Week 2 Flashcards
Where do the CNS and PNS develop from?
Ectoderm
What other structures develop from ectoderm?
Sensory epithelium of the ear, nose and eye; the epidermis, hair and nails; the subcutaneous, mammary and pituitary gland; and the enamel of teeth
When does the CNS first appear?
End of week 3
What are the first signs of the CNS appearance?
Thickening of the ectoderm layer in the mid-dorsal region of the primitive streak
How does development of the notochord begin?
From the primitive node a tube extends under the ectoderm in the opposite direction to the primitive streak- this tube forms first the axial process, then the notochord process, and finally the notochord
What is the role of the notochord?
Role in molecular signalling and controlling the direction of embryonic folding, as well as an inductive relationship with overlying ectoderm
What is the initial event in the process of neurulation?
Thickening of the ectoderm (induced by the appearance of the notochord and mesoderm) to form the neural plate; the cells of which make up the neuroectoderm
Describe the neural plate:
Made of neruoectoderm, it lengthens and its lateral edges elevate (forming neural folds, and a depressed mid-region forms the neural groove)
How is the neural tube formed?
Neural folds approach each other in the midline and fuse
What factors define the being of the neural plate?
Intrinsic factors: cytoskeleton, stage of cell cycle; and extrinsic factors: adhesion points e.g. within notochord, surface ectoderm
What signals are expressed in neurulation?
Up-regulation of FGF, inhibition of BMP-4 caused induction of the neural plate; chordin and noggin are expressed’ neural plate switched from E-cadherin to N-cadherin expression
How are neural crest cells formed?
Tissue at the top of the neural folds becomes pinched off- neural crest tissue
What do neural crest cells give rise to?
Ganglia, Schwann cells, adrenal medulla, melanocytes and connective tissue in the head
What malformations can result from disruption of neural crest cell migration?
Treacher Collins syndrome- under development of the zygomatic bones and ears
Di George syndrome- cleft palate, cardiac abnormalities, abnormal facies, thymic aplasia
How does closure of the neural tube take place?
Fusion begins in the cervical region and proceeds in cephalic and caudal directions; open ends of the tube form the anterior and posterior neuropores (connect with the overlying amniotic cavity)
When is closure of the neural tube complete?
In week 4- anterior by day 25 and posterior by day 27
How does differentiation of the spinal cord occur?
Once the neural tube closes, the neuroepithelial cells give rise to neuroblasts and form the mantle layer (later forms the grey matter of the spinal cord); the outer layer- marginal layer- contains nerve fibres emerging from neuroblasts in the mantle layer
Where do motor axons grow from?
Out of neurones in the basal plate (ventral horn)
Where do neurons in dorsal root ganglia extend towards?
The dorsal horn and periphery
When does development of the brain begin?
Week 3
What are the 3 primarily brain vesicles?
Forebrain (prosencephalon), midbrain (mesencephalon) and hindbrain (rhombencephalon)
What does uneven growth give rise to?
Folds, or flexures: cephalic flexure (convex dorsally), pontine flexure (convex ventrally) and cervical flexure (convex dorsally)
How does the brain develop in between week 3 and 5?
The forebrain becomes the telencephalon (gives rise to cerebrum) and diencephalon (becomes eye cup, thalamus, hypothalamus, and epithalamus); the midbrain remains; and the hindbrain becomes the metencephalon (gives rise to pons and cerebellum) and the myelencephalon (gives rise to medulla oblongata)
Where do meninges develop from?
Mesenchymal cells and neural crest cells- at day 20-35 these cells migrate around the neural tube
Where do the choroid plexuses develop from?
Where pia mater and ependyma (roof plate of myelencephalon region) come into direct contact (e.g. roof of fourth ventricle)
When does the developing eye appear?
Day 22 (to week 10) as a pair of shallow grooves
What are optic vesicles?
Outgrowths from the diencephalon of forebrain; in contact with surface ectoderm and induce changes necessary for lens formation
What is the placode?
A thickening of ectoderm formed by invagination of placode cells
What is the blood supply of the developing eye?
