Module B Flashcards
1
Q
What are the common features of somatosensory receptors that sense the environment?
A
Contains 3 neurons - Primary afferent , secondary afferent and tertiary afferent
Decussation and include a thalamic nucleus
2
Q
What are the 3 neurons in somatosensory pathways?
A
Primary afferent - psuedounipolar neuron with a peripheral axon that innervates on receptor and a central process that synapses with a secondary neurons
Secondary neurons - synapse with a tertiary neuron in the thalamus
Tertiary - synapses with neurons in the cerebral cortex
3
Q
Describe decussation
A
Can occur in the spinal cord or brain stem. Allows better separation of tracts - decussated arrangement one more robust against wiring errors than simpler same-sided wiring schemes.
4
Q
Describe a mechanoreceptor
A
Sensory receptor that responds to mechanical pressure or distortion leads to pressure sensitive action potential.The different types for them allow for perception of different sensation and sensitivity. Can either be capsulated or incapsulated.
5
Q
Which cells are the only mechanorecptors in the skin?
A
Merkel cells
6
Q
What are free nerve endings for?
A
Touch pressure and stretching
7
Q
What are Ruffini corpuscles?
A
detect tension deep in the skin
8
Q
What are merkel cells and tactile discs?
A
detect sustained touch and pressure sensitive to fine touch
9
Q
What areTactile corpuscles?
A
Detect light touch movement, vibration and changes in intensity
10
Q
What are lamellated corpuscles?
A
Detect deep pressure. most sensitive to rapid vibration
11
Q
Describe slow adaptation of somatosensory receptors
A
Produced sustained response to stat stimulation. slow to return to normal firing - tonic
Useful for detecting touch and pressure
12
Q
Describe rapid adaptation of somatosensory receptors
A
Produce transient response. quick to return to normal firing - Phasic
Using for sensing such things as texture and vibration
13
Q
What is a receptive field?
A
Areas that need an accurate taction (sense of touch) have mechanoreceptors with small accurate receptive fields e.g. fingertips have merkel cells and tactile corpuscles. This leads to 2 point discrimination
14
Q
What is proprorecption
A
has both conscious (awareness of body position, control of voluntary movement) and unconscious (righting reflex) components In order to control movement the neurons system must receive continuous feedback from muscles/joints and there are nerve endings to control this.
15
Q
What is a golgi tendon organ?
A
A proprioreceptor that monitors tension pressure/joint movement
16
Q
What is neuromuscluar spindle?
A
Detect rate and size of changes in length of the muscle. Generate supra spinal responses to control muscle contraction and spinal reflexes
17
Q
What are nocioreceptors?
A
Free nerve endings in large receptive fields. Pain is sensed by a number of parts of the brain.
Sensory discriminative allows detection of location and intensity and quality of pain. Receptors have small sensory field. Affective motivational - the fear, anxiety associated with pain
18
Q
what types of nerve fibres are mechanoreceptors innervated by?
A
Abeta and Aomega
19
Q
What types of nerve fibres are proprireceptors inenrvated by?
A
Aalpha and Abeta
20
Q
What are the best myelinated receptors?
A
proprioreceptors
21
Q
What is a dermatome?
A
Primary afferent collect to forma a posterior root to enter the cord. The area innervated by a single posterior root is the sum of the receptor fields of the primary afferents.
22
Q
What is sensory modality segregation of somatosensory tracts?
A
Fibres are arranged according to information carried
23
Q
What is the somatotopic arrangement segregation of somatosensory tracts?
A
Fibres are arranged according to the site of origin
24
Q
What is the medial-lateral segragation of somatosensory tracts?
A
Inferior nerves travel more medially
25
What do the neurons of the dorsal column-medial lemniscus tract do?
first order - axons enter spinal cord through dorsal root and ascend fasiculus gracialsis (below T6) or cuneatus (above T6)
Second order - From the nuclei grascilis and cuneatus, axons travel up medial lemniscus to synaps in thalamus (VPL)
Third order neurons - Axons carry info to the primary sensory cortex
26
What do the neurons of the spinothalamic tracts do?
first order neurons - axons enter spinal cord the dorsal root and synapses in the dorsal horn
Second order neurons - Cross to the opposite side of the cord and ascend the appropriate spinothalamic tract to the thalamus
Third order - axons carry info to primary sensory cortex
27
What is the purpose of the spinocerebellar tract?
Conveys unconscious proprioreceptive information to the cerebellum. Important to central muscle contraction for movement. Posterior tract - carries info from lower limb and body. Anterior tract - integrates proprioreceptor information with descending inputs.
