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Central Nervous System Dr. Anderson RCGC Animal Body Plans Cephalization • Organisms that have a proper and distinct “head end” • Why is this important? Cephalization Major Divisions • Brain – Processes information coming in from afferent nerves – Sends signals (motor) out to body via spinal cord and cranial nerves • Spinal Cord – Connects brain to peripheral nerves – May also initiate motor responses (reflexes) Brain Divisions - Anatomical • • • • Cerebrum (Cerebral Hemispheres) Diencephalon Brain Stem (Pons, midbrain, medulla) Cerebellum Each of these divisions can be divided further, into anatomical AND functional divisions Brain Ventricles • “Spaces” in the brain that are left over from embryonic brain development • Spaces are filled with cerebro-spinal fluid • Why? Hydrocephaly • “Water on the brain” • Pressure inside the brain inceases due to too much cerebrospinal fluid (CSF) being produced or drainage is blocked Functional Anatomy Major Brain Divisions Cerebrum Cerebrum • Divided into hemispheres bilaterally • Each half of the cerebrum is further divided into regions by: – Gyri “Twisters” – Sulci “shallow grooves” – Fissures “Deeper grooves” Major Fissures Longitudinal Fissure Transverse cerebral fissure Major Sulci and Gyri Brain and Skull Frontal lobes lie within the anterior cranial fossa The anterior parts of the temporal lobes lie within the middle cranial fossa The posterior cranial fossa houses the brain stem and cerebellum Cerebral Cortex • Only 2-4 mm thick, but 40% of brain mass • Contains BILLIONS of neurons (convolutions increase surface area) • Functional areas can be identified, but all areas of the cortex are interconnected • Each hemisphere is associated with the opposite side of the body (laterally) Stroke • People that have motor areas affected on only one side of their brain • Opposite part of the body may be paralyzed Cortex – Thin Shell of Grey Matter Functional Cortex Areas • Motor – initiates movement in areas of the body • Sensory – Sensations from the body come here to be processed • Association Areas – where incoming information from the body is processed Motor and Sensory Areas Primary Motor Cortex • Located in the pre-central gyrus • Pyramidal cells – allow conscious control and coordination of voluntary movements – Connect to spinal cord (pyramidal tracts) • Motor areas are not simply discrete, but interconnected! Premotor Cortex • Anterior to precentral gyrus • Provides a ‘memory bank’ for skilled motor activities • Also controls motor activity that rely on sensory feedback Outline the Primary and Premotor Cortices Sensory Areas – Primary Somatosensory cortex • Post-central gyrus of the parietal lobe • Neural input from the skin and proprioreceptors (from muscles and joints) is decoded and the stimulated body part is identified (spatial discrimination) Somatosensory Association Cortex • Integrates sensory inputs to produce an understanding of what is being felt • DEMO • What would damage to this area do? Label the Primary and Association Somatosensory Cortices Primary Visual Cortex • Receives input from the cells in the retina of the eye Visual Association Cortex • Uses past visual stimuli “visual memories” to determine what is being seen • Uses different aspects of the visual data (shape, contrast, depth perception, etc.) Primary Auditory Cortex • Superior margin of temporal lobe • Gathers data on pitch, loudness and location (by the difference in impulses received by each ear) • Auditory Association Area – interprets sound by relating to past auditory memories Olfactory Cortex • On medial aspect of temporal lobe • Part of the old “rhinencephalon” (nose brain) that still exists – Most of the rest of our ancestral rhinencephalon has evolved to process “higher” emotions – the limbic system Auditory and Olfactory Cortices Other Cortices • Gustatory Cortex - Perceives taste stimuli – Just deep to temporal lobe • Visceral Cortex – Perceives information from the gut – Just posterior to gustatory cortex • Vestibular Cortex – provides information about the position of the head in space – Posterior of insula Multimodal Association Areas • Generally receives information after being processed by the association cortices for each sense • Receives input from multiple stimuli, and – – – – – Give meaning to it Devote it to memory Act upon it Relate it to previous experience Senses related to conciousness Motor Homonculus (cortical) Somatosensory Homonculus Anterior Association Area • In frontal lobe • Center for – Intellect – Personality – Judgement – Planning – Abstract Ideas Posterior Association Area • Temporal, parietal, occipital lobes • Allows to recognize: – Patterns and faces – Localizing yourself in space – Self-awareness Limbic Association Area • Includes the singulate gyrus, hippocampus – Provides emotional impact that is tied to certain situations – Example? Cerebral White Matter • Deep to the cortex • Connects “grey matter” cortices to each other and to the lower CNS (spinal cord) • White color is due to the myelination of the fibers composing the tissue Grey and White Matter Distribution White Matter Fibers • Commissures – Connect corresponding grey matter of the two brain hemispheres – Allows them to act together • Association Fibers – Connect different parts of the same hemisphere • Projection Fibers – connect the brain to the rest of the nervous system (spinal cord) Diencephalon • Forms the core of the forebrain (surrounded by cerebral hemispheres) • 3 major divisions – Thalamus – Hypothalamus – Epithalamus Thalamus • Consists of 2 bilateral egg-shaped “nuclei” • Serves as a relay station for all impulses entering the brain – All afferent