7.5 Nerve Supply of the Limbs Flashcards
What makes up the central nervous system?
- Brain
- Spinal cord
- Retina and optic nerve (cranial nerve II)
What makes up the peripheral nervous system?
- Sensory pathways
- Motor pathways, which are:
- > Somatic nervous system
- > Autonomic nervous system (sympathetic, parasympathetic and enteric)
Made up of the cranial nerves and visceral autonomic nerves/ganglia/plexuses
How many pairs of symmetrically arranged spinal nerves are there?
31
Through where do the spinal nerves leave the spinal cord?
Through the intervertebral foramina of vertebrae
How many cervical nerves are there?
8 (C1-C8), but only 7 vertebrae (C1 exits spinal cord above C1 vertebrae, and C2 exits between C1 and C2 vertebrae)
How many thoracic nerves are there?
12 (T1-T12), associated with the 12 thoracic vertebrae
How many lumbar nerves are there?
5 (L1-L5), associated with the 5 lumbar vertebrae
How many sacral nerves are there?
5 (S1-S5), associated with the 5 fused sacral vertebrae
How many coccygeal nerves are there?
Only one, associated with the coccygeal vertebrae (varying numbers, frequently 4 fused vertebrae but ranges from 3-5)
How many nerves emerge from the brain?
There are 12 cranial nerves (CN I-XII)
Where does the spinal cord range from?
It is continuous with the brain stem above the foramen magnum, but extends from that point to around the level of the intervertebral disc between L1 and L2, tapering at an end point called the conus medullaris and becoming the cauda equina
What are the meninges?
The three layers of connective tissue that cover the spinal cord:
- Dura mater
- Arachnoid mater
- Pia matter
Where do thoracic, lumbar and sacral nerves emerge from the spinal cord?
From the intervertebral foramen of the respective vertebrae below them (equal numbers of nerves and vertebrae)
Where do cervical nerves emerge from the spinal cord?
From the intervertebral foramen of the respective vertebrae above them (8 cervical nerves, 7 vertebrae)
e.g. C8 emerges between C7 and T1
What is the foramen magnum?
Large hole in the skull that allows the passage of the brain stem/spinal cord, vertebral arteries/veins and the anterior/posterior spinal arteries/veins. Attached to the atlas via alar ligaments
Practise drawing out and labelling the spinal cord transverse diagram,
Do it!! Innervation of limbs lecture slide 6
What are the dorsal root ganglia (DRG)?
Swellings on the dorsal root of each nerve, contain the cell bodies of sensory nerves whose dendrites (in somatic nervous system) receive information from sensory receptors (these may be in skin, muscles or tendons)
Where do the axons of sensory nerves go to?
To the dorsal horn of the spinal cord
Describe the monosynaptic reflex arc.
- Sensory receptor detects change in environment/a stimulus
- This results in an impulse travelling up the dendrites, through the cell body and through the axons
- In the CNS, the sensory nerve has a synapse directly with a corresponding motor nerve (alternatively will synapse with a interneuron)
- Motor nerve leaves on the same segmental level and brings about a response to the stimulus
How can sensory and motor nerve information be transmitted within the CNS?
- Sensory information can travel up segmental levels to the brain if necessary, enter through the dorsal root (remember through dorsal
- Motor information can travel down the segmental levels from the brain until the necessary level is reached, emerging from ventral roots
Where can motor information be transmitted to from the spinal cord?
- The SNS (somatic nervous system), to voluntary striated muscle
- The ANS (autonomic nervous system), to cardiac muscle, glands and smooth muscle associated with viscera or blood vessels
Where do the cell bodies of motor neurons of the SNS lie?
In the ventral horn of the grey matter in the spinal cord
Where do the sensory nerves enter the spinal cord and from where do motor nerves leave?
Sensory nerves: enter through the dorsal root/rootlets
Motor nerves: emerge from the ventral root/rootlets
How is functional spinal segmentation indicated?
By the 31 PAIRS of symmetrical nerves emerging from the spinal column
Each pair refers to a ‘segment’ of the spinal cord
What forms the spinal nerves?
