Sem 2 Module 1 - The Brain Flashcards
(98 cards)
1
Q
How many neurons do brains have?
A
15-100 billion neurons
2
Q
How many synapses does the cerebral cortex have?
A
125 million
3
Q
What are the brain basics?
A
- Weighs about 1.5kg (2% of body weight)
- The brain requires constant blood flow because it has high energy demands
- Requires 15% of the cardiac output
- Consumes 70% of blood glucose
- Does not store glucose
- Cannot produce glucose - Accounts for 20% of the body’s oxygen consumption
–> deprivation of blood for just a few minutes cause irreversible damage
4
Q
What are the main divisions of the brain?
A
- Cerebrum
- Diencephalon
- Hypothalamus
- Mesencephalon
- Pons
- Medulla Oblongata
- Cerebellum
5
Q
What does the Cerebrum do?
A
- Conscious though processes
- Intellectual functions
- Memory storage and processing
- Conscious and subconscious regulation of skeletal muscle contractions
6
Q
What are other facts about the Cerebrum?
A
- It is the largest part of the brain (83% of brain mass)
- Divided along the midline into two hemispheres by the longitudinal fissure
- Separated from the cerebellum by the transverse fissure
7
Q
What else about the cerebrum?
A
- Characterised by ridges (gyrus, gryi) and grooves (sulcus, sulci) —> increases surface area (x 3)
- Each hemisphere is divided by sulci into five lobes:
- frontal
- parietal
- temporal
- occipital
- insula (deep into the temporal lobe)
8
Q
What are the cerebral hemispheres?
A
- Each hemisphere is divided into structurally and functionally distinct regions
- an outer layer of grey matter —- cortex (neuron cell bodies
- A deeper region of white matter (fibres/axons)
- Clusters of grey matter deep within the white matter —> basal nuclei
9
Q
What is the Cerebral cortex?
A
- Location of the conscious mind –> localise an interprets sensory inputs, self awareness, communication, memory, understanding, voluntary movements (skeletal muscles)
- Makes up 40% of brain mass
- The cortex of each cerebral hemisphere has 3 functional areas:
- Motor areas
- Sensory areas
- Association areas - The cortex of each hemisphere deals with the sensory and motor functions of the opposite side of the body
- The cortex of each hemisphere has distinct functions (lateralisation)
10
Q
What is hemispheric lateralisation?
A
- Although each hemisphere has many functions in common, they each have unique abilities
- 90% of people are represented by the left cerebral dominance
- 10% of people have the reverse = right cerebral dominance
11
Q
What is the primary motor cortex?
A
- Pre-central gyrus of the frontal lobe
- Controls all voluntary movement
- Contains the cell bodies of upper motor neurons of voluntary motor pathways
- Directs movements of skeletal muscles via pathways which control the contralateral side of the body —> right motor cortex controls skeletal muscles on the left side of the body and vice versa
12
Q
Other information about the primary motor cortex?
A
- Specific areas of the primary motor cortex are devoted to controlling specific body parts
- The amount of motor cortex devoted to controlling a body part is indicative of the complexity and precision of the movements of that body part e.g. hands and face
13
Q
What does the premotor area do?
A
- Controls learned motor activity e.g. typing
- Co-ordinates the movement of muscle groups
- Acts via the primary motor cortex
14
Q
What does the Broca’s area do?
A
- Directs the muscles involved in speech generation
- In only one hemisphere
- If damaged, person can understand speech but cannot speak it
15
Q
What does the frontal eye field do?
A
- Controls voluntary eye movement
16
Q
What will happen if the primary motor cortex is damaged?
A
- E.g. stroke (ischaemic tissue damage)
- Paralyses the body muscles controlled by the damaged area —> voluntary movements only, not reflexive movements
17
Q
What will happen if the premotor cortex is damaged?
A
- Loss of motor skills programmed by the damaged region but discrete movements unhindered
e. g. typing area damaged —> unable to type quickly but able to make the same discrete movements - able to reprogram another set of premotor neurons (relearn the activity)
18
Q
What is the sensory cortex?