Grooves arise on the ventral surface of the optic cup, forming the choroidal fissure; a branch of the ophthalmic artery- hyaloid artery- passes along the choroidal fissure to supply the lens and developing retina
What is the optic cup?
Bilaminar structure- outer layer forms the pigmented layer of retina, inner layer forms the nervous layer of retina- space between layers disappears as axons grow from the optic nerve, but potential weakness remains
What is the lens derived from?
Surface ectoderm
How does the lens develop?
Cells of the lens vesicle elongate anteriorly to form long lens fibres, and arrange in a laminar patter to form a transparent lens
How does optic nerve development occur?
Week 6- optic cup is connected to brain by optic stalk, hyaloid vessels in choroid fissure
Week 7- inner and outer layer fuse, cavity of the stalk disappears; inner layer cells provide a network of neuroglia that support the optic nerve fibres
Week 9- optic stalk becomes optic nerve; hyaloid artery and vein become central artery and vein of the retina
How does the eyeball develop?
Mesenchyme around optic cup condenses to form the layers of the eyeball, the choroid and sclera; the most anterior part of the cornea becomes transparent, and spaces develop in the mesenchyme between the cornea and lens (becoming the anterior chamber of the eye); fibrous tissue with a gelatinous substance fills the gap between the lens and retina, forming the vitreous body- posterior chamber
How does the eyelid develop?
Fold of ectoderm with mesenchyme between them that grow over the cornea fuse and enclose a conjunctival sac anterior to the cornea. The inner layer of ectoderm becomes the conjunctiva and over the iris, it fuses with the cornea. Eyelids separate again between the 5th and 7th month in utero
What is the key regulatory molecule expressed in eye development?
PAX6, expressed in anterior neural plate before neurulation begins; sonic hedgehog is involved in orbit separation
How do lacrimal glands develop?
As ectodermal buds from the upper conjunctival sac into the surrounding mesoderm
What are the functions of the blood brain barrier?
Maintain constant environment, protect brain from foreign substances, protect brain from peripheral transmitters
Describe general anaesthetic agents:
Drugs used to produce surgical anaesthesia; inhalation or IV; examples halothane, isoflurane (gases- inhalational), propofol (IV)
Describe anxiolytics and sedatives:
Drugs that causes sleep and reduce anxiety- act on GABA-A receptor; examples- barbiturates, benzodiazepines (diazepam)
Describe antishizophrenia drugs:
Drugs that are effective in relieving the symptoms of schizophrenic illness; examples- “typical” (chlorpromazine, haloperidol), “atypical” (clozapine, olanzapine)
Describe antidepressant drugs:
Drugs that alleviate the symptoms of depressive illness; therapeutic onset 2-4 weeks (affective disorders- of mood rather than thought/cognition); examples: monoamine oxidase inhibitors (phenelzine), tricyclic antidepressants (imipramine), SSRIs (fluoxetine), rapid onset (ketamine)
Describe analgesic drugs:
Drugs used clinically for controlling pain; examples: opiates, baclofen, NSAIDS
Describe psychomotor stimulants:
Drugs that cause wakefulness and euphoria; examples: cocaine, amphetamine, methylphenidate (Ritalin), caffeine
Describe pychotomimetic drugs:
Drugs that cause disturbances of perception and of behaviour, that cannot be simply characterised as sedative or stimulant effects; examples: LSD, mescaline, ketamine, phenycyclidine, THC
Describe cognition enhancers:
Drugs that improve memory and cognitive performance; examples: galatamine, donepezil (AChE inhibitors- Alzheimer’s disease)
What is the spinal cord protected by in the epidural space?
A cushion of fat and connective tissue found between the dura and the wall of the vertebral canal
Describe the dura mater:
- Most superficial of spinal meninges
- Thick strong layer composed of dense irregular connective tissue
- Forms a sac from the level of the foramen magnum to the second sacral vertebra
Which of the meninges is continuous with the epineurium, the outer covering of spinal and cranial nerves?
