Structure and Function of the Spinal cord

symptoms of Lou gehrids disease?

Initial limb weakness/Bulbar signs 9speech and swallowing difficulty. Spasticity present when upper motor neurons are affected. Short life span of 5years due to respiratory failure

Internal Anatomy of the spinal cord: Describe the internal anatomy of the spinal cord.

Inner core= Grey matter: -Neuronal cell bodies -H-shaped -Ventral, lateral and dorsal horns Outer white matter: -Myelinated axons -White columns/tracts or funiluci

Spinocerebellar tracts: What does it mean if the neurons are uncrossed?

Left cerebellum controls left side of the body.

Why is there flaccid paralysis?

Loss of upper motor neurons that innervate skeletal muscles--> No motor supply--> No muscle tone.

No tendon reflexes? Why? Muscle atrophy? Why?

Loss of upper motor neurons--> Incomplete circuit--> No reflexes. Loss of lower neurons--> No trophic supply--> Atrophy.

Why is there not significant muscle atrophy?

Lower motor neurons are still supplying the skeletal muscles with trophic factors.

What are the posterior and anterior ramus?

Main peripheral nerves.

What will the lower motor neurons of the medial, anterolateral and posterolateral ventral horn innervate?

Medial- Innervate the muscles of the trunk. Anterolateral- innervate proximal limb segments. Posterolateral- Distal limb segments

What forms the neural arch?

Neural arch formed by the spinus, transverse processes and the lamina that connects the two.

Why is balance loss only when visual input stops (eyes closed)?

Open eyes--> positional information through the eyes being open so the brain knows what the limbs are doing.

Damage to anterolateral column: What region of the body is affected if one side of the spinal cord is damaged?

Opposite side loses ability to feed pain, temperature and crude touch because the first order neurons crossed the midline prior the anterolateral column.

What is the effect of anterolateral column damage?

Outside compression cord: Loss of lower limb pair first (fibers sit laterally). Inside grey matter tumour= Loss of upper limb pain first then the lower limb (Fibers sit medially)

Why are tendon reflexes overactive?

Overactive reflexes due to loss of lower motor neuron control. Still have lower motor neurons and proprioceptive (afferent) component--> Reflex.

Spinocerebellar tracts: What is the spinocerebellar tract?

Proprioceptive tracts that project input form the muscles and joints to the cerebellum for smooth motor coordination.

Ascending (sensory) tracts: What types of information is carried in the ascending (sensory) tracts?

Proprioceptive: Input from inside the body (Muscles, joins, tendons) Exteroceptive: Input from outside the body e.g. the skin (Pain, temperature, touch)

What are crossing tracts?

Tracts carrying impulses to and from the cerebral hemispheres. They desiccate the midline meaning the left cerebral hemisphere controls the right side vice versa.

Whats the effects spinal damage on one side of the cord?

Uncoordinated lower limb muscular activity on same side.

What are motor neuron diseases divided into?

Upper motor neuron disease Lower motor neuron disease

white matter organization: State the organization and tracts constrained in the columns of the white matter columns (From front of the spinal cord to back)

Ventral (front)= Mainly descanting motor information down the spinal cord. Lateral middle= Ascending and descending tracts (more medial) Dorsal (back)= Ascending afferent sensory information.

Corticospinal tract: Where do upper motor neurons synapse onto the lower motor neurons?

Axons reach the ventral horn and synapse onto low motor neuron cell bodies. Low motor neuron cell bodis of the medial part of the ventral horn innervate the muscles of the trunk.

White matter organization: What are the tracts of the white matter?

- Dorsal funiculi- Ascending tracts that carry afferent (sensory) information to the brain from the periphery. -Ventral funiculi- descending tracts carry efferent (motor) impulses form the brain centres -> Spinal cord-> Periphery.

What are afferent fibers?

- Primary-sensory neurons (pseudo-unipolar) with cell bodies sitting dorsal root (Above root)

What are efferent nerve fibers?

-Axons of motor in the spinal cord. -Pre-ganglionic sympathetic neurons in the feratic region.

Extrapyramidal tracts: What are extrapyramidal tracts?

-Do not pass through the pyramids. - They are descending tracts from basal ganglia, cerebellum and pons than do not pass through the pyramids.

What are the symptoms of lower motor neuron disease (opposite upper lower motor neuron disease)?

-Flaccid paralysis (no muscle tone) -No tendon reflexes -Muscle atrophy

What is the spinal cord protected by?

-Sits within a vertebral column. -Epidural fat underneath the bone of the vertebral canal. -Meninges surround the spinal cord: Dura- Surrounds spinal cord. Arachnoid. Subarachnoid space containing CSF. Pia lining the surface of the spinal cord.

What happens to the spinal cord at the 1st lumbar vertebrate?

-Spinal cord narrows to form conus medullaris. -Pia carries on from the terminal filum to the coccyx. The thread of pia helps to tether the spinal cord to the bottom of the vertebrate column.

