11.4 Flashcards
Somatosensory System Receptors and Pathways
What parts of the body have more sensory receptors?
Areas that are highly sensitive to touch (e.g. hands, feet, lips, tongue)
What is glabrous skin?
Skin that does not have hair follicles but contains larger numbers of sensory receptors than do hairy skin areas (e.g. lips, tongue, palm of hands, feet)
What is nociception?
The perception of pain, temperature, or itch (mostly free nerve endings on nociceptors)
How do nociceptors send information about pain, temp, or itch
By secreting chemicals that stimulate the nerve to produce an action potential
What is hapsis?
The perception of fine touch and pressure; the ability to identify objects by touch
How are haptic receptors activated?
Mechanical stimulation of body hair or capsule of tissue the dendrite is encased in
What is proprioception?
The perception of the location and movement of the body; body awareness
What are the encapsulated nerve endings are proprioceptors sensitive to?
The stretch of muscles and tendons and the movement of joints
What are rapidly adapting receptors?
Body sensory receptors that respond briefly to the onset of a stimulus on the body; they activate neurons when stimulation begins and ends
What kinds of sensory receptors have rapidly adapting receptors?
Haptic receptors and Proprioceptors
What are slowly adapting receptors?
Body sensory receptors that respond as long as a sensory stimulus is on the body; detect whether a stimulus is still occurring
What kinds of sensory receptors have slowly adapting receptors?
Nociceptors and Haptic receptors
What is a posterior root ganglion neuron (PRG)?
A neuron that carries sensory information into the CNS; their dendrite and axon are continuous and the cell body is off to the side
What are the two subtypes of nociceptive neurons and what makes them distinct from each other?
C-fiber (unmyelinated for pain from prolonged stimulation) and A-fiber (sharp pain, myelinated)
What are the axons of proprioception and haptic PRGs like?
Large and well-myelinated for fast transmission
What is deafferentation?
The loss of incoming sensory input due to damage to sensory fibers; loss of afferent input to a structure
What happens to someone who had deafferentation?
They are unable to feel anything physically; but typically only one part of the body (can be all)
What are the two somatosensory pathways to the brain?
The posterior spinothalamic tract and the anterior spinothalamic tract
What kind of information does the posterior spinothalamic tract carry? How do they travel up the spinal cord?
They carry information about haptic and proprioceptive stimuli to the somatosensory cortex. Travel up the spinal cord ipsilaterally and then decussate in the brainstem
What kind of information does the anterior spinothalamic tract carry? How do they travel up the spinal cord?
Carry information about nociceptive stimuli. Travels up the spinal cord contralaterally.
What happens to both spinothalamic pathways once they enter the brain?
They project to the ventrolateral thalamus, join the medial lemniscus, and project to the somatosensory cortex
What happens to somatosensation when there is unilateral damage to the spinal cord?
Unilateral loss of hapsis and proprioception below the point of injury on the ipsilateral side of the body and loss of nociception below the point of injury on the contralateral side of the body.
What is a monosynaptic reflex? What is an example?
A reflex requiring one synapse between sensory input and movement. Happens in the spinal cord
Example is knee jerk
What is the main pain pathway to the brain?
The anterior spinothalamic tract
How is the reticular formation involved in pain perception?
Is handles arousal to deal with pain
How is the amygdala involved in the perception of pain?
It handles associative learning between pain and context (e.g. food poisoning); emotional response to pain
What is the hypothalamus’s role in the perception of pain?
Deals with the hormonal and cardiovascular response. Triggers the release of some hormones to help cope with pain (physical or emotional)
Approximately how many pain fibers are there that carry information to the somatosensory cortex?
8
What is the gate theory of pain?
Haptic-proprioceptive stimulation can reduce pain perception via a “pain gate” in our spinal cord
What is the pain gate?
The hypothetical neural circuit in which activity in fine-touch and pressure pathways diminishes the activity in pain and temperature pathways
How does the interneuron in the pain gate prevent pain signals from going to the brain?
The signals from haptic-proprioceptive receptors trigger the release of endogenous opiates which act as an inhibitor and allows the gate to close.
What happens when the periaqueductal gray matter (PAG) is electrically stimulated?
Pain is suppressed
How do PAG neurons suppress pain?
They excite pathways that project to the spinal cord where they close the pain gate (and endogenous opioid release)
What is periaqueductal gray matter?
Nuclei in the midbrain that surround the cerebral aqueduct joining the third and fourth ventricles; PAG neurons contain circuits for species-typical behaviors and play an important role in the modulation of pain
What is referred pain?
Pain that arises in one of the internal organs but is felt on the surface of the body
What is the only localized part of the somatosensory system?
The vestibular system
What do the semicircular canals do?
Signal changes in the direction and speed of head movements
What are the otolith organs? (2)
The utricle and saccule
What do the utricle and saccule do?
Tell the position of the body in relation to gravity and linear acceleration
What affect does cilia hair in the canals have on the vestibular nerve cells when they bend to the right?
The vestibular nerve has increased activation (on one side, decreased on the other)
What direction is the utricle oriented?
Horizontally
What direction is the saccule oriented?
Vertically
What is vertigo?
The sensation of spinning when one is not moving caused by disfunction of the inner ear
What is peripheral vertigo?
Displacement of otolith or calcium debris located in the posterior semicircular canal (aka: Meniere disease)
What is central vertigo?
Lesions affecting the vestibular nuclei in the brainstem or their projections to the cerebellum; more serious that peripheral vertigo
Body senses contribute to the perception of ________ (touch and pressure), _________ (location and movement), and _________ (pain and itch)
hapsis; proprioception, nociception
Haptic-proprioceptive information is carried into the CNS by the _________ spinothalamic tract; nociceptive information is carried in by the __________ spinothalamic tract
Posterior, anterior
The two tracts interact in the spinal cord to regulate pain perception via a(n) _________
Pain gate
In the midbrain, the _________ suppresses pain by activating neuromodulatory circuits that inhibit pain pathways
Periaqueductal gray matter
The only localized somatosensory system is the ________ system, which help sus maintain __________ by signaling information about the head’s position and our movement through space
Vestibular; balance
Explain how proprioception acts as the “eyes of the body”
Without proprioception, sensory information about body location and movement is lost and can be regained only by using vision
