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What Do The Brain And Spinal Cord Make Up

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White And Gray Matter

2. The Anatomy of the Spinal Cord and How it Works – Spinal Cord Injury 101

The CNS can be roughly divided into white and gray matter. As a very general rule, the brain consists of an outer cortex of gray matter and an inner area housing tracts of white matter.

Both types of tissue contain glial cells, which protect and support neurons. White matter mostly consists of axons and oligodendrocytes a type of glial cell whereas gray matter consists predominantly of neurons.

Also called neuroglia, glial cells are often called support cells for neurons. In the brain, they outnumber nerve cells 10 to 1.

Without glial cells, developing nerves often lose their way and struggle to form functioning synapses.

Glial cells are found in both the CNS and PNS but each system has different types. The following are brief descriptions of the CNS glial cell types:

Astrocytes: these cells have numerous projections and anchor neurons to their blood supply. They also regulate the local environment by removing excess ions and recycling neurotransmitters.

Oligodendrocytes: responsible for creating the myelin sheath this thin layer coats nerve cells, allowing them to send signals quickly and efficiently.

Ependymal cells: lining the spinal cord and the brains ventricles , these create and secrete cerebrospinal fluid and keep it circulating using their whip-like cilia.

Radial glia: act as scaffolding for new nerve cells during the creation of the embryos nervous system.

Nerve Roots Supply Dermatomes

With few exceptions, complete overlap exists between adjacent dermatomes. This means that the loss of a single nerve root rarely produces significant loss of skin sensitivity. The exception to this rule is found in small patches in the distal extremities, which have been termed autonomous zones. In these regions, single nerve roots supply distinct and nonoverlapping areas of skin. By their nature the autonomous zones represent only a small portion of any dermatome and only a few nerve roots have such autonomous zones.

For example, the C5 nerve root may be the sole supply to an area of the lateral arm and proximal part of the lateral forearm. The C6 nerve root may distinctly supply some skin of the thumb and index finger. Injuries to the C7 nerve root may decrease sensation over the middle and sometimes the index finger along with a restricted area on the dorsum of the hand. C8 nerve root lesions can produce similar symptoms over the small digit, occasionally extending in to the hypothenar area of the hand. In the lower limb, L4 nerve root damage may decrease sensation over the medial part of the leg, while L5 lesions affect sensation over part of the dorsum of the foot and great toe. S1 nerve root lesions typically decrease sensation on the lateral side of the foot.

What Happens Following A Spinal Cord Injury

A common set of biological events take place following spinal cord injury:

  • Cells from the immune system migrate to the injury site, causing additional damage to some neurons and death to others that survived the initial trauma.
  • The death of oligodendrocytes causes axons to lose their myelination, which greatly impairs the conduction of action potential, messages, or renders the remaining connections useless. The neuronal information highway is further disrupted because many axons are severed, cutting off the lines of communication between the brain and muscles and between the body’s sensory systems and the brain.
  • Within several weeks of the initial injury, the area of tissue damage has been cleared away by microglia, and a fluid-filled cavity surrounded by a glial scar is left behind. Molecules that inhibit regrowth of severed axons are now expressed at this site. The cavitation is called a syrinx, which acts as a barrier to the reconnection of the two sides of the damaged spinal cord.
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    Ventricles And Cerebrospinal Fluid

    Deep in the brain are four open areas with passageways between them. They also open into the central spinal canal and the area beneath arachnoid layer of the meninges.

    The ventricles manufacture cerebrospinal fluid, or CSF, a watery fluid that circulates in and around the ventricles and the spinal cord, and between the meninges. CSF surrounds and cushions the spinal cord and brain, washes out waste and impurities, and delivers nutrients.

    What Are The Parts Of The Nervous System And Their Functions

    What Is a Neurosurgeon

    4.9/5nervous systemnervesThe nervous system has 3 main functions: sensory, integration, and motor.

    • Sensory.

