NERVOUS SYSTEM

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NERVOUS SYSTEM
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Homeostasis controlled by

• Nervous system
• Endocrine system

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Divisions of the nervous system

• Central nervous system (CNS)
• Spinal cord
• brain

• Peripheral Nervous system (PNS)
• Nerves that carry impulses to and from CNS

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Functions

• Monitoring changes inside and outside of body
  (stimuli) and gathers sensory input
• Integration processes and interprets the
  sensory input and makes decision about what is to
  be done
• Effects a response by activating a muscle or
  gland response is called motor output

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Neuron

• Nerve cell

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Parts of a neuron

• Dendrite carries impulses to the cell body
• Axon carries impulses from the cell body
• Myelin sheath protective layer formed by
  Schwann cells
• Nodes of Ranvier gaps between the sheaths ( not
  present in all neurons)
• Axonal terminals branches located at the
  terminal end of the neuron

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• Neurilemma sheath of Schwann
• Collateral branch branch arising from the axon
  ( not present in all axons)
• Oligodendrocytes take the place of the Schwann
  cells in the CNS

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SUPPORTING CELLS - neuroglia

• Astrocytes numerous projections with swollen
  ends that cling to neurons. Anchoring the
  neurons to their blood supply
• Microglia phagocytes that dispose of debris
  such as dead brain cells, bacteria, ect.
• Ependymal cells line cavities of the brain and
  spinal cord. Have cilia that beat to circulate
  the cerebrospinal fluid
• Oligodendrocytes
• Satellite cells protective and cushion nerve
  cells

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TYPES OF NEURONS
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1. Afferent

• Also called sensory
• Carry nerve impulses toward CNS

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2. Efferent

• Also called motor neuron
• Carries impulses away from CNS

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3. Interneuron

• Also called association neuron
• Connect motor and sensory neuron in neural
  pathways

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CONDUCTION OF A NERVE IMPULSE
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RESTING POTENTIAL

• Membrane is polarized
• Not conducting an impulse
• -65mV to 70 mV
• Na greater concentration on outside
• K greater concentration on inside
• Overall charge is on outside and on inside
• Na/K pumps maintains this difference

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DEPOLARIZATION

• Activates the neuron to transmit and action
  potential (AP) also called a nerve impulse
• All or nothing response AP is either propagated
  or not
• Threshold must be reached 55mv
• Na gates open and Na flows inside neuron
• Voltage changes from 65 to 40

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REPOLARIZATION

• Na gate closes
• K gate open and K flows to outside
• Voltage change from 40 to 65
• Na/K pumps return Na and K back to normal
• Thus neuron returns to resting potential

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REFRACTORY PERIOD

• AP has passed
• Na gate cant open
• Keeps AP from traveling in the wrong direction

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CROSSING THE SYNAPSE

• Synapse gap between the presynaptic and
  postsynaptic membrane
• AP arrives at the presynaptic membrane
• Presynaptic membrane becomes permeable to Ca
• Vesicles move to the presynaptic mb.
• They release neurotransmitter

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Myelinated neurons

• Conduction occurs faster because the nerve
  impulses jump from node to node along the length
  of the fiber
• Saltatory conduction faster conduction in
  myelinated neurons

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External impairment of conduction

• Alcohol, sedatives, and anesthetics block nerve
  impulses by reducing membrane permeability to
  sodium ions
• Is no Na ions can enter the neuron then no AP
  will occur
• Cold and pressure hinder impulse conduction
  because the interrupt blood circulation

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• Neurotransmitter diffuses across the synaptic
  cleft
• At the postsynaptic mb. The neurotransmitter
  merges with receptor sites
• AP starts at the postsynaptic mb
• Neurotransmitters may be broken down by enzymes,
  washed away, or recycles

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• Axons may synapse with many other neurons
• 25 different neurotransmitters
• acetyocholine
• norepinephrine

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NERVE

• A bundle of axons
• also called nerve fibers

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REFLES ARC

• Rapid predictable and involuntary responses to
  stimuli

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PERIPHERAL NERVOUS SYSTEM

• Made up of nerves that lie outside the CNS
• cell bodies (called ganglia) found outside the
  CNS
• 2 structural types
• cranial nerves
• spinal nerves

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Cranial nerves

• Carry impulses to and from the brain
• 12 pairs
• some are sensory
• some are motor
• some are mixed

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Spinal nerves

• Carry impulses to and from spinal cord
• all are mixed
• 31 pairs

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Functional classification of PNS
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Sensory

• Carries information to CNS from sense organs and
  sensory receptors
• example eye, Merkel discs

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Motor

• Somatic - allows one to consciously control
  skeletal muscles
• autonomic nervous system - regulates activity of
  smooth and cardiac muscles and glands

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2 branches of the autonomic nervous system

• Sympathetic nervous system
• parasympathetic nervous system

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SYMPATHETIC

• Controls bodys response to emergency situation
  and stress
• increase blood glucose levels in blood
• in heart rate
• increases oxygen uptake
• decrease activity of digestive system and urine
  output
• dilates pupils
• goosebumps/ perspiration

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PARASYMPATHETIC

• Opposite
• normal no stress situations
• steadies heart rate
• constricts pupils
• no effect on sweat glands

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CNS
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PROTECTION

