Lecture 10: Organization of the Nervous System/Spinal Reflex Connections Flashcards
What is extrinsic control of the nervous system
Maintains homeostasis, glandular activity. Controls movements, perception of environments, transfer of information, storage of information
What is the chemical messenger released in nervous system
Neurotransmitter released into synaptic cleft
What does the specificity of action on the target cell in the NS depend on
Close anatomic relationship between neurons and their target cells
What is the major function of the nervous system
Coordinates rapid, precise responses
What are the 3 anatomical components of the neural circuit
- Inputs (afferent)
- Integrators
- Outputs (efferents)
What are the functional components of the neural circuits
- Sensory inputs (sensory neuron/receptor)
- Computational units (brain and ganglia)
- Output nerves (output to skeletal muscle, smooth muscle or glands)
What are the two divisions of the peripheral NS
Afferent and efferent
What is the afferent division
Carries information from sensory receptors in the skin, skeletal muscles and joints to the CNS via sensory neurons
What is the efferent division
Transmits impulses from the CNS to effector organs (muscles and glands)
What are the two divisions of the efferent division
Somatic and autonomic
What is the somatic nervous system
Fibers of motor neurons that supply skeletal muscle
What is the autonomic nervous system
Fibers that innervate smooth muscle, cardiac muscle, and glands
What does the cotton ball test evaluate
Vision, cranial nerves
What 4 types of movement does the nervous system control
- Voluntary
- Postural
- Rhythmic
- Reflex movement
What type of movement is more complex and may involve learning
Rhythmic
What are the two major cell types that make up NS
Neurons and neuroglia
What cells are excitable and transmit electrical impulses
Neurons
What cells communicate with and support neurons
Neuroglia
What is the soma
Body of the neuron that contains nucleus and most organelles
What are amitotic neurons
neurons do not divide to create more neurons. They lack centrioles an organelle required for cell division
Neurons have a well developed golgi and rough ER thus they are major biosynthetic centers for ___
Neuropeptides
What receives inputs from other neurons, site of synapses
Dendritic spines
What is the primary neuronal output
Axon
What is the axon hillock
Cone shaped area from which the axon arises
What makes up the transport substances within the axon
Microtubules
What releases neurotransmitters
Synaptic terminals
T or F: neuroglia initiate and conduct action potentials
False!
T or F: neuroglia have graded potentials
True
What are the 5 major classes of neuroglia
CNS glia:
1. Astrocytes
2. Microglia
2. Ependymal cells
4. Oligodendrocytes
PNS:
1. Schwann cells
What are the three types of fibers in the PNS
A, B, C
What are A fibers
Made of alpha, beta, and delta fibers
(Alpha—> delta= largest—> smallest diameter)
What do A-alpha fibers carry
Carry muscle spindle and golgi tendon information
Are A-alpha fibers fast or slow
Fast
What do A-beta fibers carry
Muscle spindle, touch and proprioception.
