Wk 6 Flashcards
The nervous systems role
Maintain homeostasis
Responsible for our perceptions, behaviours and memories
Initiates voluntary movements
Responds rapidly to stimuli using nerve impulses
Role of brain
Perception and sensory stimuli
Voluntary motor responses
Homeostatic mechanisms
Only 2% of body weight yet uses 20% O2 in blood
Uses glucose for energy but doesn’t store extra supplies hence needs constant supply of O2 and glucose
Auto regulation: cerebral perfusion, blood flows through cerebral vessels to maintain optimum blood flow
The cerebral-spinal fluid
Circulates through subarachnoid space around spinal cord and brain
80-150mls CSF in CNS
Made in choroid plexus and absorbed by arachnoid villi
Protection: acts as shock absorber, buoyancy for brain
Circulation: nutrients to CNSand removal of waste
Meninges of the brain
Scalp Skull Periosteal dura mater Meningeal dura mater Arachnoid mater Subarachnoid space Pia mater Cerebral cortex
The components within the skull
Brain 80%
CSF 10%
Blood 10%
Sums of volumes of brain, csf and intracranial blood are constant = Monroe kellie doctrine
Primary brain injury
Occurs at moment of trauma
Includes contusion, damage to blood vessels, laceration of brain tissue and axonal shearing (shearing of nerve fibers)
Blood brain barrier and meninges damaged
Different regions of brain more sensitive to mechanical damage
Primary leads to secondary injury
Cause: blow to head, penetration, acceleration/deceleration
Concussion
Momentary interruption of brain function with or without loss of consciousness
Contusion
Bruise to the brain caused by blunt head trauma, results in permanent damage
Diffuse axonal injury
Primary injury with widespread microscopic damage: shifting, shearing, rotational, acceleration, deceleration injury, that stretch and or tear nerve cell processes within the brain
Haemotoma bleeding in the brain
Extradural/epidural: commonly arterial bleeds. Compression may be rapid
Subdural: commonly venous so slower to develop can be acute or chronic
Subarachnoid: aneurysm rupture in circle of willis
Intracranial: severe motion of the brain or develop from contusion. Eked rely and alcoholics more vulnerable
Secondary brain injury
Consequence of primary injury, occurs hours and days after
Plays large role in brain damage and death
Inflammation, swelling, oedema, raised ICP, reduction in cerebral blood flow and tissue oxygenation
Altered consciousness and coma
Consciousness: awareness of self and environment, requires arousal and awareness, often first sign of severe illness
Coma: state of unresponsiveness from which a patient can’t be aroused to produce meaningful response, absence of arousal and content, often problem with cerebral cortex or brain stem reticular activating system
Skeletal muscle weakness and paralysis may result from lesions in voluntary and sensory nerve pathways (upper and lower)
Upper: corticospinal and corticobulbar tracts, basal ganglia, cerebellar
Lower: peripheral nerves, mixed sensory and motor deficits, decreased muscle tone and flaccid paralysis
Intracranial pressure ICP
Pressure exerted within the skull and meninges by the contents of the skull
Normal 0-10mmhg
Above 15mmhg is abnormal
Cerebral perfusion pressure cpp
Blood pressure gradient across the brain, an estimate of cerebral blood flow
Cpp = map - icp
Cpp less than 60mmhg neuronal hypoxia and cell death
