reflexes

reflexes

rapid, pre-programmed, involuntary reactions of muscles or glands to stimulus

survival mechanism

what are the characteristics of reflexes

stimulus required to initiate a response

rapid response

pre-programmed

involuntary

reflex arc

neural pathways controlling reflexes

what are the trajectory of the reflex arc

begins at a receptor in PNS

communicates with CNS

ends at a peripheral effector (muscle or gland)

varying number of intermediate steps

reflex arc components

1. stimulus activates receptors

2. signal travels through sensory neuron to CNS

3. information processed by interneurons

---> integrate sensory signals and transmit information to motor neuron

4. motor neuron transmits nerve signal to effector

5. effector responds to nerve signal from motor neuron

---> response intended to counteract/remove original stimulus

reflex classification

type of organ in which reflex take place

number of synapses between neurons in the arc

one or both sides of the body involved

visceral reflex

reflex arcs connected to internal organs, largely involving autonomic nervous system

somatic reflex

involve somatic sensory and somatic motor neurons

monosynaptic reflex

only one synapse between afferent and efferent neurons

postsynaptic reflex

multiple synapses between afferent and efferent neurons

monosynaptic reflexes classification

simplest of all reflexes

sensory axons directly synapsing on motor neurons

very minor synaptic delay

polysynaptic reflexes classification

more complex neural pathways

prolonged synaptic delay before response

ipsilateral reflex arcs

both receptor and effector organs on same side of spinal cord

Contralateral reflex arcs

sensory impulses from receptor on opposite sides of spinal cord

innate

born with it

acquired

develops after birth

what are four major reflexes

stretch reflex

golgi tendon reflex

crossed extensor reflex

withdrawal reflex

stretch reflex

monosynaptic reflex

reflexive muscle contraction after stretching of a muscle

regulates skeletal muscle length

reciprocal inhibition

involves the stretch reflex

skeletal muscles as antagonistic pairs

prevents activation of antagonist muscles

golgi tendon reflex

postsynaptic reflex, ipsilateral, somatic, innate

prevents muscles from contracting excessively

responds to tension

occurs in response to tension at golgi tendon organ

withdrawl reflex

polysynaptic and ipsilateral

initiated by painful stimulus

transmitted by sensory neuron to spinal cord

received by interneurons

motor neurons signaled to reflex

crossed extensor reflex

contralateral

often in conjuction with withdrawal reflex

typically in the lower limbs

variations in reflexes

hypoactive

hyperactive

hypoactive reflex

diminished or absent

May indicate damage to spinal cord, or muscle disease, or damage to neuromuscular junction

hyperactive reflex

abnormally strong response

May indicate damage to brain or spinal cord, especially if accompanied by clonus (rhythmic oscillating movements with reflex testing)