The Motor System (Lecture 7) Flashcards
1
Q
muscle contraction
A
- produced by motor neuron excitation
- basis of all movement
2
Q
Motor Neuron Cell bodies
A
- located in ventral horn of spinal cord
- send axons via the ventral root to innervate muscle fibers
3
Q
nerve
A
ventral root + dorsal root
4
Q
flexion
A
- muscle contraction
- shortening of a limb
5
Q
extension
A
- muslce contraction
- lengthening of limb
6
Q
How do muscles generate force?
A
contraction
7
Q
Types of Muscles
A
-flexors and extensors
8
Q
Synergistic Muscles
A
muscles in which contraction produced the same movement
9
Q
antagonistic Muscles
A
muscles with opposite functions
10
Q
Neuromuscular Junction
A
- motor neuron releases ACh on muscle
- ACh activates nicotinic Ach receptors (opens Na+/K= channel
11
Q
Depolarization leads to……
A
Muscle contraction
12
Q
The Nervous system controls muscle contraction by:
A
- vary the firing rate of motor neurons
- increased number of motor neurons firing on synergistic motor units
13
Q
Muscle Spindles
A
- proprioceptors deep within most skeletal muscles that provide information about muscle length
- sensory axons are wrapped around spindle
- enter dorsal root and form excitatory synapses on interneurons and motor neurons
14
Q
Sensory axon
A
- wraps around spindle
- enter dorsal root and form excitatory synapses on internuerons and motor neurons
15
Q
Mechanosensitive ion channels
A
-open and depolarize sensory axons when muscle is stretched
16
Q
Sensory axon Excitation follow the excitation of….
A
motor neurons in the spinal chord
17
Q
Monosynaptic Reflex Steps
A
- Knee jerk or patellar reflex
- tapping tendon stretches quad
- muscle spindle senses stretch
- sensory afferents activated
- motor neuron activated
- muscle contracted
18
Q
Muscle State when No beverage is in glass
A
Muscle contracts enough to hold up the glass
19
Q
Muscle State when beverage being poured into glass
A
-as beverage content increases weight of glass increases and muscle is stretched
20
Q
Role of Muscle Spindle when Muscle is being stretched (from the increasing weight of a beverage in a glass)
A
- sends message to spinal cord
- synapses on and excites motor neurons
- causes more muscle contraction to support extra weight
21
Q
Somatosensory Afferents
A
primary sensory neurons branch
- axons go through
1. dorsal colum up to brain
2. to interneurons in the spinal cord (gray matter) = important for reflexes
22
Q
Reciprocal Innervation
A
-sensory afferents also synaps on inhibitory interneurons that connect to antagonistic motor neurons
-activation of muscle spindle leads to inhibition of antagonistic muscles
-prevents opposing muscles working against each other
37***
23
Q
location of pain and temperature cell bodies
A
- dorsal root ganglion
- axons enter the spinal cord through the dorsal root
24
Q
pain afferents divide into 2 branches
A
- travel a bit up and down spinal cord in Zone of Lissauer
2. Synapses, decussates and travels up the spinothalamic tract to S1
25
Withdrawl Reflex
- withdrwl of a limb from a painful stimulus
- polysynaptic
- pain afferents travel (up/down) in Zone of Lissauer = coordinate muscle contraction
- stimulate excitatory interneurons
- interneurons excite motor neurons
- muscles contract to withdrawal limb from painful stimulus
26
Motor Programs Theory
-sensorimotor system is programmed with patterns of activity = complex movements are produced by activating conbinations of these programs
27
Nacho Example for Motor Programs Theory
1. Assocation cortex takes in the delicious site and smell of nachos and decides it is time to eat
2. high level cortical programs activated (secondary motor cortex)
3. lover level programs (brainstem) activated for reaching/putting chip into mouth
Brainstem programs activate spinal programs that control our muscles to complete the objective
28
Role of Brainstem programs
-activate spinal programs that control your muscles to complete objective
29
Activated programs continue
- once programs at each level are able to run without direct control from higher cortical levels
- YOU CAN EAT NACHOS WITHOUT EVEN THINKING ABOUT IT
30
motor equivalence
-same basic movement can be carried out in different ways using different muscles (e.g. you can eat nachos with your feet)
31
sensory information can be out of consciousness
-you may not have to consciously consider aroma of a food and just reach out and grab one
32
Practice can create motor programs
- you can learn to quickly and accurately toss a nacho into the air and carch it in your mouth
- motor programs can also develop without practice (you were born eating nachos)
33
The Motor System organization
-hierarchially
34
Motor output guided by....
Sensory input
35
What changes the nature and location of motor control?
Learning
36
Motor Association Cortex
Where movements begin
- posterior parietal
- dorsolateral prefrontal
37
Posterior Parietal Association Cortex
- receives info from the visual. auditory, and somatosensory areas
- determines position of body relative to objects it will interact with
- provides spatial information and attention
- sends output to -->
1. dorsolateral pfc motor association
2. secondary motor cortex
38
Damage: Posterior Parietal Association Cortex
- leads to apraxia
- disorder of voluntary movement
- unrelated to motor comprehension, or motivation deficit
39
contralateral neglect
- inabiliy to respond to stimuli contralateral to damage (left neglect)
- leads to someone neglecting half of a picture when drawing it
40
Dorsolateral Prefrontal Association Cortex (DLPC)
- recieves info from posterior parietal
- integrates information about stimuli
- PLANS APPROPRIATE MOVEMENT
- send information to secondary and primary motor cortex
41
Dorsolateral Prefrontal Association Cortex Neurons respond to....
