Nervous System Notes PDF

# You Get On My Last Nerves - Nervous System ## Mammal Neuron Motor Nerve Cells A motor neuron is a type of nerve cell (neuron) found in mammals and other animals that helps control muscle movement. * All Cells have the following tissue types: * Epithelial * Connective * Muscle * N...

# You Get On My Last Nerves - Nervous System ## Mammal Neuron Motor Nerve Cells A motor neuron is a type of nerve cell (neuron) found in mammals and other animals that helps control muscle movement. * All Cells have the following tissue types: * Epithelial * Connective * Muscle * Neural (Nerves) ## Neural Tissue Neural tissue is found in the brain, spinal cord & peripheral nerves. * Peripheral nerves are located outside of the brain & spinal cord. * Nerves are bundled up axons. * Neuron cell body is in the brain & spinal cord. * Ganglion cells - a group of neuron cell bodies outside the brain & spinal cord. * The human brain & spinal cord contains around 100 billion neurons. These neurons are supported by cells called neuroglia, which is 15 times more than the # of neurons. * Neuroglia cells support the neurons but is unable to generate electrical impulses. They are only supporting cells. * Nervous system is divided into central & peripheral systems. ## Central Nervous System Central nervous system contains the brain & spinal cord. ## Peripheral Nervous System Peripheral nervous system contains 31 pairs of spinal nerves & 12 pairs of cranial nerves. * In the peripheral nervous system they contain Schwann & satellite cells. * Schwann cells are the most important cells in the peripheral nervous system. * Nodes of Ranvier: Small gaps in myelin sheath (insulating layer) along an axon that help increase the speed of conduction or speedo up nerve signal transmission. ## Multiple Sclerosis * Multiple sclerosis is also known as MS. * Multiple sclerosis is caused by schwann cells being in pain. * Multiple sclerosis is an autoimmune disease. * In multiple sclerosis the normal schwann cells are replaced by scar tissue which affects the speed of conduction. ## Microglia * Microglia - type of specialized cells found in the central nervous system CNS, which includes the brain & spinal cord. They play a critical role in maintaining the health of the CNS by acting as its defense & cleanup crew. * In multiple sclerosis microglia attacks the myelin sheath, worsening the disease. ## Oligodendrocyte * Oligodendrocyte is a special type of cell in the central nervous system, in the brain & spinal cord that helps nerve cells work properly by making a protective coating called myelin sheath. * Example - nerve cell (neurons) as electrical wires that send messages in your body. Myelin sheath is made by oligodendrocytes which is like the plastic coating on those wires. This helps messages travel faster & smoother so the body can more, think & feel quickly. ## Ependymal Cells * Ependymal cells are a type of cell in central nervous system, brain & spinal cord that help make and move cerebrospinal fluid (CSF), the liquid that surrounds & protects the brain & spinal cord. * CSF cushions the brain, removes waste and delivers nutrients. ## Cessation of the Nervous System * The nervous system stops functioning or a clinical death. ## Neurons A neuron which is a bunch of nerve cells has several important parts that help it carry messages. * Parts of a neuron: * **Cell body:** The control center of the neuron. It holds the nucleus (the brain of the cell) & helps the neuron do its job. * **Dendrites:** Branch-like parts that receive messages from other neurons and send them to the cell body. * **Axon:** A long tube-like structure that carries messages away from the cell body to other neurons, muscles or glands. * **Myelin sheath:** A fatty covering around the axon that helps speed up the electrical messages. * **Axon terminals:** Branches at the end of the axon that send the message to the next neuron or muscle. * **Dendrites:** Get messages * **Cell body:** Processes them * **Axon:** Sends the messages out * **Myelin sheath:** Makes messages go faster * **Axon terminals:** Pass the messages along ## Axon Hillock * A small, cone shaped area at the base of the axon (the long part of the neuron) * It is where the axon connects to the cell body of the neuron. ## Why is the Axon Hillock Important? 1. **Axon Hillock checks if the signals from the rest of the neuron are strong enough to be sent out.** It decides if the signal should be passed along down the axon. Acts as a decision maker. 2. **Starts the signal.** If the signal is strong enough, the axon hillock triggers an electrical signal called action potential. This is like a starting gun for the nerve signal. 