Stroke Scenario- Physiology

Question 1

What are the 3 main areas of the brain + what connects the brain to the spinal cord?

Answer 1

Cerebrum, Cerebellum and brain stem.

Foramen magnum is an opening at the base of the skull connecting the brain to the spinal cord.

Question 2

What are the 3 coverings of the brain + their features?

Answer 2

Pia mater: innermost layer, directly continuous with brain and spinal cord, vascular which blood vessels pass through to internal CNS to nourish neural tissue.
Subarachnoid space: middle layer, contains cerebral arteries.
Dura mater: outermost tough layer, composed of 2 layers, innermost is the meninges.

Question 3

What is the structure of the cerebrum?

Answer 3

Largest part of brain consisting of 4 lobes:
Frontal
Parietal
Temporal
Occipital
Cortex (surface) contains the centres from which motor impulses are carried to muscles and to which sensory impulses come from sensory nerves.
It contains the thalamus in the inner core.

Question 4

What is the structure and function of the thalamus?

Answer 4

composed of 2 ovoid(egg shaped) structures.
Important relay station in the brain.
All main sensory pathways form synapses with thalamic nuclei on their way to cerebral cortex.
Pathways also serve as vehicles for transmitting pain, emotions etc.

Question 5

What is complimentary specialisation?

Answer 5

a concept that determines that different areas of the brain serve different functions.

Question 6

What are the functions of the cerebral hemispheres?

Answer 6

The categorical hemisphere is associated with:
language comprehension skills
sequential analytic processes.

The representational hemisphere is associated with:
recognition of faces, music and visual spatial relationships.

Question 7

Where is the categorical hemisphere generally located + what important areas does it contain?

Answer 7

Left hemisphere for 96% of right-handed people.
Contains :
Wernicke’s area - area for language comprehension
Broca’s area - area for speech and word formation.
Injury to this hemisphere associated with language disorders.

Question 8

What is the function of the cerebellum and where is it located?

Answer 8

It regulates coordinated activities such as gait and performance of motor tasks.
Located below and behind the cerebrum.

Question 9

What structures does the brain stem contain?

Answer 9

Midbrain
Pons
Medulla oblongata

Question 10

How are the cerebellum and brain stem connected?

Answer 10

Midbrain connects pons and cerebellum with the cerebral hemispheres.

Question 11

Where is the pons located and what is it’s function? (Cerebellum)

Answer 11

Pons located in front of cerebellum between midbrain and medulla.
Serves as a bridge between 2 halves of cerebellum as well as between medulla and cerebrum.
It contains important centres for controlling heart, respiration, BP.

Question 12

What is the function of the frontal lobe?

Answer 12

Contains areas associated with emotional attitudes and development of thought processes.

Question 13

How are nerves structured in the cortex and how is this important in stroke?

Answer 13

Nerve fibres from all portions of cortex converge in each hemisphere and make their exit in the form of tight bundles ‘internal capsule’.
These cross the corresponding bundle from the opposite side therefore, a right-sided stroke = left-sided weakness.

Question 14

What is cerebrospinal fluid and where is it located?

Answer 14

Cerebrospinal fluid is a clear fluid that bathes the surface of the brain and spinal cord, providing protection and supplying nutrients to the tissue of the nervous system.
It extends from the ventricle through narrow tubular openings.
Average amount of CSF is 150ml.

Question 15

What are neurons and what are they composed of?

Answer 15

The structural, genetic and functional unit of the nervous system.
They are composed of:
cell bodies
dendrites
axons

Question 16

Where are the cell bodies of neurons located?

Answer 16

Located in the layers on the surface of the brain and comprise gray matter.

Question 17

What intracellular structures found in many cells do neurons contain?

Answer 17

Nucleolus
Microtubles
Golgi apparatus
Rough endoplasmic reticulum.

Question 18

What neuron-specfic intracellular structures do neurons contain?

Answer 18

Neurofilaments
Synaptic vesicles
Nissl substance

Question 19

What is the energy source for neurons and what do they release?

Answer 19

They use glucose as their energy source and are dependent on oxidative metabolism.
They produce and release neurotransmitters.

Question 20

What are neurotransmitters and how are they released?

Answer 20

Neurotransmitters are chemicals synthesised in neurons that are stored in synaptic vessels in axon terminals.
Released from axon terminal by exocytosis and are reabsorbed and recycled.

Question 21

What is the function of neurotransmitters?

Answer 21

They cause changes in the cell permeability of the neutron, making it more or less able to conduct an impulse.

Question 22

What are neuralgia?

Answer 22

They are the supporting cells fir the neurons of the CNS, whereas Schwann cells have this function in PNS.
They comprise 40% of brain and spinal cord.
Outnumber neurons 4/1.

