Learning expectations for BIOL 131. Chapters 11, Nervous System Overview Read Chapter 11. You should be able to:

Transcription

1 NOTE The quiz will have question ONLY from the material we get through on Tuesday. The first midterm will cover all material from day one until the lecture before the second midterm. Learning expectations for BIOL 131. Chapters 11, Nervous System Overview Read Chapter 11. You should be able to: Describe the overall structure and organization of the nervous system. - Overall nervous system: CNS/PNS - PNS consists of sensory (afferent)/motor (efferent) - Motor: somatic/autonomic nervous system - Autonomic: sympathetic/parasympathetic/ (enteric) List the divisions and subdivision of the nervous system describing the basic roles of each division. - CNS: spinal cord/brain (processes info, initiates responses, integrates mental processes) - PNS: neurons, ganglia, sensory receptors, plexuses, all nervous tissue outside of CNS - Afferent (sensory): transmits action potentials from sensory receptors to CNS - Efferent (motor): transmits action potentials from CNS to effector organs (muscles/glands) - Motor: Somatic: action potential to CNS (neuromuscular junctions: synapse between neuron from CNS and skeletal muscle cell). - Motor: Autonomic: To smooth muscles (neuron from CNS synapses with second neuron in ganglion, second neuron then synapses with effector) - ANS: Sympathetic: prepares body for exercise - ANS: Parasympathetic: prepares body for relaxation (emptying urine, digesting food) - ANS: Enteric: Plexuses within walls of digestive tract, enteric neurons monitor/control digestive tract independently of CNS through local reflexes. Differentiate between the terms efferent and afferent, sensory and motor. - Efferent (motor): transmits action potentials from CNS to effector (muscle, gland) - Afferent (sensory): transmits action potentials from sensory receptors to CNS (cell bodies of sensory neurons in dorsal root ganglia near spinal cord/ganglia near origin of certain cranial nerves)

2 Define neuromuscular junction, synapse, ganglion and fiber. - Neuromuscular junction: Synapse between neuron from CNS and skeletal muscle cell - Synapse: functional membrane to membrane contact of nerve cell with another nerve cell, muscle gland, sensory receptor (transmits action potential from one cell to another). - Ganglion: Group of nerve cell bodies in PNS - Fiber: Makes up muscles List the cells of the nervous system and describe their functions. - Neuroglia: support, protect, influence neurons - Neurons: receive stimuli and transmit action potentials (nerve cells) o Sensory (afferent): AP towards CNS o Motor (efferent): AP away from CNS o Interneurons: within CNS from one neuron to another Label or list the parts of a neuron and state the function of each. - Cell body: contains nucleus (source of info/protein synthesis), little nucleolus in nucleus, rough ER (endoplasmic reticulum) and Golgi apparatus surround nucleus (other organelles/mitochondria present), Nissl bodies primary site of protein synthesis in neurons. - Dendrites: short, highly branched cytoplasmic extensions tapered from base of neuron cell body to the tips. Dendritic spines (small extensions axons of other neurons form synapses with other dendrites) - Axons: branch to form collaterals, trigger zone ( site where action potentials are generated), presynaptic terminals (extensions w/ long ends). Describe neuronal transport. - Axoplasm moves from cell body towards terminals - Recycled plasma membrane and substances taken in by endocytosis transported up axon to cell body to be reused/get rid of (retrograde) - ** Rabies/herpes enter axons in damaged skin/transported to CNS. Describe the different types of neuroglia describe their roles and where they are found. - CNS NEUROGLIA - Astrocytes: Cover surface of neurons/bvs, form blood brain barrier (bbb) regulates which substances reach CNS (drugs/alcohol difficult to penetrate), CNS version of cells that wrap around other cells. - Ependymal cells: Lines hollow parts of CNS form choroid

