4 14 Ependymal cells Form lining cells of ventricular system Producing circulating and monitoring cerebrospinal fluid Astrocytes Maintain blood brain barrier provide structural support create scar tissue in the brain after minor damage absorb and recycle neurotransmitters Can form tumors Oligodendrocytes Myelinate CNS axons provide structural framework Microglia Remove cell debris wastes and pathogens by phagocytosis Blood Brain Barrier BBB Isolates CNS neural tissue from general circulation Formed by network of tight junctions Formed by astrocytes Lipid soluble compounds steroids alcohol and prostaglandins can pass through the BBB and enter the cerebrospinal fluid Astrocytes control BBB by releasing chemicals that control the permeability of endothelium of blood vessels Foot extensions of astrocytes and the tight junctions of endothelium form the BBB Brain gets arterial blood supply by two pairs of major arteries both arise from arteries in the thoracic cavity one pair being the left and right vertebral arteries which travel through the transverse foramina of vertebra another being the Common Carotid specifically internal carotid artery which gives off no branches in the neck but simply goes to the base of the skull Basilar artery runs along the midline of the pons supplies most of the posterior part of each cerebral hemisphere Off of vertebral and basilar artery the vertebrals and basilar artery give off a number of branches to cerebellar arteries 3 on each side Posterior communicating artery link the posterior cerebral artery with the internal carotid Anterior cerebral artery supplies the medial parts of each hemisphere Middle cerebral artery supplies most of the lateral surface of the cerebral hemisphere Know major dural sinuses All dural sinuses flow through the transverse sinus and its continuation into the sigmoid sinus which leaves the skull and then becomes the internal jugular vein which returns deoxygenated blood from the brain to the heart Arterial aneurism is a weakening in part of the wall in an artery People who develop aneurism may have a history of high BP and may also have some congenital inheritance of vascular disease Common sign of aneurism occurs at branching point of artery blood flows towards weakened wall between branches and the blood begins to fill and dilate the artery and will eventually rupture Blood Supply ends exam 1 Graded Potentials Between neurons can be either excitatory EPSP s or inhibitory IPSP s The stronger the stimulus the greater the change in the sensory neuron and the likelihood of developing an action potential in the sensory neuron First order sensory neuron has dendrites that are thermal receptors which respond to changes in temperature First order Thermal receptors respond to temperature encapsulated nerve endings respond to pressure Receptive fields Vary in size and location Territory that is monitored by one sensory neuron Tend to overlap Small on fingertips and lips Larger on very sensitive areas Classification of sensory receptors Free nerve endings Associated with pain temperature itch tickle and some Encapsulated nerve endings Capsule that has to be deformed in order to stimulate sensory neuron and touch receptors Separate Cells Receptor cells for special senses that generate receptor touch potential Exteroceptors Respond to information in external environment Interoceptors Located in blood vessels etc Proprioceptors Located in muscles tendons joints etc Provide information about body position muscle length and tension and motion of joints Mechanoreceptors Have to be deformed to produce action potential Thermoreceptors Detect changes in temperature Nociceptors Respond to pain Photoreceptors Detect light Chemoreceptors Detect chemicals in mouth Osmoreceptors Sense osmotic pressure in bodily fluids