Nerve supply of the limbs Flashcards
Cross sectional structure of the spinal cord
- central region of grey matter surrounded by white matter
Function of white matter
arranged in columns containing the nerves containing the brain and spinal cord
Structure of grey matter
- H shape around a central canal
- grey matter broadly divided into two dorsal horns and two ventral horns (posterior and anterior respectively)
What are the dorsal and ventral roots?
Pairs of spinal nerves each formed by the fusion of nerve segments knows as the ventral and dorsal roots
What are the rami?
The dorsal root, containing sensory information and the ventral root containing motor, join together and then branch off to form the ventral and dorsal rami, each with a mixture of nerves
The posterior (dorsal) ramus structure and function
Supplies muscles and sensation to the back- extensors of spine and overlying skin
The dorsal ramus of each spinal nerve travels backward, apart from C1, L4,L5 and coccygeal
Each posterior ramus innervates a narrow strip of skin and muscle along the back, more or less at the level at which it leaves the spinal nerve
The anterior (ventral) ramus structure and function
- supply anterograde-lateral parts of the trunk and the limbs
- anger than dorsal rami
- in thoracic region, each ventral ramus supplies a narrow strip of muscle and skin along the sides, chests, ribs and abdominal wall- refereed to as intercostal nerves
- in regions other than thoracic, the nerves from different rami combine to form plexuses
What are plexuses?
A network of tangled nerves from different ventral rami, thus containing several spina; nerves
What is the benefit of nerve plexuses?
Fibres from each ventral ramus travels along different routes so that each limb muscle receives innervation from several spinal nerves, thus there is a back up plan in case of injury
What is the brachial plexus?
Group of nerve fibres that gets its contribution from the transitional area from neck into axilla, between C5-T1
Brachial plexus function
Provides almost all the innervation of the upper limb, including the back and scapular muscles that control the limb
5 stages in a plexus
root-trunk-division-cord-terminal
5 major nerves in the arm + their roots
Musculocutaneous- C5- C7
Axillary- C5-C6
Radial- C5-T1
Median- C5-T1
Ulnar- C8, T1
Lumbosacral plexus function and roots
L1-L4 is lumbar plexus and sacral is L4-S5
Lumbar innervates the anterior thigh, abnormal wall and iliopsoas muscle
Sacral innervates buttocks, pelvis, perineum and lower limb, apart from anterior and medial thigh
5 major nerves in the leg + their roots
Obturator L2-L4
femoral- L2-L4
sciatic- L4-S3
tibial- L4-S3
common fibular- L4-S2
How are sensory nerves organised?
Afferent nerve fibres from a single dorsal root of spinal nerve innervate a specific area of skin called the dermatome
Dermatome structure
Like stacks of discs forming a human
each supplied by a different spinal nerve
dermatomes run longitudinally along the limbs
Slight overlap between dermatomes
Function of dermatome + clinical significance
sensory region- allow for cutaneous innervation
If a symptom appears to follow the dermatome, such as a rash, there may indicate a pathology that involves the related nerve root
How are the spinal nerves distributed in the dermatome?
Ventral ramus supplies anterior aspect whereas dorsal ramus supplies posterior
What damage could occur to a dermatome?
entrapment or damage of a spinal nerve of spinal cord segment
e.g unilateral pain in an S1 dermatome may occur due to the compression of the S1 nerve as a result of disc herniation
Myotome definition
Unilateral portion of skeletal muscle receiving innervation from a single spinal nerve
Explain how a myotome is defined
Each region of muscle often receives innervation from many spinal nerves, thus each muscle is organised using different myotomes.
Clinical importance of a myotome
muscle weakness in a specific myotome territory indicates a lesion at that spinal segment or to that spinal nerve
Do dermatomes and myotomes occupy the same region?
No, dermatomes and myotomes of the same segmental level do not necessarily overlap spatially
myotatic reflex definition
A muscle contractual in response to stretching within a muscle
Monosynaptic reflex
a stretch reflex that provides automatic regulation of a skeletal muscle length, whereby a signal entering the spinal cord arises from a change in muscle length or velocity
How does a myotatic reflex work?
Muscle spindle structures, whose extrafusal muscle fibres lie parallel to the muscle, sense changes in length and velocity.
Eventually causes an action potential in the alpha motor neurone causing the fibres to contract and thus resist the stretching
Explain anatomical basis of biceps reflex
Examines the function of the C5/C6 reflex arc
Tendon hammer used to knock the cubital fossa in which the biceps brachii tendon resides
Depresses the muscle spindle, mainly associated with C5 than C6, due to the roots of the musculocutaneous nerve
Biceps reflex process
Arm is extended, tendon hammer used to strike the examiner’s fingers placed on the biceps tendon
Biceps Reflex types and clinical relevance
Strong contraction- brisk reflex, weak or absent- diminished
Knee jerk reflex process
Muscle in neutral position, patellar tendon struck with reflex hammer just bellow the patella
Stretches the muscle spindle of the quadriceps muscle- causes leg to kick
Explain anatomical basis of knee jerk
Examines the function of the L3 spinal nerve- femoral nerve
Clinical relevance
Absence or decrease- Westphal’s sign
Multiple oscillations (pendular reflex) - cerebellar disease
exaggerated deep tendon reflexes- hyperthyroidism
What are both these an example of ? + stages
Reflex arc
- Spindle muscles sense changes in length and velocity
- impulse carried by afferent sensory neurone from the muscle to the spinal cord
- action potential carried to the dorsal root ganglion
- action potential carried by efferent motor neurones from the ventral root of the spinal cord to the muscle does the alpha motor neurone
- synapses on the extrafusal muscle spindle fibres, causing contraction
Two types of plexus + what they innervate
autonomic- thorax, abdomen and pelvis- blood vessels and viscera
somatic- limbs- skin, muscle, bone
Where are the trunks of the brachial plexus found?
between the scalene muscle and clavicle
Different trunks and their roots
Upper- C5,C6
Median- C7
Lower- C8, T1
How does each trunk divide + what they innervate?
