Chapter 6 Flashcards
Somatosensation:
sensory information form the skin and musculoskeletal system
Superficial or cutaneous
information from the skin
Proprioception
information from the musculoskeletal system
What is the speed of information processing determined by?
Diameter of the axons
Degree of axonal myelination
Number of synapses in the pathway
Sensory information:
nerve impulses generated from original stimuli
Sensation
awareness of stimuli from the senses
Where does interpretation of sensation into meaningful forms occur?
cerebrum
What are mechanoreceptors?
respond to the mechanical deformation of the receptor by touch, pressure, stretch, or vibration
What are chemoreceptors?
respond to substances released by cells, including damaged cells after injury or infection
What are thermoreceptors?
transmit information regarding heat or cold
What is included in sensation from the skin?
touch
pain
temperature
Pain
nociceptors which are free nerve endings
Temperature:
also free nerve endings that responds to warmth or cold within a non-damaging temperature range
How is touch categorized?
fine
coarse
Fine touch:
includes a variety of receptors and subsensations
Coarse touch:
mediated by free endings throughout the skin
What do cutaneous receptors respond to?
touch, pressure, vibration, stretch, noxious stimuli, and temperature
What are receptive fields?
areas of skin innervated by a single afferent neuron
smaller distally and larger proximally
Where are somatosensory peripheral neurons?
Are outside the spinal cord in the dorsal root ganglia (DRG) or brain in the cranial nerve (CN) ganglia
How many axons do peripheral sensory neurons have?
2
distal
proximal
Distal peripheral nerve axons:
Conduct messages from the receptor to the cell body
Proximal peripheral nerve axons
Project from the cell body into the spinal cord or brainstem
A-alpha (Ia and II) axon function receptor type
proprioception
muscle spindle
A beta axon function receptor type
touch
merkel, meissner, pacinian and ruffini
A delta function receptor type
pain, temperature
free nerve endings
C fibers function receptor type
pain, temperature, itch
free nerve endings (unmyelinated)
What does the muscle spindle do?
muscle can feedback information to the CNS on its state of elongation. This is achieved by a special sensory organ at the core of the muscle called
What are the two types of intrafusal fibers?
nuclear bags fibers
nuclear chain fibers
What are nuclear bag fibers?
clumps of nuclei
What are nuclear chain fibers?
nuclei arranged in single file
What are the two different sensory endings?
primary
secondary
Primary endings:
wrap around the central region of each intrafusal fiber.
type Ia neuron
Secondary endings:
end mainly on nuclear chain fibers adjacent to the primary endings
type II afferent
Where are intrafusal fibers contractile?
only at ends; central region cannot contract
What is muscle length singled by?
type Ia and II afferents
What is velocity?
change in muscle length signaled by only type Ia afferents
Information about Golgi Tendon Organs is transmitted to the spinal cord by what fibers?
type Ib
What do mechanoreceptors in and around joints respond to?
mechanical deformation of the capsule and ligaments
Type Ia axon
Quick stretch information from the muscle spindle
Type Ib axon
Tendon or ligament tension
Type II axon
Maintained muscle stretch or joint movement
Type A-beta axon
Touch, vibration, skin stretch, or pressure
Type A-delta or C
Pain, temperature, itch, or tickle
What is a tract?
bundle of axons with the same origin and a common termination
What is high fidelity?
provide accurate details regarding the location of the stimulation
What are the three pathways bringing information to the brain?
Conscious relay
Divergent
Unconscious relay
What do conscious relay pathways do?
Transmit information to many locations in the brainstem and cerebrum and use pathways
How is information transmitted in conscious relay pathways?
high fidelity
make fine distinction about stimuli
What are the two routes pathways to consciousness travel upward in the spinal cord?
dorsal columns
anterolateral tracts
What is discriminative touch?
refers to the localization of touch and vibration and the ability to discriminate between two closely spaced points touching the skin
Pathway of discriminative touch?
DCML
What is conscious proprioception?
awareness of the movements and relative position of body parts
Pathway of conscious proprioception?
