Structure and function of the spinal cord Flashcards
Spinal cord boundaries
Starts at C1 [atlas]
to
L1
Spinal cord regions
Named according to the vertebrae which the spinal nerves leave:
Cervical [C1-8]- Thicker, supplying upper limb.
Thoracic [T1-12]
Lumbar [L1-5]- Thicker, supplying lower limb
Sacral [S1-5]
Lumbar cistern
Lumbosacral enlargment
Thickening of the spinal cord at the lumbar-sacral region due to a large number of nerves supplying the lower limbs.
Conus medullaris
Narrowing of the spinal cord at L1/L2.
- The pia mater still extends further down the spine.
Terminal filum
Extension of the pia mater from the conus medullais, into the coccyx.
Internal part- pia mater
External part- dura
Lumbar cistern
Subarachnoid space in the lower lumbal canal
- Contains cauda equina nerve roots.
- Contains terminal filum
Cauda equina
A group of:
- Lumbar/sacral dorsal and ventral nerve roots
Contained in the lumbar cistern
Surrounding of spinal cord
Spinal cord enclosed in vertebral canal.
Enclosed in meninges:
- Dura mater [meningeal]
- Arachnoid
- Pia
Grey matter, spinal nerves
Contains neuronal cell bodies and associated glia.
Thickest in the cervical and lumbosacral region—> innervation to the limbs
Horns: Ventral---->Motor [descending] neurones Dorsal-----> Receives sensory input Lateral---->Sympathetic preganglionic neurones - Only in thoracic region
Interneurones also exist within each vertebral level.
White matter, spinal nerves
Contains myelinated neuronal axons.
Tracts/Columns/ funiculi:
Dorsal—-> Sensory/ Ascending
Ventral—-> Motor/ descending
Lateral—-> Descending + Ascending.
Proprioceptive and Exteroceptive
Proprioceptive:
- Information from within the body
- From joints, Golgi tendon organs, muscle spindles
Exteroceptive:
- Information from outside the body
- Pain, temperature, touch.
All communicated through the ascending tracts of the spinal cord.
Ascending tract anatomy
1st order neurones
- Enter spinal cord at dorsal root
2nd order neurones
- Ascends spinal cord/ brainstem
3rd order
- Projects into cerebral cortex.
Dorsal column medial-lemnisucus pathway
- Function
Ascending tract
- Fibres do not cross
- Longest axons in the body
Communicates fine touch/ tactile discrimination
- Cutaneous mechanoreceptors
Proprioception
- Positional information
Dorsal column medial-lemnisucus pathway
- Sensory neurone enters dorsal horn and ascend dorsal column on the SAME SIDE
- Enters fasciculus gracile [medially]
- Fasciculus cuneatus [laterally] - First order neurones synapse with 2nd order at the medulla.
- F.gracile terminates at nucleus gracilis [Lower limb]
- F.cuneatus terminates at nucleus cuneate [upper limb]
Crossing:
- Second order fibres cross medulla and ascend the thalamus as medial lemniscus [Reil’s ribbon]
- 2nd order neurones in the thalamus synapse with third order neurones at the somatosensory cortex
1st order neurones
- Dorsal column medial lemniscus pathway
Enters the dorsal horn and ascends the dorsal columns- on the same side.
- Fasciculus gracile [medially]
- Fasciculus cuneatus [Laterally]
Synapses with 2nd order neurones in the medulla
- DOES NOT CROSS
2nd order neurones
- Dorsal column medial lemniscus pathway
Synapses with first order neurones in the medulla.
- Fasciculus gracile terminates—-> nucleus gracilis [lower limb]
- Fasciculus cuneatus terminates —-> nucleus cuneate [upper limb]
Neurones ascend to the thalamus
3rd order neurones
- Dorsal column medial lemniscus pathway
Projects from the thalamus to the somatosensory cortex,
Damage to the dorsal column medial lemniscus pathway
- Symptoms
- Sign
- Example
Lesion on one side of the spinal cord= sensory ataxia
Loss of tactile discrimination
Symptoms on the SAME side.
Sign:
Romberg’s sign
Example:
Multiple sclerosis
Sensory ataxia
Loss of co-ordination and balance due to loss of sensory input
- Seen in damage to Dorsal column medial lemniscus pathway.
- Balance and co-ordination still there with visual cues
Romberg’s sign
Clinical test used to diagnose sensory ataxia
- Seen in damage to the dorsal column medial lemniscus pathway
Individual sways off-balance when eyes are closed + feet apart.
- BUT can balance when eyes are opened.
