Neural Disorders Flashcards
Major cells of the nervous system
nervous tissues contains two types of cells - neurons and neuroglial cells.
the neurons are the functional units of the nervous system.
the neruoglial cells of the nervous system provide support for the neurons.
the neuroglial cells of the nervous system give neurons protection and metabolic support.
two types of neuroglial cells (oligodendrocytes in the CNS and Schwann cells in the PNS) produce the myelin sheath used to insulate nerve cell processes and increase the velocity of nerve impulse conduction.
in some pathologic conditions, the myelin may degenerate or be destroyed. this leaves a section of thr axonal process without myelin (demyelinated) while leaving the nearby oligodendroglial cells or Schwann cells intact. unless myelination takes place, the axon eventually dies.
Anatomy of neurons
the neuron is the functional unit of the nervous system.
neuron is composed of a cell body, one axon, and a variable number of dendrites.
dendrites are branches extensions of the nerve cell body that conduct information toward the cell body and are the main source of information for the neuron.
the axon transmits impulses away from the cell body. the axon of a neuron conducts nerve impulses from the cell body to its synaptic terminal.
transmission speed of nerve impulses from the dendrites to the synaptic terminals is enhanced by the myelin sheath, which is interrupted by the nodes of Ranvier.
Energy requirements of nervous tissue
the brain cannot store oxygen or effectively engage in anaerobic metabolism.
unconsciousness occurs almost simultaneously with cardiac arrest, and brain cell death begins within 4 to 6 minutes.
glucose is the major fuel source of the nervous system.
Components of the nervous system
the nervous system can be divided into two components - the central nervous system (CNS) and peripheral nervous system (PNS).
CNS consists of the brain and spinal cord.
PNS consists of cranial nerves (CNs) originating from the brain and spinal nerves.
nerve cells of both the CNS and PNS from incoming (afferent) sensory pathways and outgoing (efferent) motor pathways.
Central Nervous System - brain
four (4) lobes of the brain:
frontal
parietal
temporal
occipital
brain divided into two halves, each containing the four lobes of the brain.
right and left hemispheres communicate with each other through the corpus callosum.
Nervous system protection
CSF is produced by the choroid plexus. CSF flow is from lateral ventricles –> third ventricle –> fourth ventricle –> subarachnoid space. when CSF pressure exceeds venous pressure, CSF can be absorbed in the blood via the arachnoid - this is unidirectional (only out to blood).
blood-brain barrier - reduced permeability in capillaries that supply the brain provide protection of the brain from:
foreign substances
hormones and neurotransmitters in the systemic circulation
drastic environmental fluctuations
Circle of Willis
a cerebral arterial structure that connects the vertebral and carotids circulation.
the primary vascular drainage of the brain is the jugular veins.
no lymphatic system for the brain.
Meninges
the three layers of the meninges (dura mater, arachnoid mater, pia mater).
Dura mater lays up against the cranium itself. Arachnoid lays under it. CSF in between Arachnoid and Pia. Pia mater is against the brain itself.
note location of the cerebrospinal fluid in relation to the meninges layers.
Processes of neuronal injury
mature neurons do not divide - new neurons are not generated to replace damaged or injured.
in CNS - myelin that has been damaged is not replaced.
Neuronal injury
traumatic brain injury (TBI) - includes spectrum from head bonk to penetrating injury to the brain. concussion is included in this category as a subgroup.
closed head injuries are differentiated from penetrating injuries and cause a unique injury = Coup-countercoup injury. the coup injury is the injury to the brain that occurs with direct impact. the injury that results at the opposite sides of the impact is the countercoup injury.
Cerebral Palsy pathophysiology
cause: event during the antenatal or postnatal periods damaging upper motor neurons
etiology not completely understood but cerebral anoxia, hemorrhage, and other neurologic insults involved.
Cerebral Palsy pathophysiology: classification
motor dysfunctions type:
spastic = inability of muscles to relax
athetoid/dyskinetic = inability to control muscle movement
ataxic = inability to control balance and coordination
anatomic involvement:
hemiplegia = involving one arm and one leg on same side of body
diplegia = involving both legs
quadriplegia = involving all four extremities, the trunk and neck muscles
clinical manifestations: variable severity
no known cure
Seizure activity in the brain
seizure is a single event of abnormal electrical discharge from neurons in the brain that results in an abrupt, altered state of function.
seizures are classified into two broad categories:
focal onset
generalized onset
epilepsy is a chronic disorder of recurrent seizures.
seizures resulting from identifiable causes, such as substance withdrawal or fever, are not considered epilepsy.
the aura represents a focal seizure without impaired consciousness. the aura is perceived as a warning sign of impending seizures.
Generalized seizures
generalized seizure are the most common type of seizure.
symptoms include unconsciousness and involve varying degrees of symmetric motor response.
divided into two categories:
motor
nonmotor
Generalized motor seizures
tonic-clonic seizure: formerly called grand mal seizures
person has a vague warning and experiences a sharp tonic contraction of muscles with extension of muscles and loss of consciousness. incontinence is common.
tonic phase followed by clonic phase - rhythmic bilateral contraction and relaxation of extremities.
at end of clonic phase, the person remains unconscious until RAS (reticular activating system) begins to function again (postictal phase). tonic-clonic phases last approx 60-90 seconds.
