ANP1111 Lecture 15 Neuroanatomy & Neurophysiology Part 2 PDF

ANP1111 – Lecture 15 Neuroanatomy & Neurophysiology – Part 2 The Brain Stem: consists of the midbrain, pons, and medulla oblongata (i) rigidly programmed, automatic behaviours necessary to survival (ii) pathway between higher & lower neural centres (iii) associated with 10 pairs of cranial ne...

ANP1111 – Lecture 15 Neuroanatomy & Neurophysiology – Part 2 The Brain Stem: consists of the midbrain, pons, and medulla oblongata (i) rigidly programmed, automatic behaviours necessary to survival (ii) pathway between higher & lower neural centres (iii) associated with 10 pairs of cranial nerves Fig. 12.13 Lateral view Anterior (ventral) view Midbrain: 2 cerebral peduncles that contain large pyramidal (corticospinal) motor tracts hollow cerebral aqueduct runs through midbrain periaqueductal gray matter involved in pain suppression Corpora quadrigemina: superior colliculi are visual reflex centres when visually follow a moving object; inferior colliculi are part of auditory relay (also the startle reflex) Lateral view dorsal view Fig. 12.11a: Midsagittal section of brain Midbrain (cont): substantia nigra: band-like nucleus; high melanin content (precursor of dopamine); linked to basal nuclei of cerebral hemispheres (its degeneration linked to Parkinson’s disease) red nucleus: rich vascular supply, iron pigment in neuron cell bodies; relay nuclei for descending pathways influencing limb flexion also some nuclei associated with the reticular formation Fig. 12.15a Pons: at level of 4th ventricle primarily conduction tracts (“bridge”); some run longitudinally between higher brain centres & spinal cord; others oriented transversely to communicate with cerebellum cranial nerves V (trigeminal), VI (abducens) & VII facial; other pons nuclei are part of the reticular formation and others are involved in respiration) Fig. 12.15b  Fig. 12.15c Medulla oblongata: from pons to spinal cord pyramids (large motor tracts), decussation of pyramids (significance?) inferior olivary nuclei: relay sensory info re muscles & joints to cerebellum cranial nerves XII (hypoglossal), IX (glossopharyngeal), X (vagus) vestibulocochlear nerve fibers (VIII) for both auditory and balance relays Medulla oblongata: crucial role as autonomic reflex centre for homeostasis (i) Cardiovascular centre: cardiac & vasomotor centres (ii) Respiratory centres: rate & depth of breathing (iii) Other centres: eg: vomiting, hiccupping, swallowing coughing, sneezing overlaps with hypothalamus: hypothalamus controls most visceral functions by relaying instructions through medullary centres which carry them out See also Table 12.1 Table 14.1 (T&G) The Cerebellum (small brain): processes inputs from cerebral motor cortex, brainstem nuclei & sensory receptors and influences the timing & patterns of skeletal muscle contraction for smooth, daily movements – eg: driving, typing, playing a musical instrument, etc (not under conscious control) bilaterally symmetrical; connected by vermis; fine transverse fissures called folia; each hemisphere divided into 3 lobes: anterior, posterior, and flocculonodular Fig. 12.16 4. The Cerebellum (cont): anterior & posterior lobes have overlapping sensory & motor maps of body the part of a sensory map that received input from a body region also controls the output to that same body region multiple maps allow the actions of multiple muscle groups to be coordinated when a particular response is being carried out and also coordination of proprioceptive information, planning information and instructions to motor cortex (via thalamus) when carrying out a series of movements medial: trunk & girdle intermediate: distal limbs, skilled movements lateral: input from association areas of cortex (esp. planning movements) flocculonodular lobes – input from equilibrium sensors: balance and some eye movements Fig. 12.16 From Visible Body Vermis highlighted Pons highlighted Cerebellar Peduncles – what information is going to and from the cerebellum? connect cerebellum to brain stem virtually all fibers entering & leaving cerebellum