Integration of Signals - Lecture 4

Lecture 4: Integration of Signals

• This lecture covers the integration of signals in the nervous system
• Chemical synapses are points of interaction in the nervous system, transmitting electrical signals between cells
• Chemical synapses use neurotransmitters (NTs) released from presynaptic neurons to bind to receptors on postsynaptic neurons
• Two types of synapses exist
• Presynaptic neurons send signals toward a synapse
• Postsynaptic neurons transmit signals away from a synapse
• The nervous system uses summation of graded potentials to trigger action potentials
• Types of summation are temporal and spatial
• Temporal summation is when a presynaptic neuron fires repeatedly at high rates
• Spatial summation is when multiple presynaptic neurons fire at the same time, creating a larger change in membrane potential
• Graded potentials can be excitatory or inhibitory, affecting the likelihood of reaching threshold for an action potential at the axon hillock
• Spinal reflexes are simple behaviors produced by the central nervous system pathways entirely in the spinal cord
• A reflex arc involves five components: receptor, sensory neuron, integration center, motor neuron, and effector
• Examples given for a reflex action are the patellar tendon reflex (also known as the knee-jerk reflex)
• Extension is the straightening of a joint, while flexion is bending the joint
• Homeostasis is the maintenance of a relatively constant internal environment in the body
• Homeostasis is a dynamic process involving mechanisms to regulate body temperature, volume, and composition
• Negative feedback is a common control system in the body, responding to deviations from set points by initiating changes in the opposite direction
• Excitatory postsynaptic potentials (EPSPs) increase the likelihood of an action potential
• Inhibitory postsynaptic potentials (IPSPs) decrease the likelihood of an action potential
• Homeostatic control reflex systems maintain body temperature when there are changes in room temperature

Types of neurons

• Three types of neurons are present in the nervous system
• Sensory neurons carry signals from sensory receptors to the central nervous system
• Motor neurons carry signals to effector cells to determine an appropriate effector response
• Interneurons play a role integrating information within the central nervous system and connecting to motor neurons. They process signals such as emotions, learning, and memory

Neuronal circuits

• Divergence
• Information from a single neuron to multiple neurons. A mechanism for spreading signals to multiple neurons in the CNS
• Convergence
• Several neurons synapse with a single postsynaptic neuron. A mechanism for providing input to a single neuron from multiple sources

Chemical Messengers

• Neurotransmitters bind to receptors on postsynaptic neurons to trigger a response.
• Autocrine substances affect the same cell that makes them
• Paracrine substances affect cells near the source
• Hormones travel through the blood to distant target cells in the body

Termination of neurotransmitter Effects

• Neurotransmitters are removed from the synaptic cleft
• Enzymes inactivate neurotransmitters
• Neurotransmitters are reabsorbed into presynaptic terminals or transported into glial cells

Basic Concepts in Biomedical Sciences I

• Chapter 2, Homeostasis, pages 8-13 are suggested reading for further study