6: Anatomy - Spinal nerves Flashcards
Where does the spinal cord end?
L1/2
@ the conus medullaris
What is the difference between a spinal nerve and a named nerve?
Spinal nerve: contains axons from ONE spinal cord level
Named nerve: contains axons from MULTIPLE spinal cord levels, it gains them as it goes along
Which nerve modalities emerge from the
a) anterior horn
b) posterior horn
of the spinal cord?
a) Motor (including somatic motor, sympathetic and parasympathetics [from the sacral spinal nerves only])
b) Sensory
What is a spinal ganglion?
A group of nerve cell bodies found in the POSTERIOR ROOT of each spinal cord level
The neurons in here are the ‘first-order’ neurons for sensory pathways like the DC/ML and spinothalamic tracts
There’s no such thing as an anterior root ganglia, so they’re called dorsal root ganglia
Where do many sensory nerves synapse before entering the spinal cord?
Dorsal root ganglia
Which nerve modalities do spinal nerves contain?
Both sensory and motor
What nerve modalities are found in spinal nerves?
Somatic motor
Somatic sensory
Visceral afferent
Visceral efferent (sympathetics T1 - L2; parasympathetics S1 - 5)
Which arc of neurons synapse in the spinal cord to carry out involuntary movements in response to dangerous stimuli?
Reflex arc
What is neuralgia?
Nerve pain
What is the medical term for nerve pain?
Neuralgia
What is paraesthesia?
Tingling sensation
“Pins and needles”
What is the medical term for pins and needles?
Paraesthesia
What is anaesthesia?
Numbness
What is the medical term for numbness?
Anaesthesia
What is hyperaesthesia?
Increased sensitivity
What is hypotonia?
Loose, floppy muscles
What is the medical term for loose, floppy muscles?
Hypotonia
What is the medical term for a loss of coordination and balance?
Ataxia
What is ataxia?
Loss of coordination and balance
How do you test the
a) motor
b) sensory
parts of a spinal nerve?
a) Myotomal testing
b) Dermatomal testing
How can you test the sensory AND motor aspects of a spinal nerve at the same time?
Reflex testing
Which part of the brain is the end point for the main sensory pathways?
Post-central gyrus of cerebral cortex
Also known as main somatosensory area / sensory strip
How do third-order neurons of the sensory pathways get from the thalamus to the post-central gyrus?
Internal capsule
When testing somatic sensory neurons, which dermatome must you compare your findings to?
Contralateral dermatome
tells you if it’s unilateral or bilateral
In terms of C1, what is notable about its sensory component (i.e posterior ramus)?
It doesn’t have one
Describe the dermatome of C1.
Doesn’t have one
Which structures does the C2 dermatome cover
a) anteriorly
b) posteriorly?
a) Adam’s apple
b) Back of scalp
Which structures does the C3 dermatome cover
a) anteriorly
b) posteriorly?
a) Jugular notch
b) Back of neck
Which spinal nerves supply the sensory fibres for the upper limb?
C5 - T2
i.e the brachial plexus (C5 - T1) and T2
Which area of the upper limb does the C5 dermatome cover?
Regimental badge patch area
i.e proximal, lateral arm
Which spinal nerves supply sensory fibres to the
a) index finger
b) little finger
c) thumb?
a) Index finger - C7
b) Little finger - C8
c) Thumb - C6
Which spinal nerves supply sensory fibres for the
a) pubic symphysis
b) umbilicus
c) male nipple?
a) Pubic symphysis - T12
b) Umbilicus - T10
c) Male nipple - T4
Which spinal nerves supply the sensory fibres for the groin?
L1
Think “hands in pockets” to remember the areas of skin
Which area of the lower limb is given sensory fibres by L2 and L3?
Anterior thigh
Anterior knee
Which malleolus is supplied by
a) S1
b) L4?
a) Lateral malleolus (S1 supplies the heel, i.e posterior)
b) Medial malleolus (L4 supplies the medial leg)
Which area of the lower limb is given sensory fibres by L5?
Dorsum of the foot
Which aspects of the foot and ankle are given sensory fibres by S1?
Plantar surface of foot
Lateral malleolus
Which spinal nerve supplies the sensory fibres for the posterior leg and thigh?
S2
S3, S4 and S5 form a bullseye shape around which structure?
Anus
sorry for the imagery
What aspects of the trunk are supplied by the
a) anterior horn
b) posterior horn?
a) Intercostal muscles
b) Skin (segmentally)
What aspect of skin would you palpate to test the action of sensory nerves in the posterior ramus?
Back
Which area of skin would you palptate to test the action of sensory nerves coming from anterior ramus?
Chest and abdomen
Which named nerves supply sensory fibres to
a) upper trunk (anterolateral)
b) lower trunk (i.e below the ribcage)?
a) Intercostal nerves
b) Subcostal nerve
How many spinal nerves are found in named nerves?
More than one e.g musculocutaneous nerve, which contains fibres from C5 and C6
How do you figure out the dermatomes supplied by named nerves?
Figure out which spinal nerve roots are in the named nerve
e.g Femoral nerve is L2-4
so dermatomes are L2, L3 and L4 - anterior leg, thigh and medial malleolus
Which spinal nerves form the cervical plexus?
C1 - C4
Which area of the head and neck is supplied with sensory fibres by the cervical plexus (C1 - C4)?
Anterolateral area
so ear, side of neck etc
What is Erb’s point?
Where is it?
