The Nervous System A. The Divisions: 1) The Central Nervous System includes the and. The brain contains billions of nerve cells called, and trillions of support cells called. 2) The Peripheral Nervous System includes the of the body. Made up of 2 parts: A) Somatic Nervous System carries signals to muscles in response to stimuli. These are actions. B) Autonomic Nervous System- carries signals to and muscles in response to stimuli. These are actions such as rate and contractions in the to churn the food. B. The Components: 1) Nerve Cells Neurons are the cells of the body and are specialized to carry messages through an process. A neuron consists of many tiny extensions called which receive signals, a large containing the nucleus and organelles, and one elongated projection called an which conveys the nerve impulse. *The is right before the axon and is where the nerve impulse is generated. At the end of the axon there are branches with specialized endings called terminals / terminal / terminal that release chemical messengers called to other cells. The gap between the synaptic terminal and another cell is called the.
2) Support Cells Many axons are enclosed in an insulating layer called the sheath or just myelin. These layers are mostly which act as a poor conductor, but great for electrical insulation so it helps to the speed of the nerve impulse. This myelin sheath is made by / support cells and comes in 2 varieties: A) Schwann cells- this is the myelin sheath of the. They have between them called the of. B) Oligodendrocytes- this is the myelin sheath of the. Q: What disorder causes the myelin sheath to break down leading to a loss of coordination due to disrupted nerve impulses? 3) The 3 Classes of Neurons (All with very different shapes) #1) neurons communicate information about both the and world to the spinal cord and brain (CNS). For example, your / photoreceptors visually sense the world around you. Most sensory neurons make a connection at their synapse to. *Sensory neurons are also called neurons. #2) take sensory input and transmit that message to neurons. Note: not all nerve impulses require an interneuron.
*Found entirely in the matter of the spine and brain. #3) neurons now transmit impulses in the direction, away from the brain and spinal cord to cells. *Motor neurons are also called neurons. C. Nerves: A nerve is a group of bundled together like the strands of a cable. Because nerves usually have a white colored myelin sheath around them, nerves are called matter. Gray matter gets its color/name from, bodies, and axons. D. Reflex Arcs: The neural circuits involve just a neuron to a neuron s (note: no interneuron). This leads to an automatic response called a. A good example of a reflex is the reflex. *A is a group of nerve located in the and near to the cord. Ganglia enable the nervous system to carry out an without having to involve the entire system / freeing the to focus on more complex problems. 3 Types of Neural Circuits / Pathways #1) Takes information from a source. Ex: eye brain. #2) Takes information from neurons that all converge at one neuron. Ex: vision + touch + hearing identify an object. #3) Takes information from one neuron to others then back to its source, so a path. Ex: Memories are processed this way then stored at their source. E. The Nerve Impulse: Much of what we know of how axons work comes from experiments using the giant axons of.
Recall that all cells have an electrical charge difference inside and outside of their cells. The overall charge on the inside of a cell is due mostly to [A - ] like some proteins, sulfate (SO 4 2- ), and phosphate (PO 4 3- ). However, also inside the cell are positive ions like. The outside of the cell is due mostly to the presence of ions. However, also outside the cell are negative ions like. This in voltage between the inside and outside of a cell is called the. All cells have membrane potentials, but only and cells can their membrane potential s voltage. They are cells that have special channels that let ions enter or leave called channels. The Resting Potential When a neuron is not sending a signal, it is said to be and the inside of the neuron is negative relative to the outside. The membrane potential is at mv. The Action Potential channels open, letting lots of positively charged Na + into the. This causes the inside of the axon to get more and is called. If depolarization is large enough, meaning enough Na + enter the axon and gets above the value of mv, this generates an also called a nerve
along the entire length of the axon. This is an event and travels in direction only. After a few, the neuron will return to its resting state (-70mV) and it is ready to receive another depolarization. If a depolarization trigger arrived before the neuron returned to this state, no action potential would be generated. The time required between action potentials is called the period. Q: How does the nervous system distinguish strong stimuli from weak? Recall a nerve impulse is an all-or-none event where of the action potential is always the same mv. But strong stimuli have a greater of action potentials firing one after another. F. The Traveling Action Potential: A neuron first gets stimulated at the dendrites and cell body leading to the action potential along the axon. The action potential does actually travel, but gets along each sequence of the axon.
