Chapter 8: Nervous System

1
Chapter 8 Nervous System

• Sensory Input
• Integration
• Homeostasis
• Mental Activity
• Control of muscles, glands

2
Divisions

• Central Nervous System (CNS)
• - brain spinal chord
• Peripheral Nervous System (PNS)
• - everything else

3
(No Transcript)
4
Subdivisions of PNS

• Sensory division
• - sensory receptors to CNS along
• sensory neurons
• Motor division
• - CNS to effectors along motor neurons

5
Subdivisions of Motor Division

• Somatic system
• - CNS to skeletal muscles
• Autonomic system
• - CNS to cardiac, smooth muscle and
• glands

6
(No Transcript)
7
Cells of the Nervous system

• Neurons and neuroglia
• Neurons are nerve cells
• Receive stimuli, transmit action potentials
• Cell body, dendrites, axons
• Axons can be 1 mm to 1 m

8
Fig. 8.3
Action Potentials
9
Types of neurons

• Multipolar neurons
• - many dendrites, single axon
• - most of CNS and motor neurons
• Bipolar
• - one dendrite, one axon
• - some sensory organs (retina)
• Unipolar
• - one process, cell body in middle
• - most sensory neurons

10
(No Transcript)
11
Neuroglia

• Non-neuronal cells of PNS and CNS
• Astrocytes- main support cell, BBB
• Ependymal- line fluid filled cavities in CNS
• - secrete and move CSF
• Microglia- remove bacteria, debris from
• CNS
• Oligodendrocytes- surround axons in CNS
• Schwann cells- surround axons in PNS
• - also called neurolemmocytes
• Table 8.1

12
(No Transcript)
13
(No Transcript)
14
Myelin Sheaths

• Axons are surrounded in PNS and CNS
• Unmyelinated axons rest in indentations of
  oligodendrocytes and schwann cells
• Myelinated axons have specialized sheaths called
  myelin sheaths
• Support cells wrap repeatedly around axon, which
  forms myelin sheath
• Myelin is an excellent insulator

15
Myelin Sheaths

• Myelin prevents electric flow through the
  membrane
• Gaps called Nodes of Ranvier occur between
  support cells
• Current flows easily in the Nodes of Ranvier
• Permits conduction of action potentials

16
Fig. 8.6
17
Organization of Nerve tissue

• Gray matter- groups of cell bodies, dendrites, no
  myelin
• Ganglion- cluster of neuron cell bodies in PNS
• White matter- bundles of myelinated axons
• - CNS- pathways or nerve tracts
• - PNS- nerves

18
Resting Membrane Potential

• All cells exhibit electrical properties
• Outside is positively charged
• Inside is negatively charged
• Charge difference is the resting membrane
  potential
• At rest, the cell is polarized
• Like a battery, the small voltage difference can
  be measured

19
Resting Membrane Potential

• RMP comes from differences in in ion
  concentrations across membrane
• High Na outside cell
• High K inside cell
• Concentration gradients maintained by Na/K-pump,
  which is an active transporter

20
(No Transcript)
21
Resting Membrane Potential

• At rest, Na channels closed, some K channels are
  open
• Some K can diffuse out of the cell, carries
  charges with them
• Large negatively charged proteins cannot diffuse
  out
• As K leaves, the inside becomes negatively charged

22
Resting Membrane Potential

• Negative charges tend to attract positive charges
• Equilibrium is reached between the tendency for K
  to diffuse out, and the negative charges
  attracting them in
• This is the equilibrium of the resting membrane
  potential, and no more movement of K

23
(No Transcript)
24
Action Potentials

• Muscle and nerve cells are excitable
• A stimulus can open Na channels for a brief time
• Na can diffuse into the cell (local current)
• Inside becomes more positive- depolarization
• Results in a local potential