Dura mater
Describe the arachnoid mater:
- Thin avascular middle layer comprised of cells and thin, loosely arranged collagen and elastic fibres
- Deep to the dura and continuous through the foramen magnum with the arachnoid mater of the brain
What is between the arachnoid and dura mater?
Thin subdural space which contains interstitial fluid
Describe the pia mater:
- Innermost matrix, composed of thin, transparent connective tissue layer that adheres to the surface of the spinal cord and brain
- Consists of thin squamous to cuboidal cells with interlacing bundles of collagen fibres and some fine elastic fibres
- Many blood vessels within the pia mater
What are the denticulate ligaments?
Triangular-shaped membranous extensions of the pia mater that suspend the spinal cord in the middle of its dural sheath
Where do the denticulate ligaments project?
Laterally and fuse with the arachnoid mater and inner surface of the dura mater between the anterior and posterior nerve roots of spinal nerves on either side
Where do the denticulate ligaments extend?
Down the entire length of the spinal cord and protect against sudden displacement that could result in shock
What is between the arachnoid and pia mater?
Subarachnoid space which contains CSF
Where does the spinal cord extend to in adults?
From the medulla oblongata to the superior border of the second lumbar vertebra
Where does the spinal cord extend to in newborn infants?
Third or fourth lumbar vertebra
Why is the spinal cord different lengths in adults and newborns?
Spinal cord and vertebra grow, but spinal cord stops growing at around 4/5 while vertebral column growth continues
Where does the cervical enlargement extend from, and what arises at it?
The fourth cervical vertebra to the first thoracic vertebra from which the nerves to and from the upper limbs arise
Where does the inferior enlargement extend from, and what arises from it?
From the 9th to the 12th thoracic vertebra, from which nerves to and from the lower limb arise
What does the spinal cord terminate as?
A tapering, conical structure called the conus medullaris
What arises from the conus medullaris?
The filum terminale, an extension of the pia mater that extends inferiorly and fuses with the arachnoid mater and dura mater and anchors the spinal cord to the coccyx
What connects each spinal nerve to a segment of the cord?
Two bundles of axons, called roots, and by even smaller bundles of axons called rootlets
Are dorsal roots and rootlets motor or sensory?
Only sensory axons, which conduct nerve impulses from sensory receptors in the skin, muscles and internal organs to the CNS
What is the dorsal root ganglion?
A swelling in each dorsal root that contains the cell bodies of sensory neurons
Are ventral roots and rootlets motor or sensory?
Only motor, which conduct nerve impulses from CNS to effector
Where do spinal nerves exit as they branch off from the spinal cord?
Laterally through the intervertebral formamina between adjacent vertebrae
Where do the roots of lumbar, sacral and coccygeal nerves exit the cord?
They angle inferiorly alongside the filum terminale (cauda equina) and exit the vertebral column at their corresponding intervertebral space
What is the basic internal anatomy of the spinal cord?
Grey matter surrounded by white matter
What is white matter?
Primarily consists of bundles of myelinated axons of neurons
What grooves penetrate the white matter, dividing it into L and R sides?
The anterior median fissure, a wide groove on the ventral side, and the posterior median sulcus, a narrow furrow on the dorsal side
What is grey matter?
Consists of dendrites and cell bodies of neurons, unmyelinated axons and neuroglia
What is the grey commissure?
Grey matter bridging the L and R spinal cord
What is the central canal?
A small space in the centre of the grey commissure filled with CFS, extending the entire length of the spinal cord
What is the central canal continuous with in the medulla oblongata?
4th ventricle
Where and what is the ventral white commissure?
Anterior to the grey commissure, which connects the white matter of the right and left sides of the spinal cord
What are nuclei in the spinal cord?
Clusters of neuronal cell bodies in the grey matter of the spinal cord and brain
What is grey matter subdivided into?
Regions called “horns” on each side of the spinal cord
What is contained in the dorsal grey horn?
Cell bodies and axons of interneurons as well as axons of incoming sensory neurons
What is contained in the ventral grey horn?