are ipsilateral (unlike cerebral cortex) Superior (outgoing): connect cerebellum & midbrain; fibers originate from neurons in deep cerebellar nuclei & project to cerebral motor cortex via thalamus (instructions are being sent to the motor cortex) Middle (incoming): connect pons & cerebellum; one-way communication from pons to cerebellar neurons (informs cerebellum of voluntary motor activities initiated by motor cortex) Fig. 12.14c Inferior (incoming): connect cerebellum & medulla; sensory info to cerebellum from muscle proprioceptors (position of parts of the body & joints) & vestibular nuclei of brain stem (equilibrium & balance) Cerebellar processing to fine-tune motor activity: Cortex frontal motor association area indicates intent to initiate action & sends collaterals to cerebellum to notify  Cerebellum also receives proprioceptive info & info from visual & equilibrium pathways: Where is body & where going? How well are movements being done?  Cerebellar cortex receives this info & determines best way to coordinate force, direction extent of muscle contraction  Via superior peduncles, cerebellum dispatches blueprint for coordination to cerebral motor cortex; output also to brain stem nuclei (eg: red nucleus) which project to motor neurons of spinal cord Your book compares the cerebellum to a pilot comparing the readings on an airplane’s instrument panel with the planned course for that airplane – movements are constantly monitored Cerebellum allows you to correct as you are going along Cerebellar injury linked to loss of muscle tone and movements that are clumsy, not well planned There is still a lot to learn about the cerebellum and all that it can do Functional Brain Systems: networks of neurons that work together but span large distances within brain https://www.history.com/news/rise-fall-telephone-switchboard-operators Limbic system: (limbus = ring) medial aspect of each cerebral hemisphere & diencephalon; encircles the upper part of the brain stem emotional-visceral brain – esp: amygdala (anger, fear,danger), hippocampus (emotions & memory), anterior cingulate gyrus (gestures, resolve conflicts when frustrated) link between odours, memories & emotions close association with hypothalamus provides a pathway for stress to have effects on blood pressure, GI tract, heart rate Links with cortex so that we are aware of our emotions and can react emotionally if we consciously understand Also, emotions can override logic and reason can stop us from expressing our emotions Fig. 12.17 Reticular formation: central core of medulla oblongata, pons, midbrain; neurons project to hypothalamus, thalamus, cortex, cerebellum, spinal cord reticular activating system (RAS): (i) maintains arousal of brain by letting enough stuff in; (ii) filter for incoming signals (RAS & cerebral cortex disregard ~99% of all sensory stimuli so that volume of incoming is manageable) Fig. 12.18 Additional Reading in Textbook to tidy up Neuroanatomy Chapter 12: pp. 470-479, 464-467 (Finish CNS: Spinal cord) Chapter 13: pp. 496-516 (PNS: Cranial and Spinal Nerves) The Spinal Cord from foramen magnum to 1st/2nd lumbar vertebra; below this is ideal spot for lumbar puncture (i) 2-way conduction system (ii) major reflex centre (iii) initiates complex patterns of motor activity 31 pairs of spinal nerves spinal cord held in place by: (i) denticulate ligaments: pia mater shelving (ii) filium terminale: pia mater-covered conus extension What is the cauda equina? Fig. 12.29 Fig. 12.28 Fig. 12.28 b-d Gray Matter & Spinal Roots gray matter as for other regions of CNS – all neurons are multipolar organized like butterfly wings: paired anterior (ventral) & posterior (dorsal) horns connected by gray commissure (where is the central canal?) small lateral horns associated with thoracic & superior lumbar regions of cord Fig. 12.31a  Fig. 12.31b Anterior horns: nerve cell bodies of somatic motor neurons – axons exit via ventral roots largest at levels of cervical & lumbar enlargements – why?? Lateral horns: autonomic ns motor neurons to visceral organs; also exit via ventral roots  Fig. 12.31 Dorsal root ganglion: afferent fibers from peripheral sensory receptors form dorsal roots; dorsal root ganglia house cell bodies of associated sensory neurons – their axons enter cord to: (i) travel to higher cord/brain centres (ii) synapse with interneurons in posterior horns at level they enter spinal nerve = fused dorsal & ventral roots Fig. 12.32: Organization of the Gray Matter of the Spinal Cord NB: the dorsal and ventral roots are part of the PNS, not the CNS!  