brain and nervous system Flashcards
white matter
myelinated axons (nerve cell fibres) which connect various grey matter areas of the brain to each other. they carry nerve impulses between neurones. found in the central part of the brain, appearing darker on CT and lighter on MRI.
grey matter
nerve cell bodies and unmyelinated axons. handles muscle control and sensory perception such as seeing, hearing, memory, emotions, speech, decision making and self-control. appears more white on CT, and darker on MRI
cerebral cortex (grey matter)
made of multiple folds and grooves known as sulci (small inlets between the folds containing CSF) and gyri (folds in the cortex), increasing the surface area.
cerebrum
largest part of the brain occupying the anterior and middle cranial fossae. divided by a deep cleft called the longitudinal cerebral tissue. this separates the cerebrum into a right and left hemisphere, each contains a lateral ventricle . hemispheres are connected by a mass of white matter called the corpus callous
cerebellum
motor control. coordinations of voluntary muscular movement, posture and balance. damage to cerebellum causes clumsy uncoordinated muscular movement, staggering gait and an inability to carry out steady and precise movements.
midbrain and brainstem
critical functions such as cardiac and respiratory. motor and nerve supply to face and neck. regulates the CNS and facilitates motor / sensory nerve pathways from the rest of the body. consists of the thalamus and midbrain with the brainstem containing the pons, medulla oblongata and spinal cord.
meninges
brain and spinal cord surrounded by 3 layers of tissue. these lies between the skull and the brain and between the vertebral foramina and the spinal cord. made of (outside to in): dura, arachnoid then Pia mater
dura mater
made up of 2 layers of dense fibrous tissue. inner surface of skull and protective covering for the brain. forms the falx cerebri, falx cerebelli and tentorium cerebelli.
arachnoid mater
delicate alter. CSF flows in the subarachnoid space. arachnoid villi in venous sinuses allow CSF to exit subarachnoid space and enter the bloodstream.
pia mater
impermeable to fluid. works with other dura to protect and cushion the brain. allows passage of blood vessels to brain.
ventricles of the brain
main function is to create and circulate CSF.
lateral ventricles
located within the cerebral hemispheres. one on each side of MSP. inferior to corpus callous. communication with 3rd ventricle by inter ventricular foramen. has anterior/posterior horn and inferior horn. each ventricle has a choroid plexus, often calcified on CT, as is the pineal glands
third ventricle
located in the midbrain. inferior to lateral ventricles. between 2 parts of the thalamus. communicated with fourth ventricle by the cerebral aqueduct
fourth ventricle
diamond shaped. located in the brain stem. situated inferior and posterior to the third ventricle. between cerebellum and pons. continuous with central canal of the spinal cord. communicated with subarachnoid space by foramina superiorly
what is CSF?
created in the choroid plexus in the lateral ventricles. protects and cushions the brain, and allows for nutrient delivery. fluid contained in the central canal of spinal cord, subarachnoid space and cerebral ventricles. clear alkaline fluid.
absorption of CSF
mostly absorbed by arachnoid villi on the arachnoid mater into the dural (venous) sinuses. the absorption is determined by the pressure differences on each side of the villi walls. increased CSF pressure, decreased venous pressure = CSF passes into blood. increased venous pressure, decreased CSF pressure = arachnoid villi collapse preventing passage of blood constituents into CSF
the blood brain barrier
semi-permeable. oxygen and carbon dioxide pass quickly across the barrier. larger molecules pass more slowly from the blood to the brain. maintains constant environment (homeostasis) for the neurones in the CNS. protects the brain from potential toxins in the blood, although this also means antibodies/antibiotics are usually unable to pass through. prevents the escape of neurotransmitters from the CNS into general circulation.
