HUBS1416 Topic 5 Lecture Central Nervous System PDF

School of Biomedical Science and Pharmacy College of Health, Medicine & Wellbeing The central nervous system Advanced Human Bioscience HUBS1416 School of Biomedical Science and Pharmacy College of Health, Medicine & Wellbeing  Lecture Overview Part 1: Integration of information &...

School of Biomedical Science and Pharmacy College of Health, Medicine & Wellbeing The central nervous system Advanced Human Bioscience HUBS1416 School of Biomedical Science and Pharmacy College of Health, Medicine & Wellbeing  Lecture Overview Part 1: Integration of information & the spinal cord (spinothalamic, corticospinal and dorsal column tracts) Part 2: The brain: perfusion & protective features (skull, meninges, blood-brain barrier & CSF) Part 3: Regions of the brain: Brainstem, cerebellum, limbic system, cerebral cortex  Integration in the CNS CNS l receives, processes, collates and makes sense of all sensory (somatic & autonomic) information l prepares and sends out motor responses (as appropriate to sensory input) l Both the spinal cord and the brain carry out integration  Spinal cord – integration of spinal reflexes Integration within the gray matter influenced by the brain: stimulatory & inhibitory Interneuron Dorsal root (sensory neurons enter cord) Ventral root (motor neurons leave cord) Spinal cord white matter is organized into tracts according to functional information Sensory tracts Motor tracts (ascending) (descending) Thalamus sensory & motor relay center Spinothalamic Tract crude touch, pain & temperature Dorsal White/Posterior Column Tract Fine touch & proprioception Corticospinal Tract Voluntary movement The Brain  4 weeks Brainstem (midbrain & hindbrain) Spinal cord 5 weeks Forebrain Developmental Timing Explains Why Many Brain Structures are Curved There is a limit to the degree to which the skull can increase its size to accommodate an evolving brain… Why? Photo: © J.Mendoza, Colorado State University Why Does the Human Brain Have so Many Folds The arterial blood supply to Circle of Willis the brain Internal carotid arteries Vertebral arteries Common carotid arteries Aorta Venous drainage from the brain  Protection of the brain’s blood supply – occurs centrally Blood flow to the brain is only reduced when arterial BP can’t be maintained or if intracranial pressure (ICP) rises  Circle of Willis & Cerebral Arteries Anterior Cerebral Posterior Cerebral Cerebral artery territories Medial view Lateral view Anterior cerebral artery Anterior cerebral artery Middle cerebral artery Middle cerebral artery Posterior cerebral artery Posterior cerebral artery Cerebral artery territories (coronal section) Anterior cerebral artery Middle cerebral artery (deep & superficial branches) Posterior cerebral artery (deep & superficial branches) Protection of the Brain l Bone l Meninges l CSF l Blood–brain barrier Bony protection: the cranium The meninges: seatbelts for the CNS Dura Mater Sub-dural space – not a natural space Arachnoid Mater Sub-arachnoid space Pia Mater Surface of brain The dural folds The falx cerebri The tentorium Image: Stanford university medical centre Cerebrospinal fluid (airbag of the brain) The blood-brain barrier Capillary in general circulation Capillary in the brain What can cross the blood-brain barrier?  Problems created by the protective coverings of the brain l The cranium does not expand. If anything adds to the volume of the cranial contents, there will be an increase in the pressure inside the cranium – Intracranial Pressure (ICP) l What would add to the volume of the cranial contents?  What happens when a space- occupying lesion develops? 1. CSF is forced out of the cranium 2. Less blood flows into the brain, as the increased pressure inhibits in-flow 3. Structures in the brain are compressed à herniations of tissue  Classic (late) signs of raised ICP: “Cushing’s triad” Deep, irregular respiration Widening pulse pressure Bradycardia These are late signs, which indicate a final attempt by the CV system to re-establish brain blood flow by increasing perfusion pressure Possible herniations produced by a space-occupying lesion in the cranium The cerebral hemisphere on this side could be forced under the falx The lower portion of the cerebrum can be forced down under The brain the tentorium stem can be forced down onto the foramen magnum Regions of the brain  The Brainstem Midbrain Pons Medulla Brainstem Functions The Cerebellum  Cerebellum Functions l Coordination and control of voluntary movements l Postural adjustment during movements l Advance planning of rapid movements l Learning of movement sequences The limbic system consists of a number of structures clustered around the brainstem The cingulate cortex Hippocampus Amygdala l Motivation (emotions) for survival purposes Olfactory bulbs l Learning and memory l Linking of autonomic and endocrine responses to emotional states The Amygdala: hub of fear & aggression l involved in emotional learning – association of a sensory experience with an emotion (usually fear) l allows recognition of fear in others (facial expression) l strongly activated during exposure to aversive stimuli (visual, taste, auditory, smell) People with damage to the amygdala: l Do not show fear to fearful stimuli l Are unable to make risk-benefit estimates - tend not to avoid an activity when the risk outweighs the benefit l Are unable to recognise fearful expressions on faces l Avoid eye contact during social interactions and stand closer to others during contact Source: NIMH Genes, Cognition and Psychosis Program  Functions of the hippocampus l Conversion of short-term memory to long term memory l Memory for place The Cerebral Cortex  Functions of the cerebral cortex l divided according to cortical regions l some degree of lateralisation of function  Processing of touch and proprioceptive stimuli, body perception and relation to external space Integration of senses Voluntary movements Reasoning, problem solving, predicting, social behaviour Processing of Personality visual stimuli Fluency & Auditory processing & construction of language speech comprehension Short term memory The primary sensory processing areas of the cortex Primary somatic sensory cortex Gustatory cortex Primary visual cortex Olfactory cortex Primary auditory cortex The primary sensory processing areas of the cortex Primary somatic sensory cortex Somatic sensory association area Gustatory cortex Primary visual cortex Olfactory cortex Visual association area Primary auditory cortex Auditory association area The motor areas of the cortex Primary somatic Premotor and motor cortex supplementary motor cortices Neurons in the somatic sensory and motor cortices are arranged topographically... The motor homunculus The sensory homunculus Lateralisation of function The hemisphere which contains your language & speech areas is your dominant hemisphere  How to find out which is your dominant hemisphere – the Wada test The person is given an object in their left hand and an anaesthetic (amytal sodium) is injected into their The person, when left carotid artery à brief asked to point to the anaesthesia of one object on a page, can hemisphere. do so with their left arm, indicating that only the left Then the person is hemisphere is asked to say what anaesthetised object they were given. If the left hemisphere contains the language centres, there will be no reply. What about the areas of the cerebral cortex that aren’t primary sensory processing or motor control areas? Somatic sensory association area Prefrontal association area Visual association area Limbic association area (continues on the medial surface of the cerebral hemisphere) Auditory association area Medial view of the limbic association cortex What does association cortex do?  What are the functions of the various association areas? Somatic sensory association area: Integration of touch and other sensations, appreciation of space and body position Prefrontal association area: Social behaviour, planning, predicting Visual association area: Complex recognition Limbic association area: of forms Memory and emotional responses Auditory association area: Meaning & significance of sounds