3. **Controls signal strength.** It ensures that only strong enough signals get sent. If the signals aren't strong enough, the axon hillock won't start action potential. * Think of Axon Hillock as a gatekeeper. It checks if the signal is strong enough to pass through and if it is, it lets it go. If not the signal is stopped right there. 4. **Schwann cells cover the axon.** 5. **The gap between two schwann cells is called a node of Ranvier.** 6. **Node of Ranvier increases the speed of conduction of the electrical impulse.** * Rough endoplasmic reticulum (ER) of a neuron is called Nissal bodies. * Nissal bodies are responsible for building proteins needed for the neuron to grow, repair itself and communicate with other neurons. ## Where are the neuron cells located? Neuron cells are located in different parts of your body: 1. **Brain:** Neuron cell bodies are mostly in the brain. The brain controls everything, thinking, emotions, memory and movement. 1. **Spinal cord:** Neurons are also in the spinal cord which runs down your back. It helps send messages between the brain & the rest of the body. 2. **Peripheral nervous system:** Neurons can be found outside the brain and spinal cord in places like your arms, legs & organs & sensory systems like touch or sight. ## Why Doesn't the Neuron Cell Divide? Neuron cells don't divide because they are highly specialized for their job of sending and processing messages in the body. * The number of neurons you have is the same as when you were born, there is no new neuron that develops. ## Myelin Sheath * A protective covering around the axon of a neuron that helps electrical signals travel faster. * The myelin Sheath acts like insulation on a wire, helping the signal move quickly down the axon. * The myelin sheath shields the Axon from damage, keeping the neuron healthy. * The myelin sheath helps communication by speeding up signals. The myelin sheath ensures your brain and body can communicate efficiently. * In PNS one axon is covered by multiple Schwann cells. * In CNS many axons covered by 1 oligodendrocyte. * CSF - Ceberal spinal fluid * CSF passes through the central canal. ## Nervous System * Broken into two parts: * **Central & Peripheral Systems** * (CNS) Central system houses the Brain & Spinal cord. * Peripheral system is anything outside of the Brain & Spinal cord. ## Peripheral System * Peripheral system has 31 pairs of spinal nerves & 12 pairs of cranial nerves. * Peripheral System (PNS) has Schwann cells & Satellite cells. ## Neural Tissue Contains: * Brain, Spinal cord & Peripheral nerves ## Ganglion Cells * Group of neuron cell bodies outside of the brain & spinal cord. ## Neuroglia * Support cells - 5 times more ## Node of Ranvier: * Increases the speed of conduction & are also gaps between the myelin sheaths that cover around the axons of neurons. ## Myelin * Myelin is produced by Schwann cells in the Peripheral nervous system (PNS). * Myelin is produced by Oligodendrocytes in the central nervous system (CNS). * Inflammation of Schwann cells causes the auto immune disease multiple sclerosis. ## The Cells Located in the Central Nervous System CNS are: 1. **Microglia:** 2. **Oligodendrocytes** 3. **Ependymal** ## Peripheral Nervous System Broken Down PNS divides into somatic which is voluntary & Autonomic which is involuntary. ## Somatic Nervous System * Somatic then divides into Somatic, Afferent & Somatic Efferent. 1. **Somatic Nervous system- controls voluntary movements. 2. **Autonomic Nervous System- controls involuntary functions like heart rate digestion & respiratory rate.** ## Autonomic Nervous System * Autonomic also divides into Afferent (sensory) & Efferent (motor) * Autonomic then subdivides into Sympathetic & parasympathetic divisions. ## Somatic Afferent (Sensory pathway) * Signals coming to the brain or spinal cord. These nerves carry information from the body to the central nervous system (CNS). * **Somatic means they deal with the body parts you can control like, skin, muscles & joints.** ## Examples of Somatic Afferent: 1. **Touch:** Feeling something hot or cold 2. **Pain:** Sharp object poke your foot. 3. **Position** Knowing where your arm is without looking. ## Somatic Efferent (Motor Pathway) * Think: signals going out from the brain or spinal cord. * These nerves carry motor commands from the CNS to your skeletal muscles telling them to contract or move. * **Somatic means this involves voluntary movements you control like, lifting your arm or kicking a ball.