• Meninges - connective tissue membranes around the
  brain
• cerebrospinal fluid - cushions,
• formed by choroids plexuses,
• fluid continually moves through ventricles and
  between the brain and spinal cord,
• 1/2 cup of fluid

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SPINAL CORD

• 17 inches long
• 2 way connection with brain
• ends at lumbar vertebrae 2
• rest of column filled with spinal fluid
• has gray and white matter

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• Caudal equina collection of spinal nerves that
  extend from the end of the spinal cord
• Paralysis result of injury to cord
• Severity due to location on spinal cord

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GRAY MATTER

• Contains cell bodies and nonmyelinated fibers
• contains portions of sensory and motor neurons

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WHITE MATTER

• Myelinated axons of interneurons that run to the
  brain and from one side of the SC to the other
  side ( called tracts)

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PARTS OF THE BRAIN

• http//www.psych.ualberta.ca/ITL/brain/

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Ventricles

• Interconnecting cavities filled with CSF
• 4 4th, 3rd, and 2 lateral ventricles

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Medulla Oblongata

• Regulates heart beat, blood pressure, and
  breathing,
• Has reflex centers for swallowing, coughing,
  sneezing, hiccupping and vomiting
• Has nerve tracts between the spinal cord and brain

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Pons

• Works with medulla to regulate breathing rate
• Mostly a fiber tract

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MIDBRAIN

• Relay station for tracts passing between the
  cerebrum and the spinal cord or cerebellum
• Has reflex centers for visual, auditory, and
  tactile responses
• Contains the cerebral peduncles and corpora
  quadrigemina

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CEREBELLUM

• Maintains normal muscle tone, posture, balance
• Ensures that all of the skeletal muscles work
  together to produce smooth and coordinated
  movements
• Essential for skills such as playing the piano or
  hitting a baseball.

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hypothalamus

• Forms floor of the 3rd ventricle
• Maintains homeostasis by regulating hunger,
  sleep, thirst, body temperature and water
  balance.
• Sex, pain , and pleasure centers are located here
  
• Part of the limbic system
• Called emotion visceral brain
• Regulates the pituitary gland therefore it is the
  link between the nervous system and the endocrine
  system

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THALAMUS

• Serves as a relay station for sensory impulses
  traveling upward to other parts of the brain to
  the cerebrum
• Involved in arousal and higher mental functions
  such as memory and emotion
• Gives one a crude awareness of whether the
  sensation will be pleasant or not

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Pineal gland

• Secretes the hormone melatonin
• At night the pineal gland produces melatonin -
  causes one to fall asleep

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LIMBIC SYSTEM

• System of tracts and nuclei
• Surround the brain stem
• Called emotional brain
• Blends higher mental functions and primitive
  emotions into a whole
• Area that makes eating and sexual behavior seem
  pleasant

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Parts of limbic system

• Hippocampus
• Amygdala
• Thalamus
• Hypothalamus
• Frontal lobe

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hippocampus

• Area through which incoming sensory signals
  generate particular limbic response
• example

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Amygdala

• Associated with fear conditioning and associating
  danger with sensory stimuli
• May be responsible for controlling human
  aggression

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Frontal lobe

• Keeps limbic system in check
• It uses reason to keep us from acting out strong
  feelings
• Alcohol suppresses the frontal lobe and the
  limbic system takes over

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RETICULAR FORMATION

• Nuclei and fibers that extend the length of the
  brain stem
• Reticular activating system
• Controls the sleep/wake cycle
• Severe damaged can cause one to be comatose

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CEREBRUM
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CEREBRUM

• Largest portion of the brain
• Divided into left and right cerebral hemispheres
• Surface has gyri elevated ridges of tissue
• Sulci shallow grooves
• Fissures deeper grooves
• Divided into lobes

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• Lobes named after cranial bones
• Gray matter
• Center for association, integration, and learning

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CORPUS CALLOSUM

• Bridge of nerve tracts that connect the right and
  left hemispheres
• Tracts cross left controlled by right side of
  brain

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• White matter tracts that carry information from
  1 part of cerebrum to another part
• Basal nuclei relay stations that help to
  regulate motor activities islands of gray
  matter found deep within the white matter

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LOBES

• Occipital vision
• Temporal hearing
• Frontal - olfactory and higher learning
• Parietal

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Functional areas of the cerebral cortex

• Somatic sensory area
• Impulses from the bodys sensory receptors,
  except for the special senses, are localized and
  interpreted in this area of the brain
• Primary motor area
• Allows us to consciously move our skeletal
  muscles

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GENERAL INFORMATION
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Falling in love

• Pleasure center in the hypothalamus
• Brain neurotransmitters norepinephrine and
  dopamine
• They give brain a pleasure flush (cousins of
  amphetamines)
• Falling in love pleasure center is bathed with
  dopamine and norepinephrine

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BLOOD BRAIN BARRIER

• Composed of least permeable capillaries in the
  body
• Prevents urea and most drugs from entering the
  brain tissue
• Useless against fats, respiratory gases
• Keeps internal environment of brain very
  controlled

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DISEASES/DISORDERS

• Multiple sclerosis
• Huntingtons chorea
• Parkinsons disease
• Meningitis
• Hydrocephalus
• Concussion
• Contusion
• Cerebral edema

• CVA
• TIA
• Alzheimers disease
• Quadriplegic
• Paraplegic
• Type A personality
• Cerebral palsy
• Spina
• bifida