Download Module Four: The Brain

Module Four: The Brain
1. Describe the structure and function of the major anatomical and functional subdivisions of the
cerebrum.
Cerebrum
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Divided along midline into two hemispheres by the longitudinal fissure
Separated from cerebellum by the transverse fissure
Gyrus (ridges) and sulcus (grooves)  increase surface area of cerebrum
Cerebral Hemispheres
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Grey matter called the cerebral cortex  contains neuron cell bodies and their cell dendrites
An internal region of white matter  contains myelinated axons (fibres)
Islands of grey matter deep within the white matter called basal nuclei  cluster of neuron cell
bodies
Cerebral Cortex
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Contains three functional areas:
o Motor: voluntary muscle movements
o Sensory: receive/localize sensory input; consciously perceive sensations
o Association areas:
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Integrate incoming sensory input to make sense of information
Plan/coordinate motor responses
Intellectual functions, memories, behaviours and personality
Motor Areas of Cerebral Cortex (located in frontal lobe of each cerebral hemisphere)
Primary Motor Cortex (located in pre-central gyrus of each frontal lobe)
- Initiates voluntary skeletal muscle movements
o Somatic motor output generated by the PMC:
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Travel from the PMC to skeletal muscles via a somatic motor pathway
 Control the muscles on the opposite side of the body
Specific areas are devoted to controlling specific body parts
Damage results in skeletal muscle paralysis
Motor Association Areas
- Plan and coordinate voluntary motor activities
- Act via primary motor cortex
- Include:
o Frontal eye field  voluntary eye movement
o Broca’s area speech production in left hemisphere
o Premotor cortex  complex, skilled skeletal muscle movements (eg typing)
Sensory Areas of Cerebral Cortex (located in insula, parietal, temporal and occipital lobes)
- Primary somatosensory cortex
- Visual, auditory, olfactory, visceral and vestibular cortices
- Wernicke’s area
Primary Somatosensory Cortex (located in post-central gyrus of each parietal lobe)
- Receives general sensory input:
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From receptors in skin
From proprioceptors in skeletal muscles, joints and tendons
Via sensory pathway
From opposite side of the body
Perceives sensations of touch, pain, vibration, pressure, temperature and proprioception
Locates stimulus origin
Somatosensory Association Areas
- Posterior to primary somatosensory cortex in each parietal lobe
- Damage = lose the ability to identify objects by touch alone
Special Sensory Areas
- Visual cortex (occipital lobe)
o Receives visual input detected by photoreceptors
- Visual association area
o Interprets visual input; recognize what we see
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Auditory cortex (temporal lobe)
o Receives sound input to produce & locate sounds
Auditory association area
o Interprets auditory input; recognizes spoken words and sounds
Olfactory (temporal lobe)
o Awareness of different odours
Gustatory cortex (insula)
o Perceives taste sensations
Visceral cortex (insula)
o Awareness of visceral sensations (eg upset stomach)
Vestibular/equilibrium cortex (insula)
o Awareness of balance
Wernicke’s area
- Left temporal lobe
- Language comprehension understand written and spoken language
- Damage = Wernicke’s aphasia
Prefrontal Cortex (aka anterior association area)
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Located in each frontal lobe
Involved with intellect, complex learning abilities, recall, personality and behaviour
o Allows us to solve problems, reason, make rational decisions, store memories, plan for
future, concentrate, develop abstract ideas
Damage = personality disorders
Cerebral White Matter
- Responsible for communication between
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Cerebral areas and;
Cerebral cortex and lower CNS regions
Composed of myelinated axons arranged into tracts:
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Commissural tracts  connect the two cerebral hemispheres
Association tracts  connect cortical areas within the same hemisphere
Projection tracts connect thecerebral cortex and lower CNS regions; eg thalamus and spinal
cord
Cerebral Basal Nuclei
- Islands of grey matter (neuron cell bodies) deep within the white matter of cerebrum
- Adjust the motor output generated by PMC to ensure movements are smooth
o Help start, stop and dampen the intensity of skeletal muscle movements to facilitate
smooth movement
- Activity is regulated by the neurotransmitter dopamine
2. Identify the components of the diencephalon (thalamus and hypothalamus) and outline their
functions.
