Neuroanatomy (basic) and of motor systems

Label this brain

Name the major bones of the skull

frontal bone over the frontal lobe

parietal bone over the parietal lobe

occipital bone over the occipital lobe

temporal bone over the temporal lobe

What is the calvaria

The neurocranium that houses and protects the brain

Has suture points where bones meet

Meninges

Membranous layers surrounding brain and spinal cord 

Cortex

outermost area of brain where you find grey matter

arranged into gyri and sulci

Lobes

Subcortical anatomy

Deep structures within the brain such as the thalamus, ventricles, corpus callosum

Important in the control of motor movement 

label this

it’s a brainstem

What attaches the cerebellum to the brainstem

1. superior cerebellar peduncle

2. middle cerebellar peduncle

3. inferior cerebellar peduncle

Which cranial nerves do not arise from the brainstem and where do they arise from?

1. olfactory nerve

2. optic nerve

arise from the cerebrum

What is the nervous system divided into?

1. CNS- central nervous system: brain and spinal cord

2. PNS- peripheral nervous system: all other tissues outside CNS including cranial and spinal nerves 

Outline pyramidal pathways

• start in the cortex + go through the pyramids of the medulla 

• conscious movements initiated by primary motor cortex

• commands relayed downwards through the brainstem to the spinal cord to be executed by skeletal muscles

• motor pathway consists of upper + lower neuron classes

upper motor neurons

• originate in cortex + other high centres

• stimulate lower motor neurons

• originate and end in CNS

lower motor neurons

• originate in ventral horn of spinal cord or motor nucleus of a cranial nerve

• directly innervate target tissue + cause contraction 

• originate in CNS, end in PNS 

Sulcus

Groove

Gyrus

Bump

Label this

postcentral gyrus is in parietal lobe

what is M1

AKA broadmann’s area number 4

Primary motor cortex

How do we classify descending motor pathways?

Pyramidal and non-pyramidal

name the pyramidal motor pathways

1. corticospinal- body

2. corticobulbar tract- head and neck

outline extrapyramidal motor pathways

• start in brainstem + do not pass through medullary pyramids 

name the extrapyramidal tracts

1. reticulospinal

2. rubrospinal

3. tectospinal

4. vestibulospinal

Anything involving the motor cortex is?

Conscious

If it comes from the brainstem it is?

Involuntary

Draw the corticospinal pathway

List the corticospinal tract verbally

1. Originate in the grey matter of the primary motor cortex

2. Pass through white matter of corona radiata

3. Pass through Internal capsule

4. Pass through crus cerebri

5. Pass through pyramid

6. Decussate at the decussation of the pyramid

7. Reach the lateral corticospinal tract

8. Synapse with the lower motor neuron

9. Lower motor neuron leaves spinal cord

Corticospinal tract

Fibres control motor neurons in spinal cord

Innervating muscles in the trunk and limb - control voluntary skeletal muscles

Label this

Do all fibres cross over at the decussation of the pyramids?

No- about 85-90%

Those that do not, pass straight through the decussation of the pyramids and cross over in the spinal cord instead of brainstem 

Ventral vs lateral corticospinal tract

Lateral = where fibres that cross at the decussation of the pyramids reach after crossing over

Ventral = where fibres that do not cross at the decussation of the pyramids go, continue into ventral part of spinal cord

What’s happening here?

On the right, the tract is not decussating at the decussation of the pyramids and is therefore passing through the ventral corticospinal tract

On the left, the tract is decussating 

Ascending tracts

Sensory

Descending tracts

Motor

Draw how lower motor neurons leave

Leaves via the ventral root of the spinal nerve, joins spinal nerve for the level, goes to wherever its effector muscle is

Outline muscle tone

• Muscles exhibit a degree of rest tone which helps maintain normal posture and joint stability

• Clinical examination = mild resistance to passive joint flexion and extension

• Rest tone mediated by stretch reflex

Spasticity

Marked increase in muscle tone

Upper motor neuron involvement

Upper vs lower motor neuron lesions: muscle tone

Upper: increased tone (spasticity)

Lower: decreased tone (flaccidity)

Upper vs lower motor neuron lesions: reflexes

upper: hyperreflexia- cannot dampen reflex without corticospinal arc

lower: depressed or absent tendon reflexes

Upper vs lower motor neuron lesions: spasticity

Upper: present

Lower: absent

Upper vs lower motor neuron lesions: clasp-knife rigidity

Upper: present

Lower: absent

Upper vs lower motor neuron lesions: strength

Upper: weakness (loss of functionality or secondary) 

Lower: weakness (more pronounced due to denervation)

Upper vs lower motor neuron lesions: muscle wasting

Upper: not typically present due to high muscle tone

Lower: present due to denervation causing muscle atrophy

Upper vs lower motor neuron lesions: fasciculations

Involuntary muscle twitches

Upper: absent

Lower: present due to denervation

What changes how a stroke patient presents?