A
- The primary sensory and association areas are located in the parietal, temporal and occipital lobe
- Concerned with the conscious awareness of sensation
- somatosensory stimuli —> e.g. touch, pain etc.
- special sensory stimuli —> e.g. vision, taste
19
Q
What do sensory areas include?
A
- Primary somatosensory cortex and association area
- Visual cortex
- Auditory cortex
- Olfactory and gustatory cortex
- Visceral sensory area
- Vestibular (equilibrium) cortex
- General interpretive area (Wernicke’s area)
20
Q
What is the primary somatosensory cortex?
A
- Located in the post-central gyrus of the parietal lobes
- Neurons receive information from
- General sensory receptors in the skin (touch, pressure, vibration, pain, temperature)
- Proprioceptors in skeletal muscles, joints and tendons (body position)
- Neurons receive information from
- Information from one side of the body reaches the opposite sensory cortex after passing through the thalamus
e. g. pain or temperature stimuli travel to the cortex via the lateral spinothalamic pathway after decussating at the level of the spinal nerve.
21
Q
What else about the primary somatosensory cortex?
A
- Specific areas of the primary somatosensory cortex are devoted to analysing sensory information from specific body parts
- Amount of sensory cortex to particular body region —> related to that regions sensitivity
- Face and fingertips are most sensitive body parts
22
Q
What is the somatosensory association area?
A
- ;Located posterior to the primary somatosensory cortex in the parietal lobe
- Integrates incoming sensory information, comparing it to stored memories of past sensory experiences to make sense of the information
i. e. makes us aware of sensory stimuli —> the size, texture etc. of an object - Damage —> lose the ability to identify objects by touch alone
23
Q
What are the special sensory cortices?
A
- Visual areas - Occipital lobes
- Visual cortex
- Visual association area - Auditory areas - Temporal lobes
- Auditory cortex
- Auditory association area - Olfactory cortex
- Gustatory cortex
- Visceral cortex
- Vestibular (equilibrium) cortex
24
Q
What is the visual cortex?
A
- Receives impulses from the retinas
Damage —> Functional blindness
25
What is the visual association area?
-I Interprets visual image
Damage ---> Failure to recognise objects
26
What is the auditory cortex?
- Receives impulses from inner ear
Damage ---> Deafness
27
What is the auditory association area?
- Interprets auditory stimuli
Damage ---> Failure to recognise what is heard
28
What is the Olfactory cortex?
- Temporal lobe
| - Conscious awareness of odour
29
What is the gustatory cortex?
- Insula (deep into temporal lobe)
| - Perception of taste stimuli
30
What is the Visceral Cortex?
- Insula (deep into temporal lobe)
- Perception of visceral sensations
e. g. upset stomach, full bladder
31
Vestibular (equilibrium) cortex?
- Insula (deep into temporal lobe)
| - Awareness of balance
32
What is the general interpretive area?
- Also know as Wernicke's area
- Left hemisphere, in the temporal lobe
- Integrates information from sensory association areas and visual and auditory memories ---> recognition and understanding of spoken and written language
- linked to Broca's area (motor speech area)
Damage
- Affects ability to interpret visual and auditory information, aphasia (inability to understand language or even speak, read and write)
33
What is the Multimodal Association area?
- Located in the prefrontal cortex
- Most complicated corticol area
- Co-ordinates information from all association areas
- Involved in intellect, complex learning abilities, recall and personally
- Working memory ---> abstract ideas, judgment, reasoning, planning
- Maturation associated with environmental interaction
34
What is the cerebral white matter responsible for?
- Responsible for communication between hemispheres and between the cerebral cortex and other CNS areas
35
What is the Cerebral white matter made up of?
Predominantly made up of myelinated fibre tracts
- Commissures ---> connect the two hemispheres e.g. corpus callosum
- Association fibres ---> connect different parts of the same hemispheres
- Projection fibres ---> connect cerebral cortex with other CNS areas
36
What is the cerebral basal nuclei?
