CNS 6 (Oct 10) Flashcards
1
Q
What is the cochlear duct?
A
-membrane tube floating on inside of the channel (membranous labyrinth) -floats in perilymph -filled with endolymph
2
Q
A
3
Q
What is the scala vestibuli?
A
-part of bony labyrinth that is directly associated with the oval window between the bone and membranous labyrinth
4
Q
What is the scala tympani?
A
- extension of tube around the apex to the other side
- ends in the round window which relieves pressure of vibrations created by stapes on tympanic membrane
5
Q
How do vibrations move through the inner ear?
A
- vibrations move into scala vestibuli from oval windown
- they vibrate the membranous labyrinth at the vestibular membrane
- inside of cochlear duct now has vibrations which are transduced over the top of the sensory cells on the tectorial membrane
- this causes cilia on cells of cochlea to detect vibrations and depolarizes the cell turning them into an AP conducted out CNVIII
- vibrations are dampened by connective tissue called basilar membrane
- tissue in basilar membrane has various lengths so degree of dampening occurs with different frequencies
6
Q
Describe the lengths of the collagen fibres in the basilar membrane of the cochlear duct
A
- length of collagen fibres are short near the base where the window is located
- get much longer towards the apex
- frequency is tuned by the length of the fibres
- proximal part of cochlea detects high frequency sounds, part at apex detects low frequency sounds
- amplitude is detected by all of the hair cells
7
Q
Which frequency detectors are most affected by damaging loud noise?
A
- near the beginning of cochlear duct
- high frequency sounds
- first frequency that will drop out is high frequency/treble sounds
8
Q
Describe the pathway of information from the Organ of Corti to the brain
A
- Information comes from Organ of Corti into cochlear nucleus of the medulla then to superior olive and trapezoid body; brain is looking at sounds coming from left and right ear (stereo localization of sounds)
- Synapses in lateral lemniscus nucleus in the pons; interacting with the muscles responsible for moving your head (head automatically orients to loud sound- startle reflex)
- Moves into inferior colliculus; ocular coordination (visual-auditory reflexes). eg truck honking at you when you are walking across the street not paying attention- superior will pick up the truck coming at you and inferior will integrate sound of the horn
- Moves into medial geniculate nucleus; selective attention of sounds (filters out self-generated sound)
- Gets relayed to primary auditory cortex in lateral fissure; tonographic map inside brain of the frequencies (base tones are at edge of temporal lobe, high tones located towards the inside near insular cortex)
- BV affecting lateral cortex would give you deafness to base tones. BV affecting medial cortex you would have difficulty with high tones
9
Q
What is conduction deafness?
A
- outer and middle ear
- something gets into ear, wax buildup, damage to tympanic membrane, as you age arthritis can happen in synovial joints of osscicles
- reduction in sound amplitude
- sound of blood rushing in carotid because not as much sound is coming in the external ear so you hear more internal sounds
10
Q
What is sensory deafness?
A
- inner ear and CNVIII
- neuropathology: what the brain expects is a signal from peripheral systems, when they don’t get the signal from auditory nerve your brain makes it up; probably due to damage of the hair cells (tinnitis)
- BVs breaking forming an infarct, trauma to temporal bone of skull, exposure to prolonged noise, high pressure within endolymph system (Meniere’s disease)
11
Q
Where does spinal cord begin?
A
- as soon as you cross the foramen magnum and all the way down
- turns into brainstem when you go through the foramen magnum (upwards)
12
Q
Where do CNS and PNS divide?
A
- inside intervertebral foramen is the CNS
- outside is the PNS
- little bit of overlap here
13
Q
What happens to meninges as spinal nerves extend to become PNS?
A
- spinal nerves covered by dura
- at intervertebral foramen, dura fuses around periosteum of bone around intervertebral foramen
- peripheral nerves comes out covered with connective tissue called epineurium (dense irregular connective tissue)
14
Q
What is a spinal nerve composed of? Are all axons in spinal nerves myelinated?
A
- sensory
- motor
- postganglionic sympathetic
- some axons in bundles of spinal nerves are unmyelinated
- axons carrying pain and temperature are unmyelinated, motor/touch/pressure/proprioception are myelinated
15
Q
What does the spinal cord do?
A
- processes sensory input and motor output; sensory info can come in through dorsal sensory root of nerve, interacts with grey matter of spinal cord, then can create a motor output through the ventral root which is a reflex
- relays sensory information to the cortex and helps relay motor information to the PNS; ascending sensory tracts and descending motor tracts (upper motor neuron which then synapses with the lower motor neuron which contributes to mixed spinal nerves)
16
Q
What is the cauda equina?