    The nervous system has two main parts:

    • The central nervous system is made up of the brain and spinal cord.
    • The peripheral nervous system is made up of nerves that branch off from the spinal cord and extend to all parts of the body.

    Similarly, what are the main functions of the nervous system? The nervous system has three main functions: To collect sensory input from the body and external environment. To process and interpret the sensory input. To respond appropriately to the sensory input.

    Thereof, what are the parts of the central nervous system and their functions?

    The central nervous system controls most functions of the body and mind. It consists of two parts: the brain and the spinal cord. The brain is the center of our thoughts, the interpreter of our external environment, and the origin of control over body movement.

    What is the structure and function of the central nervous system?

    The central nervous system consists of the brain and spinal cord. The brain plays a central role in the control of most bodily functions, including awareness, movements, sensations, thoughts, speech, and memory. Some reflex movements can occur via spinal cord pathways without the participation of brain structures.

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    How The Spinal Cord And Internal Organs Work Together

    In addition to the control of voluntary movement, the central nervous system contains the sympathetic and parasympathetic pathways that control the “fight or flight” response to danger and regulation of bodily functions. These include hormone release, movement of food through the stomach and intestines, and the sensations from and muscular control to all internal organs.

    This diagram illustrates these pathways and the level of the spinal cord projecting to each organ.

    Peripheral Nervous System Function

    Nerve fibers that exit the brainstem and spinal cord become part of the peripheral nervous system. Cranial nerves exit the brainstem and function as peripheral nervous system mediators of many functions, including eye movements, facial strength and sensation, hearing, and taste.

    The optic nerve is considered a cranial nerve but it is generally affected in a disease of the central nervous system known as multiple sclerosis, and, for this and other reasons, it is thought to represent an extension of the central nervous system apparatus that controls vision. In fact, doctors can diagnose inflammation of the head of the optic nerve by using an ophthalmoscope, as if the person’s eyes were a window into the central nervous system.

    Nerve roots leave the spinal cord to the exit point between two vertebrae and are named according to the spinal cord segment from which they arise . Nerve roots are located anterior with relation to the cord if efferent or posterior if afferent .

    Fibers that carry motor input to limbs and fibers that bring sensory information from the limbs to the spinal cord grow together to form a mixed peripheral nerve. Some lumbar and all sacral nerve roots take a long route downward in the spinal canal before they exit in a bundle that resembles a horse’s tail, hence its name, cauda equina.

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    Judgment And Abstract Reasoning

    Planning and producing responses requires an ability to make sense of the world around us. Making judgments and reasoning in the abstract are necessary to produce movements as part of larger responses. For example, when your alarm goes off, do you hit the snooze button or jump out of bed? Is 10 extra minutes in bed worth the extra rush to get ready for your day? Will hitting the snooze button multiple times lead to feeling more rested or result in a panic as you run late? How you mentally process these questions can affect your whole day.

    The prefrontal cortex is responsible for the functions responsible for planning and making decisions. In the mental status exam, the subtest that assesses judgment and reasoning is directed at three aspects of frontal lobe function. First, the examiner asks questions about problem solving, such as If you see a house on fire, what would you do? The patient is also asked to interpret common proverbs, such as Dont look a gift horse in the mouth. Additionally, pairs of words are compared for similarities, such as apple and orange, or lamp and cabinet.

    Lobes Of The Brain And What They Control

    CNS – central nervous system- brain lobes, spinal cord, spinal and cranial reflex- A level Biology

    Each brain hemisphere has four sections, called lobes: frontal, parietal, temporal and occipital. Each lobe controls specific functions.

