The Spinal Cord, Spinal Nerves, and Spinal Reflexes Flashcards
(112 cards)
1
Q
Regions of the spinal cord
A
- Cervical
- Thoracic
- Lumbral
- Sacral
2
Q
Gray matter
A
Neuron cell bodies
3
Q
White matter
A
Myelinated axons
4
Q
Spinal nerves
A
C1-C8 T1-12 L1-L5 S1-S5 CO1
5
Q
Where does the spinal cord extend to?
A
From the brain to L1-L2
6
Q
Posterior median sulcus
A
Shallow longitudinal groove in the spinal cord
7
Q
Anterior median fissure
A
Deep groove along the anterior surface of the spinal cord
8
Q
Central canal
A
Internal passageway
9
Q
Functions of cerebrospinal fluid (CSF)
A
Acts as a shock absorber and a diffusion medium for dissolved gases, nutrients, chemical messengers, and wastes
10
Q
Where is there the most gray matter?
A
In areas dedicated to sensory and motor control of the limbs
11
Q
Cervical enlargement
A
Supplies nerves to the shoulder and upper limbs
12
Q
Lumbosacral enlargement
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Supplies nerves nerves to pelvis and lower limbs
13
Q
Conus medullaris
A
Conical, tapered region of the spinal cord
14
Q
Filum terminale
A
Slender strand of fibrous tissue that extends from the inferior tip of the conus medullaris to the sacral vetebra
Part of coccygeal ligament
15
Q
Spinal ganglia
A
Contain cell bodies of sensory neurons
16
Q
Posterior roots
A
Made up of axon roots of sensory neurons
17
Q
Anterior roots
A
Made up of axons of motor neurons that extend into periphery to control somatic and visceral effectors
18
Q
Rootlets
A
Branch out from roots of spinal nerves
19
Q
Spinal nerve
A
Sensory and motor roots bound together to form a spinal nerve
20
Q
White ramus communicans
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Containing myelinated axons
21
Q
Gray ramus communicans
A
Containing unmyelinated axons fibres that innervate flands and smooth muscles in the body walls or limbs
22
Q
Posterior ramus
A
Providing sensory and motor innervation to the skin and muscles of the back
23
Q
Anterior ramus
A
Supplying ventrolateral body surface, structures in the body wall and lumbs
24
Q
Mixed nerves
A
Containing both afferent and efferent fibres
Spinal nerves are mixed nerves
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How many spinal nerves are there?
31, each associated with adjacent vertebrae
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How are cervical nerves named?
The cervical nerve takes the name of the vertebra immediately below it
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How are the thoracic, lumbar and sacral nerves named?
The nerve takes the name of the vertenbra immediately above it
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Spinal meninges
Series of specialised membranes surrounding the spinal cord that provide stability and shock absorption
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3 layers of spinal meninges
1. Dura mater
2. Arachnoid mater
3. Pia mater
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Dura mater
- Outermost
| - Dense collagen fibres
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Epidural space
Between the dura matter and the walls of the vertebral canal
Contains areolar tissue, blood vessels and adipose tissue
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Arachnoid mater
- Middle layer
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Subarachnoid space
Filled with CSF
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Lumbar puncture, spinal tap
Needle draws CSF from subarachnoid space
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Pia mater
- Innermost
| - Meshwork of elastic collagen fibres firmly bound to neural tissue
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Denticulate ligaments
Extend from pia mater through the arachnoid mater to dura mater
Provide lateral movement
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What prevents longitudinal movement?
Dural connections at the foramen magnum and the coccygeal ligament
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Meningitis
Inflammation of the meningeal membranes
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Spinal anaesthesia
Anaesthetics injected into subarachnoid space of the spinal cord
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Horns
Areas of gray matter on each side of the spinal cord
Posterior, lateral and anterior
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Gray commissures
Posterior and anterior
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Nuclei
Masses of gray matter within the CNS
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Sensory nuclei
Receive and relay sensory information from peripheral receptors
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Motor nuclei
Issue motor commands to peripheral effectors
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Posterior horns
Contains somatic and visceral sensory nuclei
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Anterior horns
Function in somatic motor control
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Lateral horns
Contain visceral motor neurons
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Posterior white columns
Lie between the posterior horns and the posterior median sulcus
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Anterior white columns
Lie between the anterior horns and the anterior fissure
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Anterior white commissure
Connect anterior white columns
Region where axons cross from one side of the spinal cord to the other
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Lateral white column
White matter between anterior and posterior columns on each side
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Tract
Bundle of axons in the CNS
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Short tracts
Carry sensory and motor signals between segments of the spinal cord
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Long tracts
Connect spinal cord with the brain
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Ascending tracts
Carry sensory information toward the brain
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Descending tracts
Convey motor commands to the spinal cord
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Layers of spinal nerves
1. Epineurium
2. Perineurium
3. Endoneurium
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Epineurium
- Outermost layer
| - Dense network of collagen fibres
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Perineurium
- Middle layer
| - Cover one fascicle
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Endoneurium
- Innermost layer
| - Surround individual axons
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Peripheral nerves
Branch from spinal nerves
Innervate body tissues and organs
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Dermatome
Specific bilateral region of the skin surface monitored by a single pair of spinal nerves
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What happens when a spinal nerve of spinal ganglion is damaged or infected?