28
What are the neurons in the spinocerebellar tract?
First order neurons - Axons enter spinal cord though dorsal root and synapse in the dorsal horn
Second order neurons - post spinocerebellar tract afferents synapse in Clarkes nucleus then ascend to the cerebellum via the inferior cerebrall peduncle
Anterior spinocerebellar tract. Primary afferents synapse with the spinal border cells, decussate then travel to cerebellum via the superior cerebellar peduncle.
29
What do spinal border cells do?
Integrate information from lower limb, descending inputs and form reflexes
30
Is vision trivariant or bivariant?
Trivariant
31
which cones sense red?
long wave length (L) peak at 565nm
32
Which cones sense blue?
short wavelength (S) peak at 440nm
33
Which cones sense green?
Middle wavelength (M) peak at 545
34
Rods
night vision only. Low light threshold. do not detect colour
35
Cones
day vision, colour vision, cone photoreceptors, higher threshold to light. Only activated if rods are saturated
36
What is hue?
related to wavelength or dominant wave length
37
What is value?
reflectance and luminosity
38
What is chroma?
The saturation of the signal
39
What is the trichromatic theory?
The theory by Thomas Young and Hemholtz that a combination of three channels describes colour discriminate functions
40
What is the opponent colour theory?
a theory by Hering that says there are three channels red-green, blue-yellow and black-white. that respond in an antagonist way so theres never a greenish red.
41
What is stage theory?
modern model of normal vision that has two stages.
The receptor stage consists of the three photopigments.
the neural processing stages where colour opponency occurs. This is at a post receptoral level and occurs as early as the horizontal cell in the retina.
42
What is the other name for colour blindness?
Dichromacy
43
What are the forms of colour blindness?
protanopia - less sensitive to red
deuteranopia - less sensitive to green
monochromats
44
What is the Farnsworth panel?
The colour blindness test where you rearrange the colours
45
What is the ishihara test?
The colour blindness test where you look for the coloured number in the coloured dots
46
What is involved in the visual part of the where stream?
Location, movement, spatial, transformations, spatial relations
47
What is involved in the visual part of the what stream?
colour, texture, pictorial detail, shape, size
48
what is the visual field?
The portion of the surroundings that can be seen at one time. The total visual field is the sum of the left and right hemifields. So the left hemisphere recives infor about the right hemifields from both eyes
49
Visual field defects
visual field defects can occur at any part of the visual pathway. The placemetn of the lesions changes what can be seen depending on which hemifields are taken out by the lesion
50
Describe the four areas in the brain that the retina projects to
Lateral geniculate nucleus - in the thalamus, the major subcortical area relaying visual info to the primary visual cortex
Superior colliculus - of the midbrain which controls eye orientating movement
Suprachiasmatic nucleus - hypothalamus which regulates circadian rhythms
The pretectum - of the midbrain which controls the pupillary light reflex
51
How is a signal transmitted through the retina?
The electromagnetic signal is transformed into chemical and electrical signals.
A spikeless mode where membrane potential and synaptic transmission are continuous and graded (which is why vision is not all or nothing).
Under most ambient conditions most graded potential retinal neurons operate near the midpoint of their response range, so they are capable of signalling increases and decreases.
52
What factors effect out recognition of of an image in our visual field?
Background illumination (contrast)
Spatial frequency (how rapid the stimulus change across space)
Wavelength (detection by photoreceptors)
Dark adaptation (rods and cones recovery function)
Processing of information by the retina (pathways that deal with simple components such as shapes colours borders )
53
how does processing in the retina happen?
At least a dozen different representations of the visual world, each embodied at a separate sub layer of the inner plexiform layer and carried by a separate class of ganglion
54
what is the ratio of cones to rods
1:20 so there is a higher threshold to light
55
what is the sensitivity of phototopic vision to light
luminance level is about 0.03cd/m2 where the cone mechanism mediates vision
56
what is the sensitivity of scotopic vision to light
its the level below which the rod mechanism is active
57
What is the mesopic range?
combination of rods and cones
58
What are center surround receptive fields of ganglion cells?
130 million photo receptors but only 1.2 million axons of ganglion cells.
There is a center cone with some surrounding cones that are joined to the center cone by horizontal cells. These transmit to a on center bipolar cell which transmits to a on center ganglion cell.
59
What do large ganglion cells do?
they have open radiate patterns
they process fast transient impulse trains and are concerned with motion detection and alerting the animal to threatening , moving visual imagery
60
What do small ganglion cells do?