what affects the permeability of the blood brain barrier
hypertension, development, microwaves, infection, trauma, schema, inflammation and raised intracranial pressure
functions of the nervous system
detects and responds to changes inside and outside of the body. works with the endocrine system to control important aspects of body function and maintain homeostasis. nervous system provides immediate short-acting responses whilst endocrine is usually slower and more prolonged
motor divison
voluntary = somatic nervous system, movement of voluntary (skeletal) muscles
involuntary (split further) = autonomic nervous system, functioning of smooth muscle, cardiac muscle and glands
involuntary / autonomic nervous system
sympathetic = controls body’s response during perceived threat fight or flight, originates in spinal cord, shuts down responses not critical to survival
parasympathetic = controls body’s response while at rest, originates in spinal cord and medulla, restores body to state of calm
nervous tissue
neurones responsible for sending impulses to other parts of the body. glial cells support cells insulate, protect and support neurones:
astrocytes - star shaped, control the blood brain barrier
oligodensrocytes - support and insulate axons
microglia - immune defence cells
ependymal cells - CSF production
neurones
cells which make up nerve tissue, supported by a special connective tissue called neuroglia (glial cells), need a continuous supply of oxygen and glucose to survive
function of a neurone
- receive sensory input
- interpret this signal and decide how to response
- effect a response
stimulation
electrical - motor and sensory nerve endings initiate nerve impulses
chemical - transmission of impulses between one neurone and the next, or between neurone and an effector organ
nerve impulses = action potential
either:
1. sensory nerve endings are stimulated
2. an impulse is passed from one neurone to another
resting
when a neurone is resting, the nerve cell membrane is polarised due to differences in the concentrations of ions across the plasma membrane. this means there is a different
electrical charge on each side of the membrane. at rest the charge on the outside of the cell is positive, inside it is negative due to the high number of negatively charged ions
stimulation
when stimulated, the nerve cell membrane becomes more permeable to the ions. sodium channels open up which allows the positive sodium ions to move into the neurone form outside the cell. this causes rapid depolarisation which creates an action potential of a nerve impulse. movement and sodium and potassium us done by active transport as cells are moving against the concentration gradient.
repolarisation
due to the influx of sodium into the neurone, channels open ip in the cell membrane for potassium to use. potassium ions move out of the neurone due to the influx of sodium which returns the membrane potential to its resting state. although the cell is now repolarised, the potassium and sodium are in the wrong place so the sodium-potassium pump begins to pump the sodium back out and the potassium back in
synapse
point where nerve impulses pass from one neurone to another
neurotransmitters
released by the synapse into the space between 2 neurones to allow transmission of the nerve impulse.
haemorrhages
4 main types: subdural, subarachnoid, epidural, intracerebral
plain CT used often but chronic bleeds are isodense so MRI is better
mass effect
shift of the brain to one side due to presence of mass/fluid. use the falx cerebri to determine the midline position and assess deviation
subdural haemorrhage
blood pools between the dura mater and arachnoid mater. mostly traumatic, but can rarely be spontaneous. usually convex / crescent moon shaped. can cross suture lines but not falx cerebri. does not extend into the cerebrum
epidural haemorrhage
biconvex (lemon) shaped. blood enters the space between skull and the dura mater. usually cannot cross suture lines. can cross falx cerebri. does not cross into the cerebrum
subarachnoid haemorrhage
presents with a thunderclap headache. blood enters the subarachnoid space, most commonly around the circle of willis and Sylvia fissure. blood contained to gaps in the cerebrum
intracerebral haemorrhage
can be associated with stroke. blood seen within the brain tissue itself. causes mass effect. within the brain so not contained by meninges
treatment
essential to monitor inter cranial pressure, normal between 7-15mmHg. ICP bolt device inserter to monitor in real time. surgical evacuation of blood. craniotomy to release pressure
other cranial pathologies
empyema - infective collection between dura and arachnoid mater. can mimic subdural haemorrhage
meningioma - often slow growing tumour in meninges
how are stoke patients assessed in A&E?
ROSIER scoring system
CT / MR Venography
imaging for ? thrombosis
CT - scan 45-50 seconds after start of contrast injection
70-100mls contrast media
delated injection as the contrast has to travel in the blood through venous system of the arm to the heart, to through the arterial system to the brain, and then into the venous system of the brain
arteriovenous malformation
a tangle of arteries and veins. usually treated by embolisation
cerebral aneurysm
can be treated by surgical clipping. also treated with coiling / embolisation in IR
congenital hydrocephalus
cranial size enlarged. scalp veins appear distended. skin of scalp thing, fragile and shiny. underdevelopment of neck muscles. treated by insertion of a shunt. excess CSF diverted away from the head to another place in the body where it can be removed naturally or drained externally.
imaging shunts
Xray lateral skull, AP chest / neck and abdo. plain CT also performed to confirm position in ventricle.
multiple sclerosis
autoimmune condition. immune system attacks myeline sheath around nerves causing a disruption to nerve signals.
brain tumours
most common type is glioma. common subtypes include astrocytoma and glioblastoma. MRI best modality to image. biopsy to confirm diagnosis followed by chemotherapy and radiotherapy
acute meningitis
acute inflammation of the meningeal coverings of the brain. can be caused by viruses, bacteria and other microorganisms and certain drugs
bacterial meningitis
bacteria enter the subarachnoid space via the bloodstream. inflammation caused by the response of the immune system to bacteria in the CNS. increased oedema in the CNS = increased intracranial pressure. hard for blood to enter the brain, depriving it of oxygen and ultimately causing apoptosis
signs and symptoms of meningitis
fever, headache, stiff neck, photophobia, seizures, rash, confused, struggles to wake up
diagnosis of meningitis
physical examination, blood test, sample of CSF taken from a lumbar puncture, CT