- Concentrations of grey matter (nerve cell bodies ) deep within the white matter of the cerebral hemispheres
37
What does the Cerebral basal nuclei do?
- Receive input from the entire cerebral cortex, other nuclei and each other
- Send info -->the thalamus --> to the premotor cortex --> dampen muscle activity to facilitate smooth, co-ordinated movement
help to control intensity of skeletal muscle movements executed by the primary motor cortex
38
What does the diencephalon include?
- Thalamus
- Hypothalamus
- Epithalamus
39
What is the thalamus?
- Bilateral egg-shaped collection of nuclei
- Makes up 80% of the diencephalon
- Acts a "relay station" for information coming into the cerebral cortex ---> "gateway to the cerebral cortex"
- Sorts sensory information and conducts it to the relevant areas of he cerebral cortex
e. g. taste information ---> gustatory cortex
- Conducts impulses between the cerebral motor areas and cerebellum
- Involved in alertness, learning and memory processing
40
What is the Hypothalamus and its vital functions?
- Small structure, below the thalamus
- Collection of nuclei with many vital functions:
1. Chief integration centre of the autonomic nervous system ---> regulates the ANS by controlling centres in the brain stem and spinal cord
i. e. cardiac and respiratory function
2. Centre for emotional responses ---> part of the limbic system
3. Body temperature regulation ---> thermostat (initiates sweating and shivering)
41
What are other vital functions of the hypothalamus?
4. Regulation of food intake ---> appetite and satiety
5. Regulation of water balance by triggering the release of anti-diuretic hormone (ADH)and promoting thirst
6. Regulation of sleep/wake cycle ---> biological clock
7. Controls endocrine system functioning ---> primarily via the pituitary gland
42
What is the Epithalamus?
- Most posterior portion of the diencephalon
43
What does the Epithalamus do?
Incorporates the pineal gland
- Produces melatonin ---> induces sleep
- Helps the hypothalamus regulate sleep/wake cycles
44
What is the limbic system?
- A group of structures located on the medial aspect of each cerebral hemisphere and diencephalon, including the hypothalamus and olfactory bulbs, linked by a fibre tract (fornix)
45
What does the limbic system do?
Forms the emotional brain:
- Amygdala ---> recognises angry or fearful facial expressions, assesses danger and elicits the fear response (via the hypothalamus and the ANS)
- Cingulate gyrus ---> Role in physical expression of emotions and resolving mental conflicts
- Hippocampus ---> Role in emotional memory
- Olfactory bulbs ----> Links odour to memory (especially emotional memory)
Interacts with many other brain parts, including the prefrontal cortex of the cerebrum, allowing us to
- react emotionally to events
- be consciously aware of our emotions ---> interplay between emotions and logic
45
What does the brainstem include?
Includes the midbrain, pins and medulla oblongata
46
What is the midbrain?
- Located between the diencephalon and pons
Contains
- Various grey matter nuclei
- Visual and auditory reflex centres
- substantial Nigeria contains neurones that produce dopamine ---> degenerating in Parkinson's disease
- Descending corticospinal tracts (white matter)
- Cerebral aqueduct ---> flow in the cerebrospinal fluid
- Connection point for cranial nerves CN III & IV ---> involved in eye movements
47
What are the pons?
-"Pons" means bridge
- Between the midbrain and the medulla oblongata
Contains:
- fibre tracts ---> bridge various brain areas
- projection fibres that connect the higher and lower brain centres
- fibres that connect the pons with the cerebellum
- nuclei that relay information between the motor cortex and the cerebellum
- nuclei concerned with sleep, hearing, equilibrium, taste, eye movements, facial expression & sensation, respiratory rhythms, swallowing, bladder control, and posture
- connection point for several cranial nerves CN VI - VIII
48
What is the medulla oblongata?
