Outline 7 - Spinal reflexes Flashcards
The central nervous system consists of
the brain and spinal cord
The peripheral nervous system consists of
12 pairs of cranial nerves and 31 pairs of spinal nerves
The three types of fiber nerves are:
- afferent (sensory)
- efferent (motor)
- mixed
The somatic system refers to
- perception and voluntary control
- i.e. the 5 senses, equilibrium and skeletal muscles
- It can be divided into somatic sensory, motor and visceral systems
The somatic sensory system includes
- afferent nerves
- i.e. pressure, temperature, pain, vibration in the skin
it carries information toward the CNS
The somatic motor system includes
- efferent nerves
- it carries information away from the CNS to effectors
- they control skeletal muscle
The visceral system is
- The autonomic nervous system i.e. internal organs
- It can be subdivided into the sensory and motor systems
- There is no perception and involuntary control
- i.g. glandular epithelial cells, cardiac cells, smooth muscle cells
The visceral sensory system includes
- pressure, chemical and osmolarity receptors
- Can be divided into two systems: Parasympathetic and Sympathetic
The special senses include
- Audition
- Olfaction
- Gustation
- Equilibrium
- Vision
Interneurons are
- aka association neurons
- they lie between afferent and efferent nerves and shuttle signals through the CNS pathways where integration occurs
- They make up 99% of neurons in the body
All reflex arcs have a ______ and a _______.
- sensory neuron
- motor neuron
Stretch reflex, Myotatic Reflex, Knee-Jerk reflex steps
- Stimulate muscle spindle (receptor)
- Receptor (spindle) sense overstretch of extensor
- Sensory neuron (afferent) carries info to SC/alpha motor neuron
- Alpha motor neuron stimulates contraction of extensor muscles
- NOTE: reflex is monosynaptic and ipsilateral
Inverse myotatic reflex, disynaptic reflex steps
- Stimulate golgi tendon reflex (GTO receptor)
- Sensory neuron (afferent) delivers signal to SC inhibitory interneuron
- Inhibitory interneuron inhibits activity of alpha motor neuron to stop muscle contraction
- NOTE: reflex is disynaptic and ipsilateral
To stimulate muscle contraction, the _______ are stimulated
alpha motor neurons
To stop motor contraction, the _________ are inhibited
alpha motor neurons
Simple withdrawal reflex steps
- Stimulate pain receptor
- Sensory/afferent neuron carries info to SC and synapses with (+) excitatory or (-)inhibitory neurons
- The (+) neuron stimulates flexor alpha neuron and flexes muscle
- The (-) neuron inhibits extensor alpha neuron to stop contraction of extensor muscle
- This reflex is multisynaptic and ipsilateral
- Exhibits reciprocal inervation
Cross-extensor reflex steps
- Pain receptor stimulated when stepping on a tack
- Sensory neuron carries input to the SC
- (+) neuron stimulates flexor alpha neuron to contract ipsilateral flexor muscle
- (-) neuron inhibits extensor alpha neuron to inhibit extension of ipsilatoral extensor muscle
- (+) neuron stimulates the extensor alpha neuron to contract the contralateral extensor muscle
- (-) neuron inhibits the flexor alpha neuron to inhibit contraction of the flexor muscle
- Multisynaptic!
