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THE NERVOUS SYSTEM

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Title: THE NERVOUS SYSTEM


1
THE NERVOUS SYSTEM
  • HEADING
  • VOCABULARY
  • IMPORTANT INFO

2
Major Structures of the Nervous System
  • Brain, cranial nerves, spinal cord, spinal
    nerves, ganglia, enteric plexuses and sensory
    receptors

3
Nervous System Divisions
  • Central nervous system (CNS)
  • consists of the brain and spinal cord
  • Peripheral nervous system (PNS)
  • consists of cranial and spinal nerves that
    contain both sensory and motor fibers
  • connects CNS to muscles, glands all sensory
    receptors

4
Subdivisions of the PNS
  • Somatic (voluntary) nervous system (SNS)
  • neurons from cutaneous and special sensory
    receptors to the CNS
  • motor neurons to skeletal muscle tissue
  • Autonomic (involuntary) nervous systems
  • sensory neurons from visceral organs to CNS
  • motor neurons to smooth cardiac muscle and
    glands
  • sympathetic division (speeds up heart rate)
  • parasympathetic division (slow down heart rate)
  • Enteric nervous system (ENS)
  • involuntary sensory motor neurons control GI
    tract
  • neurons function independently of ANS CNS

5
Neurons
  • Functional unit of nervous system
  • Have capacity to produce action potentials
  • electrical excitability
  • Cell body
  • single nucleus with prominent nucleolus
  • Nissl bodies (chromatophilic substance)
  • rough ER free ribosomes for protein synthesis
  • Neurofilaments give cell shape and support
  • Microtubules move material inside cell
  • Cell processes dendrites axons

6
The basic unit of the nervous system
neuron?
  • Dendrites receive stimuli
  • Nerve cell body
  • _at_ nucleus transmits the stimuli
  • Axon transmits the impulse to another dendrite

7
Parts of a Neuron
Neuroglial cells
Nucleus with Nucleolus
Axons or Dendrites
Cell body
8
Dendrites
  • Conducts impulses towards cell body
  • Typically short, highly branched unmyelinated
  • Surfaces specialized for contact with other
    neurons
  • Contains neurofibrils Nissl bodies

9
Axons
  • Conduct impulses away from cell body
  • Long, thin cylindrical process of cell
  • Impulses arise from initial segment (trigger
    zone)
  • Side branches (collaterals) end in fine processes
    called axon terminals
  • Swollen tips called synaptic end bulbs contain
    vesicles filled with neurotransmitters

Synaptic boutons
10
Functional Classification of Neurons
  • Sensory (Afferent) neurons
  • transport sensory information from skin, muscles,
    joints, sense organs viscera to CNS
  • Motor (Efferent) neurons
  • send motor nerve impulses to muscles glands
  • Interneurons (Association) neurons
  • connect sensory to motor neurons
  • 90 of neurons in the body

11
What is a synapse ?
  • Junction of two neurons
  • Neurotransmitterconvert the electrical impulse
    into a chemical message

12
Axon ending terminal bud
  • Transfers the electrical nerve impulse
  • By chemical neuron-transmitters
  • From one neuron to the next

13
The Action Potential Summarized
14
Chemical Synapses
  • Action potential reaches end bulb and
    voltage-gated Ca 2 channels open
  • Ca2 flows inward triggering release of
    neurotransmitter
  • Neurotransmitter crosses synaptic cleft binding
    to receptors
  • the more neurotransmitter released the greater
    the change in potential of the postsynaptic cell
  • Synaptic delay is 0.5 msec
  • One-way information transfer

15
The Central Nervous System
  • 1) Spinal Cord
  • 2) Brain
  • medulla for
  • breathing
  • cerebellum for
  • balance
  • cerebrum for
  • higher thinking bw

16
Spinal Cord Protection
  • By the vertebral column, meninges, cerebrospinal
    fluid, and vertebral ligaments.

17
External Anatomy of Spinal Cord
  • Flattened cylinder
  • 16-18 Inches long 3/4 inch diameter
  • In adult ends at L2
  • In newborn ends at L4
  • Growth of cord stops at age 5
  • Cervical enlargement
  • upper limbs
  • Lumbar enlargement
  • lower limbs