-Inferior portion of the brain, blends into the spinal cord at the foramen magnum ---> 3 cm long
- Conduction pathways between higher centres and the spinal cord
E.g. Descending corticospinal tracts cross over in the pyramid region ---> each cerebral hemisphere controls voluntary movement of muscles on the opposite side of the body
- Relays sensory information about muscle stretch and joint positions mother cerebellum
- Connection point for cranial nerves CN VIII - XII
49
What are the autonomic reflex centres of the medulla oblongata?
They are visceral motor nuclei that is regulated by the hypothalamus
Cardiovascular system
Vasomotor centre
Respiratory centre
Centres regulating vomiting, hiccuping, swallowing, salvation, coughing, sneezing, speech, gastrointestinal secretion & sweating
50
What does the cardiovascular centre of the medulla oblongata do?
Controls force and rate of heart contraction
51
What the vasomotor centre of the medulla oblongata do?
Adjusts blood vessel diameter
52
What does the respiratory centre of the medulla oblongata do?
- Generates respiratory rhythm
| - Controls rate and depth of breathing
53
Where is the reticular formation?
It extends through the central core of the brainstem
54
What does the reticular formation contain?
Contains:
- neurons that project to all other brain regions
- reticular activating system
55
What do those neurons of the reticular formation do?
- Filters out repetitive, unfamiliar or weak signals e.g watch on wrist
- Allows strong or unusual stimuli to reach consciousness e.g. Watch band breaks
- helps control skeletal muscles during course limb movements
- incorporates autonomic centres of the medulla
56
What does the reticular activating system do?
- Maintains consciousness by regulating sensory input to the cerebrum
- Inhibited by sleep centres in the hypothalamus
- Depressed by alcohol
- Damage ---> coma
57
What is the cerebellum?
- Second largest part of the brain --> 11% of brain mass
- Located behind the brainstem and below the occipital lobes
- Bilaterally symmetrical
- Two hemispheres connected by a vermis (worm like)
- Two lobes in each hemisphere --> anterior & posterior
- Outer cortex of grey matter
- has sensory maps of the body
- the part of the cerebellar cortex that receives sensory input from a body region --> i.e proprioreceptive receptors --> influences motor output to that region
- Inner white matter - branches like a tree "arbor vitae"
- Penduncles - three paired fibres tracts ---> permit communication between the brainstem and cerebellum
58
What's re the functions to "coordinate the motor activities initiated by the primary motor cortex" of the cerebellum?
- Cerebral motor cortex "informs" the cerebellum of its motor plans (via the brainstem)
- The cerebellum receives information from proprioceptors throughout the body, visual and equilibrium pathways ---> evaluates body position and movements
- The cerebellum compares the "plans" with the "actions" and then adjusts the output of the motor cortex, basal nuclei and brain stem so the resulting muscle actions are balanced, smooth and coordinated
- Damage ---> loss of muscle tone, clumsy, uncoordinated movements
59
What is the "role in cognitive functions" of the cerebellum?
- Word association
| - Puzzle solving
60
What's re the areas involved in motor control?
1. Brainstem & spinal cord ---> control simple cranial and spinal reflexes
2. Pons and medulla oblongata ---> controls balance and more complex respiratory reflexes
3. Hypothalamus ---> controls reflex motor patterns related to eating, drinking and sexual activity: modifies respiratory reflexes
4. Thalamus & midbrain ---> control reflexes in response to visual and auditory stimuli
5. Basal nuclei ---> Modify voluntary and reflexive motor patterns at the subconscious level
6. Cerebral Cortex ---> Plans and initiates voluntary motor activity
61
What are the three types of brain dysfunction?
- Traumatic brain injury
- Cerebrovascular accidents
- Degenerative brain disorders
- Alzheimer's disease
- Parkinson's disease
- Huntington's disease
62
What are traumatic brain injuries?
- Concussion
- Contusion
- Intracranial pressure
63
What is concussion?
Temporary alteration in brain function due to head injury ---> dizziness, loss of consciousness
- Mild and short lived
64
What is contusion?