    • Frontal lobe. The largest lobe of the brain, located in the front of the head, the frontal lobe is involved in personality characteristics, decision-making and movement. Recognition of smell usually involves parts of the frontal lobe. The frontal lobe contains Brocas area, which is associated with speech ability.
    • Parietal lobe. The middle part of the brain, the parietal lobe helps a person identify objects and understand spatial relationships . The parietal lobe is also involved in interpreting pain and touch in the body. The parietal lobe houses Wernickes area, which helps the brain understand spoken language.
    • Occipital lobe. The occipital lobe is the back part of the brain that is involved with vision.
    • Temporal lobe. The sides of the brain, temporal lobes are involved in short-term memory, speech, musical rhythm and some degree of smell recognition.

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    Everyday Connections The Field Sobriety Test

    The neurological exam has been described as a clinical tool throughout this chapter. It is also useful in other ways. A variation of the coordination exam is the Field Sobriety Test used to assess whether drivers are under the influence of alcohol. The cerebellum is crucial for coordinated movements such as keeping balance while walking, or moving appendicular musculature on the basis of proprioceptive feedback. The cerebellum is also very sensitive to ethanol, the particular type of alcohol found in beer, wine, and liquor.

    Walking in a straight line involves comparing the motor command from the primary motor cortex to the proprioceptive and vestibular sensory feedback, as well as following the visual guide of the white line on the side of the road. When the cerebellum is compromised by alcohol, the cerebellum cannot coordinate these movements effectively, and maintaining balance becomes difficult.

    Spinal Cord And Brain Stem

    A sensory pathway that carries peripheral sensations to the brain is referred to as an ascending pathway, or ascending tract. The various sensory modalities each follow specific pathways through the CNS. Tactile and other somatosensory stimuli activate receptors in the skin, muscles, tendons, and joints throughout the entire body. However, the somatosensory pathways are divided into two separate systems on the basis of the location of the receptor neurons. Somatosensory stimuli from below the neck pass along the sensory pathways of the spinal cord, whereas somatosensory stimuli from the head and neck travel through the cranial nervesâspecifically, the trigeminal system.

    The dorsal column system and the spinothalamic tract are two major pathways that bring sensory information to the brain . The sensory pathways in each of these systems are composed of three successive neurons.

    Figure 14.5.1 â Ascending Sensory Pathways of the Spinal Cord:

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    The Autonomic Nervous System

    The autonomic nervous system is part of the peripheral nervous system. One of its main roles is to regulate glands and organs without any effort from our conscious minds.The autonomic nervous system is made up of two parts: the sympathetic and the parasympathetic. These systems act on the body in opposite ways. Together, they coordinate a multitude of adjustments required for our changing personal needs as we move through our environment. For example, the size of our pupils is adjusted automatically to allow the correct amount of light into our eyes for optimum vision, our sweat glands are turned on when we get too hot and our salivary glands produce saliva when we eat food .

    The Peripheral Nervous System

    Brain and spinal cord

    The peripheral nervous system consists of the nerves that branch out from the brain and spinal cord. These nerves form the communication network between the CNS and the body parts. The peripheral nervous system is further subdivided into the somatic nervous system and the autonomic nervous system. The somatic nervous system consists of nerves that go to the skin and muscles and is involved in conscious activities. The autonomic nervous system consists of nerves that connect the CNS to the visceral organs such as the heart, stomach, and intestines. It mediates unconscious activities.

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    Sensory Modalities And Location

    The general senses are distributed throughout the body, relying on nervous tissue incorporated into various organs. Somatic senses are incorporated mostly into the skin, muscles, or tendons, whereas the visceral senses come from nervous tissue incorporated into the majority of organs such as the heart or stomach. The somatic senses are those that usually make up the conscious perception of the how the body interacts with the environment. The visceral senses are most often below the limit of conscious perception because they are involved in homeostatic regulation through the autonomic nervous system.