Bushy cells
| concerned with processing small stationary fine detail in tonically activated messages
61
What are the 5 different classes of ganglion
Midget cells (P cells)
Parasol cells (M cells)
Bi-stratified cells (koniocellular cells)
Melasnopsin (photosensitive cells)
62
What are the properties of type P ganglion cells?
they are color sensitive
They outnumber the M ganglion cells by approximately 100:1
A small concentric receptive field produces a sustained, slowly adapting response thats lasts as long as a stimulus os centered on its receptive field.
Produces a weak response to stimuli that move across its receptive field
Signals the presence colour and duration of a visual stimulus
63
What are the properties of type M ganglion cells?
Motion detectors
Much larger than P ganglion cells
insensitive to color
large concentric receptive field more sensitive to small center surround brightness differences
responds with a transient rapidly adapting response to a maintained stimulus
responds maximally to stimuli moving across its receptive field
signals temporal variations in movement of a stimulus
64
What are starburst amacrine cells?
candidate regulators of directional selectivity ganglion cells.
release GABA and ACh
regulate directional selectivity ganglion cells in response to centrifugal movement
65
What are directional selectivity ganglions?
act as a local motion detectors for a bright stimulus moving in one direction are different from DSGCs detecting stimuli moving in opposite direction
On/Off DSGCs can be divided into 4 types differing in their directional preference. Ventral, Dorsal, nasal of Temporal.
The receptive fields are fairly large, sensitive to small changes, and direction-selective ganglion cells are located throughout the retina
66
What is S1?
somatosensory cortex 1. A mojor site of termination of axons from the thalamus.
67
What are the 4 areas of S!?
Brodmans area 3a, 3b, 1 ,2
68
What does Brodmans area 3a receive?
proprioreceptors
69
What does brodmans area 1 and 3b receive?
cutaneous stimuli
70
what does brodmans area 2 receive?
both cutaneous and proprioreceptors
71
What is S2 and what does it do?
the secondary somatosensory cortex. Sends projections to S1, association cortex, motor cortex, amygdala and hippocampus (tactile learning and memory)
72
What is the somatosensory association cortex?
involved in higher order processing. e.g. object recognition.
Receives input from visual areas
Projects to motor cortices to initiate voluntary movement
73
What is synatpic plasticity?
Changes in cortical representation occur following injury or due to experience
Can be rapid - transient due to unmasking of connections or upregulation of synaptic efficacy. The cortical map will return to normal if not continued
74
What happens during structural plasticity
over time stable enlargement of the cortical represntation can occur
75
Why does the cortical field not change normally?
under normal conditions neuronal inhibition keeps functional areas distinct. When injury occurs inhibition is lost and area can spread very quickly
synaptic strengthening due to use-dependent changes take longer
76
How does cortical changes reflect subcortical modifications?
under normal conditions distribution of input is very ordered. loss of inputs allows sprouting of other axons.
Areas of coretex formally activated via the hand now activated by the arm. Stimulation still percieved as hand - Phantom sensation
77
How does cortical plasticity occur with learning?
Braille readers need to extract very detailed information from fingertips. Followig training you get enlargement of cortical representation of the reading finger
78
What is cross modal plasticity?
deafferented area is recruited for higly demanding task
79
What is peripheral nerve injury?
loss of somatosensory sensations of areas innervated by the peripheral nerve. leads to tingling, numbness or pain. Can affect different fibrers in the nerve.
80
What can periperhal nerve injury be due to?
axon dieback
demyelination
nerve cell death
81
what is mononeuropathy?
affects only a single nerve.
| caused by trauma, infection loss of blood supply or compression
82
What is posterior cord syndrome?
Damage to the posterior portion of the spinal cord and/or interruption to the posterior spinal artery.
Causes the loss of proprioreception and sense of fine touch and sense of pain remain intact.
83
What is anterior cord syndrome?
below the level of injury crude touch, pressure, pain and temperature and motor function are lost.
Fine touch, proprioreception and sense of vibration remian intact.
causes damage to the anterior portion of the spinal cord and/or the blood supply from the anterior spinal artery.
84
What is brown-sequard syndrome?
(hemisection)
on the ipsilateral side of the injury, there is a loss of proprioreception, vibration and light touch.
Contralaterally, there is a loss of pain, temperature, pressure and crude touch sensations
85
What is central cord syndrome?
causes the loss of proprioreception and sense of vibration below the level of injury.
motor impairment in the arms and hands and the legs - inverse paraplegia
Corticospinal fibres destined for the legs are spared due to their more external location in the spinal cord
86
What happens when there is injury to the thalamus?
usually due to stroke.
