L1- Anatomy of the spinal cord and spinal nerves

How is the nervous system divided?

Central nervous system (brain and spinal cord)

Peripheral nervous system (cranial nerves and spinal nerves)

Which aspect of the brain is the spinal cord a direct continuation of, and what is another name for the spinal cord?

The brain stem (medulla oblongata). Other name is the medulla spinalis

Where does the spinal cord leave the skull?

Foramen magnum

What is at the centre of the spinal cord?

Central canal filled with cerebrospinal fluid, lined with ependymal cells

The diagram shows the dorsal and ventral roots. The roots are made of axons. What forms when the axons of each root are bound together?

Spinal nerves

What are spinal ganglion?

Cell bodies outside of the brain and spinal cord (they are in PNS)

What do dorsal roots do, and what do ventral roots do?

• Dorsal- sensory (afferent) input to spinal cord

• Ventral- motor (efferent) input to effectors (muscles and glands)

What do dorsal and ventral branches innervate?

Dorsal- innervate epaxial tissues (dorsal to transverse processes)

Ventral- innervate hypaxial tissues (ventral to transverse processes)

What is the name of the two locations where nerves to the limbs arise, and the diameter is increased?

Intumescence

How are the thoracic limbs (forelimb) supplied with nerves?

Cervical intumescence- form the brachial plexus

(C6 to T2)

How are the pelvic limbs (hindlimbs) supplied with nerves?

Lumbar intumescence- form the lumbosacral plexus

(L5 to S1/S3)

What are the spinal cord segments in a dog? (not vertebrae)

36 segments

• 8 cervical

• 13 thoracic

• 7 lumbar

• 3 sacral

• 5 caudal

In a dog, why are there 7 cervical vertebrae but 8 cervical spinal nerves?

The first cervical spinal nerve leaves from the lateral vertebral foramina in the Atlas

The rest leave through the lateral intervertebral foramina/ sacral foramina, cranial to the cervical vertebrae

In a dog what is the name of the end of the spinal cord?

Conus medullaris

What is the filum terminale?

A continuation beyond the functional end of the spinal cord, containing no neural fibres and only connective tissue

Stabilises spinal cord by attaching to coxes

Describe the structure of the grey matter of the spinal cord

Divided into two horns: dorsal (sensory) and ventral (motor)

Surrounds the central canal carrying cerebrospinal fluid

Why does grey matter appear grey?

Because it contains many neuronal cell bodies

What does the grey and white matter mainly consist of?

Grey matter- neuronal cell bodies, dendrites, axons and neuroglia

White matter- axons (myelinated and nonmyelinated)

Why does white matter appear white?

Due to the lipid composition of the myelin

What is the lateral horn?

Location of cell bodies for the autonomic nervous system

What are tracts, nerves, nucleus and ganglion?

Tract- a bundle of axons in the CNS

Nerve- a bundle of axons in the PNS

Nucleus- neuronal cell bodies in the CNS

Ganglion- neuronal cell bodies in the PNS

Describe the difference between somatic and visceral neurons

Somatic- relating to the body and skeletal muscles, often voluntary

Visceral- relating to to internal organs and involuntary functions

How is white matter arranged?

Organised into tracts, grouped into columns extending the length of the cord

What are meninges?

The three layers of connective tissue surrounding the brain and spinal cord- Dura matter, arachnoid matter and pia matter

Where in the meninges is the cerebrospinal fluid?

Subarachnoid space- space between arachnoid and pia matter

Where around the meninges is the epidural space?

Outside of the outer layer of meninges (dura matter)

It forms because the dura matter does not lie directly against vertebral periosteum