Lecture 7: Reflexes

What is the integrating center of the nervous system?

The brain and spinal cord (CNS)

What are the two divisions of the peripheral nervous system?

Afferent (sensory) and efferent (motor)

What does the autonomic nervous system primarily regulate?

Internal environment and visceral functions

What is rheostasis?

It described the dynamic adjustment of physiological "set points" to adapt to changing internal or external conditions

How many different neurons are in the efferent pathway of the autonomic nervous system (ANS)?

Two: preganglionic and postganglionic

Where are sympathetic preganglionic cell bodies located?

Intermediolateral gray column of thoracic and upper lumbar spinal cord

Where are parasympathetic preganglionic cell bodies located?

Brainstem nuclei and sacral spinal cord (S2–S4).

What organs are innervated by the ANS?

Smooth muscle, cardiac muscle, glands, secretory epithelia

What is the general function of the sympathetic nervous system?

Prepares the body for fight-or-flight

What is the general function of the parasympathetic nervous system?

Supports vegetative and resting functions

What nerve carries the largest number of visceral afferents?

Vagus nerve (CN X)

Where are visceral afferent cell bodies located?

Dorsal root ganglia or cranial nerve ganglia

What neurotransmitter is released by all preganglionic autonomic neurons?

Acetylcholine

What receptor type is on postganglionic parasympathetic targets?

Muscarinic receptors (G-protein coupled receptor that bind acetylcholine to regulate the PSNS)

What receptors are found at the neuromuscular junction?

Nicotinic N1 receptors

What cells of the adrenal medulla are modified postganglionic neurons?

Chromaffin cells

What hormones are released from the adrenal medulla?

Epinephrine and norepinephrine

What is a mixed (neuroendocrine) reflex pathway?

A reflex using both neural and hormonal output

What is the stimulus of the myotatic reflex?

Muscle stretch

What is the function of the myotatic reflex?

Maintenance of muscle length

What fibers carry the afferent limb of the myotatic reflex?

A1 afferents

What reflex causes ipsilateral flexion and contralateral extension?

Flexion-crossed extension reflex

What is the main function of the baroreflex?

Blood pressure regulation

What receptors detect blood pressure?

Stretch receptors in the carotid sinus

Where is the baroreflex integrated?

Medullary cardiovascular centers

What type of reflex controls urination?

Autonomic (micturition reflex)

Which system allows voluntary control of the external urethral sphincter?

Somatic nervous system (pudendal nerve).

Somatic motor neurons innervate __________ muscle

skeletal

Autonomic motor neurons innervate __________, __________, and glands.

smooth muscle; cardiac muscle

The sympathetic division is also called the __________ division.

thoracolumbar

The parasympathetic division is also called the __________ division.

craniosacral

Postganglionic sympathetic neurons usually use __________ receptors on target cells.

adrenergic

Sweat glands are innervated by sympathetic neurons that release __________.

acetylcholine

Nicotinic N2 receptors are located on __________ neurons.

postganglionic autonomic (both symp and parasymp)

Acetylcholine is synthesized from __________ and __________.

acetyl-CoA; choline

Catecholamines are synthesized from the amino acid __________.

tyrosine

α₁ receptors cause __________ of blood vessels.

vasoconstriction

β₁ receptors increase __________.

heart rate

Baroreceptor afferents travel in cranial nerve __________.

IX (glossopharyngeal)

Reflex pathways can be __________, __________, or __________.

nervous; endocrine; mixed

During micturition, parasympathetic activity causes bladder __________.

contraction

In the flexion-crossed extension reflex, the contralateral limb undergoes __________.

extension

True or false: Somatic reflexes use two neurons in the efferent pathway

False: somatic reflexes use only one efferent neuron; autonomic reflexes use two

True or false: Postganglionic parasympathetic neurons are usually short.

True! Terminal ganglia are near or within target organs

True or false: Visceral pain is poorly localized

True

True or false: α₂ receptors are primarily presynaptic and inhibitory

True

True or false: The adrenal medulla only affects innervated tissues

False: Hormones released into blood affect non-innervated tissues.

True or false: Increased blood pressure decreases parasympathetic discharge.

False: Increased BP increases parasympathetic activity to lower heart rate

True or false: Myotatic reflex inhibitory effects are disynaptic

True

True or false: flexion-crossed extension reflex is monosynaptic.

