Nervous System

Nervous system

Cells of the Nervous System

-Nervous system comprises two groups of cells glial cells and neurons

·        Neurons are responsible for sensing environmental change communicating with other neurons via electrochemical signals

·        Glial cells work to support nourish and insulate the neurons while also removing waste products

-Neuron is made up of several components:         

·        Cell body otherwise known as the soma that contains the nucleus and the neurons intracellular organelles

o   Site of protein synthesis

·        Dendrites

o   transmit signals received from other neurons to the soma

·        Axon

o   Arise from the Axon Hillock in the soma

o   Action potentials are initiated

o   Synaptic connections with other neurons; contain neurotransmitters which allow signal transmission between neurons

·        Neurotransmitters

o   Endogenous chemicals that allow the neurons to communicate with each other throughout the body

-Glial Cells

·        Support cells of the nervous system

·        Astrocytes:

o   help provide physical and nutritional support to the neurons of the central nervous system

·        Ependymal Cells:

o   Thin lining of the ventricular system of the brain and spinal cord; main function is the production of cerebrospinal fluid

·        Schwann Cells (PNS):

o   Insulate the Axon with myelin sheath; facilitates rapid transmission of action potentials

·        Oligodendrocytes (CNS):

o   Responsible for insulating the axons of the CNS; function by producing myelin sheath

-Make up 10-15% of cells within the brain

-Activated in response to tissue damage

-Capacity to recognize foreign antigens and initiate phagocytosis to help remove foreign material

Myelination of Axons

-Insulates axons

-Increases the rate at which action potentials are passed along the axon

-Myelin encases the axon in segments; short gaps known as nodes of Ranvier

-Support Cells

·        Schwann Cells (PNS): single axon section

·        Oligodendrocytes (CNS): Multiple axons

Gray Matter & White Matter

-Gray Matter:

·        Home to neural cell bodies, axon terminals, dendrites, and all nerve synapses

·        Abundant in the cerebellum, cerebrum, and brainstem

·        Forms butterfly shaped portion of the Central Spinal Cord

·        CNS: Nucleus

·        PNS: Ganglion

-White Matter:

·        Bundles of axons

·        Axons coated with myelin

·        Conducts processes and sends nerve signals up and down the spinal cord

Central Nervous System is made up of the Brain and Spinal Cord

Traumatic Brain Injury

- Defined as an insult to the brain that's caused by an external physical force and that results in altered brain function

-Can result from blunt trauma, penetrating trauma, acceleration, deceleration or blast wave injuries

-TBI is considered a leading cause of death and long term disability

-30% of all injury related deaths are due to TBI

- Unintentional falls are the leading cause of head trauma

- Unintentionally being struck by an object and motor vehicle accidents comprise the two other major causes of TBI

- Open head injury or closed head injury

·        Open Head Injury:

o   Skull has been penetrated and the meninges have been breached

o   Velocity determines the extent of the damage

o   Formation of aneurysms because vasculature becomes weakend

·        Closed Head Injury:

o   Occurs in the absence of a skull fracture; when soft tissue of the brain is forced in contact with the skull

o   Coupe:

§  Initial blow occurs under the point of impact

o   Counter Coup:

§  The brain decelerates against the contralateral skull, on the opposite side

§  Injury is usually worse than the coupe injury

-Brainstem involvement may result in paralysis or death

Moderate to Severe TBI

-Symptoms

·        Headaches, migraines, dizziness, vertigo, sensitivity to light, sensitivity to sound

·        Seizures, blurry vision, a lot of tears produced, dry eyes

·        Chronic pain

·        Disruption of sleep and emotional disorders

·        Formation of Heterotopic Ossification

o   Abnormal bone growth around joint

o   Onset usually 4 or 12 weeks after TBI

o   Loss of range of motion

o   Local tenderness

o   Erythema, swelling

Mild TBI or Concussion

-Loss of consciousness last relatively short time or there may be no loss of consciousness

-Post concussion syndrome

·        Occurs 7-10 days following concussion

·        Resolves within 3 months

·        Symptoms:

o   Dizziness reading, difficulty with memory, headaches, fatigue, personality changes

Peripheral Nervous System (PNS)

-Consists of the nerve that branch out from the brain and the spinal cord

-Nerves that form the communication network between the CNS and the rest of the body

PNS Division

-Sensory or Afferent Fibers:

·        Bring information from the Periphery to the CNS

-Motor or Efferent Fibers:

·        Can further subdivide into the somatic nervous system, autonomic nervous system

-Periphery nerve can contain a variety of fibers, sensory, somatic motor, autonomic motor

Myelinated Peripheral Nerve Fibers

-Myelin sheath wrapped around the axon as an extension of a Schwann cell

-Endoneurium:

·        Intravascular connective tissue (henley’s sheath

·        Connective tissue sheath that directly surrounds individual Schwann cells

·        Type III Collagen fibers

·        Endoneurial Tube – nutritive and protective function

Connective Tissue

-25 to 80% of peripheral nerve is connective tissue

-If connective tissue is injured it has to go through a repair process, results in scar

·        Affects the function of a nerve after it is injured

-When joint motion causes elongation of the nerve bed the nerve is inherently placed under tensile stress

-Convergence: Nerve glides towards the moving joint

-Divergence: Nerve bed tension is relieved during joint motion, nerve realigns along the shortened nerve bed by gliding away from the moving joint.