Somatic motor nuclei that provide nerve impulses for contraction of skeletal muscles
What lies between the ventral and dorsal grey horns in the thoracic and upper lumbar segments of the spinal cord?
Lateral grey horns, containing autonomic motor nuclei which are clusters of cell bodies of autonomic motor neurons that regulate the activity of cardiac muscle, smooth muscle and glands
What regions is white matter arranged into?
Ventral, posterior and lateral white columns
What do the columns of white matter contain?
Distinct bundles of axons having a common origin or destination and carrying similar information. These bundles which may extend long distances up and down the spinal cord are called tracts
What is the difference between a tract and a nerve?
Tracts are bundles of axons in the CNS, while nerves are bundles of axons in the PNS
What spinal nerves are involved in medial rotation of the hip?
L1, L2 and L3
What spinal nerves are involved in lateral rotation of the hip?
L5, S1
What spinal nerves are involved in adduction of the hip?
L1, L2 and L3
What spinal nerves are involved in abduction of the hip?
L5 and S1
What spinal nerves are involved in extension of the hip?
L4 and L5
What spinal nerves are involved in flexion of the hip?
L2 and L3
What spinal nerves are involved in extension of the knee?
L3 and L4
What spinal nerves are involved in flexion of the knee?
L5 and S1
What spinal nerves are involved in dorsiflexion of the ankle?
L4 and L5
What spinal nerves are involved in plantarflexion of the ankle?
S1 and S2
Describe A alpha fibres:
13-20 micrometres in diameter, 80-120 m/sec speed and involved in proprioception of skeletal muscles
Describe A beta fibres:
6-12 um in diameter, 35-75 m/sec and involved in mechanoreceptors of skin
Describe A delta fibres:
1-5 um, 5-30 m/sec, involved in pain and temperature conduction
Describe C fibres:
0.2-1.5 um, 0.5-2 m/sec, involved in temperature, pain and itch conduction
What stimuli can cause pain?
Extreme temperatures intense mechanical stimulation and chemical stimuli
What are nociceptors?
Free nerve endings, whose cell bodies are located in the spinal ganglia for the body and trigeminal ganglia for the face
When are nociceptors activated?
Only when the stimulus reaches a noxious threshold
How do nociceptors respond to stimuli?
Progressively according to the intensity of the stimulus =
What is sensitisation?
Continued stimulation decreasing the threshold at which nociceptors respond
What are myelinated a-delta fibres responsible for?
Localised, sharp ‘first’ pain and respond to intense mechanical and thermal stimuli
What are unmyelinated C fibres responsible for?
They mediate the poorly localised, diffuse “second” pain (slow burning pain)
C fibres are polymodal, responding to mechanical, thermal and chemical stimuli
What neurotransmitters are used by nociceptive fibres?
Glutamate, substance P and calcitonin gene-related peptide (CGRP)
Where are NTs produced?
In the cell body with the spinal ganglion
What does nociceptor activation lead to?
NT release centrally and peripherally, causing redness, swelling and tenderness in periphery
What do peripheral NTs also activate?
Silent nociceptors which expand the receptive field for painful stimulus
What does the activation of nociceptors lead to?
Opening of cation channels (mainly sodium) and membrane depolarisation and generation of action potentials
How does thermal activation of nociceptors occur?
- Detected by both A-delta and C fibres
- Hot leads to TRPV1 receptor activation
- Cold leads to TRPM8 receptor
- Activation will result in behaviours that will either cool or warm the body
- Mediated through projections to the hypothalamus
How does mechanical activation of nociceptors occur?
- Found in both A-delta and C fibres
- Cannot be activated by light touch
- High threshold and are only activated when the stimulus is noxious and may result in tissue damage
How does chemical activation of nociceptors occur?
- C fibres only
- Can be external irritation or substances released during tissue damage
What does tissue injury cause release of (sensitisation of peripheral receptors)?
- bradykinin
- 5-HT
- prostaglandins
- K+ ions
How does the release of substances cause sensitisation of peripheral receptors?
