Lecture 12 Flashcards
Briefly explain how the semicircular canals work in the inner ear.
As the head moves, otoliths in the fluid bend the hair cells, which depolarizes the cells. These hair cells provide input to vestibular nerve cells.
What are the four types of sensory neurons used for somatosensation?
Tactile, Pain, Temperature, and Proprioception
Define tactile.
Response to being touched. Includes Ruffini ending, Meissner’s corpuscle, Pacinian corpuscle. Pacinian corpuscle is the deepest layer.
Define Pain.
Response to noxious stimuli.
Define Temperature.
Response to hot/cold.
Define Proprioception.
Response to position or mechanical movement of the muscle/joint. “Golgi Tendon Organ”
How are somatosensory neurons connected from the skin to brain?
Sensory receptors in the skin travel to the spinal cord (dorsal root ganglion) and then to the brain.
What is a dermatome?
A dermatome is a skin area that provides input to a single sensory nerve
Where does somatosensory information go in the brain and how is it represented? (hint: homunculus)
Somatosensory information is represented in the somatosensory specifically the postcentral gyrus.
Skin areas that are needed for tactile information have a lot more representation in this brain area than others such as the lips or hands.
Briefly describe the phantom limb phenomenon
Phantom limb is when a limb such as the hand is amputated but the area of cortex that represents the hand is still intact.
There are three ways phantom limb sensations can happen:
1. spontaneous activity in the ‘hand’ area of somatosensory cortex
2. stimulation of nerves in the cut wrist
3.the ‘hand’ area can be “taken over” by the ‘face’ area.
Describe the pain reflex arc… does it require the brains input?
Sensory neurons that sense pain send their signals to the spinal cord which in turn sends their signals back to the muscles to contract away from the aversive stimulus. This pain reflex arc does
not involve the brain but signals for pain also go to the brain.
Which neurotransmitter is released in response to pain? What are the post synaptic cells it is released onto? (a picture may be helpful here)
Substance P is the pain neurotransmitter and sensory neurons release substance P onto spinal cord neurons.
What endogenous neurotransmitter inhibits the release of substance P?
The body has its own analgesic process to inhibit pain (gate theory). The endogenous neurotransmitter that inhibits substance P release is the endorphin (endogenous morphine),
Enkephalin. Descending spinal cord neurons from the brain release enkephalin onto the axon terminals of the sensory neurons inhibiting the release of substance P.
If you have endogenous neurotransmitter that limits substance P, why do you still continue to feel pain?
When you are injured and still feel pain it is because prostaglandins and inflammation increase the sensitivity of pain neurons allowing them to still respond.
What is the vestibular system?
It is involved in our sense of balance.
What are the things in each of our inner ears that help with our 3 planes of our body?
3 fluid-filled semicircular canals
How does touch from the skin go to the brain?
-sensory neurons/receptors in skin (whose axons travel together as the “sensory nerve”) -> spinal cord -> brain
Looking at a spinal cord segment, please explain how receptors in your skin go to your brain.
-receptors in the skin travel down the sensory nerve
-sensory nerve coming from your skin goes into the spinal cord
-then project son the center part of the spinal cord (which is called gray matter)
-dorsal root ganglion - the cell body for sensory neurons lives there
-sensory neuron makes a connection to another neuron
-that sends a signal to the brain through the white matter
-which lets you know something is happening !
How does your muscles move?
-motor cortex from the brain
sends a signal down the spinal cord to the gray matter
-then provides input to a motor neuron,
-which is going to send an output through the motor nerve to a muscle to move a body part
How many segments does the spinal cord have?
31
What are the two requirements for this phantom limb phenomenon?
1) the area of cortex that originally received input from the lost body part is still intact
2) activity in that area still “represents” that part of body
How does the pain reflex arc work?
-you touched something noxious
-sends a signal through the pain sensory nerves into the spinal cord
-spinal cord neurons immediately project onto an interneurons
-interneuron sends a signal directly a motor neuron
-which makes your muscle automatically pull away
-no brain need but there’s some neurons send signals to the brain
-if you had a spinal cord injury at T4, you still have a knee jerk reflex
What are the 3 levels of pain?
1) sensation of pain (mediated by sensory neurons)
2) perception (emotion) of pain (unpleasant vs. neutral vs. pleasant)
3) response to pain
What is the Gate Theory [of pain]?
It’s a mechanism that inhibits pain
-The pain afferent comes into the spinal cord
-(spinal cord neurons tells there’s pain)
-another neuron releases endorphins (one type is called enkephalin)
-enkephalin neuron releases endorphins, and attaches to endorphin receptors on axon terminals of pain afferents, which inhibits or limits release of Substance P
-mediated by descending projections from the brain to the spinal cord
What causes pain to last?
-injury produces Prostaglandins (PG) and Inflammation (part of the healing/clotting processes)
-Prostaglandins (PG) and Inflammation increase the sensitivity of pain sensory neurons, allowing them to continue to respond
What are the two places of drug action?
) Works directly at the site of injury
2) Works on the pain “signal” in the nervous system