DCML
What is stereognosis?
the ability to use touch and proprioceptive information to identify an object
Pathway of sterognosis?
DCML
Primary neuron in pathway for discriminative touch and conscious proprioception?
conveys information from the receptors to the medulla
Secondary neuron in pathway for discriminative touch and conscious proprioception?
conveys information from the medulla to the thalamus
Tertiary neuron in pathway for discriminative touch and conscious proprioception?
conveys information from the thalamus to the cerebral cortex
Primary neurons of DCML include:
Many collateral branches entering the gray matter
Secondary neurons of DCML include:
Cell bodies located in the nucleus gracilis or cuneatus
Axons that cross the midline as the internal arcuate fibers, then ascend to the thalamus
Tertiary neurons of DCML include:
Those that connect the thalamus to the sensory cortex
What does anterolateral tract transmit?
discriminative information about pain, temperature, and course touch
What are heat and cold detected by?
specialized free nerve endings of small myelinated and unmyelinated neurons
What do A-delta fibers carry?
impulses produced by cooling
What do C-fibers carry?
information regarding heat
What is fast pain
(spinothalamic pain) is the initial and immediate sharp sensation that indicates the location of the injury
What is slow pain?
(spinolimbic pain) is the dull, throbbing ache following fast pain that is not well localized
Fast, localized pain, what system?
lateral pain system
Primary neuron in fast pain:
bring information into the dorsal horn of the spinal cord
Secondary neuron in fast pain:
cross the midline and project from the spinal cord to the thalamus.
Tertiary neurons in fast pain:
project from the thalamus to the cerebral cortex
In the anterolateral column, second order neuron:
ascends contralaterlly
cross midline at spinal cord
In the DCML, first order neuron
ascends ipsilaterally
In the DCML, second order neurons
crosses midline at medulla
Slow pain impulses travel:
C fibers which are smaller, unmyelinated axons
How is aching pain transmitted?
via divergent pathways to many locations in the brainstem and cerebrum
medial pain system
Where is the first neuron in the medial pain system?
resides in the dorsal root ganglion and has a small, unmyelinated C fiber
What is the activity of medial pain system?
elicits affective, motivational, withdrawal, arousal, and autonomic responses
What are the three tracts that axon of ascending projection neurons reach the midbrain, reticular formation and limbic areas?
spinomesencephalic
spinoreticular
spinolimbic
What are the two areas of the spinomesencephalic tract in the midbrain that carry noceiceptive information?
periaqueductal gray
superior colliculus
The periaqueductal gray is part of what system?
descending pain control system
What is the reticular formation?
A neural network in the brainstem that includes the reticular nuclei and their connections
What does the reticular formation do?
Modulates arousal, attention, and sleep-waking cycles
What do axons of the spinolimbic tract do?
transmit slow pain information to the medial and intralaminar nuclei in the thalamus
What is the trigeminoreticulolibic pathway?
Slow pain information is transmitted via this pathway from the face
C fibers in trigeminal nerve
What do unconscious relay tracts do?
Transmit information from proprioceptors and information about activity in spinal interneurons.
- relay information critical for adjusting movements
- cerebellum
What is the posterior spinocerebellar pathway?
Transmits information from the legs and the lower half of the body
What is the cuneocerebellar pathway?
Begins with primary afferents from the arm and upper half of the body; the central axons travel via the posterior columns to the lower medulla
What are internal feedback tracts?
Tracts monitor the activity of spinal interneurons and of descending motor signals from the cerebral cortex and brainstem
What are the two types of internal feeback tracts?
anterior spinocerebellar
rostrospinocerebellar
What does the anterior spinocerebellar tract do?
Transmits information from the thoracolumbar spinal cord
What does the rostrospinocerebellar tract do?
Transmits information from the cervical spinal cord to the ipsilateral cerebellum
Where does the information in the spinocerebellar tract come from?
the proprioceptors, spinal interneurons, and descending motor pathways
What does information that does not reach conscious awareness do?
contributes to automatic movements and postural adjustments
