The Spinal Cord Study Guide

What structures are a part of the central nervous system? Peripheral nervous system?

Structural Divisions 1. Central nervous system (CNS) • Brain • Spinal cord (Center) 2. Peripheral nervous system (PNS) •Cranial nerves - 12 pairs •Spinal nerves - 31 pairs

Be prepared to label diagram of the spinal cord and spinal nerves.

prepared.

Differentiate between neurons that are made by schwann cells and neurons that are made by oligodendrocytes. Make sure your answer includes a description of neurilemma and myelin.

1. Nerves of the PNS: • Myelin is produced by Schwann cells • Nodes separate sections of the myelin to help speed up the conduction of nerve impulses • The thin outer layer of the Schwann cells form the neurilemma. - Allows for the nerve to repair itself 2. Nerves of the CNS • Myelin made by oligodendrocyte • Do not contain neurilemma - damage is permanent. Notes: Myelin is an insulating layer, or sheath that forms around nerves, including those in the brain and spinal cord. It is made up of protein and fatty substances. This myelin sheath allows electrical impulses to transmit quickly and efficiently along the nerve cells. neurilemma Is the plasma membrane surrounding a Schwann cell of a myelinated nerve fiber and separating layers of myelin. Neurilemma serves a protective function for peripheral nerve fibers. Notes: oligodendrocyte A cell that forms the myelin sheath (a layer that covers and protects nerve cells) in the brain and spinal cord. In diseases such as Multiple Sclerosis, oligodendrocytes are damaged and myelin that normally insulates the axons of nerve cells is lost, a process known as demyelination. When nerve cells become demyelinated due to oligodendrocyte death they become dysfunctional.

What are the two major functions of the nervous system?

1. Nervous system coordinates all body systems. 2. Detects and responds to stimuli (a thing or event that evokes a specific functional reaction in an organ) Notes: • a stimulus is anything that can trigger a physical or behavioral change. • detectable change in the internal or external environment. • the external stimulus includes touch and pain, vision, smell, taste, sound, and balance.

Outline the steps involved in sending a nerve impulse along a neuron (make sure to cover resting state, depolarization and repolarization)

1. Plasma membrane of a neuron carries electrical charge (potential) 2. Plasma membrane is polarized - the inside of the membrane has a negative charge and the outside is positively charged, more NA+ outside, K+ inside 3. As a nerve impulse reaches the membrane negative and positive charges reverse, generates electrical charge (action potential) • Resting state • Depolarization-channels open, NA+ rushes in changes charges • Repolarization-channel open, K+ rushed out, charges change back - NA+/K+ pumps actively move NA outside and K back inside 4. Myelin sheath speeds conduction (jump from node to node)

Describe the function of the three types of neurons.

1. Sensory neurons (afferent neurons, feeling) • Conduct impulses to spinal cord, brain. Sensory neurons help you: taste, smell, hear, see, and feel things around you. Afferent neurons, also called sensory neurons, are the nerve fibers responsible for bringing sensory information from the outside world into the brain. Sensory information may involve special senses, such as vision, hearing, smell, or taste, as well as the sense of touch, pain, and temperature. 2. Motor neurons (efferent neurons) • Conduct impulses to muscles, glands. Motor neurons play a role in movement, including voluntary and involuntary movements. These neurons allow the brain and spinal cord to communicate with muscles, organs, and glands all over the body. Efferent neurons, also called motor neurons, are the nerve fibers responsible for carrying signals from the brain to the peripheral nervous system in order to initiate an action. In other words, they are the neurons that tell your body to perform an action, such as removing your hand from a hot pan. 3. Interneurons (central or association neurons) • Conduct information within CNS when you touch something sharp like a cactus, sensory neurons in your fingertips send a signal to interneurons in your spinal cord. Some interneurons pass the signal on to motor neurons in your hand, which allows you to move your hand away. Notes: 1. Neurons, also known as nerve cells, send and receive signals from your brain. 2. axons allow neurons to transmit electrical and chemical signals to other cells. Neurons can also receive these signals via rootlike extensions known as dendrites. 3. Sensory neurons are triggered by physical and chemical inputs from your environment. Sound, touch, heat, and light are physical inputs. Smell and taste are chemical inputs.

Describe the two major functional divisions of the nervous system (include what is controlled by each division).

1. Somatic nervous system (body cells) • Controlled voluntarily • Effectors are skeletal muscles • No further subdivisions. 2. Automatic (or visceral) nervous system (ANS) • Controlled involuntarily (no control) • Effectors are smooth muscle, cardiac muscle, and glands. Notes: The somatic nervous system is a component of the peripheral nervous system associated with the voluntary control of the body movements via the use of skeletal muscles. Your somatic nervous system allows you to move and control muscles throughout your body. Your autonomic nervous system is a network of nerves throughout your body that control unconscious processes. These are things that happen without you thinking about them, such as breathing and your heart beating. Your autonomic nervous system is always active, even when you're asleep, and it's key to your continued survival.

What is the difference between white matter and gray matter?

1. White fibers in the white matter of brain /SC and nerves. 2. Gray matter - fibers and cell bodies without myelin Notes: White matter is found in the deeper tissues of the brain (subcortical). It contains nerve fibers (axons), which are extensions of nerve cells (neurons). Many of these nerve fibers are surrounded by a type of sheath or covering called myelin. Myelin gives the white matter its color. allows the exchange of information and communication between different areas of your brain. The white matter and grey matter are similar as they are both essential sections of both the brain as well as the spinal cord. Grey matter makes up the outer most layer of the brain. The grey matter gets its grey tone from a high concentration of neuronal cell bodies.

