W6 - spinal cord and spinal nerves Flashcards
Describe the gross anatomy of the spinal cord and its protective structures
Serves as a pathway for the:
Transmission of impulses for the periphery of the brain - afferent pathways
Transmission of impulses from the brain to the effector muscles and organs - efferent pathways
Coordination of spinal reflexes - quick reactions to stimuli
Gross anatomy of spinal cord
Cylindrical in shape
Commences at the foramen magnum at the base of the cranium and during development fills the entire vertebral canal
Spinal cord segments
2 enlargements: of spinal cord
Cervical enlargement: due to increased amount of the grey and white matter that supplies nerves to the upper limbs
Lumbar enlargement: due to increased amount of the grey and white matter that supplies nerves to the pelvis and lower limbs
Spinal minges
Epidural Block
Lumbar puncture
Internal structure of the spinal cord
Grey matter = central (consists of neuronal cell bodies, unmyelinated axons and glial cells)
White matter = around grey (primarily myelinated axons)
The central canal is the continuation from the 4th ventricle and the central canal of the medulla oblongata.
It travels throughout the length of the spinal cord and contains CSF.
It is encircled by the grey matter known as the grey commissure.
The external surface of the spinal cord has two longitudinal depressions
Posterior Median Sulcus: midline, posteriorly a narrow groove
Anterior Median Fissure: midline anteriorly slightly wider and deeper groove
Grey Matter of the Spinal Cord
Morphology depends on area taken from
The diameter of the spinal cord in the cervical region, particularly in its lower segments, and the lumbar region, are the largest due to amount of grey matter needed for the supply of the muscles of the upper and lower limbs.
These regions correspond to the spinal cord enlargements
grey matter (horns)
White Matter of the Spinal Cord
3 regions:
Posterior column
Lateral column
Anterior column
Name the spinal nerves, describe how they emerge from the spinal cord through intervertebral foramina and describe the typical structure of a spinal nerve
Mixed nerves
axons of motor and sensory neurons that form the spinal nerves
31 pairs: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
The cervical spinal nerves exit the vertebral canal through the intervertebral foramen above the corresponding vertebra. For example: C4 spinal nerve exits the vertebral canal through the intervertebral foramen between C3 and C4 vertebra.
In the thoracic region and below, the spinal nerves exit the vertebral canal inferior to the corresponding vertebra: T2 spinal nerve exits the vertebral canal below the corresponding vertebra so between T2 and T3 vertebra.
Peripheral Nerve
Epineurium: connective tissue sheath that holds motor and sensory axons of the peripheral nerve together
Perineum: tissue sheath bound to fascicles (within the nerve axons are separated into smaller groups - fascicles)
Endoneurium: loose areolar connective tissue that surrounds each axon within the fascicle
Connective tissue provides extra support and cushioning for the delicate nervous tissue and channelise the blood vessels around the axons.
Dermatome
Area of the skin supplied by a single spinal nerve
Substantial area of overlapping
Shingles:
Painful rush and blisters of the skin with dermatomal distribution are common symptoms and signs in shingles.
After the childhood infection with chickenpox virus, the virus stays inactivated (latent) in the root ganglia of the spinal nerves. Reactivation of the virus during the adulthood causes proliferation of the virus through the sensory axons of the dermatome and cause changes on the skin.
Myotome:
Portion of a skeletal muscle innervated by a single spinal cord level or by a single nerve.
More difficult to test than dermatomes because each muscle is usually innervated by nerves deriving from more than one spinal cord level (spinal nerve).
For example: biceps brachii is innervated by the musculocutaneous nerve that has a spinal root value C5, C6 and C7.
Define a nerve plexus and identify the cervical, brachial, lumbar and sacral plexuses
Nerve plexus: network of anterior rami of spinal nerves
Either somatic or visceral
The posterior rami of the spinal nerves are short and do not form plexuses. Posterior rami supply the deep muscles and skin of the back.
SOMATIC plexuses
formed of the anterior rami of the spinal nerves
Cervical, brachial, lumbar, sacral
Cervical plexus
(right and left) are formed by the anterior rami of the cervical spinal nerves C1-C4.
The plexus delivers 2 sets of nerves:
motor nerves that supply the infrahyoid muscles of the neck, and anterior rami of the C3 and C4 join the C5 spinal nerve join to form phrenic nerve for the innervation of diaphragm.
cutaneous branches supply the skin of the neck auricle of the ear and skin over the shoulder.
Brachial plexus
The brachial plexuses (right and left) are networks of the anterior rami of C5 –C8 and T1 spinal nerves.
Main terminal branches of the brachial plexus are:
musculocutaneous nerve supplies the muscles of the anterior compartment of the arm (flexors of the forearm at elbow joint)
median nerve supplies muscles of the anterior compartment of the forearm (with an exception of 1 1/2 muscles). These muscles are flexors at the elbow and wrist joint
ulnar nerve is a chief nerve for the supply of most of the intrinsic muscles of the hand and 1 1/2 muscles of the forearm
axillary nerve supplies deltoid muscle
radial nerve supplies extensor muscles of the posterior compartment of the arm and forearm.
Lumbar plexus
Lumbar plexuses (right and left) are formed by anterior rami of spinal nerves L1-L4 on the posterior wall of the abdominal cavity.
The main nerves arising from the lumbar plexus are:
femoral nerve, supplies the muscles of the anterior compartment of the thigh (extensors at the knee)
obturator nerve, supplies the muscles of the medial compartment of the thigh (adductors of the thigh at the hip joint
Sacral plexus
Sacral plexuses (right and left) are formed by the anterior rami of the spinal nerves L4/L5 and S1-S3/4.
The nerves arising from the sacral plexus supply the pelvis, gluteal region, posterior compartment of the thigh and leg muscles and anterior and lateral compartments of the leg.
The largest and longest nerve in our body the sciatic nerve is formed by the anterior rami of L4/5 and S1-S3. It consists of two divisions that split into 2 nerves in the popliteal fossa:
tibial nerve (supplies the muscles of the posterior compartment of the leg - these muscles are plantar flexors at the ankle joint and weak flexors at the knee) and supplies intrinsic muscles of the sole of the foot.
common fibular nerve (formed of the posterior division of the sciatic nerve. The nerve wraps around the neck of the fibula and divides into:
superficial fibular nerve (supplies muscles of the lateral compartment of the leg)
deep fibular nerve (supplies muscles of the anterior compartment of the leg – dorsiflexors of the foot at ankle joint)
Visceral Plexuses
Visceral plexuses are formed of sympathetic and parasympathetic afferent and efferent components and form:
cardiac
pulmonary
oesophageal
abdominal prevertebral plexuses
thoracic spinal nerves
Describe what a simple spinal reflex is, name a few (stretch, tendon, withdrawal) and discuss their importance
stretch reflex (monosynaptic)
monosynaptic (consists of 2 neurons)
sensory neuron synapses directly onto the motor neuron in the anterior horn of the spinal cord.
withdrawal reflex (polysynaptic)
polysynaptic (more than 2 neurons as it involves interneurons)
Since there are more than one synapse the response is slower than in monosynaptic reflex.
Golgi tendon reflex: polysynaptic