impulses are directed to the relevant areas of the brain – All efferent impulses are directed to the relevant areas of the body Hypothalamus • Located inferior to the thalamus • The main visceral control center of the body, maintains homeostasis Hypothalamus Functions • Autonomic control center – Heart rate, blood pressure, digestive tract movements, etc. • Emotional Responses – Pleasure, fear, rage, sex drive • Body Temperature – Fever, sweating, shivering, Hypothalamus Functions (con’d) • Food intake – Monitors glucose levels in the blood • Water balance and thirst – Monitors levels of solute concentrations in the blood • Sleep-wake cycles • Major controller of the endocrine system Epithalamus • Most dorsal portion of the diencephalon • Most notably contains the pineal gland, which secretes the hormone melatonin – Helps regulate the sleep-wake cycle Brain Stem • Directly inferior to diencephalon • Three major areas – Midbrain – Pons – Medulla Oblongata Midbrain • Function – Fight-or-flight response – Visual reflex centers (visual tracking) – Startle reflex Pons • Helps to maintain the normal rhythm of breathing • Serves as a bridge between the motor cortex and the cerebellum Medulla Oblongata • Located just in the opening of the foramen magnum (top of spinal cord) • Regulates many homeostatic functions – Cardiovascular regulation – Respiratory rhythm – Hiccuping, coughing, vomiting, swallowing, sneezing Cerebellum • Bilaterally symmetrical organ that occurs inferiorly to the occipital lobe • Times our efferent motor impulses, resulting in smooth coordinated movements The Limbic System • Our “emotional” brain • Composed of organs that surround the upper brain stem – Rhinencephalon – Cingulate gyrus – Amygdala – Hypothalamus – Fornix Emotional Brain • Amygdala – Recognizes fearful facial expressions – Core of the fear response • Cingulate gyrus – Helps to express emotions as gestures – Resolves mental conflicts The Reticular Activating System • The reticular neural formation extends from the brain stem into many major areas of the brain – Makes this system ideal for arousing the brain as a whole • The RAS filters out “typical” stimuli, but arouses the brain when something unusual or significant happens Levels of Consciousness Alert Drowsy/Lethargic Stupor Coma What causes us to shift along this continuum? Memory • The storage and retrieval of information • Memories are stored in parts of the brain that need them (e.g. visual association cortex for memories of shapes) • What affects the vividness and length of memories? – Emotional State – Repetition – Association (mnemonic devices) Protection of the Brain • Meninges (Physical protection) • Cerebrospinal Fluid (Physical Protection) • Blood-Brain Barrier (Chemical Protection and Immune Function) Meninges • Sheets of fibrous connective tissue that surrounds the brain – Dura Mater • Continues inferiorly as the spinal dura mater – Arachnoid membrane – Pia mater Dura Mater Cerebrospinal Fluid • Fills the spaces in and around the brain and spinal cord – Ventricles – Meninges • Absorbs shock, provides buoyancy and delivers materials (electrolytes, etc.) to the brain Spinal Tap • CSF may need to be sampled to check for infection/injury – No blood/bacteria should be isolated from CSF in healthy individuals Blood-Brain Barrier • Brain needs to be protected from – Pathogens – Wild swings in chemistry • Capillaries serving the brain are only permeable to the smallest molecules essential for brain function – Tight junctions in blood vessel epithelia – Astrocytes – limit what comes in and out of brain tissue Always a good thing? Concussion • Generally due to a violent jarring or twisting of the brain inside the cranium Progressive Brain Diseases • What types of diseases are responsible for slow, progressive loss of mental function? • • • • • Name of disease Symptoms Mode of pathology Prognosis Treatment Spinal Cord - Anatomy • Enclosed by the neural arches of the vertebrae • Extends from the base of the skull to the 1st-2nd lumbar vertebrae Spinal Cord - Function • Provides afferent and efferent nerve pathways to and from the brain and peripheral nerves • Major reflex center Spinal Cord – Protection • Resides within the spinal canal (vertebrae) • Also surrounded by meninges – Spinal Dura Mater – Arachnoid Membrane – Pia Mater • CSF between arachnoid membrane and pia mater Spinal Meninges Epidurals • Anesthetic is placed in epidural space using a fine needle (catheter) • Often used during labor, surgery or diagnostic procedures Spinal Cord Terminus • Spinal cord ends at the conus medullaris at 1st2nd Lumbar vertebra • Filum terminale anchors the spinal cord to the coccyx • Nerve roots for lumbar and sacral region extend through the vertebral canal and exit through their respective vertebrae Cauda Equina Spinal Cord Cross-Sectional Anatomy Dorsal and Ventral Roots • Dorsal – carries afferent impulses into the spinal cord – Linked to grey matter of dorsal horn • Ventral – Carries motor impulses out from the spinal cord – Linked to grey matter of ventral horn White Matter • Made of myelinated (and some unmyelinated) fibers that allow communication between – Different areas of the spinal cord – The spinal cord and the brain • These fibers form tracts that allow impulses to travel through the spinal cord Spinal Tracts - Function • All are multi-neuron pathways • Neuron pathways facilitate: – Decussation – travel from one side of the CNS to the other – Relay – signals are transferred between neurons in the same path Spinal Tracts - Arrangement • Arrangement – Somatotopy – neuronal paths are spatially organized in the spinal tissue – Symmetry – all tracts are paired bilaterally Major Tracts in White Matter