3 plexuses (secretes cerebrospinal fluid into ventricles of brain), free surface contains cilia to move fluid throughout brain cavities. - Microglia: in CNS become mobile and phagocytic in response to inflammation. Phagocytize necrotic tissue, microorganisms, other foreign substances in CNS. Migrate to area of infection. - Oligodendrocytes: cytoplasmic extensions surrounding axons (wrapped several times = myelin sheaths). Forms myelin sheaths around portions of several axons ** - PNS NEUROGLIA - Schwann cells: wrap several times around axons to form myelin sheaths around only ONE axon. - Satellite cells: surround neuron cell bodies in sensory ganglia. Provide support/nutrition to neurons, protect from heavy metal poisons (absorb them/reduce access to neuron cells) Differentiate between grey matter and white matter. - White matter: bundles of parallel axons w myelin sheaths, forms conduction pathways propogating AP s from one area of CNS to another. - Nodes of Ranvier (gaps between one myelinating cell and the next) - 1 yr old, axons aren t myelinated yet, don t have as much control over actions - Grey matter: groups of neuron cell bodies/dendrites, very little myelin. Gray matter on surface of brain (cortex), clusters deeper in brain (nuclei). PNS = ganglion Describe in detail how resting membrane potentials are produced and maintained. - Potential difference = unequal distribution of charge btw inside/outside of plasma (-70 to -90mV) - Inside negative of outside - Potential difference maintained by sodium/potassium pump. Each ATP, 3 sodium move out, 2 potassium move in - Outside plasma membrane is therefore slightly positive (polarized membrane because 2 sides are different) Differentiate between depolarization and hyperpolarization when they occur and how they may or may not contribute to graded, summated or action potentials. - Depolarization: potential difference becomes smaller (less polar) - Hyperpolarization: potential difference becomes greater (more polar) Describe in detail how action potentials are produced and how

4 they are propagated in myelinated and unmyelinated axons. Make sure to include the ions involved. - When graded potentials cause depolarization of plasma membrane to threshold (series of permeability changes) results in action potential. - Depolarization (membrane potential moves away from resting state, becoming more positive), Repolarization (membrane potential returns towards resting state becoming more negative), Afterpotential (plasma membrane is slightly hyperpolarized for short period of time). - Propogate (AP at one location stimulates production of new AP at adjacent location, stimulates another, etc. > domino effect) - unmyelinated axons (continuous conduction) next AP generated directly adjacent to first AP, inside of membrane more positive than outside, on outside positive ions from adjacent area attach to negative charges of AP site. On inside, positive charged ions on AP site attach to adjacent negative charged part of membrane. Movement of positive ions = ionic current. Outside of membrane immediately adjacent to AP more negative (loss of positive charges), Inside of membrane more positive, gain of positive charges. When depolarization reaches threshold, AP produced. - Myelinated axons (saltatory conduction): AP conducted from one node of Ranvier to next. Lipids within membranes of myelin sheath insulate, forcing local AP currents to flow from one node to next. Voltage-gated sodium channels are highly concentrated in nodes, current quickly flows to node/stimulates voltage-gated sodium channels to open, resulting in production of AP. Heavier myelinated cells conduct AP more quickly. Describe the roles of voltage-gated channels. - Open and close in response to small voltage changes across plasma membrane. In unstimulated cell, inside of plasma membrane is negative compared to outside. When stimulated, permeability of plasma membrane changes (gated ion channels open/close). Mvmnt of ions in/out of cell changes charge difference across plasma membrane (voltage gated channels open or close). Specific for Na/K in most electrically excitable tissues, or Ca in smooth/cardiac muscle fibers. Describe the refractory periods and what physiological role they play in nerve transmission. - Once AP produced on certain part of plasma membrane,