Impact of Compression

-Compression stress of low magnitude and short duration may result in reversible physiological and minor structural changes.

-High Magnitude compressive stresses may result in structural alterations in myelin sheaths

Nerve Injury

-Peripheral Nerve Vulnerabilities:

·        Tunnels – nerve can rub against the walls of the tunnel

·        Proximity to Surface – more vulnerable to external compression

Categories of Nerve Injury

-Neurapraxia:

·        Local conduction block, axon continuous, innervates tissue patent

-Axonotmesis

·        Loss axonal continuity, some degeneration of distal axons

-Neurotmesis

·        Loss of continuity by severance or scar

Response to Axonal Transection

-Wallerian Degeneration

·        Within two to three days wallerian degeneration commences

·        Axonal and myelin disintegration both in an anterograde and retrograde direction

·        Antegrade wallerian degeneration then continues with schwann cells and macrophage infiltration to help remove that cellular debris

·        3-6 weeks Schwann cells begin to proliferate and organize; guides axonal sprouts between the basement membrane of two nerve ends

·        Sprouts can enter the wrong endoneurial tube and that will grow in an incorrect target resulting in altered function

·        If that sprout encounters scar tissue then a neuroma can form and that nerve Axon does not return to its original target

Peripheral nerve Pathology

-Gillian-Barre Syndrome

·        Is a rapid onset muscle weakness and it's caused by the immune system

·        immune system damages the peripheral nervous system

·        Initial symptoms are changes in sensation & pain and then progress to muscle weakness; develops distally in the feet and hands and then it spreads proximally to the upper body

·        Symptoms can develop in a few hours or a longer period of time during the acute phase

·        15% of people have weakness in breathing muscles and may require ventilation to survive

-Poliomyelitis

·         

poliomyelitis commonly shortened to just known being known as polio this is an infectious disease that's caused by the polio virus about 75% of cases are asymptomatic or have mild symptoms which can include like a sore throat and a fever but the rest have more severe symptoms and that could lead to things like paresthesia and permanent paralysis and that could you know lead to possible death in extreme cases post polio syndrome usually occurs about 20 to 30 years after a polio infection and recovery post polio syndrome is believed to result from a deterioration of motor neurons over many years leading to the loss of muscle strength and dysfunction now unlike polio post polio syndrome is not contagious only a polio survivor can develop post polio syndrome yet not everyone who survives polio is going to develop post polio syndrome

diabetes associated polyneuropathy is um this is synonymous with just the term diabetic neuropathy this is the bane of my existence as a PT because I deal with patients I deal with the consequence of diabetic neuropathy every shift that I work it is the most common neurologic complication of diabetes and a major cause of morbidity diabetic neuropathy leads to gradual loss of integrity of nerve fibers the symptoms begin distally and symmetrically in the toes and feet in addition to neurologic disability related to sensory loss and the risk of foot ulcers and amputations approximately 15 to 20% of patients have just painful symptoms so they they they develop neuropathic pain which is this very odd phenomenon right because the patients feel like they've got sensation because they have all of this pain but if you actually sensory test them they do not have sensation and so sometimes they take risks like they want to soak their feet for instance in hot water because their feet ache so bad but they don't realize that they don't have sensation in their feet so then they put their their feet in a tub of hot water the water is too hot but they can't sense that extreme temperature of the water and then they develop really severe burn injury as a result

 I'll syndrome occurs when the carpal tunnel narrows or if the synovium surrounding the flexor tendons swell and this is going to put pressure on the median nerve and reduce its blood supply so if we reduce blood supply to the median nerve the result is going to be numbness tingling pain and weakness in the hand there we so many things could could potentially cause carpal tunnel syndrome it could be just due to the patients of anatomy but in addition there are other factors that can contribute to inflammation and increase pressure pressure this can include things like rheumatoid arthritis infections tumors cysts previous history of a wrist fracture or dislocation of the wrist most commonly I think are repetitive motions that are performed at home or in a patient's work now there are some risk factors that increase the chances of getting carpal tunnel syndrome for example women are more likely than men to experience it it's also more likely to occur with aging especially once you hit that year of 40 and and you get older than 40 it's also more common in people that have obesity that have diabetes that have alcohol addiction fibromyalgia and hypothyroidism also during pregnancy hormonal changes and extra body fluid retention may add swelling and pressure to the tunnel

 Does not affect the size or the number of nerve fascicles but the perineurium and epineurium do thicken with age and the endoneurium often becomes fibrosed with increased collagen there are reduced numbers of unmyelinated and myelinated fibers blood vessels to nerves may become atherosclerotic with aging and this occlusion and reduced blood supply could contribute to the loss of nerve fibers the prevalence of peripheral neuropathy you seen in older people is usually attributed to this vascular pathology the cause of aging neuropathy can be attributed to a combination of factors so the loss of motor and sensory cell bodies and chronic the a lifetime of chronic compression of the peripheral nerves or repetitive traumas that damage these nerves over time like all of these factors combined with comorbidity so additional medical conditions things like atherosclerosis nutritional deficiencies these can all contribute to the neuropathy of the aging