MSN II- NEURO UDAN

• Nervous system


  Carries out the following functions:

  • Receives stimuli from the internal and external environments through afferent or sensory pathways
  • Communicates information between distant parts of the body to the central nervous system
  • Processes the information received at various reflex and conscious levels to determine appropriate responses
  • Transmits information rapidly over efferent or motor pathways to effector organs for body action control or modifications

  
• Neuron


  The basic structural and functional unit of the nervous system, consisting of a cell body, dendrites and an axon
• Neuron


  • The axon transmits information away from the cell body to adjacent neurons

  The dendrites receive information from axon terminals at synapses and transmit it to the cell body

  The axon is covered by the myelin sheath which is interrupted by nodes of Ranvier, allowing for faster conduction velocity
• Synapse


  The specialized site where neurons make functional contact with one another, involving chemical transmission that can be excitatory or inhibitory
• Divisions of the nervous system

  • Central nervous system (brain and spinal cord)

  Peripheral nervous system

  
• Central nervous system


  • The brain is divided into the brain stem, cerebrum, and cerebellum

  The cerebral cortex is divided into lobes with specialized functions

  
• Functions of cerebral lobes

  • Frontal lobe: Conceptualization, abstraction, motor ability, judgment formation, ability to write words

  Parietal lobe: Integrative and coordinating center for perception and interpretation of sensory information, ability to recognize body parts, discrimination of left versus right

  Temporal lobe: Memory storage, integration of auditory stimuli

  Occipital lobe: Visual center, understanding of written material

  
• Speech centres


  Broca's area (frontal lobe): Motor (expressive) speech centre

  Wernicke's area (temporal lobe): Auditory speech centre

  
• Basal ganglia


  • Structures within the cerebrum that are part of the extrapyramidal system, responsible for postural adjustments and gross volitional movements

  
• Brain stem structures and functions

  • Diencephalon: Thalamus, epithalamus, subthalamus, hypothalamus

  Midbrain: Relays impulses from cerebral cortex to subcortical structures

  Pons: Contains pneumotaxic centre that controls rhythmic respiration

  Medulla: Contains vital centres for respiration, vasomotor control, swallowing, and vomiting reflex

  
• Cerebellum


  • Maintains orientation in space, controls antigravity muscles, checks or halts volitional movements
• Brain blood supply


  • Internal carotid arteries: Supply most of cerebral hemispheres

  Vertebral arteries: Supply brainstem, cerebellum, occipital lobes

  These systems anastomose at the circle of Willis

  
• Blood-brain barrier


  Layer of least permeable capillaries that selectively allows entry of certain substances while preventing others
• Cerebrospinal fluid (CSF)


  Fluid found in the ventricles of the brain, central canal of spinal cord, and subarachnoid space

  Produced by choroid plexus, functions to cushion, nourish, and regulate intracranial pressure
• Spinal cord


  • Contains central gray matter surrounded by white matter columns with ascending and descending tracts

  Site of reflex pathways that do not require relay to the brain

  
• Meninges


  • Dura mater (outermost), arachnoid, pia mater (innermost)

  Associated spaces: epidural, subdural, subarachnoid
• Peripheral nervous system


  • Cranial nerves (12 pairs)

  Spinal nerves (31 pairs)

  Somatic nervous system (innervates skeletal muscles)

  Autonomic nervous system (sympathetic and parasympathetic)

  
• Neurotransmitters


  Sympathetic: Norepinephrine

  Parasympathetic: Acetylcholine
• Sympathetic nervous system


  Increases heart rate, dilates brain vessels, dilates bronchi, decreases peristalsis, closes anal sphincter, relaxes bladder
• Parasympathetic nervous system


  Decreases heart rate, constricts brain vessels, constricts bronchi, increases peristalsis, opens anal sphincter, contracts bladder
• Spinal nerves


  • Cervical
  • Thoracic
  • Lumbar
  • Sacral
  • Coccygeal
• Spinal nerves form the cauda equina
• Spinal nerves that transmit motor information toward the CNS are somatic and autonomic nerves

  
• Effects of sympathetic nervous system

  • Increased heart rate
  • Dilated pupils
  • Dilated bronchi
  • Decreased peristalsis
  • Closed anal sphincter
  • Relaxed bladder
  • Closed bladder sphincter
  • Dilated blood vessels in brain
  • Increased skin reactions
  • Decreased gastric and salivary secretions
  • Stimulated glycogenolysis
  • Diminished pancreatic enzyme secretion
  • Stimulated norepinephrine production
• Effects of parasympathetic nervous system

  • Decreased heart rate
  • Constricted pupils
  • Constricted bronchi
  • Increased peristalsis
  • Opened anal sphincter
  • Contracted bladder
  • Opened bladder sphincter
  • Accommodated near vision
  • Increased gastric and salivary secretions
  • Increased pancreatic enzyme secretion
  • Caused erection
• Loss of brain cells with actual loss of brain weight occurs with aging
• Gyri of the brain surface atrophy, causing widening and deepening of spaces between the gyri with aging
• Decrease in blood flow and increased reaction time and increased time required for decision making occurs with aging
• Impairment in short-term memory occurs with aging
• Ability of the brain to autoregulate its blood supply lessens with aging
• Alteration of sleep-wakefulness ratio occurs with aging
• Decreased ability to regulate body temperature because of changes in the function of the hypothalamus occurs with aging
• Sensory and motor conduction decreases in velocity of nerve impulses with aging, with sensory conduction decreasing faster than motor, especially in peripheral nerves
• 1. ray visualization of the skull confirms skull fracture
• 1. ray visualization of the spine
• Computerized reconstruction of body part by passage of multiple X-ray beams is a CAT scan
• Graphical recording of spontaneous electrical impulses of the brain from scalp electrodes is an electroencephalography (EEG)
• EMG records electrical activities in muscles at rest, during voluntary contraction, and in response to electrical stimulation
• NCV studies record speed of conduction in motor and sensory fibers of peripheral nerves

  
• Brain scan involves administration of radionuclide to detect brain tumors and cerebral vascular diseases