A union of the dorsal and ventral roots
- These are in turn formed of various dorsal and ventral rootlets
What emerges from the intervertebral foramen?
A mixed nerve, comprised of the joining of the dorsal and ventral roots
What structures do mixed nerves split into after emerging from the intervertebral foramen?
They split into posterior/dorsal and anterior/ventral rami, which can contain a mix of nerves
Which of the rami is larger, anterior or posterior?
- Anterior is a larger ramus
- Posterior is a smaller ramus
- Where do the thoracic rami innervate?
- Posterior/dorsal ramus supplies motor fibres of the back and sensation for the skin of the same region via a cutaneous branch
- Anterior/ventral ramus innervates muscles of the anterolateral thoracic wall, and sensation over the skin through a cutaneous branch
What are dermatomes?
Unilateral bands of skin/cutaneous regions that are provided with sensation by the same single spinal nerve
What are myotomes?
Unilateral portion of skeletal/striated muscle (can stretch over a large distance) that are all innervated or partly innervated by the same single spinal nerve
How can impingement of a nerve affect its dermatome and myotome?
- Pain may shoot down the nerve
- Regions may tingle or become numb
What do posterior/dorsal rami in the thoracic region innervate?
- Extensors of the spine
- Overlying skin
What do anterior/ventral rami in the thoracic region innervate?
- Limbs
- Ventral trunk
Do dermatomes overlap?
- Yes, adjacent dermatomes overlap fairly significantly, so transection of a single nerve is unlikely to lead to a massive/whole band where sensation is lost
- Difficulty in finding where dermatomes are (especially as they can vary from person to person) means that mapping dermatomes exactly in a diagram is extremely difficult, meaning ones in textbooks aren’t always 100% reliable
Do limb muscles receive innervation from a single spinal nerve/segment?
They can, but it is more likely for them to receive innervation from multiple segments/nerves (e.g. biceps brachii receives innervation from the C5, C6 and C7 spinal segmental levels via the musculocutaneous nerve, but majority of nerves come from the C5 segment so muscle ‘belongs’ to the C5 myotome, despite having regions that correspond to all 3)
What happens during limb development that affects dermatomes?
- Upper limb rotates laterally/dorsally so that flexors face anteriorly
- Lower limb rotates medially/ventrally so that extensors face anteriorly
This results in the twisting of dermatomes seen across the limbs
What does cutaneous mean?
Under/in the skin
What does loss of sensation or pain localised to a dermatome indicate?
Entrapment or damage to spinal nerves/spinal cord segments e.g. unilateral pain in dermatome S1 indicates the compression of the S1 spinal nerve, perhaps due to herniation of an intervertebral disc)
What is paraesthesia?
‘Pins and needles’, strange sensations occurring in a dermatome due to the brief compression or impingement of a peripheral nerve
How can compression of a peripheral nerve be indicated?
- Paraesthesia
- Pain localised to a limb peripheral nerve territory
What does loss of sensation below a specific dermatome indicate?
Damage to the spinal cord at that dermatomal level (e.g. bilateral loss of sensation below the T7 level dermatome indicates spinal cord trauma or pathology at that level
What does muscle weakness in a specific myotome indicate?
- A lesion at that spinal segment or to that spinal nerve
What myotome(s) controls shoulder abduction?
C5, e.g. deltoid (innervated by axillary nerve)
What myotome(s) controls shoulder adduction?
C6, C7, C8
What myotome(s) controls shoulder flexion?
C5
What myotome(s) controls shoulder extension?
C6, C7, C8
What myotome(s) controls elbow flexion?
C5, C6, e.g. biceps brachii (innervated by musculocutaneous nerve)
What myotome(s) controls elbow extension?
C6, C7, C8, e.g. triceps brachii (innervated by radial nerve)
What myotome(s) controls supination?
C6
What myotome(s) controls pronation?
C7, C8
What myotome(s) controls wrist flexion and extension?
C6, C7
What myotome(s) controls finger flexion and extension?
C7, C8, e.g. flexion by flexor digitorum superficialis (innervated by median nerve)
What myotome(s) controls finger abduction and adduction?