Question 23

What are the 4 types of neuralgia?

Answer 23

Microglia: phagocytic properties to ingest and ingest debris, found throughout CNS and play a role in fighting infection.
Ependyma: line ventricular system and involved in production of CSF.
Astroglia: located between blood vessels and neurons. Provide defence for CNS and maintain homeostasis.
Oligodendroglia: glial cells responsible for myelin production in CNS.

Question 24

What is myelin and where is it found?

Answer 24

Myelin is a white lipid-protein complex, it provides insulation along a nerve process.
Prevents flow of sodium and potassium ions across neuronal membrane.
Found within white matter, fibres that have no myelin found in grey matter.

Question 25

How is the brain supplied with blood?

Answer 25

Through the left and right common carotid arteries and the left and right subclavian/vertebral arteries.

Question 26

How are the carotid arteries divided?

Answer 26

Into internal and external.
Internal: supply blood to most of the cerebrum
External: supply blood to face and scalp.

Question 27

Where do the vertebral arteries supply blood?

Answer 27

They enter the skull via foramen magnum, fusing at brainstem to form basilar artery.
Posterior two fifths of cerebrum
part of cerebellum
brain stem.

Question 28

What are the effects of a decrease in blood supply from the internal carotid arteries?

Answer 28

Can result in impairment of function of the frontal lobes.
Causing:
numbness
weakness
paralysis
affecting the opposite side of the body to the obstruction.

Question 29

What are the effects of a decrease in blood supply from the vertebral arteries?

Answer 29

Can cause serious consequences such as blindness and paralysis.

Question 30

How are cerebral arteries classified and what is the function of each one?

Answer 30

Either penetrating or conducting.
Conducting: form extensive network over surface of brain.
Penetrating: nutrient vessels derived from conduction arteries, enter brain at right angles and provide blood supply for deep cerebral structures.

Question 31

What is the arterial circle of willis?

Answer 31

The carotid and vertebral arteries unite at base of brain to form a circle of communicating arteries.
Only slight blood flow through these arteries but they serve a fail-safe mechanism in case of dramatic changes in arterial blood pressure.

Question 32

How does brain metabolism occur?

Answer 32

It is steady and continuous with no rest periods, therefore requires a continuous supply of glucose and oxygen.
Highly dependent on oxygen, accounting for 20% of the body’s oxygen use.

Question 33

How does a lack of oxygen or glucose effect brain metabolism?

Answer 33

If blood flow ceases, consciousness may be lost in as little as 10 seconds.
The brain does not switch to anaerobic metabolism, therefore a lapse of just a few minutes can cause irreversible damage.
A lack of glucose or sustained hypoglycaemia can damage brain tissue as glucose is its major energy source.

Question 34

How is blood flow regulated in the brain?

Answer 34

The normal brain can regulate its own blood supply to maintain arterial pressure between 65-140mmHg.
Factors that affect this are either extrinsic or intrinsic.

Question 35

What extrinsic(outside) factors effect blood flow to the brain?

Answer 35

Primarily related to cardiovascular system; blood pressure, cardiovascular function and blood viscosity.
If mean BP drops below 60mmHg the brains auto regulatory mechanism decreases.
If BP continues to drop sign os cerebral ischemia will appear.
If cardiac output decreases by more than a third there is a fall in cerebral blood flow.
CBF increases with anaemia but decreases with polycythemia due to increase viscosity.

Question 36

What intrinsic(internal) factors affect blood flow to the brain?

Answer 36

Influenced by cerebral perfusion pressure (pressure difference between cerebral arteries and veins), should remain constant despite changes in BP.
Cerebral blood vessels important because of their response in maintaining flow.

Question 37

What is middle cerebral artery stroke ?

Answer 37

MCA stroke describes sudden onset of focal neurological deficit resulting from brain infarction or ischaemia in the territory supplied by MCA.
The MCA is the largest cerebral artery, it supplies most of the outer convex brain surface, basal ganglia and posterior and interior cap.

Question 38

What areas can MCA stroke affect?

Answer 38

MCA is an interruption of blood flow to areas that receive blood through the MCA:
frontal, parietal and temporal lobes and internal capsule.
Blockage of whole MCA results in large vessel stroke affecting the whole MCA territory.

Question 39

What are the impairments caused by MCA stroke?

Answer 39

language deficits
weakness
sensory deficits
visual defects
cognitive deficits

Question 40

What causes MCA stroke?

Answer 40

They are generally thrombotic, usually caused by a blood clot that travelled from elsewhere in the body (heart, carotid artery) that they becomes lodged in MCA blocking blood flow.

Question 41

What are the risk factors for MCA stroke?

Answer 41

heart disease
carotid artery disease
Hugh cholesterol
hypertension
diabetes