General principles Flashcards
What forms the gray matter of the spinal cord?
- Cell bodies
- Unmyelinated axons
What forms the white matter of the spinal cord?
- Myelinated axons
What runs in the central canal of the spinal cord?
CSF - continuous with 4th ventricle
What information does the dorsal column medial lemniscus pathway carry?
Fine touch and pressure, vibration and proprioception
enters spinal cord and ascends 1-2 levels before crossing
Cuneatus = upper
Gracilis = lower
What information does the spinothalamic pathway carry?
Pain and temperature
Ennters spinal cord, crosses straight away
What is the function of the spinocerebellar tract?
Control of posture and coordination of movements
What is the function of the tectospinal tract?
Mediate reflex postural movements of the head in response to visual and auditory stimuli
What is the substantia gelatinosa?
- one point (the nucleus proprius being the other) where first order neurons of the spinothalamic tract synapse.
- Many μ and κ-opioid receptors, presynaptic and postsynaptic, are found on these nerve cells; they can be targeted to manage pain of distal origin
What is the role of the corticospinal tracts?
Voluntary muscle control
Upper motor neurons that synpase with lower motor neurons in the spinal cord
90% of fibres cross at the pyramidal decusation (lateral corticospinal tract - distal muscle movement)
10% cross in the spinal cord (anterior corticospinal tract - proximal muscle movement)
Discuss Bell’s Palsy
Damage to facial nerve
Weakness or paralysis on one side of the face
Idiopathic - unknown cause
What does vitamin B1 deficiency cause?
B1 = thiamine
Low in alcoholics
Wernicke-Korsakoff syndrome
Causes a confused mental state, confabulation (story telling) and hallucinations
Which cranial nerve nuceli are located in the pons?
5,6,7,8
Which cranial nerve nuclei are located in the medulla?
9,10,11,12
Which cranial nerve nuclei are located in the midbrain?
3 and 4
Discuss decorticate and decerebrate rigidity
Decorticate: arms adducted, flexed over chect and feet plantar flexed. Due to corticospinal tract damage
Decerebrate: arm adducted, extended down body and feet plantar flexed. Due to upper brain stem damage
Which cranial nerve exits the posterior brainstem?
Trochlear (4)
Where does the pituitary sit?
Sella turcica
What would a midline optic chiasmic lesion lead to?
Bipolar hemianopia
What is the somatic nervous system?
Controls conscious and sensation and voluntary movement
Two types of pathway:
- Afferent pathways carrying sensory input
- efferent pathways carrying motor output from the brain to the muscles
What is the autonomic nervous system?
Division of the afferent motor system that provides automaic/ unconscious control of the viscera and homeostasis
2 divisions:
- Sympathetic
- Parasympathetic
Temporal lobe functions
Language, learning, memory, emotional interpretation, hearing, olfaction, gustation
Parietal lobe functions
Sensory function
Discuss grey and white matter
Cerebral hemispheres and spinal cord composed of grey and white matter
- Grey: forms outer layer of cerebrum, composed of cell bodies of cerebral neurones and glia. Neurones are organised into layers
- White: inner region of the cerebral hemispheres, axonal projections from the neurones which connect the cortex to the rest of the CNS (white colour comes from the myelin sheath that wraps the axons)
What is the diencephalon?
Thalamus and hypothalamus comprises the diencephalon
What comprises the peripheral nervous system?
43 pairs of nerves
- 31 spinal nerves
- 12 pairs cranial nerves
What are UMN lesions?
Occur in the brain or spinal cord - a lesion in the neuronal pathway above the anterior horn cells
Causes:
- TBI
- Cerebral palsy
- Stroke
Frontal lobe functions
Motor functioning and higher cognition
- Problem solving
- Behavioural control
What is the corticospinal tract?
AKA the pyramidal tract because it passes through the medullary pyramids
a) lateral corticospinal tract: voluntary movement of contralateral limbs
b) anterior corticospinal tract: voluntary movement of the trunk, neck and shoulders (axial muscles)
Discuss the descending tracts of the nervous system
Pyramidal tracts: originate in the cortex and carry motor fibres to the spinal cord and brain stem. Responsible for voluntary control of the musculature of the body and face
Extrapyramidal tracts: originate in the brain stem and carry motor fibres to the spinal cord, responsible for the involuntary and autonomic control of al musculature e.g. muscle tone, balance, posture and locomotion
Discuss the extrapyramidal tracts
Descending tracts, automatic control of musculature e.g. tone, balance, posture
- Vestibulospinal
- Tectospinal
What are the pyramidal tracts?
Originate in the cerebral cortex, carry motor fibres to the spinal cord and brain stem - responsible for the voluntary control of the muscles of the body and face
What are the extrapyramidal tracts?
Originate in the brain stem, carry motor fibres to the spinal cord - responsible for the involuntary control of all musculature e.g. tone, balance, posture, locomotion
What are the corticobulbar tracts?
UMNs that synapse with LMNs n the cranial nerve nuclei and control muscles of the face and neck
Signs if there was a UMN lesion
This is anything affecting the cerebral cortex down to the anterior horn cells of the spinal cord
Signs equate to spasticity: contralateral, unilateral hemiparesis
- Flexed upper limb (weak extensors)
- Extended lower limb (weak flexors)
- Increased tone
- Brisk reflexes (nothing to fine tune it)
Spastic gait (scissor legs if bilateral, hemiplegic gait if unilateral)
What are the common brain causes of spastic hemiparesis?
