Spinal Pathways Flashcards
What are the 4 types of mechanoreceptors in glabrous skin?
From superficial to deep:
Meissner corpuscles, Merkel complexes, Ruffini organs, Pacinian corpuscles
Which mechanoreceptors are rapidly adapting?
Meissner corpuscles and Pacinian corpuscles
Which mechanoreceptors are slowly adapting?
Merkel complexes and Ruffini organs
What is the receptor field?
Over which region of space a specific receptor responds to
- size determines how fine the detail of information you can resolve is
What does mechanical distortion do?
Opens sodium channels which are tethered to the membrane, allowing Na+ through and depolarising the axon
Which mechanoreceptors have small receptor fields and which have large receptor fields?
Merkel and Meissner have small receptor fields
Ruffini and Pacinian have large receptor fields
What do Meissner corpuscles encode?
Rate of force
What do Merkel complexes encode?
Grip force (indentation)
What do Ruffini endings encode?
Hand posture (proprioception)
What do Pacinian corpuscles encode?
Vibrations
What are the dorsal columns?
Gracile (lower limb, closer to midline) and cuneate (upper limb) tracts travel up the spinal cord (dorsal side). Carry information about fine touch and proprioception
What is the 3 neuron sequence in the dorsal column-medial lemniscus pathway?
First synapse is in the medulla, then the tracts decussate (at the caudal medulla), form a band/ribbon (medial lemniscus) which travels along the midline. Projects to the thalamus where is synapses with the ventral posterior lateral nucleus of thalamus. These neurons then project up to the cerebral cortex
What is the sensory mapping of the tissue?
The tissue is somatotopically organised
- neurons that are close to each other in the cortex represent areas that are close to each other in the periphery
- maps are of the contralateral side of the body
What is the concept of plasticity?
The cerebral cortex can be reassigned to respond to different things - can happen with increased or decreased use. THE IDENTITIES DO NOT CHANGE
What is different about nerve root C1?
It does NOT have a cutaneous distribution (no dermatome), as it only has motor branches
What are segmental reflexes in the spinal cord?
When information comes in at one level, gets processed and goes out at the same level
What are inter-segmental reflex in the spinal cord?
When multiple segments of the spinal cord are involved in a reflex
eg. bilateral (cross-extensor) if withdraw one of the limbs form a noxious stimulus then have to make sure that the remaining limb is functional for the whole body
- interneurons activate the flexors and inhibit the extensors of one leg, and at the same time on the contralateral leg excites the extensors and inhibits the flexors
What is the general organisation of the spinal cord?
White matter on the outside, surrounding the nerve cells/bodies of the dorsal and ventral horns
- as you go down the cord see less white matter, because more information is coming up
What is the arrangement of the spinal cord in terms of motor distribution?
Midline spinal cord –> proximal muscles
Lateral spinal cord –> distal muscles
What is a motor pool?
All the motor neurons in the spinal cord that innervate a particular muscle
- one motoneuron innervates many fibres (motor unit) –> can control how many motor units are active at a time
What are muscle spindles?
Intrafusal sensory structure, reports back about how much stretch the muscle is undergoing (length)
- fastest conducting fibre
- in parallel with the muscle
- low threshold
What are golgi tendon organs?
The sensory nerve coming in interdigitates with the tendon
- reports back about how much force is being transmitted through the tendon
- in series with the muscle
- high threshold
What is the monosynaptic stretch reflex?
Only one synapse involved
- tap the tendon –> activate the muscle spindles –> burst of neural activity back to the spinal cord –> muscle contraction
How is the brain involved in the control of the spinal cord reflexes?
Brain sends inhibitory signals
- if see larger tendon reflexes then it means that the balance of power has changed and input isn’t coming from the brain