18
Spinal Cord Spinal Nerves
  • Spinal nerves begin as roots
  • Dorsal or posterior root is incoming sensory
    fibers
  • dorsal root ganglion (swelling) cell bodies of
    sensory nerves
  • Ventral or anterior root is outgoing motor fibers

19
Spinal Nerves
  • 31 Pairs of spinal nerves
  • Named numbered by the cord level of their
    origin
  • 8 pairs of cervical nerves (C1 to C8)
  • 12 pairs of thoracic nerves (T1 to T12)
  • 5 pairs of lumbar nerves (L1 to L5)
  • 5 pairs of sacral nerves (S1 to S5)
  • 1 pair of coccygeal nerves
  • Mixed sensory motor nerves

20
The Brain and Cranial Nerves
  • almost 3 lb.
  • Brain functions in sensations, memory, emotions,
    decision making, behavior

21
Principal Parts of the Brain
  • Cerebrum
  • Diencephalon
  • thalamus hypothalamus
  • Cerebellum
  • Brainstem
  • medulla, pons midbrain

22
Medulla Oblongata
  • Continuation of spinal cord
  • Ascending sensory tracts
  • Descending motor tracts
  • Nuclei of 5 cranial nerves
  • Cardiovascular center
  • force rate of heart beat
  • diameter of blood vessels
  • Respiratory center
  • medullary rhythmicity area sets basic rhythm of
    breathing
  • Information in out of cerebellum
  • Reflex centers for coughing, sneezing, swallowing
    etc

23
Pons
  • One inch long
  • White fiber tracts ascend and descend
  • Pneumotaxic apneustic areas help control
    breathing
  • Middle cerebellar peduncles carry sensory info to
    the cerebellum
  • Cranial nerves 5-7

24
Midbrain
  • One inch in length
  • Extends from pons to diencephalon
  • Cerebral aqueduct connects 3rd ventricle above to
    4th ventricle below

25
Cerebellum
  • 2 cerebellar hemispheres and Vermis (central
    area)
  • Function
  • correct voluntary muscle contraction and posture
    based on sensory data from body about actual
    movements
  • sense of equilibrium

26
Thalamus
  • 1 inch long mass of gray mater in each half of
    brain (connected across 3rd ventricle by
    intermediate mass)
  • Relay station for sensory information on way to
    cortex
  • Crude perception of some sensations

27
Hypothalamus
  • Dozen or so nuclei in 4 major regions
  • mammillary bodies are relay station for olfactory
    reflexesinfundibulum suspends the pituitary
    gland
  • Major regulator of homeostasis
  • receives somatic and visceral input, taste, smell
    hearing information monitors osmotic pressure,
    temperature of blood

28
Functions of Hypothalamus
  • Controls and integrates activities of ANS which
    regulates smooth, cardiac muscle and glands
  • Synthesizes regulatory hormones that control the
    anterior pituitary
  • Contains cell bodies of axons that end in
    posterior pituitary where they secrete hormones
  • Regulates rage, aggression, pain, pleasure
    arousal
  • Feeding, thirst satiety centers
  • Controls body temperature
  • Regulates daily patterns of sleep

29
Epithalamus
  • Pineal Gland
  • endocrine gland the size of small pea
  • secretes melatonin during darkness
  • promotes sleepiness sets biological clock
  • Habenular Nuclei
  • emotional responses to odors

30
Cerebrum (Cerebral Hemispheres)
  • Cerebral cortex is gray matteroverlying white
    matter
  • 2-4 mm thick containing billionsof cells
  • grew so quickly formed folds(Gyri) and grooves
    (Sulci or Fissures)
  • Longitudinal fissure separates left right
    cerebral hemispheres
  • Corpus Callosum is band of white matter
    connecting left and right cerebral hemispheres
  • Each hemisphere is subdivided into 4 lobes

31
Right versus left Cerebrum
32
Limbic System
  • Emotional brain--intense pleasure intense pain
  • Strong emotions increase efficiency of memory

