Lecture 7 - Neural control of movement (3).pptx

Neural control of movement SSBR 304 UKZN INSPIRING Neural control of movement UKZN INSPIRING Nervous system UKZN INSPIRING  CNS Brain: Cerebrum: The largest part of the brain. It controls thinking, memory, emotions, and voluntary movements. C...

Neural control of movement SSBR 304 UKZN INSPIRING Neural control of movement UKZN INSPIRING Nervous system UKZN INSPIRING  CNS Brain: Cerebrum: The largest part of the brain. It controls thinking, memory, emotions, and voluntary movements. Cerebellum: Located at the back of the brain. It coordinates muscle movements and maintains posture and balance. Brainstem: Connects the brain to the spinal cord. It controls automatic functions necessary for survival, such as breathing, heart rate, and blood pressure. Spinal Cord: A long, thin, tubular structure that runs from the brainstem down the back. It carries messages between the brain and the rest of the body. It also coordinates reflexes, which are quick, automatic responses to certain stimuli. UKZN INSPIRING  Anatomy of the neuron A neuron is a specialised cell in the nervous system that is responsible for transmitting information throughout the body. Dendrites: Receive signals from other neurons and convey this information to the cell body. Cell body: Contains the nucleus and other organelles; integrates incoming signals. Axon: Transmits electrical impulses away from the cell body to other neurons, muscles, or glands. Axon terminals: release neurotransmitters to communicate with other neurons, muscles, or glands. UKZN INSPIRING Neuron communication UKZN INSPIRING  Ion concentration in human fluids Ion Cytosol (Intracellular) Interstitial Fluid (Extracellular) Potassium (K+) High (~140 mM) Low (~4-5 mM) Sodium (Na+) Low (~10-15 mM) High (~135-145 mM) Chloride (Cl-) Low (~4-10 mM) High (~100-110 mM) Calcium (Ca2+) Very low (~0.0001 mM) Higher (~1-2 mM) Magnesium (Mg2+) Higher (~0.5-1.0 mM) Lower (~1-2 mM) Proteins (-) High Lower UKZN INSPIRING  Resting membrane potential The cell membrane of a neuron at rest has a negative electrical potential of about -70 mV. The imbalance in number of ions is known as the resting membrane potential. Neuron has high concentration of Na+ outside the cell and high K+ inside. Chemical gradient and electronic gradient across membrane produce electrochemical gradient. Cell leakage to K+ allows potassium out of the cytosol. Sodium-potassium pump: active transport, energy provided by ATP. 3 Na+ out; 2 K+ in. UKZN INSPIRING  The action potential An action potential is a rapid, temporary change in the electrical membrane potential of a neuron or muscle cell, which allows for the transmission of electrical signals along the cell. Depolarization Trigger: A stimulus causes the cell membrane to become less negative. If the stimulus is strong enough, it reaches the threshold potential (usually around -55 mV). Action: Voltage-gated sodium channels open, allowing an influx of Na+ ions to rush into the cell due to the electrochemical gradient. Result: The membrane potential becomes more positive, rising towards +30 mV. This phase is called depolarization. Repolarization Action: After a brief period, the voltage-gated sodium channels close, and voltage- gated potassium channels open. Effect: K+ ions exit the cell, restoring the negative charge inside the cell. Result: The membrane potential starts to return to its resting state. UKZN INSPIRING  The action potential Hyperpolarization Action: Potassium channels remain open slightly longer than needed to reach the resting potential, causing an overshoot. Result: The membrane potential becomes more negative than the resting membrane potential, known as hyperpolarization. UKZN INSPIRING  Synapse For a neuron to communicate with another neuron,  First an action potential must occur. Once the action potential occurs, it travels the full length of the axon, ultimately reaching the axon terminals.  How does the action potential move from the neuron in which it starts to another neuron?  Neurons communicate with each other across synapses.  A synapse is the site of action potential transmission from one neuron to another. UKZN INSPIRING  Synapse The neuron sending the action potential across the synapse is called the presynaptic neuron, so axon terminals are presynaptic terminals. Similarly, the neuron receiving the action potential on the opposite side of the synapse is called the postsynaptic neuron, and it has postsynaptic receptors. A narrow gap, the synaptic cleft, separates them. The presynaptic terminals of the axon contain a large number of saclike structures, called synaptic vesicles. These sacs contain neurotransmitter chemicals. When the impulse reaches the presynaptic axon terminals, the synaptic vesicles respond by dumping their chemicals. The neuromuscular junction is a specialised synapse where a motor neuron communicates with a muscle fiber to stimulate muscle contraction. UKZN INSPIRING