Anything that causes a unilateral UMN lesion
- Stroke (hyperacute)
Space occupying lesion (more degenerative and chronic)
- Haemorrhage (can be acute or chronic)
- Abscess (acute/ chronic)
- Inflammation
Why are the corticospinal tracts prone to damage?
They span the full length of the CNS and pass through the internal capsule which is a common site of cerebrovascular events
Discuss UMN lesions in the spinal cord
Likely to cause bilateral UMN signs below the level of the lesion bevaise it is unlikely only one side of cord affected
Thoracic spinal cord: spastic paraparesis
Cervical spinal cord: spastic quadriparesis
What are the categories of spinal cord lesion?
Extrinsic
- Trauma: fracture, disc prolapse, haematoma
- Infection: osetomyelitis, discitis, abscess
Neoplastic: breast/ prostate mets, myeloma
Intrinsic
Inflammatory: MS, infections
Other: B12 deficiency, spinal ischaemia (stroke), intrinsic neoplasm, hereditary spastic paraparesis
You have a patient who cannot feel their legs when you touch them - how do we find the sensory level?
Go up the thorax trying to find where sensation is present
T4 = nipple
T10 = umbilicus
Differentiating from a spinal UMN lesion and a brain UMN lesion?
Spinal = bilateral (usually)
Brain = unilateral (usually)
What are lower motor neurons?
Peripheral nerves starting at the anterior horn cell in the spinal cord
- Nerve roots
- Cauda equina
Brachial and sacral plexus
- Cranial nerves 3-12 are peripheral nerves
Clinical signs of a LMN lesion
Think Lower think Loss
- Loss of tone
- Muscle wasting (severe and quick)
- Loss of power
- Loss of reflexes
- Gait is often high stepping or slapping due to foot drop
Signs of cerebellar disease
V: Vertigo
A: Ataxia
N: Nystagmus
I: Intention tremor
S: Slurred speech
H: Hypotonia
E: Exaggerated broad-based gait
D: Dysdiadochokinesia
If there is a lesion in the left of the cerebellum, where will the signs be present?
On the left - this is because the fibres of the cerebellum do not cross
Both afferent and efferent fibres remain ipsilateral
What can commonly cause bilateral cerebellar signs?
Paraneoplastic syndrome
Alcohol
What would a lesion in the vermis of the cerebellum cause?
Truncal ataxia - inability to sit upright or stand without support
Can be caused by haematomas that only affect the vermis - although this is rare
What are the basal ganglia?
Think about a gang sitting under the cortex
Subcortical nuclei strongly connected withc erebral cortex
Functions:
- Control/ selection/ initiation of voluntary movement (sub. nigra is a basal ganglia structure) - best known role
- Procedural learning
- Habits
- Eye movements
- Congition
- Emotion
What are the main input nuceli of the basal ganglia?
Striatum = caudate and putamen
- Information comes into the striatum from the cortex for fine tuning
What are the main output nuclei of the basal ganglia?
Globus pallidus + sub. nigra
They send most of their outputs to the thalamus and some to brainstem nuclei
Reminder of the direct and indirect pathways
Theory suggests that the thalamus wants to allow movement all the time but the basal ganglia is there to keep it in check
Direct pathway: signal comes from the motor cortex to move, signal goes through basal ganglia and thalamus, movement is fine tuned and we move - controlled by D1 receptors
Indirect pathway: normal function is to stop movement by inhbiting the feedback from the thalamus to the motor cortex - controlled by D2 receptors
Think of it like dopamine and the basal ganglia have the final say about movement
How might a sensory problem present?
- Numbness
- Tingling
- Pain
- Pins and needles
What is important to look for when doing a sensory examination?
- Dermatomal/ glove and stocking sensory loss
- Pressure ulcers, muscle wasting
- Gait: Romberg’s test/ sensory ataxia, swaying occurs when eyes closed because lack of feedback from peripheral nerves
Rigidity vs spasticity on examination
Rigidity: resistance feels the same in all movements and does not depend on velocity
Spasticity: resistance is felt in one direction and is velocity dependent - the faster you go the worse the spasticity gets
What causes spasticity?
UMN lesion
Lesion in the pyramidal tract
- Stroke
- Spinal cord compression
- MND
Types of rigidity
- Cogwheel: due to a tremor + hypertonia
- Lead pipe
Neurotransmitters in the CNS and PNS
CNS
Glutamate = main excitatory NT
Gaba = main inhibitory NT
PNS
- Ach for somatic & autonomic transmission
NA main NT for sympathetic branch of autonomic NS
Cerebral dominance
-
Each hemisphere has separate & combined functions.
- Motor/sensory control is bi-lateral.
- Certain functions however are uni-lateral.
-
Dominant hemisphere is responsible for;
- Language.
- Mathematical processing.
- Writing.
- In Right handed & 70% of left handed pt. this is in the left hemisphere.
-
Non-dominant is responsible for;
- Spatial recognition.
- Musical interpretation.
- Interpretation of emotional salience & tone of speech.
