes
  • secondary endings: II afferents, length changes, type 2 fibers
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26
Q

nuclear bag fibers vs nuclear chain fibers

A

nuclear bag fibers are bulky and have receptors that respond to rate of chain. Activated by how fast they are being stretched
-nuclear chain fiber is a type of muscle spindle that transmit info on their absolute length of stretch, speed is irrelevant.

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27
Q

what types of fibers are normal skeletal muscle fibers

A

-extrafusal fibers

28
Q

characteristics of muscle spindles embedded in skeletal muscle

A
  • specialized muscle fibers inside the spindle are called intrafusal fibers
  • spindles are contractile only at the ends (central region can not contract)
  • ends of intrafusal fibers attach to extrafusal fibers so streches of the muscles stretches the spindles
29
Q

what are the two types of intrafusal fibers

A
  • nuclear bag fibers-clumps of nuclei

- nuclear chain fbers-nuclei arranged single file

30
Q

extrafusal vs intrafusal

A

intrafusal fibers dont generate force, extrafusal fibers do

31
Q

two types of sensory endings

A
  • primary endings of type Ia neurons-wrap around the central region of each intrafusal fiber
  • secondary endings of type II afferents-mainly on nuclear chain fibers adjacent to primary endings
32
Q

where are gamma motor neurons located and what is their function

A
  • motor neurons are located in ventral horn of spinal cord
  • innervate intrafusal muscle spindle receptors
  • travel adjacent to alpha motor neurons to skeletal muscles
  • activation of gamma motor neurons sets the spindle sensitivity and compensates for changes in muscle length
  • muscle spindle must be under tension to function properly
  • muscle spindle activity responsible for stretch reflexes
33
Q

alpha gamma coactivation

A
  • happens in order for muscle spindles to function properly
  • everytime an alpha motor neuron fires its corresponding gamma motor neuron also fires
  • this needs to happen because if shortening doesnt happen after stretching the fiber will go slack and information will not be properly transmitted
  • activation of both is happening at the same time
  • during passive stretch, spindles are elongated and muscle is stretched, stretch activates spindle sensory receptors. Excitation of alpha motor neuron via the corticospinal neuron results in contraction of extrafusal muscle fibers. if gamma motor neurons do not fire when alpha motor neurons to the extrafusal muscles fire, intrafusal central region will be relaxed and the afferent neurons inactivate. normally alpha and gamma motor neurons willbe simutaneoulsy active. the firing of gamma motor neurons causes the ends of intrafusal fibers to contract maintaining the stretch on the intrafusal central region and preserving the ability of sensory endings to indicate stretch.
34
Q

golgi tendon organs

A
  • relays tension in tendons
  • utilize Ib afferents
  • signal the force generated by the muscle contraction or by passive stretch of the tendon
  • they are encapsulated nerve endings woven among the collagen strands near the musculotendious junction that monitor tension in tendons
35
Q

joint receptors

A
  • respond to mechanical deformation of joint capsules and ligaments
  • ligament receptors respond to tension of ligaments
  • paciniform corpuscles respond to movement
  • ruffini’s corpuscles signal extreme ranfes in motion
  • free nerve endigns stimualted byinflammation
36
Q

3 types of pathways that bring sensory information to the brain (somatosensory)

A
  • conscious relay pathways:discrimative sensory perception. composed of 2 pathways
    2. divergent: conscious and unconscious sensory info to many locations in cerebrum and brainstem
    3. unconscious: unconscious proprioception and posture info to cerebellum
37
Q

3 projection neuron pathways

A
  1. first order neuron: receptor to brainstem or spinal cord
  2. second order neuron: brain stem or spinal cord to thalamus. Axons decussate in spinal cord or brainstem before reaching thalamus. This is contralateral
  3. Third order: thalamus to primary somatosensory area (cerebral cortex)
38
Q

two conscious relay systems to cerebral cortex

A
  1. dorsal column or medial lemniscus tract: fine touhc, proprioception and vibration
  2. Anterolateral column or spinothalmic tract: fast pain, temperature and crude touch
    - routes composed of white matter for rapid transmission
39
Q

what is conscious proprioception

A

the awareness of movements and relative positions of body parts

40
Q

what allows odentificatin of an object by touch and pressure info

A

integration of touch and proprioceptive information

41
Q

stereognosis

A

the ability to use touch and proprioceptive information to identify an object

42
Q

neuron orders in the dorsal column-medial lemniscus

A

first order neuron: from DRG to medulla. Fasciculus gracillis (medial column to lower body)
fascicullus cuneatus (lateral column to upper body)
second order neuron: axons from first order neuron synapse with that of the second in medula. Axons of second order neurons cross over the medulla and ascend as the medial lemniscus tract to the thalamus
third order neuron: 2nd order synapses with 3rd in thalamus. Info is carried to appropriate area in primary somatosensory region in cortex

43
Q

discriminative touch from the face

A
  • provided by three branches of the trigeminal nerve
    1. first order neuron: receptor through trigeminal gangliion to main sensory nucleus
    2. Second order neuron: cross pons to thalamus via trigeminal leminscus
    3. Third order neuron: thalamus to sensory cortex
44
Q

where does temperature sensation project to

A

primary sensory cortex

45
Q

which tract transmits course touch, fast pain and temperature

A

the spinothalamic tract

46
Q

Anterolateral or spinothalamic tract order neurons

A

-responsible for pain, temperature and crude touch
first order neuron: in DRG. Axons from 1st neuron synapse on 2nd in dorsal horn of spinal cord
second: in dorsal horn. axons cross over the spinal cord and ascend as spinothalamic tract
third: 2nd order neurons synapse with 3rd order neurons in thalamus. carry info to appropriate area in primary somatosensory region in cortex

