neuro 500 (lumbar and sacral plexuses and pathologies, dermatomes) + BRAIN Flashcards
femoral nerve injuries
E.g.
gunshot, stab, wound
Difficulty:
–> flex thigh, extend leg @ knee
-can’t extend leg (at knee), trouble flexing hip (other innervation? “lumbar plexus” for some hip flexors)
-wasting of quads
-no sensation over ant/medial thigh
injury to obturator nerve
-paralysis of adductor muscles
-no sensation over medial thigh
-can occur from pressure on nerve by fetal head during
pregnancy
why obturator neve during pregnancy?
baby’s head compresses obturator nerve against bone (nerve is near/inferior to arcuate line)
-lateral femoral cutaneous nerve entrapment
Meralgia paresthetica
Meros = thigh
-occurs near the ASIS as the nerve passes under the
inguinal ligament
-sensory nerve – sensory alteration +/or burning pain
on the lateral thigh
meralgia paresthetica potential causes/risk factors
-cause – trauma (seat belt in car accident)
- during delivery (in stirrups)
- tight clothing
- complication of surgery (hernia)
SCENARIOS WHERE YOU MAY MISTAKE NERVE ISSUES WITH MUSCLE ISSUES
E.g.
Lateral thigh (meralgia paresthetica)
—> Must also consider lateral femoral nerve, not necessarily ITB/vastus lateralis
Tarsal Tunnel Syndrome – causes
Swelling after trauma
Space-occupying lesion (eg ganglion)
Inflammation (eg paratendonitis)
Valgus deformity
Chronic inversion
Tarsal Tunnel Syndrome
The tibial nerve can be compressed at the ankle as it passes
through the tarsal tunnel
tarsal tunnel location
The tarsal tunnel is formed by the medial malleolus, calcaneus and talus (on the floor of the tunnel) and the flexor retinaculum on the roof
tarsal tunnel syndrome – SSx
- Pain and paresthesias into sole of foot
- Symptoms often worse after long periods of standing or walking or at night
- Pain localized or radiates over medial ankle, distal to medial malleolus
possible misdiagnosis of tarsal tunnel syndrome
- Has been misdiagnosed as plantar fasciitis
CAUSES OF SCIATIC NERVE LESIONS
Fractures (pelvis, femur, tibia, fib head, ankle)
Dislocation (hip, knee, ankle)
Iatrogenic reasons (glut inj, hip surgery, meniscal repair,
improper positioning during surgery)
Compression from internal sources
-piriformis (piriformis syndrome)
-flexor retinaculum (tarsal tunnel syndrome)
-ganglion
-morton’s foot
Compression from external sources
-against fib head (cast, splint)
-crossing legs
-trauma
Symptoms of Sciatic Nerve Lesions
Pain at butt and down lateral leg and possibly to lateral foot
Foot drop - paralysis of dorsiflexors and everters
- leads to steppage gait
steppage gait
“Steppage gait is an abnormal walking pattern that results from foot drop, which is the inability to raise the front of the foot. People with steppage gait lift their knees higher than normal to avoid dragging their toes on the ground. “
Neuritis
-inflammation of the nerve
-mainly the sheath and connective tissue are affected
(usually the axon is not)
-constant dull pain
-can also get numbness and tingling
neuritis – etiology
causes :
– secondary to a pathology (DM, leprosy, TB)
-trauma to nerve
-chronic exposure (to a toxin like lead, drugs or alcohol)
Neuralgia
-nerve pain
-recurrent attacks of sudden excruciating pain along distribution of the nerve
-no associated pathology
-has a trigger zone
trigger zone
-area that causes an attack when stimulated
-usually it’s an area of skin supplied by the nerve
-movement of the area increases pain
commonly affected nn by neuralgia
TRIGEMINAL/INTERCOSTAL
-commonly affected are trigeminal and intercostal nerves
intercostal neuralgia
-affects intercostal nerves that travel between the
internal and innermost intercostal muscles
intercostal neuralgia possible causes
- diabetes
- post-herpes zoster
Herpes Zoster/ Post-Herpetic Neuralgia
(herpes zoster = SHINGLES)
-starts with chicken pox
-varicella zoster virus is the virus that causes chicken pox in children
-after recover from chicken pox in childhood, the virus is not eliminated from the body but lies dormant within the sensory ganglia of cranial or spinal nerves and can become activated later in life to cause herpes
zoster (shingles)
varicella zoster
“Chickenpox and shingles are both caused by the varicella-zoster virus (VZV), but they are different illnesses. Chickenpox is usually a childhood illness, while shingles is more common in adults.”
