The Nervous System - Chapter 2 PDF

Structure and Function of the Nervous System dgshwertqwert  The Structure of Neurons (and some functions)  Action Potentials  Neurotransmission  The Role of Glial Cells  Overview of the Nervous System  Guided Tour of the Brain  The Cerebral Cortex  Developmen...

Structure and Function of the Nervous System dgshwertqwert  The Structure of Neurons (and some functions)  Action Potentials  Neurotransmission  The Role of Glial Cells  Overview of the Nervous System  Guided Tour of the Brain  The Cerebral Cortex  Development of the Nervous System  The list of components you should know:  Cell body (soma)  Dendrites  Axon  Axon terminal  Myelin sheath  Synapse  Nodes of Ranvier  Vesicles  Receptors Neuron from the vestibular area of the brain—glial cells are the thin white structures (confocal light micrograph); Hippocampal neuron (fluorescent micrograph); Mouse neuron and spinal cord ganglia (transmission electron micrograph); Multipolar neuron cell body from human cerebral cortex (scanning electron micrograph); Neuron from the brain; Nerve culture from dorsal root ganglia of an embryonic rat (fluorescent micrograph). Unipolar = only 1 extension (axonal or dendritic Bipolar = 2 extensions: axonal and dendritic Pseudounipolar = axon split into 2 branches, 1 to periphery & 1 to spinal cord Multipolar = single axon & many dendrites (most common)  Within Neurons ▪ Electrical currents  Between Neurons ▪ Neurotransmitters or Electrical ▪ Neuron  Neuron ▪ Neuron  Muscles/Glands  Presynaptic  Axon makes connection to other neurons.  Postsynaptic  Other neurons make a connection to dendrites.  2 Types of information processing: 1. Electrical communication: ▪ Communication within the neuron ▪ Action potential 2. Chemical communication: ▪ Communication between neurons ▪ Neurotransmission  The Structure of Neurons (and some functions)  Action Potentials  Neurotransmission  The Role of Glial Cells  Overview of the Nervous System  Guided Tour of the Brain  The Cerebral Cortex  Development of the Nervous System  Electrical charge difference (-70mv) across the neuronal membrane, when the neuron is not being stimulated, (or is inhibited).  The difference in electric charge between the inside & outside of a cell.  Ion Channels  (Na+) Sodium, (K+) Potassium, (Cl-) Chloride, (A-) Protein molecule, (Ca2+) Calcium  Neurons have Selective Permeability ▪ Gated ion channels open or close based on voltage or as a response to physical or chemical stimuli ▪ Also non-gated ion channels (exhibiting static permeability)  Ion Pumps  Active transport proteins  Use energy (ATP - adenosine triphosphate) to exchange ions  Na+/K+ pump moves 3 Na+ out and 2 K+ into cell with the use of 1 ATP  A resting neuron is at electrochemical equilibrium:  The electrical and ionic gradient (difference) forces are equal  EPSPs  Maximum effective transmission is ~1 millimeter  Good for short distances (e.g., cells in the retina)  Longer transmissions require an Action Potential  Regeneration requires voltage-gated ion channels ▪ (Found at the spike-triggering zone in the axon hillock) ▪ (& also along Nodes of Ranvier)  Action Potential  A rapid depolarization and repolarization of a small region of the membrane caused by the opening and closing of ion channels. 1) Graded potential reaches the axon and depolarizes above a threshold, causing electrical discharge. 2) The neuron “fires” (Follows “all-or-nothing” law) 3) Charge originates near the cell body. Positively charged particles rapidly flow into the axon, then rapidly flow out. 4) A spike in positive charge followed by a sudden decrease in charge shoots down the axon terminal.  Absolute refractory period = another action potential cannot be generated during hyperpolarization.  Relative refractory period = neurons CAN generate action potentials; but only with very large depolarizing currents.  Resting potential  difference in electric charge between the inside & outside of a cell.  Threshold  membrane potential necessary to trigger an action potential  Action potential  electrical impulse that travels down the axon (triggers the release of neurotransmitters)  Refractory period  time during which another action potential is impossible; limits max firing rate What does the action potential achieve?  