47
Q

fast pain for face

A
  • provided by 3 branches of trigeminal nerve
    first: receptor through trigeminal ganglion to spinal nucelus of trigeminal nerve
    second: cross pons to thalamus via trigeminal lemniscus
    third: thalamus to sensory cortex
48
Q

fast vs slow pain

A

fast pain: initial and immediate sharp sensation that indicates location of the injury. Transmitted through spinothalmic tract. reaches primary somatosensory cortex ad individual is consciously aware of sharp pain and its specific location. When there is significant tissue damage fast pain is followed by slow pain
slow pain: dull, throbbing ache following fast pain that is not well localized.

49
Q

lesions which interrupt the pathways conveying nociceptive information produce what

A

analgesia: the absence of pain in response to stimuli that would normally be painfull

50
Q

what is crossed analgesia

A

-a pathologic circumstance where a single lesion can cause pain sensation to be lost on the ipsilateral side of the face and the contralateral side of the body

51
Q

lesion to the ST tract

A
  • effect on fast pain and temperature
  • contralateral loss
  • loss of pain and temp sensation from contralateral side of body one or two levels below lesion
52
Q

medial pain system

A
  • part of the divergent pathway
  • medial pain system is divergent ascending network of neurons responsible for slow pain
  • activity of medial pain system elicits motivational, withdrawal, arousal and autonomic responses to pain
  • we are not consciously aware of medial pain
  • system utilizes several different pathways with variable numbers of projection neurons
  • not a 3 neuron pathway
  • only one divergent pathway provides perceived pain
  • information is not somatotopically organized
  • therefore slow pain cannot be precisely localized
53
Q

first neuron characteristics

A
  • small unmyelinated c fibers
  • receptors are specialized free nerve endings sensitive to chemical stimulation and noxious heat or mechanical stimulation
  • has high threshold c fiber endings that become sensitized with repeated stimulation
  • neurotransmitter is Substance P
  • synapse and zone 1 and 2 of dorsal horn of spinal cord
54
Q

ascending projection neurons of medial pain pathway

A
  • spinomesencephalic
  • spinoreticular
  • spinolimbic
  • tracts are parallel and ascending
  • only information from spinolimbic tract is perceived as pain
55
Q

what is the trigeminoreticulolimbic

A

-Responsible for transmitting slow pain information to the face also using trigeminal nerve

56
Q

the spinomensencephalic tract carries nociceptive information to what two areas?

A
  • the superior colliculus (midbrain): involved in turning eyes and head toward source of noxious input. Made up of sensory neurons carrying slow pain
  • periaqueductal gray: activates descending pain control system
57
Q

what is the spinoreticular tract

A

pathway of ascending neurons synapse in the reticular formation
-modulates arousal, attention and sleep walking cycles in response to pain (become pale, heart racing, feel faint, nauceous, emotionally distressed, pain not localized).

58
Q

reticular formation

A

a neural network in the brainstem that includes the reticular nuclei and their connections.

59
Q

axons of the spinolimbic tract

A
  • transmit slow pain information to the limbic lobe in cerebral cortex
  • relay to cortex through thalamus
  • responsible for emotional response to pain
60
Q

how unconscious relay tracts transmit information (2)

A
  • proprioceptive receptors

- activity in spinal interneurons

61
Q

what do spinocerebellar tracts do?

A
  • transmit info to the cerebellum
  • information does not reach conscious awareness
  • controls autonomic movements and postural adjustments
  • relay tracts are critical for adjusting movements
62
Q

what did inadequate proprioceptive input cause

A
  • ataxia

- loss of sensory feedback disrupts movement control

63
Q

two high fidelity pathways

A
  • two neuron pathways which relay information from proprioceptive receptors to the cerebellar cortex
    1. posterior spinocerebellar pathway: transmits proprioceptive informatoin from the legs and lower half of the body
    2. cuneocerebellar pathway: transmits proprioceptive informaiton from the arm and upper half of the body
  • pathways are ipsilateral
64
Q

internal feedback tracts

A
  • tracts responsible for relaying the activity of spinal interneurons from the spinal cord to the cerebellum
  • monitor the activity of descending motor signals from the cerebral cortex and brainstem
65
Q

two types of internal feedback tracts

A
  1. anterior spinocerebellar tract: transmits info from thoraxolumbar spinal cord. tract fibers divide to connect both sides of cerebellum. bilateral projection reflects autonomic coordination of lower limbs.
  2. rostrospincerebellar tract: transmits info from the cervical spinal cord to the ipsilateral cerebellum
66
Q

what is information from the spinocerebellar tracts used for

A

unconscious adjustments to movement and posture

  • coordination and learning of movements
  • internal feedback tracts reach cerebellum before signals from the motor neurons reach the target muscles
67
Q

by using the high fidelity and internal feedback tracts information the cerebellum compares what

A

intended motor output versus actual movement output

Neuroscience (2 decks)

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