Lecture 35: Major Neuroanatomical Pathways II Flashcards
Peripheral receptors encode somatosensory information through what type of neurons
Pseudounipolar neurons
Where are the cell bodies of pseudounipolar neurons located
Dorsal root ganglia
Axons of pseudounipolr neurons have ___ and ___ parts or branches
Local (reflex) and ascending branches (all the way to brain)
Peripheral receptors are distributed throughout the ___ and ___
Dermis and epidermis
What are local circuits
Paths of local control in spinal cord
Sensory neuron—> interneuron—> motor neuron
What are central pathways
Axon tracts to and from the brain that carry motor commands or sensory information
What are sensory tracts
Carry information on stimuli ascending to the brainstem and cortex
What are motor tracts
Leave the cortex and descend through the spinal cord carrying motor commands
Are reflexes an example of a central pathway or local circuits
Local circuits
What are two somatosensory pathways
- Dorsal column/ medial lemniscal system
- Anterolateral system/spinothalamic tract
What is the dorsal colum/medial lemniscal system
Senses tactile (touch) and conscious proprioception
Where do the axons cross in the dorsal column/medial lemniscal pathway
Axons traveling towards the thalamus cross to the contralateral side in the medulla
What is the anterolateral system/spinothalamic tract
Senses pain, itch, temperature, non-conscious proprioception, unpleasant sensations
Where do axons cross in anterolateral system/spinothalamic tract
Axons cross to contralateral side of spinal cord at the level of entry before changing direction and ascending toward thalamus
What are muscle spindle sensory receptors
Encapsulated intramural fibers with both sensory and motor innervation that are distributed throughout the muscle
Continuously detect tension and changes in length within the muscle itself
What are golgi tendon organs
Detect tension within tendons (produced by muscle contraction) when nerve fibers intertwined with collagen fibrils fold and touch
Where do muscle spindle receptors and golgi tendon organs send stretch information to
Dorsal horn of the spinal cord along pseudounipolar neurons
What is the motor unit
One LMN and the skeletal muscle fibers it innervates
Where do lower motor neurons originate
Brainstem and spinal cord
Local circuits are composed of neurons located at each ____
Spinal cord level
Are motor neuron cell bodies located in ventral or dorsal horn
Ventral
What is the sequence of patellar reflex
- Patellar tendon hit which stretches the tendon and increases tension within the quadriceps muscle
2-3. Stretch sensory signal sent as action potential along pseudounipolar neuron to Dorsal horn - Synapse on LMN in ventral horn
- Axons carry action potential to quadriceps
- Synapse at motor endplates—quadriceps contract, lower leg extends stifle joint
What is the role of inhibitory interneurons
Inhibit LMNs that innervate antagonist muscle of stretched muscle which inhibits muscle contraction
In order to maintain correct muscle tension to maintain posture against gravity if you contract quadriceps to prevent joint collapse what muscle must be inhibited by inhibitory interneuron
Bicep femoris
Describe the flexor reflex- withdrawal reflex from a negative stimulus
- Painful stimulus encountered
- Excitatory interneurons excite LMN that innervate ipsilateral flexor muscles
- Inhibitory interneurons inhibit LMN’s that innervate ipsilateral extensor Muscles
Describe the Postural Reflex
When tested or affected limb is raised the contralateral limb will extend
Describe ipsilateral and contralateral flexion and extension during withdrawal reflex
Excitatory neurons on ipsilateral side will innervate flexor muscles to remove limb from stimulus. While sending inhibitory neurons to ipsilateral extensors
Excitatory neurons on contralateral side will innervate extensor muscles to support flexed contralateral limb
