Muscles and Nerves Flashcards
Function of muscles
- Movement
- Static support
- Heat production
Give the 3 types of muscle and briefly describe each
- Skeletal: straitions and voluntary
- Cardiac: Involuntary
- Smooth: involuntary and “thinner”
Describe the structure of skeletal muscle moving inwards
- Tendon - attaches muscle to bone
- Epimysium: out CT layer
- Perimysium: CT layer eround bundles (fasclicles) of muscle fibres
- Endomysium: Ct layer that covers each muscle fibre
Also have blood vessels
see diagram
How do we normally classify skeletal muscles
Fascicle direction:
Bipenate/unipenate/multipenate
Aponeurosis
Flat sheet of tendon with wide are a of attachment
Feature of multipenate muscle
Packs more fibres in the same volume = denser and more powerful
Tendons
Give some general facts
- Dense fibrous CT
- does not shorten
- can alter force direction
- some muscles share common tendons
How do muscles act
By passing over a joint, they will act on that joint (can be more than one joint)
What can some muscles have in terms of action
More than 1: e.g. shoulder (deltoid) can do flexion, extension and adduction
Do all muscles have “traditional” controls (e.g. movement)
No: some maintain posture (erector spinae) and oppose gravity
What do muscles often work in?
Pairs: with flexors and extensors woring in opposition
agonist and antagonist
give examples of muscle compartements in the arm and forearm
- Arm: flexor (bicep anterior) and extensor (tricep posterior)
- Forearm: flexor-pronator and extensor-supinator
What are muscles of the same compartment usually innervated by
The same nerve (e.g. rafial nerve supplies all extensors in the upper limb)
What are the structural and functional divisions of the nervous system
- Structural: CNS and PNS
- Functional: somatic (voluntary) and autonomic (involuntary)
nerve structure
see sheet/diagram
How many spinal nerves do we have and expalin numbering of them
- 31 pairs in 5 regions
- Named after associated vertebrae, with C1 spinal nerve existin gbetween skull and atlas
What can catch you out when naming spinal nerves
C1-7 vertebrae but C1-8 nerves
What is a nerve plexus
network
Where do plexus exist
In nerves supplying upper and lower limbs originate in these plexuses
Ramus
branch
What can roots, spinal nerves and rami be in terms of sensory or motor neurons?
- Roots: sensory or motor
- Spinal nerves: sensory and motor
- Rami: sensory and motor
What can only 1 neurone supply
Multiple muscle fibres (attach at neuromuscluar junction)
Where do we find sensory and motor fibres in spine
- sensory: dorsal side
- Motor: ventral side
Somatic pathway
1 long axon and no synapsing so goes directly: CNS —> muscle
What pathway do reflex arcs use
Somatic: don’t need to go up to brain though
Motor fibre synamsing of Autonomic pathway
CNS—>Ganglion—>muscle
What do myotomes and dermatomes show
Area supplied by a single spinal nerve - used clinically to test for lesions at specific levels of the spinal cord
Cuaneous nerve maps
Areas supplied by same cutaneus nerve (skin) - can be combination of fibres from different spinal nerves because of plexuses
4 types of neuroglial cell found in CNS
- Astrocytes
- microglial cells
- ependymal cells
- oligodentrocytes
What is myelin
(biochemistry)
Lipid and protein substance
What secretes myelin
- Schwann cells in PNS
- Oligodendrocytes in CNS
What does the myelin sheath do (function)?
Ince velocity of impulse conduction (insulation)
How are peripheral nerves resiliant
Protected by 3 layers of connective tissue coverings
Dermatome
Area of skin supplied by a single spinal nerve
Myotome
Part of muscle supplied by a single spinal nerve
What may 1 muscle myotome involve
multiple spinal segments
What is the clinical relevance of dermatome and myotome
useful to test motor or sensory loss of one/more spinal nerves/segments by testing joint movements or an area of skin in neurological disorders
What is a motor end plate
aka n-m junction: specialised chemical synapses formed at the sites where the terminal branches of the axon of a motor neuron contact a target muscle cell.
How can we differentiate between a peripheral nerve and CNS grey matter
(histology)
Peripheral nerve: axons/fascicles
How can the nervous system be divided
In terms of the parts of the body it reaches
- Somatic: motor (voluntary; skeletal muscle) and sensory (pain/touch/proprioception/temp etc. skin) - muscles/skin
- Visceral: motor (involuntary - autonomic NS) and sensory (chemoreception, stretch reception, organs) - organs
What is the fuunction of the somatic nervous system (what do somatic sensory and motor fibres do?
