4: Brain Flashcards
List the 4 protection methods of the brain
1- the cranium (skull)
2- the meninges
3- the blood-brain barrier
4- cerebrospinal fluid
Structure and function of the cranium
s= bones f= protection from external mechanical impact
Overview of the structure and function of the meninges
S= 3 connective tissue membranes that cover the external surface of the brain (and spinal cord) F= protect from external mechanical impacts
each membrane is called a mater 1- dura mater - subdural space 2- arachnoid mater 3- Pia mater
Structure and function of the dura mater
S= strong, tough, leathery protective membrane
- dual-layered
outer posterial= attached directly to inner surface of skull
inner meningeal layer= attached directly to brain - usually fused except in places where dura sinuses (channels that drain venous blood)
F= inner meningeal layer folds in with the brain in part such as between the two hemispheres acting like a seat belt and holding the brain in place.
Structure and function of the arachnoid mater
separated from dura mater from subdural space
- Web-like extensions of the arachnoid mater span the subarachnoid
space to attach the arachnoid mater to the underlying pia mater
-fingerlike projections
of arachnoid mater protrude through the dura mater into the dural sinuses to form
arachnoid villi
Structure and function of the subdural space
separated from dura mater from sub dural space.
- contains a thin film of serous fluid and veins that connect the
dura and arachnoid mater.
Web-like extensions of the arachnoid mater span the subarachnoid
space to attach the arachnoid mater to the underlying pia mater, and
Structure and function of the subarachnoid space
S= major cerebral blood vessels and cerebrospinal fluid F= cushions the brain to further protect from mechanical forces
Structure and function of the pia mater
S= very thin, delicate membrane that clings to the surface of the brain. F= contain small blood vessels which supply underlying neural tissue
Structure and function of cerebrospinal fluid
S= clear, colourless, liquid similar composition to plasma.
F= completely surrounds the brain and spinal cord, forming a ‘liquid cushion’
that;
- absorbs shock
- floats the brain to reduce its weight and stop its from crushing its self.
- diffusion medium for O2, nutrients and waste products between blood and neural tissue.
Where is CSF produced?
within 4 ventricles known as choroid plexus
- these ventricles are interconnected
1+2 lateral ventricle= in each cerebral hemisphere
3rd= in diencephalon
4th= central canal and connects to spinal cord
Choroid plexus structure and function
S= cluster of thin walled capillaries surrounded by a thin layer of ependymal cells.
F= These cells are tightly joined together and secrete selected substances (in particular water, oxygen and glucose) filtered from the blood plasma into the ventricles to produce CSF.
They also bare long cilia that help keep the CSF
in constant motion once it has been produced.
- aprox 150 ml in adults
- replaced approx. every 8 hours, around 500 ml is produced /day.
Describe the flow of CSF
- flows through the ventricles and into the subarachnoid space via openings in the walls of
the fourth ventricle - circulates through the subarachnoid space of the cranial and spinal meninges and
through the central canal of the spinal cord - is absorbed into the dural sinuses (venous circulation) via the arachnoid villi
Describe hydrocephalus and its consequences
the accumulation of CSF in ventricles that exerts pressure on the brain.
Obstructions such as by a tumour, blood
clot, subarachnoid haemorrhage or inflammation as a result of an infection (e.g.
meningitis)
- the pressure will eventually crush the brain and its blood supply
Patients commonly show signs of sleepiness, headache, vomiting without nausea and
neural dysfunction (e.g. seizures, visual disturbances, changes in behaviour, muscle
weakness) and they may suffer a stroke due to impaired blood flow.
- Excessive pressure will
cause the brain to move and eventually push the brain stem through the large hole
(foramen magnum) in the base of the skull. This is known as coning or herniation of the brain
stem. As the brain stem contains the autonomic centres that control cardiovascular and
respiratory functions (see section on the medulla oblongata in lecture notes), coning results
in death.
treatment= Hydrocephalus can be treated by inserting a shunt into the ventricles to drain the
excess fluid into a vein in the neck or into the abdominal cavity.