Convergence of cervical plexus (C1-4)
Midpoint of posterior border of SCM
Where is Erb’s point found?
Midpoint of posterior border of SCM
At which point do the cutaneous nerves of the cervical plexus (C1-C4) enter the skin?
Erb’s point
Midpoint of the posterior border of SCM
Which nerves supply sensory fibres to the
a) anterolateral head and neck
b) face
c) posterior neck and scalp?
a) Cervical plexus (C1-4)
b) Trigeminal nerve (CN V1, V2 and V3)
c) C2-8
The supraclavicular nerves supply sensory fibres to the clavicle and shoulder.
Why is pain from the diaphragm referred to the shoulder?
Diaphragm receives somatic motor fibres and sends visceral afferent fibres via the PHRENIC NERVE (C3, 4 and 5)
Supraclavicular nerves send sensory fibres to C3, 4 and 5
The visceral afferents and supraclavicular nerves plug into the spinal cord at the same levels, so pain can be referred
From an anterior dermatome of skin to the posterior horn, what structures does an action potential travel through?
Skin
Nerve plexus
Anterior ramus
Spinal nerve
Posterior root, rootlets
Posterior horn
If the sensation was felt posteriorly the AP would travel through the posterior ramus
What are the named nerves of the cervical plexus and their spinal levels?
Lesser occipital nerve (C2)
Greater auricular nerve (C2 & 3)
Transverse cervical nerve (C2 & 3)
Supraclavicular nerve (C3 & 4)
Little goats tread softly
Why does anginal pain sometimes radiate to the upper arm?
Myocardium sends visceral afferents to T1 and T2 spinal nerves
T1 and T2 dermatomes are the medial arm and forearm
Where is the motor centre of the brain found?
What is it also known as?
Pre-central gyrus of the frontal lobe, anterior to the central sulcus
Primary somatomotor cortex / motor strip
Which muscles are supplied with somatic motor fibres by the cervical plexus (C1-4)?
Muscles of the neck (postural and strap muscles)
Diaphragm (C3,4,5 keeps the diaphragm alive)
Which muscles are supplied by somatic motor fibres by the cervical plexus?
Neck muscles - postural and strap
Diaphragm
Which spinal nerves contribute to the
a) cervical plexus
b) brachial plexus?
a) Cervical plexus - C1-C4
b) Brachial plexus - C5-T1
Which muscles are supplied by somatic motor fibres by the brachial plexus?
Extrinsic back muscles (levator scapulae, rhomboids major and minor and latissimus dorsi; EXCEPT trapezius, which is CN IX)
Upper limb muscles
Which muscles are controlled by
a) anterior rami
b) posterior rami
originating from spinal nerves T2-L3?
a) Intercostal muscles
b) Intrinsic back muscles (erector spinae and transversospinalis groups)
How do you figure out the myotomes supplied by a named nerve?
Figure out the spinal nerve roots of the named nerve and then apply all the myotomes of those spinal nerves
Which skeletal muscles are supplied by the lumbosacral plexus?
Lower limb muscles
Perineal skeletal muscles
Where generally are the deltoid muscles found?
Shoulder joint
Which spinal nerve gives somatic motor fibres to the deltoid?
C5
Which action does the deltoid muscle perform at the shoulder?
Abduction
Which named nerve supplies the deltoid muscle?
What are its nerve roots?
Axillary nerve
C5-6
Which muscle is most responsible for flexion at the elbow?
Which named nerve supplies it?
Biceps brachii
Musculocutaneous nerve (C5-6)
Which muscle is most responsible for extension at the elbow?
Which named nerve supplies it?
Triceps brachii
Radial nerve (C5-T1)
What is a reflex?
An INVOLUNTARY response to a dangerous stimulus
What is the reflex arc?
Pathway that action potentials take to trigger a reflex response
Do action potentials travel up and down the ascending and descending tracts to trigger a reflex response?
Why?
No
Takes too long
In a reflex arc, where do action potentials
a) enter the spinal cord
b) exit the spinal cord?
Which type of neuron carries the action potential on their axons?
a) Posterior root (sensory)
b) Anterior root (motor)
Lower motor neurons (or LMNs)
In a reflex response, action potentials cross straight from the posterior horn to the anterior horn to enact a quick motor response.
Which neurons
a) carry the action potentials
b) act as “descending controls” to stop unwanted movements?
a) Lower motor neurons (LMNs)
b) Upper motor neurons (UMNs)
What happens to muscle movements if there’s a lesion in the
a) upper motor neurons
b) lower motor neurons
of a reflex arc?
a) Spasticity
b) Flaccidity
How can spinal reflexes be tested?
Tap muscle tendons with a hammer to elicit a reflex (“jerk”) response
What reflex tests C5-6 by flexing the elbow?
Biceps jerk
Flexion of elbow by biceps brachii
What reflex tests C7 by extending the elbow?
Triceps jerk
Extension of the elbow by triceps brachii
Which reflex tests C6 by supinating/pronating the forearm?
Brachioradialis reflex
What is the knee jerk reflex?
Which spinal nerve, named nerve and muscle does it test?
Extension of flexed knee in response to tapping on patellar tendon
L3; femoral nerve; quadriceps femoris
What is the ankle jerk reflex?
Which spinal nerve, named nerve and muscle does it test?
Plantarflexion of dorsiflexed foot in response to tapping on Achilles tendon
S1; superficial fibular nerve; gastrocnemius
