What are the major components of a spinal
nerve?
Figure 13–6
Spinal Nerves
Organization of Spinal Nerves
• Every spinal cord segment:– is connected to a pair of spinal nerves
• Every spinal nerve:– is surrounded by 3 connective tissue
layers– that support structures and contain
blood vessels
3 Connective Tissue Layers
• Epineurium:– outermost layer– dense network of collagen
fibers• Perineurium:
– middle layer– divides nerve into
fascicles (axon bundles)• Endoneurium:
– inner layer– surrounds individual
axons
Peripheral Nerves
• Interconnecting branches of spinal nerves
• Surrounded by connective tissue sheaths
How does the distribution pattern of spinal nerves
relate to the regions they innervate?
Peripheral Distribution of Spinal Nerves
• Spinal nerves:– form lateral to intervertebral foramen– where dorsal and ventral roots unite– then branch and form pathways to
destination
Figure 13–9
3D Rotation of Peripheral Nerves and Nerve Plexuses
PLAYPLAY
Nerve Plexuses
• Contain no synapses!• For pre-midterm
(Summarized in tables in text and lab guide):– Know cord roots (“ventral
rami,” actually) that contribute to the plexus
– Know the names of the major peripheral nerves that each plexus gives rise to.
Figure 13–10
The Cervical Plexus
Figure 13–12a, b
3D Rotation of Lumbar and Sacral PlexusesPLAYPLAY
The Lumbar and Sacral Plexuses
• Innervate pelvic girdle and lower limbs
Figure 13–12c, d
The Lumbar and Sacral Plexuses
Medical Example: Shingles
• Post-Viral inflammation of the sensory nerves• Rash follows dermatomes.• Notice it does not cross the midline.
Figure 13–8
Dermatomes
• Bilateral region of skin• Monitored by specific
pair of spinal nerves
Figure 13–7b
Peripheral Distribution of Spinal Nerves
• Sensory fibers
Figure 13–7a
Peripheral Distribution of Spinal NervesPLAYPLAY
Peripheral Distribution of Spinal Nerves
• Motor fibers
Functional Organization of Neurons
• Sensory neurons:– about 10 million– deliver information to CNS
• Motor neurons:– about 1/2 million– deliver commands to peripheral
effectors
Functional Organization of Neurons
• Interneurons:– about 20 billion– interpret, plan, and coordinate signals
in and out– often organized into functional
“neuronal pools”
Figure 13–13a
5 Patterns of Neural Circuits in Neuronal Pools
1. Divergence:– spreads stimulation to
many neurons or neuronal pools in CNS
Figure 13–13b
5 Patterns of Neural Circuits in Neuronal Pools
2. Convergence:– brings input from many
sources to single neuron
Figure 13–13c
5 Patterns of Neural Circuits in Neuronal Pools
3. Serial processing:– moves information in
single line
Figure 13–13d
5 Patterns of Neural Circuits in Neuronal Pools
4. Parallel processing:– moves same
information along several paths simultaneously
Figure 13–13e
5 Patterns of Neural Circuits in Neuronal Pools
5. Reverberation:– positive feedback
mechanism– functions until inhibited
Reflexes
Development of Reflexes A reflex is a rapid, predictable
motor response to a stimulus. Innate reflexes are unlearned
and involuntary Acquired reflexes are complex,
learned motor patterns
Nature of Reflex Responses
Somatic: Reflexes involving skeletal muscles and somatic motor neurons.
Autonomic (visceral) Reflexes controlled by autonomic neurons Heart rate, respiration, digestion, urination,
etc Spinal reflexes are integrated within the
spinal cord gray matter while cranial reflexes are integrated in the brain.
Reflexes may be monosynaptic or polysynaptic
Components of a Reflex Arc
1. Activation of a Receptor: site of stimulus 2. Activation of a Sensory Neuron: transmits
the afferent impulse to spinal cord (CNS) 3. Information processing at the Integration
center: synapses (monosynaptic reflexes) or interneurons (polysynaptic) between the sensory and motor neurons. In CNS
Spinal reflexes or cranial reflexes
Components of a Reflex Arc 4. Activation of a Motor Neuron:
transmits the efferent impulse to effector organ
5. Response of a peripheral Effector: Muscle or gland that responds
Interneuron
Spinal Reflexes
4 important somatic spinal reflexes Stretch Tendon Flexor(withdrawal) Crossed extensor reflexes
Stretch Reflexes 1. Stretching of the muscle activates a
muscle spindle (receptor) 2. An impulse is transmitted by afferent
fibers to the spinal cord 3. Motor neurons in the spinal cord
cause the stretched muscle to contract 4. The integration area in the spinal cord
Polysynaptic reflex arc to antagonist muscle causing it to to relax (reciprocal innervation)
Stretch Reflex
Notice hammer
Stretch Reflex ExamplePatellar Reflex
Tap the patellar tendon muscle spindle signals stretch of muscle motor neuron activated & muscle contracts
Quadriceps muscle contracts Hamstring muscle is inhibited (relaxes)
Reciprocal innervation (polysynaptic- interneuron) antagonistic muscles relax as part of reflex
Lower leg kicks forward Demonstrates sensory and motor connections
between muscle and spinal cord are intact.
