CHAPTER 10: COORDINATION
OBJECTIVES • State the organization of the nervous system (C1) • Define membrane potential (C1) • Resting potential; and action potential • Explain generation of action potentials along the membrane of axon (C3) • Describe the characteristic of nerve impulse along the membrane of axon (C2) • All or nothing event, Refractory period; and Speed of conduction • Describe the structure of synapse (C2) • Explain transmission of impulse at synapse (C3) • Differentiate transmission of impulse along the axon and across the synapse (C3) • Explain the mechanism of cocaine action at synapse (C3) • Describe nervous system disorders in relation to dopamine (C2) • Excess of dopamine: Schizophrenia; and Lack of dopamine: Parkinson’s disease 10.1: NERVOUS SYSTEM W i l l b e d i s c u s s e d d u r i n g t u t o r i a l W i l l b e d i s c u s s e d d u r i n g t u t o r i a l
a) State the organization of the nervous system (C1) NERVOUS SYSTEM Central Nervous System Sensory (Afferent) Division (send impulse from receptor to CNS) Motor (Efferent) Division (send impulse from CNS to muscles & glands) Somatic Nervous System (control voluntary movements) Parasympathetic Division (“Rest & Digest”) Sympathetic Division (“Fight or flight”) Peripheral Nervous System Spinal cord (conduct signals to & from the brain, control reflex activities) Brain (receive & process sensory information, initiate responses, store memories, generates thoughts & emotions) Autonomic Nervous System (control involuntary movements)
Living cells have an electrical charge difference across their cell surface membrane • Due to the difference in the electrical charge or voltage (concentration of ions) on the outside and inside of a cell • Known as Membrane Potential The difference in electrical charge between outside and inside of axon membrane due to the difference in ionic composition. b) Define membrane potential (C1)
FORMATION OF RESTING POTENTIAL Develops when the charge is more negative within the cell than from the outside In neurons, the resting membrane potential value is -70 mV. A cell that exhibits a membrane potential is said to be polarised. Resting Potential The membrane potential of a neuron that is not transmitting signals Plasma membrane Microelectrode inside cell Axon Neuron Microelectrode outside cell Voltmeter –70 mV
Resting potential is caused by the cell membrane’s ability to maintain • a +ve charge on its OUTER surface • a -ve charge on its INNER (cytoplasmic) surface Plasma membrane Microelectrode inside cell Axon Neuron Microelectrode outside cell Voltmeter –70 mV
Resting potential is generated and maintained with help from • Active transport • Sodium-potassium pumps Pump 2K+ into the cell and 3Na+ out of the cell OUTSIDE OF CELL Na+ Na+ channel Na+ Na+ Na+ Na K + + K + Na+ Na+ Na+ Na+ Na+ K + Plasma membrane Protein Na+ K + K + K + K + K + K + K + K + K + K + Na+ - K + pump Na+ Na+ K + channel INSIDE OF CELL
OUTSIDE OF CELL Na+ Na+ channel Na+ Na+ Na+ Na K + + K + Na+ Na+ Na+ Na+ Na+ K + Plasma membrane Protein Na+ K + K + K + K + K + K + K + K + K + K + Na+ - K + pump Na+ Na+ K + channel INSIDE OF CELL Passive transport (diffusion) • Passive ions channels (Na+ and K+ )
During resting potential: • Sodium-potassium pump • Pump Na+ out and K+ in actively • Passive ions channels • Allows more K+ out than Na + in passively • Voltage-gated ions channels CLOSED OUTSIDE OF CELL Na+ Na+ channel Na+ Na+ Na+ Na K + + K + Na+ Na+ Na+ Na+ Na+ K + Plasma membrane Protein Na+ K + K + K + K + K + K + K + K + K + K + Na+ - K + pump Na+ Na+ K + channel INSIDE OF CELL
• An action potential or impulse is a sequence of rapidly occurring events that changes the membrane potential and then eventually restoring it to the resting state. • Membrane potential of neuron changes in response to a variety of stimuli. Action Potential
Where does Action Potential arise? • At the trigger zone- the junction of the axon hillock and the initial segment. • Then propagates along the axon to the axon terminals.