    Figure 14.5.6 â Dermatomes:

    The various stimuli used to test sensory input assess the function of the major ascending tracts of the spinal cord. The dorsal column pathway conveys fine touch, vibration, and proprioceptive information, whereas the spinothalamic pathway primarily conveys pain and temperature. Testing these stimuli provides information about whether these two major ascending pathways are functioning properly. Within the spinal cord, the two systems are segregated. The dorsal column information ascends ipsilateral to the source of the stimulus and decussates in the medulla, whereas the spinothalamic pathway decussates at the level of entry and ascends contralaterally. The differing sensory stimuli are segregated in the spinal cord so that the various subtests for these stimuli can distinguish which ascending pathway may be damaged in certain situations.

    Show/hide Words To Know

    Central nervous system : a part of the nervous system which includes the brain and spinal cord.

    Parasympathetic nervous system: the part of your nervous system that unconsciously controls your organs and glands when your body is at rest.

    Peripheral nervous system : a part of the nervous system which includes all the nerves outside of the brain and spinal cord.

    Sympathetic nervous system: The part of your nervous system that unconsciously controls your organs and glands when youre excited or frightened.

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    How Does The Brain Work

    The brain sends and receives chemical and electrical signals throughout the body. Different signals control different processes, and your brain interprets each. Some make you feel tired, for example, while others make you feel pain.

    Some messages are kept within the brain, while others are relayed through the spine and across the bodys vast network of nerves to distant extremities. To do this, the central nervous system relies on billions of neurons .

    What Are Relay Neurons

    Anatomy of the Spinal Cord and How it Works

    The neurons, which are found in the brain and spinal cord and allow sensory and motor neurons to communicate are called relay neurons. Relay neurons are located between sensory input and motor output response.

    A neuron can be either a sensory neuron or a motor neuron, but not both. This means it either carries a signal toward the brain or away from it.

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    Blood Supply To The Brain

    Two sets of blood vessels supply blood and oxygen to the brain: the vertebral arteries and the carotid arteries.

    The external carotid arteries extend up the sides of your neck, and are where you can feel your pulse when you touch the area with your fingertips. The internal carotid arteries branch into the skull and circulate blood to the front part of the brain.

    The vertebral arteries follow the spinal column into the skull, where they join together at the brainstem and form the basilar artery, which supplies blood to the rear portions of the brain.

    The circle of Willis, a loop of blood vessels near the bottom of the brain that connects major arteries, circulates blood from the front of the brain to the back and helps the arterial systems communicate with one another.

    Subdivisions Of The Peripheral Nervous System

    The sensory division carries sensory signals by way of afferent nerve fibers from receptors in the central nervous system . It can be further subdivided into somatic and visceral divisions. The somatic sensory division carries signals from receptors in the skin, muscles, bones and joints. The visceral sensory division carries signals mainly from the viscera of the thoracic and abdominal cavities.

    The motor division carries motor signals by way of efferent nerve fibers from the CNS to effectors . It can be further subdivided into somatic and visceral divisions. The somatic motor division carries signals to the skeletal muscles. The visceral motor division, also known as the autonomic nervous system, carries signals to glands, cardiac muscle, and smooth muscle. It can be further divided into the sympathetic and parasympathetic divisions.

    The sympathetic division tends to arouse the body to action. The parasympathetic divisions tend to have a calming effect.

    Nerve fibers of the PNS are classified according to their involvement in motor or sensory, somatic or visceral pathways. Mixed nerves contain both motor and sensory fibers. Sensory nerves contain mostly sensory fibers they are less common and include the optic and olfactory nerves. Motor nerves contain motor fibers.

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    Neurons In Nervous Tissue Relay Rapid

    All nervous tissue, from the brain to the spinal cord to the furthest nerve branch, includes cells called neurons. Neurons are charged cells: they conduct electrical signals to pass information through the body. A typical neuron consists of a cell body, dendrites, and an axon with an axon terminal. The dendrites receive signals from body tissues or other neurons and pass them into the cell body. If an outgoing signal is produced, it zips down the axon to the axon terminal and passes to the next neuron or target cell. This conductive capability sends information up and down nerve pathways and through the central nervous system at incredible speed. Some 100 billion neurons give the brain its awesome processing power.

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