Chapter 12: Spinal Cord and Spinal Nerves

Exam 2 Material

Dorsal root ganglion

collections of cell bodies of pseudo-unipolar sensory neurons forming dorsal roots

Where are motor neuron cell bodies located

anterior (multipolar/somatic) and lateral (autonomic) horns of the spinal cord gray matter

axons of motor neurons form ventral roots and pass into spinal nerves

Reflex

automatic response to a stimulus that occurs without conscious thought; homeostatic

Reflex arc

neural pathway that controls a reflexcompe

Components of a reflex arc

sensory receptor →sensory neuron → interneuron (not always) → motor neuron → effector organ

Different ways a reflex is classified

number of synapses, development, effector type, and location of integration centerMon

monosynaptic reflex

no interneurons

single synapse in excitatory arc

stretch reflex (patellar, achilles)

polysynaptic reflexes

multiple synapses with interneurons

more complex

innate reflexes

part of normal development

babinski reflex in babies, patellar

learned reflexes

develop as activities are repeated

skills required for a task (ride a bike)

somatic reflex

skeletal muscle

anterior horn of gray matter

autonomic (visceral) reflexes

smooth muscle, cardiac, glands

cranial reflexes

integrate at the brain

spinal reflexes

integrate at the spinal cord

Steps in a reflex arc

1. sensory receptor detects a stimuli and generates an AP
2. sensory neuron sends AP through nerve → dorsal root → spinal cord
3. AP carried to integration center (may or may not involve a interneuron
4. interneuron synapses w motor neuron
5. motor axon conducts AP through ventral root and spinal nerve to an effector organ

Stretch Reflex

muscles contract dues to stretching force detected by muscle spindle

no interneuron

sensory neurons synapse with alpha motor neurons with cause muscles to contract

muscle spindle

3-10 specialized muscle cells that respond to stretch

gamma motor neurons control the sensitivity (activate in response to alpha motor neuron signal)

Golgi Tendon Reflex

prevents contracting muscles from applying excessive tension to tendons

prevents damage to tendons that could be caused by excessive tension

produces sudden relaxation of the muscles

example of neuromodulation

GTO → sensory neurons → inhibitory interneurons → inhibit alpha motor neurons → muscle relaxes

Golgi tendon organ

encapsulated nerve endings that have their ends numerous terminal branches with small swellings associated with bundles of collagen fibers in tendon

located in tendon near muscle

Withdrawal Reflex

function: remove a body part from a painful stimulus

reciprocal innervation

causes relaxation of extensor muscle when flexor muscle contracts

also involved in stretch reflex

Crossed Extensor Reflex

when a withdrawal reflex is initiated in one lower limb, the crossed extensor reflex causes extension of opposite lower limb

Interactions with spinal cord reflexes

sensory information goes to brain

descending tracts from brain carry information to reflexes

neurotransmitters produce IPSPs or EPSPs modifying the reflex