False: it’s POLYsynaptic

True or false: baroreceptors respond to chemical changes in blood.

False: They respond to stretch (pressure)

True or false: Rheostasis allows regulated variables to change with demand.

True

What is a reflex?

A rapid, automatic, stereotyped response to a stimulus

What are the five components of a reflex arc?

• Receptor
• Afferent neuron
• Integrating center
• Efferent neuron
• Effector

What determines whether a reflex is somatic or autonomic?

The type of effector organ

What effectors are used in somatic reflexes?

Skeletal muscle

What effectors are used in autonomic reflexes?

Smooth muscle, cardiac muscle, and glands

What is reciprocal inhibition?

Inhibition of antagonistic muscles during contraction of agonists

What is the stimulus for the Golgi tendon reflex?

Increased muscle tension

What is the function of the Golgi tendon reflex?

Prevents excessive force and muscle damage

What type of sensory receptor is in the Golgi tendon organ?

Ib afferent endings

What is the difference between monosynaptic and polysynaptic reflexes?

Monosynaptic reflexes have one synapse; polysynaptic reflexes have multiple synapses

Which reflex uses muscle spindles as receptors?

Stretch (myotatic) reflex

What type of receptor detects muscle length?

Muscle spindle

What is gamma motor neuron function?

Adjusting muscle spindle sensitivity

What is central integration in reflexes?

Processing of sensory input in the spinal cord or brainstem

What reflex helps maintain posture?

Stretch (myotatic) reflex

A reflex is an __________ and __________ response to a stimulus.

automatic; stereotyped

The sensory limb of a reflex is called the __________ limb.

afferent

The motor limb of a reflex is called the __________ limb

efferent

The integrating center of spinal reflexes is the __________.

spinal cord

Golgi tendon organs monitor muscle __________

tension

Gamma motor neurons innervate __________ fibers of muscle spindles.

intrafusal

In reciprocal inhibition, the __________ muscle is inhibited

antagonist

Monosynaptic reflexes involve __________ synapse(s).

one

Polysynaptic reflexes involve __________ synapse(s).

multiple

Autonomic reflex effectors include __________ and glands

smooth muscle

True or false: Reflexes don’t require conscious processing

true

True or false: The Golgi tendon reflex causes muscle contraction when tension increases

False: it causes muscle relaxation to prevent damage from excessive tension

True or false: gamma motor neurons increase spindle sensitivity

True

True or false: Reciprocal inhibition enhances co-contraction of antagonistic muscles.

False: it inhibits antagonists to allow smooth agonist contraction

True or false: Monosynaptic reflexes are faster than polysynaptic reflexes.

True: they have fewer synapses

True or false: Muscle spindles detect changes in muscle force

False: Muscle spindles detect muscle length; Golgi tendon organs detect force.

True or false: Autonomic reflexes can regulate glandular secretion

True

True or false: The stretch reflex is important for maintaining upright posture

True

What is summation in reflex pathways?

The combined effect of multiple excitatory or inhibitory inputs on a neuron

What is temporal summation in reflexes?

Summation caused by repeated input from the same synapse over time

What is spatial summation in reflexes?

Summation caused by input from multiple presynaptic neurons

What is afterdischarge in a reflex?

Continued response after the stimulus ends due to interneuron circuits

What is divergence in a reflex pathway?

One afferent neuron synapsing with multiple interneurons or motor neurons

What is convergence in reflex pathways?

Multiple afferent neurons synapsing on a single interneuron or motor neuron

What is the withdrawal (flexor) reflex designed to protect against?

Painful or damaging stimuli

What type of receptor initiates the withdrawal reflex?

Nociceptor

What happens to extensor muscles on the stimulated side during withdrawal?

They are inhibited

What happens to flexor muscles on the stimulated side during withdrawal?

They contract

What is the role of interneurons in reflexes?

To process and distribute sensory information within the CNS

What type of reflex is the corneal blink reflex?

Brainstem reflex

What is the purpose of the pupillary light reflex?

Regulates the amount of light entering the eye

What spinal cord level mediates the patellar reflex?

L2–L4

What is the clinical purpose of reflex testing?

To assess integrity of sensory and motor pathways