These substances (see above question) stimulate C fibres, and active C fibres release CGRP and substance P -> stimulate mast cells to release histamine and cause dilation of blood vessels, plasma extravasation, oedema and release of bradykinin
How does the above process cause sensitisation of peripheral receptors?
The above processes lower the activation threshold of nociceptors so that they will be activated by stimuli that would normally not be perceived as pain, response to a normally painful stimulus is heightened -> hyperalgesia and normally non-painful stimuli are perceived as painful -> allodynia
What are silent nociceptors?
- release of inflammatory molecules and NTs in the periphery also recruits silent nociceptors
- further amplify the signal to the posterior horn by increasing the temporal and special summation of the incoming signal
- only signal in response to the molecules secreted by other activated nociceptors
What is the gate control theory of pain modulation?
- Balance between A-delta, C and A-beta fibres
- When hurt, individual tends to rub the area that is sore to alleviate pain
- Balance of inputs is shifted towards touch (A-beta fibre activation) and away from pain
How is the projection neuron inhibited according to the gate control theory?
- Firing go the projection neuron determines pain
- Inhibitory interneurons are inhibited by nociceptive input which results in more signalling of the projection neuron
- Firing of the A-beta fibres activates the inhibitory interneuron reducing the chances the projection neuron will fire
Where is the periaqueductal grey (PAG) matter found?
In midbrain
What is the PAG matter involved in?
Pain appreciation can be blocked by stimulating the PAG matter
How does the PAG matter block pain appreciation?
Sends descending, inhibitory pathways that suppress the transmission of pain signals (activated by endogenous opioids and opiates)
How does descending modulation occur in the PAG matter?
Stimulation of the PAG matter activates enkephalin releasing neurons that project to the raphe nuclei in the brainstem, causing release of 5-HT
How does descending modulation occur in the PAG matter, and how does 5-HT mediate descending inhibiton?
Descending inhibition mediated by 5-ht and enkephalins, noradrenaline and adenosine -> form excitatory connections with the inhibitory interneurons and inhibitory connections with projection neurons
How does descending modulation occur in the PAG matter, and what role do the interneurons play?
These interneurons release encephalins which bind to mu-opiod receptors on the incoming axons, activation of the mu-opiod receptor inhibits the release of substance P and transmission of pain signal up the spinothalamic tract
How do opioids cause analgesia?
By activating descending pathways from PAG and inhibiting the dorsal horn
What are the three main classes of endogenous opioid?
Endorphins, enkephalins and dynorphins
What are three types of opioid receptor?
Mu, kappa and delta
How is back pain managed, if patient is between ages of 20 and 50?
Pain between these ages is likely to be mechanical and is managed with analgesia, brief rest if necessary and physiotherapy
What is important for patients with pain?
Patients should stay active within the limits of their pain
What are general principles of pain management?
- early treatment of the acute episode, advice and exercise programmes reduce long-term problems and prevent chronic pain syndromes
- Physical of uncomplicated back pain produces short-term relief and enjoys high patient satisfaction rates
- psychological and social factors may influence the time of presentation
- appropriate early management reduces long-term disability
What is the role of the GP in the management of back pain?
- Diagnostic triage -> patients with possible spinal pathology should be urgently referred for specialist investigation
- Give accurate information, advice, simple symptomatic measures, encouragement and support to resume daily activities
- Additional support is needed for patients who fail to return to work
- GPs may refer them to physiotherapist or chiropractors
- Act as gatekeeper who controls referral to the most appropriate services and coordinates management
What is the role of the physiotherapist in the management of back pain?
- Builds up muscles to cope with problem
- Primarily interested in and responsible for the prevention and management of a wide variety of MSK disorders as well as respiratory and other health problems
- Works in a hospital or community setting -> sees patients at health centres or in patient’s own home
- Passive modalities to assist in pain management -> electrical stimulation
- Aim is to provide pain relief and help patients return to normal activities -> rehabilitation
What is the role of the osteopath and chiropractor in the management of back pain?
