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Nervous System Marieb 11.1 Classification Anatomically CNS Brain PNS Peripheral nerves Spinal cord Functionally Somatic nervous system (SNS) Skeletal or voluntary muscles Autonomic nervous system (ANS) Automatic functions 29-2 Nervous system Computer Input circuit Output circuit Simple computers (output directly controlled by input) Brain and spinal cord Complex computers (input and previous memory) Control mechanisms in lower brain CPU (sequence of information processing) Sensory receptors and nerves Effectors and motor nerves Spinal cord CNS: Brain and Spinal Cord 29-4 PNS: Cranial Nerves (12) Marieb 13.5a PNS: Spinal Nerves (31) Spinal cord : Slender structure continuous with the brain Descends into the vertebral canal and ends around the level of the first or second lumbar vertebra 31 spinal segments: 8 cervical segments 12 thoracic segments 5 lumbar segments 5 sacral segments 1 coccygeal segment Marieb 13.6 Martini 13-11 Comparison of Somatic and Autonomic Systems Marieb 14.2 Freeman 45-20 Meninges Marieb 12.24a CNS: Brain Four sections and three levels Cerebrum (higher brain):Thoughts and memory Diencephalons (subcortical or lower brain):subconcious activities like arterial pressure, emotions, feeding reflexes Brain stem (lower and mid brain): respiration, visual and auditory reflexes Cerebellum (lower brain) :Coordination in movement 29-11 Space Restriction and Brain Development Marieb 12.3 CNS: Brain – Cerebrum Largest section Two cerebral hemispheres Connected by a thick bundle of nerve fibers called the corpus callosum Longitudinal fissure between hemispheres Sulci – grooves on surface Gyri or convolutions – bumps of brain matter 29-13between sulci Marieb 12.6ab Previous slide 29-17 CNS: Brain – Cerebrum (cont.) Cortex Ventricles Outer layer – gray matter Contains about 75% of all neurons Interconnected cavities within the brain Filled with CSF Inner layer – white matter Functions Interpret sensory information Initiate body movements 29-18 Stores memories and creates emotions Ventricles of the Brain Marieb 12.5 Diencephalon: Thalamus and Hypothalamus Marieb 12.12 CNS: Brain – Diencephalon Between the cerebral hemispheres superior to the brain stem Thalamus Relay station for sensory information going to the cerebral cortex for interpretation Hypothalamus Maintains homeostasis by regulating vital activities 29-21 CNS: Brain – Brain Stem Connects the cerebrum to the spinal cord Midbrain (mesencephalon, amygdala) Medulla oblongata Just beneath diencephalon Controls both visual and auditory reflexes, eg.feeding reflexes Pons Rounded bulge on underside of brain stem Between midbrain and medulla oblongata Regulates respiration 29-22 Inferior portion of brain stem Directly connected to spinal cord Controls many vital activities, such as heart rate, blood pressure, and breathing CNS: Brain – Cerebellum Location Inferior to the occipital lobes of the cerebrum Posterior to the pons and medulla oblongata Coordinates Complex skeletal muscle contractions that are needed for body movements Fine movements 29-23 Brain CNS: Brain – Cerebrum (cont.) Lobes Frontal Motor areas for voluntary body movements Frontal Parietal Parietal Somatosensory – interprets sensations Temporal Auditory – interprets sounds Temporal Occipital Occipital Interprets what a person sees 29-24 Spinal Cord Marieb 12.29a Gray Matter and Spinal Roots Marieb 12.31b Cross-Sectional Anatomy of the Spinal Cord Anterior median fissure – separates anterior funiculi Posterior median sulcus – divides posterior funiculi Marieb 12.31a Gray Matter: Organization Marieb 12.32 18_26_nerve_lymphoc.jpg Alberts 18-26 Marieb 11.4 Neuron Structure (cont.) White matter – axons with myelin sheath Dendrites Schwann cells – neurological cells Wrap around some axons Cell membranes contain myelin Myelin insulates axons and enables axons to send nerve impulses more quickly Schwann cells Axon Gray matter – axons without myelin sheath 29-31 Marieb 11.3 Myelin Sheath and Neurilemma: Formation Marieb 11.5abc Freeman 45-12a Comparison of Structural Classes of Neurons Marieb T11.1.1 Martini 12-4 Saltatory Conduction Marieb 11.16 Dendrites Cell body Nucleus Synapse Signal Axon direction Axon hillock Presynaptic cell Postsynaptic cell Myelin sheath Axon terminals Campbell 48.5 Structure of a Nerve Marieb 13.3b Nerve Impulse Impulse travels down axon to synaptic knob Vesicles or small sacs in synaptic knob Produce chemicals called neurotransmitters Neurotransmitters are released by synaptic knob Allow impulse transmission to postsynaptic structures Dendrites Cell bodies 29-41 Axons of other neurons Nerve Impulse Functions of neurotransmitters Cause muscles to contract or relax Cause glands to secrete products Activate or inhibit neurons 29-42 Nerve Impulse Membrane potential Neuron cell membrane at rest is in a polarized state Inside of cell membrane is negative (-90 mV) Outside of cell membrane is positive due to more Na+ and K+ As Na+ and K+ move into the cell, the membrane becomes depolarized Inside becomes more positive (+ 45 mV) Action potential (nerve impulse) is created Repolarization occurs when K+ and later Na+ move to the outside of the cell membrane 29-43 Return of the cell to polarized (resting) state Synaptic Cleft: