A&P Chapter 13
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Classification by Stimulus type of the PNS (5 types)
- Mechanoreceptors: respond to mechanical force
- Thermoreceptors: sensitive to temperature changes
- Photoreceptors: respond to light energy
- Chemoreceptors: respond to chemicals in solution
- Nociceptors: respond to pain
Name the three types of classification of sensory receptors
- Type of stimulus
- Body Location
- Structural complexity
What is the afferent and efferent pathways
- Afferent: Ascending and sensory pathways
- Efferent: Descending and motor pathways
Name the 3 types of receptors based upon location
- Exteroceptors: sensitive to stimuli arising outside the body
- Interoceptors: sensitive to stimuli inside the body
- Proprioceptors: occur in skeletal muscles, tendons, joints, and ligaments and in connective tissue.
What are the three levels of organization of the Somatosensory System
- Receptor: Sensory receptors
- circuit : ascending pathways
- perceptual: neuronal circuits in the cerebral cortex
What is adaptation?
- The ability for a receptor to change in sensitivity in the presence of a constant stimulus.
- Phasic receptors: Fast adapting
- Tonic receptors: (nocioceptors and proprioceptors) do not adapt
What does the spinothalamic ascending pathways transmit?
- coarse touch impulses
Describe the spinocerebellar tracts.
- coordinate skeletal muscle activity
- on not contribute to conscious sensation
What are the main aspects of perceptual detection?
- Perceptual detection: ability to detect that a stimulus has occurred
- Magnitude estimation: ability to detect how intense the stimulus
- Spatial discrimination: ability to determine the site of the stimulus
- Feature abstraction: ability to focus on a specific feature
- Quality discrimination: ability to differentiate the submodalities
- Pattern recognition: ability to recognize patterns in the environment
What is a ganglia?
a collection of neuron bell bodies in the PNS.
What are enkephalins?
Inhibitor neurotransmitters that quash the pain signals generated by the nociceptive neurons.
Describe the anatomy of a nerve.
- Endoneurium: surrounds the axon
- Fascicles: bundles of groups of fibers
- Perineurium: a connective tissue that bounds fascicles together
- Epineurium: Tough fibrous sheath that encloses the fascicles.
Can a nerve regenerate?
Cut or compressed axons of peripheral nerves can regenerate successfully if the cell body remains in tact.
Oligodendrocytes of the CNS are studded with growth inhibiting hormones
Describe the regeneration of a nerve fiber in the PNS.
- 1. The axon becomes fragmented at the injury site.
- 2. Macrophages clean out the dead axon distal to the injury
- 3. Axon sprouts, or filaments, grow through a regeneration tube formed by schwann cells.
- 4. The axon regenerates and a new myelin sheath forms.
What is the difference between roots and rami?
Roots lie medial to and form spinal nerves and each root is strictly sensory or motor.
Rami lie distal to and are lateral branches of the spinal nerves and each root is strictly sensory or motor.
What form the nerve plexuses?
Only the ventral rami form nerve plexuses.
What is an ischemia?
Deprivation of blood supply
What forms the sciatic nerve?
- Tibial nerve
- Common fibular nerve
What is the only spinal nerve that does not innervate dermatomes?
What is Hiltons Law?
Any nerve serving a muscle that produces movement at a joint also innervates the joint and the skin over the joint.
What is different about the somatic cleft at neuromuscular junctions?
They are filled with a glycoprotein rich basal lamina, a structure not seen at other synapses. the basal lamina contains acetylcholinesterase.
What are the levels of Motor Control?
- Segmental level: lowest level of the hierarchy; spinal cord and contains central pattern generators (CPG's)
- Projection level: Motor cortex (pyramidal system) and brain stem nuclei; the convey instructions to spinal cord motor neurons and send a copy of that information to higher levels
- Precommand level: Cerebellum and basal nuclei; program and instructions
What are varicosities?
knolike swellings containing mitochondria and synaptic vesicles, found in cardiac and smooth muscle.
What are the five components of the reflex arc?
- Receptor: Site of stimulus action
- Sensory neuron: transmits afferent impulses to the CNS
- Integration center: A single synapse (monosynaptic reflex) or multiple synapse (polysynaptic reflex)
- Motor Neuron: Conducts efferent impulses from the integration center to an effector neuron
- Effector: Muscle fiber or gland cell that responds to the efferent impulses
What is a proprioceptor?
A receptor locate in a joint muscle or tendon concerned with locomotion, posture or tone.
What is the function of a muscle spindle?
To provide information on muscle length
What tis the function of a golgi tendon organ?
To indicate muscle tension.
They also help to prevent muscles and tendons from tearing when they are subjected to possibly damaging stretching force.
What is the purpose of the stretch reflex?
makes sure that the muscle stays at that length
All stretch reflexes are monosynaptic and ipsilateral
What is reciprocal inhibition?
Branches of the afferent fibers that also synapse with interneurons that inhibit motor neurons controlling antagonistic muscles
What is the flexor (withdrawal) reflex?
An automatic withdrawal of the threatened body part by stimulus.
What is the crossed-extensor reflex?
Accompanies the flexor reflex in weight-bearing limbs and is particularly important in maintaining balance.
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