- instant relief of pain but pain returns -> no cure
- Chiropractic based on theory that all disorders can be traced to the incorrect alignment of bones, with consequent malfunctioning of nerves and muscles throughout the body -> involves manipulation, mainly of vertebrae
- Osteopathy is a system of diagnosis and treatment based on the theory that many diseases are associated with disorders of the MSK system -> involves palpation, manipulation and massage
- Practitioners work with bones, muscles and connective tissue using hands to diagnose and treat abnormalities of structure and function -> manual therapy
- Based in community and private sector
What is the role of the hospital specialist in the management of back pain?
- Further evaluates, manages and treats the underlying problem causing the back pain
- Underlying problem may be of mechanical, metabolic, malignant or infectious cause -> different specialist involved for different cause
What are yellow flags, in reference to pain?
Psycho-social barriers to recovery
What are some yellow flags?
- Belief that pain is harmful and severely disabling -> activity is also harmful
- Fear-avoidance behaviours and reduced activity
- Sickness behaviours such as extended rest
- Social withdrawal
- Emotional problems such as low or negative mood, depression, anxiety and stress
- Problems and dissatisfaction at work
- Financial problems, such as problems with claims or compensation or time off work
- Overprotective family or lack of support
- Inappropriate expectations of treatment -> expectation of passive treatment rather than a belief that active participation will help
How is development of chronic pain and disability prevented?
- Managing symptoms with analgesics such as paracetamol or NSAIDs is usually effective
- Early detection and assessment of psycho-social risk factors -> screening questionnaires by GP
- Advice and education of patient and family members
- Discharge of patient -> failure to discharge reinforces sickness role
What cranial nerve innervates all muscles of facial expression?
Facial nerve (CN VII)
What two muscles are associated with the orbital group?
Orbicularis occuli and corrugator supercilii
Describe orbicularis oculi:
- Large muscles that completely surrounds each orbital orifice and extends into each eyelid
- Closes the eyelids
What are the two major parts of orbicularis occuli
- Outer orbital part -> board ring that encircles the orbital orifice and extend beyond the orbital rim
- Inner palpebral part -> in the eye lids and consists of muscle fibres originating in the medial corner of the eye that arch across each lid to attach laterally
What are the functions of each part of orbicularis oculi?
Palpebral part -> closes eyes gently
Orbital part -> closes eyes more forcefully and produces some wrinkling on the forehead
Describe corrugator supercili:
- Smaller than OO
- Deep to the eyebrows and the OO
- Active during frowning
- Arises from the medial end of the superciliary arch, passing upward and laterally to insert into the skin of the medial half of the eyebrow
- Draws the eyebrows towards the midline causing vertical wrinkles above the nose
What three muscles make up the nasal group?
Nasalis, procerus and depressor septi nasi
Describe the nasalis muscle:
- Largest and best developed of the muscles of the nasal group
- Active when the nares are flared
- Consists of a transverse part (compressor naris) and an alar part (dilator naris)
- Transverse part -> compresses the nares and forms an aponeurosis with its partner across the dorsum of the nose
- Alar part -> opens the nares
Describe the procerus muscle:
- Small muscle superficial to the nasal bone
- Active during frowning
- Draws the medial border of the eyebrows downwards to produce wrinkles over the bridge of the nose
Describe the depressor septi nasi muscle:
- Assists in widening the nares
- Pulls nose inferiorly, so assisting the alar part of the nasalis in opening the nares
What muscles make up the oral group?
Orbicularis oris, buccinator and an upper and lower group of muscles
Describe the orbicularis oris:
- Complex muscle consisting of fibres that completely encircle the mouth
- Function is apparent when pursing the lips, as occurs during whistling
- Contraction narrows the mouth and closes the lips
Describe the buccinator:
- Forms the muscular component of the cheek
- Used every time air expanding the cheek is forcefully expelled
- Between the mandible and maxilla, deep to the other facial muscles in the area
- Contraction presses the cheek against the teeth
- Keeps the cheek taut and aids in mastication by preventing food from accumulating between the teeth and cheek
- Assists in the forceful expulsion of air from the cheeks
What muscles make up the lower group of oral muscles?