25
Action Potentials

• If a threshold is not reached, Na channels close
  (chemically gated), local potential disappears
• If enough Na enters, and the local potential
  reaches a threshold value, then many Na channels
  open
• As more Na enters, depolarization occurs until
  the charges across the membrane are reversed

26
Action Potentials

• Charge reversal causes Na channels to close and K
  channels to open
• Repolarizes cell to resting membrane potential
• Depolarization and repolarization constitute an
  action potential
• Action potentials are all-or-none

27
Fig. 8.9
28
Fig. 8.10
29
Action Potential Conduction

• Unmyelinated axons- slow
• Action potential in one part of membrane
  stimulates local currents in adjacent areas
• Local currents produce action potentials
• Action potentials travel one-way
• - due to refractory period of Na channels
  during repolarization

30
Fig. 8.11
31
Action Potential Conduction

• Myelinated axons- very fast
• Action potential in one Node of Ranvier causes
  current to flow through extracellular fluid and
  cause an action potential in adjacent node
• Action potentials jump from node to node
• Saltatory conduction
• Walking vs. running

32
Fig. 8.12
33
Synapse

• Junction of one neuron with another neuron of
  effector organ
• End of axon presynaptic terminal
• Membrane of dendrite/organ postsynaptic membrane
• Space between membranes synaptic cleft
• Neurotransmitters stored in synaptic vesicles

34
Synapse

• Neurotransmitters released by exocytosis
• Diffuse across synaptic cleft
• Bind to receptor molecules on postsynaptic
  membrane
• Causes Na, K, or Cl channels to open or close
• Depends upon neurotransmitter and receptor
• Response stimulation or inhibition of action
  potential

35
Synapse

• Na channels open depolarization of postsynaptic
  membrane
• K or Cl channels open hyperpolarization
• - inside becomes more negative
• - action potential is inhibited

36
Fig. 8.13
37
Neurotransmitters

• Actetylcholine, norepinephrine, serotonin,
  dopamine, glycine, endorphins
• Rapidly broken down
• Transported back into presynaptic terminal
• Effects are short term
• Postsynaptic cell can be stimulated many times
  per second
• Table 8.2

38
Reflexes

• Involuntary response to stimulus applied to
  periphery
• Does not involve conscious thought
• Reflex arc- neuronal pathway
• Basic functional unit of nervous system

39
Reflexes

• 5 components
• Sensory receptor
• Sensory neuron
• Interneuron
• Motor neuron
• Effector organ
• Most reflexes occur in spinal cord

40
(No Transcript)
41
Neuronal Pathways

• Neurons organized into pathways
• 2 simplest types
• Converging- two or more neurons synapse with a
  third neuron
• Diverging- axon from one neuron divides and
  synapses with 2 neurons

42
(No Transcript)
43
Spinal Cord

• Extends from foramen magnum to second lumbar
  vertebrate
• Inferior end resembles a horses tail cauda
  equina
• Cross section
• Peripheral white matter, central gray matter

44
Fig. 8.16
45
Spinal Cord

• There is central canal filled with cerebrospinal
  fluid
• In the center there is gray matter and on the
  periphery is the white matter.
• White matter- divided into three columns in each
  half (r/left) of spinal cord
• Dorsal, ventral, lateral columns contain nerve
  tracts
• Ascending tracts- APs from PNS to CNS
• Descending tracts- CNS to PNS

46
Spinal Cord

• Gray matter shaped by letter H
• Posterior and anterior horns
• Small lateral horns in areas associated with
  autonomic system
• Fluid filled central canal

47
Spinal Cord

• Spinal nerves arise from rootlets along dorsal
  and ventral surfaces of s.c.
• Ventral rootlets form ventral root
• Dorsal rootlets form dorsal root
• Roots unite and form spinal nerve (31 pairs)
• Dorsal root has a ganglion- cell bodies of
  unipolar neurons
• Axons originate in periphery, synapse with
  interneurons or pass into the white matter