Thalamus
- A relay station for information coming to cerebral cortex  “gateway to cerebral cortex”
o Sorts, groups & prioritises incoming sensory input
o Relays sensory input to relevant sensory area of cerebral cortex
o Relays the “motor adjustments” made by the cerebellum and basal nuclei to PMC
- Involved in cortical arousal (alertness), emotion and memory  part of limbic and reticular
systems
Hypothalamus
- Controls the autonomic system
- Involved in emotional responses
- Regulates body temperature
- Regulates food intake and water balance
- Regulates sleep-wake cycles
- Produces hormones  ADH, oxytocin and hormones that control anterior pituitary function
3. Identify the three major regions of the brain stem and outline their functions.
Midbrain
- Neurons located include:
o Visual reflex centres  control eye, head, neck in response to visual stimuli
o Auditory reflex centres  control head, neck and trunk in response to loud noise
o Substantia niagra  produces dopamine
Pons
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Hearing
Balance
Taste
Eye movements
Facial expressions/sensations
Respiratory rhythms
Chewing
Secretion of saliva and tears
Medulla Oblongata
- Vital autonomic centers
o Cardiovascular centre:
 Cardioacceleratory centre
 Cardioinhibitory centre
 Vasomotor centre
o Respiratory centre
o Centres that regulate vomiting, hiccupping, swallowing, coughing, sneezing
4. Describe the structure and function of the cerebellum.
Cerebellum
- Divided into two hemispheres  connected by vermis
o Divided into anterior and posterior lobes
- Each lobe contains:
o Outer cortex grey matter  cerebellular cortex
o Inner white matter  arbor vitae
Cerebellular Cortex
- Mainly composed to neuron cell bodies and their dendrites
- Ensures smooth, coordinated skeletal muscle movements and maintains balance and posture
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Receives visual, equilibrium & proprioceptive information and uses this to ‘fine tune’ the motor
activities initiated by the PMC
Damage = loss of muscle tone, clumsy uncoordinated movements
Arbor Vitae
- Composed of myelinated axons arrange into tracts
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Allows cerebellum to communicate with other brain regions
Relay proprioceptive, visual & equilibrium input to cerebellum
Relay ‘motor plans’ to cerebellum
Relay ‘motor adjustments’ to PMC
5. Locate the limbic system and the reticular formation, and explain the role of each functional
system.
Limbic system
- Includes specific cerebral areas (prefrontal cortex & hippocampus), hypothalamus and thalamus;
axon tracts that link these together (fornix)
- Allows us to be consciously aware of and control our emotions
o Establishes emotions
o Allows us to recognize emotions, express and react
o Controls emotional responses
- Facilitates memory storage and retrieval (hippocampus)
Reticular formation
- Located in brain stem
- Extends through the central core of the brainstem and has connections with many cerebral
areas
- Acts as sensory filter
o Filters out repetitive, familiar or weak signals (eg wearing a watch)
o Allows strong or unusual stimuli to reach cerebral cortex and consciousness (eg watch
band breaks)
- Contains Reticular Activating System (RES)
o Maintains cortical alertness (consciousness)