A
- spinal cord is shorter than the vertebral column
- spinal cord ends at L2
- nerve roots have to extend down to exit through the correct intervertebral foramen
17
Q
Why are cervical and lumbar sections of spinal cord thicker?
A
- cervical region has brachial plexus (C5-T1) which provides motor and sensory to upper limbs
- lumbar region has lumbosacral plexus (L2-S4) which provides motor and sensory to lower limbs
18
Q
What are the general regions of dermatomal map?
A
- head/upper part of shoulder/forearm/hand: cervical
- underside of arm/back/trunk: thoracic
- hips and around back/halfway down butt/anterior part of leg: lumbar
- posterior portion of leg and butt: sacral
21
Q
Where is the lateral horn?
A
- in thoracic region of the spine
- few neurons in sensory and motor horns
- preganglionic sympathetic fibres located here which join mixed spinal nerve to innervate sphincters of BVs, arrector pili muscles
22
Q
How does white matter and grey matter change from top to bottom of spinal cord?
A
- white matter tracts are larger at top of spinal cord and become smaller as you descend (corticospinal tract starts off large but as it gives off to areas down the spinal cord it gets much smaller)
- grey matter is larger in areas innervating the limbs
23
Q
What neurons are found in cervical region of spine?
A
-more neurons for upper limbs
24
Q
What neurons are found in lumbar and sacral regions of spinal cord?
A
- neurons for lower limbs
- many more grey matter neurons receiving information into dorsal horn and ventral horn giving rise to fine control of motor movement
25
Q
How does dorsal column tract change moving up the spinal cord?
A
- begins small
- as you add in input from lower limbs, upper limbs, etc. the tract becomes larger
28
Q
What makes up the dorsal spinal columns?
A
-fasciculus gracilis and fasciculus cuneatus
30
Q
What happens when touch, pressure, proprioception, pain, and temperature information enters the spinal cord?
A
- touch, pressure, and proprioception go through dorsal columns
- pain and temperature cross over and go through the lateral spinothalamic tract
35
Q
How does touch and pressure information get to cortex?
A
- comes in through dorsal horn of the spinal cord
- goes up the columns (depending if it’s coming from upper or lower limb)
- synapses in medulla at cuneate/gracile nucleus then crosses over
- travels through medial lemniscus to the thalamus
- goes through internal capsule to the post central gyrus
- sensations coming from lower limb (gracile) go to medial aspect of postcentral gyrus while sensations from upper limb (cuneate) go to lateral aspect
36
Q
How does proprioceptive information get to the cortex and cerebellum?
A
- information from muscle spindles and Golgi tendon organs comes in through dorsal columns
- synapses in medulla at gracile/cuneate nucleus then travels to thalamus through medial lemniscus
- goes through internal capsule to postcentral gyrus
- more proprioception goes into cerebellum than you are consciously aware of; axons come off of gracile/cuneate nucleus and augmented through special proprioceptive pathway for unconscious proprioception (dorsal spinocerebellar tract) which move through inferior cerebellar peduncle to spinocerebellum
37
Q
How does pain and temperature get to the cortex?
A
- free nerve endings in the skin (pain and temp) and muscles (pain) are unmyelinated so slow moving
- come into dorsal horn where they synapse and cross over to lateral spinothalamic tract
- go through medullary reticular formation, pontine reticular formation, periaqueductal grey matter, and into thalamus
- on way to the thalamus, axon collaterals are given off in spinal cord up and down which is why it’s difficult to precisely indicate where a painful stimulus is coming from
- goes from thalamus through internal capsule to postcentral gyrus
38
Q
What is the emotional response to pain?
A
- the thalamus projects to the temporal lobe in addition to the cortex
- the limbic system is in the temporal lobe
- you remember not to expose yourself to a painful stimulus anymore
- creates upsetting environment because of its impact on amygdala
- might get a sympathetic response because amygdala projects to the hypothalamus
39
Q
What is spinal cord “gate” control of pain?
A
- unmyelinated pain/temp axons create a time difference between inputs of pain/temp and touch/pressure/proprioception
- spinal cord looks at the time difference and activates the following:
- When pain fibres come in dorsal horn, they cross over to opposite side and go to brain through spinothalamic tract. If you rub the painful area, you activate the mechanoreceptors which are much faster and activate an inhibitory neuron that silences the neuron going up spinothalamic tract. Quantitative senses of touch, pressure, proprioception then dominate and they are relayed to dorsal columns through the brain. Mechanism by which chiropractors etc. practice
40
Q
What is central control of pain (RAS)?
A
- axons of pain system give off collaterals to the reticular formation
- reticular formation has descending reticular pathway which uses enkephalins and endorphins to activate opiate receptor on dorsal horn neurons