5 sensitivity of that part decreases for some time (refractory period) - Absolute refractory period (complete insensitivity): once AP begins, depolarization/repolarization phases will be completed before another AP can begin. Strong stimulus cannot lead to a prolonged depolarization of plasma membrane (muscle cell can only fire so often) - Relative refractory period (follows absolute): stronger than threshold stimulus can initiate another AP. Between refractory periods, strong stimulus CAN produce another AP. Membrane more permeable to potassium bc many voltage gated potassium channels are open. Ends when these channels close. Explain the differences in conduction rate between myelinated and unmyelinated axons. - Faster in myelinated than unmyelinated (generation of AP in nodes of ranvier occurs more rapidly) - Lipids act as insulation, forcing AP currents to jump from node to node - Affected by thickness of myelin sheath - Larger diameter axons conduct more rapidly than small diameter (large have greater surface area, more voltage gated sodium channele open during depolarization resulting in greater local current flow (stimulating more adjacent membrane areas) Describe, in detail, the structures of chemical and electrical synapses. State where electrical synapses are likely to be found. - Electrical synapse: gap junctions allowing local current flow between adjacent cells. Membranes of adjacent cells separated by 2nm gap spanned by tubular proteins (connexons). Movement of ions thru connexons generates local current (AP in one cell generates local current that generates AP in adjacent cell). AP s conducted quickly between cells, cell s activity is synchronized. - Exist between adjacent cardiac muscle cells/smooth muscles (causes coordinated contractions of muscle cells) - Chemical synapse: AP s in presynaptic terminals cause release of neurotransmitters from its terminal. Voltage gated calcium channels open, calcium diffuses into presynaptic terminal. Ions cause synaptic vesicles to fuse w/ presynaptic membrance/release neurotransmitters by exocytosis into synaptic cleft. - Neurotransmitters released from presynaptic terminal, diffuse across synaptic cleft, bind to specific receptors in postsynaptic membrane. Binding produces depolarizing/hyperpolarizing graded potential in

6 postsynaptic membrane. (binding of acetylcholine to sodium channels causes them to open, allowing Na to diffuse into postsynaptic cell. If resulting depolarizing graded potential reaches threshold, AP is produced! Discuss the physiology of chemical neurotransmission include modes of removal and how some have inhibitory actions while others have stimulatory activity. - Neurotransmitter affects only cells with receptors for that neurotransmitter (acetylcholine>acetylcholine), (norepinephrine> norepinephrine) - More than one type of receptor molecule for each cell with different effects on permeability of postsynaptic membranes - Ex. Norepinephrine can bind to one receptor causing depolarization in one synapse / another receptor causing hyperpolarization in one synapse (inhibitory OR stimulatory) - Removed to stop effect. Enzymes digest neurotransmitter, products taken up by presynaptic neuron. Recycled whole by presynaptic neuron or diffuses away from synapse. Compare and contrast EPSPs and IPSPs. - EPSP s depolarization occurs/response is stimulatory, depolarization might reach threshold, therefore producing AP/response from cell. Occurs by excitatory neurons, membrane has become more permeable to sodium (concentration gradient is large for sodium, and negative charge inside cell attracts positive charge sodium, diffuses into cell causing depolarization.). If cause a depolarizing graded potential that reaches a threshold, AP is produced. - IPSP s combination of neurotransmitter w/ receptor results in hyperpolarization of postsynaptic membrane, response is inhibitory. Decrease likelihood of producing AP by moving membrane potential farther from threshold. Released by inhibitory neurons, results from increase of permeability of plasma membrane to Cl or K. - EX. In spinal cord, glycine binds to its receptors, Cl channels open, Cl diffuses in (membrane s permeability to Cl increases), inside of cell more negative (hyperpolarization). Describe the mechanisms of summation. - Spatial summation: multiple AP s arrive simultaneously at 2 different presynaptic terminals/synapse with same postsynaptic neuron. In postsynaptic neuron each AP causes depolarizing graded potential that undergoes summation at trigger zone. If summated depolarization reaches threshold, AP is produced.

7 - Temporal summation: 2 AP s arrive in close succession at presynaptic membrane. First AP causes production of graded potential that does not reach threshold at trigger zone. 2 nd results in production of second graded potential that summates with first to reach threshold, resulting in production of AP. - Combined summation: AP is produced at trigger zone when graded potentials produced as a result of the EPSP and IPSP summate to reach threshold. Discuss the structure and roles of neuronal pathways and circuits. - Convergent pathways: many neurons converge/synapse with a smaller number of neurons (ex. Data synthesis in brain) - Divergent pathways: small number of presynaptic neurons synapse with large number of postsynaptic neurons. (important info can be transmitted to many parts of brain) - Oscillating circuit: neurons arranged in circular fashion (AP entering circuit causes neuron farther along circuit to produce AP more than once). Once stimulated, continues to discharge until synapses become fatigued/inhibited by other neurons.