Tendon Reflexes Monitors external tension produced during
muscular contraction to prevent tendon damage Controls muscle tension by causing muscle relaxation
Golgi tendon organs in tendon (sensory receptor) activated by stretching of tendon inhibitory neuron is stimulated motor neuron is hyperpolarized and muscle relaxes
Both tendon & muscle are protected Reciprocal innervation (polysynaptic)
causes contraction
Martini pg 443 states the receptor is unidentified; this is incorrect.
Tendon Reflex
Notice no hammer
Flexor Reflex Withdrawal reflex
When pain receptors are activated it causes automatic withdrawal of the threatened body part.
Flexor (Withdrawal) Reflex
Is this a monosynaptic or a polysynaptic reflex?
Is this an ipsilateral or a contralateral reflex?
Crossed Extensor Reflex Complex reflex that consists of an
ipsilateral withdrawal reflex and a contralateral extensor reflex
This keeps you from falling over, for example if you step on something painful. When you pull your foot back, the other leg responds to hold you up.
Crossed Extensor Reflex
Superficial Reflexes Elicited by gentle cutaneous
stimulation
Important because they involve upper motor pathways (brain) in addition to spinal cord neurons
Superficial ReflexesPlantar Reflex
Tests spinal cord from L4 to S2 Indirectly determines if the corticospinal
tracts of the brain are working Draw a blunt object downward along the
lateral aspect of the plantar surface (sole of foot)
Normal: Downward flexion (curling) of toes
Normal
Abnormal(Babinski’s)
Plantar Reflex
Abnormal Plantar Reflex: Babinski’s Sign
Great toe dorsiflexes (points up) and the smaller toes fan laterally
Happens if the primary motor cortex or corticospinal tract is damaged
Normal in infants up to one year old because their nervous system is not completely myelinated.
Preview of the ANS
Figure 16–2
Organization Similarities of SNS and ANS
Visceral Reflexes
• Provide automatic motor responses
• Can be modified, facilitated, or inhibited by higher centers, especially hypothalamus
Figure 16–11
Visceral Reflexes
Case of the Woman with HT• Name the two parts of the ANS• Describe the two major groups of receptors
and their subtypes (and their usual ligands.)• Distinguish between receptor stimulation
and cell stimulation.• Explain what “specificity” means when we
are referring to a ligand’s specificity for receptors.
• Provide a background for studying examples of somatic and autonomic reflexes.
• review
Nerve Plexuses
• Complex, interwoven networks of nerve fibers
• Formed from blended fibers of ventral rami of adjacent spinal nerves
• Control skeletal muscles of the neck and limbs
The 4 Major Plexuses of Ventral Rami
1. Cervical plexus2. Brachial plexus3. Lumbar plexus4. Sacral plexus
Dorsal and Ventral Rami
• Dorsal ramus:– contains somatic and visceral motor
fibers– innervates the back
• Ventral ramus:– larger branch– innervates ventrolateral structures and
limbs– contribute to plexuses
Table 13-1
Summary: Cervical Plexus
Figure 13–10
The Cervical Plexus
Table 13–2 (1 of 2)
Summary: Brachial Plexus
Table 13–2 (2 of 2)
Summary: Brachial Plexus
Major Nerves of Brachial Plexus
• Musculocutaneous nerve (lateral cord)
• Median nerve (lateral and medial cords)
• Ulnar nerve (medial cord)• Axillary nerve (posterior cord)• Radial nerve (posterior cord)
Figure 13–12a, b
3D Rotation of Lumbar and Sacral PlexusesPLAYPLAY
The Lumbar and Sacral Plexuses
• Innervate pelvic girdle and lower limbs
Figure 13–12c, d
The Lumbar and Sacral Plexuses
The Lumbar Plexus
• Includes ventral rami of spinal nerves T12–L4
• Major nerves:– genitofemoral nerve– lateral femoral cutaneous nerve– femoral nerve
The Sacral Plexus
• Includes ventral rami of spinal nerves L4–S4
• Major nerves:– pudendal nerve – sciatic nerve
• Branches of sciatic nerve:– fibular nerve – tibial nerve
Table 13-3 (1 of 2)
Summary: Lumbar and Sacral Plexuses
Table 13-3 (2 of 2)
Summary: Lumbar and Sacral Plexuses
Medical Example: Poliomyelitis
• Polio means gray matter
• Virus causes inflammation of the gray matter in the anterior horn motor neurons.
• Results in paralysis which could kill a patient if it reaches the respiratory muscles
• Patients who recover have permanent weakness or paralysis in parts of the body (usually the legs)
Lou Gehrig’s Disease Amyotrophic Lateral Sclerosis
• ALS is a genetic disease that causes progressive destruction of anterior horn motor neurons.
• Leads to paralysis and death within 5 years.
• Stephen Hawking has this disease.
Medical Example: Shingles
• Post-Viral inflammation of the sensory nerves• Rash follows dermatomes.• Notice it does not cross the midline.
Figure 13–19
The Babinski Reflexes
• Normal in infants• May indicate CNS damage in adults
end