1. Unit IV: Coordination Reflex Arc
Chapter 11 – pp
Chapter 12 – pp

2. Internal Coordination
Endocrine and nervous system maintain internal coordination
endocrine =
nervous =
Reflex Arc:
sense organs receive information
brain and spinal cord determine responses
brain and spinal cord issue commands to glands and muscles

3. Subdivisions of Nervous System
Central nervous
system (CNS)
Peripheral nervous
system (PNS)
Brain
Two major anatomical subdivisions
Central nervous system (CNS)
Peripheral nervous system (PNS)
consists of nerves and ganglia
Spinal
cord
Nerves
Ganglia

4. Neural Tissue
A nerve is a bundle of nerve fibers (axons) wrapped in fibrous connective tissue.
emerge from the CNS to carry signals between organs
Neurons and neuroglial cells

5. Functions of Neurons Excitability (irritability) stimuli Conductivity
produce traveling electrical signals
Secretion
at end of nerve fiber, a neurotransmitter is secreted

6. Structure of a Neuron Soma (cell body) Dendrites Axon (nerve fiber)
trigger zone
Myelin Sheath
some nerve fibers
insulating layer (mostly lipid)
formed by neuroglia

7. A Representative Neuron

8. Functional Classes of Neurons

9. Structural Classes of Neurons
Dendrites
Axon
Synaptic
terminals
Structural Classes of Neurons
Cell body
Dendrites
Dendritic
process
Axon
Synaptic
terminals
Multipolar neuron
Bipolar neuron
Unipolar neuron
Peripheral fiber carries impulses from source of sensation
Central fiber carriers impulses to spinal cord
Anaxonic neuron
Dendrites
Initial
segment
Axon
Synaptic
terminals

10. Neuroglial Cells Also known as Glial cells Outnumber neurons
General functions:
Protect
Support, maintain physical structure of neural tissue
Repair
Maintain nutrient supply to neurons

11. Types of Neuroglial Cells
Occur in the Central Nervous System
Oligodendrocytes
form myelin sheaths in CNS
Ependymal cells
line cavities of brain and spinal cord
produce and circulate CSF
Microglia
macrophages (WBC)
Phagocytosis
in areas of infection, trauma or stroke

12. Types of Neuroglial Cells
Astrocytes
most abundant glial cells
cover brain surfaces
formation of blood-brain barrier
regulate composition of cerebrospinal fluid
remove neurotransmitters and potassium ions from ICF
repairing damaged tissue with scar tissue
Occur in the Peripheral Nervous System
Schwann cells
form myelin sheath in PNS
Satellite cells
surround somas of neurons in ganglia

13. Neuroglial Cells of CNS
Section of
spinal cord
Ependymal cell
Microglial cell
Neurons
Gray matter
White matter
Myelinated
axons
Astrocytes
Oligodendrocyte
Capillary
Axon
Myelin
(cut)
Nodes
Unmyelinated
axon

14. Myelination

15. Demyelination Hallmark of some neurodegenerative autoimmune diseases:
Multiple Sclerosis
Demyelination in CNS
Own immune system attacks and damages myelin
Scars form in white matter of CNS
Cause unknown, no cure
Cerebral Palsy
Damage to developing oligodendrocytes usually during infancy
Mutations, lack of oxygen, interruption of blood flow
Treatment of symptoms, no cure
Leukodystrophies
Results from defect in the gene that controls the production of only one component molecule of myelin
Affects growth and maintenance of white matter
Inherited, no cure

16. Nerve Signal Depends on two factors: Presence/absence of myelin
Diameter of fiber
- large/thicker fibers have more surface area for signals
Functions
fast signals employed when speedy responses are needed
slow signals used when quick responses are not important

17. Regeneration of Nerve Fiber in PNS
Axon
Myelin
Step 1: the axon
and myelin
degenerate and
fragment.
Step 2: The Schwann
cells proliferate and
macrophages remove
the debris distal to the
injury site.
Macrophage
Regeneration Tube
Step 3: The axon
grows along the
path created by the
Schwann cells.
Step 4: As the axon
elongates, the Schwann
cells wrap around it.
Site of injury

18. Reflexes Properties: Require stimulation Quick Involuntary Stereotyped
Reflex Arc:
Somatic receptors → afferent nerves → integrating center → efferent nerves → skeletal muscles

19. The Stretch Reflex
When a muscle is stretched, it contracts and maintains increased muscle tone (stretch reflex)
helps maintain equilibrium and posture
balances tension in extensors and flexors
mediated by the brain
Reciprocal inhibition prevents muscles from working against each other
Very sudden muscle stretch causes tendon reflex
knee-jerk (patellar) reflex is monosynaptic reflex

20. The Tendon Reflex 6 Primary afferent neuron stimulates
inhibitory interneuron
To brain 4
Primary afferent
neuron stimulates
alpha motor neuron
to extensor muscle 7
Interneuron inhibits
alpha motor neuron
to flexor muscle 5
Alpha motor neuron
stimulates extensor
muscle to contract 3
Primary afferent
neuron excited 2
Muscle spindle
stimulated 1
Extensor muscle
stretched 8
Flexor muscle
(antagonist) relaxes

21. Flexor (Withdrawal) Reflexes
Occurs during withdrawal of a limb from pain
Contract flexor muscles
Polysynaptic reflex arc
Not just one sudden response as in stretch reflex
Ipsilateral reflex arc

22. Crossed Extensor Reflexes
Maintains balance by extending other limb
Contract extensor muscles
Contralateral reflex arcs explained by pain at one foot causes muscle contraction in other leg

23. Golgi Tendon Reflex
Golgi tendon organs in a tendon near its junction with a muscle
Excessive tension on tendon inhibits motor neuron
muscle contraction decreased
Also functions when some parts of muscle contracts more than others