Each trunk forms an anterior and posterior division
anterior divisions will supply anterior flexor compartments of the rubber limb
posterior divisions will innervate the posterior compartments of the upper limn
What do the divisions form?
Cords
How are they named?
Named relative to the axillary artery- li with the axillary arteries and vein surrounded by the axillary sheath
3 cords + divisions + trunks
posterior- all posterior divisions of all trunks
lateral cord- anterior division of upper and middle trunks
medial cord- anterior division of lower trunk
What are the branches?
major nerves supplying the upper limb
Musculocutaneous nerve origin, location and function
- C5,C6- upper trunk- terminal branches of lateral and medial cord
Passes anteriorly to supple the anterior muscle compartment of the arm
supplies the coracobrachialis, biceps brachii and brachialis muscles
Elbow and shoulder flexion, forearm supination
sensory nerve which supplies skin of the lateral forearm
median nerve origin, location and function
C5-T1
- at cubital fossa, nerve lies medial to brachial artery
- passes into the forearm and at the wrist passes through the carpal tunnel and enters the palm of the hand
- anterior compartment of the forearm and hand and skin over the lateral aspect of hand
- innervates wrist, finger, thumb flexion
- thenar muscle group- abduction, flexion and opposition of thumb
Ulnar nerve origin, location and function
C8- T1
- lies medial to brachial artery, passes between medial epicondyle of the humorous in the cubital tunnel
- motor to muscle of anteromedial aspect of the forearm and hand
Radial, nerve origin, location and function
C5-T1
- posterior, extensor, compartments of the arm and forearm
- supplies no muscle in the hand but does innervate the skin of the dorsum of the hand
- elbow extension due to the triceps brachii, wrist extension
Axillary nerve, origin, location and function
C5-C6
- Innervates deltoid and teres minor muscles, shoulder joint and skin overlying deltoid muscle - regimental badge
Lumbar plexus roots
L1-part of L4
Where is the lumbar plexus located?
Deep two psoas major muscle
lumbar sacral trunk roots
L4, ventral ramus L5
Sacral plexus roots
S1,S2,S3
Sacral plexus location
anterior to piriformis muscle
Where do the branches pass?
greater sciatic foramen to the gluteal region and lower limb
Femoral nerve, origin, location and function
-L2,L3,L4
innervates muscles of the anterior compartment of the thigh- quadriceps femurs group, sartorius and the skin overlying he anterior thigh
- carries sensory information from the knee and hip joint
- lateral to psoas major, enters thigh behind inguinal ligament
- lies lateral to femoral blood vessels
- in the femoral triangle
Obturator nerve, origin, location and function
L2, L3, L4
- emerges from medial border of psoas major muscle
- follows the curve of lateral pelvic wall
- passes through the obturator foramen of the pelvis t
-enter the medial compartment of the thigh where it supplies adductor muscles and skin overlying the medial aspect of the thigh
Sciatic nerve, origin, location and function
L4-S3
- emerges from pelvis via the greater sciatic foramen and passes midway between the greater tech-anger and ischial tuberosity
- supplies all leg and foot muscles
What does the sciatic nerve divide into + where?
Common perineal and tibial nerve at about the mid-thigh level, above the popliteal fossa
Tibial nerve, origin, location and function
L4-S3
- passes into leg to run deep to the soleus muscle
- innervates muscles in posterior compartment of the leg
- responsible for plantar flexion and inversion
- enters sole of foot behind medial mallows
What does the tibial nerve divide into + where?
medial and lateral plantar nerves
Common perineal nerve, origin, location and function
L4-S2
- curves posteriorly around the neck of the fibula
- supply anterior and lateral compartment of the leg
What does the common perineal nerve divide into + where?
Superficial peroneal nerve- supplies muscles in lateral compartment, and anterolateral distal 1/3 of the leg and dorsal surface of foot
deep perineal nerve- anterior compartment
Different ways in which a nerve is damaged explained
neurapraxia- nerve is bruised or squashed but the outer layer and inner fibres are still in tact- works properly again after a few weeks
axonotmesis- nerve is crushed, inner nerve fibres damaged but outer layer in tact
neurotmesis- both layers are cut
Main effects of damage
loss of sensation, loss of dexterity or paralysis
Examples of common nerve injuries, explained
Erb palsy- upper trunk of brachial plexus caused by excessive lateral flexion of the neck- causes weak biceps etc
axillary nerve injury- anterior shoulder isolation- paralysis of deleted muscle- impaired arm abduction
carpal tunnel syndrome- median nerve trapped as it travels through the wrist at the carpal tunnel - causes pain, numbness and tingling