Corresponding region of skin loses sensation
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Peripheral neuropathies
Regional losses of sensory and motor function most often resulting from nerve trauma or compression
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Shingles
Attacks neurons within the posterior roots of spinal nerves and sensory ganglia of cranial nerves
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Nerve plexus
Complex, interwoven network of nerves
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Four major plexuses
1. Cervical plexus
2. Brachial plexus
3. Lumbar plexus
4. Sacral plexus
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Cervical plexus
Consists of the anterior rami of spinal nerves C1-C5
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Phrenic nerve
Major nerve of the cervical plexus
Supply the diaphragm
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Brachial plexus
Innervates pectoral girdle and upper limb
Consists of anterior rami of spinal nerves C5-T1
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Trunks
Large bundles of spinal nerve axons
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Cords
Smaller branches of trunks
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Musculocutaneous nerve
Formed from lateral cord
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Median nerve
Made of medial cord and median nerve
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Lumbar and sacral plexuses
Innervate pelvic girdle and lower limbs
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Lumbar plexus
Contains axons from the anterior rami of spinal nerves T12-L4
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Major nerves of lumbar plexus
Genitofemoral nerve
Lateral femoral cutaneous nerve
Femoral nerve
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Sacral plexus
Contains axons from the anterior rami of spinal nerves L4-S4
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Major nerves of sacral plexus
Sciatic nerve
| Pudendal nerve
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What does the sciatic nerve branch into?
Fibular and tibial nerve
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Reflexes
Automatic responses
| Motor responses to specific stimuli
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Sensory information
1. Sympathetic nerve carries sensory information from the visceral organs
2. Anterior ramus carries sensory information from ventrolateral surface, structures in the body wall, and the limbs
3. Posterior ramus carries sensory information from the skin and skeletal muscles of the back
4. Posterior root of each spinal nerves carries sensory information to the spinal cord
83
Motor commands
1. Anterior root of each spinal nerve contains the axons of somatic motor and visceral motor neurons
2. Spinal nerve forms just lateral to the invertebral foramen, where the posterior and anterior roots unite
3. Posterior ramus contains somatic motor and visceral motor fibers that innervate the skin and skeletal muscles of the back
4. The axons in the relatively large anterior ramus supply the ventrolateral body surface, structures in the body wall and the limbs
5. White ramus communicans is the first branch from the spinal nerve and carries visceral motor fibres to a nearby sympathetic ganglion
6. The gray ramus communicans contains postganglionic fibres that innervate glands and smooth muscles in the body wall or limbs
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Which ganglionic branches are myelinated?
Preganglionic axons - white ramus
| Postganglionic axons - gray ramus
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Rami communicantes
White and gray rami together
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Where are white and gray rami found?
White - between T1 and L2
| Graya - associated with each spinal nerve
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Reflex arc
1. Arrival of a stimulus and activation of a receptor
2. Activation of a sensory neuron
3. Information processing in the CNS
4. Activation of a motor neuron
5. Response by a peripheral effector
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Receptor
Specialised cell or the dendrites of a sensory neuron
Sensitive to chemical of physical changes
Respond to stimuli that cause or accompany tissue damage
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Innate reflexes
Result from connections that form between neurons during development e.g. withdrawal reflex
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Acquired reflexes
Learned motor patterns e.g. experienced driver steps on the brakes when trouble appears
Repetition enhances acquired reflexes
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Somatic reflexes
Provide a mechanism for the involuntary control of the muscular system
Immediate
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Visceral reflexes
Control the activities of other systems
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Monosynaptic reflexes
Involve the simplest reflex arc
Sensory neuron innervate a motor neuron directly
Motor neuron performs the information processing
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Polysynaptic reflexes
Have at least one interneuron between the sensory neuron and the motor neuron
Longer delay between stimulus and response
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Spinal reflexes
The important interconnections and processing events occur in the spinal cord
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Cranial reflexes
Reflexes processed in the brain
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Intersegmental reflex arcs
Most complicated polysynaptic reflex arcs
| Many segments interact to produce a coordinated highly variable motor response
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Stretch reflex
Monosynaptic
Automatically regulates skeletal muscle length
e.g. patellar reflex (knee-jerk)
Stimulus (increase in muscle length > sensory neuron activated > immediate motor neuron response (muscle contracts) > stimulus counteracted
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Muscle spindles
Sensory receptors involved in the stretch reflex
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Intrafusal muscle fibres
A bundle of small, specialised skeletal muscle fibres
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Extrafusal muscle fibres
Large skeletal muscle fibres that surround muscle spindles
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Gamma motor neurons
Motor neurons innervating intrafusal fibres
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Gamma efferents
Axons of motor neurons innervating intrafusal fibres
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Function of muscle spindles
Stretching muscle spindles produce a sudden burst of activity in the sensory neurons > stimulation of motor neurons > rapid muscle shortening
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Postural reflexes
Maintains a person's upright posture
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Tendon reflex
Monitors the tension produced during muscular contractions and prevents damage to tendons
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Withdrawal reflex
Move affected portions of the body away from a source of stimulation
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Flexor reflex
A withdrawal reflex affecting muscles of a limb
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Crossed extensor reflex
Complements withdrawal reflexes
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What do all polysynaptic reflexes involve?
1. Involve pools of interneurons
2. Are intersegmental in distribution
3. Involve reciprocal inhibition
4. Have reverberating circuits, which prolong the reflexive motor response
5. Can cooperate to produce a coordinated response
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Reinforcement
Enhancement of spinal reflexes produced by facilitation
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Plantar reflex
Replaces Babinski reflex in infants
