Anatomy Exam 4: Conduction Pathways, Spinal Nerves, Reflexes, and Senses

Sensory pathways

Signals from sensory receptors ascending to brain

Motor pathways

Signals from brain to muscles or glands

Spinothalamic pathway

pain (nociception) and temperature-lateral; "crude touch"-anterior

Spinocerebellar tract

Propioception (orientation of body parts)

Cotricospinal pathway

Motor (voluntary): walking, writing, reaching, typing

Corticobulbar

Motor: cranial nerves (trigeminal, facial, glossopharyngeal, vagus, accessory, hypoglossal)

Rubrospinal pathway

Motor: reflexes, posture. Red nucleus + spinal cord.

Anterior root

contains motor neurons

Posterior root

contains sensory neurons

Posterior root ganglion

contains cell bodies of sensory neurons

Posterior ramus

innervates the muscles and joints in that region of the spine and the skin of the back

Anterior ramus

innervates the anterior and lateral skin and muscles of the trunk and gives rise to nerves of the limbs

Rami communicantes

autonomic nerve fibers that attach to ventral rami

Dermatome

Segments of skin supplied by single spinal nerves; can help localize damage to one or more spinal nerves

Nerve plexus

axons from anterior rams extend through different branches to different body structures

ansa cervicalis

phrenic nerve

controls diaphragm, signals diaphragmatic contraction

segmental branches

greater auricular

lesser occipital

supraclavicular

Innervate area over clavicle, parts of the shoulder, and proximal chest

transverse cervical nerve

Brachial plexus

Axillary nerve

posterior cord: innervates deltoid and teres minor muscles

Median nerve

medial cord: innervates flexor muscles of forearm (lateral palm)

Musculocutaneous nerve

lateral cord that innervates biceps brachii, brachialis, and corocobrachialis

Radial nerve

posterior cord that innervates most extensor muscles of the upper limb

Ulnar nerve

Medial cord that innervates flexor muscles of forearm (lateral palm)

Femoral nerve

Innervates the quadriceps muscles

Obturator nerve

innervates the adductor muscles

Tibial nerve

-Supplies the posterior compartment muscles

-sural nerve

-medial and lateral plantar nerve

Sciatic nerve

tibial and common fibular nerves in one sheath

common fibular

Innervate knee joint

deep fibular

Superficial fibular

Reflex arc

A relatively direct connection between a sensory neuron and a motor neuron that allows an extremely rapid response to a stimulus, often without conscious brain involvement.

Ipsilateral

receptor and effector organs on same side of spinal cord

Contralateral

sensory impulses from receptor organ cross over through SC to activate effector organs in opposite limb

Monosynaptic reflex

direct communication between sensory and motor neuron (e.g., stretch reflex)

Polysynaptic reflex

Interneuron facilitates sensory-motor communication (e.g., withdrawal reflex)

Spinal reflex

A simple automatic action of the spinal cord not requiring involvement of the brain, such as the knee-jerk reflex

Cranial reflex

reflex that is processed in the brain

Somatic reflex

Involve skeletal muscles as the effectors

Visceral reflex

Cardiac muscle, smooth muscle, or gland as the effector

Stretch reflex

Monosynaptic reflex; shortest latency among spinal reflexes

(Patellar reflex is example of this as tendon stretches when hammer strikes)

Golgi tendon reflex

Polysynaptic reflex; prevents muscles from contracting excessively; responds to tension (results in muscle lengthening)

Withdrawal reflex

• polysynaptic reflex initiated by painful stimulus

• transmitted by sensory neuron to spinal cord

• received by interneurons

• motor neurons signaled to flex

Crossed extensor reflex

-sensory transmission to spinal cord

-synapse with interneurons in stretch and crossed-extensor reflex

-Synapse with motor neurons on antagonistic muscle in opposite limb

Stimuli

events in the environment that can be detected and that might produce responses

Sensation

stimulus that we are consciously aware of

General senses

distributed throughout the body; structurally simple

Special senses

located only in head; structurally complex sense organs. Sensory receptors for smell, taste, vision, hearing, and equilibrium

Receptors

convey signals to CNS by sensory neurons

Receptor field

distribution area of the endings of a sensory neuron

exteroreceptors

detect stimuli from external environment, receptors in skin for special senses (membranes lining nasal cavity, oral cavity, vagina, anal canal

interoreceptors

detect stimuli in internal organs, primarily stretch receptors in smooth muscle walls (mostly unaware of these sensations)

proprioceptors

detect body and limb movements, skeletal muscle contraction and stretch, provide awareness of body joint position and skeletal muscle contraction

somatic sensory receptors

provide position, touch, pressure, pain, and temperature sensations

visceral sensory receptors

found in walls of internal organs, they monitor stretch, chemical environment, temperature, pain

Special sensory receptors