reflexes Flashcards
what are the two functions of the spinal chord
- neuronal link bw the brain and the PNS
- integrating centre for spinal reflexes
how many pairs of spinal nerves are there
31
where do spinal nerves come out from
from spaces between adjascent vertebrae
how many pairs of cervical (neck) nerves are there
8
how many pars of thoracic (chest) nerves are there
12
how many pairs of lumbar (abdominal) nerves are there
5
how many pairs of coccygeal (tailbone) nerves are there
1
how many nerves of sacreal (pelvic) nerves are there
5
what connects spinal nerves with each side of the spinal chord
dorsal root and ventral root
what fibres are there in the spinal nerve
afferent and efferent fibres
what is a nerve
a bundle of peripheral neuronal axons enclosed by a connective tissue covering and following the same pathway
nerve fascicle
many axons bunbdled in connective tissue
how is white matter organized
into nerve tracts
what are nerve tracts
bundles of nerve fibres with a similar function. each begins or ends with a particular area of the brain
ascending nerve tracts
afferent, sensory input
descending nerve tracts
efferent, motor output
how many and what are the horns that divide up the grey matter
- dorsal horn: contains cell bodies of interneurons on which afferent neurons terminate
- ventral horn: contains cell bodies of efferent motor neurons supplying skeletal muscles
- lateral horn: contains cell bodies of autonomic sympathetic nerve fibres
reflex
involuntary stereotyped response to a sensory input occuring automatically without conscious effort linking biological stimulus with response
how many and what are the two types of reflexes
- simple or basic (innate)- built in unlearned responses
- acquired or conditioned reflexes (practice and learning)- result of practice and learning
range of reflexes
simple to complex neural subroutines
somatic (monosynaptic or polysynaptic)
somatic motor neurons and skeletal muscles
-spinal- integrated in spinal chord
-cranial- integrated in the brain
autonomic or visceral (polysynaptic)
involve autonomic neurons (sympathetic or parasympathetic)
- spinal- urination/ defication
-integrated in brain- brainstem, hypothalamus, thalamus, homeostasis (gag, vomiting, sneezing, coughing, swallowing)
how many components are in a reflex pathway
5
what are the five components in a reflex pathway
- sensory receptor (muscle spindles in the case of somatic muscle reflexes)
- afferent pathway to CNS (sensory axon)
- integrating centre consisting of one or more synapses in the CNS
- efferent pathway to the periphery (motor axon)
- effector (mucsle)
monosynaptic reflex
has a single synapse between the afferent and efferent neurons
what kind of reflex is a stretch reflex
monosynaptic reflex
example of stretch reflex
pateller tendon (knee jerk reflex)
what is the preliminary assesment of the nervous system function
stretch reflex
polysynaptic reflexes
have two or more synapsys
example of a polysynaptic reflex
flexion (withdrawal) reflex
touching something hot
muscle spindles
in muscles and sense stretch
golgi tendon organ
in tendon and sense force
joint receptors
sense pressure. position
proprioceptros
skeletal muscle reflex sensory receptors
isotonic contraction
alpha motor neurons are stimulated to generate contraction.
muscle contraction and receptor response
alpha motor neurons are stimulated to generate contraction. the length changes by tension is constant. when the whole muscle mass shortens, the spindle also passively shortens. the firing rates of the spindle afferent axons are reduces because the tension in the receptor portion of the intrafusal fibres is relieved. without adjustment, they will no longer detect changes in muscle length
function of v neurons
modulate sensitivty of the spindles
unloading spindles
the intrafusal fibres slacken when a muscle shortens
how is it ensured that info on cahnges in muscle length are transmitted
the CNS regulates the loading of the intrafusal fibres with v motor neurons
what is this called “the CNS regulates the loading of the intrafusal fibres with v motor neurons”
innervation via reticulospinal and vestibulospinal tracts
isometric contraction
a motor neurons are stimulated with the muscle firmly fixed at both ends. tension inc but length is constant therefore due to no change in length, the fiting of spindle afferents stays the same. tension is transferred to GTO and those afferents (IB) inc firing
golgi tendon organs
sense tension
loss or reduction of reflex
interruption of refllex arc by either peripheral sensory or lower motor neuron lesions (LMN). reduces or eliminates muscle stretch reflex and reduces muscle tone. loss of innervation to the muscle
increased reflex and muscle tone (spasticity)
injury to upper motor neurons - UMN- above the anterior horn cell (spinal chord, motor cortex,) leads to loss of descending inhibition. increases muscle tone - hyperreflexia
UMN
neurons in higher brain levels that influence neurons in spinal chord
LMN
effector neurons in spinal chord
muscle stretch reflex
