Somatic NS

Question 1

What are the divisions of somatic nerves and what type of nerves are they?

Answer 1

Sensory afferents - pseuounipolar

Motor efferents - multipolar

Question 2

What are the main motor areas?

Answer 2

Pre motor cortex
Cerebellum: Coordination, balance, muscle tone + posture
Basal ganglia : Deep gray mater for involntary and voluntary movement, they can increase or decrease movement

Question 3

What does the stretch reflex do?

Answer 3

Controls muscle tone

Controlling muscle length constant for posture

Question 4

How does the stretch reflex work?

Answer 4

Muscle spindle is stretched and sensory info is transmitted back to the DRG of the spinal cord

Intrafusal fibres synapse with alpha motor neurones

Alpha motor neurone innervates quadriceps muscle

Quadcriceps contacts and hamstrings relax

Question 5

What are the 2 types of intrafusal fibres?

Answer 5

Primary dynamic gamma neurones = velocity dependent

Secondary Static gamma neurones = velocity independent

Question 6

Describe the descending motor pathways?

Answer 6

Motor fibres descend and converge through the internal capsule
Travel to the thalamus and synapse with a 2nd ON
Fibres descend down midbrain -> PONS -> medulla
- Most fibres will dessucate in the medulla ( lateral)
- Some will remain ipsilateral and desiccate further down in the spinal cord = anterior
- Terminates in the ventral horn

Question 7

What are LMN?

What symptoms typically show LMN lesions?

Answer 7

LMN originate in the spinal cord and travel to muscles to provide innervation
Fascinations - occasionally LMN firing causes weak contraction
Hypotonia - Loss of stretch reflex which maintains muscle tone + muscle length for posture
Hyporeflexia/areflexia
atrophy

Question 8

What are UMN?

What symptoms typically indicate UMN lesions?

Answer 8

UMN remain in the brain and spinal cord
Hypertonia: spasticity or rigidity
Hypereflexia - UMN can modulate firing of LMN, with the UMN the lower motor neurones continuously fire
Clonus - strong rhythmic contractions
Clasp knife - muscle suddenly becomes activated
Babinski sign - plantar extensor reflex, toe fanning instead of toe curling when touch the palmar surface

Question 9

What are the 2 types of hypertonia ?

Answer 9

Spasticity = pyramidal lesion which is velocity dependent 
Rigidity = extrapyramidal lesion which is not velocity dependent

Question 10

Why do UMN lesions cause hypereflexia ?

Answer 10

UMN can modulate LMN responses without control from UMN the LMN will fire continuously -> hypereflexia

Question 11

What is cerebral palsy?

What are the 3 types of cerebral palsy?

Answer 11

Non progressive damage within the CNS

Spastic: Affects motor areas and CST = pyramidal
Dyskinetic = basal ganglia
Ataxic: Cerebellum damage

Mixed

Question 12

What are symptoms of spastic cerebral palsy?

Answer 12

Hypertonia 
Hypotonia of head + trunk
hypereflexia 
Atrophy with time
Babinski sign - toe fanning instead of curling when palmar surface is stroked 
Clasp knife

Question 13

What are symptoms of dyskinetic cerebral palsy?

Answer 13

• Dystonia : Simultaneous contraction of antagonistic pair
• Chorea
• Athetosis

Question 14

What are symptoms of ataxic cerebral palsy?

Answer 14

• Lack of coordination + posture
• Balance issues
• Ataxic gait
• Intention tremor

Question 15

What is dystonia ?

Answer 15

Simultaneous contraction of antagonistic pair