Lecture 5: Motor And Sensory Pathways

Question 0

Most ascending sensory pathways (except olfactory) are relayed via the ____and project to ______.

Major descending motor tracts from cerebral cortex generally bypass the _____on way down to spinal cord.

Answer 0

Most ascending sensory pathways (except olfactory) are relayed via the thalamus and project to cerebral cortex.

Major descending motor tracts from cerebral cortex generally bypass thalamus on way down to spinal cord.

Question 1

Basal ganglia concerned with_______. They integrate info from cerebral cortex, process it and project it back to cortex through the _____.
Functional disturbances of basal ganglia will cause _______

Answer 1

Basal ganglia concerned with controlled purposeful movements. They integrate info from cerebral cortex, process it and project it back to cortex through the thalamus.
Functional disturbances of basal ganglia will cause movement disorders

Question 2

Describe the motor pathway

Answer 2

• Corticospinal tract is the main pathway
controlling voluntary movement.
• Axons originate from upper motor neuron cell bodies in the cerebral motor cortex (in posterior frontal lobe) and pass to medulla where they form the medullary pyramids.
• Most fibres decussate at pyramids to form the lateral corticospinal tract.
• Fibres that don’t decussate form the anterior (ventral) corticospinal tract.
• Synapse with lower motor neurons in the anterior (ventral) horn of spinal cord grey matter.

From lecture
Neurons coming from pre central gyrus.
The fibres are coming down the corona radiata which are then coming down into the internal capsule, they then go through the mid brain to the cerebral peduncles in that basis pedunculi part there. They then go through pons into medulla oblongata forming the pyramids. They then decussate now they are going to effect muscles on other side, they come down corticospinal tract then to lateral funiculus, then they are going to synapse in anterior horn out to effector muscles.

Question 3

Motor system: Extrapyramidal tracts

Name them

Answer 3

Other descending tracts:
• Rubrospinal tract 
•Vestibulospinal tract 
• Reticulospinal tract 
• Tectospinal tract
• Olivospinal tract

If you have a lesion in your brain you don’t have full paralysis, because you have these extra ones. If you have lesion in spinal cord you have full paralysis

Question 4

Summary of motor tracts 
Lateral corticospinal 
Ventral corticospinal 
Rubrospinal 
Vestibulospinal

Answer 4

• Lateral corticospinal => mediates voluntary control of movement of limbs and motor functions of CN IX, CN X and CN XII (decussates at pyramids).
• Ventral corticospinal => uncrossed tract that eventually crosses the spinal cord to synapse with anterior horn and control of axial muscles.
• Rubrospinal => from red nucleus to spinal cord. Role in control of flexor tone.
• Vestibulospinal => from vestibular nuclei to spinal cord. Role in control of extensor tone and maintenance of posture and balance.

Question 5

Somatosensory “body sense”

Answer 5

• Pain
• Temperature
• Simple touch
• Proprioception (perception of position)
• Kinesthesia (perception of movement)
• Stereognosis (perception of size and shape of objects by touch).
• Somatosensory afferents feed into reflexes and also distribute to cerebral cortex and cerebellum.

Question 6

Receptors of somatosensory system

Answer 6

Nociceptors (pain) = 50% skin receptors

Proprioceptive info transmitted via muscle spindles, golgi tendon organ, joint receptors (not shown

Question 7

Sensory pathways

Answer 7

Cell bodies of the first
afferent neuron for all pathways is located in the DRG (dorsal root ganglion)
Typically cross the midline => contralateral.
Travel via medial lemniscus through the thalamus to postcentral gyrus

Question 8

Fasciculus cuneatus and fasciculus gracilis originate in the ______ and decussate in the _____ in the medulla
Slide 18

Answer 8

Fasciculus cuneatus and fasciculus gracilis originate in the ipsilateral spinal ganglia and decussate in the medial leminscus in the medulla

Question 9

Learn the diagram on slide 19 of cross section of medulla oblongata.
Also midbrain cross section on slide 20

Answer 9

Yeh

Question 10

Summary of sensory tracts

List them and there function

Answer 10

• Anterior (ventral) spinothalamic => crude
(non-discriminative) touch
• Lateral spinothalamic => itch, pain & temperature
• Fasciculus gracilis => fine touch, pressure, vibration, conscious proprioception of lower limb.
• Fasciculus cuneatus => fine touch, pressure, vibration conscious proprioception of upper limb.
• Spinocerebellar => unconscious proprioception from muscle spindles/tendon organs/joint & skin receptors to cerebellum.

Question 11

Sensorimotor system

Voluntary movements require constant feedback
Cerebral cortex works with ____, ____ and _____ to plan & program movements.
Efferent fibres project through _____and down spinal cord to effector muscles
Afferent fibres project through the _____ back to brain

Answer 11

Voluntary movements require constant feedback
Cerebral cortex works with basal ganglia, cerebellum and thalamus to plan & program movements.
Efferent fibres project through brainstem and down spinal cord to effector muscles
Afferent fibres project through dorsal funiculus back to brain