Spinothalmic tract
- Function
Ascending tract
Communicates pain, temperature, CRUDE touch
- Nociceptors [receptors that response to damaging/potentially damaging stimuli]
Spinothalmic tract pathway
- First order neurones enter dorsal horn—> Forms tract of Lissauer
- Gives collateral branches at the tip that runs up 1/2 segments
- Synapses in dorsal horn with 2nd order neurones. - 2nd order neurones cross in dorsal horn at each vertebral level
- Ascends anterolateral column to thalamus
- Lateral fibres= lower limb
- Medial fibres= upper limb - Third order neurones project from thalamus to somatosensory cortex
Spinothalmic tract pathway
- First order neurones
Enter dorsal horn and forms tract of Lissauer
- Gives off collateral branches to 1/2 segments
Synapses with 2nd order neurones in dorsal horn
Spinothalmic tract pathway
- Second order neurones
Crosses at dorsal horn
- Ascends anterolateral column to the thalamus
Medial= upper limb fibres
Lateral- lower limb fibres
Spinothalmic tract pathway
- Third order neurones
Projects from the thalamus to the somatosensory cortex.
Damage to spinothalmic tract
Lesion on one side of the spinal cord gives rise to symptoms on the OTHER side
- Loss of pain, temperature, crude touch.
Compressing lesion= loss in lower limb first
Inner, grey matter tumour= loss in upper limb first.
Spinocerebellar tracts
- Description
- Function
- Examples
Ascending tract
- Communicates unconscious, muscle proprioception
- Smooth, muscle co-ordination
Only 2 neurones in circuit
- 4 tracts altogether
Fibres DO NOT CROSS
Anterior and posterior spinocerebellar tracts
- Proprioceptive information from the trunk and lower limbs
Posterior spinocerebellar tract pathway
- First order neurone synapses in dorsal horn
- Second order neurone ascends lateral column —-> into cerebellum
- Very quick axons [fastest sensory neurone in body]
Anterior spinocerebellar tract pathway
- First order neurone synapses at dorsal horn.
- 2nd order neurone crosses dorsal horn then ascends the lateral column—–> cerebellum
- Fibre crosses back at the cerebellum.
Damage to post/ant spinocerebellar tract
Causes loss of co-ordination of lower limb on the same side
- Rarely affected in isolation
Corticospinal tract
Voluntary motor pathway [descending tract]
2 neurones:
- Fibres from the cerebral cortex synapse at ventral horn.
- Fibres from ventral horn synapse at skeletal muscle
Pyramidal tract
Part of the corticospinal tract
- Fibres from primary motor cortex —-> posterior limb of internal capsule
- Fibres from post. limb of internal capsule—-> cerebral peduncle
- Cerebral peduncle—-> Pons
- Pons —> Medulla pyramids
- Pyramids—-> Lat/ anterior corticospinal tract—–> ventral horn etc
Pyramidal decussation
In the pyramidal tract:
- Lateral corticospinal tract crosses in the MEDULLA.
[80% of tract] - Anterior tract is on the same side [20%]
- cross at cervical region to supply neck muscle
Topographical organisation in ventral horn of corticospinal tract
Medial horn- innervation of trunk
Anterolateral- proximal limb
Posterolateral- distal limb
Upper motor neurone disease
- Definition
- Presentation
- Example
Disruption of the corticospinal tract—> upper neurones
Region affected
- Above pyramid = opposite side
- Below pyramid= same side
Presentation
- Spatic paralysis
- Overactive tendon reflexes
- No significant muscle atrophy
Example:
Following stoke
Lower motor neurone disease
- Definition
- Presentation
- Cause
Disruption of corticospinal tract—-> lower neurones
Presentation:
- Flaccid paralysis
- No tendon reflexes
- Muscle atrophy
Example:
- Spinal muscular atrophy
Spinal muscular atrophy
Lower motor neurone disease
- Mutation of SMN1 gene—» codes for survival of motor neurone
Amyotrophic lateral sclerosis [ALS]
Motor neurone disease that affects lower and upper neurones
Presentation:
- Progressive muscle weakness
- Progressive muscle atrophy
- Intact mind without control of body
- Bulbar signs in later stage [speech, eating]
Spasticity–> upper neurones affected
Causes:
Potential genetic mutation [SOD1 gene]
Extrapyramidal tracts
Descending tracts
- Do not pass through medullary pyramid
Instead descend through:
- Basal ganglia
- Cerebellum
- Pons
Example
- Reticulospinal tract
Reticulospinal tract
Descending, extrapyramidal tract.
- Locomotion and posture
Reticular formation in pons—–> Ventral horn in spinal cord
- Regulates its motor activity and reflexes
- Facilitates/ inhibits lower motor neurones