Damage to VPN will lead to loss of all somatosensory modalities - as thalamic aras are small more than one area is usually effected
87
What happens when there is damage to the primary somatosensory cortex?
loss of vibration, proprioreception, and discriminative touch
reduction in crude touch, temperature and pain sensation
- S1 neurons have small receptive fields so lose ability to accurately localise pain
88
What is hemineglect?
a deficit in attention to and awareness of contralateral side of the body.
89
What is Agraphesthesia?
inability to recognize orientation of cutaneous sensation
90
What is somatosensory agnosia?
inability to identify an object without visual input
91
What is memory?
The encoding, storage and retrieval of learned information
92
What is declarative memory?
Avaliable to consciousness and can be expressed by language i.e declared
93
What is non-declarative (procedural) memory?
Involve skills and associations that are acquired and retrieved at an unconscious level
94
What is immediate memory?
The ability to hold ongoing experiences for a fraction of a second, large capacity, each sensory modality had its own memory register.
95
What is working memory?
Ability to hold information in the mind for seconds to minutes while it is used to achieve a certain goal, limited in duration and capacity
96
What is long term memory?
retained for day, lifetime etc. Immediate or working memory can enter long term memory by conscious of unconscious rehearsal
97
What is an Engram?
A physical embodiment of memory in the neuronal machinery which depends on changes in synaptic connections and or growth/reordering of these connections
98
Why do we forget?
It is important that we don't retain everything. some patients such as patient S could never forget anything. could not distinguish important information from trivial information
99
What is retrograde amnesia?
where they forget what happened before the trauma and some of their life before (The Vow). particularly anterior hippocampus
100
What is anterograde amnesia?
Where they can remember up to the incident but not remember what has happened since (50 first dates). Particularly C1 area of the hippocampus
101
Which lesions have more effect on declarative memory consolidation radial arm and spatial maze learning ? Hippocampal or Perirhinal?
Hippocampal. Perirhinal has less effect.
102
Which lesions have more effect n delayed matching and non matching to sample?
Perirhinal
103
What is conditioned learning?
generation of a novel response that arises from pairing a novel stimulus with the stimulus that generates the response being studied
104
What is classical conditioning?
innate reflex is modified by associating its normal triggering stimulus with an unrelated stimulus (palovs dog)
105
What is operant conditioning?
alter probability of a response by associating it with reward/punishment. (skinners box)
106
What is phylogenetic memory?
memories stored in the genes. arise from the experience of a species over eras. Established by natural selection acting on neural development
107
What are the three classes of movement?
Voluntary (forebrain)
Reflexes -somatic (brainstem/spinal cord)
Rhythmic motor patterns - breathing etc (brainstem/spinal cord)
108
What is an alpha motor neuron?
innervates extrafusal muscle fibres: directly responsible for generation of force by muscles
109
What are gamma motor neurons?
innervate intrafusal muscle fibres: responsible for controlling the excitability of stretch receptors in muscle spindles.
110
What are the sources of synaptic inputs to alpha motoneurons?
Descending tract - e.g corticospinal tract. and reticulo-spinal tract which originates in the reticular formation of the brainstem
Segmental interneurons (such as renshaw cells, 1a and 1b inhibitory neurons)
Propriospinal neurons (spinal neurons with ascending and or descending axons, have a role in co ordination of movements between the upper and lower limbs)
Muscle receptors (1a afferents from the muscle spindles)
111
What are the three classes of movement?
Voluntary (forebrain)
Reflexes -somatic (brainstem/spinal cord)
Rhythmic motor patterns - breathing etc (brainstem/spinal cord)
112
What is an alpha motor neuron?
innervates extrafusal muscle fibres: directly responsible for generation of force by muscles
113
What are gamma motor neurons?
innervate intrafusal muscle fibres: responsible for controlling the excitability of stretch receptors in muscle spindles.
114
What are the sources of synaptic inputs to alpha motoneurons?