T1, e.g. interossei (innervated by ulnar nerve)
What myotome(s) controls hip flexion?
L2, L3, e.g. psoas major (innervated by ventral rami of L1-L3 nerves)
What myotome(s) controls hip extension?
L4, L5
What myotome(s) controls hip abduction?
L5, S1
What myotome(s) controls hip adduction?
L2, L3
What myotome(s) controls medial hip rotation?
L2, L3
What myotome(s) controls lateral hip rotation?
L5, S1
What myotome(s) controls knee flexion?
L5, S1, e.g. hamstrings (innervated by the sciatic nerve)
What myotome(s) controls knee extension?
L3, L4, e.g. quadriceps group (innervated by femoral nerve)
What myotome(s) controls ankle plantarflexion?
S1, S2, e.g. gastrocnemius (innervated by tibial nerve)
What myotome(s) controls ankle dorsiflexion?
L4, L5
What myotome(s) controls ankle inversion?
L4, L5
What myotome(s) controls ankle eversion?
L5, S1
What myotome(s) control toe abduction and toe adduction?
S2, S3, e.g. interossei (innervated by the lateral plantar nerve)
What are deep tendon reflexes?
- Monosynaptic stretch (myotactic) reflexes
- Normal stimulus-response time of around 20 milliseconds
- Tapping tendons with a hammer (e.g. patella tendon) is detected by muscle spindles, which are sensitive to changes in muscle length
- This sends sensory information back to the CNS via different sensory neurones
- Monosynaptic component of reflex arc operates using sensory nerve input synapsing directly onto and activating alpha motor neurons (at L4 spinal level for patella tendon reflex)
- This will cause the muscle to contract (quadriceps for patella tendon reflex, triggering the ‘knee jerk’)
Do myotomes and dermatomes of the same segmental level overlap?
Not necessarily - they may be in different locations spacially but originate from the same segment of the spine/spinal root
What is the most common tool for initiating knee jerk reflexes?
Tendon hammer
What is involved in the knee jerk reflex?
- Patella tendon
- L4 spinal level (dominant)
- Quadriceps muscle contracts to cause jerk/knee extension
What is involved in the biceps reflex?
- Biceps tendon
- C5 spinal level (dominant)
- Biceps brachii muscle contracts to cause elbow flexion
What are the two main types of nerve plexuses in the PNS and their features?
- Somatic plexuses, formed from anterior/ventral rami of spinal nerves, supply skin, voluntary skeletal muscle and joints, formed in relationship to the limbs (except for the cervical plexus).
- Autonomic plexuses, found in the thorax, abdomen and pelvis, distribute nerves to blood vessels and viscera, formed of both sympathetic and parasympathetic nerves (will be covered in more depth in another set of flashcards)
Are ventral rami modified during limb development?
Yes, the segmental pattern of each ventral ramus innervating its own area of skin and muscle adapts to suit the limbs as they develop
What are some of the features of the brachial plexus?
- Ventral rami of nerves C1-C4 join together to form the cervical plexus
- Several branches supply the head, neck and shoulder region
What are some of the features of the brachial plexus?
- Ventral rami of nerves C5-C8 and T1 form the brachial plexus
- Supplies skin and muscles of the upper limb
Nerves present: - Axillary (C5-C6)
- Radial (C5-T1)
- Ulnar (C8-T1)
- Median (C5-T1)
- Musculocutaneous (C5-C7)
What are some of the features of the lumbar plexus?
- Ventral rami of nerves L1-L4 join to form the lumbar plexus
- Supplies much of the muscle and skin of the lower limb
Nerves present: - Obturator (L2-L4)
- Femoral (L2-L4)
What are some of the features of the sacral plexus?
- Ventral rami of nerves L4-L5 and S1-S3 join to form the sacral plexus
- Supplies much of the muscle and skin of the lower limb
Nerves present: - Sciatic nerve (L4-S3), which forms the
-> tibial nerve (L4-S3)
-> common peroneal (fibular) nerve (L4-S2)
Common peroneal divides to form: - Superficial peroneal (fibular) nerve
- Deep peroneal (fibular) nerve
What innervates the deltoid?