What are dermatomes?

1. skin surface mapped into distinct regions that are supplied by a single spinal nerve. Notes: Dermatomes are areas of skin on your body that rely on specific nerve connections on your spine. In this way, dermatomes are much like a map. The nature of that connection means that dermatomes can help a healthcare provider detect and diagnose conditions or problems affecting your spine, spinal cord or spinal nerves.

What is meant by action potential?

1. the sudden electrical change in the membrane of the neuron that is transmitted along the axon 2. An action potential is a rapid sequence of changes in the voltage across a membrane.

What is a synapse? Describe how a nerve impulse is sent at the synapse.

Junction point for transmitting nerve impulse • Axon (presynaptic cell) - sends impulse • Dendrite (postsynaptic cell) - receives impulse • Synaptic cleft - gap between neurons • Neurotransmitter - electrical impulse is translated into a chemical messenger that travels across the synaptic cleft • Receptors - proteins on the dendrite membrane that neurotransmitters bind to in order to "deliver" the nerve impulse Notes: 1. A synapse is a small gap at the end of a neuron that allows a signal to pass from one neuron to the next. Neurons are cells that transmit information between your brain and other parts of the central nervous system. Synapses are found where neurons connect with other neurons. 2. 1) An electrical impulse travels along an axon of the presynaptic neuron. 2) When the impulse reaches the nerve-ending, it releases chemical messengers called neurotransmitters. 3) These chemicals diffuse across the synapse and bind with specific receptor molecules on the membrane of the next neuron.

What is a nerve? What is a tract?

Nerves and Tracts: fiber bundle (axons/dendrites) • Nerve: within PNS • Tract: within CNS • Nerve/Tract has many neuron fibers, organized into fascicles Notes: 1. A nerve is a bundle of neuron fibers in the peripheral nervous system; a tract is a bundle of neuron fibers in the central nervous system. 2. A tract is a collection of nerve fibers (axons) in the central nervous system. A nerve is a collection of nerve fibers (axons) in the peripheral nervous system.

What are neuroglia and what is their function? Give two examples of neuroglia.

Neuroglia (glial (glue) cells) - non conducting cells that serve to support and protect the system. • Protect nervous tissue • Support nervous tissue • Aid in cell repair • Remove pathogens and impurities • Regulation composition of fluids around and between cells •Examples: (CNS) • Schwann cells • Astrocytes • Oligodendrocyte

Describe the structures of the neuron and give their functions.

Neurons: functional cells of the nervous system. 1. Cell body • Nucleus • Other organelles 2. Cell fibers • dendrites: conduct nerve impulses to cell body. • axons: conduct nerve impulses away from cell body. Some are protected by myelin sheath. Notes: A neuron has three main parts: dendrites, an axon, and a cell body or soma (see image below), which can be represented as the branches, roots and trunk of a tree, respectively. All neurons have three different parts: dendrites, cell body and axon. The neuron structure is specially adapted to carry messages over large distances in the body quickly in the form of electrical signals. Many axons are insulated with a fatty substance called myelin. Myelin helps axons to conduct an electrical signal. The two work together. Axons help messages move through your body systems, and dendrites receive and process those messages from the axons. Quantity: A neuron may have just one axon, while it may have more than one set of dendrites.

What is a neurotransmitter? Give three examples of a neurotransmitter. Where do neurotransmitters bind?

Neurotransmitter - electrical impulse is translated into a chemical messenger that travels across the synaptic cleft. Examples: • Epinephrine (adrenaline) •Norepinephrine (noradrenaline) • Acetylcholine • Serotonin

What is myelin? What cells make up myelin?

Notes: 1. Myelin is an insulating layer, or sheath that forms around nerves, including those in the brain and spinal cord. It is made up of protein and fatty substances. This myelin sheath allows electrical impulses to transmit quickly and efficiently along the nerve cells. 2. CNS myelin is produced by special cells called oligodendrocytes. PNS myelin is produced by Schwann cells. The two types of myelin are chemically different, but they both perform the same function — to promote efficient transmission of a nerve impulse along the axon.

Describe the two subdivisions of the autonomic nervous system.

Subdivided into: 1. Sympathetic nervous system: • stimulated in situations that require action like the fight-or-flight reaction; triggered by epinephrine. 2. Parasympathetic nervous system: • functions in response to normal everyday situations; "rest and digest" Notes: Sympathetic nervous system: This system activates body processes that help you in times of need, especially times of stress or danger. This system is responsible for your body's "fight-or-flight" response. Parasympathetic nervous system: This part of your autonomic nervous system does the opposite of your sympathetic nervous system. This system is responsible for the "rest-and-digest" body processes. The fight or flight response is an automatic physiological reaction to an event that is perceived as stressful or frightening. The perception of threat activates the sympathetic nervous system and triggers an acute stress response that prepares the body to fight or flee. Rest and digest is responsible for energy conservation and maintaining vital bodily functions, including digestion, urination and defecation, especially when the body is at rest

Outline the pathway of the reflex arc.

The pathway through the nervous system from stimulus to response (simple/automatic, spinal reflex, stretch reflex): 1. Receptor detects stimulus 2. Sensory (afferent) neuron transmits impulses to CNS (goes in back side or dorsal horn of SC) 3. CNS coordinates impulses and organizes response - Interneurons 4. Motor (effort) neuron carries impulses away from CNS (comes out of the front side or ventral horn of SC) 5. Effector carries out response (skeletal muscle)