o Inhibited by hypothalamic sleep centres
o Damaged = coma
6. Briefly describe types of brain dysfunction.
Traumatic brain injuries
- Concussion: mild brain injury with short lived effects
o Temporary alteration in brain function (eg headache, dizziness, loss of consciousness)
- Contusion: bruising of the brain
o May cause permanents neurological damage
o May result in coma
- Increased Cranial Pressure (ICP)
o Can result from head injuries that lead to:
 An intracranial haemorrhage
 Cerebral oedema swelling of the brain due to an accumulation of fluid (eg
interstitial fluid)
 These two can also be caused by a tumour, hydrocephalis or infection
(meningitis)
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Compresses brain tissue and/or blood vessels
 Damages neural tissue
 Impairs brain blood flow (cerebral ischemia)
 = ischemic tissue damage
Excessive pressure  herniation of brain stem (coning) = death
Cerebrovascular Accidents (stroke)
- Blood circulation to a brain area is blocked and tissue dies = ischemic tissue damage
- Commonly caused by a clot in a cerebral artery
- Generally leads to one-sided paralysis (hemiplegia)
o Some function can be recovered
- Transient ischemic attacks last for 5-50 minutes temporary numbness, paralysis or impaired
speech [warning of serious CVA]
Alzheimer’s Disease
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Progressive degeneration and death of brain neurons  shrinkage of brain
Symptoms: memory loss (especially short term), shortened attention span, language loss,
irritability, confusion, dementia
Parkinson’s Disease
- Unknown cause
- Degeneration of substantia niagra  no dopamine
o Basal nuclei become overactive and over-control motor activity
- Symptoms: persistent termors at rest, forward bent poster, shuffling gait, stiff facial expressions
7. Describe how meninges, cerebrospinal fluid (CSF) and the blood-brain barrier protect the brain.
Include a brief description of the formation and circulation of CSF, the location of the ventricles
and the blood supply to the brain.
The Meninges
- Are three connective tissue membranes that:
o Cover and protect neural tissue of the brain (& spinal cord)
o Protect blood vessels and enclose venous sinuses
o Contain CSF
o Form partitions in the skill
- Membranes are superficial to deep:
o Dura mater (strong outer membrane)
o Arachnoid mater (middle membrane)
o Pia mater (inner membrane)
Cerebrospinal Fluid (CSF)
- Clear fluid – derived from blood plasma
- Circulates within and around brain and spinal cord
- Functions include:
o Buoyancy – reduces brain weight by 97% and thus prevents crushing of inferior brain
tissues
o Shock absorption
o Helps nourish brain & remove wastes
- Formation:
o Produced by a choroid plexus found in roof of each ventricle (chamber)
o Ventricles = 4 interconnected chambers within brain
 2 paired, lateral ventricles deep to cerebrum and around diencephalon
 3rd ventricle is in diencephalon
 4th ventricle runs through the brain stem and connects to the central canal of
the spinal cord
o Choroid plexus: a network of thin-walled capillaries surrounded by ependymal cells that
carefully control the composition of the CSF.
 Ependymal cells bear cilia which keeps CSF in motion
- Circulation:
o Flows through the 4 ventricles into the subarachnoid space
o Through the subarachnoid space around the brain
o Through the central canal and subarachnoid space of the spinal cord
o Absorbed into the venous circulation (dural sinuses) via the arachnoid villi
The Blood-Brain Barrier
- Protects brain cells from harmful substances and pathogens
o Regulates what substances can move from the bloodstream into the interstitial fluid of
the brain
- Selectively permeable barrier  formed by tight junctions that seal together the endothelial
cells of brain capillaries
o Permeable to liquid soluble substances (eg oxygen, Co2 , alcohol, nicotine and
anaesthetics), and some ions
o Impermeable to metabolic wastes, proteins, most drugs, certain toxins and K+ ions
Blood supply to the brain
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Right and left carotid arteries and the right and left vertebral arteries take blood to the
cerebrum
Once inside cranium each internal carotid artery branches to form a/an:
o Anterior cerebral artery (supplies anterior cerebrum)
o Middle cerebral artery (supplies lateral cerebrum)
The vertebral arteries fuse to form the basilar artery which divides to form:
o The right and left posterior cerebral arteries  supply posterior cerebrum
Communicating arteries unite anterior and posterior blood supplies to form the cerebrum
arterial circle