48
Spinal Cord

• Cell bodies of motor neurons are located in
  anterior and lateral horns of gray matter
• Somatic- anterior horn
• Autonomic- lateral horn
• Axons from motor units- ventral horn
• Dorsal root- sensory
• Ventral root- motor
• Spinal nerve- both

49
(No Transcript)
50
Fig. 8.18
51
Knee-Jerk Reflex

• Simplest reflex is stretch reflex
• Tap patellar ligament, quadriceps femoris tendons
  and muscles are stretched
• Sensory receptors in muscle are stretched
• Stretch reflex is activated
• Contraction of muscles extends leg
• Descending neurons synapse with relfex neurons
  and modulate their activity
• Test if higher CNS centers are functional

52
Fig. 8.19
53
Withdrawal Reflex

• Remove limb or body part from painful stimulus
• APs from pain receptors conducted by sensory
  neurons, synapse with interneuron, synapse with
  motor neuron
• Motor neurons synapse with muscles

54
(No Transcript)
55
Fig. 8.25b
56
Fig. 8.22
57
co
58
Fig. 8.23
59
Brainstem

• Medulla oblongata regulation of heart rate,
  Blood vessel diameter, breathing, swallowing,
  vomiting, coughing, sneezing, balance and
  coordination
• Pons several nuclei of MO and chewing and
  salvation
• Midbrain mainly ascending and descending tracts
  pathways for auditory visual reflexes, turning
  head and general body movement.

60
Cerbellum

• Little brain
• Comparator compares all the information and
  allows smooth coordinated movements
• Learned motor skills

61
Fig. 8.24
62
Diencephalon

• Thalamus Sensory neuron come to thalamus and
  then be directed to right parts of cerebrum
  influences moods, and registers unlocalized,
  uncomfortable perception of pain.
• Epithalamus Pineal gland, an endocrine gland
  that circadian rhythm and light-dark cycles
• Hypothalamus Maintain homeostasis. Hunger, body
  temperature, sexual pleasure, satisfaction after
  a good meal, fear, rage..

63
Fig. 8.28
64
Cerebrum

• Frontal lobe voluntary motor functions,
  motivation, aggression, mood, olfactory
  reception.
• Parietal Lobe reception and conscious perception
  of most sensory information
• Occipital Lobe visual
• Temporal lobe olfactory and auditory important
  in memory

65
Left and right hemispheres

• Left half of the brain control right part of the
  body and vice versa.
• Left half analytical and right half artistic
• Speech in left half
• Functional systems
• Limbic system cerebrum and diencephalon for
  survival hunger, thirst, emotions, motivation
  and mood. Related to hypothalamus
• Reticular formation Scattered through out
  brainstem. Maintaining consciousness. Sleep wake
  cycle input from visual and auditory.

66
Fig. 8.35
67
Fig. 8.36
68
Autonomic System

• Somatic motor neuron cell bodies are located in
  CNS, axons extend to skeletal muscles
• Autonomic- 2 neurons in series extend from CNS to
  target organs
• First, perganglionic neuron
• Second, postganglionic neuron
• Autonomic ganglia are located outside CNS

69
Autonomic System

• Autonomic functions are unconscious
• Symapathetic and Parasympathetic divisions
• Sympathetic neurons prepare individual for
  physical activity
• Parasympathetic neurons prepare body for rest
• Most organs are innervated by both divisions
  (sweat glands, blood vessels, smooth muscles of
  eye)

70
Sympathetic Division

• Fight or flight system
• Cell bodies located in lateral horn of spinal
  cord gray matter
• Axons exit through ventral roots
• Sympathetic chain ganglia- connected alongside
  spinal cord
• Collateral ganglia- located near target organ
• Long postganglionic neurons arise in these ganglia

71
Parasympathetic Div.

• Preganglionic cell bodies located in lateral part
  of central gray matter, or brain stem
• Axons extend through spinal nerves
• Ganglia located near or in target organ
• Short postganglionic fibers

72
Fig. 8.39