The Spinal Cord and Periphery Flashcards
Where do the cell bodies of the ventral horns (motor neurons) reside?
In the ventral horns of the spinal cord (grey matter)
What is Motor Neuron disease?
A group of diseases affecting the motor neuron in the ventral horn of the spinal cord - the lower motor neuron
The neuron dies and the supplied muscle atrophies
Progressive and incurable
Is all sensory information sent to the brain before it is acted on?
No, some is too urgent and is dealt with as reflexes where the spinal cord or other lower centres making the decision
What is the name of reflexes mediated at the level op the spinal cord?
Spinal reflexes
Name a monosynaptic spinal reflex
Stretch reflex
Name a polysynaptic spinal reflex
Flexor reflex
What part of the spinal cord is grey matter?
The centre
What part of the spinal cord is white matter?
The periphery
What are the basic components of the white matter?
Tracts made up of axons transmitting information between the higher centres in the brain and peripheral nerves
What fibres do ascending tracts carry?
Sensory fibres
What fibres do descending tracts carry?
Motor fibres
What are the columns of the spinal tract?
Posterior, lateral, anterior
To where in the brain does sensory information travel?
Cerebral cortex and cerebellum
what are the common characteristics of sensory pathways reaching the conscious level?
Always three neurons between peripheral receptor and cortex
What sensory information is carried in the posterior or dorsal column?
Fine touch, tactile localisation, vibration sense, proprioception
Where does the first order neuron synapse in the dorsal column?
In the gracile and cuneate nucleii of the medulla
Where does the second order neuron of the dorsal column synapse?
In the VPL nucleus in the thalamus (of diencephalon)
To where does the third order neuron of the dorsal column travel?
The post central gyrus of the parietal lobe
What sensory information is carried in the lateral spinothalmic tract?
Pain and temperature from the contralateral side
Where does the second order neuron of the dorsal column dessucate?
In the medulla
What is the name of the second order neuron of the dorsal column after it has dessucated?
The medial meniscus
Where does dessucation of the second order neuron occur in the lateral spinothalmic tract?
In the spinal column at the level of entry
Where do the descending motor tracts of the brain originate?
The cerebral cortex and the brainstem
How many neurons are in the tracts coming from the cerebral cortex?
2
Where does the decussation occur in the descending motor tracts?
In the brainstem
What movements are governed by the corticospinal or pyramidal tract?
Voluntary skilled movements
Where do the corticobulbar fibres go from the motor cortex?
The contralateral cranial nuclei. The upper motor neuron carries t the nuclei and the lower motor neurons are the cranial nerves
Where do the corticospinal fibres cross?
The decussation of the pyramids (lateral corticospinal tract)
What is the lower motor neuron?
Fibres responsible for muscle tone and reflexes before the synapse, in the corticospinal instance after the synapse in the spinal cord, in the corticobulbar instance after the synapse in the cranial nuclei
What is the upper motor neuron?
Fibres after the synapse in the motor neurons, in the corticospinal instance after the synapse in the spinal cord, in the corticobulbar instance after the synapse in the cranial nuclei. If it is damaged but the LMN is intact, reflexes and tone are exaggerated
What is the purpose of reflexes?
To provide an immediate response if it it needed, faster than the message can be communicated to the brain. These decisions can be made by the spinal cord or other lower centres
Describe the process of the stretch reflex
Tendon stretched Intrafusal muscle fibres stimulated Sensory neuron activated Monosynaptic reflex arc Polysynaptic reflex arc to inhibitory interneuron Muscle contraction Reciprocal innervation
What are the important functional features of the stretch reflex?
It is important in control of muscle tone and posture
Describe the process of the flexor and crossed extensor reflex
Pain stimulus
Sensory neuron activated
Polysynaptic reflex arc
Flexion and withdrawal from noxious stimulus
Crossed extensor response to contralateral limb (only in weight bearing limbs)
What is the important functional feature of the flexor and crossed extensor reflex?
Helping to protect the body from painful stimuli
What is the effect on reflexes of an upper motor neuron lesion?
As reflexes use the lower motor neuron only, reflexes remain intact. However, they become exaggerated. Muscle tone also increases and leads to spasticity
I.e with UMNL there is spastic paralysis with hyperreflexia
What do cortical lesions often affect?
Speech
What should be considered with regard to presenting motor paralysis and weakness?
Which side, is it spastic or fluid, what happens to the reflexes
What should be considered with regard to cranial nerve weakness?
Which side it presents on
What should be considered with regard to sensory defects?
Which side it is on for pain and temperature
Which side it is on for touch, vibration, proprioception etc
Describe the organisation of the autonomic nervous system
The motor division of the PNS is split into the somatic motor system and the autonomic motor system. The somatic motor system affects the skeletal muscles and is controlled by conscious thought. The autonomic nervous system which deals with subconscious mechanism controls the smooth muscle, cardiac muscle and the glands
How many neurons do basic autonomic pathways have?
2
Where is the outflow of the sympathetic nervous system?
Thoracolumbar - T1-12, L1 & 2
Where is the outflow of the parasympathetic nervous system?
Craniosacral - CN III, VII, IX, X, S2-4
Where are the preganglionic fibres in sympathetic nerves?
Near the spinal cord
Where are the preganglionic fibres in parasympathetic nerves?
Near the target organ
What are the targets of postganglionic fibres in sympathetic nerves?
Every cell in the body
What are the targets of the postganglionic fibres in parasympathetic nerves?
Exocrine glands, heart, other selected organs
