Term
| The monosynaptic stretch reflex is very important. Explain it... |
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Definition
When the tendon is struck the quadriceps muscle is stretched. This stimulates stretch sensory receptors (muscle spindles) that trigger an afferent impulse in a sensory nerve fiber of the femoral nerve leading to the lumbar region (L4) of the spinal cord. There, the sensory neuron synapses directly with a motor neuron that conducts an efferent impulse to the quadriceps femoris muscle, triggering contraction. This contraction, coordinated with the relaxation of the antagonistic flexor hamstring muscle causes the leg to kick. This reflex helps maintain posture and balance, allowing one to walk without consciously thinking about each step.
The patellar reflex is a clinical and classic example of the monosynaptic reflex arc. There is no interneuron in the pathway leading to contraction of the quadriceps muscle. Instead the bipolar sensory neuron synapses directly on a motor neuron in the spinal cord. However, there is an inhibitory interneuron used to relax the antagonistic hamstring muscle.
If there is to great a response after the jerk then there is a possibiltiy of upper motor neuron faults. If there is a weak kick or no kick then there is a problem in the lower motor neuron.
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Term
| Why is there the babinski sign in infants but not adults? |
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Definition
This happens because the corticospinal pathways that run from the brain down the spinal cord are not fully myelinated at this age, so the reflex is not inhibited by the cerebral cortex. The extensor response disappears and gives way to the flexor response around 12-24 months of age. |
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Term
Lower motor neurons and upper motor neurons.
One major characteristic used to identify a lower motor neuron lesion is flaccid paralysis - paralysis accompanied by muscle loss. This is in contrast to a upper motor neuron lesion, which often presents with spastic paralysis - paralysis accompanied by severe hypertonia |
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Definition
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Term
| How do we know that the locomotor pattern exists in the spinal cord? |
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Definition
| The walking test done on infants that are held and do a walking motion, as well as studies on decerberate cats on treadmills. These cats are able 2 speed up and slow down given the speed of the treadmill without brain input. They receive input from sensors in the muscle (muscle spindles for length and golgi tendon organs for force) that inform the spinal cord circuits of locomotion. |
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Term
| Golgi tendon organs usually are inhibitory. But in walking do they do this? |
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Definition
No, in walking having a loaded leg we dont want to unload it.
During locomotion, muscle sensory organ (muscle spindles and Golgi tendon organs) signal muscle stretch and load during walking (extensors bearing weight) - they have an excitatory effect on extensor motoneurons, which maintains support to loaded limbs.
Evidence of ongoing modulation of locomotor pattern
activity: the withdrawal reflex is modulated with step cycle. Also, gait disorders provide and illustration of how the locomotor centres in spinal cord are strongly modulated by other inputs.
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Definition
| The spinal cord contains the pattern for locomotion, it is modified by sensory input from the golgi tendon organs and the muscle spindals and can actually modify that output given the stregnth of the descening signal from brainstem (troting to galloping all in spinal cord) |
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Term
When we do tests on posture like sticking out leg the spinal cord actually does alot. e.g.
Person is standing on platform and the motor control is measures using EMG. The platform is removed from underneath them. 1st trail they sorta fall and sway. The 2nd time they are prepared and the gastroctnemus is ready and fires to keep posture. This shows the spinal cord is very plastic and changes rapidly given some trials. |
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Definition
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Term
| The optic tectum or simply tectum is a paired structure that forms a major component of the vertebrate midbrain. In mammals this structure is more commonly called the superior colliculus (Latin, higher hill), but, even in mammals, the adjective tectal is commonly used. The tectum is a layered structure, with a number of layers that vary by species. The superficial layers are sensory-related, and receive input from the eyes as well as other sensory systems.[1] The deep layers are motor-related, capable of activating eye movements as well as other responses. There are also intermediate layers, with multi-sensory cells and motor properties. |
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Definition
| The reason the superior colliculus is important is becasue it is involved in eye movements. |
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Term
| The motor cortex can be broken into 4 main parts: |
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Definition
Primary motor cortex (M1) = responsible for generating the neural impulses controlling execution of movement
3 other secondary motor cortices
Posterior motor cortex
Pre motor area (PMA)
Supplementary motor area (SMA)
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