Which blood supply their stroke cut off- different arteries supply blood to different parts of brain, whichever part has been starved of blood will be damaged 

Draw the corticobulbar tract

Corticobulbar tract

Fibres control motor neuron in cranial nerve nuclei 

Innervating skeletal muscles- head and neck 

Where are the lower motor neurons that supply the skeletal muscle of the head and neck located?

Motor nuclei of cranial nerves- in the brainstem

What are cranial nerve nuclei?

discrete areas, places where upper neurons synapse to lower neurons

in the brainstem

contain lower motor neuron cell bodies of corticobulbar tract

Outline how lesions are associated with symptoms

• most cranial nerve nuclei receive projections from both cerebral hemispheres

  • upper part of face = controlled by both

  • lower part of face = controlled by opposite side

• exceptions = cortical projections controlling tongue + lower part of face (which arise mainly from the opposite motor cortex)

• isolated facial paralysis sometimes occurs after a stroke, with the upper part of the face spared since it is controlled by both cerebral hemispheres

Draw the rubrospinal tract 

list the rubrospinal tract verbally

1. originates in red nucleus

2. decussates immediately in midbrain

3. travels down opposite side’s substantia nigra and crus cerebri

4. travels through pons and medulla

5. passes down into cervical spinal cord

6. passes through ventral grey matter

7. synapses with lower motor neuron

what is the rubrospinal tract for?

Muscle tone

Needed for posture + holding joints in place

Muscle tone = resistance to passive movement of a joint

Draw the tectospinal tract

List the tectospinal tract verbally

contralateral

1. originates in the superior colliculus

2. decussates- dorsal tegmental decussation

3. goes down into the pons, medulla, and then cervical cord

what is the tectospinal tract for?

• receiving visual stimulus

• mediates reflex movement in response to visual stimuli- when you turn around suddenly if someone taps you on the shoulder 

• terminates in cervical region

• coordination of head and eye movements 

What is the reticulospinal tract for?

• automatic movement such as locomotion and breathing

• originates from reticular formation in brainstem

• nuclei for reticulospinal tract spread out in brainstem = one part injured, rest ok, reduces risk of injuring everything at the same time (means that it’s important!)

What is the vestibulospinal tract for?

Balance and posture

Ipsilateral from vestibular nuclei in pons and medulla- does not cross over

Lateral vestibular nucleus (pons) = excites extensor muscle

Medial vestibular nucleus (medulla) = coordinate head + eye movement 

What is the reticular formation?

Set of interconnected nuclei in brainstem, continues rostrally into thalamus and hypothalamus

Very spread out 

Important for automatic movement such as breathing and walking 

Reticulospinal tract

From reticular formation of pons and medulla

Ipsilateral

Influence voluntary movement

Mediate muscle tone + vital functions

Reflex activity + muscle tone

Globus pallidus + putamen

Lentiform nucleus

Lentiform nucleus + caudate nucleus 

Basal ganglia 

PD or normal?

PD

Outline dopamine’s role in the basal ganglia 

• Stimulates direct pathway neurons 

• Inhibits indirect pathway neurons 

• Releasing dopamine from substantia nigra 

• excitatory = direct pathway straight line from cortex—>BG—> thalamus and back out

• inhibitory = indirect pathway, cortex —> basal ganglia —> basal ganglia via subthalamic nucleus, then thalamus, then out 

• work together in coordination to help movement 

Parkinson’s disease

• characterised by tremor at rest + rigidity

• balance is in favour of indirect pathway = unwanted movements

• substantia nigra not producing dopamine anymore —> difficulty initiating movement

Cerebellum

• Largest part of hindbrain

• Connected to midbrain by cerebellar peduncles

• Responsible for unconscious motor control + alternating movements

• Fine-tunes motor activity

What does the decussation of fibres explain?

Why skeletal muscles on the left side of the body are controlled by the right hemisphere of the brain