** * **Example: Deciding to wave at someone or moving your legs to walk** * **Afferent:** Arrival of sensory signals at the brain/spinal cord * **Efferent:** Exit of motor commands from the brain/spinal cord to muscles. ## Autonomic Afferent (Sensory Pathway) * Think: Signals coming to the brain or Spinal cord. * These nerves carry sensory information from internal organs and tissues to the central nervous system (CNS). * **They monitor, Blood pressure, oxygen levels & Gut stretch during digestion** * **Example - When your stomach is full autonomic afferent nerves send this sensation to your brain. If your blood pressure drops, sensory input informs your CNS to make adjustments.** ## Autonomic Efferent (Motor pathway) * Think: Signals going out from the brain or spinal cord. * These nerves carry commands from the CNS to internal organs & glands to regulate automatic body functions. ## Divided into two paris: 1. **Sympathetic (fight or flight):** Prepares your body for action - Increases heart rate, Dilates pupils, slows digestion. 2. **Parasympathetic (Rest & Digest):** Calms your body - Slows heart rate, Stimulates digestion, promotes relaxation. ## Neuroglial Cells * Also known as glial cells are the supportive cells of the nervous system. ## Nerve Tissue * Nerve tissue is composed of 2 main types of cells: * **Neurons:** Nerve cells that are specialized to detect and react to stimuli by generating and conducting nerve impulses. * **Neuroglial cells:** Supporting cells for filling spaces & supporting neurons ## Neurons * All neurons have a cell body called soma which has a nucleus, organelles and a modified endoplasmic reticulum called Nissal body. * Although there is DNA in the neuron, somehow DNA replication and mitosis do not occur, resulting in the neurons lack of ability to reproduce or regenerate. ## Types of Neurons: A. **Multipolar neuron:** Brain & Spinal cord - many dendrites, 1 axon. B. **Bipolar neuron:** Retina, internal ear & nose - 1 dendrite, 1 axon. C. **Pseudo unipolar neuron:** Skin - no axon, no dendrites. ## Spinal Cord * The spinal cord is the continuation of the brain. * **Where does the spinal cord begin?** * The spinal cord begins at the Foramen Magnum. * **Spinal cord:** Continuation of brain, starts at the level of foramen magnum, extends up to L1 (Lumbar 1). * **Spinal cord:** Continuation of Brain, passes through the vertebral foramen & ends up to L1. * **Gray matter:** contains the cell bodies of neurons (thinking part of the neuron) & some short connections. * **It is called gray because it looks darker than white matter.** * **Gray matter processes & interprets information**. Sort of like the control center where decisions are made. * **Gray matter is found in the brain, mostly on the outside layer called the cortex.** * **In the spinal cord, in the center shaped like a butterfly you can also find gray matter**. ## White Matter: * Contains the axons (the wires) covered in myelin, which makes it look white. * **White matter:** Transmits signals between different parts of the brain & spinal cord. * **Think of it as the highway system that carries messages**. * **White matter is found in the brain mostly inside under gray matter**. * **White matter is found in the spinal cord on the outside, surrounding gray matter**. * **Neuron cell body are located in the gray matter.** * **Myelinated fibers are located in the white matter.** * **Myelinated fiber (Lipid Content, (Axon).** ## Nerve - A Bundle of Axons * **Spinal Nerves:** The nerves that come out of your spinal cord & connect your brain to the rest of your body. They carry messages back and forth between your brain, spinal cord and body parts. * **Spinal nerves come out from the spinal cord through small openings in your backbone. We have 31 pairs of spinal nerves.** * **There are 7 cervical vertebrae but there are 8 cervical nerves.** ## Spinal Tap * **A medical procedure to collect cerebrospinal fluid (CSF) that helps protect your brain & spinal cord** * **A spinal tap is usually done in region L2-L3, L4-L5, L3-L4. The safest part to do a spinal tap is L3-L4.** ## Cutaneous Meningitis * Inflammation of the meninges which are the protective membranes covering the brain & spinal cord. ## Nerve Plexus * A network of nerves that combine to create larger nerves that serve specific body parts. * **There are 4 plexus in our body:** 1. **Cervical:** Shoulders & diaphragm - Important for breathing. 2. **Brachial:** Arms & hands. 3. **Lumbar:** Lower back & abdomen & legs. 4. **Sacral:** Legs, feet & Pelvic. 5. **There is no thoracic plexus.** ## From the Cervical Plexus * **The most important nerve is the Phrenic Nerve. The Phrenic nerve supplies the Diaphragm** ## From the Brachial Plexus * **The nerves from the Brachial plexus (median) from our upper hand all comes.** ## The Biggest Nerve Of Our Body * **Is the Siatic Nerve which comes from the Sacral Plexus.**