Axillary nerve
What innervates the anterior compartment of the arm?
Musculocutaneous nerve
What innervates the posterior compartment of the nerve?
Radial nerve
What innervates the anterior compartment of the forearm?
Median and ulnar nerves
What innervates the posterior compartment of the forearm?
Radial nerve
What innervates the gluteal region?
Superior and inferior nerves
What innervates the anterior compartment of the thigh?
Femoral nerve
What innervates the posterior compartment of the thigh?
Sciatic nerve
What innervates the medial compartment of the thigh?
Obturator nerve
What innervates the lateral compartment of the leg?
Superficial peroneal/fibular nerve
What innervates the anterior compartment of the leg?
Deep peroneal/fibular nerve
What innervates the posterior compartment of the leg?
Tibial nerve
What structures (going medially to laterally) make up a plexus?
Roots, trunks, divisions, cords and branches
From what rami is the brachial plexus made up from?
C5-T1
What are the three trunks of the brachial plexus and what are they made up of?
- Upper/superior trunk: C5-C6 roots
- Middle trunk: C7 root
- Lower/inferior trunk: C8 and T1 roots
Found in the neck between the scalene muscles and the clavicle
What type of nerve is derived from the anterior division of the brachial plexus?
Divides just after the clavicle, supplies anterior (flexor) compartments of the upper limb. This includes anterior flexor muscles and skin of the:
- Arm
- Forearm
- Hand
What type of nerve is derived from the posterior division of the brachial plexus?
Divides just after the clavicle, innervates the posterior (extensor) compartments of the upper limb. This includes posterior extensor muscles and skin of the:
- Arm
- Forearm
- Hand
What are the cords of the brachial plexus?
Cords are all named with respect to their position relative to the axillary nerve
- Posterior cord is formed from all posterior divisions
- Lateral cord is formed from the anterior division of the upper and middle trunks
- Medial cord is formed from the anterior division of the lower trunk
What are the branches of the brachial plexus?
The major nerves supplying the upper limb
- Posterior cord gives off the radial and axillary nerves
- Lateral cord gives off the musculocutaneous nerve
- Medial cord gives off the ulnar nerve
- The median nerve is formed from both the medial and lateral cords
- Also many smaller peripheral nerves that innervate muscles of the upper limb and pectoral girdle (e.g. axillary, long thoracic nerve (causes winging of scapula if damaged), thoracodorsal nerve, pectoral nerves, suprascapular nerve, subscapular nerve)
What is the axillary nerve and what does it innervate?
- Terminal branch of the posterior cord of the brachial plexus
- Innervates the deltoid and teres minor, the shoulder joint and skin covering the deltoid
- If the nerve is damaged (e.g. following a shoulder dislocation) the doctor can diagnose this by checking for sensation in the skin covering the deltoid
- Deltoid is a powerful abductor of the arm (following initiation of abduction by supraspinatus)
What rami make up the lumbar plexus and where does it lie?
Ventral rami of spinal nerves L1-L3 and part of L4, formed deep to the psoas muscle
What do the direct branches from the lumboar plexus innervate?
- Psoas major
- Sometimes the iliacus muscles (innervated by the femoral nerve which is L2-L4)
What are the major peripheral nerves from the lumbar plexus innervate the lower limb?
- Femoral nerve (L2-L4)
- Obturator (L2-L4)
- Lateral femoral cutaneous (L2-L3, provides sensation across lateral thigh)
What are the peripheral nerves derived from the L1 nerve root?
- Iliohypogastric
- Ilioinguinal
- Genitofemoral
(will be studied later in the course)
What rami make up the sacral plexus and where does it lie/pass through?
- The ventral rami of the rest of L4 which isn’t part of the lumbar plexus and L5 make up the lumbosacral trunk
- This joins the ventral rami of S1, S2 and S3 to form the sacral plexus
- Lies anterior to the piriformis muscle, with most of the nerves passing through the greater sciatic foramen to the gluteal region and the lower limb
What are the main nerves of the sacral plexus?
