Exam II Study Guide PET3322 Anatomy Physiology 1 Dr Arturo Figueroa Chapter 11 The Nervous System Functions of the nervous system o Sensory function to sense changes in internal and external environment through sensory receptors o Integration analyze the sensory information store some aspects and make decisions regarding appropriate behaviors o Motor function respond to the stimuli by initiating action The nervous sytem can be divided into two major separate parts 1 Central Nervous System a Consists of the brain and spinal cord 2 Peripheral Nervous System a Consists of cranial and spinal nerves that contain both motor and sensory fibers Connects the CNS to glands and all sensory receptors The peripheral nervous system can be divided into a sensory component and a motor component somatic fibers receive sensory impulses from skin skeletal o Sensory afferent muscles and joints to the brain Visceral fibers do the same thing but send signals from visceral organs to the brain o Motor efferent sends motor impulses from the CNS to effector organs This is also divided into two sections 1 Somatic The portion of the peripheral nervous system consisting of somatic sensory afferent neurons and somatic motor efferent neurons skin skeletal muscle etc 2 Autonomic Visceral sensory afferent and visceral motor efferent neurons So named because this part of the nervous system was thought to be self governing or spontaneous cardiac muscle NEURONS The basic cell unit of the nervous system they have the ability to send signals in the form of electric potential most neurons have 3 main parts 1 Cell body nucleus of the cell 2 Dendrites processes extending from the cell body that receive electrical signals from other neurons 3 Axon single long process that extends the opposite direction of dendrites Send electrical signals along to other neurons These three parts comprise the main functions of the neuron Other important parts include o Axon terminal the branching off of the axon into many fine processes o Axon hillock cone shaped elevation on the axon where it joins the cell body FLOW OF INFORMATION THROUGH A NEURON dendrites cell body axon axon terminals Sometimes neurons are coated in a white fatty sheath called myelin to increase the speed of a nerve impulse o Neurons can be myelinated by special cells in the nervous system called schwann cells White matter myelinated cells Grey matter unmyelinated cells cell bodies axon terminals ACTION POTENTIAL o An action potential AP or nerve impulse is a sequence of rapidly occurring events that decrease and eventually reverse the membrane potential depolarizing phase and then restore it to the resting state repolarizing phase So how do these electrical signals between neurons work o Neurons are excitable due to the voltage difference across their membrane o Chemical messengers called neurotransmitters kick start the process Before we understand action potentials we must understand the two types of ion channels that allow for the change in electric potential 1 Ligand gated channels neurotransmitter or other chemical stimulus binds to 2 Voltage gated channels change in membrane potential causes the channel to be channel and opens it opened In order to best understand how an action potential works it is easiest to break it down into a few steps 1 Resting Membrane Potential negative ions inside of cell and positive ions outside of cell potential exists b c the concentration of ions is different inside and outside a The resting membrane potential of a cell is 70 mV b Membrane permeability is different for Na and K 2 Depolarizing phase chemical or mechanical stimulus causes a potential to reach the threshold 55 mV a Voltage gated sodium channels open and Na rushes into the cell changing the membrane potential b These channels close after a few thousandths of a second 3 Repolarizing phase K channels open when Na channels have already closed K rushes out of the cell returning the cell potential to 70 mV 4 Hyperpolarizing phase sometimes so much K leaves the cell that it becomes hyperpolarized However once the K gate closes the cell will return back to resting membrane potential SYNAPSES A synapse is a functional junction between neurons There are two types only one which we will really cover 1 Chemical 2 Electrical don t worry about Post synaptic neurons on are on the receiving end of the electrical signal while pre synaptic neurons are the ones sending the signal Chemical synapses conduct one way information transfer from a pre synaptic neuron to a post synaptic neuron Axodendritic from axon to dendrite Axosomatic from axon to cell body The action potential reaches the end of the axon and opens voltage gated Ca 2 channel This inward flow of calcium triggers the release of a neurotransmitter which crosses the synaptic cleft and binds to ligand gated receptors in the next neuron o The more neurotransmitter released the greater the change in action potential in the neighboring cell and the more likely threshold will be reached Termination of NTs effects NTs bound to a post synaptic neuron produce a constant post synaptic effect They must be removed from the receptor in order to terminate these effects o NTs can be removed in two ways 1 Degraded by enzymes 2 Diffused from synaptic cleft 3 Uptake by glial cells NTs and their Affects Neurotransmitters can be excitatory or inhibitory o Excitatory results from the opening of ligand gated Na channels o Inhibitory results from opening of ligand gated Cl or K channels Causes the post synaptic cell to become more negative or hyperpolarized This makes the post synaptic cell less likely to reach threshold Chapter 12 The Central Nervous System As stated earlier the CNS is made up the brain and spinal cord Pain o Their job is to integrate sensory information and cause a certain response based on the information Axons of different neurons travel together in bunches These are called tracts CNS or nerves PNS The Process of Sensation Four events typically involved when a sensation happens o A sensory receptor is stimulated o The sensory receptor transduces the sensory stimulus creating a potential in response to a specific type of stimuli o The sensory neuron creates one or more nerve impulses which travel toward the CNS o integration of the sensory input occurs in specific regions of the CNS Pain sensations are how we naturally learn something is harmful It serves as a protective function Receptors for pain are called nociceptors They
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