PET3322 Exam 2 Nervous System made up of nervous tissue with the main cell being a neuron The nervous system controls our behaviors memories and movements Functions Sensory senses changes both internally and externally via sensory receptors Also known as afferent Muscle Brain Integrative allows us the ability to analyze the sensory info received store aspects and make decisions Motor function response via movement in reaction to stimuli by initiating action Also known as efferent because it causes an EFFECT Brain Muscle A before E the sensory afferent neurons need to be stimulated first the impulse travels to the brain which analyzes it then the brain sends a signal to the motor efferent neurons to cause an effect such as muscle contraction Since the motion involves the brain it is NOT a reflex Two divisions of the Nervous System 1 Central Nervous System CNS consists of the brain and spinal cord Think Central like central part of the body so the brain and spinal cord are in the center 2 Peripheral Nervous System PNS consists of everything outside the CNS Consists of cranial and spinal nerves which contain both sensory and motor fibers Connects CNS to muscles glands and all sensory receptors Made up of 2 systems Autonomic Nervous System ANS controls internal organs Do not worry about Somatic Nervous System SNS control muscles connected to bone this division for exam 2 Two types of Neurons in the PNS 1 Sensory Neurons afferent Somatic fibers carry impulses from the skin skeletal muscles and joints to the brain Visceral fibers carry impulses from visceral organs to the brain organ brain 2 Motor Neurons efferent impulses are sent from the CNS to effector organs brain organ They produce an EFFECT Neurons cells for all Nervous System Functional unit of nervous system Single nucleus with prominent nucleolus Have capacity to produce action potentials electrical excitability signal There are two types of neurons as seen above sensory and motor Structure of a neuron We have everything in a neuron that we have in a cell because a neuron is a cell The difference is that the neuron has an axon and dendrites Dendrites receive chemical signals Axons contains plasma membrane and end in axon terminals Some contain myelin and some don t see below for more info Axon terminals release neurotransmitters to transmit electrical impulses that travelled down the axon Soma the body where all the organelles are located has a receptive or input region contains receptors that receives the stimulus connected to dendrites produces neurotransmitters and electrical impulses Action potential the signal that will propagate through the dendrites or soma down the axon to the axon terminal can travel long distances Example he gave in class think of baseball the player is the receptor the ball is the neurotransmitter and the pitcher is the axon terminal Neurotransmitters transmit the neural impulses released from the axon terminals when the soma is stimulated Myelinated and Unmyelinated Axons Myelin is a whitish lipid fat found on some axons that increases the speed of nerve impulses conduction from the soma to the axon terminal Myelin does not cover the entire axon see picture of neuron above Unmyelinated axons have slower nerve conduction Another factor that determines the rate of nerve conduction is the diameter of the axon The larger the diameter the faster the impulse so the fastest nerve impulse would be one where the axon was wide and myelinated Distribution of Gray and White Matter White matter primarily made up of myelinated axons this makes sense because myelin is made of whitish fat giving it the white color Found in the inside of the brain and the outside of the spinal cord Gray matter made up of neuronal cell bodies somas dendrites unmyelinated axon and axon terminals Soma is more dense therefore it makes up the gray matter Found in the cortex of the brain and the inside of the spinal cord In the gray matter we will find the somas of the motor neurons Neurons Communicate with Other Cells Neurons are electrically excitable due to the voltage difference across their membrane Communicate with 2 types of electric signals action potentials that can travel long distances In living cells a flow of ions occurs through ion channels in the cell membrane Types of Ion Channels excitability Na diffuses into the cell 1 Ligand gated channels open and close in response to a stimulus These result in neuron Think of the example given in class of a parking lot The car Na trying to get through the gate needs a key neurotransmitter Acetylcholine The box that reads the card receptor and opens allows the car to move through the gate when the key activates it The gate can be opened instantly when the key opens it the key doesn t need to stay in the box 2 Voltage gated channel responds by opening to a direct change in the membrane potential Resting Membrane Potential Negative ions on the inside and positive ions along the outside of the cell is the resting membrane potential usually around 70 mV Resting potential exists in a cell because the concentration of ions is different inside and outside Na and Cl on outside K on the inside The membrane permeability differs for Na and K 50 100 times greater permeability for K Therefore the flow of Na to the inside of the cell can t keep up with the outward flow of K The Sodium Potassium pump removes Na as soon as it leaks in Action Potentials This section will be really important so understand depolarizing repolarizing and hyperpolarizing phase Action Potential a nerve impulse that triggers a neurotransmitter and will cause the INSIDE of the cell to become more positive but then the cell will continue to get more negative until the resting membrane potential is restored What happens during an action potential is the voltage gated Na and K channels open in sequence If a stimulus reaches threshold the action potential is always the same A stronger stimulus will NOT cause a larger impulse Depolarizing Phase During this phase Repolarizing Phase During this phase The neurotransmitter opens the Na activation gates of the channel which allows the Na to go into the cell and cause DEPOLARIZATION The inside of the cell becomes LESS negative and causes the potential to become more positive than the threshold 55mV If threshold isn t reached an action potential will NOT occur Positive Feedback Process The inside of the cell becomes negative again in this phase The positivity of the cell 30mV causes
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