- Superior gluteal nerve
- Inferior gluteal nerve
- Sciatic nerve
What are the sensory territories of the major nerves of the upper limb?
- Musculocutaneous nerve (C5-C7), anterior arm compartment muscles, upper nerve root
- Median nerve (C5-T1), most anterior compartment forearm muscles as well as thenar muscles and lumbricals
- Radial nerve (C5-T1), posterior arm and forearm compartment muscles
- Axillary nerve (C5-C6), deltoid and teres minor, upper nerve roots
- Ulnar nerve (C8-T1), most small muscles of the hand, lower nerve roots
LOOK AT PICTURES IN LECTURE TO SEE THE DERMATOMES
Where does the median nerve come from and what does it innervate?
- C5-C7
- Lateral cord of the brachial plexus
- Passes laterally to supply the muscles in the anterior muscle compartment of the arm
- > allows shoulder and elbow flexion, as well as forearm supination
- > innervates biceps brachii, coracobrachialis, brachialis
- Terminates as a sensory nerve (lateral cutaneous nerve of the forearm) supplying the skin of the lateral forearm
Where does the median nerve come from and what does it innervate?
- C5-T1
- Arises from both the lateral and medial cords of the brachial plexus
- At the cubital fossa, lies medial to the brachial artery
- Passes through the carpal tunnel to get to the hand
- Supplies most of the muscles in the anterior compartment of the forearm and hand EXCEPT FOR flexor carpi ulnaris and the medial half of flexor digitorum profundus (see ulnar nerve flashcard)
- > this allows wrist, finger and thumb flexion
- Innervates the thenar muscle group at the base of the hand
- > this allows abduction, flexion and opposition of the thumb
- Innervates the lateral two lumbricals
- > this allows flexion of the metacarpophalangeal and extension of the interphalangeal joints of digits 2 and 3
- Supplies sensation for the skin over the lateral aspect of the hand and lateral 3 and a half digits
Where does the ulnar nerve come from and what does it innervate?
- C8-T1
- Arises from the medial cord of the brachial plexus
- Lies medial to the brachial artery in the arm, passes behind the medial epicondyle of the humerus in the ‘cubital tunnel’
- Enters medial side of forearm
- Passes over flexor retinaculum to enter the hand NOT through the carpal tunnel
- Vulnerable to damage at the elbow and at the wrist
- Innervates the anteromedial aspect of the forearm and the hand
- > flexor carpi ulnaris (wrist flexion) and medial half of flexor digitorum profundus (flexion of the medial two digits) of the forearm
- > hypothenar muscles at the base of the little finger (abductor, flexor and opposer)
- > palmar and dorsal interossei (abduction and adduction of fingers)
- > medial two lumbrical muscles (flexion of the metacarpophalangeal and extension of the interphalangeal joints)
- Provides sensation over the medial aspect of the hand and medial one and a half digits
Where does the radial nerve come from and what does it innervate?
- C5-T1
- Arises from posterior cord of the brachial plexus
- Gives sensation to the skin over the dorsum of the hand
- Supplies the posterior (extensor) compartments of the arm and the forearm
- Supplies NO muscles in the hand
What happens if the radial nerve is damaged?
- Extent of paralysis/sensory loss depends on where the nerve was damaged
- > e.g. if lesion is at axilla (armpit region) then effectively all upper limb extensor action is lost
- No elbow extension due to paralysis of triceps brachii
- No wrist extension (‘wrist drop’) and no extension of digits will be caused by loss of function to the posterior compartment of the forearm
- Thumb abduction weakened (abductor pollicus longus is lost, but motion still possible as abductor pollicus brevis innervated by median nerve)
- Sensory loss present in the dorsolateral forearm and hand
- Distal damage may preserve the elbow, but loss of extension in the wrist and hand, as well as weakened thumb abduction, will be seen
Where does the radial nerve come from and what does it innervate?