shingles decription
“A painful rash that appears 1–5 days after the virus reactivates. It’s also known as herpes zoster. Shingles is characterized by severe pain and numbness along nerve pathways, often on the face or trunk. Other symptoms include headache, fever, fatigue, and sensitivity to light. “
shingles (herpes zoster) after chicken pox
-years later, when the immune system is depressed, the
virus reactivates
-usually only 1 nerve affected
-when reactivated, the virus causes a generalized
inflammatory response starting in the sensory ganglion and spreading along the nerves causing demyelination and degeneration
-inflammation produces pain and tingling in the involved dermatome with a rash and then vesicles that burst and encrust
how long do lesions last (Herpes Zoster)
-skin lesions can last up to a month and disappear as the effects of the virus resolve
-thoracic and trigeminal nerves are the most common
-intermittent attacks of deep, burning, sharp shooting pain along the affected nerve
-trigger is often light touch and movement over affected area
herpes zoster (aka) is CAUSED by which virus?
Varicella virus
it is NOT caused by “herpes zoster virus”
—> There is no herpes zoster virus (?)
ONLY ____ & ___ TRACTS
sensory and motor
NO MIXED TRACTS
2 main sensory tracts
Spinothalamic tract
Posterior column
Spinothalamic tract:
conveys nerve impulses for
sensing pain, temperature, itch, tickle,
and touch, pressure, vibration
Posterior column
made up of 2 tracts
gracile fasciculus & cuneate fasciculus
- conveys nerve impulses for touch, light
pressure, vibration and conscious
proprioception
Conscious proprioception:
the awareness of the
positions and movements of muscles, tendons
and joints
2 main motor tracts
Direct pathways
Indirect pathways
Direct pathways
- lateral corticospinal tract
- anterior corticospinal tract
- corticobulbar tract
- nerve impulses originate in cerebral cortex
- cause voluntary movements of skeletal muscle
Indirect pathways
- rubrospinal tract
- tectospinal tract
- vestibulospinal tract
- lateral reticulospinal tract
- medial reticulospinal tract
- nerve impulses originate in brain stem
- causes automatic movements
- helps coordinate body mvts with visual stimuli
- maintains skeletal muscle tone
- sustained contraction of postural muscles
- major role in equilibrium by regulating muscle
tone in response to movements of head
Reflexes and Motor Arcs
..
stimulus
- a change in the internal or external environment
Reflex
- a fast, involuntary, unplanned sequence of actions that occurs in response to a particular stimulus
- can be inborn or learned
Spinal reflex
-when integration happens in grey matter of SC
Cranial reflex
-when integration happens in brain stem
Somatic reflex
-involves contraction of skeletal muscle
Autonomic reflexes
-not usually consciously perceived
-involve responses of smooth mm, cardiac
mm and glands
Reflex Arc
-the reflex arc or reflex circuit is the pathway for nerve
impulses that produce a reflex
-it’s made up of 5 things:
- Sensory receptor
- Sensory neuron
- Integrating center
- Motor neuron
- Effector
- Integrating center
Monosynaptic reflex arc:
– most simple
-a reflex pathway with only 1 synapse in the CNS
(so 2 neurons and 1 synapse)
Polysynaptic reflex arc:
- when the integrating center consists of at least one interneuron
- involves more than 1 synapse in the CNS
(so at least 3 neurons and 2 synapses)
The stretch reflex
-contraction of a skeletal muscle in response to stretching of that muscle
-monosynaptic reflex arc
-can be elicited by tapping on tendons attached to muscles at elbow, wrist, knee and ankle joints
stretch reflex vs mm spindle (reflex)
- Stretch reflex stimulates muscle spindles
- muscle spindles are sensory receptors in the mm
- they monitor the change in length of the mm
- the stretch reflex is an ipsilateral reflex
- sensory nerve impulses enter the same side that the motor nerve impulses come out
muscle spindles vs mm tone
-tone of a muscle is also set through muscle spindles
Muscle tone = the small degree of contraction present
when a muscle is at rest
more detailed explanation of muscle spindles vs muscle tone
(small motor neurons innervate specialized fibers within the muscle spindle – this is how the brain regulates tone. By adjusting how much a muscle spindle responds to stretching, the brain sets an overall level of muscle tone)
Reciprocal innervation (reciprocal inhibition = type of reciprocal innervation)
-when parts of a neural circuit simultaneously cause
contraction of 1 muscle and relaxation of its antagonists
stretch reflex function
-the stretch reflex helps avoid injury by preventing overstretching of the muscle
how does the brain come into play during the stretch reflex?
