Motor and Somatosensory Pathways

Spinal cord location

Upper two-thirds of the vertebral canal inside the vertebrae.

Spinal nerves count

31 bilateral pairs (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal).

Plexus definition

A branching network of nerves originating from high concentrations of cell bodies.

Spinal nerve roots

Anterior contains efferent motor fibers; posterior contains afferent sensory fibers.

Grey matter location

Inside the spinal cord; responsible for processing and integrating information.

Ascending tracts function

Run through white matter to carry somatosensory information up to the brain.

Third-order neurons

Transmit sensory information from the thalamus to the somatosensory cortex.

Association cortices role

Provide the highest order of information processing to assign meaning.

Agnosia

Inability to interpret sensory information based on past experience.

Apraxia

Inability to make functional movements when complex movement components are intact.

Descending tracts function

Carry motor information from the brain down the white matter of the spinal cord.

Pyramidal motor tracts

Direct activation pathways responsible for voluntary control.

Extrapyramidal motor tracts

Indirect activation pathways responsible for involuntary control.

Internal capsule vulnerability

Packed tightly with fibres, white matter, making it prone to strokes (CVAs).

Lateral corticospinal tract

90 percent of its fibers cross in the pyramids of the medulla.

Indirect activation pathways

Vestibulospinal, reticulospinal, rubrospinal, and tectospinal tracts.

Upper motor neuron damage

Causes spastic paralysis and exaggerated reflexes.

Lower motor neuron damage

Causes flaccid paralysis, muscle atrophy, and decreased reflexes.

Dysarthria

Impairment of the muscles used for speech.

Phrenic nerve function

Supplies the diaphragm.

Proprioception

Sensory information about muscle length, tension, and joint position.

Primary sensory cortex

Receives raw sensory information first upon arrival in the brain.

How do corticobulbar tracts innovate?

They innovate bilaterally.

Where do corticobulbar tracts terminate?

At the motor nuclei of cranial nerves in the brainstem.

Do corticobulbar tracts terminate in the spinal cord?

No, they terminate in the brainstem.

Alexia

Impaired reading from left parietal association cortex damage.

Agraphia

Impaired writing from left parietal association cortex damage.

Fasciculations

Tiny muscle twitches caused by lower motor neuron damage.

Dysphagia

Difficulty swallowing due to impaired motor control of swallowing muscles.

What do first-order neurons carry?

Sensory information from peripheral receptors into the spinal cord.

How do first-order neurons enter the spinal cord?

They enter via the dorsal root.

Do first-order neurons remain ipsilateral or contralateral?

They remain ipsilateral (don't turn).

Where do first-order neurons terminate?

By synapsing with a neuron in the grey matter of the spinal cord.

What happens to first-order neurons after entering the dorsal horn?

They ascend to synapse with second-order neurons in the medulla.