The Structure of Neurons (and some functions)  Action Potentials  Neurotransmission  The Role of Glial Cells  Overview of the Nervous System  Guided Tour of the Brain  The Cerebral Cortex  Development of the Nervous System  Neurotransmission is chemical communication between neurons.  Acetylcholine (Ach) : voluntary motor control  Epinephrine (Adrenaline) : arousal  Dopamine (DA) : motor behavior, motivation, pleasure, and emotional arousal  Glutamate (Glu) : information transmission  GABA : primary inhibitory NT  Noreprinephrine (NE) : influences mood & arousal  Serotonin (5HT): sleep, eating, aggression, & mood  Endorphins : act on pain pathways & emotion centers  A process that halts neurotransmission. 3 ways: 1) Reuptake through transport proteins in pre-synaptic membrane (passive) ▪ OR autoreceptors which regulate amount of NT in synapse. 2) Enzymatic breakdown (NTs are “recycled”). 3) Diffusion away from region of synapse. Significant in the role of psychotropic medications  Gap junctions = places where multiple transmembrane proteins in pre-and post-synaptic neurons connect to create pathways connecting the cytoplasms of the 2 neurons.  Isopotential ▪ Having the same electrical potential  Bidirectional  Rectifying synapses ▪ Limit current flow in one direction  Less plasticity  Cannot amplify  The Structure of Neurons (and some functions)  Action Potentials  Neurotransmission  The Role of Glial Cells  Overview of the Nervous System  Guided Tour of the Brain  The Cerebral Cortex  Development of the Nervous System  Roughly equal to neurons in number  > half the volume of the brain  Structural support  Form blood-brain barrier  Aiding in speed of transmission  Modulate neural activity  4 types  Astrocytes ▪ Large, round/radial, surround neurons, close to vasculature, transmit ions, forms BBB, ▪ Keeps out bacteria & large hydrophilic molecules ▪ Lets in +O2, + CO2, + hormones ▪ Respond to and release neurotransmitters, moderate neural activity  Microglial cells ▪ Deals with tissue damage and removing damaged cells  Oligodendrocytes: Form myelin in CNS  Schwann cells: Form myelin in PNS  The Structure of Neurons (and some functions)  Action Potentials  Neurotransmission  The Role of Glial Cells  Overview of the Nervous System  Guided Tour of the Brain  The Cerebral Cortex  Development of the Nervous System  Rostral / Anterior Dorsal / Superior Rostral / Caudal / Anterior Posterior Lateral Medial Lateral Ventral / Inferior Caudal / Posterior  (Axial) Dorsal Lateral Medial Ventral  Protecting the brain Ventricle  Skull, dura, ventricles Cortex “Dura” = hard Skull  Protecting the brain Ventricle  Skull, dura, ventricles Cortex  Supplying the brain “Dura” = hard  Arteries Cortex Dura Ventricles: Contain Cerebrospinal Fluid (CSF) - allows brain to “float” - Helps regulate pressure - Shock absorption - Damage to ventricle system = dangerous  Anterior Cerebral Artery Middle Cerebral Artery Posterior Cerebral Artery Blood flow to brain: - If blood flow is blocked (e.g. stroke)  Cortical areas supplied by that artery are damaged  Cognitive functions impaired - Built-in redundancy  The Structure of Neurons (and some functions)  Action Potentials  Neurotransmission  The Role of Glial Cells  Overview of the Nervous System  Guided Tour of the Brain  The Cerebral Cortex  Development of the Nervous System  Reflex & communication to higher areas  Senses information from peripheral sensory receptors  Relay to brain & conducts final motor signals from brain to muscles  Each level has reflex pathways  5 major sections  31 segments  Each segment has a spinal nerve that passes through foramen  Each nerve has sensory & motor axons  Dorsal horn  Sensory neurons & interneurons  Ventral horn  Motor neurons  Central Canal  CSF “The Hindbrain” A collection of structures running the length of the brainstem’s core from upper medulla into midbrain; participates in control of mood, arousal, & sleep. Bundles of nerve fibers connecting to higher portions of brain; manages heart rate & blood pressure.  Myelencephalon  Contiguous with spinal cord  Houses bodies of many of the 12 cranial nerves  Sensory & motor innervations to face, neck, abdomen, throat, & heart  Respiration, heart rate, arousal  Pons ▪ Bridge, connection between cerebral cortex and cerebellum ▪ Eye & facial movements & expressions ▪ Management of REM sleep & arousal ▪ Connects to cerebellum.  