Bruising of the brain and permanent neurological damage ---> coma
65
What does intracranial pressure do?
Compresses neutral tissue --> impairs neutral function and may cause tissue damage (temporary or permanent)
Excessive pressure ---> brain stem can exit foramen magnum --> death
Can result from:
- Subdural or subarachnoid haemorrhage
- Cerebral oedema = swelling (accumulation of ISF or CSF)
66
What are Cerebrovascular accidents?
- "Stroke" - most common nervous system disorder
- --> blood circulation to brain area is blocked and tissue dies = ischaemia
- --> most commonly a clot in the middle cerebral artery
- --> generally leads to one side paralysis = hemiplegia ---> some function can be recovered
- Transient ischaemia attacks last for 5-50 minutes ---> temporary numbness, paralysis or impaired speech
- Treatment = dissolving of the blood clots
67
What is Alzheimer's disease?
Progressive degeneration and death of brain tissue --> shrinkage of brain
- Peptide plaques between neurons --> kill neurons
- protein tangles inside neurons ---> disrupts transport mechanisms and kills neurons
69
What are the symptoms of Alzheimer's disease?
- Memory loss (especially short term)
- Shortened attention span
- Disorientation
- Language loss
- Irritability
- Confusion
- dementia
70
What is the treatment for Alzheimer's disease?
.- Drugs that prevent acetylcholine breakdown or block the actions of glutamate
71
What is Parkinson's disease?
- Disease of unknown cause, diagnosed around 50-60 years of age
- Degeneration of dopamine-releasing neurons in them midbrain (substantia nigra) --> dopamine deprived basal nuclei become overactive --> over-inhibits motor activity --> persistent tremors at rest, head-nodding, forward bent posture, shuffling gait, stiff facial expression
72
What is the treatment for Parkinson's disease?
- L-dopa (a drug that is converted to dopamine within the brain) alleviates symptoms but does not prevent death of neurons in midbrain
73
What is Huntington's disease?
- Fatal hereditary disorder, strikes in middle age
- Death of brain tissue due to the accumulation of a mutant protein which cause the degeneration of basal nuclei and cerebral cortex
74
What are the symptoms of Huntington's disease?
- Hyperkinetic manifestations ---> wild, jerky movements
- Mental deterioration
- Death within 15 years of onset
75
What is the treatment of Huntington's disease?
Drugs that block the effects of dopamine
76
What protects the brain?
- Nervous tissue is soft and delicate, and even slight pressure can injure neurons
The brain is protected by:
- The cranium
- Meninges
- Cerebrospinal fluid
- The blood-brain barrier
77
What are the meninges?
Three connective tissue membranes that lie external to the central nervous system which:
1. Cover and protect the CNS
2. Protect blood vessels and enclose venous sinuses
3. Contain CSF
4. Form partitions in the skull
78
What are the membranes of the meninges?
Membranes (superficial ---> deep)'
- Dura mater = "tough mother"
- Arachnoid mater = "spider mother"
- Pia mater = "gentle mother"
79
What is meningitis?
Virus or bacterial infection --> inflammation of the meninges and increase intracranial pressure
80
What is the dura mater?
- The strongest meninx ---> "tough mother"
- Two- layered sheet of fibrous connective tissue
- Dural periosteal layer - superficial, attached to the inner surface of the skull
- Dural meningeal layer - deep, covers the brain and spinal tissue
Two layers are fused, except in certain areas where they form venous sinuses ---> collect and drain venous blood
81
What divisions within the skull do the folds of the dura mater form?
- Falx cerebri dips into the longitudinal fissure
- Falx cerebelli divides the cerebellar hemispheres
- Tentorium cerebellum dips into the transverse fissure
82
What is the arachnoid mater?
Middle meninx ---> "spider mother"
- Separated from the dura mater by the narrow subdural space
- which contains small amount of serous fluid and blood vessels (site of subdural haemorrhage)
- Loose covering with web-like extension that extend into the subarachnoid space
83
What is the subarachnoid space?
