Spinal Cord Pathways Flashcards
What are 5 characteristics of the spinal cord?
Cylindrical cable of pathways to and from the brain and rest of the body
Extends from base of skull (medulla) to L1-2 (between L1/2)
Has cervical (brachial plexus) and lumbar (lumbosacral plexus) enlargements accommodating extra axons
Meninges cover it like the brain
Central canal continuous with ventricles of the brain
What are the four regions of the spinal cord?
Medulla oblongata
L1-L2 conus medullaris
Cauda equina (nerve roots hang down from CM into this)
Filum terminale (tether of connective tissue formed with meninges that attaches at coccyx so the spine does not move up and down)
What is the lateral horn?
Sympathetic, cell bodies of the sympathetic nervous system, at T3 and L1 and S3
Which part of the spinal canal grows faster and how if this compensated for?
As an infant the vertebral column grows faster and longer than the spinal cord leading to a length discrepancy, therefore nerve roots grow longer to accommodate this.
All the long nerve roots hanging down are known as the cauda equina, and the tether (filum terminale) also grows longer.
The nerve roots are in CSF, therefore you can extract CSF through here easily because hard to touch the nerves as they are floating in fluid
How is the spinal cord organized? (matter, dorsal, ventral…)
Organized into inner grey matter and outer white matter
Grey matter: has posterior (dorsal, sensory) and anterior (ventral, motor) horns
Dorsal and ventral horns lead to dorsal and ventral roots
Dorsal and ventral roots join up to form a spinal nerve
What is the process of the flow of information in the spinal cord?
Continuous flow of information between the brain, spinal cord, peripheral nerves and organ systems
Any moment: millions of sensory neurons delivering info to processing centers in CNS, millions of motor neurons going out and controlling or adjusting peripheral effector activities
This process continues around the clock
How is information transported to the cerebrum?
Communication between the CNS, PNS and peripheral organ systems involved ascending and descending pathways that relay sensory and motor information between periphery and higher centers
Each ascending (sensory) or descending (motor) pathway consists of a chain of neurons and associated nuclei or ganglia
The number of neurons and synapses (interneuronal connections) vary from one pathway to another
How are pathways named?
According to site of origin and destination
Spinothalamic: form spinal cord to thalamus
Corticospinal: from cerebral cortex to the spinal cord
What are the three major somatic sensory pathways?
Dorsal column/ medial lemniscal pathway: limb/joint position, motion sense, proprioception, light touch (discriminant, stereognosis, graphesthesia)
Spinothalamic (anterolateral) pathway: pain, temp, deep touch (pressure)
Spinocerebellar pathway: unconscious proprioception (recruiting muscles, correct amount of tension determine power)
What is involved in the Dorsal Column pathway?
Proprioception and discriminant touch
Sensory info comes in dorsally (dorsal root/horn) on unipolar neurons and skin/joint receptors, then travel up through dorsal columns into the medulla and synapses onto a second order neurons that crosses the midline and travels superior through the medial lemniscus, midbrain, to the ventral nuclei of the thalamus, and a third order neuron sends info from the thalamus to the primary sensory cortex in homotopic nature
What are the two parts of the dorsal column? What is stereognosis?
Fasciculus cuneatus: info from thorax and upper extremity
Fasciculus gracilis: info from lower torso and extremity
Contained in the medulla
Stereognosis: 3D recognition of objects without vision
What is involved in the spinothalamic tract? What is the difference between the lateral and anterior parts?
Deep touch, pain and temperature
First order neuron from skin receptors goes to the dorsal horn spinal grey and synapses onto the second order neuron which crosses the midline in spine and ascends to the thalamus and third order neurons from thalamus go to primary sensory cortex
Lateral: pain and temperature
Anterior: crude touch (deep)
What is involved in the spinocerebellar pathway?
Unconscious proprioception from trunk and extremities
First order neuron from receptor in joint capsules tendons and muscle spindles synapse onto second order neuron in dorsal horn and then travel superiorly through medulla to the cerebellum through the anterior and posterior spinocerebellar tracts
What is the difference between the anterior and posterior spinocerebellar tracts?
Anterior: second order neuron splits and crosses contralaterally in the spinal cord, and then travels up and crosses back in the pons
Posterior: second order neuron does NOT cross and moves ipsilaterally to the pons and cerebellum
What are 4 characteristics of the motor systems?