Mechanoreceptors of skin
What do A-delta fibers carry
Pain and temperature information
Mechanical nociceptors
Are A-delta fibers fast or slow
Less fast
What are B fibers
Preganglionic efferent ANS fibers
What are the smallest, non-mylenated PNS fibers
C fibers
Are C fibers fast or slow
Slow, non-mylenated
What do C fibers carry
Pain information
Poylmodal nociceptors
What is the link between PNS and SNS
Spinal cord
Each spinal nerve has a ____, ____, ____, and _____
- Dorsal root (dorsal horn)
- Ventral root (ventral horn)
- Relay circuits
- Ganglia
Are corticospinal tracts intentional or involuntary
Intentional
Where do UMN originate
Primary motor cortex
What do UMN control
Skeletal muscle tone and conscious skilled movements
What is another name for corticospinal tract
Pyramidal tract
Where does the lateral corticospinal tract cross
Medulla
Where does the ventral corticospinal tract cross
Termination in spinal cord, aka uncrossed
Where do LMN exit
Ventral horn
What do LMN do
Stimulate/excite skeletal muscle
What controls skeletal movement in both tracts
Contralateral tracts
What are the 4 descending efferent tracts
- Lateral corticospinal
- Rubrospinal tract
- Ventral corticospinal
- Vestibulospinal; reticulospinal;tectospinal tract
What does the rubrospinal tract control
Involuntary control of skeletal muscle
What does the vestiulospinal; reticulospinal; tectospinal tract control
Involuntary control of muscle tone to maintain balance and equilibrium
What is degenerative myelopathy
Damage to the spinal cord that causes pathways between the body and brain to be interrupted. Result of demyelination
Demyelination detected through loss of ___staining
Cresyl violet
Is DM an UMN or LMN disorder? And where is it localized
UMN, localized to T3-L3
What are the spinal reflex abnormalities associated with degenerative myelopathy
spastic paresis; exaggerated reflexes
Why is fiber size important to clinical outcomes, especially in differentiating DM from other neurological disorders
Important to determine if DM or if symptoms are result of spinal compression
Do large or small diameter fibers lose function first
Large diameter fibers lose function first
Prognosis for tactile loss vs deep pain negative
Prognosis for tactile loss much better compared to deep pain negative, worsening prognosis if doesn’t return in 2 days
What is the function of the largest fiber size
General proprioception
What are the signs for increasing compression on the largest fiber size
Proprioceptive deficits
What is the function of the 2nd largest fiber size
Voluntary motor
What are the signs associated with increasing compression damage to the second largest fibers
Paresis, paralysis
What is the function of the 2nd smallest fiber size
Superficial pain
What are the signs associated with increasing compression of 2nd smallest fiber size
Loss of cutaneous sensation
What is the function of the smallest fiber size
Deep pain
What is the signs of increasing compression associated with the smallest fiber size
Loss of deep pain
What is feline diabetic neuropathy
Demyelination of distal axons associated with DM
What are some physical symptoms associated with feline diabetic neuropathy
Plantigrade and palmigrade stance, suggestive of diabetes neuropathy
Do cats with feline diabetic neuropathy have dysfunction to sensory or motor neurons
Sensory
is feline diabetic neuropathy UMN or LMN
LMN
What is a reflex
Any response that occurs automatically without conscious effort
What are the two types of reflexes
- Simple/basic
- Acquired or conditioned
What is the simple/basic reflex
Built in, unlearned response
What is the acquired or conditioned reflex
Result of practice or learning
What are the 5 basic components of reflex circuits
- Receptor
- Afferent pathway
- Integrating center
- Efferent pathway
- Effector
Describe the reflex circuit
- Stimulus activates receptor on skin
- Stimulus travels on sensory neuron (afferent) to synapse at integration center in dorsal horn on inter neuron
- Inter neuron synapses onto motor neuron in ventral horn
- Motor neuron travels and synapses on muscle
What are the two proprioceptor receptors
- Golgi tendon organs
- Muscle spindles
What are the nociceptor receptors
Free nerve endings in joint capsules and skin
What do Golgi tendon organs measure
Muscle tension
What are type Ib afferents in Golgi tendon organs
Neurons that respond to passive stretch and active contraction
Where are muscle spindles located
Within muscle tissue, parallel to muscle fibers
What does a muscle spindle consist of
Contractile end and non-contractile middle with sensory innervation
What neurons innervate the contractile end of muscle spindles
Y-motor neurons
What neurons innervate the non-contractile muscle spindles
