6: Anatomy - Spinal nerves Flashcards by Ross Wilson

Where does the spinal cord end?

L1/2

@ the conus medullaris

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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

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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

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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

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Where do many sensory nerves synapse before entering the spinal cord?

Dorsal root ganglia

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Which nerve modalities do spinal nerves contain?

Both sensory and motor

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What nerve modalities are found in spinal nerves?

Somatic motor

Somatic sensory

Visceral afferent

Visceral efferent (sympathetics T1 - L2; parasympathetics S1 - 5)

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Which arc of neurons synapse in the spinal cord to carry out involuntary movements in response to dangerous stimuli?

Reflex arc

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What is neuralgia?

Nerve pain

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What is the medical term for nerve pain?

Neuralgia

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What is paraesthesia?

Tingling sensation

“Pins and needles”

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What is the medical term for pins and needles?

Paraesthesia

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What is anaesthesia?

Numbness

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What is the medical term for numbness?

Anaesthesia

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What is hyperaesthesia?

Increased sensitivity

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What is hypotonia?

Loose, floppy muscles

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What is the medical term for loose, floppy muscles?

Hypotonia

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What is the medical term for a loss of coordination and balance?

Ataxia

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What is ataxia?

Loss of coordination and balance

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How do you test the

a) motor

b) sensory

parts of a spinal nerve?

a) Myotomal testing

b) Dermatomal testing

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How can you test the sensory AND motor aspects of a spinal nerve at the same time?

Reflex testing

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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

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How do third-order neurons of the sensory pathways get from the thalamus to the post-central gyrus?

Internal capsule

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When testing somatic sensory neurons, which dermatome must you compare your findings to?

Contralateral dermatome

tells you if it’s unilateral or bilateral

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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) ## Footnote **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** ## Footnote **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 ## Footnote **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**