- Depressor anguli oris (active during frowning, depresses the corner of the mouth)
- Depressor labii inferioris (arises from the front of the mandible, deep tot he depressor anguli oris, depresses the lower lip and moves it laterally)
- Mentalis (helps position the lip when drinking from a cup or when pouting, deepest muscle of the lower group and raises and protrudes the lower lip as it wrinkles the skin of the chin)
What muscles make up the upper group of oral muscles?
- Risorius
- helps produce a grin
- thin, superficial muscle that extends laterally from the corner of the mouth in a slightly upward direction
- contraction pulls the corner of the mouth laterally and upward
- Zygomaticus major and minor
- help produce a smile
- raise the corner of the mouth and move it laterally
- Levator labii superioris
- deepens the furrow between the nose and the corner of the mouth during sadness
- Levator labii superioris alaeque nasi
- medial to the levator labii
- may assist in flaring the nares
- Levator Anguli Oris
- more deeply placed and covered by the other two levators and the zygomaticus muscles
- elevates the corner of the mouth and may help deepen the furrow between the nose and the corner of the mouth during sadness
Describe the platysma muscle:
Large, thin sheet of muscles in the superficial fascia of the neck and tenses the skin of the neck and can move the lower lip and corners of the mouth down
Describe the auricular muscles:
- Anterior, superior and posterior auricular muscles
- Anterior muscle -> anterolateral and pulls the ear upwards and forwards
- Superior muscle -> superior and elevates the ear
- Posterior muscle -> posterior and retracts and elevates the ear
Describe the occipitofrontalis muscle:
- Associated with the scalp
- Consists of a frontal belly anteriorly and an occipital belly posteriorly
- Aponeurotic tendon connects the two
- Frontal belly -> covers the forehead and is attached to the skin of the eyebrows
- Occipital belly -> arises from the posterior aspect of the skull and is smaller than the frontal belly
- Occipitofrontalis moves the scalp and wrinkles the forehead
What nerve innervates all the muscles of mastication?
The mandibular branch of the trigeminal nerve (V3)
Describe the masseter muscle:
- Most powerful muscle of mastication
- Quadrangular in shape
- Elevates the mandible, closing the mouth
- Lies superficial to the pterygoids and temporalis
Describe the temporalis muscle:
- Originates from the temporal fossa
- Inserts on the coronoid process of the mandible
- Elevates the mandible, closing the mouth
- Also retracts the mandible, pulling the jaw posteriorly
Describe the medial pterygoid:
- Quadrangular in shape, with two heads
- Located inferiorly to the lateral pterygoid
- Elevates the mandible, closing the mouth
Describe the lateral pterygoid:
- Triangular shape with two heads
- Horizontally orientated muscle fibre
- Major protractor of the mandible
- Produces the “side to side” movement of the jaw
What are the main blood vessels that supply the face?
Facial artery and superficial temporal artery, with the supraorbital and supratrochlear vessels above the orbits
Describe the facial artery:
- From the external carotid
- Should be palpable as it comes onto the face
- Crosses the lower border of the mandible 2.5 cm in front of the angle of the mandible
- Runs beneath the facial muscles towards the side of the nose and inner angle of the eye, with the facial vein behind it
- Artery is tortuous while the vein is straight
- Make good anastomoses with their counterparts on the other side, especially by the superior and inferior labial branches -> makes a vascular ring within the tissues of the lips
Describe the superficial temporal artery:
- from the maxillary branch of the external carotid
- runs upwards, immediately in front of the tragus of the ear, where it is easily palpable
Describe the venous drainage of the face:
Main veins drain to the internal jugular
What are the 3 main salivary glands?
Parotid (paired), submandibular and sublingual
Where are the parotid glands found?
Tucked in behind the ramps of the mandible below the ear and in front of the mastoid process, underneath the skin, each gland overlaps part of the masseter muscle which covers the ramus of the mandible
What nerve, artery and vein are embedded within the parotid gland?
Facial nerve and its main branches, and the end of the external carotid artery (where it divides into the superficial temporal and maxillary branches) and the retromandibular vein
How does the parotid gland discharge its secretion into the mouth?