- Somatic motor fibres regulate voluntary control of body movements via skeletal muscles
- Somatic sensory fibres transmit general sensation (pain/touch…) to the CNS.
anatomy of spinal nerve
see sheet
What does the anterior root control
(ventral root)
Motor
What does the posterior root control
dorsal
Sensory information
What does the spinal nerve itself control
Both motor and sensory
What do the Rami control
(both ventral and dorsal)
Both motor and sensory loss
What would happen if the ventral ramus was damaged
Motor and sensory loss of anterolateral trunk and limbs
(front and side)
What would happen if the dorsal ramus was damaged
motor and sensory loss of the back
What kind of fibres do spinal nerves also carry
sumpathetic fibres
What are nerve plexuses and what are their functions
Bundles of nerves that form a plexus communicate information to your brain about pain, temperature, and pressure. These nerve plexuses also send messages from the brain to the muscles, allowing for movement to occur.
What does the spinal neve run through?
Intervertebral foramen in adacent vertebrae
What is the somatic reflex action
Breif summary
An involuntary motor response:
* sensory detection (stimulus)
* Interpretation of sensory input in the CNS
* Motor response
What does the radial nerve supply
back of arm (extensors of elbow) and forearm (extensor of wrist) muscles
Peripheral nerve injury
Damage to lower motor neurone cell bodies on their peripherl axons results in paralysis or weaness of the affected muscles
Intercostal muscles
muscles that present within the rib cage. Consist of three layers of muscles external, internal, and innermost layer they combine to fill the space between the ribs.
What compartments can muscles be divided into
Flexor and extensor compartemnts
(in arm, have anterior flexors and posterior extensors)
What is the innervation like for muscles of the same compartment
Usually supplied by same nerve (e.g. radial nerve supplies all extensor muscles in the upper limb)
How do flexor and extensor muscles work?
In pairs: agonists and antagonists (one contracts and other slackens)
Which nerves innervate which parts of the upper arm?
- Flexors (anterior): musculocutaneous nerve
- Extensors (posterior): Radial nerve
How many joints can muscles cross
Multiple (usually 1/2/3 but could be more)
Flexors of the upper arm
(anterior)
- Biceps brachii
- Brachialis
- Coracobrachialis
Extensors of the upper arm
posterior
Triceps brachii
What functions can muscles have other than agonist/antagonist
give examples
- Fixator (stabiliser e.g. Deltoid)
- Synergist (augment action of agonist e.g. brachialis)
Give the forarm muscle compartments and which nerves innervate them
- Flexors and pronators (anterior) - 8 muscles - median and ulnar nerves
- Extensors and supinators (posterior) - 10 muscles - radial nerve
(Brachioradialis - posterior - causes flexion of forearm at elbow)
Explain the gluteal muscles (movements/names/innervation)
Actions on hip joint
* G.maximus - extension
* G.medius and minimus - abduction
Sciatic nerve
see sheet for diagram
Explain the muscles of the thigh
(names/compartments/innervation/function)
- Anterior: Quadriceps (4 muscles join to make 1 tendon) - Extension - Femoral nerve
- Posterior - Hamstrings - flexion - sciatic nerve
- Medial - Adductors - obturator nerve
Explain the leg muscles
(compartments/names/innervation/function)
- Anteroir - dorsiflexors and control dorsiflexion
- Posterior - plantarflexors and controol plantarflexion
- Lateral - Evertors which evert/invert the foot
All innervated by the sciatic nerve
What are the fucntions of the intrinsic muscles of the hand and foot
- Hand: precision (forarm muscles for strength)
- Foot: support walking and maintain arches of the foot
what are the upper/more medial and lower/more lateral muscle attachements described to as
- Upper/medial - proximal/superior - origin
- Lower/lateral - distal/inferior - insertion
What attaches muscles to bone
Tendoes - fibrous, dense-regular connective tissue embedded into the periosteum of bone
Flat tendon
name and example
Aponeurosis - abdominal oblique muscles (flat, thin and broad)
What do muscles do on bones
Pull: either flex or extend the joint
What joints do the biceps brachii cross
- Glenohumeral - shoulder
- Elbow joint
- Radial-ulnar joint
What is the action of the biceps brachii at the upper and lower joints?
- Upper - flexion
- Lower - flexion
Also supinate forearm
Which joints does the triceps brachii cross
shpoulder and elbow joints
What action does contraction of the triceps brachii have on the upper and lower joints
- Upper - extension (and adduction)
- Lower - extension at elbow
extension at elbow is main function
What muscles cross the median sagittal plane from one side of the body to the other (attach to bones either side of the midline of the body)
Diaphragm - ususally have main tendon situated in centre of muscle
What happens when the diaphragm contracts
Contracts downwards so it decends
domes move inferiorly on contraction
What action does the diaphragm contracting have
Increased area of throatic cavity so lungs fill with air
Describe the deltoid muscle and the different fibres it has, as well as their functions
muscle has anterior, middle and posterior fibres that can “pull” on the shoulder joint in different directions:
* flexion (anterior fibres)
* extension (posterior fibres)
* abduction (middle fibres)
Synergists
(help) perform the same set of joint motions as the agonist. Stabilize muscle movements to keep them even, and control the movement so that it falls within a range of motion which is safe and desired.