Descending tract - e.g corticospinal tract. and reticulo-spinal tract which originates in the reticular formation of the brainstem
Segmental interneurons (such as renshaw cells, 1a and 1b inhibitory neurons)
Propriospinal neurons (spinal neurons with ascending and or descending axons, have a role in co ordination of movements between the upper and lower limbs)
Muscle receptors (1a afferents from the muscle spindles)
115
What is a motor unit?
the functional and anatomical elements of the motor system
116
What are the components of a motor unit?
cell body of an alpha motoneuron
axon with all its branches
all neuromuscular junctions (synapses) formed by this motoneuron
All muscle fibres (extrafusal) innervated by this motoneuron
117
What are the properties of S type fibres (type 1)
```
make up a lot of the muscle
few axon terminals
slow speed of contraction
little fatigue
aerobic metabolism
rich supply of capillaries
small red muscle fibres
early recruitment
high density mitochondria
```
118
What are the properties of FF type fibres (type 2b)
```
few
many axon terminals
fast speed of contraction
rapid fatigue
anaerobic
few capillaries
large and pale
late recruitment
low density mitochondria
```
119
Which muscle fibres are recruited during weak muscle contraction?
S type (type 1)
120
Whaich fibres fire always except during REM?
S type
121
Which fibres are best suited to carrying small sustained loads?
S type
122
Can weak or strong contractions be graded with greater precision?
weak
123
What is frequency coding?
increase frequency of APs into the muscle which leads to an increase in force
124
What is recruitment?
recruitment of additional alpha motoneurons
125
What is neuromuscluar matchmaking?
Properties of muscle fibres are determined by an alpha motoneuron as first demonstrated by the cross-innervation experiment. conducted by J Eccles.
126
What is a twitch?
A single contraction of all fibers belonging to a motor unit. If the frequency of twitches increases then it causes sustained contraction
127
What are the five elements of spinal reflex?
```
Receptors
Afferent (sensory fibres)
Synaptic relay
Efferent (motor) fibre making synaptic contacts with muscles (or glands)
Effectors (muscles or glands)
```
128
What are the roles of receptors in control of movement?
To move a part of the body you must first have information about the current position of that part of the body and the length of the muscle that controls it
Necessary to continuous info about the state of teh muscle, the velocity with which its relationship to the target is changing
can not only affect existing movements initiated voluntary
129
What are major receptors of reflexes?
Muscle spindles
Golgi tendon organs
Nocioceptive pain receptors
joint receptors
130
Describe msucle spindles
not present in the diaphragm or facial muscles
Located in parallel to the extrafusal muscle fibres. Monitor muscle length and speed of length changes Innervate 1a afferents. group 2 afferents and axons of gamma motoneurons
131
Describe Golgi tendon organs
in series with extrafusal muscle fibres: monitor muscle tension
innervate 1b afferents
132
Describe Nociceptive (pain) receptors
in the skin
Evoke a flexor (withdrawl reflex and a crossed extensor reflex
innervate group 3 and 4 afferents
133
Waht is the stretch tendon reflex?
myotactic
Evoked from muscle spindles by a stretch, vibration or passive extension of the msucles (not golgi tendon organ)
it is the only monosynaptic reflex in our body
134
What are the components of the stretch reflex?
receptors - annulospiral endings in muscle spindles
afferents - 1a. the fastest nerve fibers ~ 100m/s
synaptic connections - glutamatergic excitatory synapses on alpha motoneurons. They also make synapses with 1a inhibaotry neurons which send info about the length of the muscles to the cerebellar cortex
efferents - axons of alpha motoneurons
135
What causes latency of the knee jerk reflex?
- Delay from the onset of stretch to the first AP
- conduction time in the afferent pathway
- synaptic delay in the spinal cord
- conduction time in the efferent pathway
- synaptic delay in the neuromuscular junction
- spread of an action potential along the muscle fibres
- time for the excitation contraction coupling
136
What is reciprocal inhibition?
When there is a reflex and a muscle is contracted, the antagonistic muscle is relaxed by inhibition to make it easier to contract the other muscle
abductor and adductors are not reciprocal
137
What is the inverse myotactic reflex?
This reflex plays a role in adjusting tension in muscles during a motor task. This is invoked through the inhibition of the tone in the msucle whose tendon has been stretched (homonymous muscle) and excitation of the motoneurons to antagonistic muscles
it also protects muscles from overloading and compensation for the muscle fatigue.
138
What is the clasp knife reflex?
evoked by attempting to stretch muscle during a strong isometric contraction
139
What is the flexion/withdrawal reflex?
fast withdrawal from pain
receptors - nociceptors
afferents - type 3 and 4 (c fibers) slow conducting
synaptic relays - to excitatory neurons which excite an alpha motoneuron controlling the flexors. Also activate inhibitory interneurons which inhibit MNs to extensors
efferents - axons of alpha MNs
effectors - muscles (flexors)
