CNS 3 Flashcards
Sensory function is dependent on:
- Intact afferent cellular circuits
- damage to peripheral nerves, spinal cord, lower brainstem, or thalamus, message wont be received by brain
sensory “pathway”
- sensory receptors transduce changes in environmental energy into electronic signals
- receptors connect to primary afferent neurons which bring this “information” to the spinal cord and brain via action potentials
- Primary afferent neuron cell bodies housed in dorsal root and cranial nerve ganglia two processes
- peripheral process that extends distally within a peripheral nerve to appropriate sensory recepters.
- a central process that enters the spinal cord/brain through a dorsal root or cranial nerve.
afferent
toward the CNS
Dermatomes:
T1, C7-C8
- related to hands and medial FA
- *when administering block, numb hands could mean you block is migrating up
- will affect phrenic nerve, airway control, and cardiac accelerants
What does the Phrenic nerve innervate?
the diaphragm
*provides only innervation to diaphragm
Exteroceptive information
- interaction of the skin with the environment
- Two types
- Fine, discriminatory touch
- A(alpha)
- Pain and temperature
- A(delta)
- Fine, discriminatory touch
Dermatome:
T3, 4, and 5
Cardiac accelerator fibers
*person with T4 spinal injury or block, they are more likely to go into shock; unable to compensate by increasing HR
Dermatome:
T 10
Umbilicus
Proprioceptive information
Where your body/limb is positioned “in space”
Enteroceptive information
internal status of the body
Types of receptor activation
- Mechanoreceptor- compression or stretch
- Chemicoreceptor
- Thermoreceptors- expand and contract with different temperatures (different receptors for each change)
- nociceptors (pain)-detect physical or chemical damage
- electromagnetic (detect photons)- used for sight
- open in the dark, allows flux of ions, close when they see light
Fine Discriminatory touch
Mechanosensitive afferent fibers
- Fast adaptive tactile fibers
- quickly stop noticing
- Slow adaptation tactile fibers
- keep noticing stimulus for a while (pain)
- Type 1- small receptive field, higher density of fibers
- Type 2 fibers- large receptive field
Meissner’s corpuscles
- Type of mechanoreceptor
- Fast adaptive
- right beneath the non-hairy skin
- senses change in pressure and velocity
- can discriminate precisely where the stimulus is because it is located so shallowly in the skin
Labeled line principle
- Each nerve tract terminates at a specific point in the CNS and carries a selective sensory modality
- sensation is perceived when a specific stimulated nerve leads to specific areas in the CNS
- alteration of the specific nerve tracts activity will only change the intensity of the stimulus (quantitative) vs changing the type of stimulus perceived (qualitative)
Dorsal Column
Medial Lemniscal pathway
How does it work?
- primary afferent neurons have cell bodies in the dorsal root.
- Their axons ascend to the medulla where they encounter the dorsal column nuclei:
- Nucleus gracilis (lower body/leg)
- Nucleus cuneatus (upper body/arm)
- 2nd order neuron axons then cross to the other side of medulla and project to the thalamus via the medial lemniscus
The Anterolateral System
Spinothalamic
- Enters the spinal cord from the dorsal spinal nerve roots, immediately synapses in the dorsal horns
- dessucates to the other side of the cord
- travels upward through anterior and lateral white columns
- tracts terminate at all levels of the lower brain stem and in the thalamus
Spinocerebellar
Proprioceptive Pathway
- Perception of position, awareness of body movements and local reflexes
- Carries both cutaneous and proprioceptive information to cerebellum and cerebral cortex
Dorsal Column Nuclei
- Contains the second order neurons
- gracile and cuneate nuclei
- in the medulla
How the dorsal column neurons differ from primary afferent neurons
- receptive fields cover a greater area
- multiple primary afferent fibers synapse on each dorsal column neuron
- Several types of primary afferent neurons (different sensory modalities) converge on the second-order neurons allowing a greater diversity in sensory responses
- Dorsal column neurons often modulated by adjacent interneurons that provide inhibition to the served receptive fields.
Thalamus
Third order neurons
- these neurons project to the somatosensory cortex
- inhibitory and excitatory
- sleep/wake cycle and anesthesia will influence excitability
Parts of the Basal ganglia (5)
- caudate nucleus
- putamen
- globus pallidus
- substantia nigra
- subthalamic nucleus
lesions of the basal ganglia cause _______
abnormal movement and posture
Pacinian corpuscle
- type of mechanoreceptor
- Fast adaptive
- onion-like structure in the subcutaneous skin (surrounding unmyelinated nerve endings)
- sensation: vibration; tapping
Ruffini corpuscle
- type of mechanoreceptor
- slow adapting
- encapsulated
- Senses pressure
Merkel disk
- Type of mechanoreceptro
- slow adaptive
- transducer is on epithelial cells
- senses location
Dorsal column somatosensory system
What does it sense?
- fine touch
- pressure
- two-point discrimination
- vibration
- proprioception
