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Chapter 14 The Brain and Cranial Nerves • Largest organ in the body at almost 3 lb. • Brain functions in sensations, memory, emotions, decision making, behavior 14-1 Principal Parts of the Brain • Cerebrum • Diencephalon – thalamus & hypothalamus • Cerebellum • Brainstem – medulla, pons & midbrain 14-2 Blood Supply to Brain • Arterial blood supply is branches from circle of Willis on base of brain (page 699 or next slide) • Vessels on surface of brain----penetrate tissue • Uses 20% of our bodies oxygen & glucose needs – blood flow to an area increases with activity in that area – deprivation of O2 for 4 min does permanent injury • at that time, lysosome release enzymes 14-3 14-4 Subarachnoid Haemorrhage 14-5 Middle Meningeal Artery –epidural 14-6 Venous Drainage • Superior saggital sinus etc- in subdural 14-7 Bridging Veins – subdural space 14-8 Subdural Haemorrhage 14-9 Protective Coverings of the Brain • Bone, meninges & fluid • Meninges same as around the spinal cord – dura mater – arachnoid mater – pia mater • Dura mater extensions – falx cerebri – tentorium cerebelli – falx cerebelli 14-10 Meninges 14-11 Blood Brain Barrier • Blood-brain barrier (BBB) – protects cells from some toxins and pathogens • proteins & antibiotics can not pass but alcohol & anesthetics do – tight junctions seal together epithelial cells, continuous basement membrane, astrocyte processes covering capillaries 14-12 What goes in and What Doesn’t • Lipid Soluble- O2, CO2, ETOH, anesth all pass easily the BBB • Watersoluble, glucose, urea, creatinine, ions pass slowly or in the case of glucose, via active transport only • BBB is not uniform throughout, some areas are more permeable and thus bacteria can get in 14-13 Cerebrospinal Fluid (CSF) • 80-150 ml (3-5oz) • Clear liquid containing glucose, proteins, & ions • Functions – mechanical protection • floats brain & softens impact with bony walls – chemical protection • optimal ionic concentrations for action potentials – circulation • nutrients and waste products to and from bloodstream 14-14 Origin of CSF • Choroid plexus = capillaries covered by ependymal cells – 2 lateral ventricles, one within each cerebral hemisphere – roof of 3rd ventricle – fourth ventricle 14-15 Drainage of CSF from Ventricles • One median aperture & two lateral apertures allow CSF to exit from the interior of the brain 14-16 Cerebral Perfusion Pressure • CPP = MABP – ICP • Cerebral auto regulation 14-17 Hydrocephalus • Blockage of drainage of CSF (tumor, inflammation, developmental malformation, meningitis, hemorrhage or injury • Continued production cause an increase in pressure --- hydrocephalus • In newborn or fetus, the fontanels allow this internal pressure to cause expansion of the skull and damage to the brain tissue • Neurosurgeon implants a drain shunting the CSF to the veins of the neck or the abdomen 14-18 Medulla Oblongata • • • • • Continuation of spinal cord Ascending sensory tracts Descending motor tracts Nuclei of 5 cranial nerves Cardiovascular center – force & rate of heart beat – diameter of blood vessels • Respiratory center – medullary rhythmicity area sets basic rhythm of breathing • Information in & out of cerebellum • Reflex centers for coughing, sneezing, swallowing etc 14-19 Injury to the Medulla • Hard blow to the back of the head may be fatal • Cranial nerve malfunctions on same side as injury; loss of sensation or paralysis of throat or tongue; irregularities in breathing and heart rhythm 14-20 Pons • One inch long • White fiber tracts ascend and descend • Pneumotaxic & apneustic areas help control breathing • Middle cerebellar peduncles carry sensory info to the cerebellum • Cranial nerves 5 thru 7 14-21 Midbrain • One inch in length • Extends from pons to diencephalon • Cerebral aqueduct connects 3rd ventricle above to 4th ventricle below • Visual reflex centers and auditory relay (startle reflex) 14-22 Midbrain in Section • Cerebral peduncles---clusters of motor & sensory fibers • Substantia nigra---helps controls subconscious muscle activity • Red nucleus-- rich blood supply & iron-containing pigment – cortex & cerebellum coordinate muscular movements by sending information here from the cortex and cerebellum 14-23 Reticular Formation • Scattered nuclei in medulla, pons & midbrain • Reticular activating system – alerts cerebral cortex to sensory signals (sound of alarm, flash light, smoke or intruder) to awaken from sleep – maintains consciousness & helps keep you awake with stimuli from ears, eyes, skin and muscles • Motor function is involvement with maintaining muscle tone 14-24 Cerebellum • 2 cerebellar hemispheres and vermis (central area) • Function – correct voluntary muscle contraction and posture based on sensory data from body about actual movements – sense of equilibrium 14-25 Cerebellum • Transverse fissure between cerebellum & cerebrum • Cerebellar cortex (folia) & central nuclei are grey matter • Arbor vitae = tree of life = white matter 14-26 Diencephalon Surrounds 3rd Ventricle • Surrounds 3rd ventricle • Superior part of walls is thalamus • Inferior part of walls & floor is hypothalamus 14-27 Thalamus • 1 inch long mass of gray mater in each half of brain (connected across the 3rd ventricle by intermediate mass) • Relay station for sensory information on way to cortex • Crude perception of some sensations 14-28 Thalamic Nuclei • Nuclei have different roles – relays auditory and visual impulses, taste and somatic sensations – receives impulses from cerebellum or basal ganglia – anterior nucleus concerned with emotions, memory and acquisition of knowledge (cognition) 14-29 Hypothalamus • Dozen or so nuclei in 4 major regions – mammillary bodies are relay station for olfactory reflexes; infundibulum suspends the pituitary gland • Major regulator of homeostasis – receives somatic and visceral input, taste, smell & hearing information; monitors osmotic pressure, temperature of blood 14-30 Functions of Hypothalamus • Controls and integrates activities of the ANS which regulates smooth, cardiac muscle and glands • Synthesizes regulatory hormones that control the anterior pituitary • Contains cell bodies of axons that end in posterior pituitary where they secrete hormones • Regulates rage, aggression, pain, pleasure & arousal • Feeding, thirst & satiety centers • Controls body temperature • Regulates daily patterns of sleep 14-31 Cerebrum (Cerebral Hemispheres) • Cerebral cortex is gray matter overlying white matter – 2-4 mm thick containing billions of cells – grew so quickly formed folds (gyri) and grooves (sulci or fissures) • Longitudinal fissure separates left & right cerebral hemispheres • Corpus callosum is band of white matter connecting left and right cerebral hemispheres • Each hemisphere is subdivided into 4 lobes 14-32 Lobes and Fissures • Longitudinal fissure (green) • Frontal lobe • Central sulcus (yellow) – precentral & postcentral gyrus • • • • • Parietal lobe Parieto-occipital sulcus Occipital lobe Lateral sulcus (blue) Temporal lobe 14-33 Basal Ganglia • Connections to red nucleus, substantia nigra & subthalamus • Input & output with cerebral cortex, thalamus & hypothalamus • Control large automatic movements of skeletal muscles 14-34 Limbic System • Parahippocampal & cingulate gyri & hippocampus • Emotional brain--intense pleasure & intense pain • Strong emotions increase efficiency of memory 14-35 Brain Injuries • Causes of damage – – – – displacement or distortion of tissue at impact increased intracranial pressure infections free radical damage after ischemia • Concussion---temporary loss of consciousness – headache, drowsiness, confusion, lack of concentration • Contusion--bruising of brain (less than 5 min unconsciousness but blood in CSF) • Laceration--tearing of brain (fracture or bullet) – increased intracranial pressure from hematoma 14-36 Types of Injuries Cont • Epidural bleed –arterial- Middle meningeal artery – retrograde unconsiousness -treated Burr holes • SubDural Bleed –venous- bridging