Why can children cope with increased fluid?
their cranial ones haven’t fused yet so they can expand, unlike in adults where they are fixed so immense pressure is created.
Structure and function of the blood brain barrier
F= protect neural tissue from harmful substances and pathogen (e.g. bacteria and viruses) circulating blood.
S= mainly consists of endothelial cells of the brain capillaries and the feet of astrocytes (glial cells)
- very tightly jointed making them the least permeable capillaries.
Is the blood brain barrier is selectively permeable?
yes, permeable to
- lipid-soluble compounds such as oxygen, carbon dioxide, lipids,
alcohol, nicotine and anesthetics
- nutrients such as glucose
- impermeable to metabolic wastes, proteins, toxins, potassium ions (as this will alter the
resting membrane potential and affect the generation of action potentials), most drugs
and antibiotics
Function of the circle of connecting arteries
- unite anterior and posterior blood supplies
- equalise cerebral blood pressure
- allow blood to continue flowing to all areas of the cerebrum if an internal carotid
or vertebral artery becomes occluded (e.g. if the internal carotid arteries
become occluded, blood entering the brain via the vertebral arteries can still
reach all six cerebral arteries and therefore the entire cerebrum).
Venous circulation- where does the blood go?
Most cerebral veins drain into the dural sinuses surrounding the brain. These sinuses empty
into a sigmoid sinus which directs blood back to the heart via the internal jugular veins and
superior vena cava.
Structure and function of the brain
F=
- receive, localise and interpret sensory input.
- Performs intellectual (cognitive) function
- Stores memories
- Responsible for emotional, behaviours and personality.
- Sensory areas of the brain generate and interpreted sensory impute.
- Motor areas of the brain generate the somatic or autonomic output that control muscle and glands.
S=
- Two fists
- Wrinkles like walnut
- Cold porridge texture
- Men have bigger brains
What is the brain composed of?
Gray matter
- neuroglia
- cell bodies of interneurons organised into nuclei
(nuclei make it dense, hence its grey colour)
White matter
- neuroglia
- myelinated axons of interneurons organised into tracts
Why do neurons need a high oxygen supply?
- have very high metabolic rate so they constantly need oxygen and glucose.
Failure to supply the brain with oxygen will quickly cause irreversible brain damage.
Structure and function of the cerebrum
- largest part of the brain
- the whole top part
- divided into two cerebral hemispheres by longitudinal fissure. Known as left and right
- separated from the cerebellum by the transverse fissure
Define fissure
deep groove
Define a gyrus/gyri
ridge
Define sulcus/sulci
shallow grove
Function of sulcus/sulci and gyrus/gyri
to increase surface area of the cerebrum= more neurons
Describe the lobes of the cerebrum
clockwise from forehead - frontal lobe central sulcus - parietal lobe parietal-occipital sulcus - occipital lobe lateral sulcus (sylvian fissure) - temporal lobe insula= inside/under/deep
Identify and describe the three internal divisions of the cerebral hemisphere?
- cerebral cortex
- outer. region of grey matter that holds nuclei interneuron cell bodies - Cerebral white matter
- inner region of white matter- contains tracts - basal nuclei
- gray matter deep within white matter
Structure and function of the cerebral cortex
s= contains nuclei
f=
- receives, localises and interprets sensory info.
- controls voluntary skeletal muscle movements
- performs intellectual and language functions
- stores memory
- controls emotions, behaviours and determines personality.
The neurons in the cerebral cortex are organised into three main areas. What are they?
- Motor - voluntary skeletal muscle movements.
- Sensory areas- receive, identify where stimulation is and allow for you to consciously perceive where you are experiencing something.
- Association areas= interpret and give meaning to the sensory input to info received by the brain., plan and coordinate motor response and perform intellectual function, create and store memories and determine behaviours and personalities.