Transmission at Chemical Synapses: From Action Potentials to Ion Channels and Receptors, Slides of Psychology

Download Transmission at Chemical Synapses: From Action Potentials to Ion Channels and Receptors and more Slides Psychology in PDF only on Docsity! 3 The Sequence of Transmission Processes at Chemical Synapses The sequence of transmission: 1. Action potential travels down the axon to the axon terminal. 2. Voltage-gated calcium channels open and calcium ions (Ca2+) enter. 3. Synaptic vesicles fuse with membrane and release transmitter into the cleft. Docsity.com 3 The Sequence of Transmission Processes at Chemical Synapses 4. Transmitters bind to postsynaptic receptors – cause an EPSP or IPSP. 5. EPSPs or IPSPs spread toward the postsynaptic axon hillock. 6. Transmitter is inactivated or removed – action is brief. 7. Transmitter may be bound by presynaptic autoreceptors, decreasing release. Docsity.com 3 The Sequence of Transmission Processes at Chemical Synapses Ligands fit receptors and activate or block them: • Endogenous ligands – neurotransmitters and hormones • Exogenous ligands – drugs and toxins from outside the body Docsity.com 3 The Sequence of Transmission Processes at Chemical Synapses A synapse that uses acetylcholine (ACh) has recognition sites for ACh within the receptor molecules in the postsynaptic membrane. ACh can be excitatory, and open channels for Na+ and K+, or inhibitory, and open channels for Cl-. Docsity.com Figure 3.12 A Nicotinic Acetylcholine Receptor Intracellular space 5nm gical Psychology 5e, Figure 3.12 ©2007 Sinai acai com 3 The Sequence of Transmission Processes at Chemical Synapses Receptors control ion channels in two ways: Ionotropic receptors open when bound by a transmitter (also called a ligand- gated ion channel). Metabotropic receptors recognize the transmitter but instead activate G proteins. Docsity.com Figure 3.13 Two Types of Chemical Synapses (Part 1) Docsity.com 3 The Sequence of Transmission Processes at Chemical Synapses G proteins, or first messengers, sometimes open channels or may activate another chemical to affect ion channels. The chemical is known as the second messenger – it amplifies the effects of the G protein and may lead to changes in membrane potential. Docsity.com 3 The Sequence of Transmission Processes at Chemical Synapses • Reuptake – transmitter is taken up into the presynaptic cell Pinocytosis is the process of repackaging transmitter into vesicles. Transporters are special presynaptic receptors involved in reuptake. Docsity.com 3 The Sequence of Transmission Processes at Chemical Synapses Types of synapses: Axo-dendritic – axon terminal synapses on a dendrite Axo-axonic - between two axons Dendro-dendritic – between two dendrites Retrograde – uses gas to signal presynaptic cell to release transmitter Docsity.com 3 The Sequence of Transmission Processes at Chemical Synapses Ectopic transmission occurs outside of conventional synapses. Varicosities are axonal swellings where transmitter may diffuse out. These nondirected synapses release transmitter steadily to broad areas. Docsity.com Figure 3.14 The Knee Jerk Reflex (Part 1) Quadriceps muscle ~ Stimulus Patellar (B.. Psychology 5e, Figure 3.14 (Part 1) ©2007 Shaye seri tom Figure 3.14 The Knee Jerk Reflex (Part 2) Muscle stretch —| receptor “Ar Action potential Trigger zone Initial segment of sensory neuron Unipolar sensory cell body Synapse Axon terminal Postsynaptic potential Motor neuron cell ynaplic p body in ventral horn Axon hillock Trigger zone Action potentials Muscle fiber \ AN gical Psychology 5e, Figure 3.14 (Part 2) ©2007 Shaye seri tom 3 Neurons and Synapses Combine to Make Circuits The visual system is a circuit with other features: Convergence – many cells send signals to one cell Divergence – one cell send signals to many cells Units are arranged in parallel, and have lateral interaction across units. Docsity.com 3 Gross Electrical Activity of the Human Brain An encephalogram (EEG) is a recording of brain potentials, or brain waves. Brain potentials indicate sleep states and provide data in seizure disorders. Docsity.com Figure 3.16 Gross Potentials of the Human Nervous System (Part 1) Docsity.com 3 Gross Electrical Activity of the Human Brain In the normal brain, activity tends to be desynchronized across regions. A symptom of epilepsy is seizure – a synchronization of electrical activity in the brain. The brain wave pattern during seizure is described as epileptiform activity. Docsity.com 3 Gross Electrical Activity of the Human Brain Petit mal seizure – brain waves show patterns of seizure activity for 5 to 15 seconds, can be several times a day No unusual muscle activity, except for stopping and staring Events during seizure are not remembered. Docsity.com Box 3.3 (B) Seizure Disorders LF - left frontal RF - right frontal LT - left temporal RT - right temporal LO - left occipital RO - right occipital Docsity.com 3 Gross Electrical Activity of the Human Brain Complex partial seizures – do not involve entire brain Aura – unusual sensation that may precede a seizure Kindling – experimentally inducing a seizure by repeatedly stimulating a brain region Docsity.com