Nervous System Part IV PDF

Organisation of Nervous System Part IV Mohamad Razif bin Othman PRH 1016 Previously In Part III Spinal cord 1 Spinal and cranial nerves 2 Somatic vs Autonomic 3 Action potential 4 Transmission along axon 5  LEARNING OUTCOME 6 Describe the...

Organisation of Nervous System Part IV Mohamad Razif bin Othman PRH 1016 Previously In Part III Spinal cord 1 Spinal and cranial nerves 2 Somatic vs Autonomic 3 Action potential 4 Transmission along axon 5  LEARNING OUTCOME 6 Describe the process of synapse List and name neurotransmitters and their function. Compare the transmission of impulse at the synapse and along the axon Disease of the brain  Synapse Nerve impulses travel from one neuron to another across a small space that separates them-this juncture is called a synapse Synapse is junction between: i. Two neurons ii. Neuron & effector iii. Sensory receptor & sensory neuron Synaptic knob is a tiny bulge at the end of a terminal branch of a presynaptic neuron’s axon that contains vesicles housing neurotransmitters. Synaptic cleft is space between a synaptic knob and the plasma membrane of a postsynaptic neuron  Synapse An action potential cannot cross the synaptic cleft between neurons, and instead the nerve impulse is carried by chemicals called neurotransmitters. These chemicals are made by the cell that is sending the impulse (the pre-synaptic neuron) and stored in synaptic vesicles at the end of the axon. The cell that is receiving the nerve impulse (the post- synaptic neuron) has chemical-gated ion channels in its membrane, called neuroreceptors. These have specific binding sites for the neurotransmitters  Synapse: How it happens? 1. At the end of the pre-synaptic neuron there are voltage-gated calcium channels. When an action potential reaches the synapse these channels open, causing calcium ions to flow into the cell. 2. These calcium ions cause the synaptic vesicles to fuse with the cell membrane, releasing their contents (the neurotransmitter chemicals) by exocytosis. 3. The neurotransmitters diffuse across the synaptic cleft. 4. The neurotransmitter binds to the neuroreceptors in the post-synaptic membrane, causing the channels to open. In the example shown these are sodium channels, so sodium ions flow in.  Synapse: How it happens? 5. This causes a depolarisation of the post-synaptic cell membrane, which may initiate an action potential 6. The neurotransmitter is broken down by a specific enzyme in the synaptic cleft; for example the enzyme acetylcholinesterase breaks down the neurotransmitter acetylcholine. 7. The breakdown products are absorbed by the pre-synaptic neuron by endocytosis and used to re-synthesis more neurotransmitter, using energy from the mitochondria. This stops the synapse being permanently on. Neurotransmitters Neurotransmitters  Effects of drugs on synapse In normal synapse excess dopamine in synaptic cleft is sent back to presynaptic neuron by dopamine transporter via endocytosis​ Cocaine attaches to the dopamine transporter and blocks endocytosis in the pre-synaptic neuron. As long as cocaine occupies the transporter, dopamine cannot re-enter the neuron.  Effects of drugs on synapse It builds up in the synapse and extended firing of the postsynaptic neurons will affect the drug user with euphoria, increased energy, arousal, and stimulation. The reward circuit eventually adapts to the excess of dopamine caused by cocaine, and becomes less sensitive to it. As a result, people take stronger and more frequent doses in an attempt to feel the same high Researchers have found that cocaine may speed up the aging of the brain. People who are addicted to the drug lose twice the brain volume (grey matter) each year as compared to non-drug users. Comparison between transmission of impulse along the axon and at the synapse Comparison between transmission of impulse along the axon and at the synapse  17 Disease of the brain The four common diseases of the brain: 1. Alzheimer’s Disease 2. Parkinson Disease 3. Multiple Sclerosis 4. Epilepsy  Alzheimer’s Disease Progressive loss of mental function – loss of memory and confusion in older individuals Not-life threatening but result in dramatic changes Symptoms start slowly - forgetfulness, irritability, lack of initiative Overtime, may not remember recent events and may be unable to recognize own children Cause unknown, probably brain damage caused by protein known as beta-amyloid- binds to nerve cells causing cell death  Multiple Sclerosis Caused by a destruction of myelin sheaths of nerve cells in the CNS Damaged myelin results in nerve cell death that lead to numbness, slurred speech and paralysis Symptoms include numb, temporary weakness, blurred vision, slurred speech and difficulty controlling urination Disease treatable but incurable, only a small number are crippled by the disease  Epilepsy Epilepsy is a brain disorder in which the patient experiences repeated, unpredictable seizures, or episodes of disturbed brain activity that cause changes in attention or behaviour. Epilepsy may be a result of a medical condition or brain injury or an unknown cause. Seizures due to a tumour, stroke, abnormal blood vessels or bleeding in the brain may be surgically treated. For other patients, medication to prevent seizures, called anticonvulsants, may reduce the number of seizures experiences.  Parkinson’s Disease Is a neurological disorder caused by a lack of dopamine in certain region of brain Caused by progressive deterioration of certain brain centres that control movement, especially semioutomatic movements such as swinging the arms when walking Characterised by tremors- hands and head (sometimes both) shake involuntarily Tremors disappear of decrease – if the disease worsens, symptoms worsen and it becomes difficult to write and walk. Patients treated by drugs- one is known as levodopa but effects may diminish after years of usage Finally. End of nervous system