Gated Ion Channels • Voltage-gated ion channels are found in axons & open or close when the membrane potential changes. • Voltage-gated Potassium Channels • Voltage-gated Sodium Channels
Action Potential • Changes in the membrane potential resulting from ion movement through voltage-gated ion channels • Na+ /K+ pumps and passive ion channels stop operating • Only the voltage-gated ion channels are operating
Action potential involves: Depolarization Repolarization Hyperpolarization
Resting state: voltage gated Na+ and K+ channels closed; resting potential is maintained. 1 2 3 4 A stimulus opens some Na+ channels; if threshold is reached, action potential is triggered. Additional Na+ channels open, K + channels are closed; interior of cell becomes more positive. 5 The K+ channels close relatively slowly, causing a brief undershoot. Na+ channels close and inactivate. K+ channels open, and K+ rushes out; interior of cell more negative than outside. Neuron interior Action potential Threshold potential Resting potential 1 2 3 4 5 Na+ Na+ Na+ Na+ 1 Return to resting state. 1 Neuron interior K + K +
c) Explain generation of action potentials along the membrane of axon (C3)
All-or-nothing event d) Describe the characteristic of nerve impulse along the membrane of axon (C2) Impulse is either generated or not If stimulus is weak, depolarization occur; but still below the threshold level, no impulse can be generated If stimulus is strong enough; depolarization occur & reach threshold level; impulse is generated The intensity of stimulus does not affect the “size” of the impulse Once impulse is generated, a stronger stimulus won’t increase the size of impulse
2. Refractory period d) Describe the characteristic of nerve impulse along the membrane of axon (C2) A recovery phase for axon that had just transmit impulse A time delay before next action potential can be generated Impulse travels one-way along axon from the excitable region to the resting region next to it. This is controlled by refractory period; a period immediately following a response to stimulation during which a cell or organ is unresponsive to further stimulation. (Campbell 12th,page G-28) 2 phases Absolute refractory period The axon membrane cannot transmit another action potential at the same time. Relative refractory period During this period, a new action potential can be produced if the stimulus is above the threshold level
Larger-diameter axons propagate action potentials faster than smaller ones due to their large surface areas. 2. Diameter of axon 1. Presence of myelin sheath The action potential will ‘jump’ from one node of Ranvier to another Saltatory Conduction Speed of Conduction Faster conduction of impulse
Larger-diameter axons propagate action potentials faster than smaller ones due to their large surface areas. 4. Number of synapse involved 3. Temperature Axons propagate action potentials at lower speeds when cooled. Speed of Conduction
SYNAPSE • The junction where a neuron communicates with another cell across a narrow gap via a neurotransmitter or an electrical coupling. (Campbell 12th, page G-32) e) Describe the structure of synapse (C2)
• Synaptic knob • Enlargement of the terminal end of the axon • Contains: • Synaptic vesicles • Mitochondria • Synaptic cleft • A gap between the presynaptic neuron and the postsynaptic neuron • About 20nm-50nm width Structure of synapse
• Presynaptic neuron • A nerve cell that carries a nerve impulse towards a synapse. • Postsynaptic neuron • A nerve cell that carries a nerve impulse away from a synapse/ to an effector cell that responds to the impulse at the synapse.
Ligand-gated channels • Found on the postsynaptic membrane. • Have receptors for the neurotransmitter. • Allow the movement of ions into the postsynaptic neurons.
Mechanism of Synaptic Transmission f) Explain transmission of impulse at synapse (C3)
The Mechanism of Cocaine Action at Synapse g) Differentiate transmission of impulse along the axon and across the synapse (C3)
The Mechanism of Cocaine Action at Synapse h) Explain the mechanism of cocaine action at synapse (C3)
i) Describe nervous system disorders in relation to dopamine (C2)
Excess of dopamine Lack of dopamine Schizophrenia Parkinson’s disease 1. Schizophrenia is a severe mental disturbance characterized by psychotic episodes in which patients have a distorted perception of reality. 2. Schizophrenia is caused by disruptions in the neural pathway that use dopamine as a neurotransmitter. 3. Dopamine – dependent brain regions might become overactive & release excessive amount of dopamine. 4. Excess of dopamine is responsible for schizophrenic symptoms such as hallucinations & delusions. (Biology Campbell 12th, page 1160) 1. Parkinson’s disease is a neuron disorder including muscle tremors, poor balance, flexed posture and shuffling gait. 2. It is a progressive brain illness 3. Involve the death of neuron in the midbrain called substantia nigra that normally release dopamine at synapse. 4. The degeneration of dopamine releasing neurons will cause less dopamine release. 5. Thus, it leads to Parkinson’s disease. (Campbell 12th , page 1162)
a) Describe the structure of neuromuscular junction (C2) b) Explain transmission of impulse at the neuromuscular junction (C3) c) Describe the structure of sarcomere (C2) d) Explain the mechanism of muscle contraction based on Sliding-filament theory (C3) OBJECTIVES: W i l l b e d i s c u s s e d d u r i n g t u t o r i a l W i l l b e d i s c u s s e d d u r i n g t u t o r i a l
A synapse between terminal ends of motor neurons with skeletal muscle or smooth muscle. i.e. the synapse occurs between the “synaptic terminal” of the motor neuron and “motor end plate” of muscle fiber. a) Describe the structure of neuromuscular junction (C2)
Between synaptic terminal of motor neuron and motor end plate of muscle fiber NEUROMUSCULAR JUNCTION • Composed of three parts: • Synaptic terminal • Motor end plate • Synaptic cleft
NEUROMUSCULAR JUNCTION: STRUCTURE
NEUROMUSCULAR JUNCTION: IMPULSE TRANSMISSION b) Explain transmission of impulse at the neuromuscular junction (C3)
Muscle tissue consists of several bundles of muscle fibres one muscle fibre consist of groups of myofibrils that have repetitive unit called sarcomere c) Describe the structure of sarcomere (C2)
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Sarcomere Sarcolemma Sarcoplasm Sarcoplasmic reticulum Transverse tubules (T-tubules) STRUCTURE OF MUSCLE FIBER
Sarcoplasm * * * *Contain in Sarcoplasm STRUCTURE OF MUSCLE FIBER
STRUCTURE OF SARCOMERE
Basic unit of the myofibrils between two Z lines Consist of thin and thick filaments STRUCTURE OF SARCOMERE
Thin filaments contain • Actin • troponin • tropomyosin Thick filaments (myosin) • myosin head provide binding site for ATPase
STRUCTURE OF SARCOMERE