33
2 Types of Nervous Responses?
  • A. Voluntary
  • the brain
  • spinal cord
  • B. Involuntary or
  • Autonomic System
  • Sympathetic
  • Parasympathetic

34
Somatic Sensory Pathways
  • First-order neuron conduct impulses to brainstem
    or spinal cord
  • either spinal or cranial nerves
  • Second-order neurons conducts impulses from
    spinal cord or brainstem to thalamus--cross over
    to opposite side before reaching thalamus
  • Third-order neuron conducts impulses from
    thalamus to primary somatosensory cortex
    (postcentral gyrus of parietal lobe)

35
Somatic Motor Pathways
  • Control of body movement
  • motor portions of cerebral cortex
  • initiate control precise movements
  • Basal Ganglia help establish muscle tone
    integrate semivoluntary automatic movements
  • Cerebellum helps make movements smooth helps
    maintain posture balance
  • Somatic motor pathways
  • direct pathway from cerebral cortex to spinal
    cord out to muscles
  • indirect pathway includes synapses in basal
    ganglia, thalamus, reticular formation
    cerebellum

36
The Autonomic Nervous System
  • Regulate activity of smooth muscle, cardiac
    muscle certain glands
  • Structures involved
  • general visceral afferent neurons (Sensory)
  • general visceral efferent neurons (Motor)
  • integration center within the brain
  • Receives input from limbic system and other
    regions of the cerebrum

37
The Autonomic Nervous System
38
Autonomic versus Somatic NS
  • Autonomic NS
  • unconsciously perceived visceral
    sensations
  • involuntary inhibition or excitation of
    smooth muscle, cardiac muscle or glandular
    secretion
  • 2 neurons needed to connect CNS to organ
  • Preganglionic and Postganglionic neurons
  • Somatic NS
  • consciously perceived sensations
  • excitation of skeletal muscle
  • one neuron connects CNS to organ

39
Autonomic versus Somatic NS
  • Notice that the ANS pathway is a 2 neuron pathway
    while the Somatic NS only contains one neuron.

40
Divisions of the ANS
  • 2 major divisions
  • Parasympathetic
  • Sympathetic
  • Dual innervation (2 nerve supplies)
  • 1 speeds up organ
  • 1 slows down organ
  • Sympathetic NS increases heart rate
  • Parasympathetic NS decreases heart rate

41
Sympathetic Responses
  • Dominance by the sympathetic system is caused by
    physical or emotional stress
  • E situations emergency, embarrassment,
    excitement, exercise
  • Alarm Reaction Flight or Fight Response
  • dilation of pupils, increase of heart rate, force
    of contraction BP
  • decrease in blood flow to nonessential organs
  • increase in blood flow to skeletal cardiac
    muscle
  • airways dilate respiratory rate increases
  • blood glucose level increase
  • Long lasting due to lingering of NE in synaptic
    gap and release of norepinephrine by the adrenal
    gland

42
Parasympathetic Responses
  • Enhance Rest-and-Digest activities
  • Mechanisms that help conserve and restore body
    energy during times of rest
  • Normally dominate over sympathetic impulses
  • SLUDD Type Responses salivation, lacrimation,
    urination, digestion defecation and 3
    decreases--- decreased HR, diameter of airways
    and diameter of pupil
  • Paradoxical Fear when there is no escape route or
    no way to win
  • causes massive activation of parasympathetic
    division
  • loss of control over urination and defecation

43
Control of Autonomic NS
  • Not aware of autonomic responses because control
    center is in lower regions of the brain
  • Hypothalamus is major control center
  • Input emotions and visceral sensory information
  • smell, taste, temperature, osmolarity of blood,
    etc
  • Output to nuclei in brainstem and spinal cord
  • posterior lateral portions control sympathetic
    NS
  • increase heart rate, inhibition GI tract,
    increase temperature
  • anterior medial portions control
    parasympathetic NS
  • decrease in heart rate, lower blood pressure,
    increased GI tract secretion and mobility
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