Type Ia and II afferent sensory fibers
What neurons innervate the extrafusal skeletal muscle
Alpha-motor neurons
What neurons innervate both nuclear bag and nuclear chain fibers
Group 1A afferent
What neurons detect velocity and length change
Group 1A afferents
What neurons innervate the nuclear chain fibers
Group 2 afferents
What neurons detect length of muscle fiber
Group 2 afferents
What motor neurons innervate nuclear chain fibers
Static y (gamma) motor motor neurons
What motor neurons innervate nuclear bag fibers
Dynamic y (gamma) motor neurons
Where a muscle is stretched what afferent neurons are activated
Group 1A and group 2
___coactivation allows adaptation in spindle sensitivity
Alpha-y(gamma)
What motor neurons activate extrafusal fibers causing them to shorten
A motor neurons
To keep tension in the spindles constant, ___ neurons activate the intramural fibers causing them to shorten
Y(gamma) motor neurons
What is the monosynaptic stretch reflex important for
Maintaining posture and muscle tone
When is the monosynaptic stretch reflex triggered
When muscle is stretched
What measures the stretch during monosynaptic stretch reflex
Muscle spindles (intrafusals)
*length detectors
Describe the steps in the monosynaptic stretch reflex
- Sensory neuron travels and synapses on alpha motor neuron in ventral horn
- Travels back to muscle and causes monosynaptic excitation
What is an example of monosynaptic stretch reflex
Patellar tendon causing extension of quadriceps
What is the polysynaptic stretch reflex
Protective reflex in response to stretch of muscles
The polysynaptic stretch reflex has 2 or more synapses that allow ___
Reciprocal innervation
The polysynaptic stretch reflex activates the ___ and ___
Extensor and inhibit opposing flexor
What is an example of a polysynaptic stretch reflex
Patellar tendon reflex, activates extensors in quadriceps and inhibits flexors in hamstrings
Describe the polysynaptic pain reflex
- Nociceptors send signals to spinal cord
- Synapse on interneuron
- Activate flexor and inhibit opposing extensors
What reflex allows weight to be shifted to uninjured leg so we don’t fall
Flexor withdrawal/cross extensor reflex
Describe the flexor withdrawal/crossed extensor reflex when walking
1.leg raised when walking the extensor muscle is relaxed and flexor contracted
2. Contralateral leg has extensor activated and flexor relaxed
What are the 3 ascending afferent tracts
- Dorsal lemniscus columns
- Ventral spinothalamic
- Lateral spinothalmamic
What does the dorsal Lemiscus columns detect
Touch, pressure, vibration, 2-point discrimination and proprioception
What does the ventral spinothalamic tract detect
Touch
What does the lateral spinothalamic tract detect
Pain and temperature
What are cutaneous trunci
Thin, sheet of skeletal muscle that covers dorsal and lateral walls of abdomen and thorax
Describe the pathway of afferent sensory neurons in cutaneous trunci
- Afferent neurons from each spinal cord segment synapse on long tract projections and ascend spinal cord in ventrolateal funiculus
- Synapse on cutaneous trunci muscle motor neurons
- Clustered as bilateral nuclei at the cervical thoracic junction
Describe the organization of efferent neurons in cutaneous trunci
Efferent axons project out of spinal cord as component of brachial plexus terminating on cutaneous trunci muscle beneath the skin of the back via the lateral thoracic branch of the plexus
Tactile stimulation of cutaneous trunci does what in a normal animal
Skin contractions
A lesion to the spinal cord blocks ____tracts of the cutaneous trunci
Ascending conduction of the afferent sensory tracts
Blockage of ascending afferent tracts of cutaneous trunci produce ___
Areflexia below the level of the lesion in which tactile stimulation no longer produces contraction
**rostral fields are unaffected
What 3 things collect proprioception
- Golgi tendon organ
- Muscle spindles
- Free nerve endings
What is the segmental reflex
Transverse one of few segments of brain divisions
What is an example of a segmental reflex
Patellar reflex
What is the intersegmental reflex
Transverses several segments of spinal cord or several brain divisions
What is the long-loop intersegmental reflex test
Transverses many segments of the spinal cord and/or brain divisions; enters and leaves the CNS at the same location
What is an example of long-loop intersegmental reflex
postural reactions/CP deficits (flipping paw over)
Describe the reflex circuit in the menace response
- Photoreceptors activated
- Afferent neuron= CN III (optic nerve) to the thalamus
- Integrator (CNS)- response is integrated in the optic cortex of the cerebellum
- Efferent neuron= CN VII (facial)
- Target organ= obicularis oculi closes eye