Cerebellum ▪ Home to most of brain’s neurons. ▪ Cerebellar cortex, 4 pairs of deep nuclei, & white matter. ▪ Motor outputs & sensory inputs for body position. ▪ Vestibular projections, auditory, & visual inputs from brainstem. ▪ Outputs from deep nuclei to thalamus and then to motor and premotor cortex. ▪ Critical for posture & coordination (integrates & filters movements). Essential for balance & motor coordination; more neurons then rest of brain; highly complex. Cerebellar Atrophy Cerebellar Atrophy Involved in sensory reflexes, movement, & pain. Involved in sensory reflexes, movement, & pain.  Large fiber tracts from forebrain to spinal cord, cerebellum, & other parts of brainstem  Superior colliculus ▪ Peripheral object perception & gaze  Inferior colliculus ▪ Location & orientation toward auditory stimuli  Red Nucleus ▪ Motor coordination  Thalamus & Hypothalamus  Thalamus  Gateway to cortex (Grand Central Station) ▪ All sensory modalities synapse here ▪ (except olfactory inputs!) ▪ Relays continue to primary cortical sensory receiving areas ▪ Motor information toward spinal cord ▪ LGN & MGN ▪ Somatosensory information via ventral posterior (medial & lateral) nuclei.  Hypothalamus  Main link between autonomic nervous system and endocrine system.  Main site of hormone production & control.  Mammillary bodies: input from limbic system ▪ Circadian rhythms  Controls homeostasis ▪ Thirst, hunger, fatigue, body temperature  Pituitary gland  Helps maintain homeostasis  (Limbic System, Basal Ganglia, & Cerebral Cortex)  Limbic System  Neither anatomically nor functionally organized as well as other neural systems  Cingulate gyrus, hypothalamus, anterior thalamic nuclei, hippocampus, & amygdala.  Subcortical nuclei: ▪ Caudate nucleus, putamen, globus pallidus, subthalmic nucleus, & substantia nigra (extensively interconnected) ▪ Comprehensive understanding of these regions remains elusive!  Involved in: ▪ Action selection, action gating, motor preparation, timing, fatigue, & task switching. ▪ Predicted & actual reward, reward based learning, goal- oriented behavior.  Critical for creating new memories & integrating them into a network of knowledge so they can be stored indefinitely in other parts of the cortex.  Central to emotional processes, esp. forming emotional memories.  The Structure of Neurons (and some functions)  Action Potentials  Neurotransmission  The Role of Glial Cells  Overview of the Nervous System  Guided Tour of the Brain  The Cerebral Cortex  Development of the Nervous System  Why is cortex folded? - Most bang for the buck (large surface area in small space) - Reduce axonal distance & connection times “Gyrus” (gyri) = bump(s) “Sulcus” (sulci) = groove(s) “Fissure” = big sulcus (cell bodies) (axon tracts) (*myelin is white)  Location of primary motor cortex; most complex cognitive processes: imagination, decision making, executive control.  Prefrontal Cortex: planning, attention, judgment Orbitofrontal Cortex : located behind the eyes; participates in impulse control; not fully developed until adulthood (~18- 24); damage is correlated w/ anti-social behavior.  Major Divisions of the Frontal Lobe:  Dorsolateral prefrontal cortex (DLPFC)  Ventromedial prefrontal cortex (VMPFC)  Orbitofrontal cortex (OFC)  Anterior Cingulate Cortex (ACC)  Contains the primary visual cortex at the back of the head.  Home of primary auditory cortex and Wernicke’s area. Also helps in face & object recognition.  Contains primary somatosensory cortex; participates in perception of spatial movement. neocortex = contains 6 main cortical layers with a high degree of specialization of neuronal organization; most recently evolved type of cortex. minicolumns/microcolu mns = fundamental processing units in cerebral cortex.  The Structure of Neurons (and some functions)  Action Potentials  Neurotransmission  The Role of Glial Cells  Overview of the Nervous System  Guided Tour of the Brain  The Cerebral Cortex  Development of the Nervous System  Synapses form ~27 weeks gestation and continue until 15 months after birth.  synaptogenesis = the formation of synaptic connections between neurons in the developing nervous system  synapse elimination (pruning) = elimination of some synaptic contacts between neurons during development. (> 10 years!)  The Structure of Neurons (and some functions)  Action Potentials  Neurotransmission  The Role of Glial Cells  Overview of the Nervous System  Guided Tour of the Brain  The Cerebral Cortex  Development of the Nervous System