-branches of the muscle spindle sensory neuron also
relays information to the brain so that you know what
is happening
The tendon reflex (GTO)
-relaxation of a muscle when there is too much tension
-prevents tearing of a tendon
-ipsilateral
-polysynaptic
-stimulates Golgi tendon organs (GTO)
weakest link of mm
musculotendinous junction (GTO)
GTO:
sensory receptor
found within tendon near its junction with a mm
monitors changes in mm tension
The tendon reflex function
-this reflex protects the tendon and muscle from damage due to excessive tension
ALSO VIA —> -reciprocal innervation
E.g.
biceps relax and triceps contract, dropping weight (?)
The flexor (withdrawal) reflex
-when you step on a tack, you will flex or withdraw
your leg away from the painful stimulus
-it is a polysynaptic reflex arc
-it is ipsilateral
-this is a protective reflex because it moves the limb
away from a possibly damaging stimulus
The flexor (withdrawal) reflex is a …
-it is an intersegmental reflex arc
what does it mean that the flexor (withdrawal) reflex is an intersegmental reflex arc?
-nerve impulses from 1 sensory neuron ascend and descend in the spinal cord, activating interneurons in several segments of the spinal cord
-this way a single sensory neuron can activate several motor neurons
I.e. intersegmental arc means that
reflex can be quicker and more forceful
Why?
via several motor neurons for single sensory neuron, as opposed to 1:1
The crossed extensor reflex
-happens with the flexor reflex
-when you step on a tack and withdraw or flex your leg, the other leg needs to extend so you don’t fall over
-this is a contralateral reflex arc
—> sensory impulses enter one side of the spinal cord and motor impulses exit on the opposite side
the crossed extensor reflex is also ….
-intersegmental reflex arc
& reciprocal innervation
what space of meninges does not exist in skull?
NO EPIDURAL SPACE
Dura mater makes direct contact with inner side of cranial bones
Dura mater in brain other difference
two layers to the dura mater in skull
what do the two layers do?
the separate at certain spots
“DURAL VENOUS SINUSES”
—> sinuses for blood returning to heart
E.g.
Superior sagittal sinus
dura mater 2 layers
dura mater (periosteal and meningeal layers)
Major parts of the brain
Brain stem
Cerebellum
Diencephalon
Cerebrum
Brain stem
- continuous with spinal cord
= medulla oblongata
= pons
= midbrain
Cerebellum
- posterior to brain stem
Diencephalon
- superior to brain stem
= thalamus
= hypothalamus
= epithalamus
Cerebrum
- largest part of the brain
- sits on diencephalon
Protective Coverings of the Brain
Cranium & cranial meninges surround and protect the brain
cranial vs spinal meninges
Cranial meninges are continuous with the spinal meninges
- Dura mater
-outer meningeal layer
dura mater 2 layers
- periosteal layer (external)
- meningeal layer (internal)
-these 2 layers are fused together except where they separate to enclose the dural venous sinuses
Dural venous sinuses
Dural venous sinuses
-endothelial-lined venous channels -drain blood from the brain and deliver it into internal jugular veins
3 extensions of dura mater separate parts of the brain
- Falx cerebri
- Falx cerebelli
- Tentorium cerebelli
- Falx cerebri
Separates the 2 hemispheres of the cerebrum
- Falx cerebelli
Separates the 2 hemispheres of cerebellum
- Tentorium cerebelli
Separates the cerebrum from
the cerebellum
Tentorium
early 19th century: from Latin, literally ‘tent’.
blood to brain
internal carotid mainly
vertebral artery to lesser extent
blood flows to brain mainly via
the internal carotid
-vertebral arteries
blood flows out via
Dural venous sinuses which drain into
—> the internal jugular veins
brain weight vs bloodflow ratio
-in adults, brain is 2% of total body weight
but consumes 20% of all the oxygen and glucose
—> (20% of blood flow)
what happens if bloodflow to brain is interrupted
-even a brief slowing of brain blood flow can cause
disorientation or a lack of consciousness
(E.g. standing up too quick)
interrupted blood flow 1-2mins?