What's the pathway of the axon from the motor cortex to the anterior corticospinal tract?

-Upper motor neurons in primary motor cortex pass through the posterior limb internal capsule--> Cerebral peduncle--> pons--> Pyramids of the medulla--> Anterior corticospinal tract.

Summarise the spinothalamic pathway

1. 1st order neuron (nociceptor) enters dorsal horn tip forming leisure. 2. 1st synapse to 2nd order in the dorsal horn and cross the midline. 3. 2nd order goes up the antholateral column and synapse to 3rd order neurons in the thalamus. 4. 3rd neurons project from the thalamus to the somatosensory cortex.

Posterior spinocerebellar tract: First-order neruons

1. 1st order neurons enter and synapse in the dorsal horn. 2. 2nd order neurons ascent in lateral column to cerebellum- Very fast.

What are the two neurons of the corticospinal tract circuit?

1. Upper motor (premotor) neurons - From cerebral cortex to ventral horn. 2. Lower motor neurons from ventral horn to skeletal muscles

Dorsal column-medial lemniscus pathway: First order neurons:

1st order enters the spinal cord via the dorsal column. The axons ascend the dorsal column on the same side as they enter

Ascending tracts- anatomy: Describe the neuronal circuit of the ascending tract.

1st order--> 2nd order--> 3rd order. 1st order: Primary sensory neuron that enters the spinal cord via the dorsal horn. 2nd order: Secondary sensory neuron that ascends the spinal cord to the brainstem. 3rd order: Projects to the cerebral cortex.

How is the spinocerebellar tract different from the spinothalamic tract?

2 neurons. Neurons do not cross midline.

What proportion of axons don't cross and where to they project to?

20% don't cross and stay on the same side to the anterior corticospinal tract.

Spinothalamic tract- Third order neurons: Describe the passage of 2nd order neurons.

2nd order neurons cross midline the spinal cord and ascend the anterolateral column to the thalamus.

What is the topographical organization of the spinothalamic tract?

2nd order neurons from lower limb sit on the lateral aspect. 2nd order neurons from the upper limb sit on the medial aspect.

How many cervical vertebrae are there?

7 (C1-C7). The 7 exit above the lowest cervical vertebrate. C8 exits below the lowest cervical vertebrate

Spinothalamic tract: What is the spinothalamic tract responsible for?

Acts as the pain pathway. Carries information on thermal sensation, temperature and crude touch via nociceptors.

What are peripheral nerves?

All nerves outside of the CNS that carry information to and the CNS in order to enable complex bodily function.

Summary:

Anatomy of the spinal cord Ascending tracts: -Dorsal column-medial lemniscus (touch, propoioception) -Spinothalamic (pain) -Spinocerebellar (unconscious propoioception) Descending tracts: -Corticospinal (voluntary motor) -Reticulopspinal (reflexes)

What are the two type of spinocerebellar tracts?

Anterior and posterior spinocerebellar tracts carry proprioceptive information from the trunk and lower limb to the cerebellum.

Describe the crossing of the anterior spinothalamic tract and why is the tract fast?

Anterior spoinocerebellar cross to the other side and then cross back. Fast axon transmission--> Smooth movement.

Motor neuron disease: What is motor neuron disease?

Any disruption of the corticospinal tract.

Corticospinal tract/Pyramidal tract: Why is the coricospinal tract referred to as the pyramidal tract?

Axons pass through the pyramids of the medulla.

What are tracts of Lissauer?

Collateral branches given off at the dorsal horn tip. Run up or down 1-2 segments.

Spinal nerves; What is the function of spinal nerves? How many nerve pairs are there and what is each formed by?

Connect the periphery to the spinal cord. 31 pairs, each formed by dorsal and ventral root.

Corticospinal tract: What is the function?

Control all skeletal muscles in the body and is referred to as the great voluntary motor pathway.

descending motor tracts What to descending motor tracts control? Where do the neurons descend from?

Control muscular activity From the cortex

Anatomy of the spinal cord: What's the start and end point of the spinal cord?

Cranial border of the atlas (base of spinal cord) to the 1st lumbar vertebrate.

Spinothalamic tract- Second-order neurons: Describe the positioning of the second order neurons. How is this different from the dorsal-column lemniscus pathway?

Cross in the dorsal horn at each level. Dorsal-column lemniscus axons crossed in the medulla rather than the spinal cord.

Dorsal column-medial lemniscus pathway: Whats the positioning of second order neurons?

Cross the midline within the medulla to form the medial lemniscus (ribbon) --> Thalamus. 2nd order neurons synapse onto the 3rd order neurons. 3rd neuron then projects up via the internal capsule to the somatosensory cortex (Post central gyrus)

Lower motor neuron disease: What is lower motor disease?

Degeneration of lower motor neurons in the ventral horn.

