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.
Define contralateral control
left side of brain deals with sensory input from right side of the body.
e. g. right cerebral cortex
- receives sensory information from and controls skeletal muscles on the LHS of body.
Primary motor cortex location and function
L= precentral gyrus F= responsible for generating somatic motor output for voluntary skeletal muscle movements.
specific areas of PMC are devoted to controlling specific body parts.
- the amount of PMC devoted is proportionate to the complexity of movement of that part.
What does damage to the PMC result in?
paralysis (loss of volunatry movement)
- if brain is damaged on left hand said, right will stop functioning.
Explain the motor homunculus
This man shows what we would look life if the area allocated to each part of us in the brain was translated to size of body part.
List the three motor association areas of the cerebral cortex.
1- frontal eye field
2- broca’s eye field
3- premotor cortex
Frontal eye field function and location
F= controls voluntary eye movement L= posterior to PMC, anterior to Pre motor cortex
Broca’s area function and location
F= controls muscles used in speech production L= left frontal lobe only
damage= Broca’s aphasia
- When an individual looses ability to speak fully. They know what they want to say however they cant say it. This is very frustrating!!!
Pre motor cortex function and location
F= controls learning, skilled motor activities of a complex nature e.g. typing and tying a bow L= posterior to PMC anterior to premotor cortex Damage= loss of complex motor skills
What are some examples of general sensory receptors?
for;
- pain
- temp
- touch
- vibration
- pressure
- proprioception
What are some examples of special sensory receptors?
for; - vision - smell - taste - hearing balance
Primary somatosensory cortex (PSC) location and function
L= post central gyrus of each parietal lobe F= receives general sensory info - Pain - Touch - tactile receptors in skin - Vibration - Pressure - Temp - thermo receptors in skin - Proprioception- proprioceptors receptors in skeletal muscles
- Allows us to be conscious of these sensations
Define cerebral cortex
the outside layer of the brain used for motor and sensory function
What are the 4 sensory areas of the cerebral cortex?
- insula
- parietal
- temporal
- occipital
Somatosensory association area location and function
F= general sensory input from the primary somatosensory cortex L= posterior to Primary somatosensory cortex
Damage= failure t identify objects by touch alone
Special sensory areas- visual areas
visual cortex location and function
L= occipital lobe- most posterior part F= receives visual input detected by photoreceptors
damage= blindness
Special sensory areas- visual areas
visual association areas location and function
L= occipital lobe- anterior to visual cortex
F= interpret visual input- allowing us to recognise what we see;
- stores memories of the past
damage= failure to recognise objects
Special sensory areas- auditory areas
Auditory cortex area location and function
L= temporal lobe under primary somatosensory cortex F= receives sound input detected by the hair cells in the ear to produce and locate sounds. Allows us to hear multiple sounds at once.
damage= deafness
Special sensory areas- auditory areas
Auditory association area location and function
L= temporal lobe under occipital lobe
F= interprets auiotory inout- allows us to recognise sounds
- stores memories of past sounds
damage= failure to recognise what is heard
Special sensory areas- Olfactory cortex
location and function
L= temporal lobe F= perceives odours
Special sensory areas- Gustatory cortex
location and function
L= insula F= perceives taste sensation
Special sensory areas- visceral cortex
location and function
L= insula F= visceral sensations of internal organ sensations e.g hunger
Special sensory areas- vestibular (equilibrium) cortex
location and function
L=insula
F= balance
Wernicke’s area
- association area
location and function
L= left temporal lobe only F= comprehend written and spoken language
Damage= Wernicke’s aphasia
-They can still speak word but they have no context or make sense. They don’t know it don’t make sense
Pre-frontal cortex (anterior association area)
location and function
L= frontal lobe F= intellectual, complex learning abilities (cognition), personality and behaviour
Damage= personality disorders
Prefrontal cortex - Most complex This area lets us - Behave in a socially acceptable manner - Plan ahead - Solve problems - Recall info - Be attentive - Focused - Make good decisions - Make good ideas - Reason and think about consequences
It does this by communicating with other areas of the brain.
Not fully developed till mid 20’s hence why young adolescents don’t think about the consequences of their actions
Cerebral white matter function
F=communication
S= myelinated axons organised into tracts
- It consists of myelinated axons which means fast moving signals
What are the three tracts of white matter
1- commissural tract
2- association tracts
3- projection tracts
Commissural tracts structure and function
F= conduct info between hemispheres
- Allows two hemispheres to function as one
- Largest commissural tract= corpus callosum
Association tract structure and function
conduction info between cortical areas in the same hemisphere
Projection tracts structure and function
conducts info between cerebral cortex and lower part of CNS e.g. thalamus to cerebral cortex
Cerebral basal nuclei- structure and function
S= islands of grey matter deep within white matter
F= facilitate smooth skeletal muscle movements
- regulated by dopamine
Loss of dopamine= Parkinson’s disease
- Exact role still unclear
- Communicate through complex neural path ways from cerebral cortex to smooth skeletal muscles to make them move.
