Lab # 2: Spinal Cord & Nerves, Reflexes and General Senses

A & P II Spring, 2014

Objectives

Be able to identify specified spinal cord structures and spinal nerves on models Be familiar with spinal nerve plexuses and the major nerves arising from

each plexus, and the anatomical structures/muscles innervated by these nerves

Know the different parts of the nervous system, origins of different

neurons in the spinal cord, cholinergic and adrenergic neurons and receptors Be able to compare and contrast different reflexes

Be familiar with the specified sensory receptors

Overview of the Nervous System

Difference between spinal cord & nerves: Spinal cord: Spines and skull protect the nerves Spinal nerves: No skeletons protect the nerves

output feedback

Sympathetic: Fight & flight Parasympathetic: Feed & Breed

• Ganglion: a nerve cell cluster • Pre- Post-

• Sympathetic Chain: • Synapse closer to spinal cord, so

we got more control of it which make the response quicker (fight and flight)

Sympathetic chain

Rami (branches)

Adrenal gland Sweat gland Blood vessel Only controlled by sympathetic system

N= Nicotinic receptor M= Muscarinic receptor

Small nerves in the Adrenal medulla, release NT when needed Pre-Ach-N Post-Ah-M

Neurotransmitters and Receptors

CNS-Spinal Cord

Cerebrospinal fluid here

D-outer, thickest A-middle, spider web like P-innermost, hug spinal cord

Transverse view

CSF

Lateral horn Dorsal root ganglion

Ventral root Spinal nerve

Ventral horn

Dorsal horn Central canal (contains CSF)

Anterior Median Fissure

Posterior Median Sulcus

Spinal Cord Anatomy

Spinal Cord Anatomy

Spinal Cord Segments

Large/thick anterior & posterior horns

Small anterior & posterior horns, Small lateral horn present

Large anterior horns, small posterior horns

Large anterior & posterior horns Lateral horn present

Peripheral Nervous System: Autonomic NS

Sympathetic (thoraco-lumbar)

Parasympathetic (cranio-sacral)

Spinal Nerves

• 31 Pairs attached to Spinal Cord • 8 Cervical • 12 Thoracic • 5 Lumbar • 5 Sacral • 1 Coccygeal

• 4 Spinal Plexuses • Cervical • Brachial • Lumbar • Sacral

• 2 Enlargements • Cervical Enlargement (C3 or C4 to T1)

• contains nuclei for upper extremities • Lumbar Enlargements (T9 to T12)

• contains nuclei for lower extremities

• Cauda equina • Spinal Nerves extend inferiorly to the spinal cord

and form a cauda equina.

• 31 Pairs attached to Spinal Cord • 8 Cervical • 12 Thoracic • 5 Lumbar • 5 Sacral • 1 Coccygeal

• 4 Spinal Plexuses • Cervical • Brachial • Lumbar • Sacral

• 2 Enlargements • Cervical Enlargement (C3 or C4 to T1)

• contains nuclei for upper extremities • Lumbar Enlargements (T9 to T12)

• contains nuclei for lower extremities

• Cauda equina • Spinal Nerves extend inferiorly to the spinal cord

and form a cauda equina.

Spinal Nerves (12) & Plexuses (4)

• Cervical Plexus • Phrenic

• Brachial Plexus • Axillary • Ulnar • Median • Musculocutaneous • Radial

o Lumbar Plexus o Femoral o Obturator

o Sacral Plexus

o Pudendal o Sciatic o Tibial o Common Fibular

Cervical Plexus

• Phrenic • Innervate diaphragm

Irritaion of the phrenic nerve causes diaphragm spasms or hiccups

Brachial Plexus • Axillary • Innervate shoulders area • Deltoid, teres minor

• Ulnar

• Innervate flexors • Flexor carpi ulnaris, flexor digitorum

profundis, lumbricals, opponens digiti minimi, flexor digiti minimi, abductor digiti minimi, adductor pollicis

• Median

• Innervate flexors and lumbricals • Anterior compartment of the forearm,

lumbricals

• Musculocutaneous • Innervate biceps, brachialis • Anterior compartment of the arm • Close to biceps

• Radial • Innervate extensors • Posterior compartment

Axillary

Ulnar

Median

Anterior view of left shoulder

Bicep

Median

Musculocutaneous

Axillary

Ulnar

Anterior view of left shoulder

Axillary Median

Radial

Ulnar

Median

Musculocutaneous

Ulnar

Median Radial

Ulnar

Phrenic

Lumbar Plexus

• Femoral • Innervate anterior compartment of

the thigh • Innervate extensors of upper leg

• Obturator • Innervate medial compartment of

the thigh • Innervate Adductors

Sacral Plexus • Pudendal

• Innervate penis and anal sphincter

• Sciatic (upper leg) • Posterior compartment of the thigh • Pass under piriformis muscle and moves down

the posterior leg

• Tibial (lower leg & foot) • Branches from sciatic nerve • Moves down the lower posterior leg • Innervate posterior compartment of leg

(flexors), and medial compartment of leg • Gastrocnemius, flexor digitorum longus, flextor

halluces longus, lumbricals • Injury: pain in the bottom of foot and toes

• Common fibular (lower leg & foot)

• Branches from sciatic nerve • Mover down the lower anterior leg • Innervate anterior compartment of leg

(extensors), lateral compartment of leg • extensor digitorum brevis • Injury: foot drop (not able to do dorsi flexion)

Tibial Nerve Femoral Nerve

Sciatic

Fibular Nerve

Anterior view Posterior view

Fibular Nerve

Tibial Nerve (medial foot)

MEDIAL VIEW

General Senses

• Sensory receptors respond to changes from the environment

• Unencapsulated (free) or encapsulated

• Sensory Receptors (classified by stimulus type) • Mechanoreceptor: mechanical force (touch/pressure/vibration)

• Meissner corpuscle, hair root plexus, merkel discs, ruffini corpuscle, pacinian corpuscle

• Thermoreceptors: temperature • Photoreceptors: light • Nocioceptors: pain • Proprioceptors: stretch (muscle-sense)

Mechanoreceptor Locations

Specific Types of Mechanoreceptors

• Merkel Disk (slow-adapting) • Unencapsulated (free) • Superficial - very sensitive • Respond to light touch (pressure and texture)

• Meissner corpuscle (fast-adapting ) • Superficial, located in the glabrous skin on fingertips and eyelids • Respond to touch and vibration

• Ruffini corpuscle (slow-adapting) • More deeper compared to Merkel disc and Meissner corpuscle • Respond to sustained pressure, skin stretch

• Hair root plexus • Sensitive • Wrapped around every hair follicle

• Pacinian corpuscle (fast-adapting, ) • Respond to vibration and deep pressure

Two Point Discrimination

• An indirect measure of cutaneous touch receptor density

• Tactile sensitivity varies by

body part • Number of receptors in area

(touch receptor density) • Amount of brain tissue

devoted to sensory information

Two Point Discrimination Test

Directions •Eyes closed during test •Put 2 caliper points together and place on skin area. Be sure to place both points at the same time

•Ask if 1 or 2 points were felt

•Increase caliper distance until 2 points are felt

•Finger & Palm: +1mm •Cheek, forearm, leg: +2mm

Next Week – Exam 1

Exam 1