Chapter 13 and Lab 9: Spinal Cord and Spinal Nerves Flashcards
What are the two divisions of the Nervous System and their main components?
- Peripheral nervous system
- Sensory Nervous system
- Motor (somatic nervous system)
- Motor (autonomic/visceral nervous system)
- sympathetic division
- parasympathetic division
- Central nervous system
- decision maker
- takes input from PNS
What are the two principal cell types of the nervous system and their basic components?
- Neurons
- generate and transmit electrical signals
- functional units of nervous system
- 3 major types
- sensory (carry info about sensations)
- Interneurons (part of the CNS)
- Motor neurons (carry impulses to effectors)
- Neuroglia
- support or protection for neurons
- One type is Schwann cell (neurolemmocyte)
- found in PNS
- Neurons often wrapped in multiple Schwann cells-myelin sheath
- gaps between Schwann cells called Nodes of Ranvier
What are the parts of a neuron?
- Basic components: cell body, dendrites, axon
-
Cell body
- nucleus, Nissl Bodies (rough ER), organelles
- collections of cell bodies in CNS are nuceli, in PNS are ganglia
-
Dendrites
- plasma membrane of a neuron
-
Axons
- up to 3 feet long
- collection of axons in CNS is tract, in PNS is nerve
- usually does not touch next neuron or effector
- synapse bridged by neurotransmitter
What are the 3 protective membranes of the brain and spinal cord listed in order of superficial to deep?
- Dura mater
- subdural mater
- Arachnoid Mater
- subarachnoid mater
- Pia Mater
What nerves are in the Cervical plexus?
Phrenic nerve
What nerves are in the Brachial Plexus?
Axillary Nerve, Radial Nerve, Medial Nerve, and Ulnar Nerve
What nerves are in the lumbar plexus?
Femoral nerve, obturator nerve
What nerves are in the Sacral plexus?
sciatic nerve, pudendal nerve
What movement is associated with the Phrenic nerve?
Contraction causing inhalation
What movement is associated with the Axillary nerve?
- abduction of arm
- rotates humerus laterally
What movement is associated with the Radial nerve?
- extesion of wrist
- extension of fingers
What movement is associated with the median nerve?
- flexion of wrist
- flexion of fingers
- pronation
What movement is associated with the ulnar nerve?
- flexion of wrist
What movement is associated with the Femoral nerve?
- extension of knee
- flexion of hip
- flexion/abduction/lateral rotation of hip
- (innervates sartorius)
What movement is associated with the obturator nerve?
- adduction of hip
What movement is associated with the sciatic nerve?
- extension of hip
- flexion of knee
What movement is associated with the pudendal nerve?
- voluntary control of urination and defecation
What are the functions of the spinal cord?
- conduction
- ascending tracts: (Sensory) to brain
- descending tracts: (motor) from brain
- neural integration
- gray matter
- thinking
- locomotion
- groups of neurons that coordinate repetitive sequences of contraction
- reflexes
What is the anatomy of the spinal cord?
- flattened cylinder
- arises from brainstem (medulla oblongata)
- extends from foramen magnum to L1-L2
- growth of cord stops at age 5
- gives rise to 31 pairs of spinal nerves
- each pair of spinal nerves is a segment
What is spina bifida?
- congenital defect
- one or more vertebrae fail to completely enclose spinal cord
- lack of folic acid (form of vitamin B) increases risk
- 1 in 1000
How do gray matter and white matter differ?
- gray matter
- neuron cell bodies, unmyelinated axosn, dendrites
- site of information processing, synaptic integration
- white matter
- myelinated axons in 3 columns
- carry signals from one part of the CNS to another
What is the anatomy of gray matter?
- pair of posterior (dorsal) horns
- pair of anterior (ventral) horns
- Gray commissure connects right and left sides
- has central canal lined with ependymal cells and filled with CSF
- Lateral horns: visible from T2 through L1
- contains neurons of sympathetic nervous system
What is the anatomy of white matter?
- Bundles of axons that course up and down the cord providing communication between different levels of the CNS
- Columns or funiculi (3 pairs)
- posterior (dorsal), lateral, and anterior (ventral) columns
- Tracts or fasciculi (subdivisions of each column)
What are the components of spinal tracts?
- Fibers in a given tract have similar origin, destination, and function
- Ascending v. descending
- Decussation
- they cross over
- Contralateral v. ipsilateral
What are the functions of the ascending spinal tracts?
- Carry sensory signals up to spinal cord
- Uses 3 neurons from origin (receptors) to destintation (sensory area in brain)
- First order: detect stimulus and transmit signal to spinal cord or brain stem
- Second order: continues to the thalamus at the upper end of the brainstem
- Third order: carries the signal the rest of the way to the sensory region of the cerebral cortex
What are the functions of the descending spinal tracts?
- Carry motor signals down brainstem and spinal cord
- Involve 2 motor neurons
- Upper motor neuron
- originates in cerebral cortex or brainstem and terminates on a lower motor neuron
- Lower motor neuron
- soma is in brainstem or spinal cord
- axon leads to muscle or other target organ
- Upper motor neuron
Define a nerve and a mixed nerve.
- Spinal cord communicates with the rest of the body by way of nerves
- Nerve: cordlike organ composed of numerous nerve fibers (axons) bound together by connective tissue
- Mixed nerves contain both afferent (sensory) and efferent (motor) fibers
What is the general anatomy of a nerve?
- Nerve fibers of the PNS surrounded by Schwann cells forming neurilemma/myelin sheath around axon
- Endoneurium: wrapping external to neurilemma
- PErineurium: surrounds each fasicle
- Epineurium: covering of entire nerve
- Blood vessels penetrate connective tissue coverings
What are Poliomyelitis and ALS (Lou Gehrig’s Disease)?
