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Ch 17 Nervous System Pathways
Terms in this set (35)
CNS communicates with peripheral body structures with pathways (sensory/motor)
Pathways travel through the white matter and/or the spinal cord as they connect various CNS regions with cranial and spinal nerves
A tract may work with multiple nuclei groups in the CNS
collection of neuron cells bodies located in the CNS
Sensory information from the body to the brain
Motor information from the brain to muscles or glands
90% of pathways crossover from one side to the other so that the left side of the brain processes information on the right side of the body, and vice versa
Most pathways exhibit a precise correspondence of receptors in body regions, through axons, to specific functional areas in the cerebral cortex.
Ascending. primary, secondary and sometimes tertiary neurons.
conducts information about limb position, touch, temperature, pressure, and pain to the brain.
upper motor and lower motor neurons
process stimuli received from receptors within skin, muscle, and joints.
process stimuli received from the viscera
Three Types of Somatosensory Pathways
1. posterior funiculus-medial
2. anterolateral pathway
3. spinocerebellar pathway
Posterior Funiculus Medial Lemniscus Pathway
projects through the spinal cord, brainstem, and diencephalon before terminating within the cerebral cortex.
The pathway conducts sensory stimuli concerned with proprioceptive information about limb position, discriminative touch, precise pressure, and vibration.
The tracts within the spinal cord are collectively called the posterior funiculus; they ascend the spinal cord within either the: fasciculus cuneatus & fasciculus gracilis
fasciculus cuneatus—houses axons from sensory neurons originating in the upper limbs, superior trunk, neck, and posterior region of the head
houses axons from sensory neurons originating in the lower limbs and inferior trunk
tracts within the brainstem
Anterolateral Pathway (Spinothalamic Pathway)
is located in the anterior and lateral white funiculi of the spinal cord. The pathway is composed of the:
anterior spinothalamic tract
lateral spinothalamic tract
Axons entering these pathways conduct stimuli related to crude touch and pressure as well as pain and temperature.
Axons of secondary neurons cross over to the opposite side of the spinal cord before ascending to the brain. This decussation occurs in the anterior white commissure.
conducts proprioceptive information to the cerebellum for processing to coordinate body movements.
anterior spinocerebellar tracts
posterior spinocerebellar tracts
These are major routes for transmitting postural input to the cerebellum.
The sensory pathways do not use tertiary neurons
Information conducted in the pathways is integrated and acted upon at the subconscious level.
Formed from cerebral nuclei, cerebellum, descending projection tracts, and motor neurons
Regulate skeletal muscle activity
and are Descending projection tracts
Atleast 2 motor neurons, upper and lower
Descending Projection Tracts
are motor pathways that originate from the cerebral cortex and brainstem
Upper motor neuron
cell body is housed either within the cerebral cortex or a nucleus within the brainstem
excites or inhibits the activity of the lower motor neuron
Lower motor neuron
cell body is housed either within the anterior horn of the spinal cord or within a brainstem cranial nerve nucleus
always excitatory because its axon connects directly to skeletal muscle fibers
Direct Motor Pathways (Pyramidal tract)
conscious control of skeletal muscle activity
It originates in the pyramidal cells of the
primary motor cortex.
Axons descend through the internal
capsule, enter the cerebral peduncles,
and ultimately form three descending
lateral corticospinal tract
anterior corticospinal tract
unconscious control of skeletal muscle activity
upper motor neurons originate within brainstem nuclei.
The axons of the indirect pathway take a complex, circuitous route before conducting the motor impulse into the spinal cord.
The axons descend into major tracts of the spinal cord and terminate on either interneurons or lower motor neurons.
The indirect pathway modifies or helps control the pattern of somatic motor activity by:
altering motor neuron sensitivity to
incoming impulses in order to control
muscles individually or in groups
activating feedback loops that project
to the primary motor cortex
two different tracts:
lateral pathway, and rubrospinal tracts
originate from the facial region within the motor homunculus of the primary motor cortex.
Axons synapse with lower motor neuron cell bodies housed within the brainstem cranial nerve nuclei.
Axons of the lower motor neurons help form the cranial nerves.
Corticobulbar tracts transmit motor information to control:
Eye movement via CN III, IV, and VI (*MLF!!!)
Cranial, facial, pharyngeal, and laryngeal
muscles—via CN V, VII (L is uni), IX, and X
Some superficial muscles of the back and
neck—via CN XI
Intrinsic and extrinsic tongue muscles—via CN
descend from the cerebral cortex and form a pair of thick anterior bulges in the medulla oblongata called the pyramids.
Axons of upper motor neurons synapse on lower motor neurons in the anterior horn of the spinal cord.
both lateral and anterior
Lateral Corticospinal Tracts
axons of the lower motor neurons innervate skeletal muscles that control skilled movements in the limbs.
include about 85% of the axons of the upper motor neurons that extend through the medulla oblongata.
They decussate within the pyramids of the medulla oblongata and then form the lateral corticospinal tracts in the lateral funiculi of the spinal cord.
Upper axons innervate lower motor neurons of the anterior horn of the spinal cord and interneurons within the spinal cord.
Anterior Corticospinal Tracts
axons of the lower motor neurons innervate axial skeletal muscle
represent the remaining 15% of the axons of upper motor neurons. The axons of the upper neurons remain on their original side in the medulla
The tracts descend the spinal cord in the anterior white funiculi.
At each spinal cord segment some of the axons decussate in the anterior white commissure.
After they decussate, they synapse either with interneurons or lower motor neurons in the anterior horn of the spinal cord.
regulates and controls precise, discrete movements and tone in flexor muscles of the limbs
that originate in the red nucleus of the mesencephalon
regulates muscle tone and gross movements of the muscles of the head, neck, proximal limb, and trunk. It consists of three groups of tracts:
1. reticulospinal tracts
2. tectospinal tracts
3. vestibulospinal tracts
originate from the reticular formation in the mesencephalon
help control more unskilled automatic movements related to posture and maintaining balance
Facilitates/inhibits voluntary movements
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