- Is filled with CSF and contains large blood vessels (site of subarachnoid haemorrhage)
84
What is the arachnoid villi?
Arachnoid villi = Projections of the meninx through the dura mater into the dural venous sinus ----> allows CSF to drain into the venous blood
85
What is the pia mater?
- The "gentle mother"
- Delicate connective tissue that clings tightly to the brain (bound by glial cells called astrocytes) and closely follows its contours
- Contains mostly small blood vessels
86
What is the cerebrospinal fluid?
- Clear fluid found within and around the brain and spinal cord
- Derived from plasma but has very little protein (capillary filtrate)
- Total volume - 150mL, replaced every 8 hours
87
What are the functions of the CSF?
1. Buoyancy ----> reduces brain weight by 97% and thus prevents crushing of the inferior brain tissues
2. Shock absorption
3. Nourishment ---> help nourish the brain and remove wastes
88
What does the CSF circulate through?
Circulates through he subarachnoid space around the brain ---> within the brain through the four ventricles (chambers) ---> through the central canal of the spinal cord ----> exits this space through arachnoid villi into the sub-dural sinuses
89
How is the CSF formed?
- CSF is produced by the choroid plexuses found in the root of each ventricle (chamber)
- Network of thin-walled capillaries surrounded by ependymal cells that carefully control the composition of the capillary filtrate
- ependymal cells bear cilia which keep the CSF in motion
90
What are the ventricles?
- 4 Chambers within the brain
- Continuous with each other
- 2 paired, C-shaped lateral ventricles deep to the cerebrum and around the diencephalon
- 3rd and 4th ventricles run through the diencephalon and into the brainstem (connect to the central canal of the spinal cord)
91
What happens if CSF is accumulated?
CSF is produced and drained at a constant rate
Accumulation of CSF:
Caused by:
- Blockage to flow e.g. tumour, haemorrhage
- Inflammation e.g. meningitis
- Exerts pressure on the brain ---> Impairs neuron function, may damage neuron
- Condition = hydrocephalus
- Children ---> enlargement of the head as skull bones are not yet fused
- Adults (where bones are fused) ---> can compress blood vessels ---> ischemia, damage nervous tissue, may lead to herniation
92
What is the blood-brain barrier?
- A protective mechanism that helps provide a stable environment for the brain ---> Controls ISF composition
- Formed by astrocytes (glial cells) that encircle capillaries and stimulate the endothelial cells to form tight junctions ----> least permeable capillaries in the body
93
How is the blood-brain barrier selective (not impermeable)?
- Nutrients (glucose, essential amino acids) and some electrolytes move in passively by facilitated diffusion
- Metabolic wastes, proteins, certain toxins and most drugs are denied entry
- Non-essential amino acids and K+ ions are excluded and actively pumped out
- Ineffective against lipid-soluble substances (alcohol, nicotine and anaesthetics)
94
When is the barrier incomplete?
Incomplete at/in the:
- Vomiting centre of brainstem
- Hypothalamus - monitors chemical composition of the blood
- newborn brain
95
How does the brain receive blood?
- Right and Left internal carotid and vertebral arteries take blood to the brain
- The R & L internal carotid arteries branch to form the R. & L. anterior and middle cerebral arteries
- The R. & L. vertebral arteries form the basilar artery which form the R. & L. posterior cerebral arteries which give rise to the R. & L. posterior communicating arteries
96
What is the cerebral arterial circle?
- An anastomosis = union of large blood vessels without an intervening capillary bed
- Unites the anterior and posterior blood supplies
- Equalises blood pressure
- Provides alternate routes for blood to reach the brain if a vessel is occluded
- Provides a constant blood supply to the brain
97
What is venous drainage?
- Most venous blood and CSF drains into the dural venous sinuses
- Dural venous sinuses converge at the back of the skull to form the sigmoid sinus
98
What does the Venous drainage cover?
Dural venous sinuses coverage at the back of the skull at the sigmoid sinus and drain into the internal jugular veins ----> superior vena cava