- Poliomyelitis
- caused by poliovirus (fecal contamination of water)
- destroys motor neurons in brainstem and anterior horn of spinal cord
- paralysis, muscular dystrophy, and respiratory arrest
- ALS (Amyotrophic lateral sclerosis or Lou Gehrig’s disease)
- destruction of motor neurons and muscular atrophy
- sclerosis (scarring) of lateral regions of spinal cord
- early signs: muscular weakness, difficulty speaking, swallowing, and using hands
- sensory/intellectual functions remain unaffected
What is a ganglia? List 2 examples.
- Ganglion: cluster of neurosomas outside the CNS
- enveloped in endoneurium
- Posterior root ganglion
- Sympathetic trunk ganglion
What are the numbers for the 31 pairs of spinal nerves?
- 8 cervical (C1-C8)
- first cervical nerve exits between skull and atlas (only 7 vertebrae)
- others exit at intervertebral foramina
- 12 thoracic (T1-T12)
- 5 Lumbar (L1-L5)
- 5 Sacral (S1-S5)
- 1 Coccygeal (Co1)
What are the roots of the spinal nerves?
- Each spinal nerve is formed from two roots
- posterior (dorsal) root-sensory
- posterior (dorsal) root ganglion
- contains the somas of sensory neurons
- enters posterior horn of cord
- posterior (dorsal) root ganglion
- posterior (dorsal) root-sensory
- Anterior (ventral) root: motor
- Cauda equina
- formed from roots arising from L2 to Co1
- dorsal and ventral roots of lowest spinal nerves
What are the rami of the spinal nerves?
- Outside vertebra, nerve divides into rami (distal branches)
- Anterior ramus
- in thoracic region gives rise to intercostal nerve
- In other regions forms plexuses
- Posterior ramus
- innervates the muscles and joints in that region of the spine and the skin of the back
- Rami communicantes
- only in thoracic region
- autonomic nerve fibers (sympathetic)
- Meningeal branch
- reenters the vertebral canals
- to where the meninges are
- reenters the vertebral canals
Why doesn’t the thoracic region have a plexus?
- It goes into the intercostals and helps with breathing
What are the 2 functions of nerve plexuses?
- Somatosensory
- carry sensory signals from bones, joints, muscles, and skin
- proprioception: information about body position and movements from muscles, tendons, and joints
- Motor
- primarily to stimulate muscle contraction
What is Shingles?
- “Herpes Zoster”
- painful trail of skin discoloration and fluid-filled vesicles along path of nerve
- Chickenpox/caused by the varicella-zoster virus
- Virus remains for life in the posterior root ganglia
- kept in check by immune system
- can pop out in elderly
- Immune system is compromised: virus travels down sensory nerve
What happens if you break your neck above C3?
You can’t breathe on your own (can with break below C3)
What does irritation of the phrenic nerve do?
Causes hiccups
What are the radial and sciatic nerve injuries?
- Radial
- passes through axilla
- crutch paralysis: crutches too high, pressure on nerve, lose function
- wrist drop: cast/wrap too tight
- Sciatic
- Sciatica: sharp pain that travels from gluteal region along the posterior side of the thigh and leg to ankle
- usually caused by herniated intervertebral disc or osteoperosis of lower spine
What is a dermatome?
- A specific area of skin that conveys sensory input to a spinal nerve
- Dermatome map: a diagram of the cutaneous regions innervated by each spinal nerve
- Dermatomes overlap their edges as much as 50%
What are the traits of reflexes?
- Require stimulation
- Quick
- Involuntary
- Stereotyped
- the same for everyone
- Inclue glandular secretion and contraction for all 3 types of muscle
- Somatic reflexes inolve the somatic nervous system innervating skeletal muscle
What is the pathway of a somatic reflex?
- Somatic receptors: in skin, muscles, or tendons
- Afferent (sensory) nerve fibers
- Integrating center
- Efferent (motor) nerve fibers
- Effectors: skeletal muscle
- Example: patellar reflex
What is the muscle spindle?
- Stretch receptors embedded in skeletal muscles
- Muscle spindles inform the brain of muscle length and body movement
- Enables brain to send motor commands back to the muscles that control coordinated movement, corrective reflexes, muscle tone, and posture
- e.g. helps you stand upright while on a boat
What is the stretch reflex?
- Stretch (myotactic) reflex: when a muscle is stretched, it “fights back” and contracts
- Helps maintain equilibrium and posture
- Mediated primarily by brain, sometimes spine is involved
- Stabilizes joints by balancing tension between flexion/extension, etc.
- Testing these helps diagnosis many diseases
What is reciprocal inhibition?
- reflex phenomenon that prevents muscles from working against each other by inhibiting antagonist when agonist is excietd
What are some examples of stretch reflexes?
- patellar tendon
- flexor (withdrawal)
- e.g. man stepping on a nail
- ipsilateral
- crossed extension reflex
- e.g. man that stepped on nail maintains balance on other leg
- contralateral
What is spinal cord trauma and its types of paralysis?
- 10,000 to 12,000 people paralyzed each year by spinal cord trauma
- USually vertebral fractures
- Usually males 16 to 30
- 55% in automobile or motorcycle accidents
- Complete transection: complete severence of cord
- immediate loss of motor control below level of injury
- Above C4 threat of respiratory failure
- Paralysis
- paraplegia (lower limbs)
- quadraplegic (all 4 limbs)
- Hemiplegia (one side of body, strokes)
- Paresis (partial paralysis or weakness of limbs)