- L2-L4
- Emerges from lateral aspect of psoas major muscle
- Enters thigh behind the inguinal ligament through an area called the femoral triangle
- Lies lateral to the femoral vein and artery (order can be remembered using ‘a VAN drives through the femoral triangle’; medially to laterally, vein, artery, nerve)
- Divides below inguinal ligament to innervate the anterior compartment of the thigh
- > quadriceps femoris group
- > sartorius
- Gives sensation to the skin overlying the anterior thigh
- Femoral nerve becomes the saphenous nerve (lies with great saphenous vein), this cutaneous nerve gives sensation to the medial aspect of the leg and foot
- Femoral nerve carries information sensory information from the knee and hip joints
Where does the obturator nerve come from and what does it innervate?
- L2-L4
- Emerges from medial border of psoas major
- Follows curve of lateral pelvic wall before passing through obturator foramen of the pelvis
- Innervates the medial compartment of the thigh
- > adductor muscles
- Gives sensation to skin overlying the medial aspect of the thigh
- Carries sensory information from the hip joint
Where do the gluteal nerves (superior and inferior) come from and what do they innervate?
Superior gluteal nerve:
- L4-S1
- Posterior divisions of sacral plexus
- Leaves pelvis via greater sciatic notch
- Innervates gluteus medius and minimus
- > provides stability in the pelvis whilst walking
Inferior gluteal nerve
- L5-S2
- Posterior divisions of sacral plexus
- Leaves pelvis via greater sciatic notch
- Innervates gluteus maximus
- > powerful hip extensor
Where does the sciatic nerve come from and what does it innervate?
- L4-S3
- Largest nerve in the body
- Emerges from pelvis via greater sciatic foramen, passing midway between the greater trochanter and ischial tuberosity
- > this is essential landmarking/surface projection to know, as this nerve may be damaged by an intramuscular injection into the buttock
- Supplies ALL foot and leg muscles, much of the skin of the leg and foot and all of the joints of the lower limb via two components:
- > Tibial nerve
- > Common peroneal (fibular) nerve
- Region where this split differs but is usually around mid-thigh region/just above the popliteal fossa (anatomical region behind the knee)
- Through the tibial nerve, the sciatic nerve innervates the posterior compartment of the thigh (hamstrings) for knee flexion and hip extension
Where does the tibial nerve come from and what does it innervate?
- L4-S3
- Formed when the sciatic nerve splits in two
- Anterior divisions of the lumbosacral plexus
- Lies in the popliteal fossa
- Runs deep into the soleus muscle
- Innervates the posterior compartment of the leg, allowing dorsiflexion and plantarflexion of the ankle
- Lies with the posterior tibial artery and enters the sole of the foot behind the medial malleolus
- Divides into lateral and medial planter nerves in the foot, supplying muscles of the foot and the skin overlying the medial and lateral aspects of the sole of the foot (similar arrangement to median and ulnar nerves in the hand)
Where does the peroneal (fibular) nerve come from, what does it split into and what does it innervate?
- L4-S2
- Formed when sciatic nerve splits in two
- Lies along lateral margin of the popliteal fossa
- Curves posteriorly around the neck of the fibula
- > quite prone to injury at this point
- Divides into the superficial and deep peroneal (fibular) nerves
- > these innervate the lateral and anterior compartments of the leg
- Common peroneal (fibular) and tibial nerves contribute to the sural nerve (cutaneous, provides sensation on the posterolateral surface of the leg and the lateral part of the foot)
- Deep peroneal (fibular) nerve:
- > accompanies anterior tibial artery and innervates muscles of the anterior part of the leg
- > this allows dorsiflexion and inversion
- > gives sensation to skin overlying the adjacent sides of the 1st and 2nd toes
- Superficial peroneal (fibular) nerve:
- > supplies the muscles of the lateral compartment of the leg
- > this allows dorsiflexion and eversion
- > gives sensation to skin of the anterolateral distal 1/3 of the leg and the dorsal surface of the foot
Look at picture of sensory regions for both leg and arm
Do it!
What is carpal tunnel syndrome?
Common condition that causes numbness, tingling or pain in the hand due to the median nerve being compressed as it enters the hand through the carpal tunnel (e.g. trauma and swelling to the wrist, diabetes, high blood pressure)
Impingement of the nerve may also cause wasting/atrophy of the thenar eminence through disuse and denervation