- They help start and stop skeletal muscle movements
- Inhibit unwanted movements by causing muscles that create a movement to relax.
Dopamine is necessary for regulation. If it isn’t present then basal nuclei facilities to much movement.
List the diencephalon structures
- thalamus
- hypothalamus
- epithalamus
Thalamus structure and function
F= relay station for into coming to cerebral cortex
- processes and integrates sensory input
- relays the motor adjustments made by basal nuclei and cerebellum to the motor areas of the cerebral cortex.
Thalamus= ‘entrance to cerebral cortex’
It is a postal centre
- Takes, in sorts, and resend info to correct sensory area coming in from CNS
E.g. all touch and pain info will besent to primary somatosensory cortex
E.g. all taste info willbe grouped and sent to gustatory cortex
Hypothalamus structure and function
S= contains nuclei that... F= control autonomic nervous system regulate; - emotions- part of limbic system - body temp - hunger and thirst - sleep-wake cycles
produces hormones- antidiuretic hormones (ADH)(regulates blood pressure), oxytocin (stimulates labour contractions)
and releasing/inhibiting hormones (control endocrine function and function of pituitary gland)
Epithalamus structure and function
S= includes pineal gland
F= it produces melatonin
- indices sleep
The limbic system structure and function
S= includes specific areas of the cerebellum (e.g. prefrontal cortex and hippocampus) and diencephalon (e.g. hypothalamus)
F=
- establishes control of emotions
- involved in formation of long term memory
- Turns short term memories to long term memories.
Function of the hippocampus
converts short term memory into ling term memories
damage= issues with short term memory
List the components of the brain stem
thalamus midbrain pons medulla oblongata spinal cord
Midbrain (mesencephalon)
structure, location and function
S= contains nuclei F= - visual and auditory reflex centres - substantia nigra- produces dopamine - cranial nerves nuclei that regulate eye movement via CNIII and CN IV
L= top of brain stem
Pons
structure, location and function
S= gray matter
F=
- contain cranial nerve nuclei involved in taste, chewing, eye movement, hearing, balance and facial sensation. via CN V and VIII
- Nuclei that regulate breathing
Medulla oblongata
structure, location and function
S= grey matter
F= autonomic nuclei controlled by hypothalamus
- cardiovascular centre- controls heart rate and blood vessel diameter
- respiratory centre- control the rate and depth of breathing.
Reticular formation
structure, location and function
= a functional system that extends through the central core of the brain stem.
contains reticular activating system
- maintains consciousness
damage= coma
RAS= maintains consciousness
- Does this by sending a constant stream of signals to cerebral cortex.
RAS can be inhibited by the sleep centres in the hypothalamus which allows us to go to sleep.
- Other inhibitors= tranquilises, alcohol
Sever damage to this area= coma
Traumatic brain injuries- concussion effects
midbrain injury with short term effects- head ache, dizziness, temporary loss of consciousness
Traumatic brain injury results from extreme force, penetration etc
Not only do these forces damage the side they hit but also the opposite side as they make the brain rebound and hit the skull on the other side.
Traumatic brain injuries- Contusion
bruising of the brain
- can cause permanent neurological damage
- may result in coma
Traumatic brain injury results from extreme force, penetration etc
Not only do these forces damage the side they hit but also the opposite side as they make the brain rebound and hit the skull on the other side.
Explain a stroke
= blood flow to the brain is reduced or blocked (ischaemia) and neurons die due to lack of oxygen and glucose.
causes= blood clot in cerebral artey= ischaemic stroke
Ruptured blood vessel= haemorrhagic stroke
- most common nervous system disorder
common symptoms= head ache, muscle weakness/paralysis, loss of vision/blurred vision, difficulty speaking and understanding speech.
symptoms last more than 24hrs-life
drugs can quickly dissolve blood clots or surgery to fix a hemorrhage
explain a transient ischaemic attack
mini-stroke
- same symptoms as a stroke however blood clot quickly dissolves and returns to normal.
symptoms usually last 5-20 minutes
- warning of impending stroke
blood flow is temporary
Explain Alzheimers disease
progressive degenerative disease
- brain shrinks due to death or neurons
symptoms= memory loss, confussion, disorientation, personality chnages, inability to read talk, write, talk eat and walk.
Cause= unknown, however
- plaques in-between dying neurons are found in the brain of its victims.
- Beta-amyloid is toxic to the surrounding neurons
Tangles are found in neurons and they inhibit transport of nutrients from one part of cell to another.
Explain Parkinsons disease
progressive degerative disease
- degeneration and death of dopamine-releasing neurons of the substantia nigra= loss of dopamine
basal neucli become overactive sp movements become over controlled- stiff and slow
cause= unknown
symptoms= minimal faceial expressions, forward bent posture, shuffling gait with no arm swing, difficulty speaking and swallowing and persistant tremors at rest.