veins • Subarchnoid bleed- arterial-Circle of Willis • Moderate axonal injury • Diffuse axonal tearing injury 14-37 Sensory Areas of Cerebral Cortex Receive sensory information from the thalamus Primary somatosensory area = postcentral gyrus = 1,2,3 Primary visual area = 17 Primary auditory area = 41 & 42 Primary gustatory area = 43 14-38 Motor Areas of Cerebral Cortex • Voluntary motor initiation – Primary motor area = 4 = precentral gyrus • controls voluntary contractions of skeletal muscles on other side – Motor speech area = 44 = Broca’s area • production of speech -- control of tongue & airway 14-39 Association Areas of Cerebral Cortex (FYI) • • • • • • Somatosensory area = 5 & 7 (integrate & interpret) Visual association area = 18 & 19 (recognize & evaluate) Auditory association area(Wernicke’s) = 22(words become speech) Gnostic area = 5,7,39 & 40 (integrate all senses & respond) Premotor area = 6 (learned skilled movements such as typing) Frontal eye field =8 (scanning eye movements such as phone book) 14-40 Aphasia • Language areas are located in the left cerebral hemisphere of most people • Inability to use or comprehend words = aphasia – nonfluent aphasia = inability to properly form words • know what want to say but can not speak • damage to Broca’s speech area – fluent aphasia = faulty understanding of spoken or written words • faulty understanding of spoken or written words – word deafness = an inability to understand spoken words – word blindness = an inability to understand written words • damage to common integrative area or auditory association area 14-41 Hemispheric Lateralization • Functional specialization of each hemisphere more pronounced in men • Females have larger connections between 2 sides • Damage to left side produces aphasia • Damage to same area on right side produces speech with little emotional inflection 14-42 The Spinal Cord • Extends from the foramen magnum of the skull to L¹ or L² ; the dural and arachnoid membranes extend to the level of S², well beyond the end of the spinal cord which makes this an ideal location for a lumbar tap • 31 pairs of spinal nerves attach to the cord by paired roots and exit from the vertebral column via the intervertebral foramina to travel to the body regions they serve 14-43 14-44 The Spinal Cord • It is about the width of a thumb for most of its length, but is enlarged in the cervical and lumbosacral regions, where the nerves serving the upper and lower limbs arise • The collection of nerve roots at the inferior end of the vertebral canal is named the cauda equina 14-45 14-46 The Spinal Cord: Gray Matter and Spinal Roots • Looks like the letter “H” or a butterfly with the cross-bar of gray matter called the gray commissure that encloses the central canal 14-47 The Spinal Cord: Gray Matter and Spinal Roots • Dorsal and Ventral Roots: very short and fuse laterally to form the spinal nerves • The spinal nerves form the peripheral nervous system 14-48 The Spinal Cord: White Matter • Composed of myelinated and unmyelinated nerve fibers that allow communication between different parts of the spinal cord and between the cord and brain • (1) Ascending: up to higher centers (sensory inputs) (2) Descending: down to the cord from the brain or within the cord to lower levels (motor outputs) (3) Transversely: across from one side of the cord to the other (commissural fibers) • Ascending and descending make up most of the white matter 14-49 Spinal cord Injuries The following list outlines which muscle functions may be retained at progressively lower levels of spinal cord transection. C1–C3: no function maintained from the neck down; ventilator needed for breathing C4–C5: diaphragm, which allows breathing C6–C7: some arm and chest muscles, which allows feeding, some dressing, and propelling wheelchair T1–T3: intact arm function T4–T9: control of trunk above the umbilicus T10–L1: most thigh muscles, which allows walking with long leg braces L1–L2: most leg muscles, which allows walking with short leg braces 14-50