Q: What affects the speed of an action potential? 1) Diameter of Axon- The the axon, the it travels. This is similar to the flow of electricity being proportional to the cross-sectional of a wire. 2) Saltatory Conduction (saltatory = to )- If the axon is myelinated, the myelin is covering all parts of the axon due to the Nodes of. So the nerve impulse from node to node. G. The Synapse: The synapse is the gap junction between either A) neurons or B) a neuron and the it controls. The transmitting cell is called the cell, the receiving cell is called the cell. There are 2 types of synapses: and synapses. Electrical signals in the synapse are more, with no loss of signal strength however they are -i.e. the brains of use
electrical synapses to escape predators. Chemical signals are much more and is described below. The Chemical Signal: #1) An electrical impulse arrives at the end of the axon in the cell. #2) is then triggered to enter into the end of the axon. #3) Sacs called then form that are filled with. A neurotransmitter is any substance that is released as a messenger in the. #4) The synaptic vesicles then fuse with the presynaptic membrane neurotransmitters into the synapse. #5) Neurotransmitters then bind to specific channels of the cell the ion channels. Neurotransmitters act like to open the ion channels. #6) Specific ions in the synapse such as then may cross into the postsynaptic cell. If the voltage can get above the threshold ( ), another action potential can fire in the synaptic cell. #7) The neurotransmitters quickly get broken down by and the ion channel. For example, the neurotransmitter gets quickly broken down by the enzyme. H. Neural Integration: One postsynaptic neuron may receive thousands of signals at its and cell body. Some signals will the postsynaptic cell by allowing Na + and K + to enter the cell pushing the cell towards. Others will the postsynaptic cell by allowing either K + to exit or Cl - to enter the cell pushing the cell towards or the undershoot. It is the / combined effect of all the ions that enter here that the postsynaptic neuron measures. The part of the postsynaptic neuron that measures the combined effect is called the. Therefore, synapses close to the axon hillock have a effect. If enough excitatory postsynaptic potentials outweigh the inhibitory postsynaptic potentials, the axon hillock opens the gated channels along the axon and an action potential is fired.
Two ways to enable the action potential to fire: and summation. Two ways to disable the action potential: and. I. Neurotransmitters: The same neurotransmitter can have different effects on different cells. This is seen with the most common neurotransmitter,. For example, we saw before it can cause a skeletal muscle cell to and a heart muscle to. Other common neurotransmitters are epi/norepi, which we already know also function as as well. is widespread in the brain and generally speaking is used to. While makes one sleepy.
disease is a lack of dopamine. While is an excess of dopamine. Drugs like produce their hallucinatory effects by binding to the dopamine and serotonin receptors in the brain. is the neurotransmitter for perceiving pain (like the local regulator ), while block pain. is a common inhibitory neurotransmitter that lets in the ion to the post-synaptic cell. In addition, some neurotransmitters are like (nitric oxide) and (carbon monoxide) which act on smooth muscle. J. Invertebrate Nervous Systems: Most animals have a nervous system. Cnidarians like hydra, have nerves that branch throughout the body called a. They have no distinction between the CNS and PNS, impulses are electrical, and travel in directions. Echinoderms like sea stars have a nerve that extends through each arm. This arrangement allows movement regardless of which arm is leading and stimulates the use of during feeding. Many animals have their nerves primarily in the of their body, this is called. Some animals have many neural structures near the -region, this is called. This is because the head will most likely encounter and/or threatening stimulus first. Usually this concentration of neural structures near the head forms a in animals, with a cord extending longitudinally throughout the body. K. Vertebrate Nervous System: 1) Central Nervous System-
Vertebrate nervous systems are both ized and ized. All vertebrates belong to the phylum. This means that at some point during development vertebrates had a hollow cord which later becomes the cord and brain + a flexible, thin rod called the which later becomes the. Note: chordates also all had slits / also called arches in development + a postanal + webbed and toes. The fluid of the spine is called the fluid. It brings nutrients, hormones, and WBC s to different parts of the brain and acts as a absorber to cushion the brain inside the skull. Also protecting the brain and spinal cord are layers of tissues called. Q: What is bacterial meningitis? 2) Peripheral Nervous System- There are 2 types of nerves, nerves that come off the brain and nerves that come off the spine. Most contain both sensory and motor neurons, but some cranial nerves just contain (i.e. the eye and nose). Also, or cell cluster near the. Recall that the motor neurons have both (involuntary) nervous systems (smooth and cardiac muscle) and (voluntary) nervous systems (skeletal muscle). The nervous system is further divided into 2 divisions: A. Parasympathetic- Autonomic nerve activities that or energy, i.e. down the heart rate. B. Sympathetic- Autonomic nerve activities that energy, i.e. the heart rate.
L. Brain Regions: The vertebrate brain develops from distinct regions: the brain, brain, and brain. Q: Identify the following structures: A. Coordination, balance movement- B. Aids medulla in some functions like breathing, conducts information between the brain and spinal cord- C. Screens and relays information to and from the cerebrum- D. Regulates breathing, heart rate, digestion, and swallowing- E. Integrates sensory and motor information, thinking-
F. Produces hormones, contains the thermostat, hunger, thirst centers, homeostatic regulation- G. Sends sensory information to the forebrain, contains nuclei involved in hearing and vision- Nerves crisscross in the, this is why the left side of the body is controlled by the right half of the brain and vice versa. Each cerebral hemisphere has an outer covering of matter-the cerebral cortex and internal matter-basal ganglia (nerve cell bodies in brain). The right and left hemispheres are joined by a fiber called the made of white matter. The cerebral cortex has distinct lobes. Two functional cortical areas are the cortex which sends commands to muscles and the cortex which receives and partially integrates signals from, pain, pressure, and temperature receptors in the body. The senses -vision, hearing, smell, and taste are found in the other cortical regions. M. Brain Research: The electrical impulses of the brain are recorded on an (EEG) by placing electrodes on the scalp. The mental activity ( ), the calmer / more the brain waves on the EEG.
A group of neurons called the passes through the brain stem and regulates and. It selects which information goes up to the cortex and /ignores certain stimuli like. The hemisphere is more involved with,, calculation, and processing detailed information. While the hemisphere is more involved in,, spatial perception, and overall content.