Stroke Flashcards
What are the four main lobes of the brain?
What are the six major divisions of the brain, named from below, upwards?
a) Medulla oblongata
b) Pons
c) Midbrain
d) Cerebellum
e) Diencephalon
f) Cerebrum
- Medulla oblongata, pons, and midbrain are referred to collectively as the brainstem
What is the cerebrum? What are the five main regions?
Cerebrum – largest part of the brain – two halves – left and right cerebral hemispheres
Uppermost layer – cerebral cortex – consists of 6 layers – made up of grey matter
Note
- Each ‘sausage’ in the cerebral cortex is known as a convolution or gyrus – e.g. cingulate gyrus
- Between adjacent gyri - you find sulci (shallow grooves) or deeper grooves (fissures)
Fissures and some imaginary boundaires have been used to divide the cerebrum into five regions…
a) Frontal lobe
b) Parietal lobe
c) Temporal lobe
d) Occipital lobe
e) Insula
What do you find beneath the cortex?
Beneath the cortex - lies the large interior of the cerebrum – mostly white matter made up of numerous tracts
What are the different tracts that are found interiorly in the cerebrum?
- Three types of tracts
a) Projection tracts - extensions of the ascending, or sensory, spinothalamic tracts and descending, or motor, corticospinal tracts.
b) Association tracts - Association tracts are the most numerous of cerebral tracts; they extend from one convolution to another in the same hemisphere.
c) Commissural tracts - Commissural tracts, in contrast, extend from a point in one hemisphere to a point in the other hemisphere - make up the corpus callosum.
What are the grey matter islands that lie interiorly in the cerebrum?
A few islands of grey matter lie deep inside the white matter of each hemisphere.
Collectively these are called basal nuclei, which can be divided into…
a) Caudate nucleus
b) Lentiform nucleus (putamen and pallidum)
c) Amygdaloid nucleus – amygdala.
- Functions of the basal nuclei are still being investigated - associated with voluntary motor function + also play a role in thinking/learning.
What happens during Parkinson’s disease?
Normally neurons that innervate the basal nuclei from the substantia nigra secrete dopamine – inhibits excitatory effects of acetylcholine (produced by other neurons in basal nuclei)
In PD - degeneration of dopamine producing neurons – excitatory effects of acetylcholine are not inhibited - producing excess signals that affect voluntary muscle
Overstimulation of postural muscles - rigidity and tremors of the head and limbs, abnormal shuffling gait, absence of relaxed arm swinging while walking and forward tilting trunk.
What region of the cortex is responsible for sensory functions?
Numerous areas responsible for somatic/general sensing
Somatic sensations- touch, pressure, temperature, body position (proprioception), and similar perceptions that do not require complex sensory organs
Postcentral gyrus serves as a primary area for the general somatic senses - forms a sensory map of the body – receives sensory inputs from different regions - regions with higher levels of receptors/sensation will have a greater representation
Special sensations - vision, hearing, and other types of perception that require complex sensory organs
Information regarding vision is mapped in the visual cortex and auditory information is mapped in the primary auditory area
What region of the cortex is responsible for motor functions?
Precentral gyrus—that is, the most posterior gyrus of the frontal lobe—constitutes the primary somatic motor area - neurons in this region are said to control individual muscles especially does controlling distal joints.
Secondary motor area lies in the gyrus immediately anterior to the precentral gyrus.
Neurons in the premotor area just anterior to the precentral gyrus are thought to activate groups of muscles simultaneously.
What system is thought to play an important role in consciousness?
Reticular activating system (RAS)
RAS consists of centre’s in the brainstem reticular formation receiving impulses from the spinal cord, which are then relayed to the thalamus and from the thalamus to all other parts of the cortex
Continual excitation of the RAS system is required for consciousness.
What region of the cortex is responsible for language/speech?
Certain areas in the frontal, parietal, and temporal lobes serve as speech centres
The left cerebral hemisphere contains these areas in about 90% of the population; in the remaining 10%, either the right hemisphere or both hemispheres contain them.
What region of the brain plays an important role in emotions?
Emotions—both the subjective experiencing of them and the objective expression of them—involve functioning of the cerebrum’s Limbic system.
Structures of the limbic system - cingulate gyrus and the hippocampus
These structures have primary connections with various other parts of the brain, notably the thalamus, fornix, septal nucleus, amygdaloid nucleus, and the hypothalamus.
What regions of the brain have been shown to play an important role in memory?
Both short-term memory and long-term memory are functions of many parts of the cerebral cortex, especially of the temporal, parietal, and occipital lobes
Outline the blood supply path from the heart to the brain.
Aorta divides to the descending and ascending aorta
Ascending aorta – branches into the right and left common carotid artery
The common carotid arteries further divided/bifurcates into internal and external carotid arteries
a) Internal artery supplies the brain with blood
b) External artery supplies the brain and neck with blood
Note - Right carotid arises from brachiocephalic artery, whereas left carotid arises from the aortic arch
Vertebral artery (branching from the subclavian artery) which passes through the cervical vertebrae into to skull – Cerebral cortex and brain stem blood supply
Outline the organisation of the vasculature in the brain.
Internal carotid artery – major supplier of blood to the anterior region of the brain – supply blood to the cerebral arterial circle of Willis - splits into the middle cerebral and anterior cerebral artery
Vertebral arteries come together to form a singular basilar artery, which joins the circle of Willis and bifurcates into the posterior cerebral artery – forms the posterior circulation.
Vertebral artery - supplies the brain stem with blood
Note - circular/halo organisation is smart as it allows for some level of blockage
What blood vessels supply the anterior and posterior compartment of the brain?
Carotid - Anterior
Vertebral - Posterior
Hence…
A stroke can be defined as an interrupted/blocked blood supply to the brain, which can be either…
a) Anterior circulation stroke
b) Posterior circulation stroke
What is the neural tracks/pathways that is responsible for movement?
Pyramidal tract - Primary motor nueron starts in the somatic motor cortex - travels down the brain and crosses over to the opposite side of the body at the medulla - this neuron synapses with the second motor neuron in the spinal cord, which then sends out the efferent signal to the muscle of interest
10% of the fibers don’t cross over – back-up allows for some level of control if one side of the brain is damaged
Crossing over is relevant for strokes - as loss of function on one side implies the present of a stroke on the opposite brain hemisphere.
Note - there is also a extrapyramidal tract that is responsible for unconscious, reflexive or responsive control of musculature, eg muscle tone, balance, posture and locomotion - more nuanced role
How does a stroke normally present itself?
- Rapid, acute onset – within a few minutes
- Focal neurological defect – almost always some sort of hemiplegia (one-sided paralysis), with/without other focal neurological signs (weakness, paralysis, loss of muscle control, vision loss, slurred speech, etc.)
Most strokes are painless - some strokes affect pain sensing neurons – post-stroke pain
What are the modifiable risk factors and how do we go about attempting to change them?