CNS issues motor commands, and commands are distributed to the body by the PNS
Somatic motor commands effect contraction of skeletal muscles
Somatic motor pathways involve at least 2 motor neurons: upper motor neuron (cell body in CNS processing centers) and lower motor neuron (cell body in ventral horn of spinal cord or motor cranial nerve nucleus in brainstem)
How does the upper motor neurons modulate the lower neuron? What type of synapse is most common in the cortex?
Only the axon of the LMN extends to skeletal muscle (common final pathway)
UMN cell body in brain, synapses on LMN cell body in brainstem/spinal cord and this can be an excitatory or inhibitory synapse
Excitation: releases excitatory NT to tell LMN to contract
Inhibition: release inhibitory NT to tell LMN to not contract
Inhibitory is most common in the cortex
What happens if there is an upper motor neuron lesion, and the synapse is inhibitory?
The UMN is no longer releasing inhibitory NT onto the LMN, thus the LMN is not inhibited and can fire and cause muscles to contract (DISINHIBITION)
Spastic paralysis: muscles contract because no regulation, flexors stronger usually flex
What happens if there is a lower motor neuron lesion?
Input from UMN does not reach LMN, thus no signals going to muscle, no activity/ response
Flaccid paralysis: no activity or feedback
What are the two motor pathways?
- Corticospinal pathway (pyramidal): UMN extends from cerebral cortex to spinal cord, regulate distal muscles in limbs and trunk
- Corticonuclear pathway (corticobulbar): UMN extends from cerebral cortex to motor cranial nerve nuclei in brainstem, regulates muscles of head and neck
What are two other motor pathways?
Extrapyramidal pathways: subsidiary descending pathways important as backup systems
Basal nuclei and cerebellum: modulate and modify activity in the corticospinal tract to ensure smooth, coordinated, purposeful movement
Continuous sensory feedback is vital for motor systems
What is part of the central motor program that controls voluntary movement?
- Identification and localization of targets in space: posterior parietal cortex
- Formulation of a plan of action: premotor cortex and supplementary motor cortex
Execution of movement –> primary motor cortex
What are the 4 steps involved in the motor pathway?
- Stimuli from external and internal environment (sensory input) into spinal cord and to brain
- Information conveyed to sensory and motor areas of cortex via association fibres (posterior parietal, premotor, supplemental motor cortices)
- Central motor program fed into primary motor cortex, motor commands are conveyed via descending motor pathways (UMN, LMN/ common final pathway)
- Stimulus leads to muscle contraction (physical energy)
What area of the brain is involved in simple finger flexion?
Somatic sensory cortex and the motor cortex
What areas of the brain are involved in the finger movement sequence?
Premotor and supplementary motor area: more complex sequence of movements, these light up first because you have to plan the movement
Motor cortex lights up second to execute the plan made
What is involved in mental rehearsal of the finger movement sequence?
JUST the premotor and supplementary motor areas, because you are THINKING about the movement and not actually executing it
What is involved in the corticospinal pathway of movement?
Massive bundle of fibres forming direct pathway from the cerebral cortex to the spinal cord
Originate from pyramidal neurons in the cortex from 3 main areas: primary motor cortex, premotor/supplementary motor cortex and primary sensory cortex
Regulate distal limb muscles (important for precise, skilled, learned movements) like in the fingers
What is the pathway of structures in the corticospinal pathways?
Motor/sensory cortexes to internal capsule (dendrites of UMN), extend down to Crus Cerebri in midbrain, down the pyramids in medulla (still ipsilateral)
In the decussations of the pyramids the dendrites of the UMN cross to other side of spinal cord.
Then it splits into the lateral and anterior corticospinal pathway in the pyramids, where the lateral pathway crosses in the pyramids (85%) and the anterior pathway crosses in the spinal cord later (15%) therefore ALL end up contralateral they just cross at different times
What pathway splits off of the corticospinal pathway in the crus cerebri and right before pyramids?
Corticonuclear pathway to brainstem nuclei
What happens when there is an injury in the upper motor neuron in the corticospinal pathway?
Middle cerebral artery stroke (injury in cortex or internal capsule)
Brainstem lesion: if damaged above red nucleus the extensors take over, if below the flexors take over and the body takes rigid position
Spinal cord injury