Via the parotid duct which is 5 cm long and opens into the moth opposite the crown of the second upper molar tooth
What nerve stimulates secretion?
Parasympathetic stimulation from the glossopharyngeal nerve, which runs via the mandibular branch of the trigeminal nerve
Where is the submandibular gland found?
Lies in the angle between the lower, inner surface of the body of the mandible and the mylohyoid muscle
Where does the submandibular duct run too?
From the posterior part of the gland and runs deep to the mylohyoid to open in the floor of the mouth beside the midline frenulum of the tongue
Where is the sublingual gland?
Almond-shaped and lies beneath the mucous membrane of the floor of the mouth, and raises an elongated swelling, easily seen when the front of the tongue is raised
Where does the sublingual gland secrete to?
Through a dozen minute ducts -> some open directly into the floor and others open into the submandibular duct
What is the histology of the salivary glands?
- consists of a number of lobules surrounded by a fibrous capsule
- each lobule or acinus is made up of balls of acinar cells, which are drained by ductules that join to form larger ducts leading into the mouth
- each acinus consists of serous cells and mucous cells whose relative numbers vary from gland to gland
- fine processes of myoepithelial cells extend over the outer surface of the acini
- cell bodies lie on the basement membranes beneath the secretory cells and basal lamina
What are the functions of saliva?
- Facilitate swallowing
- Aid speech
- Initiates digestion (contains alpha-amylase)
- Contains IgA and lysozyme (acts on the cell walls of certain bacteria to cause their lysis and death)
What are the constituents of the parotid secretion?
Serous secretion, lacks mucus, contains IgA and alpha-amylase
What are the constituents of the submandibular secretion?
Viscid fluid
What are the constituents of the sublingual secretion?
Secretion rich in mucoprotein
What are the consequences of severing the parotid duct?
- Salivary mucocele-> cyst that arises in connection with minor salivary glands
- Common and are usually superficial
- Mainly appear in the lip but can also occur in cheeks and the floor of the mouth
- Appear as a blue/translucent swelling just under the lining of the mouth
- History of bursting, collapsing them refilling which may be repeated
- Treatment of choice is surgical removal
- If small -> can be left alone with no surgical intervention
What does the facial nerve consist of?
A large motor root and a smaller sensory root (intermediate nerve)
- large motor root contains general visceral efferent fibres
- intermediate nerve contains special afferent fibres for tase, parasympathetic general visceral efferent and general somatic afferent fibres
Where does the facial nerve attach?
To the lateral surface of the brainstem, between the pons and medulla oblongata
Where does the facial nerve leave the cranial cavity?
Motor and sensory roots cross the posterior cranial fossa and leave the cranial cavity through the internal acoustic meatus
Where does the facial nerve enter the facial canal, and what happens at this point?
The roots enter the facial canal in the petrous part of the temporal bone and the two roots fuse to form the facial nerve
What does the nerve enlarge as in the facial canal?
Geniculate ganglion
What nerve is given off at the geniculate ganglion?
At the geniculate ganglion the facial nerve turns and gives off the greater petrosal nerve, which carries mainly preganglionic parasympathetic fibres
Where does the facial nerve continue to after the geniculate ganglion?
Along the bony canal, giving off the nerve to stapedius and the chorda tympani, before exiting the skull through the stylomastoid foramen
What does the chorda tympani carry?
Taste fibres from the anterior two-thirds of the tongue and preganglionic fibres destined fro the submandibular ganglion
What are the five terminal groups of branches of the facial nerve, and where do they emerge from?
The groups are temporal, zygomatic, buccal, marginal mandibular and cervical, and they emerge from the upper, anterior and lower border of the parotid gland
What are the clinical tests for CN7 function?
Ask the patient to give a broad toothy grin -> full of symmetrical grin
Ask the patient to screw up their eyes and gently prise them open -> shouldn’t be able to open them
Ask them to raise eyebrows - check for symmetry
Paralysis of the facial nerve causes the face to drop - more marked with a LMN lesion than UMN