Motor neuron disease: What is upper motor neuron disease? What are the symptoms of upper motor disease?

Degeneration of upper motor neurons. Spastic paralysis (increased muscle tone) Overactive tendon reflexes

Damage to dorsal column: What is the effect of lesions to the left hand side?

Dorsal columns effected. Results in loss of fine touch and proprioception on the left side. Symptoms: Sensory ataxia- Poor coordination and balance on the left hand side without visual cues. Clinical test: Romberg's sign -Severe swaying on standing with eyes closed/ feet together.

Name and describe the position of the three spinal cord columns (white matter) (Use alphabetical order as hint)

Dorsal columns/Posterior= column on top/In the back Lateral column (T1-T12)= Mid column. Ventral column/Anterior = Bottom column/in front

Where does the first order neurons synapse onto the second order neuron?

Dorsal horn

Name and describe the position of the three spinal cord horns (Use alphabetical order as hint)

Dorsal horn/Postiror= horn on top/In the back Lateral horn (T1-T12)= Mid horn. Ventral horn/Anterior = Bottom horn/in front

Grey matter organization:

Dorsal horn= Receives and carries sensory information to the brain via ascending pathways. Primary sensory neurons pass through the dorsal to enter the back of the spinal cord. Lateral horn= Preganglionic sympathetic neurons (Autonomic function) Ventral horn= -Alpha motor neurons -Preganglionic sympathetic neurons pass through the ventral route.

Which root contain efferent and afferent fibers? (Match them by alphabetical order)

Dorsal root= Afferent fibers Ventral root= Efferent fibers

Describe the distribution of Dura in the spinal cord

Dura carries on down to the lumber cictern that contains cauda equina. Dura forms a sleeve around the pia part of the terminal filum to tether the spinal cord to the coxyccs

Dorsal column-medial lemniscus pathway: Where do 1st-order neurons synapse to?

Fasciculus cuneatus synapse on second order neurons of the cuneate (medulla). -Information from upper limb Fasciculus gracilis synapse on second order neurons of the nucleus gracilis (medulla). -Information from lower limb

Dorsal column-medial lemniscus pathway: First-order neuron divisions Describe length

Fasciculus gracilis (Medial) Fascilus cuneatus (lateral) More than ammeter in length (longest)

Describe the entering and synapsing of first order neurons (primary sensory neurons)

First order neurons: -Enters the tip of the dorsal horn. -First order neurons form tracts of lissauer--> Second order neurons.

What is the difference between grey matter at levels of the limbs and why?

Grey matter expands at the levels that supply the limbs.

Dorsal column-medial lemniscus pathway: Whats the function of the dorsal column-medial lemniscus? What does this ascending pathway carry?

Provide brain with positional information to alert it of what the muscles and the joints are doing - Exteroceptive information about Fine touch from cutaneous mechanoreceptors--> Tactile discrimination. vibration sense. -Proprioceptive information for the muscle spindles, Golgi tendon organs, joints.

Corticospinal tract: What are the pyramids referred to as and why?

Pyramids of decussation because 80% of upper motor neuron axons cross the midline within the pyramids in order to get to the lateral corticospinal tracts.

Extrapyramidal tracts: Whats an example of an extrapyramidal tract? What is the function of the reticulospinal tract?

Reticulospinal tract. From reticular formation (pons) to spinal cord. Regulates ventral horn motor activity/reflexes. Facilitates and inhibits lower motor neurons. Important for posture and locomotion.

Amyotrophic lateral sclerosis (Lou Gehrigs disease). What is Lou Gehrids disease?

Selectively affects lower an upper motor neurons --> Progressive muscle weakness but brain isn't effected so they are aware.

Is the spinal nerve short or long? Why?

Short Soon after the spinal nerve is formed it divides into posterior and anterior primary ramus.

Anatomy of the spinal cord: How many regions is the spinal cord divided into? What are the regions?

Spinal cord is divided into four regions. 1. Cervical region (C1-C8) 2. Thoracic region (T1-T2 spinal nerves) 3. Lumbar region (L1-L5) 4. Sacral region (S1-S5) regions = where the spinal nerve the region exit the vertebral columns.

Whats an example of a lower motor neurons disease and how is it caused?

Spinal muscular atrophy. Defects in SMN1 gene--> No lower motor neuron survival.

Who else has Lou Gerhrigs?

Steven Hawkins

Why do upper motor neuron suffers have spastic paralysis?

Still have innervation of the skeletal muscles by lower motor neurons but they cant control the lower motor neurons neurons.

What causes upper motor disease? When do symptoms occur on the opposite and same side?

Stroke Above pyramids= Symptoms on the opposite side. Below pyramids= Symptoms on the same side.

Why is the loss of sensation on the same side as the spinal damage?

The physiological consequences are experience on the same side of the spinal dorsal column damage because the axons have not crossed over yet.