- characteristics of object
- location of object
- both object and location
- decides what action are to be taken
42
DLPC : Planning Movement
-DLPC fires FIRST in the motor system = first step in motor planning
43
Prefrontal Cortex
-important for executive functions- select appropriate movement based on info from visual, somatosensory, and auditory input
44
Secondary Motor Cortex
-premotor cortex
-supplementary motor areas and 2 cingulate motor area
-receive info from motor association cortex
-programs patterns of movement after taking instruction from DLPC
neurons fire just before movement initiation and fire continuously throughout movement
-send info to primary motor cortex
-contains mirror neurons
45
Mirror neurons
- fire when an individual performs a certain goal directed hand movement or when they observe the same movement performed by another (Giacomo Rizzolati)
- posible mechanism for social cognition
- little known about human mirror neurons due to lack of non-invasive techniques ( fMRI)
46
Primary Motor Cortex
```
-also known as M1, precentral gyrus, brodmann's Area 4
the major (but not only) departure point of motor signals
```
47
Penfield's Montreal Procedure
- stimulate cortex and watch muscles twitch
| - showed that the cortex for sensorimotor system is somatotopic
48
Somatotopic
- more cortex devoted to body parts that make complex movements
- motor homunculus
49
Primary motor cortex conventional view
-neurons fire maximally to a certain direction of movement
50
Primary motor cortex current view
- stimulation of neurons elicits complex behaviors (feeding)
- neurons fire maximally to a particular endpoint of an action
- the route neural signals follow from m1 is extremely plastic and determined by somatosensory feedback
51
Neural signal route to m1
- plastic
| - determined by somatosensory feedback
52
Cerebellum
- little brain
- 10% of brain mass but more than 50% of its neurons
- input from primary and secondary motor cortexes
- sensory input from Pons
- feedback from motor responses
- Projects to thalamus---->M1
- involved in timing, fine tuning, motor learning
- may also do the same for cognitive responses
53
Cerebellar Damage (cerebellar ataxia)
-uncoordinated, jerky movements
-intention tremor
-slurred speech
-lack of balance
-uncoordinated gate
(like being drunk)
54
Basal Ganglia 3 parts
Comprised of:
- caudate,
- putamen
- globus Pallidus
55
Basal Ganglia output/input
- input from cortex/ substania nigra (dopamine cells in midbrain)
- outputs to thalamus (which then brings information back to motor cortex
56
Basal Ganglia function
- amplitude
- direction
- initiation of movement
57
Basal Ganglia Damage
in Parkinson's Disease:
- dopamine cells die decreasing dopamine input to the basal ganglia
- ---> in balance in excitatory and inhibitory signals within the basal ganglia
- causes tremors, muscle rigidity, difficulty initiating and terminating movements
58
Substantia Nigra
- "black substance"
| - dopaminergic cell bodies in the midbrain which project to the caudate + putamen (striatum)
59
Descending motor pathways
-carry information from the brain down the spinal cord
60
Dorsolateral Pathways
-deal with voluntary movements of distal limbs (fingers and toes)
61
ventromedial pathways
- posture and movement of trunk
| - proximal limbs (shoulder/hip)
62
Control dista (far from center) muscles
= movement of the limbs
63
Dorsolateral cortico spinal tract
- begins at M1
- decussates at medulladescends in dorsolateral spinal cord white matter
- movement of individual fingers
64
Dorsolateral cortico-rubro spinal tract
- begins in M1
- synapses and decussates at red nucleus (midbrain)
- some neurons synapse on crabial nerves that innervate the face
- the rest descend in dorsolateral white matter
65
control proximal
-near to center muscles
66
trunk and proximal limbs
-posture and walking (whole body movements)
67
ventromedial cortico spinal tract
- begins in M1
- remains ipsilateral
- descends in ventro-medial spinal cord white matter
68
ventromedial cortico-brainstem-spinal tract
- begins in M1
- synapses at various brainstem nuclei (tectum, vesicular nucleus, cranial nerve motor nuclei)
- descends bilaterally
69
Motor Cortex Control Efferent Paths
- all descending paths are under control of M1
- M1 has direct projection to spinal motor neurons (dorsolateral and ventromedial corticospinal tracts)
- M1 also projects to other (indirect) descending pathways (red nucleus and brainstem nuclei)
70
smooth muscle
- in digestive tract and arteries
| - automated by fibers of the ANS
71
striated muscle
- cardias muscle
- contracts rhythmically even without innervation
- has striped appearance
72
skeletal muscle
- a type of striated muscle
| - allows movement of bones and eyes, respiration, facial expressions, speech
73
Innervation of Striated Muscle
- muscle fibers are sparsely innervated by axons from the spinal cord in a non overlapping fashion
- motor neuron excitation produces muscle contraction
74
the only way a muscle can generate force is with a...
contraction