Fig. 12.33 White Matter myelinated & unmyelinated fibers – communication between different parts of cord & between cord & brain ascending, descending & transverse (commissural) tracts – direction of fibers Some general properties of spinal tracts: (i) Most pathways cross over from one side of CNS to other (decussation) (ii) Most consist of a chain of 2 or 3 neurons (iii) Most exhibit somatotopy: (iv) All pathways & tracts are paired  Fig. 12.22 Protection of the CNS (i) Bones (ii) Meninges (iii) Cerebrospinal fluid (iv) Blood-brain barrier Meninges (singular = meninx) 3 CT membranes that: (a) cover & protect the CNS (b) protect blood vessels & enclose venous sinuses (c) contain cerebrospinal fluid (d) form partitions within skull Dura mater: tough; 2 layers around brain: outer periosteal layer & inner meningeal layer spinal cord has only meningeal layer around brain, 2 layers fused except where enclose dural sinuses Dural septa to partition and anchor: falx cerebri (longitudinal fissure), falx cerebelli (runs along vermis), tentorium cerebelli (transverse fissure) Fig. 12.23: Dural septa and dural venous sinuses  Fig. 12.22 Arachnoid mater: loose covering separated from dura mater by subdural space subarachnoid space between arachnoid mater & pia mater – filled with CSF & contains largest blood vessels serving brain role of arachnoid granulations (villi) in accumulation of CSF Pia mater: (see also Fig. 12.22) delicate CT + tiny blood vessels – clings tightly to brain, follows convolutions What is meningitis? What is encephalitis? Cerebrospinal Fluid liquid cushion to give buoyancy to CNS tissue; also protective, nutritive roles similar to plasma but less ptn, more vit C, Na+, Cl-, Mg++ & H+, less Ca++, K+ choroid plexuses in roof of ventricles source of CSF: clusters of permeable capillaries enclosed by layer of ependymal cells (role of these cells?) total CSF = 150 ml; replaced ~ every 8 hours; choroid plexuses also clean CSF What is hydrocephalus? Fig.12.24b Fig. 12.25 Blood-Brain Barrier why?? some hormones also act as neurotransmitters; some ions can increase the rate of neuronal firing composed of 3 layers: (i) continuous epithelium of capillary wall (very impermeable tight junctions) (ii) thick basal lamina surrounding external face of capillary – contains enzymes that can destroy chemicals like E and NE that can act on neurons (iii) bulbous feet of astrocytes + smooth-muscle-like cells called pericytes – maintain endothelial cells & stimulate formation of very tight junctions Fig. 12.26 Blood-Brain Barrier (cont.) What gets in? glucose, essential amino acids, some electrolytes (facilitated diffusion, so specific transport mechanisms); also fats, fatty acids, oxygen, carbon dioxide, any other fat-soluble molecules (meaning that fat-soluble drugs like alcohol, nicotine and anesthetics can affect the brain) Not completely uniform: (i) capillaries of choroid plexuses porous but ependymal cells linked by tight junctions (ii) very permeable near vomiting centre (allows monitoring of blood for poisonous substances), hypothalamus (for water balance, regulation of body temperature); incomplete in newborns and premature infants, making their brains more vulnerable https://openi.nlm.nih.gov/detailedresult.php?img=PM C4588193_pharmaceutics-07-00175-g001&req=4  Choroid plexuses of 3rd & 4th ventricles Ventricles and the median and lateral apertures Subarachnoid space Arachnoid granulations & dural sinuses Fig. 12.24a: Formation & Circulation of Cerebrospinal Fluid Stay Tuned! Cranial nerves and spinal nerves in next lecture and we will start into the different types of sensory receptors