Problem 4 Somatosensory system

Question 1

Stretch reflex

Answer 1

o a reflex elicited by a sudden external stretching force on a muscle
o They excite motor neurons in the ventral horn of the spinal cord which respond by sending action potentials back to the muscle whose stretch actually excited them, this results in activation of this muscle

Question 2

Withdrawal Reflex

Answer 2

Firing burst in sensory neurons of finger -> Excitation of excitatory spinal interneurons which excite bicep motor neurons//Excitation of inhibitory spinal interneurons that inhibit triceps motor neurons ->Biceps contracts, Triceps relaxes ->Flexion of elbow joint -> Withdrawal

Question 3

Monosynaptic

Answer 3

Their function is to maintain normal muscle length and tone

Question 4

Polysynaptic

Answer 4

A reflex action that involves an electrical impulse being transferred from a sensory neuron to a motor neuron via at least one connecting neuron (interneuron) in the spinal cord

Question 5

Posterior parietal association cortex

Answer 5

 Directing behaviour by providing spatial information
 Directing attention
 Receives information from three sensory systems (the visual system, the auditory system, and the somatosensory system)
 Output goes to the dorsolateral prefrontal association cortex, to the various areas of secondary motor cortex, and to the frontal eye field
 Damage: deficits in the perception and memory of spatial relationships, in accurate reaching and grasping, in the control of eye movement, and in attention

Question 6

Dorsolateral prefrontal association cortex

Answer 6

 Receives projection from the posterior parietal association cortex
 Sends projections to areas of secondary motor cortex, to primary motor cortex and to the frontal eye field
 May be the spring for initiate voluntary movements
 Evaluation of stimuli

Question 7

Secondary Motor Cortex

Answer 7

o Receives much of their input from association cortex
o Send much of their output to primary motor cortex
o Supplementary motor areas: SMA, preSMA, and supplementary eye field
o Premotor cortex: One dorsal one ventral
o Cingulate motor areas
o Electrical stimulation often typically elicits complex movements
o Are involved in programming specific patterns of movements after taking general instructions from dorsolateral prefrontal cortex

Question 8

Primary Motor Cortex

Answer 8

o Is responsible for activating muscles and coordinates movement
o Motor neurons might be coded to particular angles of movement
o The target might be important as well
o Motor Homunculus: Every are in the primary motor cortex is connected to a certain body part (much more are dedicated to the hands lips and face)
o Somatotopic: whats next to each other at your body so it is in your brain

Question 9

Cerebellum

Answer 9

o Complex connectivity with other brain structure
o Receives information from primary and secondary motor cortex, information about descending motor signals from brain-stem motor nuclei, and feedback from motor responses
o The cerebellum is thought to compare these three sources of input and correct ongoing movements that deviate from their intended course
o Believed to play a major role in the learning of sequences of movements (esp. timing)

Question 10

Basal Ganglia

Answer 10

o It is part of neural loops that receive cortical input from various cortical areas and transmit it back to the cortex via the thalamus
o Projects to cortical area known to have cognitive functions
o Participates in habit learning, a type of motor learning that is usually acquired trail by trail
o Selects one movement out of all the possible movements

Question 11

Sensorimotor spinal circuits

Answer 11

o Lowest level of the sensorimotor hierarchy

o Mere cables that carry information from the brain to the muscles, also capable of independent functioning

Question 12

Motor units

Answer 12

o Smallest part of motor activity.

o Contains a single motor neuron which when it fires leads to contraction of muscle fibers of this unit

Question 13

Motor learning

Answer 13

• Often performed responses are transferred to lower levels of the CNS
• theory of learning process of movement and behaviour
• practice combines central sensorimotor programs controlling individual response to sequence behaviour programs

Question 14

Central sensorimotor programs

Answer 14

o Once activated, each level of the sensorimotor system is capable of operating on the basis of current sensory feedback without the direct control of higher levels
o These mechanisms seem to be the responsibility of the cerebellum and basal ganglia

Question 15

motor equivalence

Answer 15

same basic movements can be carried out in different ways involving different muscles

Question 16

Mirror Neurons

Answer 16

are neurons which fire when an individual performs a particular goal-directed hand movement or when they observe the same goal-directed movement performed by another

Question 17

Reciprocal Innervation

Answer 17

o Permits that when one muscle is contracted the other one is relaxed

Question 18

Recurrent Collateral Inhibition

Answer 18

o Gives the motor neurons a break by inhibitory neurons in the spinal cord
o By Renshaw cells
o It inhibits it self by using Renshaw cells which are inhibitors that are activated when the neuron fires

Question 19

dorsolateral group

Answer 19

o involved with independent limb movement
o more responsible for more delicate and precise movement in arms and fingers (proxal muscles)
o they are contra lateral and distal

Question 20

ventromedial group

Answer 20

o diffused and ipsilateral

o involved in posture and whole-body movements

Question 21

Spinal Cord injuries

Answer 21

o When you cut the left and right dorsolateral corticospinal tracts it will impair the movement of your limbs
o when you cut the ventromedial tracts walking and standing gets problematic (whole body movements are impaired)
o However, only the corticospinal division of the dorsolateral system is capable of mediating independent movements of the digits

Question 22

Frontal eye field

Answer 22

Movement of the eye (reaching and grasping)