Nervous System Lecture Notes PDF

**nervous system** The nervous system is a complex network of nerves and cells that carry messages to and from the brain and spinal cord to various parts of the body. Function What does the nervous system do? Your nervous system's main function is to send messages from various parts of your body...

**nervous system** The nervous system is a complex network of nerves and cells that carry messages to and from the brain and spinal cord to various parts of the body. Function What does the nervous system do? Your nervous system's main function is to send messages from various parts of your body to your brain, and from your brain back out to your body to tell your body what to do. #### How does the nervous system work? Your nervous system uses nerve cells called **[neurons]** to send signals, or messages, all over your body. These electrical signals travel among your brain, skin, organs, glands and muscles. The messages help you move your limbs and feel sensations, like pain. Your [eyes](https://my.clevelandclinic.org/health/body/21823-eyes), [ears](https://my.clevelandclinic.org/health/body/24048-ear), [tongue](https://my.clevelandclinic.org/health/body/22845-tongue), nose and the nerves all over your body take in information about your environment. Then, nerves carry that data to and from your brain. \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-- **[Nerve cells (neurons)]** are the basis of your nervous system. Neurons, also known as nerve cells, send and receive signals from your brain. While neurons have a lot in common with other types of cells, they're structurally and functionally unique. Specialized projections called **[axons]** allow neurons to transmit electrical and chemical signals to other cells. Neurons can also receive these signals via root like extensions known as **dendrites.** Parts of a neuron ----------------- Neurons vary in size, shape, and structure depending on their role and location. However, nearly all neurons have three essential parts: **[a cell body, an axon, and dendrites.]** - ### Cell body Also known as a **[soma]**, the cell body is the core section of the neuron. The cell body contains genetic information, maintains the neuron's structure, and provides energy to drive activities. Like other cell bodies, a neuron's soma contains a nucleus and specialized organelles. It's enclosed by a membrane that both protects it and allows it to interact with its immediate surroundings. - ### Axon An axon is a long, tail-like structure. It joins the cell body at a specialized junction called the **[axon hillock]**. Many axons are insulated with a fatty substance called **[myelin]**. Myelin helps axons to conduct an electrical signal. Neurons usually have one main axon. - ### Dendrites Dendrites are fibrous roots that branch out from the cell body. Like antennae, dendrites receive and process signals from the axons of other neurons. Neurons can have more than one set of dendrites, known as **[dendritic trees.]** **Axon** -- long nerve wire that carries the impulse from the cell body to the synapse. **Myelin** -- fatty insulation around axon that improves the conduction speed of nerve impulses **Schwann cell** -- cells that wrap around axon and coat it with myelin **Nodes of Ranvier** -- gaps between myelin where action potentials occur \_ **Dendrites** -- branches from the cell body that receive info from other cells **Synaptic knob (axon terminal**) -- end of axon that releases neurotransmitter **Impulse** -- one way electrical signal from cell body to synaptic knobs Types of neurons ---------------- Neurons vary in structure, function, and genetic makeup. Given the sheer number of neurons, there are thousands of different types, much like there are thousands of species of living organisms on Earth. However, there are three major neuron forms. Each combines several **[elements of the basic neuron shape.]**  Different kinds of neurons: 1 [Unipolar neuron](https://en.wikipedia.org/wiki/Unipolar_neuron) 2 [Bipolar neuron](https://en.wikipedia.org/wiki/Bipolar_neuron) 3 [Multipolar neuron](https://en.wikipedia.org/wiki/Multipolar_neuron)  **Multipolar neurons**. These neurons have a single axon and symmetrical dendrites that extend from it. This is the most common form of neuron in the central nervous system. **Unipolar neurons.** Usually only found in invertebrate species, these neurons have a single axon. **Bipolar neurons.** Bipolar neurons have two extensions extending from the cell body. At the end of one side is the axon, and the dendrites are on the other side. These types of neurons are mostly found in the retina of the eye. **[There are different types of neurons according to a different job:]** [Reflexes, or reflex actions], are involuntary, almost instantaneous movements in response to a specific stimulus. A reflex arc defines the pathway by which a reflex travels---from the stimulus to sensory neuron to motor neuron to reflex muscle movement 1. **Motor neurons** take signals from your brain and spinal cord to your muscles. They help you move. They also assist with breathing, swallowing and speaking. 2. **Sensory neurons** take information from your senses (what you see, touch, taste, etc.) to your brain. 3. **Interneurons** communicate between motor and sensory neurons. **What are the parts of the nervous system?**  The nervous system has two main parts: 1. **Central nervous system (CNS):** 2. **Peripheral nervous system (PNS):** Your PNS is made up of a network of nerves (41 paired). **The cranial nerves** are a set of 12 paired nerves in the back of your brain The nerves branch out from your spinal cord called **[Spinal Nerves (31 paired)]**. This system relays information from your brain and spinal cord to your organs, arms, legs, fingers and toes. - [There are two parts to your peripheral nervous system]: a. **The somatic nervous system** guides your voluntary movements. b. **The autonomic nervous system** regulates the activities you do without thinking about them (involuntary movements). The autonomic nervous system is a component of the peripheral nervous system that regulates involuntary physiologic processes including heart rate, blood pressure, respiration, digestion, and sexual arousal. It contains three anatomically distinct divisions: **sympathetic** SNS**, parasympathetic** PNS**, and enteric.** The sympathetic and parasympathetic nervous systems work together \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-- What is the difference between the Sympathetic and Parasympathetic divisions? - **[Sympathetic ]** increased activity **"fight or flight"** digestive and urinary functions stop heart rate increases, blood pressure rises, increased sweating, breathing increases. - [**Parasympathetic** ] decreased activity, **"rest and relax",** promotes digestion, blood pressure and heart rate return to normal, normal breathing rate.