-usually an interruption in blood flow for 1 or 2 minutes
impairs neuronal function
orthostatic hypotension
standing too quick
4mins disrupted ciruclation to brain
-total deprivation of oxygen for about 4 minutes may cause
permanent injury
orthostatic hypotension define
“Orthostatic hypotension, also known as postural hypotension, is a medical condition wherein a person’s blood pressure drops when they are standing up or sitting down.”
why constant supply of glucose (bloodflow) is needed in brain
-no glucose is stored in the brain so the supply of glucose
must be continuous
what if blood entering brain does not have enough glucose?
if blood entering the brain has a low level of glucose:
dizziness
convulsions
loss of consciousness mental confusion
blood brain barrier, made of
=tight junctions that seal together endothelial cells of capillaries in the brain +
=a thick basement layer that surrounds the
capillaries +
=astrocytes (their processes press up against the capillaries and secrete chemicals that maintain the permeability characteristics of tight junctions)
what crosses bbb?
-some water-soluble substances cross by active transport
(ie glucose)
-creatinine, urea, ions cross slowly
-lipid-soluble substances (O2, carbon dioxide, alcohol, most anesthetic agents)
-proteins and most antibiotic drugs do not cross
-trauma, certain toxins and inflammation can cause a breakdown of the BBB
why are brain infections difficult to treat?
most antibiotic drugs do not cross
why alcohol crosses?
because of its chemical structure
-lipid-soluble substances (O2, carbon dioxide, alcohol, most anesthetic agents)
CSF
-clear, colourless liquid
-mainly water
-protects the brain and spinal cord from chemical and
physical injuries
CSF carries small amount of ____
-also carries a small amount of O2, glucose and other
needed chemicals in blood to the neurons and neuroglia
does that mean CSF can nourish brain in place of blood?
no, not enough O2/glucose
CSF continuosly circulates through
the cavities in the brain + spinal cord and
around the brain + spinal cord in the subarachnoid space
CSF totla volume
total volume = 80-150 mL in adult
CSF contians
small amounts of glucose, proteins, lactic acid,
urea, cations, anions and some WBCs
VENTRICLES
-cavities within the brain filled with CSF
list of ventricles
2 lateral ventricles
third ventricle
fourth ventricle
septum pellucidum
“The septum pellucidum (SP) is a thin, triangular membrane in the brain that separates the lateral ventricles. It’s made up of two layers of white matter, called laminae septi pellucidi. “
4th ventrilce continuous with
CENTRAL CANAL / spinal cord
CSF functions
1) Mechanical protection
2) Homeostatic function
3) Circulation
1) Mechanical protection
-shock absorbing medium that protects brain + SC from jolts
-fluid also keeps brain floating in the cranial cavity
2) Homeostatic function
-the pH of CSF affects pulmonary ventilation & cerebral blood flow
3) Circulation
-minor exchange of nutrients + waste products btw blood and nervous tissue
choroid plexuses inside ventricles
balls of capillaries that form CSF
Formulation of CSF in Ventricles
-CSF is formed in choroid plexus
choroid plexuses
-choroid plexuses are networks of blood capillaries
in the walls of the ventricles
ependymal cells vs capillaries of choroid plexuses
-ependymal cells joined by tight junctions cover the capillaries
filtering blood during CSF formation
-substances from blood plasma (mostly water) are filtered from the capillaries through the ependymal cells to produce CSF
blood-CSF barrier
-because of the tight junctions btw ependymal cells, fluid must pass through the ependymal cells, creating a blood-cerebrospinal fluid barrier
—> -this protects the brain + SC from harmful blood-borne substances
so BBB
-so BBB is made up of tight junctions btw brain capillary
endothelial cells
and BCSFB
-and the blood-CSF barrier is made up of tight junctions
btw ependymal cells
CIRCULATION of CSF (including formation?)
Lateral ventricles
(CSF formed in choroid plexus)
—> third ventricle
(more CSF formed in choroid plexus)
—> fourth ventricle
(more CSF formed in choroid plexus)
—> central canal & subarachnoid pace
—> arachnoid villi
arachnoid villi define/funciton
“Arachnoid villi are small projections of the arachnoid membrane that extend into the venous sinuses of the brain. They are also known as arachnoid granulations or Pacchionian granulations. “
“Arachnoid villi help absorb cerebrospinal fluid (CSF) from the subarachnoid space into the venous system. “
“They act as a communication network between the CSF and the venous system. “
Arachnoid villi
-CSF is reabsorbed into blood through arachnoid villi
-arachnoid villi are fingerlike extensions of arachnoid
that project into dural venous sinuses
cluster of arachnoid villi =
-a cluster of arachnoid villi = granulation
(arachnoid granulations)