Another muscle, besides the agonist, that assists a particular movement of a joint.
Fixor/stabilising muscles
definition and example
stabilize the joint to which they are attached such that the joint can move efficiently without risk of dislocation. Ex: rotator cuff muscles around the shoulder joint.
How can we compartmentalise muscles
3
- Intermuscuar fascial septa
- Common nerves
- Common actions
Intermuscuar fascial septa
Partion muscles into compartements (e.g. fascial compartemnts inc. anterior fascial compartment of upper arm and posterior fascial compartment).
What are all arm/forearm muscle compartments innervated from
nerve network (plexus) located in the axilla - the brachial plexus
What are all thigh/leg muscle compartments innervated from
Nerve network in abdomen and pelvis - lumbosacral plexus
Where does the brachial plexus originate from
Spinal nerve roots C5 - T1
Where does the lumbosacral plexus originate from
posterior abdomen and pelvis: spinal nerve roots L1 - S4
3 layers of oblique muscle fibre directions
Approx. 90 degrees - inc strength and integrity
Direction rectus abdominis fibres travel
vertically
How many heads do biceps, triceps and quadriceps have?
- bi -2
- tri - 3
- Quad - 4
What shape is the diaphragm
dome-shaped
sphincter
Muscle fibres are arranged circularly and thickened around the wall of a structure, usually a tube. When the fibres contract, they close off the internal diameter of the tube - mostly smooth muscle but some skeletal (e.g. external anal sphincter)
Appendicular and axial muscles
- Appendicular - attach only to the limbs, or attaching the limbs to the trunk - innervated by limb nerve plexuses
- Axial - Attach only to trunk of body - innervated by other (non-limb) plexus or segmentally
Motor unit
combination of an individual motor neuron and all of the muscle fibers that it innervates
In somatic nerves, where do the sensory and motor nerve roots exit the spinal cord from
- Sensory - dorasl/posterior
- Motor - ventral/anterior
Summarise functions of main parts of spinal nerve
the dorsal root carries sensory (afferent) fibres only; the ventral root carries motor (efferent) fibres only; the mixed spinal nerve and the dorsal and ventral rami carry both motor and sensory fibres
What does each mixed spinal nerve divide into
ventral ramus and a dorsal ramus with each ramus going to the body wall of the trunk (i.e., supplying skeletal muscles, cartilage, bones and skin)
What does the dorsal ramus do at each spinal level
passes posteriorly to segmentally (=repetition of an individual spinal nerve down the trunk) supplies the main muscle of the back – the erector spinae muscle – and the skin that overlying it – with sensory and motor fibres.
What does the ventral ramus do at each spinal level
passes laterally and then forward to segmentally innervate the muscles of the anterolateral thoracic (intercostal muscles) and abdominal walls (oblique muscles and rectus abdominis), and the skin overlying these muscles
Where are the cutaneous nerves and dermatomes exactly the same and why
Tthorax and abdomen - cutaneous nerves supplying skin are single spinal nerve (so same as dermatome)
Is there overlay between adjacent cutaneous nerves
Yes
Dermatome T2
Sternum
Dermatome T4
Nipples
Dermatome T10
Belly button - umbilicus
Dermatome L1
Pelvic: lower back, around hips, then dipping down to groin
Why do dermatomes for thoracic trunk jump from C4 to T2 across the sternomanubrial joint
Dermatomes C5-T1 diverted to upper limb
What is the endoneurium
Layer of delicate CT around the myelin sheath of each nerve fibre
What is the perineurium
Each fascicle (bundle of fibres) lies within its own protective sheath called
What is the epineurium
In sufficiently large nerves multiple fascicles, each with its blood supply and fatty tissue, may be bundled within yet another sheath
Summarise the CT that surrounds each part of a nerve
- individual axon - Endoneurium
- Nerve fascicle - Perineurium
- Nerve - Epineurium
Types of neurons
(in terms of physical features)
Multipolar, bipolar, unipolar, psuedounipolar
Multipolar most common
What do individual muscles within a fascicle often have in common
Same nerve supply
What may a structural deficit in a nerve/spinal nerve cause
functional loss of muscle group and
pathology
What are the limbs supplied by
somatic/sympathetic/parasympathetic
Somatic and sympathetic
Not P as only inc blood flow in S, no “resting state” - tone
what movement does the lateral compartment of the leg control
eversion (and plantarflexion)
Key defining feature of cardiac muscle
Intercalated discs
(small black lines)
Hold adjacent cells tightly together and allow coordinated function of heart cells