Gamma motor neuron control
- Extrapyramidal pathway originates in cerebellum and regulates gamma motor neurons
- GMN starts in ventral horn and increases the sensitivity to muscle stretch
- Once stretch is perceived, alpha motor neurons are excited
- Alpha motor neurons stimulate contraction to decrease stretch
- To prevent contraction of opposing muscle, the cerebellum inhibits GMN
During flexion
alpha motor neurons =
gamma motor neurons =
- alpha motor neurons = are inhibited, extrafusal fibers relax
- gamma motor neurons = are excited, sensitivity is increased
During extension
alpha motor neurons =
gamma motor neurons =
- alpha motor neurons = excited, muscle contracts
- gamma motor neurons = inhibited, sensitivity decreased
Loss of the alpha motor neuron or lower motor neuron will result in
- flaccid paralysis
Loss of the upper motor neuron, will result in
- spastic paralysis
Damage to the gamma motor neuron will result in
loss of ability to coordinate muscle activity
Sensory info from the legs enters the spine at the level of
lumbar
Sensory info from the arms enters the spinal column at
C5 - C6
General pathway of sensory information is
- receptor, sensory neuron, SC, thalamus, parietal cortex
- or
- receptor, sensory neuron, SC, cerebellum
Dorsal columns
- Ascending/Decending
- Info carried
- Decussation (cross)
- Termination
- Result of damage
- Ascending
- 2 pt descrimination, deep pressure, vibration, conscious muscle sense
- Medulla
- Contralateral somatosensory cortex (parietal)
- sensory loss of contralateral side
Anterior spinothalamic tract
- Ascending/Decending
- Info carried
- Decussation (cross)
- Termination
- Result of damage
- Ascending
- Light touch
- Spinal cord
- Contralateral somatosensory cortex (parietal)
- Partial loss of unconsious muscle sense of the contralateral body parts
Lateral spinothalamic tract
- Ascending/Decending
- Info carried
- Decussation (cross)
- Termination
- Result of damage
- Ascending
- Pain and temperature
- Spinal cord
- contralateral somatosensory cortex (parietal)
- Pain and temp loss from contralateral body part
Posterior spinocerebellar tract
- Ascending/Decending
- Info carried
- Decussation (cross)
- Termination
- Result of damage
- ?
- Unconsious muscle and joint sense
- NO CROSS
- Parial loss of unconsious muscle sense of ipsilateral side of the body
Anterior Spinocerebellar tracts
- Ascending/Decending
- Info carried
- Decussation (cross)
- Termination
- Result of damage
- Ascending
- Unconscious muscle and joint sense
- Spinal cord/ some don’t cross
- Cerebellum
- Partial loss of unsonscious muscle sense of contralateral side
Lateral corticospinal tract
- Ascending/Descending
- Info carried
- source
- Decussation (cross)
- Termination
- Result of damage
- Descending
- voluntary muscle control of appendage
- primary motor cortex, parietal lobe
- Medulla oblongata
- Interneurons or alpha motor neurons of the cord
- spastic paralysis of ipsilateral appendage
Anterior corticospinal tract
- Ascending/Decending
- Info carried
- Source
- Decussation (cross)
- Termination
- Result of damage
- Descending
- Movement of axial muscles
- primary motor cortex parietal lobe
- SC at innervation
- spastic paralysis of contralateral axial muscles
Extracorticospinal tracts
- Ascending/Decending
- Info carried
- source
- Decussation (cross)
- Termination
- Result of damage
- Descending
- postural muscle control (balance)
- Cerebellum, superior colliculus, red nucleus
- ?
- gamma motor neurons to adjust sensitivity of muscle spindles
- inability to control muscle activites
Damage to the afferent fiber of the spnial nerve or ascending pathways results in
loss of sensation (anesthesia)
Damage above spinal cord level T2 results in
- upper and lower extremeties loss
Damage below spinal cord level T2 results in
- Lower extremeties loss ONLY
Damage to the spinal cord at level (#) would result in what regarding reflexes?
- no effect of reflexes above damage
- Loss of reflex at level of damage
- Hyperreflexia below level of damage
Sypathetic fibers have a ______ degree of divergence
high (multiple organ)
Parasympathetic fibers have a ____ degree of divergence
low (single organ)
Cholinergic receptors receive
acetylcholine
Adrenergic receptors receive
norepinephrine and epinephrine
Nicotinic NT affect
sympathetic and parasympathetic systems
all postganglionic fibers
Muscarinic NT receptors are found on
parasympathetic postganglionic fibers
causes rest/digest response
Cholinergic blockers are
hesamethonium and atropine
alpha 1 receptors
adregnergic - vasoconstriction
excited by nicotine (not blocked)
alpha 2
adrenergic - presynaptic inhibition
beta 1 receptor
HR and strenth of contraction
beta 2
relaxes smoothh msucle of bronchioles
autonomic tone
two divisions of ANS usually oppose each other and are always active, although their levels of activity vary