Information Transfer Marieb 11.18 Type of Synapses Chemical , Electrical In electrical synapses, ionic current spreads directly from one cell to another through tubular structures called connexons. A cluster of 100 or so connexons forms a pathway (connection) called a GAP JUNCTION between adjacent cells. Gap junctions are common between cardiac muscle cells (shown below, left) and between smooth muscle cells Excitatory , inhibitory GABA, glycine- inhibitory, to lower anxiety Acetyl choline, serotonin, glutamine- Excitatory Epenepherin, Norepinepherin, dopamine are both excitatory and inhibitory Postsynaptic neuron 5 µm Synaptic terminals of presynaptic neurons Campbell 48.16 Freeman 45-17a CSF Cerebrospinal fluid (CSF) is a clear, colorless body fluid found in the brain and spine. It is produced in the choroid plexuses of the ventricles of the brain. It acts as a cushion or buffer for the brain's cortex, providing basic mechanical and immunological protection to the brain inside the skull. The CSF also serves a vital function in cerebral autoregulation of cerebral blood flow. The CSF occupies the subarachnoid space (between the arachnoid mater and the pia mater) and the ventricular system around and inside the brain and spinal cord. It constitutes the content of the ventricles, cisterns, and sulci of the brain, as well as the central canal of the spinal cord. The CSF has two major pumps that help to establish healthy flow. The pump at the top of the spine is the occiput bone which makes up the lower portion of the skull. Flexion and extension motions of the occipital bone upon the atlas help to pump CSF through the brain and spinal cord The other pump is at the bottom of the spine in the sacrum. Flexion and extension of the sacrum is also critical to help pump the CSF 1. Lateral ventricle 2. Interventricular foramen 3. Third ventricle 4. Cerebral aqueduct 5. Fourth ventricle 6a. Median aperture 6b. Lateral aperture 6c. Central canal (spinal cord) 7. Subarachnoid space 8. Arachnoid villi 9. Dural sinuses Marieb 12.26b Composition CSF composition is similar to serum composition, besides protein, calcium and protein concentrations which are lower CSF is normally as clear as water and does not contain any blood cell (leukocytes, aka white blood cells and erythrocytes, aka red blood cells). However, in infections such as meningitis, leukocytes may pass into the CSF and after hemorrhage, red blood cells may be found in CSF. Protein concentration in the CSF, usually very low, is increased in case of infection and if CSF reabsorption at the level of the arachnoïd villi is impaired. In a reverse way, glucose concentration is decreased in some pathological conditions (tumor, acute bacterial infection, fungal infections...) Comparison of Average Serum and Cerebrospinal Fluid [7] Substance Cerebrospinal Fluid Serum Water Content (%) 99 93 Protein (mg/dL) 35 7000 Glucose (mg/dL) 60 90 Osmolarity (mOsm/L) 295 295 Sodium (mEq/L) 138 138 Potassium (mEq/L) 2.8 4.5 Calcium (mEq/L) 2.1 4.8 Magnesium (mEq/ L) 0.3 1.7 Chloride (mEq/L) 119 102 pH 7.33 7.41 Function of CSF Buoyancy: The actual mass of the human brain is about 1400 grams; however, the net weight of the brain suspended in the CSF is equivalent to a mass of 25 grams.[18] The brain therefore exists in neutral buoyancy, which allows the brain to maintain itsdensity without being impaired by its own weight, which would cut off blood supply and kill neurons in the lower sections without CSF.[19] Protection: CSF protects the brain tissue from injury when jolted or hit. In certain situations such as auto accidents or sportsinjuries, the CSF cannot protect the brain from forced contact with the skull case, causing hemorrhaging, brain damage, and sometimes death. Chemical stability: CSF flows throughout the inner ventricular system in the brain and is absorbed back into the bloodstream, rinsing the metabolic waste from the central nervous system through the blood–brain barrier. This allows for homeostatic regulation of the distribution of neuroendocrine factors, to which slight changes can cause problems or damage to the nervous system. For example, high glycine concentration disrupts temperature and blood pressure control, and high CSF pH causes dizziness andsyncope.[19] Blood Brain Barrier Because the brain is so specialized many of the chemicals found in the blood are actually toxic to the neurons in the brain. With such a specialized job one would think that the brain itself should actually have its own separate circulatory system. Unlike other parts of the body where the arteries and veins and capillaries bring nutrients to cells and move waste out of cells, the neurons in the brain are created with specialized capillaries made of protein fibers called “astrocytes”. These specialized capillaries essentially filter out harmful toxins and only allow through to the specialized brain cells healthy nutrients the brain needs. Alcohol too passes the Blood Brain Barrier as easily as water and that can be very bad for brain tissue. Prescription drugs however, because they are mostly synthetic have great difficulty in passing through this Blood Brain Barrier. The body recognizes the synthetic material as foreign and won’t let it pass through. C) Myelination process D) Unmelinated neuron