Unit 2

-neural plate bends - is joined together at the neural fold - epidermis forms on top - neural crest cells migrate through body to form peripheral nervous system - neural tube is formed which is the precursor of the CNS

4 weeks: - anterior end of neural tube specialized into three regions (forebrain, midbrain, hindbrain) 6 weeks: - neural tube differentiated into major brain regions present at birth (Medulla oblongata, Cerebellum and Pons, midbrain, Diencephalon, Cerebrum 11 weeks: - growth of cerebrum much more rapid than that of other regions Birth: - cerebrum covers most of other brain regions; convoluted surface due to rapid growth in confined space

• surrounded by bony cage – cranium, vertebrae • three layers of connective tissue - meninges • fluid between layers – cerebrospinal fluid

• dura mater • arachnoid mater • pia mater

• ventricles within brain, hollow central canal within spinal cord • two lateral ventricles, two descending ventricles that extend through in brain stem • CSF in ventricles continuous with fluid in central canal of spinal cord

where CSF is created in each ventricle

cells that line the choroid plexus and determine the composition of CSF

surrounds neurons and glial cells

within cerebral blood vessels

• within ventricular system • bathes external surfaces of brain, between meninges

• lower K+, Ca2+, HCO3- , glucose, pH similar Na+ • very low protein, no blood cells • increase presence of blood cells or elevated protein in CSF collected via lumbar puncture (sampling of fluid from subarachnoid space between vertebrae) suggests infection

• removed and replaced about 4 times daily • produce about 500ml of CSF daily

• flows through arachnoid villi back into venous blood

lateral ventricles <–> Third ventricle <–> fourth ventricle –> subarachnoid space –> arachnoid villi –> superior sagittal sinus –> venous return to heart

• very tight junctions • not many things get through

• lipid soluble molecules cross readily • hydrophilic substances (ions, amino acids, peptides) will only cross if specific transporters / carriers are present on endothelial cells of capillaries within CNS • considerations for drugs that are and are not wanted to reach the CNS: – antihistamines – treating diseases of the CNS

• oxygen requirement: - neurons are ‘obligate aerobes’ – unable to switch to anaerobic metabolism – O2 readily crosses blood-brain barrier • glucose requirement: - capillaries of CNS express high levels of glucose transporters to provide adequate levels of glucose - brain responsible for approximately half of body’s glucose consumption vasculature to deliver oxygen and glucose: - approximately 15% of cardiac output received by brain – critically dependent on adequate O2, glucose (and therefore blood flow) - hypoglycemia = confusion, loss of consciousness, death

• major path for information flow between CNS and skin, joints, muscles • contains neural networks involved in locomotion • divided into four regions (cervical, thoracic, lumbar, sacral), each of which is divided into segments • each segment gives rise to pair of spinal nerveswh

• dorsal columns : touch/pressure, proprioception • spinocerebellar: proprioception (posture, coordination) • spinothalamic: pain, temp

• corticospinal tracts: voluntary movement

• oldest and most primitive part of brain • contains structures derived from embryonic hind and midbrain • organized much like spinal cord • most (10 of 12) cranial nerves originate from here • carry sensory and motor info for head/neck • cranial nerve X = vagus • contains nuclei associated with reticular formation • diffuse network of neurons involves in processes such as arousal/sleep, muscle tone, coordination of breathing, blood pressure, et al

• midbrain: - coordination of eye movement, visual and auditory reflexes • pons: - relay station between cerebrum and cerebellum – works with medulla to regulate breathing • medulla: - gray matter involved in control of many involuntary functions – blood pressure, breathing, swallowing, vomiting – white matter – ascending somatosensory tracts, descending corticospinal tracts – site of decussation (crossing over) for most neurons in corticospinal tract

• between brain stem and cerebrum 1. thalamus: • relays and integrates sensory info from lower parts of CNS, ears, eyes, motor info from cerebellum 2. hypothalamus: • tiny region of brain yet major centre for homeostasis • contains centres that drive behaviour related to hunger, satiety, thirst • influences autonomic responses, endocrine systems 3. pituitary gland: • regulated by hypothalamus (more later in course) 4. pineal gland: • secretes hormone melatonin - involved in circadian and seasonal rhythms

• site of ‘higher’ brain functions – largest and most distinctive part of brain in higher primates • each cerebral hemisphere divided into four lobes: frontal, occipital, parietal, temporal • furrow or groove = sulcus (pl sulci) • convolution = gyrus